The Star Formation Newsletter
A community newsletter on Star and Planet Formation research 25 July 2021
Editor: João Alves
No. 343

www.starformation.news

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Cover image caption
Amazing Ophiuchus, a Summer favorite. The ρ Oph cluster is shown at the upper left (the three bright stars mark the cluster
center). L1688, the dark clump towards the upper right, contains the closest embedded cluster of YSOs. Many famous andwell-studied young sources, that played a fundamental role in early star formation studies, are hidden in this optical image.
The L1689 cloud lies to the lower right, below L1688, while L1709 and Oph D are seen towards the center of the image. Credit:
Leonardo Ciuolotti, Matteo Collina, Riccardo De Benedictis, Giuseppe Donatiello, Rolando Ligustri.

Note from the Editor
The Star Formation Newsletter is now on the web atwww.starformation.news. This PDF le contains the monthly Abstracts

and links to the dierent Newsletter sections. Red text in this PDF is a url link. Submitting an abstract to the SFN is as simple

Do not remove the LATEX formatting
when submitting to the arXiv. If you do, your abstract will not look great either at the arXiv (which uses MathJax toas entering the arXiv ID (e.g., 2006.10139) in a web form on the SFN web site.

A

convert L TEX math symbols to the web) or the SFN.

Abstracts

Multi-scale Dust Polarization and Spiral-like Stokes-I Residual in the Class I Protostellar System TMC-1A
Yusuke Aso, Woojin Kwon, Naomi Hirano, Tao-Chung Ching, Shih-Ping Lai, Zhi-Yun Li, Ramprasad Rao

We have observed the Class I protostar TMC-1A in the Taurus molecular cloud using the Submillimeter Array (SMA) andthe Atacama Large Millimeter/submillimeter Array (ALMA) in the linearly polarized 1.3 mm continuum emission at angularresolutions of3" and0.3", respectively.

The ALMA observations also include CO, 13CO, and C18O J=2-1 spectral lines.

The SMA observations trace magnetic elds on the 1000-au scale, the directions of which are neither parallel nor perpendicular
to the outow direction.

Applying the Davis-Chandrasekhar-Fermi method to the SMA polarization angle dispersion, we

estimate a eld strength in the TMC-1A envelope of 1-5 mG. It is consistent with the eld strength needed to reduce theradial infall velocity to the observed value, which is substantially less than the local free-fall velocity. The ALMA polarization
observations consist of two distinct components  a central component and a north/south component. The central component
shows polarization directions in the disk minor axis to be azimuthal, suggesting dust self-scattering in the TMC-1A disk. The
north/south component is located along the outow axis and the polarization directions are aligned with the outow direction.
We discuss possible origins of this polarization structure, including grain alignment by a toroidal magnetic eld and mechanicalalignment by the gaseous outow. In addition, we discover a spiral-like residual in the total intensity (Stokes I) for the rsttime. The C18O emission suggests that material in the spiral-like structure is infalling at a speed that is 20the local Keplerian
speed.

2. PV Cep and V350 Cep: stars on the way between FUors AND EXors
H. R. Andreasyan, T. Yu. Magakian, T. A. Movsessian, A. V. Moiseev

Based on new observations during 2015-2020 and published data, the unusual eruptive variables PV Cep and V350 Cep are
examined. It is shown that PV Cep underwent a regular outburst followed by a drop in brightness that lasted overall from 2011
to 2019 and is still in a deep minimum. The outburst was accompanied by substantial changes in the intensity and proles of anumber of lines, including Ha, [SII], and [OI]. The forbidden lines generally have negative radial velocities and can be divided
into four components, with variable velocities and relative intensities. V350 Cep essentially is at a maximum brightness level
over the entire time and its spectrum is practically unaltered. The available data suggest that the pronounced P Cyg prole ofthe Ha line in the spectrum of V350 Cep appeared several years after the luminosity rise, in 1986. The luminosities of the stars2

in the current state are estimated to be 20 L(sun) and 3.3 L(sun), respectively. It is concluded that both stars may represent a
so-called intermediate objects between the FUor and EXor classes.

GIARPS High-resolution Observations of T Tauri stars (GHOsT). III. A pilot study of

3. stellar and accretion properties

J. M. Alcalá, M. Gangi, K. Biazzo, S. Antoniucci, A. Frasca, T. Giannini, U. Munari, B. Nisini, A. Harutyunyan,
C. F. Manara, F. Vitali
The mass-accretion rate, Macc, is a crucial parameter for the study of the evolution of accretion disks around young low-massstellar objects (YSOs) and for planet formation studies. The Taurus star forming region (SFR) is rich in pre-main sequence(PMS) stars, most of them of the T Tauri class.

A variety of methodologies have been used in the past to measure massaccretion in samples of YSOs in Taurus, but despite being a general benchmark for star formation studies, a comprehensive andsystematic analysis of the Taurus T Tauri population, where the stellar and accretion properties are derived homogeneously andsimultaneously, is still missing. As part of the GIARPS High-resolution Observations of T Tauri stars (GHOsT) project, here
we present a pilot study of the stellar and accretion properties of seven YSOs in Taurus using the spectrograph GIARPS at
the Telescopio Nazionale Galileo (TNG). Contemporaneous low-resolution spectroscopic and photometric ancillary observations
allow us to perform an accurate ux calibration of the high-resolution spectra. The simultaneity of the high-resolution, wideband spectroscopic observations, from the optical to the near-infrared (NIR), the veiling measurements in such wide spectral
range, and many well-calibrated emission line diagnostics allows us to derive the stellar and accretion properties of the seven
YSOs in a homogeneous and self-consistent way. The procedures and methodologies presented here will be adopted in future
works for the analysis of the complete GHOsT data set. We discuss the accretion properties of the seven YSOs in comparison
with the 90% complete sample of YSOs in the Lupus SFR and investigate possibilities for the origin of the continuum excess
emission in the NIR.

of the angular momentum during gravitational fragmentation of molecular
4. Evolution
clouds
G. Arroyo-Chávez, E. Vázquez-Semadeni∼ R3/2 between the specic angular momentum j and the radius R ofmolecular clouds (MCs) and their their substructures, and of the observed near independence of β , the ratio of rotational togravitational energy, from R. To this end, we measure the angular momentum (AM) of sets of particles in an SPH simulation
We investigate the origin of the observed scaling jof the formation, collapse and fragmentation of giant MCs. The sets of SPH particles are dened either as clumps (connectedparticle sets), or as lagrangian sets that conform a connected clump only at a certain time tdef . We nd that: i) Clumps evolve
along the observed jR relation at all times, ii) Lagrangian particle sets evolve along the observed relation when the volumecontaining them also contains a large number of other intruder particles. Otherwise, they evolve with j ∼ cst.

iii) Tracking

lagrangian sets to the future, we nd that a subset of the SPH particles participates in the collapse, while another disperses
away. iv) Noting that, under AM conservation, β increases during contraction, we suggest that its near independence of radius
may arise from the competition between this increase and an increase in the AM exchange rate at higher rotational energy
density gradient.

v) We suggest that, if MCs are globally dominated by gravity, the observed jR relation arises because theobservational selection of its dense structures amounts to selecting the fragments that have lost AM via Reynolds stresses fromtheir neighbors.

5. Classication of Filament Formation Mechanisms in Magnetized Molecular Clouds
Daisei Abe, Tsuyoshi Inoue, Shu-ichiro Inutsuka, Tomoaki Matsumoto

Recent observations of molecular clouds show that dense laments are the sites of present-day star formation.

