The Star Formation Newsletter
A community newsletter on Star and Planet Formation research
No. 371 — 30 November 2023
Editor: João Alveswww.starformation.news

Cover image caption
The IC2944 and IC2948 star forming region in Centaurus is located about 2 kpc from Earth. The nebula features famous Bok
globules, resilient against ultraviolet radiation a cluster of ionizing massive stars. Notably, some of the blue stars in the image,especially the brightest star towards the upper left (λ Cen), are not part of these nebulae but belong to the Scorpius-Centaurus
Association and are significantly closer at a distance of about 100 pc.
Credits: ESO/VPHAS+ team. Acknowledgement: CASU

Note from the Editor

The Star Formation Newsletter is now on the web at www.starformation.news. This PDF file contains the monthly
Abstracts and links. Red text in this PDF is a url link. Submitting an abstract to the SFN is as simple as entering
the arXiv ID (e.g., 2006.10139) in a web form on the SFN web site. Do not remove the LATEX formatting whensubmitting to the arXiv. If you do, your abstract will not look great either at the arXiv or the SFN.

Abstracts
1.

Peculiarities of Open Star Clusters with High Vertical Velocities from the Region of the
Sco-Cen OB Association
Vadim V. Bobylev, Anisa T. Bajkova ⋆ We have studied the kinematics of a unique sample of young open starclusters (OSCs) with high vertical velocities, 15 < W < 40 km s−1 . The characteristics of these clusters were taken fromthe catalogue by Hunt and Reffert (2023), where their mean proper motions, line-of-sight velocities, and distances were
calculated using Gaia DR3 data. These OSCs are located within 0.6 kpc of the Sun and form two clumps: one in theregion of the Sco-Cen OB association and the other one in the region of the Per OB3-Per OB2 associations. The OSC
group of 47 members in the region of the Sco-Cen association is shown to expand along the y axis, ∂V /∂y = 51±12 km
s−1 kpc−1 . This group also has a positive rotation around the z axis with an angular velocity of 71 ± 11 km s−1 kpc−1
and a negative rotation around the x axis with an angular velocity of −35 ± 5 km s−1 kpc−1 . Based on the velocitiesof 27 OSCs from the region of the Per OB3-Per OB2 associations, we have found no gradients differing significantly
from zero. We have studied the kinematics of more than 1700 stars selected by Luhman (2022) as probable membersof the Sco-Cen OB association. These stars are shown to have no high vertical velocities. The expansion coefficientof the stellar system in the xy plane has been found from all stars to be Kxy = 43.2 ± 2.2 km s−1 kpc−1 . Based onstars from the three UCL, LCC, and V1062 Sco groups with a mean age ∼20 Myr, for the first time we have found a
volume expansion coefficient of the stellar system differing significantly from zero, Kxyz = 43.2 ± 3.4 km s−1 kpc−1 .

2.

CO mapping of Cygnus-X – volume density distribution
Jonah C. Baade, Shuo Kong, John H. Bieging, Thomas Folkers ⋆ We present CO(2-1) and 13 CO(2-1) maps of the

Cygnus-X molecular cloud complex using the 10m Heinrich Hertz Submillimeter Telescope (SMT). The maps cover
the southern portion of the complex which is strongly impacted by the feedback from the Cygnus OB2 association.
Combining CO(1-0) and 13 CO(1-0) maps from the Nobeyama 45m Cygnus-X CO Survey, we carry out a multitransition molecular line analysis with RADEX and derive the volume density of velocity-coherent gas components.
We select those components with a column density in the power-law tail part of the column density probability
distribution function (N-PDF) and assemble their volume density into a volume density PDF (ρ-PDF). The ρ-PDF
exhibits a power-law shape in the range of 104.5 cm−3 ≲ nH2 ≲ 105.5 cm−3 with a fitted slope of α = −1.12 ± 0.05.
The slope is shallower than what is predicted by simulations of rotationally supported structures or those undergoinggravitational collapse. Applying the same analysis to synthetic observations with feedback may help identify the causeof the shallow slope. The ρ-PDF provides another useful benchmark for testing models of molecular cloud formationand evolution.

2

onset of stellar multiplicity in massive star formation: A search for low-mass com3. The
panions of massive young stellar objects with L′ -band adaptive optics imaging
E. Bordier, W. -J. de Wit, A. J. Frost, H. Sana, T. Pauwels, E. Koumpia ⋆ Given the high incidence of binaries

among mature field massive stars, it is clear that multiplicity is an inevitable outcome of high-mass star formation.
Understanding how massive multiples form requires the study of the birth environments of massive stars, covering theinnermost to outermost regions. We aim to detect and characterise low-mass companions around massive young stellar
objects (MYSOs) during and shortly after their formation phase. To investigate large spatial scales, we carried out
an L′ -band high-contrast direct imaging survey seeking low-mass companions (down to Lbol ≈ 10L⊙ , or late A-type)around thirteen previously identified MYSOs using the VLT/NACO instrument. From those images, we looked forthe presence of companions on a wide orbit, covering scales from 300 to 56,000 au. Detection limits were determined
for all targets and we tested the gravitational binding to the central object based on chance projection probabilities.
We have discovered a total of thirty-nine potential companions around eight MYSOs, the large majority of which havenever been reported to date. We derived a multiplicity frequency (MF) of 62 ± 13% and a companion fraction (CF)of 3.0 ± 0.5. The derived MF and CF are compared to other studies for similar separation ranges. The comparisonsare effective for a fixed evolutionary stage spanning a wide range of masses and vice versa. We find an increased MF
and CF compared to the previous studies targeting MYSOs, showing that the statement in which multiplicity scaleswith primary mass also extends to younger evolutionary stages. The separations at which the companions are foundand their location with relation to the primary star allow us to discuss the implications for the massive star formation
theories.

4. The enigmatic multiple star VV Ori
Edwin Budding, John Southworth, Kresimir Pavlovski, Michael D. Rhodes, Wu Zihao, Tom Love, Mark G.
Blackford, Timothy S. Banks, Murray Alexander ⋆ New photometry, including TESS data, have been combinedwith recent spectroscopic observations of the Orion Ib pulsating triple-star system VV Ori. This yields a revised setof absolute parameters with increased precision. Two different programs were utilized for the light curve analysis,
with results in predictably close agreement. The agreement promotes confidence in the analysis procedures. The
spectra were analysed using the FDBinary program. The main parameters are as follows: M1 = 11.6 ± 0.14 andM2 = 4.8 ± 0.06 (M⊙ ). We estimate an approximate mass of the wide companion as M3 = 2.0 ± 0.3 M⊙ . Similarly,
R1 = 5.11 ± 0.03, R2 = 2.51 ± 0.02, R3 = 1.8 ± 0.1 (R⊙ ); Te1 = 26600 ± 300, Te2 = 16300 ± 400 and Te3 = 10000 ± 1000
(K). The close binary’s orbital separation is a = 13.91 (R⊙ ); its age is 8 ± 2 (Myr) and its photometric distance is396 ± 7 pc. The primary’s β Cep type oscillations support these properties and confirm our understanding of its
evolutionary status. Examination of the well-defined λ6678 He I profiles reveals the primary to have a significantly
low projected rotation: some 80% of the synchronous value. This can be explained on the basis of the precession ofan unaligned spin axis. This proposal can resolve also observed variations of the apparent inclination and address
other longer-term irregularities of the system reported in the literature. This topic invites further observations andfollow-up theoretical study of the dynamics of this intriguing young multiple star.

Density distributions, magnetic field structures and fragmentation in high-mass star
5. formation
H. Beuther, C. Gieser, J. D. Soler, Q. Zhang, R. Rao, D. Semenov, Th. Henning, R. Pudritz, T. Peters, P.
Klaassen, M. T. Beltran, A. Palau, T. Moeller, K. G. Johnston, H. Zinnecker, J. Urquhart, R. Kuiper, A.
Ahmadi, A. Sanchez-Monge, S. Feng, S. Leurini, S. E. Ragan ⋆ Methods: Observing the large pc-scale Stokes I

mm dust continuum emission with the IRAM 30m telescope and the intermediate-scale (<0.1pc) polarized submm dust
emission with the Submillimeter Array toward a sample of 20 high-mass star-forming regions allows us to quantify thedependence of the fragmentation behaviour of these regions depending on the density and magnetic field structures.
Results: We infer density distributions n r−p of the regions with typical power-law slopes p around 1.5. There isno obvious correlation between the power-law slopes of the density structures on larger clump scales ( 1pc) and thenumber of fragments on smaller core scales (<0.1pc). Comparing the large-scale single-dish density profiles to thosederived earlier from interferometric observations at smaller spatial scales, we find that the smaller-scale power-law
slopes are steeper, typically around 2.0. The flattening toward larger scales is consistent with the star-forming regions
being embedded in larger cloud structures that do not decrease in density away from a particular core. Regarding themagnetic field, for several regions it appears aligned with filamentary structures leading toward the densest central
cores. Furthermore, we find different polarization structures with some regions exhibiting central polarization holes3whereas other regions show polarized emission also toward the central peak positions. Nevertheless, the polarized
intensities are inversely related to the Stokes I intensities. We estimate magnetic field strengths between 0.2 and
4.5mG, and we find no clear correlation between magnetic field strength and the fragmentation level of the regions.
Comparison of the turbulent to magnetic energies shows that they are of roughly equal importance in this sample.
The mass-to-flux ratios range between 2 and 7, consistent with collapsing star-forming regions.

6. Galactic runaway O and Be stars found using Gaia DR3

M. Carretero-Castrillo, M. Ribó, J. M. Paredes ⋆ A relevant fraction of massive stars are runaway stars. These stars

move with a significant peculiar velocity with respect to their environment. We aim to discover and characterize thepopulation of massive and early-type runaway stars in the GOSC and BeSS catalogs using Gaia DR3 astrometric data.
We present a 2-dimensional method in the velocity space to discover runaway stars as those that deviate significantly
from the velocity distribution of field stars, which are considered to follow the Galactic rotation curve. We found 106
O runaway stars, 42 of which were not previously identified as runaways. We found 69 Be runaway stars, 47 of whichwere not previously identified as runaways. The dispersion of runaway stars is a few times higher in Z and b thanthat of field stars. This is explained by the ejections they underwent when they became runaways. The percentage
of runaways is 25.4% for O-type stars, and it is 5.2% for Be-type stars. In addition, we conducted simulations in 3
dimensions for our catalogs. They revealed that these percentages could increase to 30% and 6.7%, respectively. Our
runaway stars include seven X-ray binaries and one gamma-ray binary. Moreover, we obtain velocity dispersions of 5km/s perpendicular to the Galactic plane for O- and Be-type field stars. These values increase in the Galactic plane to
7 km/s for O-type stars due to uncertainties and to 9 km/s for Be-type stars due to Galactic velocity diffusion. The
excellent Gaia DR3 astrometric data have allowed us to identify a significant number of O-type and Be-type runaways
in the GOSC and BeSS catalogs. The higher percentages and higher velocities found for O-type compared to Be-typerunaways underline that the dynamical ejection scenario is more likely than the binary supernova scenario. Our results
open the door to identifying new high-energy systems among our runaways by conducting detailed studies.

Cloud-cloud collision in S235: triggered the formation of high-mass stars and young
7. star clusters
En Chen, Yu Gao, Shiyu Zhang, Xuepeng Chen, Min Fang, Qianru He, Xuejian Jiang, Yan Sun, Xiaolong
Wang, Hongjun Ma ⋆ We present the analysis of cloud-cloud collision (CCC) process in the Galactic molecularcomplex S235. Our new CO observations performed with the PMO-13.7m telescope reveal two molecular clouds,
namely the S235-Main and the S235-ABC, with ∼ 4 km s−1 velocity separation. The bridge feature, the possible
colliding interface and the complementary distribution of the two clouds are significant observational signatures ofcloud-cloud collision in S235. The most direct evidence of cloud-cloud collision process in S235 is that the S235-Main+33(in a distance of 1547+44−43 pc) and S235-ABC (1567−39 pc) meet at almost the same position (within 1σ error range)
13
at a supersonic relative speed. We identified ten CO clumps from PMO-13.7m observations, 22 dust cores from thearchival SCUBA-2 data, and 550 YSOs from NIR-MIR data. 63% of total YSOs are clustering in seven MST groups(M1−M7). The tight association between the YSO groups (M1 & M7) and the bridge feature suggests that the CCC
process triggers star formation there. The collisional impact subregion (the South) shows 3 ∼ 5 times higher CFE
and SFE (average value of 12.3% and 10.6%, respectively) than the non-collisional impact subregion (2.4% and 2.6%,
respectively), suggesting that the CCC process may have enhanced the CFE and SFE of the clouds compared to those
without collision influence.

