The Star Formation Newsletter
A community newsletter on Star and Planet Formation research
No. 345 — 26 September 2021
Editor: João Alveswww.starformation.news

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Cover image caption
Spectacular image of Herbig–Haro object HH111, imaged by Hubble’s Wide Field Camera 3 (WFC3). HH111 lives in L1617,
one of a series of finger-like clouds next to the better studies L1622. Newly formed stars expel very narrow jets of rapidly moving
ionised gas that collide with the gas and dust surrounding newly-formed stars at speeds of hundreds of kilometres per second.
It is these energetic collisions that create Herbig–Haro objects such as HH111. Credit: ESA/Hubble & NASA, B. Nisini.
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 to the different Newsletter sections. 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
when submitting to the arXiv. If you do, your abstract will not look great either at the arXiv (which uses MathJax toconvert LATEX math symbols to the web) or the SFN.

Abstracts
ALMA study of hub-filament systems I. On the clump mass concentration within
1. An
the most massive cores
Michael Anderson, Nicolas Peretto, Sarah E. Ragan, Andrew J. Rigby, Adam Avison, Ana Duarte-Cabral,
Gary A. Fuller, Yancy L. Shirley, Alessio Traficante, Gwenllian M. Williams F The physical processes behind thetransfer of mass from parsec-scale clumps to massive-star-forming cores remain elusive. We investigate the relation between theclump morphology and the mass fraction that ends up in its most massive core (MMC) as a function of infrared brightness,
i.e. a clump evolutionary tracer. Using ALMA 12 m and ACA we surveyed 6 infrared-dark hubs in 2.9mm continuum at ∼3"
resolution. To put our sample into context, we also re-analysed published ALMA data from a sample of 29 high mass-surface
density ATLASGAL sources. We characterise the size, mass, morphology, and infrared brightness of the clumps using Herscheland Spitzer data. Within the 6 newly observed hubs, we identify 67 cores, and find that the MMCs have masses between 15-911
M within a radius of 0.018-0.156 pc. The MMC of each hub contains 3-24% of the clump mass (fMMC ), becoming 5-36% oncecore masses are normalised to the median core radius. Across the 35 clumps, we find no significant difference in the medianfMMC values of hub and non-hub systems, likely the consequence of a sample bias. However, we find that fMMC is ∼7.9 times
larger for infrared-dark clumps compared to infrared-bright ones. This factor increases up to ∼14.5 when comparing our sample
of 6 infrared-dark hubs to infrared-bright clumps. We speculate that hub-filament systems efficiently concentrate mass within
their MMC early on during its evolution. As clumps evolve, they grow in mass, but such growth does not lead to the formationof more massive MMCs.

2. Long-term stability of planets in and around binary stars

Harry A. Ballantyne, Tore Espaas, Bethan Z. Norgrove, Bethany A. Wootton, Benjamin R. Harris, Isaac L.
Pepper, Richard D. Smith, Rosie E. Dommett, Richard J. Parker F Planets are observed to orbit the componentstar(s) of stellar binary systems on so-called circumprimary or circumsecondary orbits, as well as around the entire binary systemon so-called circumbinary orbits. Depending on the orbital parameters of the binary system a planet will be dynamically stable
if it orbits within some critical separation of the semimajor axis in the circumprimary case, or beyond some critical separation forthe circumbinary case. We present N-body simulations of star-forming regions that contain populations of primordial binaries
to determine the fraction of binary systems that can host stable planets at various semimajor axes, and how this fraction of
stable systems evolves over time. Dynamical encounters in star-forming regions can alter the orbits of some binary systems,
which can induce long-term dynamical instabilities in the planetary system and can even change the size of the habitable zone(s)of the component stars. However, the overall fraction of binaries that can host stable planetary systems is not greatly affectedby either the assumed binary population, or the density of the star-forming region. Instead, the critical factor in determining2

how many stable planetary systems exist in the Galaxy is the stellar binary fraction - the more stars that are born as singles instellar nurseries, the higher the fraction of stable planetary systems.

3. A search for transiting companions in the J1407 (V1400 Cen) system

S. Barmentloo, C. Dik, M. A. Kenworthy, E. E. Mamajek, F. -J. Hambsch, D. E. Reichart, J. E. Rodriguez, D.
M. van Dam F In 2007, the young star 1SWASP J140747.93-394542.6 (V1400 Cen) underwent a complex series of deep eclipses
over 56 days. This was attributed to the transit of a ring system filling a large fraction of the Hill sphere of an unseen substellar
companion. Subsequent photometric monitoring has not found any other deep transits from this candidate ring system, but
if there are more substellar companions and they are coplanar with the potential ring system, there is a chance that they willtransit the star as well. This young star is active and the light curves show a 5% modulation in amplitude with a dominantrotation period of 3.2 days due to star spots rotating in and out of view. We model and remove the rotational modulation of theJ1407 light curve and search for additional transit signatures of substellar companions orbiting around J1407. We combine thephotometry of J1407 from several observatories, spanning a 19 year baseline. We remove the rotational modulation by modelingthe variability as a periodic signal, whose periodicity changes slowly with time over several years due to the activity cycle ofthe star. A Transit Least Squares (TLS) analysis searches for any periodic transiting signals within the cleaned light curve.
We identify an activity cycle of J1407 with a period of 5.4 years. A Transit Least Squares search does not find any plausible
periodic eclipses in the light curve, from 1.2% amplitude at 5 days up to 1.9% at 20 days. This sensitivity is confirmed byinjecting artificial transits into the light curve and determining the recovery fraction as a function of transit depth and orbital
period. J1407 is confirmed as a young active star with an activity cycle consistent with a rapidly rotating solar mass star. With
the rotational modulation removed, the TLS analysis rules out transiting companions with radii larger than about 1 Jupiter.

Structured velocity field in the inner envelope of B335: ALMA observations of rare CO

4. isotopologues
Victoria Cabedo, Anaëlle Maury, Josep Miquel Girart, Marco Padovani F Studying Class 0 objects is very important,as it allows to characterize dynamical processes at the onset of the star formation process, and to determine the physicalmechanisms responsible for the outcome of the collapse. Observations of dense gas tracers allow the characterization of key
kinematics of the gas directly involved in the star-formation process, such as infall, outflow or rotation. This work aims atinvestigating the molecular line velocity profiles of the Class 0 protostellar object B335 and attempts to put constraints on
the infall motions happening in the circumstellar gas of the object. Observations of C17 O (1-0), C18 O (1-0) and 12 CO(2-1) transitions are presented and the spectral profiles are analyzed at envelope radii between 100 and 860 au. C17 O
emission presents a double peaked line profile distributed in a complex velocity field. Both peaks present an offset of
0.2 to 1 km s−1 from the systemic velocity of the source in the probed area. The optical depth of the C17 O emission
has been estimated and found to be less than 1, suggesting that the two velocity peaks trace two distinct velocity
components of the gas in the inner envelope. After discarding possible motions that could produce the complex velocity
pattern, such as rotation and outflow, it is concluded that infall is producing the velocity field. Because inside-out
symmetric collapse cannot explain those observed profiles, it is suggested that those are produced by non-isotropic
accretion from the envelope into the central source along the outflow cavity walls.