Thus, it isnecessary to understand the lament formation process because these laments provide the initial condition for star formation.
Theoretical research suggests that shock waves in molecular clouds trigger lament formation. Since several dierent mechanisms
have been proposed for lament formation, the formation mechanism of the observed star-forming laments requires clarication.
In the present study, we perform a series of isothermal magnetohydrodynamics simulations of lament formation. We focus on
the inuences of shock velocity and turbulence on the formation mechanism and identied three dierent mechanisms for thelament formation. The results indicate that when the shock is fast, at shock velocity vsh = 7 km/s, the gas ows driven by
the curved shock wave create laments irrespective of the presence of turbulence and self-gravity. However, at a slow shock
velocity vsh = 2.5 km/s, the compressive ow component involved in the initial turbulence induces lament formation. Whenboth the shock velocities and turbulence are low, the self-gravity in the shock-compressed sheet becomes important for lament
formation. Moreover, we analyzed the line-mass distribution of the laments and showed that strong shock waves can naturally3create high-line-mass laments such as those observed in the massive star-forming regions in a short time. We conclude thatthe dominant lament formation mode changes with the velocity of the shock wave triggering the lament formation.

6. Detection of coherent low-frequency radio bursts from weak-line TTauri stars

A. Feeney-Johansson, S. J. D. Purser, T. P. Ray, A. A. Vidotto, J. Eislöel, J. R. Callingham, T. W. Shimwell,
H. K. Vedantham, G. Hallinan, C. Tasse
In recent years, thanks to new facilities such as LOFAR capable of sensitive observations, much work has been done on thedetection of stellar radio emission at low frequencies. Such emission has commonly been shown to be coherent emission, generally
attributed to electron-cyclotron maser emission, and has usually been detected from main-sequence M dwarfs. Here we reportthe rst detection of coherent emission at low frequencies from T Tauri stars, which are known to be associated with high levelsof stellar activity. Using LOFAR, we have detected several bright radio bursts at 150 MHz from two weak-line T Tauri stars:
13
KPNO-Tau 14 and LkCa 4. All of the bursts have high brightness temperatures (10− 1014 K) and high circular polarization

fractions (60 - 90 %), indicating that they must be due to a coherent emission mechanism. This could be either plasma emission
or electron-cyclotron maser (ECM) emission. Due to the exceptionally high brightness temperatures seen in at least one of the
14
bursts (≥ 10K), and the high circular polarization levels, it seems unlikely that plasma emission could be the source and so
ECM is favoured as the most likely emission mechanism. Assuming this is the case, the required magnetic eld in the emission
regions would be 40 - 70 G. We determine that the most likely method of generating ECM emission is plasma co-rotation
breakdown in the stellar magnetosphere.

There remains the possibility, however, it could be due to an interaction with anorbiting exoplanet.

7. The Transition from Diuse Molecular Gas to Molecular Cloud Material in Taurus

S. R. Federman, Johnathan S. Rice, A. M. Ritchey, Hwihyun Kim, John H. Lacy, Paul F. Goldsmith, Nicolas
Flagey, Gregory N. Mace, David L. Lambert
We study four lines of sight that probe the transition from diuse molecular gas to molecular cloud material in Taurus.
Measurements of atomic and molecular absorption are used to infer the distribution of species and the physical conditions
toward stars behind the Taurus Molecular Cloud (TMC). New high-resolution spectra at visible and near infrared wavelengths+
of interstellar Ca II, Ca I, K I, CH, CH , C2, CN, and CO toward HD28975 and HD29647 are combined with data at

visible wavelengths and published CO results from ultraviolet measurements for HD27778 and HD30122.

Gas densities andtemperatures are inferred from C2, CN, and CO excitation and CN chemistry. Our results for HD29647 are noteworthy because
18−2−3
the CO column density is 10cm
while C2 and CO excitation reveals a temperature of 10 K and density about 1000 cm,
more like conditions found in dark molecular clouds. Similar results arise from our chemical analysis for CN through reactions
involving observations of CH, C2, and NH. Enhanced potassium depletion and a reduced CH/H2 column density ratio alsosuggest the presence of a dark cloud. The directions toward HD27778 and HD30122 probe molecule-rich diuse clouds, which
can be considered CO-dark gas, while the sight line toward HD28975 represents an intermediate case. Maps of dust temperature
help rene the description of the material along the four sight lines and provide an estimate of the distance between HD29647
and a clump in the TMC. An Appendix provides results for the direction toward HD26571; this star also probes diuse moleculargas.

Project. III. Star-by-star simulations of star cluster formation using a direct
8. SIRIUS
N-body integrator with stellar feedback
Michiko S. Fujii, Takayuki R. Saitoh, Yutaka Hirai, Long Wang

One of the computational challenges of cluster formation simulations is resolving individual stars and simulating massive
4
clusters with masses of more than 10 M
without gravitational softening. Combining direct N -body code with smoothedparticle hydrodynamics (SPH) code, we have developed a new code,

ASURA+BRIDGE, in which we can integrate stellar

particles without softening. We add a feedback model for HII regions into this code, in which thermal and momentum feedback
is given within the Strömgren radius. We perform N -body/SPH simulations of star cluster formation. Without softening, aportion of massive stars are ejected from the forming clusters.

As a result, the stellar feedback works outside the clusters.

This enhances/suppresses the star formation in initially sub-virial/super-virial clouds. We nd that the formed star clusters
are denser than currently observed open clusters, but the massdensity relation is consistent with or even higher than that is
estimated as an initial cluster density. We also nd that some clusters have multiple peaks in their stellar age distribution as aconsequence of their hierarchical formation.

4

9. X-ray Super-Flares From Pre-Main Sequence Stars: Flare Modeling
Konstantin V. Getman, Eric D. Feigelson, Gordon P. Garmire

Getman et al. (2021) reports the discovery, energetics, frequencies, and eects on environs of > 1000 X-ray super-ares with
34
X-ray energies EX ∼ 10
− 1038 erg from pre-main sequence (PMS) stars identied in the Chandra MYStIX and SFiNCs
surveys.

Here we perform detailed plasma evolution modeling of 55 bright MYStIX/SFiNCs super-ares from these events.

They constitute a large sample of the most powerful stellar ares analyzed in a uniform fashion.

They are compared withpublished X-ray super-ares from young stars in the Orion Nebula Cluster, older active stars, and the Sun.
emerge.

Several results

First, the properties of PMS X-ray super-ares are independent of the presence or absence of protoplanetary disks

inferred from infrared photometry, supporting the solar-type model of PMS aring magnetic loops with both footpoints anchoredin the stellar surface. Second, most PMS super-ares resemble solar long duration events (LDEs) that are associated with coronalmass ejections. Slow rise PMS super-ares are an interesting exception. Third, strong correlations of super-are peak emission
measure and plasma temperature with the stellar mass are similar to established correlations for the PMS X-ray emission
composed of numerous smaller ares.

Fourth, a new correlation of loop geometry is linked to stellar mass; more massive

stars appear to have thicker aring loops. Finally, the slope of a long-standing relationship between the X-ray luminosity andmagnetic ux of various solar-stellar magnetic elements appears steeper in PMS super-ares than for solar events.

10. The Macroporosity of Rubble Pile Asteroid Ryugu and Implications for the Origin of

Chondrules

William Herbst, James P. Greenwood, Teng Ee Yap
We use the known surface boulder-size distribution of the C-type rubble pile asteroid Ryugu (NEA 162173) to determine
its macroporosity, assuming it is a homogeneous granular aggregate.