Near-Infrared Observations of Outflows and YSOs in the Massive Star-Forming Region
8. AFGL 5180
S. Crowe, R. Fedriani, J. C. Tan, M. Whittle, Y. Zhang, A. Caratti o Garatti, J. P. Farias, A. Gautam, Z.
Telkamp, B. Rothberg, M. Grudic, M. Andersen, G. Cosentino, R. Garcia-Lopez, V. Rosero, K. Tanaka, E.
Pinna, F. Rossi, D. Miller, G. Agapito, C. Plantet, E. Ghose, J. Christou, J. Power, A. Puglisi, R. Briguglio,
G. Brusa, G. Taylor, X. Zhang, T. Mazzoni, M. Bonaglia, S. Esposito, C. Veillet ⋆ Methods: Broad- andnarrow-band imaging of AFGL 5180 was made in the NIR with the LBT, in both seeing-limited (∼ 0.5 arcsec) andhigh angular resolution (∼ 0.09 arcsec) Adaptive Optics (AO) modes, as well as with HST. Archival ALMA continuum
data was also utilized. Results: At least 40 jet knots were identified via NIR emission from H2 and [FeII] tracing
shocked gas. Bright jet knots outflowing from the central most massive protostar, S4, are detected towards the east4

of the source and are resolved in fine detail with the AO imaging. Additional knots are distributed throughout thefield, likely indicating the presence of multiple driving sources. Sub-millimeter sources detected by ALMA are shown
to be grouped in two main complexes, AFGL 5180 M and a small cluster ∼ 15 arcsec to the south, AFGL 5180
S. From our NIR continuum images we identify YSO candidates down to masses of ∼ 0.1 M⊙ . Combined with the
sub-mm sources, this yields a surface number density of such YSOs of N∗ ∼ 103 pc−2 within a projected radius of
about 0.1 pc. Such a value is similar to those predicted by models of both Core Accretion from a turbulent clump
environment and Competitive Accretion. The radial profile of N∗ is relatively flat on scales out to 0.2 pc, with only
modest enhancement around the massive protostar inside 0.05 pc. Conclusions: This study demonstrates the utilityof high-resolution NIR imaging, in particular with AO, for detecting outflow activity and YSOs in distant regions.
The presented images reveal the complex morphology of outflow-shocked gas within the large-scale bipolar flow ofa massive protostar, as well as clear evidence for several other outflow driving sources in the region. Finally, thiswork presents a novel approach to compare the observed YSO surface number density from our study against different
models of massive star formation.

9.

A dusty streamer infalling onto the disk of a class I protostar. ALMA dual-band constraints on grain properties and mass infall rate
L. Cacciapuoti, E. Macias, A. Gupta, L. Testi, A. Miotello, C. Espaillat, M. Kuffmeier, S. van Terwisga, J.
Tobin, S. Grant, C. F. Manara, D. Segura-Cox, J. Wendeborn, R. S. Klessen, A. J. Maury, U. Lebreuilly, P.
Hennebelle, S. Molinari ⋆ Observations of interstellar material infalling onto star- and planet-forming systems havebecome increasingly common thanks to recent advancements in radio interferometry. These structures replenish diskswith fresh material, have the potential to significantly alter their dynamics, trigger the formation of substructures,
induce shocks, and modify their physical and chemical properties. In this study, we combine new ALMA band 3
and archival band 6 observations to characterize the dust content and mass infall rate of a 4,000 au arc-like structure
infalling onto M512, a class I young stellar object located in the Lynds 1641 region of the Orion A molecular cloud. We
measure for the first time spectral index maps and derive a dust opacity index profile along a streamer, constraining
grain properties and its dust mass. We measure a spectral index α ∼ 3.2 across the entire structure, and a dust
opacity index β ∼ 1.6. Given grain properties consistent with the measured β, the structure can host up to 245 M⊕ ofdust, being comparable or even exceeding the mass of the inner, unresolved 600 au, which contains the protoplanetary
disk of M512. Such a massive streamer can strongly affect the evolution of the star- and planet-forming inner system.
Assuming typical ISM dust-to-gas ratio of 1%, free-fall timescales (50 kyr) imply total mass infall rates up to 1.5 ·10−6 M⊙ /yr. M512 has been classified as an outbursting source with multi-epoch photometry, thus representing aninteresting case study to explore the possible connection between infalling streamers and accretion outbursts.

10. Photoevaporation obfuscates the distinction between wind and viscous angular momentum transport in protoplanetary discs
Gavin A. L. Coleman, Joseph K. Mroueh, Thomas J. Haworth ⋆ How protoplanetary discs evolve remains anunanswered question. Competing theories of viscosity and magnetohydrodynamic disc winds have been put forward
as the drivers of angular momentum transport in protoplanetary discs. These two models predict distinct differencesin the disc mass, radius and accretion rates over time, that could be used to distinguish them. However that expectation is built on models that do not include another important process - photoevaporation, both internally by thehost star and externally by neighbouring stars. In this work we produce numerical models of protoplanetary discs
including viscosity, magnetohydrodynamic disc winds, and internal and external photoevaporation. We find that evenweak levels of external photoevaporation can significantly affect the evolution of protoplanetary discs, influencing
the observable features such as disc radii, that might otherwise distinguish between viscous and wind driven discs.
Including internal photoevaporation further suppresses differences in evolution between viscous and wind driven discs.
This makes it much more difficult than previously anticipated, to use observations of nearby star forming regions
to determine whether discs are viscous or wind driven. Interestingly we find that evolved protoplanetary discs inintermediate FUV environments may be the best cases for differentiating whether they evolve through viscosity ormagnetohydrodynamic disc winds. Ultimately this work demonstrates the importance of understanding what are thekey evolutionary processes and including as many of those as possible when exploring the evolution of protoplanetary
discs.

5

Protostellar chimney flues: are jets and outflows lifting submillimetre dust grains from
11. discs into envelopes?
L. Cacciapuoti, L. Testi, L. Podio, C. Codella, A. J. Maury, M. De Simone, P. Hennebelle, U. Lebreuilly, R.
S. Klessen, S. Molinari ⋆ Low dust opacity spectral indices (β < 1) measured in the inner envelopes of class 0/I

young stellar objects (age ∼ 104−5 yr) have been interpreted as the presence of (sub-)millimetre dust grains in theseenvironments. The density conditions and the lifetimes of collapsing envelopes have proven unfavorable for the growthof solids up to millimetre sizes. As an alternative, magneto-hydrodynamical simulations suggest that protostellar jets
and outflows might lift grains from circumstellar discs and diffuse them in the envelope. We reframe available data
for the CALYPSO sample of Class 0/I sources and show tentative evidence for an anti-correlation between the valueof β1−3mm measured in the inner envelope and the mass loss rate of their jets and outflows, supporting a connection
between the two. We discuss the implications that dust transport from the disc to the inner envelope might have forseveral aspects of planet formation. Finally, we urge for more accurate measurements of both correlated quantities
and extension of this work to larger samples, necessary to further test the transport scenario.

Variation of the high-mass slope of the stellar initial mass function: Theory meets
12. observations
Sami Dib ⋆ We present observational evidence of the correlation between the high-mass slope of the stellar initial

mass function (IMF) in young star clusters and their stellar surface density, σ∗ . When the high-mass end of the IMF
is described by a power law of the form dN/dlogM∗ ∝ M∗−Γ , the value of Γ is seen to weakly decrease with increasingσ∗ , following a Γ = 1.31 σ∗−0.095 relation. We also present a model that can explain these observations. The model isbased on the idea that the coalescence of protostellar cores in a protocluster forming clump is more efficient in highdensity environments where cores are more closely packed. The efficiency of the coalescence process is calculated asa function of the parental clump properties and in particular the relation between its mass and radius as well as itscore formation efficiency. The main result of this model is that the increased efficiency of the coalescence processleads to shallower slopes of the IMF in agreement with the observations of young clusters, and the observations are
best reproduced with compact protocluster forming clumps. These results have significant implications for the shapeof the IMF in different Galactic and extragalactic environments and have very important consequences for galactic
evolution.

13. Tomographic Imaging of the Sagittarius Spiral Arm’s Magnetic Field Structure

Yasuo Doi, Kengo Nakamura, Koji S. Kawabata, Masafumi Matsumura, Hiroshi Akitaya, Simon Coudé, Claudia
V. Rodrigues, Jungmi Kwon, Motohide Tamura, Mehrnoosh Tahani, Antonio Mario Magalhães, Reinaldo
Santos-Lima, Yenifer Angarita, José Versteeg, Marijke Haverkorn, Tetsuo Hasegawa, Sarah Sadavoy, Doris
Arzoumanian, Pierre Bastien ⋆ The Galactic global magnetic field is thought to play a vital role in shaping Galactic

structures such as spiral arms and giant molecular clouds. However, our knowledge of magnetic field structures in the
Galactic plane at different distances is limited, as measurements used to map the magnetic field are the integrated
effect along the line of sight. In this study, we present the first-ever tomographic imaging of magnetic field structuresin a Galactic spiral arm. Using optical stellar polarimetry over a 17′ × 10′ field of view, we probe the Sagittarius
spiral arm. Combining these data with stellar distances from the Gaia mission, we can isolate the contributions offive individual clouds along the line of sight by analyzing the polarimetry data as a function of distance. The observed
clouds include a foreground cloud (d < 200 pc) and four clouds in the Sagittarius arm at 1.23 kpc, 1.47 kpc, 1.63
kpc, and 2.23 kpc. The column densities of these clouds range from 0.5 to 2.8 × 1021 cm−2 . The magnetic fields
associated with each cloud show smooth spatial distributions within their observed regions on scales smaller than 10
pc and display distinct orientations. The position angles projected on the plane-of-sky, measured from the Galactic
north to east, for the clouds in increasing order of distance are 135◦ , 46◦ , 58◦ , 150◦ , and 40◦ , with uncertainties of afew degrees. Notably, these position angles deviate significantly from the direction parallel to the Galactic plane.

614. JWST Detects Neon Line Variability in a Protoplanetary Disk

C. C. Espaillat, T. Thanathibodee, C. V. Pittman, J. A. Sturm, M. K. McClure, N. Calvet, F. M. Walter, R.
Franco-Hernandez, J. Muzerolle Page ⋆ We report the first detection of variability in the mid-infrared neon line

emission of a protoplanetary disk by comparing a JWST MIRI MRS spectrum of SZ Cha taken in 2023 with a Spitzer
IRS SH spectrum of this object from 2008. We measure the [Ne III]-to-[Ne II] line flux ratio, which is a diagnostic of
the high-energy radiation field, to distinguish between the dominance of EUV- or X-ray-driven disk photoevaporation.
We find that the [Ne III]-to-[Ne II] line flux ratio changes significantly from ∼ 1.4 in 2008 to ∼ 0.2 in 2023. This points
to a switch from EUV-dominated to X-ray-dominated photoevaporation of the disk. We present contemporaneous
ground-based optical spectra of the Halpha emission line that show the presence of a strong wind in 2023. We proposethat this strong wind prevents EUV radiation from reaching the disk surface while the X-rays permeate the wind
and irradiate the disk. We speculate that at the time of the Spitzer observations, the wind was suppressed and EUV
radiation reached the disk. These observations confirm that the MIR neon emission lines are sensitive to changes inhigh-energy radiation reaching the disk surface. This highlights the [Ne III]-to-[Ne II] line flux ratio as a tool to gauge
the efficiency of disk photoevaporation in order to provide constraints on the planet-formation timescale. However,multiwavelength observations are crucial to interpret the observations and properly consider the star-disk connection.