5. The SVS13-A Class I chemical complexity as revealed by S-bearing species. SOLIS XIII

C. Codella, E. Bianchi, L. Podio, S. Mercimek, C. Ceccarelli, A. Lopez-Sepulcre, R. Bachiller, P. Caselli, N.
Sakai, R. Neri, F. Fontani, C. Favre, N. Balucani, B. Lefloch, S. Viti, S. Yamamoto F Aims: The goal is toobtain a census of S-bearing species using interferometric images, towards SVS13-A, a Class I object associated witha hot corino rich in interstellar complex organic molecules. Methods: We used data at 3mm and 1.4mm obtained with
IRAM-NOEMA in the framework of the Large Program SOLIS. Results: We imaged the spatial distribution of theline emission of 32SO, 34SO, C32S, C34S, C33S, OCS, H2C32S, H2C34S, and NS. The low excitation (9 K) 32SO line
is tracing the fast collimated jet driven by the nearby SVS13-B. Conversely, the rest of the lines are confined in the
inner SVS13-A region, where complex organics have been previously imaged. The non-LTE LVG analysis of SO, SO2,
and H2CS indicates a hot corino origin (60-120 au). Temperatures between 50 K and 300 K, and volume densities
larger than 105 cm-3 have been derived. The abundances are in the following ranges: 0.3-6 10− 6 (CS), 7 10− 9 - 1 10− 7(SO), 1-10 10− 7 (SO2), a few 10− 10 (H2CS and OCS), and 10−10 - 10−9 (NS). The N(NS)/N(NS+ ) ratio is larger than10, supporting that the NS+ ion is mainly formed in the extended envelope. Conclusions: The [H2CS]/[H2CO] ratio
increases with time (from Class 0 to Class II objects) by more than one order of magnitude. This suggests that [S]/[O]changes along the Sun-like star forming process. The estimate of the [S]/[H] budget in SVS13-A is 2%-17% of the
Solar System value (1.8 10− 5), being consistent with what was previously measured towards Class 0 objects (1%-8%).
3

This supports that the enrichment of the sulphuretted species with respect to dark clouds keeps constant from theClass 0 to the Class I stages of low-mass star formation. The present findings stress the importance of investigating
the chemistry of star forming regions using large observational surveys as well as sampling regions on a Solar Systemscale.

The GRAVITY Young Stellar Object survey VIII. Gas and dust faint inner rings in the

6. hybrid disk of HD141569

GRAVITY Collaboration, V. Ganci et al. F The formation and evolution of planetary systems impact the primordialaccretion disk. HD141569 is the only known pre-main sequence star characterized by a hybrid disk. Observations
probed the outer-disk structure showing a complex system of rings and interferometric observations attempted tocharacterize its inner 5 au region, but derived limited constraints. The goal of this work was to explore with new
high-resolution interferometric observations the properties of the dust and gas in the internal regions of HD141569. We
observed HD141569 on mas scales with GRAVITY/VLTI in the near-infrared at low and high spectral resolution. We
interpreted the visibilities and spectral energy distribution with geometrical models and radiative transfer techniques
to constrain the dust emission. We analyzed the high spectral resolution quantities to investigate the properties of the
Br-Gamma line emitting region. Thanks to the combination of three different epochs, GRAVITY resolves the innerdusty disk in the K band. Data modeling shows that an IR excess of about 6% is spatially resolved and that the originof this emission is confined in a ring of material located at a radius of 1 au from the star with a width smaller than
0.3 au. The MCMax modeling suggests that this emission could originate from a small amount of QHPs, while large
silicate grain models cannot reproduce at the same time the observational constraints on the properties of near-IR
and mid-IR fluxes. The differential phases in the Br-Gamma line clearly show an S-shape that can be best reproduced
witha gas disk in Keplerian rotation, confined within 0.09 au. This is also hinted at by the double-peaked Br-Gamma
emission line shape. The modeling of the continuum and gas emission shows that the inclination and position angleof these two components are consistent with a system showing relatively coplanar rings on all scales.

7. Measuring the Density Structure of an Accretion Hot Spot

C. C. Espaillat, C. E. Robinson, M. M. Romanova, T. Thanathibodee, J. Wendeborn, N. Calvet, M. Reynolds,
J. Muzerolle F Magnetospheric accretion models predict that matter from protoplanetary disks accretes onto thestar via funnel flows which follow the stellar field lines and shock on the stellar surface leaving a hot spot with adensity gradient. Previous work has inferred different densities in the hot spot, but has not been sensitive to theradial density distribution. Attempts have been made to measure this with X-ray observations, but X-ray emission
only traces a fraction of the hot spot and also coronal emission. Here we report periodic ultraviolet and optical light
curves of the accreting star GM Aur that display a time lag of about 1 day between their peaks. The periodicity arises
as the source of the ultraviolet and optical emission moves into and out of view as it rotates along with the star. The
time-lag indicates a difference in the spatial distribution of ultraviolet and optical brightness over the stellar surface.
Within the framework of the magnetospheric accretion model, this indicates a radial density gradient in a hot spot on
the stellar surface since different density parts of the hot spot are expected to emit radiation at different wavelengths.
These results are the first observational confirmation of the magnetospheric accretion model’s prediction of a density
gradient in the hot spot and demonstrate the insights gained from focusing on the wavelengths where the bulk of theaccretion energy can be observed.

8. A Solar System formation analogue in the Ophiuchus star-forming complex

John C. Forbes, João Alves, Douglas N. C. Lin F Anomalies among the daughter nuclei of the extinct short-lived
radionuclides (SLRs) in the calcium-aluminum-rich inclusions (CAIs) indicate that the Solar System must have beenborn near a source of the SLRs so that they could be incorporated before they decayed away. γ-rays from one such
living SLR, 26 Al, are detected in only a few nearby star-forming regions. Here we employ multi-wavelength observations
to demonstrate that one such region, Ophiuchus, containing many pre-stellar cores that may serve as analogs for the
emerging Solar System, is inundated with 26 Al from the neighboring Upper-Scorpius association, and so may provide
concrete guidance for how SLR enrichment proceeded in the Solar System complementary to the meteoritics. We
demonstrate via Bayesian forward modeling drawing on a wide range of observational and theoretical results that
this 26 Al likely 1) arises from supernova explosions, 2) arises from multiple stars, 3) has enriched the gas prior to
the formation of the cores, and 4) gives rise to a broad distribution of core enrichment spanning about two orders of4

magnitude. This means that if the spread in CAI ages is small, as it is in the Solar System, protoplanetary disks must
suffer a global heating event.