We show that the volume-frequency distribution of its

boulders, cobbles and pebbles, is well represented by a lognormal function with σ = 2.4 ± 0.1 and µ = 0.2 ± 0.05. Applicationof linear-mixture packing theory yields a value for the macroporosity of φ = 0.14 ± 0.04. Given its low bulk density of 1.19 gm−3−3cm, this implies an average density for Ryugu's rocks of 1.38 ± 0.07 gm cm
throughout its volume, consistent with a recent
determination for surface boulders based on their thermal properties. This supports the spectrum-based argument that IDP's
may be the best analog material available on Earth and suggests that high-density, well-lithied objects such as chondrules andchondrule-bearing chondrites may be rare on Ryugu. Implications of this result for the origin of chondrules, a long-standing
problem in cosmochemistry, are discussed. We propose that chondrules and most chondrites formed together in rare lithication
events, which occurred during the accretion of chondritic envelopes to large, dierentiated planetesimals at a time when they26
were still hot fromAl decay.

11. Misaligned Circumstellar Disks and Orbital Motion of the Young Binary XZ Tau

Takanori Ichikawa, Miyu Kido, Daisuke Takaishi, Yoshito Shimajiri, Yusuke Tsukamoto, Shigehisa Takakuwa
We report our analyses of the multi-epoch (2015-2017) ALMA archival data of the Class II binary system XZ Tau at Bands
3, 4 and 6. The millimeter dust continuum images show compact, unresolved (r <the individual binary stars; XZ Tau A and B, with a projected separation of

15 au) circumstellar disks (CSDs) around

39 au. The 12CO (2-1) emission associated withthose CSDs traces the Keplerian rotations, whose rotational axes are misaligned with each other (P.A.
and

130 deg for XZ Tau B). The similar systemic velocities of the two CSDs (VLSR-5 deg for XZ Tau A

6.0 km s-1) suggest that the orbital

plane of the binary stars is close to the plane of the sky. From the multi-epoch ALMA data, we have also identied the relative
orbital motion of the binary. Along with the previous NIR data, we found that the elliptical orbit (e = 0.742+0.025-0.034, a= 0.172+0.002-0.003, and ω = -54.2+2.0-4.7 deg) is preferable to the circular orbit. Our results suggest that the two CSDs
and the orbital plane of the XZ Tau system are all misaligned with each other, and possible mechanisms to produce such aconguration are discussed. Our analyses of the multi-epoch ALMA archival data demonstrate the feasibility of time-domainscience with ALMA.

ALMA observations of doubly deuterated water: Inheritance of water from the prestel-

12. lar environment

S. S. Jensen, J. K. Jørgensen, L. E. Kristensen, A. Coutens, E. F. van Dishoeck, K. Furuya, D. Harsono, M.
V. Persson
Establishing the origin of the water D/H ratio in the Solar System is central to our understanding of the chemical trail of water
during the star and planet formation process. Recent modeling suggests that comparisons of the D2 O/HDO and HDO/H2 O

ratios are a powerful way to trace the chemical evolution of water and, in particular, determine whether the D/H ratio is inherited

5

from the molecular cloud or established locally. We seek to determine the D2 O column density and derive the D2 O/HDO ratios
in the warm region toward the low-mass Class 0 sources B335 and L483. The results are compared with astrochemical models
and previous observations to determine their implications for the chemical evolution of water. We present ALMA observationsof the D2 O transition at 316.8 GHz toward B335 and L483 at <0.5" (< 100 au) resolution, probing the inner warm envelope
18gas. The column densities of D2 O, HDO, and H2 O are determined by synthetic spectrum modeling and direct Gaussian tting,under the assumption of a single excitation temperature and similar spatial extent for the three water isotopologs. D2 O is−2
detected toward both sources in the inner warm envelope. The derived D2 O/HDO ratios is (1.0 ± 0.2) × 10
for L483 and(1.4 ± 0.1) × 10−2 for B335. The high D2 O/HDO ratios are a strong indication of chemical inheritance of water from theprestellar phase down to the inner warm envelope. This implies that the local cloud conditions in the prestellar phase, such astemperatures and timescales, determine the water chemistry at later stages and could provide a source of chemical dierentiation
in young systems. In addition, the observed D2 O/H2 O ratios support an observed dichotomy in the deuterium fractionation ofwater toward isolated and clustered protostars, namely, a higher D/H ratio toward isolated sources

13. A Deep Search for Five Molecules in the 49 Ceti Debris Disk

Jessica Klusmeyer, A. Meredith Hughes, Luca Matra, Kevin Flaherty, Agnes Kospal, Attila Moor, Aki Roberge,
Karin Oberg, Aaron Boley, Jacob White, David Wilner, Peter Abraham
Surprisingly strong CO emission has been observed from more than a dozen debris disks around nearby main-sequence stars.
The origin of this CO is unclear, in particular whether it is left over from the protoplanetary disk phase or is second-generationmaterial released from collisions between icy bodies like debris dust.

The primary unexplored avenue for distinguishing theorigin of the material is understanding its molecular composition. Here we present a deep search for ve molecules (CN, HCN,
HCO+, SiO, and CH3OH) in the debris disk around 49 Ceti. We take advantage of the high sensitivity of the Atacama Large
Millimeter/submillimeter Array (ALMA) at Band 7 to integrate for 3.2 hours at modest spatial (1") and spectral (0.8 km/s)
resolution. Our search yields stringent upper limits on the ux of all surveyed molecular lines, which imply abundances relative
to CO that are orders of magnitude lower than those observed in protoplanetary disks and Solar System comets, and also thosepredicted in outgassing models of second-generation material. However, if CI shielding is responsible for extending the lifetimeof any CO produced in second-generation collisions, as proposed by Kral et al. (2018), then the line ratios do not reect true ice
phase chemical abundances, but rather imply that CO is shielded by its own photodissociation product, CI, but other molecules
are rapidly photodissociated by the stellar and interstellar radiation eld.

14. A high pitch angle structure in the Sagittarius Arm

M. A. Kuhn, R. A. Benjamin, C. Zucker, A. Krone-Martins, R. S. de Souza, A. Castro-Ginard, E. E. O. Ishida,
M. S. Povich, L. A. HillenbrandContext: In spiral galaxies, star formation tends to trace features of the spiral pattern, including arms, spurs, feathers, andbranches. However, in our own Milky Way, it has been challenging to connect individual star-forming regions to their larger
Galactic environment owing to our perspective from within the disk. One feature in nearly all modern models of the Milky
Way is the Sagittarius Arm, located inward of the Sun with a pitch angle of

12 deg. Aims: We map the 3D locations andvelocities of star-forming regions in a segment of the Sagittarius Arm using young stellar objects (YSOs) from the Spitzer/IRAC
Candidate YSO (SPICY) catalog to compare their distribution to models of the arm. Methods: Distances and velocities forthese objects are derived from Gaia EDR3 astrometry and molecular line surveys.

We infer parallaxes and proper motions

for spatially clustered groups of YSOs and estimate their radial velocities from the velocities of spatially associated molecular
clouds. Results: We identify 25 star-forming regions in the Galactic longitude range l 4.0-18.5 deg arranged in a narrow,1

kpc long linear structure with a high pitch angle of ψ = 56 deg and a high aspect ratio of 7:1. This structure includes massive
star-forming regions such as M8, M16, M17, and M20. The motions in the structure are remarkably coherent, with velocities
in the direction of Galactic rotation of 240 ± 3 km/s (slightly higher than average) and slight drifts toward the Galactic center(-4.3 km/s) and in the negative Z direction (-2.9 km/s). The rotational shear experienced by the structure is 4.6 km/s/kpc.
Conclusions: The observed 56 deg pitch angle is remarkably high for a segment of the Sagittarius Arm. We discuss possible
interpretations of this feature as a substructure within the lower pitch angle Sagittarius Arm, as a spur, or as an isolated
structure.