15. The hierarchical formation of 30 Doradus as seen by JWSTK. Fahrion, G. De Marchi ⋆ The 30 Doradus region in the Large Magellanic Cloud (LMC) is the most energetic

star-forming region in the Local Group. It is powered by the feedback from the massive stars in R136, the 1-2 Myr oldcentral massive cluster. 30 Doradus has therefore long been regarded as a laboratory for studying star and star cluster
formation under conditions reminiscent of the early Universe. We use JWST NIRCam observations to analyse how
star formation proceeds in the region. Using selections based on theoretical isochrones on colour-magnitude diagrams,
we identify populations of different ages. We select pre-main-sequence (PMS) stars and young stellar objects thatshow excess emission from warm dust or emission lines. Studying the spatial distribution of the different populations,
we find that the youngest PMS stars with ages < 0.5 Myr are located in an elongated structure that stretches towards
the north-east from the central cluster. The same structure is found in the sources that show an infrared excess,appears to be overlapping with cold molecular gas, and covers previously investigated sites of ongoing star formation.
Pre-main-sequence stars with ages between 1 and 4 Myr and upper main-sequence stars are concentrated in thecentre of R136, while older stars are more uniformly distributed across the field and likely belong to the LMC field
population. Nonetheless, we find stars with excess emission from on dust or emission lines as far as 100 pc from thecentre, indicating extended recent star formation. We interpret the elongated structure formed by the youngest PMS
stars to be an indication of the still-ongoing hierarchical assembly of the R136 cluster. Additionally, the lower densityof old PMS stars with emission due to ongoing accretion in the central region suggests that feedback from the R136
stars is effective in disrupting the disks of PMS stars.

16. The external photoevaporation of structured protoplanetary disks

Matías Gárate, Paola Pinilla, Thomas J. Haworth, Stefano Facchini ⋆ The dust in planet-forming disks evolve
rapidly through growth and radial drift, and external photoevaporation also contributes to this evolution in massive
star-forming regions. We test whether the presence of substructures can explain the survival of the dust component
and observed millimeter continuum emission in protoplanetary disks located within massive star-forming regions. We
also characterize the dust content removed by the photoevaporative winds. For this, we performed hydrodynamical
simulations of protoplanetary disks subject to irradiation fields of FU V = 102 , 103 , and 104 G0 , with different dust trap
locations. We used the FRIED grid to derive the mass loss rate for each irradiation field and disk properties, and thenmeasure the evolution of the dust mass over time. For each simulation we estimate continuum emission at λ = 1.3 mm
along with the radii encompassing 90% of the continuum flux, and characterize the dust size distribution entrained in
the photoevaporative winds, along with the resulting far-ultraviolet (FUV) cross section. Our simulations show thatthe presence of dust traps can extend the lifetime of the dust component of the disk to a few millionyears if the FUV
irradiation is FU V ≲ 103 G0 , but only if the dust traps are located inside the photoevaporative truncation radius. The
dust component of a disk quickly disperse if the FUV irradiation is strong (104 G0 ) or if the substructures are locatedoutside the photoevaporation radius. We do find however, that the dust grains entrained with the photoevaporative
winds may result in an absorption FUV cross section of σ ≈ 10−22 cm2 at early times of evolution (<0.1 Myr), whichis enough to trigger a self-shielding effect that reduces the total mass loss rate, and slow down the disk dispersal in anegative feedback loop process.

7

17. The formation of wide-orbit giant planets in protoplanetary disks with a decreasing
pebble flux
Nerea Gurrutxaga, Anders Johansen, Michiel Lambrechts, Johan Appelgren ⋆ The presence of distant proto-

planets could explain the observed gaps in dust emission in protoplanetary disks. Here we derive a novel analyticalmodel to describe the temporal decay of the pebble flux through a protoplanetary disk as a result of radial drift. This
allows us to investigate the growth and migration of distant protoplanets throughout the lifespan of the disk. We
find that early-formed Moon-mass protoplanets can grow to their pebble isolation mass between approximately 20
and 80 M⊕ within less than 1 Myr in the 20 to 80 AU region around solar-like stars. Subsequent fast migration at theearly stages of gas accretion after pebble accretion has been halted nevertheless transports these giant planets into
final orbits at < 10 AU. However, our pebble decay model allows us to include a new pathway which can trigger thetransition from pebble accretion to gas accretion after the pebble flux has decayed substantially. With this pebble
decay pathway, we show that it is possible to form gas giants also beyond 10 AU. The occurrence of these wide-orbit
gas giants should be relatively low, since their core must attain sufficient mass to accrete gas before the pebble flux
decays while avoiding excessive migration. Since these gas giants do not reach the pebble isolation mass, their heavy
element content is typically less than 10 M⊕ . Our results imply that the observed gaps in protoplanetary disks could
be caused by distant protoplanets that reached the pebble isolation mass and then migrated, while gas giants in wide
orbits, such as PDS 70 b and c, accreted their gas after the decay in the pebble flux.

18. Astrochemical Diagnostics of the Isolated Massive Protostar G28.20-0.05

Prasanta Gorai, Chi-Yan Law, Jonathan C. Tan, Yichen Zhang, Ruben Fedriani, Kei E. I. Tanaka, Melisse
Bonfand, Giuliana Cosentino, Diego Mardones, Maria T. Beltran, Guido Garay ⋆ We study the astrochemical

diagnostics of the isolated massive protostar G28.20-0.05. We analyze data from ALMA 1.3 mm observations withresolution of 0.2 arcsec (∼1,000 au). We detect emission from a wealth of species, including oxygen-bearing (e.g., H2 CO,CH3 OH, CH3 OCH3 ), sulfur-bearing (SO2 , H2 S) and nitrogen-bearing (e.g., HNCO, NH2 CHO, C2 H3 CN, C2 H5 CN)
molecules. We discuss their spatial distributions, physical conditions, correlation between different species and possible
chemical origins. In the central region near the protostar, we identify three hot molecular cores (HMCs). HMC1 ispart of a mm continuum ring-like structure, is closest in projection to the protostar, has the highest temperature of∼ 300 K, and shows the most line-rich spectra. HMC2 is on the other side of the ring, has a temperature of ∼ 250 K,
and is of intermediate chemical complexity. HMC3 is further away, ∼ 3, 000 au in projection, cooler (∼ 70 K) and is theleast line-rich. The three HMCs have similar mass surface densities (∼ 10 g cm−2 ), number densities (nH ∼ 109 cm−3 )and masses of a few M⊙ . The total gas mass in the cores and in the region out to 3, 000 au is ∼ 25 M⊙ , which iscomparable to that of the central protostar. Based on spatial distributions of peak line intensities as a function of
excitation energy, we infer that the HMCs are externally heated by the protostar. We estimate column densities andabundances of the detected species and discuss the implications for hot core astrochemistry.

Discovery of Two Different Full Disk Evolutionary Patterns of M-type T Tauri Stars
19. with LAMOST DR8
Hasitieer Haerken, Guang-Wei Li, Min Li, Fuqing Duan, Yongheng Zhao ⋆ The full disk, full of gas and dust,
determines the upper limit of planet masses, and its lifetime is critical for planet formation, especially for giant planets.
In this work, we studied the evolutionary timescales of the full disks of T Tauri stars (TTSs) and their relations toaccretion. Combined with Gaia EDR3, 2MASS, and WISE data, 1077 disk-bearing TTS candidates were found in
LAMOST DR8, and stellar parameters were obtained. Among them, 783 are newly classified by spectra as classicalT Tauri stars (CTTSs; 169) or weak-lined T Tauri stars (WTTSs). Based on EW and FWHM of Ha, 157 TTSs in
accretion were identified, with 82% also having full disks. For TTSs with M<0.35 Mo, about 80% seem to alreadylose their full disks at 0.1 Myr, which may explain their lower mass, while the remaining 20% with full disks evolveat similar rates of non-full disks within 5 Myr, possibly suffice to form giant planets. The fraction of accreting TTSs
to disk-bearing TTSs is stable at 10% and can last ∼ 5-10 Myr, suggesting that full disks and accretion evolve withsimilar rates as non-full disks. For TTSs with M>0.35Mo, almost all full disks can survive more than 0.1 Myr, mostfor 1 Myr and some even for 20 Myr, which implies planets are more likely to be formed in their disks than those ofM<0.35 Mo, and thus M dwarfs with M>0.35Mo can have more planets. The fraction of full-disk TTSs to disk-bearing
TTSs decreases with age following the relation f ∝ t−0.35 , and similar relations existed in the fraction of accreting
TTSs and the fraction of full-disk CTTSs, suggesting faster full disks and accretion evolution than non-full disks.
For full disk stars, the ratio of accretion of lower-mass stars is systematically lower than that of higher-mass stars,

8confirming the dependence of accretion on stellar mass.

ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): Discovery of an
20. extremely dense and compact object embedded in the prestellar core G208.68-19.92-N2
Naomi Hirano, Dipen Sahu, Sheng-Yaun Liu, Tie Liu, Ken’ichi Tatematsu, Somnath Dutta, Shanghuo Li,
Chin-Fei Lee, Pak Shing Li, Shih-Ying Hsu, Sheng-Jun Lin, Doug Johnstone, Leonardo Bronfman, Huei-Ru
Vivien Chen, David J. Eden, Yi-Jehng Kuan, Woojin Kwon, Chang Won Lee, Hong-Li Liu, Mark G. Rawlings,
Isabelle Ristorcelli, Alessio Traficante ⋆ The internal structure of the prestellar core G208.68-19.02-N2 (G208-N2)

in the Orion Molecular Cloud 3 (OMC-3) region has been studied with the Atacama Large Millimeter/submillimeter
Array (ALMA). The dust continuum emission revealed a filamentary structure with a length of ∼5000 au and an
average H2 volume density of ∼6 × 107 cm−3 . At the tip of this filamentary structure, there is a compact object,which we call a “nucleus", with a radius of ∼150–200 au and a mass of ∼0.1 M⊙ . The nucleus has a central densityof ∼2 × 109 cm−3 with a radial density profile of r−1.87±0.11 . The density scaling of the nucleus is ∼3.7 times higher
than that of the singular isothermal sphere. This as well as the very low virial parameter of 0.39 suggest that thegravity is dominant over the pressure everywhere in the nucleus. However, there is no sign of CO outflow localized
to this nucleus. The filamentary structure is traced by the N2 D+ 3–2 emission, but not by the C18 O 2–1 emission,
implying the significant CO depletion due to high density and cold temperature. Toward the nucleus, the N2 D+ also
shows the signature of depletion. This could imply either the depletion of the parent molecule, N2 , or the presence ofthe embedded very-low luminosity central source that could sublimate the CO in the very small area. The nucleus in
G208-N2 is considered to be a prestellar core on the verge of first hydrostatic core (FHSC) formation or a candidate
for the FHSC.

Nuclear spin ratios of deuterated ammonia in prestellar cores. LAsMA observations of
21. H-MM1 and Oph D
Jorma Harju, Jaime E. Pineda, Olli Sipilä, Paola Caselli, Arnaud Belloche, Friedrich Wyrowski, Wiebke Riedel,
Elena Redaelli, Anton I. Vasyunin ⋆ We determine the ortho/para ratios of NH2D and NHD2 in two dense, starlesscores, where their formation is supposed to be dominated by gas-phase reactions, which, in turn, is predicted to result
in deviations from the statistical spin ratios. The Large APEX sub-Millimeter Array (LAsMA) multibeam receiverof the Atacama Pathfinder EXperiment (APEX) telescope was used to observe the prestellar cores H-MM1 and Oph
D in Ophiuchus in the ground-state lines of ortho and para NH2D and NHD2. The fractional abundances of thesemolecules were derived employing 3D radiative transfer modelling, using different assumptions about the abundance
profiles as functions of density. We also ran gas-grain chemistry models with different scenarios concerning proton ordeuteron exchanges and chemical desorption from grains to find out if one of these models can reproduce the observed
spin ratios. The observationally deduced ortho/para ratios of NH2D and NHD2 are in both cores within 10% of theirstatistical values 3 and 2, respectively, and taking 3-sigma limits, deviations from these of about 20% are allowed. Of
the chemistry models tested here, the model that assumes proton hop (as opposed to full scrambling) in reactions
contributing to ammonia formation, and a constant efficiency of chemical desorption, comes nearest to the observed
abundances and spin ratios. The nuclear spin ratios derived here are in contrast with spin-state chemistry models thatassume full scrambling in proton donation and hydrogen abstraction reactions leading to deuterated ammonia. The
efficiency of chemical desorption influences strongly the predicted abundances of NH3, NH2D, and NHD2, but has alesser effect on their ortho/para ratios. For these the proton exchange scenario in the gas is decisive. We suggest that
this is because of rapid re-processing of ammonia and related cations by gas-phase ion-molecule reactions.