9. PENELLOPE II. CVSO 104: a pre-main sequence close binary with an optical companion in Ori OB1

A. Frasca, H. M. J. Boffin, C. F. Manara, J. M. Alcalá, P. Ábrahám, E. Covino, M. Fang, M. Gangi, G. J.
Herczeg, Á. Kóspál, L. Venuti, F. M. Walter, J. Alonso-Santiago, K. Grankin, M. Siwak, E. Alecian, S. Cabrit

F We present results of our study of the close pre-main sequence spectroscopic binary CVSO 104 in Ori OB1, basedon data obtained within the PENELLOPE legacy program. We derive, for the first time, the orbital elements of thesystem and the stellar parameters of the two components. The system is composed of two early M-type stars and hasan orbital period of about 5 days and a mass ratio of 0.92, but contrarily to expectations does not appear to havea tertiary companion. Both components have been (quasi-)synchronized, but the orbit is still very eccentric. The
spectral energy distribution clearly displays a significant infrared excess compatible with a circumbinary disk. The
analysis of HeI and Balmer line profiles, after the removal of the composite photospheric spectrum, reveals that bothcomponents are accreting at a similar level. We also observe excess emission in Hα and Hβ, which appears redshiftedor blueshifted by more than 100 km/s with respect to the mass center of the system depending on the orbital phase.
This additional emission could be connected with accretion structures, such as funnels of matter from the circumbinary
disk. We also analyze the optical companion located at about 2".4 from the spectroscopic binary. This companion,that we named CVSO 104B, turns out to be a background Sun-like star not physically associated with the PMS system
and not belonging to Ori OB1.

accretion shocks at the disk-envelope interface – Sulfur chemistry
10. Modeling
M. L. van Gelder, B. Tabone, E. F. van Dishoeck, B. Godard F As material from an infalling protostellar
envelope hits the forming disk, an accretion shock may develop which could (partially) alter the envelope material
entering the disk. Observations with the Atacama Large Millimeter/submillimeter Array (ALMA) indicate thatemission originating from warm SO and SO2 might be good tracers of such accretion shocks. The goal of this work is
to test under what shock conditions the abundances of gas-phase SO and SO2 increase in an accretion shock at the
disk-envelope interface. Detailed shock models including gas dynamics are computed using the Paris-Durham shockcode for non-magnetized J-type accretion shocks in typical inner envelope conditions. The effect of pre-shock density,
shock velocity, and strength of the ultraviolet (UV) radiation field on the abundance of warm SO and SO2 is explored.
Warm gas-phase chemistry is efficient in forming SO under most J-type shock conditions considered. In lower-velocity( 3 km/s) shocks, the abundance of SO is increased through subsequent reactions starting from thermally desorbed
CH4 toward H2 CO and finally SO. In higher velocity (>4 km/s) shocks, both SO and SO2 are formed through reactionsof OH and atomic S. The strength of the UV radiation field is crucial for SO and in particular SO2 formation throughthe photodissociation of H2 O. Thermal desorption of SO and SO2 ice is only relevant in high-velocity (>5 km/s)
shocks at high densities (> 107 cm−3 ). Warm emission from SO and SO2 is a possible tracer of accretion shocks at
the disk-envelope interface as long as a local UV field is present. Additional observations with ALMA at high-angularresolution could provide further constraints. Moreover, the James Webb Space Telescope will give access to otherpossible slow, dense shock tracers such as H2 , H2 O, and [S I] 25µm.

Comparing the spatial and kinematic distribution of gas and young stars around the

11. shell-like structure in the CMa OB1 association

Jane Gregorio-Hetem, Bertrand Lefloch, Annibal Hetem, Thierry Montmerle, Beatriz Fernandes, Edgar F.
Mendoza, Marta De Simone F The relationship between young stellar clusters and respective parental molecular

clouds is still an open issue: for instance, are the similarities between substructures of clouds and clusters just a
coincidence? Or would they be the indication of a physical relationship? In order to address these issues, we havestudied the CMa OB1/R1 region that shows evidence for a complex star formation history. We obtained molecular
clouds mapping with the IRAM-30 metre telescope to reveal the physical conditions of an unexplored side of the CMaregion aiming to compare the morphology of the clouds with the distribution of the young stellar objects (YSOs). We
also study the clouds kinematics searching for gradients and jet signatures that could trace different star formation
scenarios. The YSOs were selected on the basis of astrometric data from Gaia EDR3 that characterise the moving
groups. The distance of 1099+25−24 pc was obtained for the sample, based on the mean error-weighted parallax. Optical5and near-infrared photometry is used to verify the evolutionary status and circumstellar characteristics of the YSOs.
Among the selected candidates we found 40 members associated with the cloud: 1 Class I, 11 Class II, and 28 Class
III objects. Comparing the spatial distribution of the stellar population with the cores revealed by the 13CO map, we
verify that peaks of emission coincide with the position of YSOs confirming the association of these objects to theirdense natal gas. Our observations support the large-scale scenario of the CMa shell-like structure formed as a relic of
successive supernova events.

12. Detection of Substructures in Young Transition Disk WL 17

Hannah Gulick, Sarah Sadavoy, Luca Matra, Patrick Sheehan, Nienke van der Marel F WL 17 is a youngtransition disk in the Ophiuchus L1688 molecular cloud complex. Even though WL 17 is among the brightest disksin L1688 and massive enough to expect dust self-scattering, it was undetected in polarization down to ALMA’s
instrument sensitivity limit. Such low polarization fractions could indicate unresolved polarization within the beamor optically thin dust emission. We test the latter case by combining the high sensitivity 233 GHz Stokes I data fromthe polarization observations with previous ALMA data at 345 GHz and 100 GHz. We use simple geometric shapes
to fit the observed disk visibilities in each band. Using our simple models and assumed dust temperature profiles,
we estimate the optical depth in all three bands. The optical depth at 233 GHz peaks at τ233 ∼ 0.3, which suggests
the dust emission may not be optically thick enough for dust self-scattering to be efficient. We also find the higher
sensitivity 233 GHz data show substructure in the disk for the first time. The substructure appears as brighter lobes
along the major axis, on either side of the star. We attempt to fit the lobes with a simple geometric model, but they
are unresolved in the 233 GHz data. We propose that the disk may be flared at 1 mm such that there is a higher
column of dust along the major axis than the minor axis when viewed at an inclination. These observations highlightthe strength of high sensitivity continuum data from dust polarization observations to study disk structures.

13. A wide-field CO survey towards the California Molecular Filament

Weihua Guo, Xuepeng Chen, Jiancheng Feng, Li Sun, Chen Wang, Yang Su, Yan Sun, Yiping Ao, Shaobo
Zhang, Xin Zhou, Lixia Yuan, Ji Yang F We present the survey of 12 CO/13 CO/C18 O (J=1-0) toward the California

Molecular Cloud (CMC) within the region of 161.75◦ 6 l 6 167.75◦ ,-9.5◦ 6 b 6-7.5◦ , using the Purple Mountain
Observatory (PMO) 13.7 m millimeter telescope. Adopting a distance of 470 pc, the mass of the observed molecular
cloud estimated from 12 CO, 13 CO, and C18 O is about 2.59×104 M , 0.85×104 M , and 0.09×104 M , respectively.
A large-scale continuous filament extending about 72 pc is revealed from the 13 CO images. A systematic velocity
gradient perpendicular to the major axis appears and is measured to be ∼ 0.82 km s−1 pc−1 . The kinematics along
the filament shows an oscillation pattern with a fragmentation wavelength of ∼ 2.3 pc and velocity amplitude of ∼ 0.92
km s−1 , which may be related with core-forming flows. Furthermore, assuming an inclination angle to the plane of thesky of 45◦ , the estimated average accretion rate is ∼ 101 M Myr−1 for the cluster LkHα 101 and ∼ 21 M Myr−1 forthe other regions. In the C18 O observations, the large-scale filament could be resolved into multiple substructures andtheir dynamics are consistent with the scenario of filament formation from converging flows. Approximately 225 C18 O
cores are extracted, of which 181 are starless cores. Roughly 37% (67/181) of the starless cores have αvir less than
1. Twenty outflow candidates are identified along the filament. Our results indicate active early-phase star formation
along the large-scale filament in the CMC region.