15. The density structure of supersonic self-gravitating turbulence

Shivan Khullar, Christoph Federrath, Mark R. Krumholz, Christopher D. Matzner
We conduct numerical experiments to determine the density probability distribution function (PDF) produced in supersonic,
isothermal, self-gravitating turbulence of the sort that is ubiquitous in star-forming molecular clouds. Our experiments cover a6

wide range of turbulent Mach number and virial parameter, allowing us for the rst time to determine how the PDF responds
as these parameters vary, and we introduce a new diagnostic, the dimensionless star formation eciency versus density (ff (s))
curve, which provides a sensitive diagnostic of the PDF shape and dynamics. We show that the PDF follows a universal functional
form consisting of a log-normal at low density with two distinct power law tails at higher density; the rst of these represents
the onset of self-gravitation, and the second reects the onset of rotational support. Once the star formation eciency reaches a
few percent, the PDF becomes statistically steady, with no evidence for secular time-evolution at star formation eciencies fromabout ve to 20 percent. We show that both the Mach number and the virial parameter inuence the characteristic densities atwhich the log-normal gives way to the rst power-law, and the rst to the second, and we extend (for the former) and develop(for the latter) simple theoretical models for the relationship between these density thresholds and the global properties of the
turbulent medium.

16. The Transition of Polarized Dust Thermal Emission from the Protostellar Envelope to

the Disk Scale

Ka Ho Lam, Che-Yu Chen, Zhi-Yun Li, Haifeng Yang, Erin G. Cox, Leslie W. Looney, Ian Stephens
Polarized dust continuum emission has been observed with ALMA in an increasing number of deeply embedded protostellar
systems.

It generally shows a sharp transition going from the protostellar envelope to the disk scale, with the polarization

fraction typically dropping from ∼5% to ∼1% and the inferred magnetic eld orientations becoming more aligned with the
major axis of the system. We quantitatively investigate these observational trends using a sample of protostars in the Perseus
molecular cloud and compare these features with a non-ideal MHD disk formation simulation. We nd that the gas density
increases faster than the magnetic eld strength in the transition from the envelope to the disk scale, which makes it moredicult to magnetically align the grains on the disk scale. Specically, to produce the observed ∼1% polarization at ∼100 au
scale via grains aligned with the B-eld, even relatively small grains of 1 µm in size need to have their magnetic susceptibilities
signicantly enhanced (by a factor of ∼20) over the standard value, potentially through superparamagnetic inclusions. Thisrequirement is more stringent for larger grains, with the enhancement factor increasing linearly with the grain size, reaching∼2 × 104 for millimeter-sized grains. Even if the required enhancement can be achieved, the resulting inferred magnetic eldorientation in the simulation does not show a preference for the major axis, which is inconsistent with the observed pattern.
We thus conclude that the observed trends are best described by the model where the polarization on the envelope scale isdominated by magnetically aligned grains and that on the disk scale by scattering.

17. The link between gas and stars in the S254-S258 star-forming region

D. A. Ladeyschikov, M. S. Kirsanova, A. M. Sobolev, M. Thomasson, V. Ossenkopf-Okada, M. Juvela, S. A.
Khaibrakhmanov, E. A. Popova
The paper aims to study relation between the distributions of the young stellar objects (YSOs) of dierent ages and the gas-dust
constituents of the S254-S258 star-formation complex. This is necessary to study the time evolution of the YSO distribution withrespect to the gas and dust compounds which are responsible for the birth of the young stars. For this purpose we use correlation+
analysis between dierent gas, dust and YSOs tracers. We compared the large-scale CO, HCO , near-IR extinction, and far-IR

Herschel maps with the density of YSOs of the dierent evolutionary Classes. The direct correlation analysis between thesemaps was used together with the wavelet-based spatial correlation analysis. This analysis reveals a much tighter correlation of
the gas-dust tracers with the distribution of Class I YSOs than with that of Class II YSOs. We argue that Class I YSOs whichwere initially born in the central bright cluster S255-IR (both N and S parts) during their evolution to Class II stage (∼2 Myr)
had enough time to travel through the whole S254-S258 star-formation region. Given that the region contains several isolated
YSO clusters, the evolutionary link between these clusters and the bright central S255-IR (N and S) cluster can be considered.
Despite the complexity of the YSO cluster formation in the non-uniform medium, the clusters of Class II YSOs in the S254-258
star-formation region can contain objects born in the dierent locations of the complex.

18. SiO Outows as Tracers of Massive Star Formation in Infrared Dark Clouds

Mengyao Liu, Jonathan C. Tan, Joshua Marvil, Shuo Kong, Viviana Rosero, Paola Caselli, Giuliana Cosentino
To study the early phases of massive star formation, we present ALMA observations of SiO(5-4) emission and VLA observationsof 6 cm continuum emission towards 32 Infrared Dark Cloud (IRDC) clumps, spatially resolved down to . 0.05 pc. Out of
the 32 clumps, we detect SiO emission in 20 clumps, and in 11 of them the SiO emission is relatively strong and likely tracing
protostellar outows. Some SiO outows are collimated, while others are less ordered. For the six strongest SiO outows, weestimate basic outow properties. In our entire sample, where there is SiO emission, we nd 1.3 mm continuum and infraredemission nearby, but not vice versa. We build the spectral energy distributions (SEDs) of cores with 1.3 mm continuum emission

7

and t them with radiative transfer (RT) models. The low luminosities and stellar masses returned by SED tting suggest theseare early stage protostars. We see a slight trend of increasing SiO line luminosity with bolometric luminosity, which suggests
more powerful shocks in the vicinity of more massive YSOs. We do not see a clear relation between the SiO luminosity and the2evolutionary stage indicated by L/M . We conclude that as a protostar approaches a bolometric luminosity of ∼ 10 L , theshocks in the outow are generally strong enough to form SiO emission. The VLA 6 cm observations toward the 15 clumps withthe strongest SiO emission detect emission in four clumps, which is likely shock ionized jets associated with the more massive
ones of these protostellar cores.

19. Massive Protocluster of a Periodic Maser Source G188.95+0.89

M. M. Mutie, J. O. Chibueze, K. El Bouchefry, G. C. MacLeod, J. Morgan, P. BakiWe report the results of ongoing monitoring of the 6.7 GHz CH3 OH masers associated with G188.95+0.89. In these observations
ve features are periodically varying and at least two exhibit evidence of velocity drifts. It is not clear the cause of these velocity
1drifts. The spectra have varied signicantly since detection in 1991. The 11.45 km s feature has decreased exponentially from2003.

Complementary ALMA 1.3 mm continuum and line observational results are also presented.

Eight continuum cores(MM1 - MM8) were detected in G188.95+0.89. We derived the masses of the detected cores. G188.95+0.89 MM2 was resolved
into 2 continuum cores (separated by 0.1 arcsec) in ALMA band 7 observations. Also CH3 OH (4(2,2) -3(1,2) ) thermal emission
associated with MM2 is double peaked. We propose the presence of multiple (at least binary) young stellar objects in MM2.
12
SiO emission exhibit a bow-shock morphology in MM2 while strong emission of
CO at the east and west of MM2 suggest thepresence of an east-west bipolar outow.