KAgoshima Galactic Object survey with Nobeyama 45-metre telescope by Mapping
22. in Ammonia lines (KAGONMA): Discovery of parsec-scale CO depletion in the Canis
Major star-forming region
Yushi Hirata, Takeru Murase, Junya Nishi, Yoshito Shimajiri, Toshihiro Omodaka, Makoto Nakano, Kazuyoshi
Sunada, Takumi Ito, Toshihiro Handa ⋆ In observational studies of infrared dark clouds, the number of detectionsof CO freeze-out onto dust grains (CO depletion) at pc-scale is extremely limited, and the conditions for its occurrence
are, therefore, still unknown. We report a new object where pc-scale CO depletion is expected. As a part of Kagoshima
Galactic Object survey with Nobeyama 45-m telescope by Mapping in Ammonia lines (KAGONMA), we have mademapping observations of NH3 inversion transition lines towards the star-forming region associated with the CMa OB1

9including IRAS 07077-1026, IRAS 07081-1028, and PGCC G224.28-0.82. By comparing the spatial distributions of the
NH3 (1,1) and C18O (J=1-0), an intensity anti-correlation was found in IRAS 07077-1026 and IRAS 07081-1028 on
the 1 pc scale. Furthermore, we obtained a lower abundance of C18O at least in IRAS 07077-1026 than in the otherparts of the star-forming region. After examining high density gas dissipation, photodissociation, and CO depletion,
we concluded that the intensity anti-correlation in IRAS 07077-1026 is due to CO depletion. On the other hand, in thevicinity of the centre of PGCC G224.28-0.82, the emission line intensities of both the NH3 (1,1) and C18O (J=1-0)
were strongly detected, although the gas temperature and density were similar to IRAS 07077-1026. This indicatesthat there are situations where C18O (J=1-0) cannot trace dense gas on the pc scale and implies that the conditional
differences that C18O (J=1-0) can and cannot trace dense gas are unclear.

23. Formation of giant planets around intermediate-mass stars

Heather Johnston, Olja Panic, Beibei Liu ⋆ To understand giant planet formation, we need to focus on host stars
close to 1.7 M⊙ , where the occurrence rate of these planets is the highest. In this initial study, we carry out pebbledriven core accretion planet formation modelling to investigate the trends and optimal conditions for the formationof giant planets around host stars in the range of 1−2.4 M⊙ . We find that giant planets are more likely to form insystems with a larger initial disk radius; higher disk gas accretion rate; pebbles of ∼ millimeter in size; and birth
location of the embryo at a moderate radial distance of ∼ 10 AU. We also conduct a population synthesis study ofour model and find that the frequency of giant planets and super-Earths decreases with increasing stellar mass. This
contrasts the observational peak at 1.7 M⊙ , stressing the need for strong assumptions on stellar mass dependencies inthis range. Investigating the combined effect of stellar mass dependent disk masses, sizes, and lifetimes in the context
of planet population synthesis studies is a promising avenue to alleviate this discrepancy. The hot-Jupiter occurrence
rate in our models is ∼ 0.7−0.8% around 1 M⊙ - similar to RV observations around Sun-like stars, but drasticallydecreases for higher mass stars.

measurements in protoplanetary disks indicate fragile pebbles and low tur24. Grain-size
bulence
Haochang Jiang, Enrique Macías, Osmar M. Guerra-Alvarado, Carlos Carrasco-González ⋆ Recent laboratory

experiments have revealed that destructive collisions of icy dust particles may occur at much lower velocities than previously believed. These low fragmentation velocities push down the maximum grain size in collisional growth models.
Motivated by the smooth radial distribution of pebble sizes inferred from ALMA/VLA multi-wavelength continuum
analysis, we propose a concise model to explain this feature and aim to constrain the turbulence level at the midplaneof protoplanetary disks. Our approach is built on the assumption that the fragmentation threshold is the primarybarrier limiting pebble growth within pressure maxima. Consequently, the grain size at the ring location can provide
direct insights into the turbulent velocity governing pebble collisions and, by extension, the turbulence level at thedisk midplane. We validate this method using the Dustpy code, which simulates dust transport and coagulation. We
apply our method to 7 disks, TW Hya, IM Lup, GM Aur, AS 209, HL Tau, HD 163296, and MWC 480, for which grain
sizes have been measured from multi-wavelength continuum analysis. A common feature emerges from our analysis,
with an overall low turbulence coefficient of α ∼ 10−4 observed in five out of seven disks when taking fragmentation
velocity vfrag = 1 m s−1 . A higher fragmentation velocity would imply a turbulence coefficient significantly larger thanthe current observational constraints. IM Lup stands out with a relatively higher coefficient of 10−3 . Notably, HL Tau
exhibits an increasing trend in α with distance, which supports enhanced turbulence at its outer disk region, possibly
associated with the infalling streamer onto HL Tau. The current (sub)mm pebble size constrained in disks implies low
levels of turbulence, as well as fragile pebbles consistent with recent laboratory measurements.

Analytic description of the gas flow around planets embedded in protoplanetary disks
25. Ayumu Kuwahara, Hiroyuki Kurokawa ⋆ A growing planet embedded in a protoplanetary disk induces threedimensional gas flow, which exhibits a midplane outflow that can suppress dust accretion onto the planet and form
global dust substructures (rings and gaps). Because analytic formulae for the planet-induced outflow are usefulfor modeling its influences on local and global dust surface densities and planet accretion, we derive the analytic
formulae that describe the morphology and velocity of the planet-induced outflow. We first perform three-dimensional,
nonisothermal hydrodynamical simulations of the gas flow past a planet, which enables us to introduce a fitting formula
describing the morphology of the outflow. We then derive an analytic formula for the outflow speed using Bernoulli’s

10theorem. We successfully derived a fitting formula for the midplane outflow morphology (the shape of the streamline),
which is valid when the dimensionless thermal mass falls below m ≲ 0.6. The obtained analytic formulae for theoutflow, such as the maximum outflow speed and the velocity distributions of the outflow in the radial and verticaldirections to the disk, show good agreement with the numerical results. We find the following trends: (1) the maximum
outflow speed increases with the planetary mass and has a peak of ∼30–40% of the sound speed when the dimensionlessthermal mass is m ∼ 0.3, corresponding to a super-Earth mass planet at 1 au for the typical steady accretion disk
model, and (2) the presence of the headwind (namely, the global pressure force acting in the positive radial direction of
the disk) enhances (reduces) the outflow toward the outside (inside) of the planetary orbit. The planet-induced outflow
of the gas affects the dust motion when the dimensionless stopping time of dust falls below St ≲ min(10m2 , 0.1).

The Strength and Variability of the Helium 10830 Å Triplet in Young Stars, with
26. Implications for Exosphere Detection
Daniel M. Krolikowski, Adam L. Kraus, Benjamin M. Tofflemire, Caroline V. Morley, Andrew W. Mann,
Andrew Vanderburg ⋆ Young exoplanets trace planetary evolution, particularly the atmospheric mass loss that ismost dynamic in youth. However, the high activity level of young stars can mask or mimic the spectroscopic signalsof atmospheric mass loss. This includes the activity-sensitive He 10830 Å triplet, which is an increasingly important
exospheric probe. To characterize the He-10830 triplet at young ages, we present time-series NIR spectra for youngtransiting planet hosts taken with the Habitable-zone Planet Finder. The He-10830 absorption strength is similar
across our sample, except at the fastest and slowest rotation, indicating that young chromospheres are dense andpopulate metastable helium via collisions. Photoionization and recombination by coronal radiation only dominates
metastable helium population at the active and inactive extremes. Volatile stellar activity, such as flares and changing
surface features, drives variability in the He-10830 triplet. Variability is largest at the youngest ages before decreasing
to ≲ 5 − 10 mÅ (or 3%) at ages above 300 Myr, with 6 of 8 stars in this age range agreeing with no intrinsic
variability. He-10830 triplet variability is smallest and age-independent at the shortest timescales. Intrinsic stellar
variability should not preclude detection of young exospheres, except at the youngest ages. We recommend out-oftransit comparison observations taken directly surrounding transit and observation of multiple transits to minimize
activity’s effect. Regardless, caution is necessary when interpreting transit observations in the context of stellar
activity, as many scenarios can lead to enhanced stellar variability even on timescales of an hour.

27. A planetary collision afterglow and transit of the resultant debris cloud

Matthew Kenworthy, Simon Lock, Grant Kennedy, Richelle van Capelleveen, Eric Mamajek, Ludmila Carone,
Franz-Josef Hambsch, Joseph Masiero, Amy Mainzer, J. Davy Kirkpatrick, Edward Gomez, Zoë Leinhardt,
Jingyao Dou, Pavan Tanna, Arttu Sainio, Hamish Barker, Stéphane Charbonnel, Olivier Garde, Pascal Le
Dû, Lionel Mulato, Thomas Petit, Michael Rizzo Smith ⋆ Planets grow in rotating disks of dust and gas aroundforming stars, some of which can subsequently collide in giant impacts after the gas component is removed from thedisk. Monitoring programs with the warm Spitzer mission have recorded significant and rapid changes in mid-infrared
output for several stars, interpreted as variations in the surface area of warm dusty material ejected by planetary-scalecollisions and heated by the central star: e.g., NGC 2354-ID8, HD 166191 and V844 Persei. Here we report combined
observations of the young (about 300 Myr), solar-like star ASASSN-21qj: an infrared brightening consistent with ablackbody temperature of 1000 K and a luminosity of 4 percent of that of the star lasting for about 1000 days, partiallyoverlapping in time with a complex and deep wavelength-dependent optical eclipse that lasted for about 500 days.
The optical eclipse started 2.5 years after the infrared brightening, implying an orbital period of at least that duration.
These observations are consistent with a collision between two exoplanets of several to tens of Earth masses at 2 to
16 au from the central star. Such an impact produces a hot, highly-extended post-impact remnant with sufficientluminosity to explain the infrared observations. Transit of the impact debris, sheared by orbital motion into a longcloud, causes the subsequent complex eclipse of the host star.

11

The merger of hard binaries in globular clusters as the primary channel for the formation
28. of second generation stars
Valery Kravtsov, Sami Dib, Francisco A. Calderon ⋆ We have recently presented observational evidence whichsuggests that the origin of the second generation (G2) stars in globular clusters (GCs) is due to the binary-mediatedcollision of primordial (G1) low-mass main-sequence (MS) stars. This mechanism avoids both the mass budget problem
and the need of external gas for dilution. Here, we report on another piece of evidence supporting this scenario: (1)the fraction of MS binaries is proportional to the fraction of G1 stars in GCs and, at the same time, (2) the smaller thefraction of G1 stars is, the more deficient binaries of higher mass ratio (q> 0.7) are. They are, on average, harder thantheir smaller mass-ratio counterparts due to higher binding energy at a given primary mass. Then (2) implies that(1) is due to the merging/collisions of hard binaries rather than to their disruption. These new results complemented
by the present-day data on binaries lead to the following conclusions: (i) the mass-ratio distribution of binaries,
particularly short-period ones, with low-mass primaries, MP < 1.5 M⊙ , is strongly peaked close to q= 1.0, whereas(ii) dynamical processes at high stellar density tend to destroy softer binaries and make hard (nearly) twin binaries tobecome even harder and favor their mergers and collisions. G2 stars formed this way gain mass that virtually doubles
the primary one, 2MP , at which the number of G1 stars is ∼ 5 times smaller than at MP according to the slope of a
Milky Way-like IMF at MMS < 1.0 M⊙ .