14. Which Molecular Cloud Structures Are Bound?

Neal J. Evans II, Mark Heyer. Marc-Antoine Miville-Deschênes, Quang Nguyen-Luong. Manuel Merello F We

analyze surveys of molecular cloud structures defined by tracers ranging from CO J = 1 − 0 through 13 CO J = 1 − 0
to dust emission together with NH3 data. The mean value of the virial parameter and the fraction of mass in boundstructures depends on the method used to identify structures. Generally, the virial parameter decreases and thefraction of mass in bound structures increases with the effective density of the tracer, the surface density and massof the structures, and the distance from the center of a galaxy. For the most complete surveys of structures in the
Galaxy defined by CO J = 1 − 0, the fraction of mass that is in bound structures is 0.19. For catalogs of other galaxies
based on CO J = 2 − 1, the fraction is 0.35. These results offer substantial alleviation of the fundamental problem
of slow star formation. If only clouds found to be bound are counted and they are assumed to collapse in a free-falltime at their mean cloud density, the sum over all clouds in a complete survey of the Galaxy yields a predicted starformation rate of 46 solar masses per year, a factor of 6.5 less than if all clouds are bound.

615. Touching the Stars: Using High-Resolution 3D Printing to Visualize Stellar Nurseries

Nia Imara, John C. Forbes, James C. Weaver F Owing to their intricate variable density architecture, and as aprincipal site of star formation, molecular clouds represent one of the most functionally significant, yet least understoodfeatures of our universe. To unravel the intrinsic structural complexity of molecular clouds, here we leverage the powerof high-resolution bitmap-based 3D printing, which provides the opportunity to visualize astrophysical structures in a
way that uniquely taps into the human brain’s ability to recognize patterns suppressed in 2D representations. Usinga new suite of nine simulations, each representing different physical extremes in the turbulent interstellar medium,as our source data, our workflow permits the unambiguous visualization of features in the 3D-printed models, suchas quasi-planar structures, that are frequently obscured in traditional renderings and animations. Our bitmap-based
3D printing approach thus faithfully reproduces the subtle density gradient distribution within molecular clouds ina tangible, intuitive, and visually stunning manner. While laying the groundwork for the intuitive analysis of otherstructurally complex astronomical data sets, our 3D-printed models also serve as valuable tools in educational andpublic outreach endeavors.

16. Modeling of CO ro-vibrational line emission of HD 141569

Stanley K. Jensen Jr., Sean D. Brittain, Joan R. Najita, John S. Carr F HD 141569 is a Herbig Ae/Be starthat straddles the boundary between the transition disks and debris disks. It is a low dust mass disk that reveals
numerous structural elements (e.g. gaps and rings) that may point to young planets. It also exhibits a reservoir
of CO gas observed at both millimeter and IR wavelengths. Previous observations (Goto et al. 2006) reported a
possible asymmetry in the CO gas emission. Herein the IR ro-vibrational emission lines are analyzed and modeled
both spectroscopically and spectroastrometrically. We find emission features from both 12CO and 13CO isotopologues
heated to a temperature of approximately 200 K in the radial extent of 13 to 60 au. We do not see evidenceof thepreviously reported asymmetry in CO emission, our results being consistent with a Keplerian, axisymmetric emitting
region. This raises the question of whether the emission profile may be evolving in time, possibly as a result of anorbiting feature in the inner disk such as a planet.

17. Linking Outer Disk Pebble Dynamics and Gaps to Inner Disk Water Enrichment

A. Kalyaan, P. Pinilla, S. Krijt, G. D. Mulders, A. Banzatti F Millimeter continuum imaging of protoplanetarydisks reveals the distribution of solid particles and the presence of substructures (gaps and rings) beyond 5-10 au,
while infrared (IR) spectra provide access to abundances of gaseous species at smaller disk radii. Building on recent
observational findings of an anti-correlation between the inner disk water luminosity and outer dust disk radius, we
aim here at investigating the dynamics of icy solids that drift from the outer disk and sublimate their ice inside thesnow line, enriching the water vapor that is observed in the IR. We use a volatile-inclusive disk evolution model toexplore a range of conditions (gap location, particle size, disk mass, and alpha-viscosity) under which gaps in the outerdisk efficiently block the inward drift of icy solids. We find that inner-disk vapor enrichment is highly sensitive to thelocation of a disk gap, yielding for each particle size a radial "sweet spot" that reduces the inner-disk vapor enrichment
to a minimum. For pebbles of 1-10 mm in size, which carry the most mass, this sweet spot is at 7-15 au, suggestingthat inner gaps may have a key role in reducing ice delivery to the inner disk and may not allow the formation ofEarths and super-Earths. This highlights the importance of observationally determining the presence and properties
of inner gaps in disks. Finally, we argue that the inner water vapor abundance can be used as a proxy for estimating
the pebble drift efficiency and mass-flux entering the inner disk.

young stellar objects in the Local Group irregular galaxy NGC6822 identified
18. Massive
using machine learning
David A. Kinson, Joana M. Oliveira, Jacco Th. van Loon F We present a supervised machine learning methodology

to classify stellar populations in the Local Group dwarf-irregular galaxy NGC6822. Near-IR colours (J-H, H-K, andJ-K), K-band magnitudes and far-IR surface brightness (at 70 and 160 micron) measured from Spitzer and Herschelimages are the features used to train a Probabilistic Random Forest (PRF) classifier. Point-sources are classified into
eight target classes: young stellar objects (YSOs), oxygen- and carbon-rich asymptotic giant branch stars, red giant
branch and red super-giant stars, active galactic nuclei, massive main-sequence stars and Galactic foreground stars.
The PRF identifies sources with an accuracy of 90 percent across all target classes rising to 96 percent for YSOs.
We confirm the nature of 125 out of 277 literature YSO candidates with sufficient feature information, and identify

7

199 new YSOs and candidates. Whilst these are mostly located in known star forming regions, we have also identified
new star formation sites. These YSOs have mass estimates between 15-50 Msun, representing the most massive YSO
population in NGC 6822. Another 82 out of 277 literature candidates are definitively classified as non-YSOs by the
PRF analysis. We characterise the star formation environment by comparing the spatial distribution of YSOs to thoseof gas and dust using archival images. We also explore the potential of using (unsupervised) t-distributed stochastic
neighbour embedding maps for the identification of the same stellar population classified by the PRF.