20. Proper motions of spectrally selected structures in the HH 83 outow
T. A. Movsessian, T. Yu. Magakian, A. V. Moiseev

We continue our program of investigation of the proper motions of spectrally separated structures in the Herbig-Haro outows
with the aid of Fabry-Perot scanning interferometry. This work mainly focuses on the physical nature of various structures in
the jets. The aim of the present study is to measure the proper motions of the previously discovered kinematically separated
structures in the working surface of the HH 83 collimated outow.

We used observations from two epochs separated by 15

years, which were performed on the 6m telescope with Fabry-Perot scanning interferometer. We obtained images corresponding
to dierent radial velocities for the two separate epochs, and used them to measure proper motions.

In the course of ourdata analysis, we discovered a counter bow-shock of HH 83 ow with positive radial velocity, which makes this ow a relatively
symmetric bipolar system. The second epoch observations conrm that the working surface of the ow is split into two structures−1
with an exceptionally large (250 km s
) dierence in radial velocity. The proper motions of these structures are almost equal,
which suggests that they are physically connected. The asymmetry of the bow shock and the turning of proper motion vectors
suggests a collision between the outow and a dense cloud. The prole of the Hα line for the directly invisible infrared source HH
83 IRS, obtained by integration of the data within the reection nebula, suggests it to be of P Cyg type with a broad absorption
component characteristic of the FU Ori like objects. If this object underwent an FU Ori type outburst, which created the HH
83 working surfaces, its eruption took place about 1500 years ago according to the kinematical age of the outow.

21. Characterization of dense Planck clumps observed with Herschel and SCUBA-2

E. Mannfors, M. Juvela, L. Bronfman, D. J. Eden, Jinhua He, Gwanjeon Kim, Kee-Tae Kim, H. Kirppu, T.
Liu, J. Montillaud, H. Parsons, Patricio Sanhueza, Hsien Shang, A. Soam, K. Tatematsu, A. Tracante, M. S.
Väisälä, Chang Won Lee
We aim to characterize a diverse selection of dense, potentially star-forming cores, clumps, and clouds within the Milky Way interms of their dust emission and SF activity. We studied 53 elds that have been observed in the JCMT SCUBA-2 continuum
survey SCOPE and have been mapped with Herschel.

We estimated dust properties by tting Herschel observations withmodied blackbody functions, studied the relationship between dust temperature and dust opacity spectral index

β , andestimated column densities. We extracted clumps from the SCUBA-2 850 µm maps with the FellWalker algorithm and examined
their masses and sizes. Clumps are associated with young stellar objects found in several catalogs. We estimated the gravitational
stability of the clumps with virial analysis. The clumps are categorized as unbound starless, prestellar, or protostellar. We nd
22
−2
22
−2
529 dense clumps, typically with high column densities from (0.3-4.8)×10
cm, with a mean of (1.5±0.04)×10
cm, low
temperatures (T∼10-20 K), and estimated submillimeter β =1.7±0.1. We detect a slight increase in opacity spectral index
to 4259 M . Mass, linear size, and temperature aretoward millimeter wavelengths. Masses of the sources range from 0.04 M

correlated with distance. Furthermore, the estimated gravitational stability is dependent on distance, and more distant clumps
appear more virially bound. Finally, we present a catalog of properties of the clumps.Our sources present a large array of SF

8regions, from high-latitude, nearby diuse clouds to large SF complexes near the Galactic center. Analysis of these regions willcontinue with the addition of molecular line data, which will allow us to study the densest regions of the clumps in more detail.

22. A major asymmetric ice trap in a planet-forming disk: I. Formaldehyde and methanol
N. van der Marel, A. S. Booth, M. Leemker, E. F. van Dishoeck, S. Ohashi

The chemistry of planet-forming disks sets the exoplanet atmosphere composition and the prebiotic molecular content. Dust
traps are of particular importance as pebble growth and transport are crucial for setting the chemistry where giant planets are
forming. The asymmetric Oph IRS 48 dust trap located at 60 au radius provides a unique laboratory for studying chemistryin pebble-concentrated environments in warm Herbig disks with low gas-to-dust ratios down to 0.01.

We use deep ALMABand 7 line observations to search the IRS 48 disk for H2 CO and CH3 OH line emission, the rst steps of complex organic
chemistry. We report the detection of 7 H2 CO and 6 CH3 OH lines with energy levels between 17 and 260 K. The line emission
shows a crescent morphology, similar to the dust continuum, suggesting that the icy pebbles play an important role in thedelivery of these molecules. Rotational diagrams and line ratios indicate that both molecules originate from warm molecular14−2−8
regions in the disk with temperatures >100 K and column densities ∼ 10cm
or a fractional abundance of ∼ 10
andwith H2 CO/CH3 OH∼0.2, indicative of ice chemistry. Based on arguments from a physical-chemical model with low gas-to-dust
ratios, we propose a scenario where the dust trap provides a huge icy grain reservoir in the disk midplane or an `ice trap',
which can result in high gas-phase abundances of warm COMs through ecient vertical mixing.

This is the rst time thatcomplex organic molecules have been clearly linked to the presence of a dust trap. These results demonstrate the importance ofincluding dust evolution and vertical transport in chemical disk models, as icy dust concentrations provide important reservoirs
for complex organic chemistry in disks.

23. A stellar mass dependence of structured disks: a possible link with exoplanet demo-

graphics

Nienke van der Marel, Gijs Mulders
Gaps in protoplanetary disks have long been hailed as signposts of planet formation. However, a direct link between exoplanetsand disks remains hard to identify. We present a large sample study of ALMA disk surveys of nearby star-forming regions todisentangle this connection. All disks are classied as either structured (transition, ring, extended) or non-structured (compact)
disks. Although low-resolution observations may not identify large scale substructure, we assume that an extended disk must
contain substructure from a dust evolution argument. A comparison across ages reveals that structured disks retain high dust
masses up to at least 10 Myr, whereas the dust mass of compact, non-structured disks decreases over time.

This can beunderstood if the dust mass evolves primarily by radial drift, unless drift is prevented by pressure bumps. We identify a stellar
mass dependence of the fraction of structured disks. We propose a scenario linking this dependence with that of giant exoplanet
occurrence rates. We show that there are enough exoplanets to account for the observed disk structures if transitional disks
are created by exoplanets more massive than Jupiter, and ring disks by exoplanets more massive than Neptune, under theassumption that most of those planets eventually migrate inwards.

On the other hand, the known anti-correlation between

transiting super-Earths and stellar mass implies those planets must form in the disks without observed structure, consistent
with formation through pebble accretion in drift-dominated disks. These ndings support an evolutionary scenario where theearly formation of giant planets determines the disk's dust evolution and its observational appearance.

index of synchrotron emission: insights from the diuse and magnetised inter24. Spectral
stellar medium
Marco Padovani, Andrea Bracco, Vibor Jeli¢, Daniele Galli, Elena Bellomi

The interpretation of Galactic synchrotron observations is complicated by the degeneracy between the strength of the magnetic
eld perpendicular to the line of sight (LOS), B⊥ , and the cosmic-ray electron (CRe) spectrum. Depending on the observing
frequency, an energy-independent spectral energy slope s for the CRe spectrum is usually assumed: s = −2 at frequencies below'400 MHz and s = −3 at higher frequencies. Motivated by the high angular and spectral resolution of current facilities such as
the LOw Frequency ARray (LOFAR) and future telescopes such as the Square Kilometre Array (SKA), we aim to understandthe consequences of taking into account the energy-dependent CRe spectral energy slope on the analysis of the spatial variationsof the brightness temperature spectral index, β , and on the estimate of the average value of B⊥ along the LOS. We illustrate
analytically and numerically the impact that dierent realisations of the CRe spectrum have on the interpretation of the spatial
variation of β . We nd that the common assumption of an energy-independent s is valid only in special cases. We show thatfor typical magnetic eld strengths of the diuse interstellar medium ('2−20 µG), at frequencies of 0.1−10 GHz, the electrons
that are mainly responsible for the synchrotron emission have energies in the range '100 MeV−50 GeV. This is the energy

9range where the spectral slope, s, of CRe has its greatest variation. We also show that the polarisation fraction can be muchsmaller than the maximum value of ' 70% because the orientation of B⊥ varies across the telescope's beam and along the LOS.
Finally, we present a look-up plot that can be used to estimate the average value of B⊥ along the LOS from a set of values ofβ measured at centimetre to metre wavelengths, for a given CRe spectrum.