The CO-to-H2 Conversion Factor of Galactic Giant Molecular Clouds using CO isotopo29. logues: High-resolution
X mapsCO

Mikito Kohno, Yoshiaki Sofue ⋆ We investigated the correlation between intensities of the 12 CO and 13 CO (J = 1-0)

lines toward the Galactic giant molecular clouds (GMCs) W51A, W33, N35-N36 complex, W49A, M17SW, G12.0200.03, W43, and M16 using the FUGIN (FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45-m
telescope) CO line data. All the GMCs show intensity saturation in the 12 CO line when the brightness temperature of13
CO is higher than a threshold temperature of about ∼ 5 K. We obtained high-resolution (∼ 20”) distribution mapsof the XCO factor (XCO,iso ) in individual GMCs using correlation diagrams of the CO isotopologues. It is shown that
XCO,iso is variable in each GMC within the range of XCO,iso ∼ (0.9−5) × 1020 cm−2 (K km s−1 )−1 . Despite the variability in the GMCs, the average value among the GMCs is found to be nearly constant at XCO,iso = (2.17±0.27)×1020
cm−2 (K km s−1 )−1 , which is consistent with that from previous studies in the Milky Way.

Inviscid protostellar disc ring formation and high density ring edges due to the ejection
30. and subsequent infall of material onto a protostellar disc
Kurt Liffman ⋆ Discs of gas and dust are ubiquitous around protostars. Hypothetical disc viscosity is thought tocause the gas and dust to accrete onto the star. Turbulence within the disc might be the source of this disc viscosity.
However, observed protostellar disc turbulence often appears to be small and not always conducive to disc accretion.
In addition, theories for disc and planet evolution have difficulty in explaining the observed disc rings/gaps which
form much earlier than expected. Protostellar accretion discs are observed to contain significant quantities of dust
and pebbles. Observations show that some of this material is ejected from near the protostar, where it travels to theouter regions of the disc. Such solid infalling material has a relatively small amount of angular momentum comparedto the material in the disc. This infalling material lowers the angular momentum of the disc and should drive a radialflow towards the protostar. We show that the local radial speed of the disc is proportional to the mass rate of infallingmaterial onto the disc. Higher rates of infall onto the disc implies higher radial accretion disc speeds. As such, regionswith high rates of infall will produce gaps on relatively short timescales in the disc, while regions associated withrelative low rates of infalling material will produce disc rings. As such, the inner edge of a disc gap will tend to havea higher surface density, which may enhance the probability of planet formation. In addition, the outer edge of a disc
gap will act as a dust trap and may become a site for planet formation. For the early Solar System, such a process may
have collected O16 -poor forsterite dust from the inner regions of the protosolar disc and O16 -rich CAIs and AOAs fromthe inner edge regions of the protosolar disc, thereby constructing a region favourable to the formation of prechondritic
planetesimals.

1231. Binary planet formation through tides

C. Lazzoni, K. W. Rice, A. Zurlo, S. Hinkley, S. Desidera ⋆ The search for satellites around exoplanets represents
one of the greatest challenges in advancing the characterization of planetary systems. Currently, we can only detectmassive satellites, which resemble additional planetary companions rather than rocky moons. It is not yet wellunderstood whether such substellar pairs, known as binary planets, are common or how they form. In this study,
we investigated the formation scenario for binary planets resulting from tidal dissipation during close encounters in
the gravitational instability scenario. We conducted seven sets of simulations, varying the number of initial planets
injected into the system from two to five, as well as the amount of energy lost due to tides. Our results demonstratethat this formation mechanism is quite efficient in producing binary planets, with an average occurrence rate for thesimulated systems of 14.3%. Additionally, we present the distribution of relevant physical parameters (semi-majoraxis, eccentricity, mass ratios, and formation time) for planet-planet pairs. We also provide comprehensive statistics
for single planets and planet-planet pairs.

32. A Near-infrared Variability Survey of Young Planetary-mass Objects
Pengyu Liu, Beth A. Biller, Johanna M. Vos, Niall Whiteford, Zhoujian Zhang, Michael C. Liu, Clemence
Fontanive, Elena Manjavacas, Thomas Henning, Matthew A. Kenworthy, Mariangela Bonavita, Mickael Bonnefoy, Emma Bubb, Simon Petrus, Joshua Schlieder ⋆ We present a photometric variability survey of youngplanetary-mass objects using the New Technology Telescope in the Js and Ks bands. Surface gravity plays an important role in the atmospheric structure of brown dwarfs, as young low gravity L dwarfs have a higher variability rate
than field L dwarfs. In this study, we extend variability studies to young T-type planetary-mass objects and investigate the effects of surface gravity on the variability of L and T dwarfs across a large sample. We conduct continuous
monitoring for 18 objects with spectral types from L5 to T8 and detect four new variables and two variable candidates.
Combining with previous variability surveys of field and young L and T objects, we find that young objects tend to be
more variable than field objects within peak-to-peak variability amplitude ranges of 0.5-10 per cent and period rangesof 1.5-20 hr. For the first time, we constrain the variability rate of young T dwarfs to be 56 per cent compared to
25 per cent for field T dwarfs. Both field and young samples have higher variability rates at the L/T transition thanoutside the L/T transition. The differences in the variability rates between field and young samples are about 1 sigma
and therefore larger sample sizes are needed to confirm and refine the results. Besides the L/T transition, young L
dwarfs with strong variability tend to assemble in a narrow spectral type range of L6-L7.5. This work supports thecritical role of surface gravity on the atmospheric structure from L to T spectral types.

The disk of the eruptive protostar V900 Mon; a MATISSE/VLTI and MUSE/VLT
33. perspective
F. Lykou, P. Ábrahám, F. Cruz-Sáenz de Miera, J. Varga, Á. Kóspál, J. Bouwman, L. Chen, S. Kraus, M.
L. Sitko, R. W. Russell, M. Pikhartova ⋆ In this work, we study the silicate dust content in the disk of one of

the youngest eruptive stars, V900 Mon, at the highest angular resolution probing down to the inner 10 au of said
disk, and study the historical evolution of the system traced in part by a newly discovered emission clump. We
performed high-angular resolution mid-infrared interferometric observations of V900 Mon with MATISSE/VLTI witha spatial coverage ranging from 38-m to 130-m baselines, and compared them to archival MIDI/VLTI data. We also
mined and re-analyzed archival optical and infrared photometry of the star to study its long-term evolution since its
eruption in the 1990s. We complemented our findings with integral field spectroscopy data from MUSE/VLT. The
MATISSE/VLTI data suggest a radial variation of the silicate feature in the dusty disk, whereby at large spatial
scales (≥ 10 au) the protostellar disk’s emission is dominated by large-sized (≥ 1 µm) silicate grains, while at smaller
spatial scales and closer to the star (≤ 5 au), silicate emission is absent suggesting self-shielding. We propose that the
self-shielding may be the result of small dust grains at the base of the collimated CO outflow previously detected by
ALMA. A newly discovered knot in the MUSE/VLT data, located at a projected distance approximately 27,000 aufrom the star, is co-aligned with the molecular gas outflow at a P.A. of 250o (±5o ) consistent with the position angle
and inclination of the disk. The knot is seen in emission in Hα, [N II], and the [S II] doublet and its kinematic age isabout 5150 years. This ejected material could originate from a previous eruption.

13

34. Magnetic fields of the starless core L 1512
Sheng-Jun Lin, Shih-Ping Lai, Kate Pattle, David Berry, Dan P. Clemens, Laurent Pagani, Derek WardThompson, Travis J. Thieme, Tao-Chung Ching ⋆ We present JCMT POL-2 850 um dust polarization observations

and Mimir H band stellar polarization observations toward the starless core L1512. We detect the highly-ordered corescale magnetic field traced by the POL-2 data, of which the field orientation is consistent with the parsec-scale magnetic
fields traced by Planck data, suggesting the large-scale fields thread from the low-density region to the dense core region
in this cloud. The surrounding magnetic field traced by the Mimir data shows a wider variation in the field orientation,suggesting there could be a transition of magnetic field morphology at the envelope scale. L1512 was suggested to bepresumably older than 1.4 Myr in a previous study via time-dependent chemical analysis, hinting that the magnetic
field could be strong enough to slow the collapse of L1512. In this study, we use the Davis-Chandrasekhar-Fermi
method to derive a plane-of-sky magnetic field strength (Bpos ) of 18±7 uG and an observed mass-to-flux ratio (λobs )of 3.5±2.4, suggesting that L1512 is magnetically supercritical. However, the absence of significant infall motion andthe presence of an oscillating envelope are inconsistent with the magnetically supercritical condition. Using a Virial
analysis, we suggest the presence of a hitherto hidden line-of-sight magnetic field strength of 27 uG with a mass-to-flux
ratio (λtot ) of 1.6, in which case both magnetic and kinetic pressures are important in supporting the L1512 core. On
the other hand, L1512 may have just reached supercriticality and will collapse at any time.

35. The first Ka-band (26.1-35 GHz) blind line survey towards Orion KL
Xunchuan Liu, Tie Liu, Zhiqiang Shen, Sheng-Li Qin, Qiuyi Luo, Yan Gong, Yu Cheng, Christian Henkel, Qilao
Gu, Fengyao Zhu, Tianwei Zhang, Rongbing Zhao, Yajun Wu, Bin Li, Juan Li, Zhang Zhao, Jinqing Wang,
Weiye Zhong, Qinghui Liu, Bo Xia, Li Fu, Zhen Yan, Chao Zhang, Lingling Wang, Qian Ye, Aiyuan Yang,
Fengwei Xu, Chao Zhang, Somnath Dutta, Shanghuo Li, Meizhu Liu, Dongting Yang, Chuanshou Li, Li Chen

⋆ We conducted a Ka-band (26.1–35 GHz) line survey towards Orion KL using the TianMa 65-m Radio Telescope(TMRT). It is the first blind line survey in the Ka band, and achieves a sensitivity of mK level (1–3 mK at a spectral
resolution of ∼1 km s−1 ). In total, 592 Gaussian features are extracted. Among them, 257 radio recombination lines(RRLs) are identified. The maximum ∆n of RRLs of H, He and C are 20, 15, and 5, respectively. Through stacking,we have detected the β lines of ion RRLs (RRLs of C+ with possible contribution of other ions like O+ ) for the firsttime, and tentative signal of the γ lines of ion RRLs can also be seen on the stacked spectrum. Besides, 318 otherline features were assigned to 37 molecular species, and ten of these species were not detected in the Q-band survey of
TMRT. The vibrationally excited states of nine species were also detected. Emission of most species can be modeled
under LTE. A number of transitions of E-CH3OH (J2 −J1 ) display maser effects, which are confirmed by our modeling,
and besides the bumping peak at J ∼ 6 there is another peak at J ∼ 13. Methylcyanoacetylene (CH3 C3 N) is detectedin Orion KL for the first time. This work emphasizes that the Ka band, which was long-ignored for spectral line
surveys, is very useful for surveying RRLs and molecular lines simultaneously.

36. The need for spatially resolved observations of PAHs in protoplanetary discs
K. Lange, C. Dominik, A. G. G. M. Tielens ⋆ The signatures of polycyclic aromatic hydrocarbons (PAHs) havebeen observed in protoplanetary discs, and their emission features obtained from spectral energy distributions (SED)
have been used in the literature to characterise their size and determine their abundance. Two simple disc models(uniform PAH distribution against a PAH gap in the inner disc) are compared to investigate the difference of their SED
and obtainable information. We used the radiative transfer code RADMC-3D to model the SED of two protoplanetary
discs orbiting a typical Herbig star, one of which features a depletion of PAHs in the inner disc. We further createdartificial images of the discs at face-on view to extract radial profiles of the PAH emission in the infrared. We findthat the extracted PAH features from an SED provide limited information about the PAHs in protoplanetary discenvironments, except for the ionisation state. The distribution of PAHs in a protoplanetary disc influences the total
observed PAH luminosity in a non-linear fashion and alters the relative strength between the 3.3 µm and 11.3 µm
features. Furthermore, we produced radial profiles at the 3 µm, 6 µm and, 11 µm PAH emission features and findthat they follow a double power-law profile where the slope reflects the radiative environment (single photon regime
vs. multi-photon regime) in which the PAHs lie. Using spatially resolved techniques such as IFU or imaging in theera of the James Webb Space Telescope, we find that multi-wavelength radial emission profiles will not only provide
information on the spatial distribution of the PAHs, but may also provide information on their size and underlying
UV environment, which is crucial for photo-evaporative disc wind models.