The Near Stellar Environment of Class 0 Protostars: A First Look with Near-Infrared

19. Spectroscopy

S. Laos, T. P. Greene, J. R. Najita, K. G. Stassun F We present near-infrared K-band spectra for a sample

of 7 Class 0 protostars in the Perseus and Orion star-forming regions. We detect Br gamma, CO overtone, and H2emission, features that probe the near circumstellar environment of the protostar and reveal evidence of magnetosphericaccretion, a hot inner disk atmosphere, and outflows, respectively. Comparing the properties of these features withthose of Class I sources from the literature, we find that their Br gamma and CO emission are generally consistent
in strength and velocity width. The Br gamma line profiles are broad and centrally peaked, with FWHMs of 200
km/s and wings extending to 300 km/s. The line ratios of our H2 emission features, which are spatially extended forsome sources, are consistent with shock excitation and indicate the presence of strong jets or a disk wind. Within oursmall sample, the frequency of CO band emission (67%) is high relative to that of Class I samples (15%), indicatingthat Class 0s have high inner disk accretion rates, similar to those of the most actively accreting Class I sources.
Collectively, our results suggest that Class 0 sources have similar accretion mechanisms to the more evolved classes,with strong organized stellar magnetic fields established at the earliest observable stage of evolution.

Molecules with ALMA at Planet-forming Scales (MAPS) III: Characteristics of Radial

20. Chemical Substructures

Charles J. Law, Ryan A. Loomis, Richard Teague, Karin I. Öberg, Ian Czekala, Sean M. Andrews, Jane
Huang, Yuri Aikawa, Felipe Alarcón, Jaehan Bae, Edwin A. Bergin, Jennifer B. Bergner, Yann Boehler, AliceS. Booth, Arthur D. Bosman, Jenny K. Calahan, Gianni Cataldi, L. Ilsedore Cleeves, Kenji Furuya, Viviana V.
Guzmán, John D. Ilee, Romane Le Gal, Yao Liu, Feng Long, François Ménard, Hideko Nomura, Chunhua Qi,
Kamber R. Schwarz, Anibal Sierra, Takashi Tsukagoshi, Yoshihide Yamato, Merel L. R. van’t Hoff, Catherine
Walsh, David J. Wilner, Ke Zhang F The Molecules with ALMA at Planet-forming Scales (MAPS) Large Programprovides a detailed, high resolution (∼10-20 au) view of molecular line emission in five protoplanetary disks at spatial
scales relevant for planet formation. Here, we present a systematic analysis of chemical substructures in 18 molecularlines toward the MAPS sources: IM Lup, GM Aur, AS 209, HD 163296, and MWC 480. We identify more than 200
chemical substructures, which are found at nearly all radii where line emission is detected. A wide diversity of radialmorphologies - including rings, gaps, and plateaus - is observed both within each disk and across the MAPS sample.
This diversity in line emission profiles is also present in the innermost 50 au. Overall, this suggests that planets formin varied chemical environments both across disks and at different radii within the same disk. Interior to 150 au, themajority of chemical substructures across the MAPS disks are spatially coincident with substructures in the millimeter
continuum, indicative of physical and chemical links between the disk midplane and warm, elevated molecular emission
layers. Some chemical substructures in the inner disk and most chemical substructures exterior to 150 au cannot bedirectly linked to dust substructure, however, which indicates that there are also other causes of chemical substructures,such as snowlines, gradients in UV photon fluxes, ionization, and radially-varying elemental ratios. This implies
that chemical substructures could be developed into powerful probes of different disk characteristics, in addition to
influencing the environments within which planets assemble. This paper is part of the MAPS special issue of the
Astrophysical Journal Supplement.

with ALMA at Planet-forming Scales (MAPS) IV: Emission Surfaces and21. Molecules
Vertical Distribution of MoleculesCharles J. Law, Richard Teague, Ryan A. Loomis, Jaehan Bae, Karin I. Öberg, Ian Czekala, Sean M. Andrews,
Yuri Aikawa, Felipe Alarcón, Edwin A. Bergin, Jennifer B. Bergner, Alice S. Booth, Arthur D. Bosman, Jenny
K. Calahan, Gianni Cataldi, L. Ilsedore Cleeves, Kenji Furuya, Viviana V. Guzmán, Jane Huang, John D. Ilee,
Romane Le Gal, Yao Liu, Feng Long, François Ménard, Hideko Nomura, Laura M. Pérez, Chunhua Qi, Kamber

8

R. Schwarz, Daniela Soto, Takashi Tsukagoshi, Yoshihide Yamato, Merel L. R. van’t Hoff, Catherine Walsh,David J. Wilner, Ke Zhang F The Molecules with ALMA at Planet-forming Scales (MAPS) Large Program provides

a unique opportunity to study the vertical distribution of gas, chemistry, and temperature in the protoplanetary disks
around IM Lup, GM Aur, AS 209, HD 163296, and MWC 480. By using the asymmetry of molecular line emission
relative to the disk major axis, we infer the emission height (z) above the midplane as a function of radius (r).
Using this method, we measure emitting surfaces for a suite of CO isotopologues, HCN, and C2 H. We find that 12 CO
emission traces the most elevated regions with z/r > 0.3, while emission from the less abundant 13 CO and C18 O
probes deeper into the disk at altitudes of z/r . 0.2. C2 H and HCN have lower opacities and SNRs, making surface
fitting more difficult, and could only be reliably constrained in AS 209, HD 163296, and MWC 480, with z/r . 0.1,
i.e., relatively close to the planet-forming midplanes. We determine peak brightness temperatures of the opticallythick CO isotopologues and use these to trace 2D disk temperature structures. Several CO temperature profiles andemission surfaces show dips in temperature or vertical height, some of which are associated with gaps and rings inline and/or continuum emission. These substructures may be due to local changes in CO column density, gas surface
density, or gas temperatures, and detailed thermo-chemical models are necessary to better constrain their origins andrelate the chemical compositions of elevated disk layers with those of planet-forming material in disk midplanes. This
paper is part of the MAPS special issue of the Astrophysical Journal Supplement.

JCMT Transient Survey: Four Year Summary of Monitoring the Submillimeter
22. TheVariability of Protostars
The JCMT Transient Survey Collaboration - Yong-Hee Lee et al. F We present the four-year survey results ofmonthly submillimeter monitoring of eight nearby (< 500pc) star-forming regions by the JCMT Transient Survey.
We apply the Lomb-Scargle Periodogram technique to search for and characterize variability on 295 submillimeter
peaks brighter than 0.14 Jy beam−1 , including 22 disk sources (Class II), 83 protostars (Class 0/I), and 190 starlesssources. We uncover 18 secular variables, all of them protostars. No single-epoch burst or drop events and noinherently stochastic sources are observed. We classify the secular variables by their timescales into three groups:
Periodic, Curved, and Linear. For the Curved and Periodic cases, the detectable fractional amplitude, with respect tomean peak brightness, is ∼ 4 % for sources brighter than ∼ 0.5 Jy beam−1 . Limiting our sample to only these brightsources, the observed variable fraction is 37% (16 out of 43). Considering source evolution, we find a similar fraction ofbright variables for both Class 0 and Class I. Using an empirically motivated conversion from submillimeter variability
to variation in mass accretion rate, six sources (7% of our full sample) are predicted to have years-long accretion
events during which the excess mass accreted reaches more than 40% above the total quiescently accreted mass: two
previously known eruptive Class I sources, V1647 Ori and EC 53 (V371 Ser), and four Class 0 sources, HOPS 356,
HOPS 373, HOPS 383, and West 40. Considering the full protostellar ensemble, the importance of episodic accretionon few years timescale is negligible, only a few percent of the assembled mass. However, given that this accretionis dominated by events of order the observing time-window, it remains uncertain as to whether the importance of
episodic events will continue to rise with decades-long monitoring.