25. Molecular line signatures of cloud-cloud collisions
F. D. Priestley, A. P. Whitworth

Collisions between interstellar gas clouds are potentially an important mechanism for triggering star formation. This is because
they are able to rapidly generate large masses of dense gas. Observationally, cloud collisions are often identied in positionvelocity (PV) space through bridging features between intensity peaks, usually of CO emission.

Using a combination ofhydrodynamical simulations, time-dependent chemistry, and radiative transfer, we produce synthetic molecular line observationsof overlapping clouds that are genuinely colliding, and overlapping clouds that are just chance superpositions. Molecules tracing
denser material than CO, such as NH3 and HCN, reach peak intensity ratios of 0.5 and 0.2 with respect to CO in the `bridging
feature' region of PV space for genuinely colliding clouds. For overlapping clouds that are just chance superpositions, the peakNH3 and HCN intensities are co-located with the CO intensity peaks.

This represents a way of conrming cloud collisions

observationally, and distinguishing them from chance alignments of unrelated material.

26. Understanding the angular momentum evolution of T Tauri and Herbig Ae/Be stars

Giovanni Pinzón, Jesús Hernández, Javier Serna, Alexandra García, Ezequiel Manzo-Martínez, Alexandre
Roman-Lopes, Carlos G. Román-Zúñiga, Maria Gracia Batista, Julio Ramírez-Vélez, Yeisson Osorio, Ronald
Avendaño
We investigate a sample of 6 Herbig Ae/Be stars belonging to the Orion OB1 association, as well as 73 low mass objects,
members of the σ Orionis cluster, in order to explore the angular momentum evolution at early stages of evolution, and its

possible connection with main-sequence Ap/Bp magnetic stars. Using FIES and HECTOCHELLE spectra, we obtain projectedrotational velocities through two independent methods. Individual masses, radii, and ages were computed using evolutionarymodels, distance, and cluster extinction. Under the assumption that similar physical processes operate in both, T Tauri and
Herbig Ae/Be stars, we construct snapshots of the protostar's rotation against mass during the rst 10 Myr with the aid of arotational model that includes a variable disc lifetime, changes in the stellar moment of inertia, a dipolar magnetic eld withvariable strength, and angular momentum loss through stellar winds powered by accretion. We use these snapshots, as well as
the rotational data, to infer a plausible scenario for the angular momentum evolution. We nd that magnetic eld strengthsof a few kG at 3 Myr are required to match the rotational velocities of both groups of stars. Models with masses between 2-3

M

display larger angular momentum by a factor of ∼ 3, in comparison to stars of similar spectral types on the main-sequence.

Even though some quantitative estimates on this dramatic decrease with age, for Ap/Bp magnetic main-sequence stars arepresented, the results obtained for the angular momentum evolution do not explain their low rotation.

27. Self-Sustaining Vortices in Protoplanetary Disks: Setting the Stage for Planetary Sys-

tem Formation

Zsolt Regaly, Kundan Kadam, Cornelis P. Dullemond
The core accretion scenario of planet formation assumes that planetesimals and planetary embryos are formed during theprimordial, gaseous phases of the protoplanetary disk.
barriers is not well understood.

However, how the dust particles overcome the traditional growth

The recently proposed viscous ring-instability may explain the concentric rings observed inprotoplanetary disks by assuming that the dust grains can reduce the gas conductivity, which can weaken the magneto-rotational
instability. We present an analysis of this model with the help of GPU-based numerical hydrodynamic simulations of coupled
gas and dust in the thin-disk limit. During the evolution of the disk the dusty rings become Rossby unstable and break up
into a cascade of small-scale vortices. The vortices form secularly stable dusty structures, which could be sites of planetesimalformation by the streaming instability as well as direct gravitational collapse. The phenomenon of self-sustaining vortices is
consistent with observational constraints of exoplanets and sets a favorable environment for planetary system formation.

10

conditions in the warped accretion disk of a massive star. 349 GHz ALMA
28. Physicalobservations of G023.01−00.41
A. Sanna, A. Giannetti, M. Bonfand, L. Moscadelli, R. Kuiper, J. Brand, R. Cesaroni, A. Caratti o Garatti,
T. Pillai, K. M. Menten

Young massive stars warm up the large amount of gas and dust which condenses in their vicinity, exciting a forest of lines fromdierent molecular species.

Their line brightness is a diagnostic tool of the gas physical conditions locally, which we use to

set constraints on the environment where massive stars form. We made use of the Atacama Large Millimeter/submillimeter00
Array at frequencies near 349 GHz, with an angular resolution of 0.1 , to observe the methyl cyanide (CH3 CN) emission whicharises from the accretion disk of a young massive star. We sample the disk midplane with twelve distinct beams, where we getan independent measure of the gas (and dust) physical conditions.

The accretion disk extends above the midplane showing

a double-armed spiral morphology projected onto the plane of the sky, which we sample with ten additional beams: along−1
these apparent spiral features, gas undergoes velocity gradients of about 1kms
per 2000 au. The gas temperature (T) rises
symmetrically along each side of the disk, from about 98 K at 3000 au to 289 K at 250 au, following a power law with radius,
−0.43
15
−2
17
−2
R
. The CH3 CN column density (N) increases from 9.2 × 10 cm
to 8.7 × 10 cm
at the same radii, following a power−1.8
law with radius, R. In the framework of a circular gaseous disk observed approximately edge-on, we infer an H2 volume
9−3
density in excess of 4.8 × 10 cm
at a distance of 250 au from the star. We study the disk stability against fragmentation
following the methodology by Kratter et al. (2010), appropriate under rapid accretion, and we show that the disk is marginallyprone to fragmentation along its whole extent.

29. FORCAST imaging of two small nearby Clusters: The Coronet and B59
G. Sandell, B. Reipurth, W. D. Vacca, N. S. Bajaj

We present mid infrared imaging of two young clusters, the Coronet in the CrA cloud core and B59 in the Pipe Nebula, using
the FORCAST camera on the Stratospheric Observatory for Infrared Astronomy. We also analyze Herschel Space Observatory
PACS and SPIRE images of the associated clouds. The two clusters are at similar, and very close, distances. Star formationis ongoing in the Coronet, which hosts at least one Class 0 source and several pre-stellar cores, which may collapse and formstars. The B59 cluster is older, although it still has a few Class I sources, and is less compact. The CrA cloud has a diameter ofabout 0.16 pc, and we determine a dust temperature of 15.7 K and a star formation eciency of about 27 twice as large, has adust temperature of about 11.4 K and a star formation eciency of about 14 the Coronet, which has also formed intermediate
mass stars, while B59 has only formed low-mass stars.