14

37. β Pictoris b through the eyes of the upgraded CRIRES+
Rico Landman, Tomas Stolker, Ignas Snellen, Jean Costes, Sam de Regt, Yapeng Zhang, Siddharth Gandhi,
Paul Mollière, Aurora Kesseli, Arthur Vigan, Alejandro Sánchez-López ⋆ Context: High-resolution spectrographs

fed by adaptive optics (AO) provide a unique opportunity to characterize directly imaged exoplanets. Observations
with such instruments allow us to probe the atmospheric composition, spin rotation, and radial velocity of the planet,
thereby helping to reveal information on its formation and migration history. The recent upgrade of the Cryogenic
High-Resolution Infrared Echelle Spectrograph (CRIRES+) at the VLT makes it a highly suitable instrument for characterizing directly imaged exoplanets. Aims: In this work, we report on observations of β Pictoris b with CRIRES+
and use them to constrain the planets atmospheric properties and update the estimation of its spin rotation. Methods:
The data were reduced using the open-source pycrires package. We subsequently forward-modeled the stellar, planetary, and systematic contribution to the data to detect molecules in the planet’s atmosphere. We also used atmosphericretrievals to provide new constraints on its atmosphere. Results: We confidently detected water and carbon monoxidein the atmosphere of β Pictoris b and retrieved a slightly sub-solar carbon-to-oxygen ratio, which is in agreement withprevious results. The interpretation is hampered by our limited knowledge of the C/O ratio of the host star. We also
obtained a much improved constraint on its spin rotation of 19.9 ± 1.0 km/s, which gives a rotation period of 8.7 ± 0.8
hours, assuming no obliquity. We find that there is a degeneracy between the metallicity and clouds, but this has
minimal impact on the retrieved C/O, v sin i, and radial velocity. Our results show that CRIRES+ is performing welland stands as a highly useful instrument for characterizing directly imaged planets.

38. C I Traces the Disk Atmosphere in the IM Lup Protoplanetary Disk
Charles J. Law, Felipe Alarcón, L. Ilsedore Cleeves, Karin I. Öberg, Teresa Paneque-Carreño ⋆ The central starand its energetic radiation fields play a vital role in setting the vertical and radial chemical structure of planet-forming
disks. We present observations that, for the first time, clearly reveal the UV-irradiated surface of a protoplanetary
disk. Specifically, we spatially resolve the atomic-to-molecular (C I-to-CO) transition in the IM Lup disk with ALMA
archival observations of [C I] 3 P1 -3 P0 . We derive a C I emitting height of z/r ≳ 0.5 with emission detected out toa radius of ≈600 au. Compared to other systems with C I heights inferred from unresolved observations or models,the C I layer in the IM Lup disk is at scale heights almost double that of other disks, confirming its highly flared
nature. C I arises from a narrow, optically-thin layer that is substantially more elevated than that of 12 CO (z/r ≈0.3-0.4), which allows us to directly constrain the physical gas conditions across the C I-to-CO transition zone. We
also compute a radially-resolved C I column density profile and find a disk-averaged C I column density of 2×1016
cm−2 , which is ≈3-20× lower than that of other disks with spatially-resolved C I detections. We do not find evidence
for vertical substructures or spatially-localized deviations in C I due, e.g., to either an embedded giant planet or aphotoevaporative wind that have been proposed in the IM Lup disk, but emphasize that deeper observations are
required for robust constraints.

circumstellar disk lifetimes to the rotational evolution of low-mass stars
39. Linking
Kristina Monsch, Jeremy J. Drake, Cecilia Garraffo, Giovanni Picogna, Barbara Ercolano ⋆ The high-energy
radiation emitted by young stars can have a strong influence on their rotational evolution at later stages. This isbecause internal photoevaporation is one of the major drivers of the dispersal of circumstellar disks, which surroundall newly born low-mass stars during the first few million years of their evolution. Employing an internal EUV/X-ray
photoevaporation model, we have derived a simple recipe for calculating realistic inner disk lifetimes of protoplanetarydisks. This prescription was implemented into a magnetic morphology-driven rotational evolution model and is used
to investigate the impact of disk-locking on the spin evolution of low-mass stars. We find that the length of the disklocking phase has a profound impact on the subsequent rotational evolution of a young star, and the implementation ofrealistic disk lifetimes leads to an improved agreement of model outcomes with observed rotation period distributions
for open clusters of various ages. However, for both young star-forming regions tested in our model, the strong
bimodality in rotation periods that is observed in hPer could not be recovered. hPer is only successfully recovered,if the model is started from a double-peaked distribution with an initial disk fraction of 65 %. However, at an age of
only ∼ 1 Myr, such a low disk fraction can only be achieved if an additional disk dispersal process, such as external
photoevaporation, is invoked. These results therefore highlight the importance of including realistic disk dispersal
mechanisms in rotational evolution models of young stars.

15

Line profiles of forbidden emission lines and what they can tell us about protoplanetary
40. disk winds
Ahmad Nemer, Jeremy Goodman ⋆ Emission in forbidden lines of oxygen, neon, and other species are commonlyused to trace winds from protoplanetary disks. Using Cloudy, we calculate such emission for parametrized windmodels of the magnetothermal type, following Bai et al. (2016). These models share characteristics with bothphotoevaporative and magnetocentrifugal winds, which can be regarded as end members, and are favored by recent
theoretical research. Both broad and narrow low-velocity components of the lines can be produced with plausible windparameters, something that traditional wind models have difficulty with. Line luminosities, blueshifts, and widths, aswell as trends of these with accretion luminosity and disk inclination, are in general accord with observations

41. Identifying the population of T-Tauri stars in Taurus: UV-optical synergy

Prasanta K. Nayak, Mayank Narang, Manoj Puravankara, Himanshu Tyagi, Bihan Banerjee, Saurabh Sharma,
Rakesh Pandey, Arun Surya, Blesson Mathew, R. Arun, K. Ujjwal, Sreeja S. Kartha ⋆ With the third data

release of the Gaia mission Gaia DR3 with its precise photometry and astrometry, it is now possible to study the
behaviour of stars at a scale never seen before. In this paper, we developed new criteria to identify T-Tauri stars(TTS) candidates using UV and optical CMDs by combining the GALEX and Gaia surveys. We found 19 TTS
candidates and 5 of them are newly identified TTS in the Taurus Molecular Cloud (TMC), not catalogued before as
TMC members. For some of the TTS candidates, we also obtained optical spectra from several Indian telescopes. We
also present the analysis of the distance and proper motion of young stars in the Taurus using data from Gaia DR3.
We found that the stars in Taurus show a bimodal distribution with distance, having peaks at 130.171.31−1.24 pc and156.251.86
pc.
The
reasonfor
thisbimodality,
wethink,
is
due
to
the
fact
that
different
cloudsinthe
TMC region−5.00
are at different distances. We further show that the two populations have similar ages and proper motion distribution.
Using the Gaia DR3 colour-magnitude diagram, we show that the age of Taurus is consistent with 1 Myr.

PDRs4All VI: Probing the Photochemical Evolution of PAHs in the Orion Bar Using
42. Machine Learning Techniques
S. Pasquini, E. Peeters, B. Schefter, B. Khan, A. Sidhu, R. Chown, J. Cami, A. Tielens, F. Alarcon, A. Canin,
I. Schroetter, B. Trahin, D. Van De Putte, C. Boersma, E. Dartois, T. Onaka, A. Candian, P. Hartigan, T.
S. -Y. Lai, G. Rouille, D. A. Sales, Y. Zhang, E. Habart, O. Berne ⋆ [Abridged] JWST observations of theOrion Bar have shown the incredible richness of PAH bands and their variation on small scales. We aim to probe thephotochemical evolution of PAHs across the key zones of the photodissociation region (PDR) that is the Orion Bar
using unsupervised machine learning. We use NIRSpec and MIRI IFU data from the JWST ERS Program PDRs4All.
We lever bisecting k-means clustering to generate detailed spatial maps of the spectral variability in several wavelength
regions. We discuss the variations in the cluster profiles and connect them to the local physical conditions. We interpretthese variations with respect to the key zones: the HII region, the atomic PDR zone, and the three dissociation fronts.
The PAH emission exhibits spectral variation that depends strongly on spatial position in the PDR. We find the 8.6um
band to behave differently than all other bands which vary systematically with one another. We find uniform variationin the 3.4-3.6um bands and 3.4/3.3 intensity ratio. We attribute the carrier of the 3.4-3.6um bands to a single sidegroup attached to very similarly sized PAHs. Cluster profiles reveal a transition between characteristic profiles classesof the 11.2um feature from the atomic to the molecular PDR zone. We find the carriers of each of the profile classes tobe independent, and reason the latter to be PAH clusters existing solely deep in the molecular PDR. Clustering also
reveals a connection between the 11.2 and 6.2um bands; and that clusters generated from variation in the 10.9-11.63um
region can be used to recover those in the 5.95-6.6um region. Clustering is a powerful tool for characterizing PAH
variability on both spatial and spectral scales. For individual bands as well as global spectral behaviours, we find
UV-processing to be the most important driver of the evolution of PAHs and their spectral signatures in the Orion
Bar.

16

Forming Giant Planets Around Late-M Dwarfs: Pebble Accretion and Planet-Planet
43. Collision
Mengrui Pan, Beibei Liu, Anders Johansen, Masahiro Ogihara, Su Wang, Jianghui Ji, Sharon X. Wang,
Fabo Feng, Ignasi Riba ⋆ We propose a pebble-driven core accretion scenario to explain the formation of giant

planets around the late-M dwarfs of M⋆ =0.1−0.2 M⊙ . In order to explore the optimal disk conditions for giant
planet, we perform N-body simulations to investigate the growth and dynamical evolution of both single and multiple
protoplanets in the disks with both inner viscously heated and outer stellar irradiated regions. The initial masses ofthe protoplanets are either assumed to be equal to 0.01 M⊕ or calculated based on the formula derived from streaming
instability simulations. Our findings indicate that massive planets are more likely to form in disks with longer
lifetimes, higher solid masses, moderate to high levels of disk turbulence, and larger initial masses of protoplanets.
In the single protoplanet growth cases, the highest planet core mass that can be reached is generally lower than
the threshold necessary to trigger rapid gas accretion, which impedes the formation of giant planets. Nonetheless,in multi-protoplanet cases, the cores can exceed the pebble isolation mass barrier aided by frequent planet-planet
collisions. This consequently speeds up their gas accretion and promotes giant planet formation, making the optimal
parameter space to grow giant planets substantially wider. Taken together, our results suggest that even around very
low-mass stellar hosts, the giant planets with orbital periods of ≲100 days are still likely to form when lunar-mass
protoplanets first emerge from planetesimal accretion and then grow rapidly by a combination of pebble accretion andplanet-planet collisions in disks with a high supply of pebble reservoir >50 M⊕ and turbulent level of αt ∼10−3 −10−2 .

Insight into the Formation of β Pic b through the Composition of Its Parent Protoplan44. etary Disk as Revealed by the β Pic Moving Group Member HD 181327
Henrique Reggiani, Jhon Yana Galarza, Kevin C. Schlaufman, David K. Sing, Brian F. Healy, Andrew
McWilliam, Joshua D. Lothringer, Laurent Pueyo ⋆ It has been suggested that β Pic b has a supersolar metal-

licity and subsolar C/O ratio. Assuming solar carbon and oxygen abundances for the star β Pic and therefore theplanet’s parent protoplanetary disk, β Pic b’s C/O ratio suggests that it formed via core accretion between its parent protoplanteary disk’s H2 O and CO2 ice lines. β Pic b’s high metallicity is difficult to reconcile with its mass
Mp = 11.7 MJup though. Massive stars can present peculiar photospheric abundances that are unlikely to record theabundances of their former protoplanetary disks. This issue can be overcome for early-type stars in moving groups
by infering the elemental abundances of the FGK stars in the same moving group that formed in the same molecular
cloud and presumably share the same composition. We infer the photospheric abundances of the F dwarf HD 181327,
a β Pic moving group member that is the best available proxy for the composition of β Pic b’s parent protoplanetary
disk. In parallel, we infer updated atmospheric abundances for β Pic b. As expected for a planet of its mass formed
via core-accretion beyond its parent protoplanetary disk’s H2 O ice line, we find that β Pic b’s atmosphere is consistent
with stellar metallicity and confirm that is has superstellar carbon and oxygen abundances with a substellar C/O
ratio. We propose that the elemental abundances of FGK dwarfs in moving groups can be used as proxies for theotherwise difficult-to-infer elemental abundances of early-type and late-type members of the same moving groups.