23. The discovery of the largest gas filament in our Galaxy, or a new spiral arm?
Chong Li, Keping Qiu, Bo Hu, Yue Cao F Using the Five-hundred-meter Aperture Spherical radio Telescope(FAST), we detect a giant HI filamentary structure in the sky region of 307.◦ 7 < α < 311.◦ 0 and 40.◦ 9 < δ < 43.◦ 4. The
structure has a velocity range of −170 km s−1 to −130 km s−1 , and a mean velocity of −150 km s−1 , putting it to a
Galactocentric distance of 22 kpc. The HI structure has a length of 1.1 kpc, which appears to be so far the furthest
and largest giant filament in the Galaxy and we name it Cattail. Its mass is calculated to be 6.5 × 104 M and thelinear mass density is 60 M pc−1 . Its width is 207 pc, corresponding to an aspect ratio of 5:1. Cattail possesses asmall velocity gradient (0.02 km s−1 pc−1 ) along its major axis. Together with the HI4PI data, we find that Cattail
could have an even larger length, up to 5 kpc. We also identify another new elongated structure to be the extension
into the Galactic first quadrant of the Outer Scutum-Centaurus (OSC) arm, and Cattail appears to be located far
behind the OSC. The question about how such a huge filament is produced at the extreme Galactic location remains
open. Alternatively, Cattail might be part of a new arm beyond the OSC, though it is puzzling that the structure
does not fully follow the warp of the Galactic disk.

924. Physical Properties and Real Nature of Massive Clumps in the Galaxy
Zu-Jia Lu, Veli-Matti Pelkonen, Mika Juvela, Paolo Padoan, Troels Haugbølle, Åke Nordlund F Systematicsurveys of massive clumps have been carried out to study the conditions leading to the formation of massive stars. Theseclumps are typically at large distances and unresolved, so their physical properties cannot be reliably derived from theobservations alone. Numerical simulations are needed to interpret the observations. To this end, we generate synthetic
Herschel observations using our large-scale star-formation simulation, where massive stars explode as supernovae
driving the interstellar-medium turbulence. From the synthetic observations, we compile a catalog of compact sources
following the exact same procedure as for the Hi-GAL compact source catalog. We show that the sources from thesimulation have observational properties with statistical distributions consistent with the observations. By relating
the compact sources from the synthetic observations to their three-dimensional counterparts in the simulation, we findthat the synthetic observations overestimate the clump masses by about an order of magnitude on average due toline-of-sight projection, and projection effects are likely to be even worse for Hi-GAL Inner Galaxy sources. We alsofind that a large fraction of sources classified as protostellar are likely to be starless, and propose a new method topartially discriminate between true and false protostellar sources.

of a Highly Collimated Flow from the High-Mass Protostar ISOSS J23053+5953
25. Discovery
SMM2
T. M., Rodríguez, P. Hofner, E. D. Araya, Q. Zhang, H. Linz, S. Kurtz, L. Gómez, C. Carrasco-González, V.
Rosero F We present Very Large Array C, X, and Q-band continuum observations, as well as 1.3 mm continuum andCO(2-1) observations with the Submillimeter Array toward the high-mass protostellar candidate ISOSS J23053+5953
SMM2. Compact cm continuum emission was detected near the center of the SMM2 core with a spectral index of
0.24 between 6 and 3.6 cm, and a radio luminosity of 1.3 mJy kpc2 . The 1.3 mm thermal dust emission indicates amass of the SMM2 core of 45.8 Msun. The CO(2-1) observations reveal a large, massive molecular outflow centeredon the SMM2 core. This fast outflow (> 50 km/s from the cloud systemic velocity) is highly collimated, with abroader, lower-velocity component. The large values for outflow mass (45.2 Msun), and momentum rate (6 x 10−3
Msun km/s/yr) derived from the CO emission are consistent with those of flows driven by high-mass YSOs. The
dynamical timescale of the flow is between 1.5 - 7.2 x 104 yr. We also found from the C18O to thermal dust emission
ratio that CO is depleted by a factor of about 20, possibly due to freeze out of CO molecules on dust grains. Our data
are consistent with previous findings that ISOSS J23053+5953 SMM2 is an emerging high-mass protostar in an earlyphase of evolution, with an ionized jet, and a fast, highly collimated, and massive outflow.

26. Dynamical effects of the radiative stellar feedback on the H I-to-H2 transition

Vincent Maillard, Emeric Bron, Franck Le Petit F The atomic-to-molecular hydrogen (H/H2) transition has been

extensively studied as it controls the fraction of gas in a molecular state in an interstellar cloud. This fraction islinked to star-formation by the Schmidt-Kennicutt law. While theoretical estimates of the column density of the H
I layer have been proposed for static photodissociation regions (PDRs), Herschel and well-resolved ALMA (Atacama
Large Millimeter Array) observations have revealed dynamical effects in star forming regions, caused by the processof photoevaporation. We extend the analytic study of the H/H2 transition to include the effects of the propagationof the ionization front, in particular in the presence of photoevaporation at the walls of blister H II regions, andwe find its consequences on the total atomic hydrogen column density at the surface of clouds in the presence of an
ultraviolet field, and on the properties of the H/H2 transition. We solved semi-analytically the differential equation
giving the H2 column density profile by taking into account H2 formation on grains, H2 photodissociation, and theionization front propagation dynamics modeled as advection of the gas through the ionization front. Taking thisadvection into account reduces the width of the atomic region compared to static models. The atomic region may
disappear if the ionization front velocity exceeds a certain value, leading the H/H2 transition and the ionization front
to merge. For both dissociated and merged configurations, we provide analytical expressions to determine the total H
I column density. Our results take the metallicity into account. Finally, we compared our results to observations of
PDRs illuminated by O-stars, for which we conclude that the dynamical effects are strong, especially for low-excitation
PDRs.