30. Chandra X-ray Observations of V830 Tau: A T Tauri Star Hosting an Evanescent Planet
Stephen L. Skinner, Manuel Guedel

A radial velocity study by Donati et al. (2016) reported the detection of a close-in giant planet in a 4.93 d orbit around the 2
Myr old weak-lined T Tauri star V830 Tau. Because of the stringent timescale constraints that a very young host star like V830
Tau would place on hot Jupiter formation models and inward migration mechanisms, independent conrmation of the planet's
existence is needed but so far has not been obtained. We present new Chandra X-ray observations of V830 Tau. The Chandra
observations in combination with previous XMM-Newton observations reveal strong variable X-ray emission with an X-ray
luminosity spanning the range log Lx = 30.10 - 30.87 ergs/s.

Chandra High Energy Transmission Grating (HETG) spectra

show emission lines formed over a range of plasma temperatures from 4 MK (Ne IX) to 16 MK (S XV). At the separation
6
7of the reported planet (0.057 au) the X-ray ux is 10 - 10 times greater than the Sun's X-ray ux at Jupiter. We provide
estimates of the X-ray ionization and atmospheric heating rates at the planet's separation and identify areas of uncertainty thatwill need to be addressed in any future atmospheric models.

X-raying the Sco-Cen OB association: The low-mass stellar population revealed by

31. eROSITA

J. H. M. M. Schmitt, S. Czesla, S. Freund, J. Robrade, P. C. Schneider
We present the results of the rst X-ray all-sky survey (eRASS1) performed by the eROSITA instrument on board the SpectrumRoentgen-Gamma (SRG) observatory of the Sco-Cen OB association.

Bona de Sco-Cen member stars are young and are

therefore expected to emit X-rays at the saturation level. The sensitivity limit of eRASS1 makes these stars detectable down
to about a tenth of a solar mass. By cross-correlating the eRASS1 source catalog with the Gaia EDR3 catalog, we arrive at
a complete identication of the stellar (i.e., coronal) source content of eROSITA in the Sco-Cen association, and in particularobtain for the rst time a 3D view of the detected stellar X-ray sources. Focusing on the low-mass population and placing the11

optical counterparts identied in this way in a color-magnitude diagram, we can isolate the young stars out of the detected
X-ray sources and obtain age estimates of the various Sco-Cen populations. A joint analysis of the 2D and 3D space motions,the latter being available only for a smaller subset of the detected stellar X-ray sources, reveals that the space motions of theselected population show a high degree of parallelism, but there is also an additional population of young, X-ray emitting andessentially cospatial stars that appears to be more diuse in velocity space.

Its nature is currently unclear.

We argue thatwith our procedures, an identication of almost the whole stellar content of the Sco-Cen association will become possible oncethe nal Gaia and eROSITA catalogs are available by the end of this decade. We furthermore call into question any source
population classication scheme that relies on purely kinematic selection criteria.

32. The lamentary structures in the CO emission toward the Milky Way disk

J. D. Soler, H. Beuther, J. Syed, Y. Wang, Th. Henning, S. C. O. Glover, R. S. Klessen, M. C. Sormani, M.
Heyer, R. J. Smith, J. S. Urquhart, J. Yang, Y. Su, X. Zhou
We present a statistical study of the lamentary structure orientation in the CO emission observations obtained in the Milky
Way Imaging Scroll Painting (MWISP) survey in the range 25.8 deg < l < 49.7 deg, |b| ≤ 1.25 deg, and −100 < vLSR < 13512
13km/s. We found that most of the lamentary structures in the
CO andCO emission do not show a global preferential
orientation either parallel or perpendicular to the Galactic plane. However, we found ranges in Galactic longitude and radial
12
13
velocity where the
CO andCO lamentary structures are parallel to the Galactic plane. These preferential orientations
are dierent from those found for the HI emission. We consider this an indication that the molecular structures do not simply
inherit these properties from parental atomic clouds.

Instead, they are shaped by local physical conditions, such as stellar

feedback, magnetic elds, and Galactic spiral shocks.

33. The general applicability of self-similar solutions for thermal disc winds
Andrew D. Sellek, Cathie J. Clarke, Richard A. Booth

Thermal disc winds occur in many contexts and may be particularly important to the secular evolution and dispersal of
protoplanetary discs heated by high energy radiation from their central star. In this paper we generalise previous models of
self-similar thermal winds - which have self-consistent morphology and variation of ow variables - to the case of launch from anelevated base and to non-isothermal conditions. These solutions are well-reproduced by hydrodynamic simulations, in which,as in the case of isothermal winds launched from the mid-plane, we nd winds launch at the maximum Mach number for which
the streamline solutions extend to innity without encountering a singularity.
that lower Mach number solutions do not ll the spatial domain.

We explain this behaviour based on the fact

We also show that hydrodynamic simulations reect thecorresponding self-similar models across a range of conditions appropriate to photoevaporating protoplanetary discs, even whengravity, centrifugal forces, or changes in the density gradient mean the problem is not inherently scale free. Of all the parameters
varied, the elevation of the wind base aected the launch velocity and ow morphology most strongly, with temperature gradients
causing only minor dierences. We explore how launching from an elevated base aects Ne II line proles from winds, nding it
increases (reduces) the full width at half maximum (FWHM) of the line at low (high) inclination to the line of sight comparedwith models launched from the disc mid-plane and thus weakens the dependence of the FWHM on inclination.

34. Long-term optical photometric monitoring of the FUor star V900 Mon
Evgeni Semkov, Stoyanka Peneva, Sunay Ibryamov

We present results from photometric monitoring of V900 Mon, one of the newly discovered and still under-studied object fromFU Orionis type. FUor phenomenon is very rarely observed, but it is essential for stellar evolution. Since we only know about
twenty stars of this type, the study of each new object is very important for our knowledge. Our data was obtained in the
optical spectral region with BVRI Johnson-Cousins set of lters during the period from September 2011 to April 2021. In orderto follow the photometric history of the object, we measured its stellar magnitudes on the available plates from the Mikulski
Archive for Space Telescopes. The collected archival data suggests that the rise in brightness of V900 Mon began after January
1989 and the outburst goes so far. In November 2009, when the outburst was registered, the star had already reached a level ofbrightness close to the current one. Our observations indicate that during the period 2011-2017 the stellar magnitude increased
gradually in each pass band. The observed amplitude of the outburst is about 4 magnitudes (R). During the last three years,
the increase in brightness has stopped and there has even been a slight decline. The comparison of the light curves of the known
FUor objects shows that they are very diverse and are rarely repeated. However, the photometric data we have so far showsthat the V900 Mon's light curve is somewhat similar to this of V1515 Cyg and V733 Cep.