45. A HST Study of the Substellar Population of NGC 2024

Massimo Robberto, Mario Gennaro, Nicola Da Rio, Giovanni Maria Strampelli, Leonardo Ubeda, Elena Sabbi,
Dana Koeppe, Jonathan C. Tan, David R. Soderblom ⋆ We performed a HST/WFC3-IR imaging survey of theyoung stellar cluster NGC 2024 in three filters probing the 1.4 µm H2 O absorption feature, characteristic of the
population of low mass and sub-stellar mass objects down to a few Jupyter masses. We detect 812 point sources,
550 of them in all 3 filters with signal to noise greater than 5. Using a distance-independent two-color diagram wedetermine extinction values as high as AV ≃ 40. We also find that the change of effective wavelengths in our filters
results in higher AV values as the reddening increases. Reconstructing a dereddened color-magnitude diagram wederive a luminosity histogram for both the full sample of candidate cluster members and for an extinction-limited
sub-sample containing the 50% of sources with AV ≲ 15. Assuming a standard extinction law like Cardelli et al.
(1989) with a nominal RV =3.1 we produce a luminosity function in good agreement with the one resulting from a
Salpeter-like Initial Mass Function for a 1 Myr isochrone. There is some evidence of an excess of luminous stars in
the most embedded region. We posit that the correlation may be due to those sources being younger, and therefore
overluminous than the more evolved and less extinct cluster’s stars. We compare our classification scheme based on
the depth of the 1.4µm photometric feature with the results from the spectroscopic survey of Levine et al. (2006), andwe report a few peculiar sources and morphological features typical of the rich phenomenology commonly encountered17

in young star-forming regions.

46. Massive star-formation in the hub-filament system of RCW 117
Arun Seshadri, S. Vig, S. K. Ghosh, D. K. Ojha ⋆ We present a multiwavelength investigation of the hub-filament

system RCW 117 (IRAS 17059-4132), which shows intricate filamentary features in the far-infrared, mapped using
Herschel images. We obtain the column density and dust temperature maps for the region using the Herschel images,
and identify 88 cores and 12 filaments from the column density map of the region (18′ ×18′ ). We employ the ThrUMMS
13
CO (J=1-0) data for probing the kinematics in RCW 117, and find velocity gradients (∼ 0.3 − 1 km s−1 pc−1 ) withhints of matter inflow along the filamentary structures. Ionised gas emission from the associated HII region is examinedusing the Giant Metrewave Radio Telescope (GMRT) at 610 and 1280 MHz, and is found to be of extent 5 × 3 pc2 withintensity being brightest towards the hub. We estimate the peak electron density towards the hub to be ∼ 750 cm−3 .
Thirty four Class 0/I young stellar objects (YSOs) have been identified in the region using the Spitzer GLIMPSE
colour-colour diagram, with many lying along the filamentary structures. Based on the (i) presence of filamentary
structures, (ii) distribution of cores across the region, with ∼ 39along the filamentary structures, (iii) massive starformation tracers in the hub, and (iv) the kinematics, we believe that global hierarchical collapse can plausibly explain
the observed features in RCW 117.

47. Outcomes of Planetary Collisions: Importance of Gravity and Material Properties

Jeremy L. Smallwood, Jeffrey S. Lee, Lorin S. Matthews, Bryant M. Wyatt ⋆ The final sizes, composition, andangular momenta of solid planetary bodies depend on the outcomes of collisions between planetary embryos. The
most common numerical method for simulating embryo collisions is to combine a gravity solver with a hydrodynamic
solver, allowing pressure gradients, shock waves, and gravitational torques to loft material into orbit. Here, we performthe first direct comparison between hydrodynamic methods and a simplified method employing only gravity and aquadratic repulsive force. The formation of Earth’s Moon, perhaps the most heavily simulated planetary collision,is used as a test case. Many of the main features of a collision between two planetary embryos, including collisions
in which an orbiting disc of material and/or intact moons are formed, are controlled solely by gravitational forces.
Comparison of the methods shows that the mass and orbit of the satellite, as well as the extent of physical mixing
between the protoearth and impactor, are similar regardless of the inclusion of the inclusion of hydrodynamic effects
or the equation of state employed. The study of thermal and chemical effects of the impact, and determining the timescale for lunar accretion, still require a full hydrodynamic calculation. The simplified gravity plus quadratic repulsive
force approach allows rapid testing of various initial conditions to identify cases for further detailed study.

and its fashionable nebula: a four year long period Young Stellar Object
48. VVV-WIT-12
with a light echo?
Roberto K. Saito, Bringfried Stecklum, Dante Minniti, Philip W. Lucas, Zhen Guo, Leigh C. Smith, Luciano
Fraga, Felipe Navarete, Juan Carlos Beamín, Calum Morris ⋆ We report the serendipitous discovery of VVV-

WIT-12, an unusual variable source that seems to induce variability in its surrounding nebula. The source belongs
to the rare objects that we call WITs (short for What Is This?) discovered within the VISTA Variables in the Vía
Láctea (VVV) survey. VVV-WIT-12 was discovered during a pilot search for light echoes from distant Supernovae(SNe) in the Milky Way using the near-IR images of the VVV survey. This source has an extremely red spectralenergy distribution, consistent with a very reddened (AV ∼ 100 mag) long period variable star (P ∼ 1525 days).
Furthermore, it is enshrouded in a nebula that changes brightness and color with time, apparently in synch withthe central source variations. The near-IR light curve and complementary follow-up spectroscopy observations are
consistent with a variable Young Stellar Object (YSO) illuminating its surrounding nebula. In this case the source
periodic variation along the cycles produces an unprecedented light echo in the different regions of the nebula.

49. Aligned Grains and Scattered Light Found in Gaps of Planet-Forming Disk
Ian W. Stephens, Zhe-Yu Daniel Lin, Manuel Fernandez-Lopez, Zhi-Yun Li, Leslie W. Looney, Haifeng Yang,
Rachel Harrison, Akimasa Kataoka, Carlos Carrasco-Gonzalez, Satoshi Okuzumi, Ryo Tazaki ⋆ Polarized(sub)millimeter emission from dust grains in circumstellar disks was initially thought to be due to grains alignedwith the magnetic field. However, higher resolution multi-wavelength observations along with improved models foundthat this polarization is dominated by self-scattering at shorter wavelengths (e.g., 870 µm) and by grains aligned
18with something other than magnetic fields at longer wavelengths (e.g., 3 mm). Nevertheless, the polarization signal is
expected to depend on the underlying substructure, and observations hitherto have been unable to resolve polarizationin multiple rings and gaps. HL Tau, a protoplanetary disk located 147.3 ± 0.5 pc away, is the brightest Class I or
Class II disk at millimeter/submillimeter wavelengths. Here we show deep, high-resolution 870 µm polarization
observations of HL Tau, resolving polarization in both the rings and gaps. We find that the gaps have polarization
angles with a significant azimuthal component and a higher polarization fraction than the rings. Our models showthat the disk polarization is due to both scattering and emission from aligned effectively prolate grains. The intrinsic
polarization of aligned dust grains is likely over 10%, which is much higher than what was expected in low resolution
observations ( 1%). Asymmetries and dust features are revealed in the polarization observations that are not seen in
non-polarimetric observations.

50. The RMS survey: a census of massive YSO multiplicity in the K-band

Robert G. Shenton, Rebecca J. Houghton, René D. Oudmaijer, Simon P. Goodwin, Stuart L. Lumsden, Evgenia
Koumpia, Maria Koutoulaki ⋆ Close to 100 per cent of massive stars are thought to be in binary systems. The

multiplicity of massive stars seems to be intrinsically linked to their formation and evolution, and Massive Young
Stellar Objects are key in observing this early stage of star formation. We have surveyed three samples totallinghundreds of MYSOs (> 8M⊙ ) across the Galaxy from the RMS catalogue, using UKIDSS and VVV point source data,
and UKIRT K−band imaging to probe separations between 0.8-9 arcsec (approx 1000-100,000 au). We have usedstatistical methods to determine the binary statistics of the samples, and we find binary fractions of 64 ± 4 per cent for
the UKIDSS sample, 53±4 per cent for the VVV sample, and 49±8 per cent for the RMS imaging sample. Also we use
the J− and K−band magnitudes as a proxy for the companion mass, and a significant fraction of the detected systems
have estimated mass ratios greater than 0.5, suggesting a deviation from the capture formation scenario which would
be aligned with random IMF sampling. Finally, we find that YSOs located in the outer Galaxy have a higher binary
fraction than those in the inner Galaxy. This is likely due to a lower stellar background density than observed towards
the inner Galaxy, resulting in higher probabilities for visual binaries to be physical companions. It does indicate abinary fraction in the probed separation range of close to 100 per cent without the need to consider selection biases.

JWST imaging of edge-on protoplanetary disks II. Appearance of edge-on disks with a
51. tilted inner region: case study of IRAS04302+2247
M. Villenave, K. R. Stapelfeldt, G. Duchene, F. Menard, S. G. Wolff, M. D. Perrin, C. Pinte, R. Tazaki, D.
Padgett ⋆ We present JWST imaging from 2µm to 21µm of the edge-on protoplanetary disk around the embedded

young star IRAS04302+2247. The structure of the source shows two reflection nebulae separated by a dark lane. The
source extent is dominated by the extended filamentary envelope at ∼4.4µm and shorter wavelengths, transitioning at
7µm and longer wavelengths to more compact lobes of scattered light from the disk itself. The dark lane thickness does
not vary significantly with wavelength, which we interpret as an indication for intermediate-sized (∼ 10µm) grainsin the upper layers of the disk. Intriguingly, we find that the brightest nebula of IRAS40302 switches side between
12.8µm and 21µm. We explore the effect of a tilted inner region on the general appearance of edge-on disks. We findthat radiative transfer models of a disk including a tilted inner region can reproduce an inversion in the brightest
nebula. In addition, for specific orientations, the model also predicts strong lateral asymmetries, which can occur
for more than half possible viewing azimuths. A large number of edge-on protoplanetary disks observed in scattered
light show such lateral asymmetries (15/20), which suggests that a large fraction of protoplanetary disks might host atilted inner region. Stellar spots may also induce lateral asymmetries, which are expected to vary over a significantly
shorter timescale. Variability studies of edge-on disks would allow to test the dominant scenario for the origin of theseasymmetries.

Mid-infrared spectra of T Tauri disks: Modeling the effects of a small inner cavity on
52. CO2 and H2O emission
Marissa Vlasblom, Ewine F. van Dishoeck, Benoît Tabone, Simon Bruderer ⋆ [Abridged] The inner few AU ofdisks around young stars are best probed in the infrared. The James Webb Space Telescope (JWST) is now starting
to characterize the chemistry of these regions in unprecedented detail. One peculiar subset of sources are the so-called“CO2-only sources”, in which only a strong 15 µm CO2 feature was detected in the spectrum. One scenario that could
explain the weak emission from H2O is the presence of a small, inner cavity in the disk. If this cavity were to extend

19past the H2O snowline, but not past the CO2 snowline, this could strongly suppress the H2O line flux w.r.t. that of
CO2. In this work, we aim to test the validity of this statement. Using the thermo-chemical code Dust And LInes(DALI), we created a grid of T Tauri disk models with an inner cavity, meaning we fully depleted the inner region of
the disk in gas and dust starting from the dust sublimation radius and ranging until a certain cavity radius. We present
the evolution of the CO2 and H2O spectra of a disk with inner cavity size, showing that, when a large-enough cavity
is introduced, a spectrum that was initially dominated by H2O lines can become CO2-dominated instead. However,the cavity size needed for this is around 4-5 AU, exceeding the nominal position of the CO2 snowline in a full disk.
The cause of this is most likely the alteration of the thermal structure by the cavity, which pushes the snowlines
outward. Alternative explanations for bright CO2 emission are also briefly discussed. Our modeling work shows that
it is possible for the presence of a small inner cavity to explain strong CO2 emission in a spectrum. However, thecavity needed to do so is larger than what was initially expected. As such, this scenario will be easier to test with
sufficiently high angular resolution (millimeter) observations.