10

27. Characterization of the dust content in the ring around Sz 91: indications for planetesimal formation?

Karina Maucó, Carlos Carrasco-González, Matthias R. Schreiber, Anibal Sierra, Johan Olofsson, Amelia Bayo,
Claudio Caceres, Hector Canovas, Aina Palau F One of the most important questions in the field of planet forma-tion is how mm-cm sized dust particles overcome the radial drift and fragmentation barriers to form kilometer-sizedplanetesimals. ALMA observations of protoplanetary disks, in particular transition disks or disks with clear signs of
substructures, can provide new constraints on theories of grain growth and planetesimal formation and therefore represent one possibility to progress on this issue. We here present ALMA band 4 (2.1 mm) observations of the transition
disk system Sz 91 and combine them with previously obtained band 6 (1.3 mm) and 7 (0.9 mm) observations. Sz
91 with its well defined mm-ring, more extended gas disk, and evidence of smaller dust particles close to the star,is a clear case of dust filtering and the accumulation of mm sized particles in a gas pressure bump. We computed
the spectral index (nearly constant at ∼3.34), optical depth (marginally optically thick), and maximum grain size(∼ 0.61 mm) in the dust ring from the multi-wavelength ALMA observations and compared the results with recently
published simulations of grain growth in disk substructures. Our observational results are in very good agreementwith the predictions of models for grain growth in dust rings that include fragmentation and planetesimal formation
through the streaming instability.

Signatures of UV radiation in low-mass protostars I. Origin of HCN and CN emission

28. in the Serpens Main region

A. Mirocha, A. Karska, M. Gronowski, L. E. Kristensen, Ł. Tychoniec, D. Harsono, M. Figueira, M. Gładkowski,
M. Żółtowski F Context: Ultraviolet radiation (UV) influences the physics and chemistry of star-forming regions, but

its properties and significance in the immediate surroundings of low-mass protostars are still poorly understood. Aims:
We aim to extend the use of the CN/HCN ratio, already established for high-mass protostars, to the low-mass regime
to trace and characterize the UV field around low-mass protostars on ∼ 0.6 × 0.6 pc scales. Methods: We present
50 × 50 maps of the Serpens Main Cloud encompassing 10 protostars observed with the EMIR receiver at the IRAM 30
m telescope in CN 1-0, HCN 1-0, CS 3-2, and some of their isotopologues. The radiative-transfer code RADEX andthe chemical model Nahoon are used to determine column densities of molecules, gas temperature and density, and theUV field strength, G0 . Results: The spatial distribution of HCN and CS are well-correlated with CO 6-5 emission that
traces outflows. The CN emission is extended from the central protostars to their immediate surroundings also tracing
outflows, likely as a product of HCN photodissociation. The ratio of CN to HCN total column densities ranges from ∼1
to 12 corresponding to G0 ≈ 101 − 103 for gas densities and temperatures typical for outflows of low-mass protostars.
Conclusions: UV radiation associated with protostars and their outflows is indirectly identified in a significant part of
the Serpens Main low-mass star-forming region. Its strength is consistent with the values obtained from the OH andH2 O ratios observed with Herschel and compared with models of UV-illuminated shocks. From a chemical viewpoint,
the CN to HCN ratio is an excellent tracer of UV fields around low- and intermediate-mass star-forming regions.

The ALMA Survey of 70 µm Dark High-mass Clumps in Early Stages (ASHES). IV.
29. Starformation signatures in G023.477
Kaho Morii, Patricio Sanhueza, Fumitaka Nakamura, James M. Jackson, Shanghuo Li, Henrik Beuther, Qizhou
Zhang, Siyi Feng, Daniel Tafoya, Andrés E. Guzmán, Natsuko Izumi, Takeshi Sakai, Xing Lu, Ken’ichi Tatematsu, Satoshi Ohashi, Andrea Silva, Fernando A. Olguin, Yanett Contreras F With a mass of ∼1000 M anda surface density of ∼0.5 g cm−2 , G023.477+0.114 also known as IRDC 18310-4 is an infrared dark cloud (IRDC)
that has the potential to form high-mass stars and has been recognized as a promising prestellar clump candidate.
To characterize the early stages of high-mass star formation, we have observed G023.477+0.114 as part of the ALMA
Survey of 70 µm Dark High-mass Clumps in Early Stages (ASHES). We have conducted ∼1."2 resolution observations
with the Atacama Large Millimeter/submillimeter Array (ALMA) at 1.3 mm in dust continuum and molecular line
emission. We identified 11 cores, whose masses range from 1.1 M to 19.0 M . Ignoring magnetic fields, the virial
parameters of the cores are below unity, implying that the cores are gravitationally bound. However, when magnetic
fields are included, the prestellar cores are close to virial equilibrium, while the protostellar cores remain sub-virialized.
Star formation activity has already started in this clump. Four collimated outflows are detected in CO and SiO. H2 COand CH3 OH emission coincide with the high-velocity components seen in the CO and SiO emission. The outflows are
randomly oriented for the natal filament and the magnetic field. The position-velocity diagrams suggest that episodic
mass ejection has already begun even in this very early phase of protostellar formation. The masses of the identified
11cores are comparable to the expected maximum stellar mass that this IRDC could form (8-19 M ). We explore
two possibilities on how IRDC G023.477+0.114 could eventually form high-mass stars in the context of theoreticalscenarios.

Interpretation of optical and IR light curves for transitional disk candidates in NGC

30. 2264 using the extincted stellar radiation and the emission of optically thin dust inside
the hole
Erick Nagel, Fernando Gutiérrez-Canales, Sebastián Morales-Gutiérrez, Alana P. Sousa F In the stellar forming

region NGC 2264 there are objects catalogued as hosting a transitional disk according to spectrum modeling. Fourmembers of this set have optical and infrared light curves coming from the CoRoT and Spitzer telescopes. In thiswork, we try to simultaneously explain the light curves using the extinction of the stellar radiation and the emissionof the dust inside the hole of a transitional disk. For the object Mon-296, we were successful. However, for Mon-314,
and Mon-433 our evidence suggests that they host a pre-transitional disk. For Mon-1308 a new spectrum fitting using
the 3D radiative transfer code Hyperion allows us to conclude that this object hosts a full disk instead of a transitional
disk. This is in accord to previous work on Mon-1308 and with the fact that we cannot find a fit for the light curves
using only the contribution of the dust inside the hole of a transitional disk.

Quantifying Variability of YSOs in the Mid-IR Over Six Years with NEOWISE

31. Wooseok Park, Jeong-Eun Lee, Carlos Contreras Peña, Doug Johnstone, Gregory Herczeg, Sieun Lee, Seonjae
Lee, Anupam Bhardwaj, Gerald H. Moriarty-Schieven F Variability in young stellar objects (YSOs) can becaused by various time-dependent phenomena associated with star formation, including accretion rates, geometricchanges in the circumstellar disks, stochastic hydromagnetic interactions between stellar surfaces and inner disk edges,
reconnections within the stellar magnetosphere, and hot/cold spots on stellar surfaces. We uncover and characterize∼1700 variables from a sample of ∼5400 YSOs in nearby low-mass star-forming regions using mid-IR light curves
obtained from the 6.5-years NEOWISE All Sky Survey. The mid-IR variability traces a wide range of dynamical,
physical, and geometrical phenomenon. We classify six types of YSO mid-IR variability based on their light curves:
secular variability (Linear, Curved, P eriodic) and stochastic variability (Burst, Drop, Irregular). YSOs in earlier
evolutionary stages have higher fractions of variables and higher amplitudes for the variability, with the recurrence
timescale of FUor-type outbursts (defined here as ∆W1 or ∆W2 > 1 mag followed by inspection of candidates) of∼1000 years in the early embedded protostellar phase. Known eruptive young stars and subluminous objects show
fractions of variables similar to the fraction (∼ 55%) found in typical protostars, suggesting that these two distinct
types are not distinct in variability over the 6.5-year timescale. Along with brightness variability, we also find a diverse
range of secular color variations, which can be attributed to a competitive interplay between the variable accretion
luminosity of the central source and the variable extinction by material associated with the accretion process.