12

35. Which molecule traces what: chemical diagnostics of protostellar sourcesukasz Tychoniec, Ewine F. van Dishoeck, Merel L. R. van 't Ho, Martijn L. van Gelder, Benoît Tabone,
Yuan Chen, Daniel Harsono, Charles L. H. Hull, Michiel R. Hogerheijde, Nadia M. Murillo, John J. Tobin
The physical and chemical conditions in Class 0/I protostars are fundamental in unlocking the protostellar accretion process andits impact on planet formation. The aim is to determine which physical components are traced by dierent molecules at subarcsecond scales (100 - 400 au). We use a suite of Atacama Large Millimeter/submillimeter Array (ALMA) datasets in Band 6(1 mm), Band 5 (1.8 mm) and Band 3 (3 mm) at spatial resolutions 0.5 - 3" for 16 protostellar sources. The protostellar envelope
18++
is well traced by C O, DCO
and N2 D , with the freeze-out of CO governing the chemistry at envelope scales. Molecularoutows are seen in classical shock tracers like SiO and SO, but ice-mantle products such as CH3 OH and HNCO released withthe shock are also observed. The molecular jet is prominent not only in SiO and SO but also occasionally in H2 CO. The cavity
walls show tracers of UV-irradiation such as C2 H c-C3 H2 and CN. The hot inner envelope, apart from showing emission from13complex organic molecules (COMs), also presents compact emission from small molecules like H2 S, SO, OCS and H CN, most
likely related to ice sublimation and high-temperature chemistry. Sub-arcsecond millimeter-wave observations allow to identify
those (simple) molecules that best trace each of the physical components of a protostellar system. COMs are found both in the
hot inner envelope (high excitation lines) and in the outows (lower-excitation lines) with comparable abundances. COMs cancoexist with hydrocarbons in the same protostellar sources, but they trace dierent components. In the near future, mid-IR
observations with JWST-MIRI will provide complementary information about the hottest gas and the ice mantle content, atunprecedented sensitivity and at resolutions comparable to ALMA for the same sources.

36. Probing protoplanetary disk evolution in the Chamaeleon II region

M. Villenave, F. Menard, W. R. F. Dent, M. Benisty, G. van der Plas, J. P. Williams, M. Ansdell, A. Ribas,
C. Caceres, H. Canovas, L. Cieza, A. Hales, I. Kamp, C. Pinte, D. A. Principe, M. R. Schreiber
Context. Characterizing the evolution of protoplanetary disks is necessary to improve our understanding of planet formation.
Constraints on both dust and gas are needed to determine the dominant disk dissipation mechanisms. Aims. We aim to compare
the disk dust masses in the Chamaeleon II (Cha II) star-forming region with other regions with ages between 1 and 10Myr.
Methods. We use ALMA band 6 observations (1.3 mm) to survey 29 protoplanetary disks in Cha II. Dust mass estimates arederived from the continuum data. Results. Out of our initial sample of 29 disks, we detect 22 sources in the continuum, 10 in
12CO, 3 in 13CO, and none in C18O (J=2-1). Additionally, we detect two companion candidates in the continuum and 12CO
emission. Most disk dust masses are lower than 10Mearth, assuming thermal emission from optically thin dust. We compare
consistent estimations of the distributions of the disk dust mass and the disk-to-stellar mass ratios in Cha II with six otherlow mass and isolated star-forming regions in the age range of 1-10Myr: Upper Sco, CrA, IC 348, Cha I, Lupus, and Taurus.
When comparing the dust-to-stellar mass ratio, we nd that the masses of disks in Cha II are statistically dierent from thosein Upper Sco and Taurus, and we conrm that disks in Upper Sco, the oldest region of the sample, are statistically less massive
than in all other regions. Performing a second statistical test of the dust mass distributions from similar mass bins, we nd
no statistical dierences between these regions and Cha II. Conclusions. We interpret these trends, most simply, as a sign ofdecline in the disk dust masses with time or dust evolution. Dierent global initial conditions in star-forming regions may also
play a role, but their impact on the properties of a disk population is dicult to isolate in star-forming regions lacking nearby
massive stars.

37. From downtown to the outskirts: a radio survey of the Orion Nebula Cluster
Jaime Vargas-González, Jan Forbrich, Sergio A. Dzib, John Bally

We present a newly enlarged census of the compact radio population towards the Orion Nebula Cluster (ONC) using high−100sensitivity continuum maps (3-10 µJy bm) from a total of ∼ 30 h centimeter-wavelength observations over an area of ∼20 ×20
obtained in the C-band (4−8 GHz) with the Karl G. Jansky Very Large Array (VLA) in its high-resolution A-conguration. We
thus complement our previous deep survey of the innermost areas of the ONC, now covering the eld of view of the Chandra
Orion Ultra-deep Project (COUP). Our catalog contains 521 compact radio sources of which 198 are new detections. Overall,
we nd that 17COUP sources have radio counterparts, while 53counterparts. Most notably, the radio detection fraction of X-ray
0
1
sources is higher in the inner cluster and almost constant for r > 3 (0.36 pc) from θ Ori C suggesting a correlation between
the radio emission mechanism of these sources and their distance from the most massive stars at the center of the cluster, forexample due to increased photoionisation of circumstellar disks. The combination with our previous observations four years−1
prior lead to the discovery of fast proper motions of up to ∼373 km sfrom faint radio sources associated with ejecta of the
OMC1 explosion. Finally, we search for strong radio variability. We found changes in ux density by a factor of .5 within ourobservations and a few sources with changes by a factor >10 on long timescales of a few years.

13

of Accretion Burst: The Viscously Heated Inner Disk of the Embedded Pro38. Evidence
tostar IRAS 16316-1540

Sung-Yong Yoon, Jeong-Eun Lee, Seokho Lee, Gregory J. Herczeg, Sunkyung Park, Gregory N. Mace, Jae-Joon
Lee, Daniel T. Jae
Outbursts of young stellar objects occur when the mass accretion rate suddenly increases. However, such outbursts are dicultto detect for deeply embedded protostars due to their thick envelope and the rarity of outbursts. The near-IR spectroscopy
is a useful tool to identify ongoing outburst candidates by the characteristic absorption features that indicate a disk origin.
However, without high-resolution spectroscopy, the spectra of outburst candidates can be confused with the late-type stars since
they have similar spectral features. For the protostar IRAS 16316-1540, the near-IR spectrum has line equivalent widths thatare consistent with M-dwarf photospheres. However, our high-resolution IGRINS spectra reveal that the absorption lines haveboxy and/or double-peaked proles, as expected from a disk and not the star. The continuum emission source is likely the hot,−1
optically thick disk, heated by viscous accretion. The projected disk rotation velocity of 41±5 km s
corresponds to ∼ 0.1

AU. Based on the result, we suggest IRAS 16316-1540 as an ongoing outburst candidate. Viscous heating of disks is usuallyinterpreted as evidence for ongoing bursts, which may be more common than previously estimated from low-resolution near-IR
spectra.

ALMA discovery of a dual dense probably rotating outow from a massive young stellar

39. object G18.88MME

I. I. Zinchenko, L. K. Dewangan, T. Baug, D. K. Ojha, N. K. Bhadari
We report the discovery of a very dense jet-like fast molecular outow surrounded by a wide-angle wind in a massive youngstellar object (MYSO) G18.88MME (stellar mass ∼8 M

) powering an Extended Green Object G18.89−0.47. Four cores MM1-

4 are identied in the Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum map (resolution ∼0.”8)
toward G18.88MME, and are seen at the center of the emission structure (extent ∼0.3 pc × 0.2 pc) detected in the ALMAmap.

G18.88MME is embedded in the core MM1 (mass ∼13-18 M), where no radio continuum emission is detected. The
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CO(2-1) lines. The detection of HC3 N

molecular outow centered at MM1 is investigated in the SiO(5-4), HC3 N(24-23) andin the outow is rare in MYSOs and indicates its very high density.

The position-velocity diagrams display a fast narrowoutow (extent ∼28000 AU) and a slower wide-angle more extended outow toward MM1, and both of these components show
a transverse velocity gradient indicative of a possible rotation. All these observed features together make G18.88MME as aunique object for studying the unication of the jet-driven and wind-driven scenarios of molecular outows in MYSOs.

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