53. Molecular clouds in M51 from high-resolution extinction mapping
Helena Faustino Vieira, Ana Duarte-Cabral, Timothy A. Davis, Nicolas Peretto, Matthew W. L. Smith, MiguelQuerejeta, Dario Colombo, Michael Anderson ⋆ Here we present the cloud population extracted from M51, follow-

ing the application of our new high-resolution dust extinction technique to the galaxy (Faustino Vieira et al. 2023).
With this technique, we are able to image the gas content of the entire disc of M51 down to 5 pc (0.14"), which allows us to perform a statistical characterisation of well-resolved molecular cloud properties across different large-scale
dynamical environments and with galactocentric distance. We find that cloud growth is promoted in regions in thegalaxy where shear is minimised; i.e. clouds can grow into higher masses (and surface densities) inside the spiral arms
and molecular ring. We do not detect any enhancement of high-mass star formation towards regions favourable tocloud growth, indicating that massive and/or dense clouds are not the sole ingredient for high-mass star formation. We
find that in the spiral arms there is a significant decline of cloud surface densities with increasing galactocentric radius,
whilst in the inter-arm regions they remain relatively constant. We also find that the surface density distribution forspiral arm clouds has two distinct behaviours in the inner and outer galaxy, with average cloud surface densities atlarger galactocentric radii becoming similar to inter-arm clouds. We propose that the tidal interaction between M51
and its companion (NGC 5195) - which heavily affects the nature of the spiral structure - might be the main factor
behind this.

The role of turbulence in high-mass star formation: Subsonic and transonic turbulence
54. are ubiquitously found at early stages
Chao Wang, Ke Wang, Feng-Wei Xu, Patricio Sanhueza, Hauyu Baobab Liu, Qizhou Zhang, Xing Lu, F.
Fontani, Paola Caselli, Gemma Busquet, Jonathan C. Tan, Di Li, J. M. Jackson, Thushara Pillai, Paul T. P.
Ho, Andrés E. Guzmán, Nannan Yue ⋆ Context. Traditionally, supersonic turbulence is considered to be one of

the most likely mechanisms to slow down the gravitational collapse in dense clumps, thereby enabling the formationof massive stars. However, several recent studies have raised differing points of view based on observations carriedout with sufficiently high spatial and spectral resolution. These studies call for a re-evaluation of the role turbulence
plays in massive star-forming regions. Aims. Our aim is to study the gas properties, especially the turbulence, ina sample of massive star-forming regions with sufficient spatial and spectral resolution, which can both resolve thecore fragmentation and the thermal line width. Methods. We observed NH3 metastable lines with the Very Large
Array (VLA) to assess the intrinsic turbulence. Results. Analysis of the turbulence distribution histogram for 32
identified NH3 cores reveals the presence of three distinct components. Furthermore, our results suggest that (1) suband transonic turbulence is a prevalent (21 of 32) feature of massive star-forming regions and those cold regions areat early evolutionary stage. This investigation indicates that turbulence alone is insufficient to provide the necessaryinternal pressure required for massive star formation, necessitating further exploration of alternative candidates; and(2) studies of seven multi-core systems indicate that the cores within each system mainly share similar gas properties
and masses. However, two of the systems are characterized by the presence of exceptionally cold and dense cores thatare situated at the spatial center of each system. Our findings support the hub-filament model as an explanation forthis observed distribution

20

The Gaia-ESO Survey: 3D dynamics of young groups and clusters from GES and Gaia
55. EDR3
Nicholas J. Wright, R. D. Jeffries, R. J. Jackson, G. G. Sacco, Becky Arnold, E. Franciosini, G. Gilmore,
A. Gonneau, L. Morbidelli, L. Prisinzano, S. Randich, Clare C. Worley ⋆ We present the first large-scale 3D

kinematic study of 2000 spectroscopically-confirmed young stars (<20 Myr) in 18 star clusters and OB associations(hereafter groups) from the combination of Gaia astrometry and Gaia-ESO Survey spectroscopy. We measure 3D
velocity dispersions for all groups, which range from 0.61 to 7.4 km/s (1D velocity dispersions of 0.35 to 4.3 km/s).
We find the majority of groups have anisotropic velocity dispersions, suggesting they are not dynamically relaxed.
From the 3D velocity dispersions, measured radii and estimates of total mass we estimate the virial state and findthat all systems are super-virial when only the stellar mass is considered, but that some systems are sub-virial whenthe mass of the molecular cloud is taken into account. We observe an approximately linear correlation between the 3D
velocity dispersion and the group mass, which would imply that the virial state of groups scales as the square root of
the group mass. However, we do not observe a strong correlation between virial state and group mass. In agreementwith their virial state we find that nearly all of the groups studied are in the process of expanding and that the
expansion is anisotropic, implying that groups were not spherical prior to expansion. One group, Rho Oph, is found to
be contracting and in a sub-virial state (when the mass of the surrounding molecular cloud is considered). This work
provides a glimpse of the potential of the combination of Gaia and data from the next generation of spectroscopic
surveys.

A Pathway for Collisional Planetesimal Growth in the Ice-Dominant Regions of Proto56. planetary Disks
Elizabeth Yunerman, Diana Powell, Ruth Murray-Clay ⋆ We present a semi-analytic model for the growth, drift,

desorption, and fragmentation of millimeter- to meter-sized particles in protoplanetary disks. Fragmentation occurs
where particle collision velocities exceed critical fragmentation velocities. Using this criterion, we produce fragmentation regions in disk orbital radius-particle size phase space for particles with a range of material properties, structures,and compositions (including SiO2 , Mg2 SiO4 , H2 O, CO2 , and CO). For reasonable disk conditions, compact aggregate H2 O, CO2 , and CO ice particles do not reach destructive relative velocities and are thus not likely to undergo
collisional fragmentation. Uncoated silicate particles are more susceptible to collisional destruction and are expected
to fragment in the inner disk, consistent with previous work. We then calculate the growth, drift, and sublimationof small particles, initially located in the outer disk. We find that ice-coated particles can avoid fragmentation as
they grow and drift inward under a substantial range of disk conditions as long as the particles are aggregates composed of 0.1 µm-sized monomers. Such particles may undergo runaway growth in disk regions abundant in H2 O or
CO2 ice depending on the assumed disk temperature structure. These results indicate that icy collisional growth toplanetesimally-relevant sizes may happen efficiently throughout a disk’s lifetime, and is particularly robust at earlytimes when the disk’s dust-to-gas ratio is comparable to that of the interstellar medium.

A Systematic Observational Study on Galactic Interstellar Ratio 18O/17O. II. C18O
57. and C17O J=2-1 Data Analysis
Y. P. Zou, J. S. Zhang, C. Henkel, D. Romano, W. Liu, Y. H. Zheng, Y. T. Yan, J. L. Chen, Y. X. Wang, J. Y.
Zhao ⋆ To investigate the relative amount of ejecta from high-mass versus intermediate-mass stars and to trace thechemical evolution of the Galaxy, we have performed with the IRAM 30m and the SMT 10m telescopes a systematic
study of Galactic interstellar 18O/17O ratios toward a sample of 421 molecular clouds, covering a galactocentric
distance range of 1-22 kpc. The results presented in this paper are based on the J=2-1 transition and encompass 364
sources showing both C18O and C17O detections. The previously suggested 18O/17O gradient is confirmed. For the 41
sources detected with both facilities, good agreement is obtained. A correlation of 18O/17O ratios with heliocentric
distance is not found, indicating that beam dilution and linear beam sizes are not relevant. For the subsample of
IRAM 30 m high-mass star-forming regions with accurate parallax distances, an unweighted fit gives 18O/17O =(0.12±0.02) RGC +(2.38±0.13) with a correlation coefficient of R=0.67. While the slope is consistent with our J=1-0
measurement, ratios are systematically lower. This should be caused by larger optical depths of C18O 2-1 lines,
w.r.t the corresponding 1-0 transitions, which is supported by RADEX calculations and the fact that C18O/C17O ispositively correlated with 13CO/C18O. After considering optical depth effects with C18O J=2-1 reaching typically an
optical depth of 0.5, corrected 18O/17O ratios from the J=1-0 and J=2-1 lines become consistent. A good numerical
fit to the data is provided by the MWG-12 model, including both rotating stars and novae.
21Exploring the dust grain size and polarization mechanism in the hot and massive Class
58. 0 disk IRAS 16293-2422 B
Joaquin Zamponi, María José Maureira, Hauyu Baobab Liu, Bo Zhao, Dominique Segura-Cox, Chia-Lin Ko,
Paola Caselli ⋆ Multiwavelength dust continuum and polarization observations arising from self-scattering have beenused to investigate grain sizes in young disks. However, the polarization by self-scattering is low in face-on opticallythick disks and puts some of the size constraints from polarization on hold, particularly for the younger and more
massive disks. The 1.3 mm emission detected toward the hot (≳400 K) Class 0 disk IRAS 16293-2422 B has been
attributed to self-scattering, predicting grain sizes between 200-2000 µm. We investigate the effects of grain size inthe resultant flux and polarization fractions from self-scattering using a hot and massive Class 0 disk model andcompare with observations. We compared new and archival high-resolution observations between 1.3 and 18 mm to aset of synthetic models. We have developed a new public tool to automate this process called Synthesizer. This is aneasy-to-use program to generate synthetic observations from numerical simulations. Optical depths are in the range of
130 to 2 from 1.3 to 18 mm, respectively. Predictions from significant grain growth populations, including millimetricgrains are comparable to the observations at all wavelengths. The polarization fraction produced by self-scatteringreaches a maximum of ∼0.1% at 1.3 mm for a maximum grain size of 100 µm, being an order of magnitude lower
than that observed with ALMA. From the comparison of Stokes I fluxes, we conclude that significant grain growth
could be present in the young Class 0 disk IRAS 16293 B, particularly in the inner hot region (< 10 au, T > 300 K)
where refractory organics evaporate. The polarization produced by self-scattering in our model is not high enoughto explain the observations at 1.3 and 7 mm, and effects like dichroic extinction or polarization reversal of elongatedaligned grains remain other possible but untested scenarios.

59. Observing planetesimal formation under streaming instability in the rings of HD 163296

Francesco Zagaria, Cathie J. Clarke, Richard A. Booth, Stefano Facchini, Giovanni P. Rosotti ⋆ We introduce

a new technique to determine the gas turbulence and surface density in bright disc rings, under the assumption that
dust growth is limited by turbulent fragmentation at the ring centre. We benchmark this prescription in HD 163296,
showing that our measurements are consistent with available turbulence upper limits and agree with independent
estimates of the gas surface density within a factor of two. We combine our results with literature measurementsof the dust surface density and grain size to determine the dust-to-gas ratio and Stokes number in the 67 au and
100 au rings. Our estimates suggest that particle clumping is taking place under the effect of streaming instability(SI) in the 100 au ring. Even though in the presence of external isotropic turbulence this process might be hindered,we provide evidence that turbulence is non-isotropic in both rings and likely originating from mechanisms (such as
ambipolar diffusion) that could ease particle clumping under SI. Finally, we determine the mass accretion rate under
the assumption that the disc is in steady state and turbulence regulates angular momentum transport. Our results arein tension with spectroscopic measurements and suggest that other mechanisms might be responsible for accretion, in
qualitative agreement with the detection of a magneto-centrifugal wind in this system. Applying our method to larger
samples can be used to statistically assess if SI is a viable mechanism to form planetesimals in bright rings.

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