32. The first spectroscopically confirmed brown dwarfs in NGC 2264

Samuel Pearson, Aleks Scholz, Paula S Teixeira, Koraljka Mužić, Víctor Almendros-Abad F We present spectro-

scopic follow-up observations of 68 red, faint candidates from our multi-epoch, multi-wavelength, previously publishedsurvey of NGC 2264. Using near-infrared spectra from VLT/KMOS, we measure spectral types and extinction for
32 young low-mass sources. We confirm 13 as brown dwarfs in NGC 2264, with spectral types between M6 and M8,
corresponding to masses between 0.02 and 0.08M . These are the first spectroscopically confirmed brown dwarfs inthis benchmark cluster. 19 more objects are found to be young M-type stars of NGC 2264 with masses of 0.08 to
0.3 M . 7 of the confirmed brown dwarfs as well as 15 of the M-stars have IR excess caused by a disc. Comparing
with isochrones, the typical age of the confirmed brown dwarfs is <0.5 to 5Myr. More than half of the newly identified
brown dwarfs and very low mass stars have ages <0.5Myr, significantly younger than the bulk of the known cluster
population. Based on the success rate of our spectroscopic follow-up, we estimate that NGC 2264 hosts 200-600
brown dwarfs in total (in the given mass range). This would correspond to a star-to-brown dwarf ratio between 2.5:1
and 7.5:1. We determine the slope of the substellar mass function as α = 0.43+0.41−0.56 , these values are consistent withthose measured for other young clusters. This points to a uniform substellar mass function across all star forming
environments.

1233. Close stellar flybys common in low-mass clusters

Susanne Pfalzner, Amith Govind F Numerous protoplanetary discs show distinct spiral arms features. Whilepossibly caused by a range of processes, detailed pattern analysis points at close stellar flybys as cause for someof them. Surprisingly, these discs reside in young low-mass clusters, where close stellar flybys are expected to be
rare. This fact motivated us to take a fresh look at the frequency of close flybys in low-mass clusters. In the solar
neighbourhood, low-mass clusters have smaller half-mass radii than their more massive counterparts. We show that
this observational fact results in the mean and central stellar density of low-mass clusters being approximately thesame as in high-mass clusters, which is rarely reflected in theoretical studies. We perform N-body simulations of thestellar dynamics in young clusters obeying the observed mass-radius relation. Taking the mean disc truncation radius
as a proxy for the degree of influence of the environment, we find that the influence of the environment on discs ismore or less the same in low- and high-mass clusters. Even the fraction of small discs(< 10 au) is nearly identical.
Our main conclusion is that the frequency of close flybys seems to have been severely underestimated for low-massclusters. A testable prediction of this hypothesis is that low-mass clusters should contain 10%-15% of discs smaller
than 30 au truncated by flybys. These truncated discs should be distinguishable from primordially small discs by theirsteep outer edge.

An unbiased NOEMA 2.6 to 4 mm survey of the GG Tau ring: First detection of CCS

34. in a protoplanetary disk

N. T. Phuong, A. Dutrey, E. Chapillon, S. Guilloteau, J. Bary, T. L. Beck, A. Coutens, O. Denis-Alpizar, E.
Di Folco, P. N. Diep, L. Majumdar, J-P. Melisse, C-W. Lee, V. Pietu, T. Stoecklin, Y-W. Tang F Molecularline surveys are among the main tools to probe the structure and physical conditions in protoplanetary disks (PPDs),
the birthplace of planets. The large radial and vertical temperature as well as density gradients in these PPDs lead to
a complex chemical composition, making chemistry an important step to understand the variety of planetary systems.
We aimed to study the chemical content of the protoplanetary disk surrounding GG Tau A, a well-known triple T
Tauri system. We used NOEMA with the new correlator PolyFix to observe rotational lines at 2.6 to 4 mm from a few
dozen molecules. We analysed the data with a radiative transfer code to derive molecular densities and the abundance
relative to 13 CO, which we compare to those of the TMC1 cloud and LkCa15 disk. We report the first detection of
CCS in PPDs. We also marginally detect OCS and find 16 other molecules in the GG Tauri outer disk. Ten of themhad been found previously, while seven others (13 CN, N2 H+ , HNC, DNC, HC3 N, CCS, and C34 S) are new detectionsin this disk. The analysis confirms that sulphur chemistry is not yet properly understood. The D/H ratio, derived
from DCO+ /HCO+ , DCN/HCN, and DNC/HNC ratios, points towards a low temperature chemistry. The detectionof the rare species CCS confirms that GG Tau is a good laboratory to study the protoplanetary disk chemistry, thanks
to its large disk size and mass.

35. An orbital release model for the Orion BN/KL fingers

A. C. Raga, P. R. Rivera-Ortiz, A. Rodriguez-Gonzalez, A. Castellanos-Ramirez F We present a simple modelin which the bullets that produce the "Orion fingers" (ejected by the BN/KL object) are interpreted as protoplanets
or low mass protostars in orbit around a high mass star that has a supernova explosion. As the remnant of the SN
explosion has only a small fraction of the mass of the pre-supernova star, the orbiting objects then move away in free
trajectories, preserving their orbital velocity at the time of release. We show that a system of objects arranged inapproximately co-planar orbits results in trajectories with morphological and kinematical characteristics resembling
the Orion fingers. We show that, under the assumption of constant velocity motions, the positions of the observed
heads of the fingers can be used to reconstruct the properties of the orbital structure from which they originated,
resulting in a compact disk with an outer radius of ∼ 2.4 AU.

13

Globules and pillars in Cygnus X III. Herschel and upGREAT/SOFIA far-infrared spec-

36. troscopy of the globule IRAS 20319+3958 inCygnus X

N. Schneider, M. Roellig, E. T. Polehampton, F. Comeron, A. A. Djupvik, Z. Makai, C. Buchbender, R. Simon,
S. Bontemps, R. Guesten, G. White, Y. Okada, A. Parikka, N. Rothbart F IRAS 20319+3958 in Cygnus X Southis a rare example of a free-floating globule (mass 240 Msun, length 1.5 pc) with an internal HII region created by
the stellar feedback of embedded intermediate-mass stars, in particular, one Herbig Be star. Here, we present a Herschel/HIFI CII 158 mu map of the whole globule and a large set of other FIR lines (mid-to high-J CO lines observedwith Herschel/PACS and SPIRE, the OI 63 mu line and the CO 16-15 line observed with upGREAT on SOFIA),covering the globule head and partly a position in the tail. The CII map revealed that the whole globule is probably
rotating. Highly collimated, high-velocity CII emission is detected close to the Herbig Be star. We performed a PDR
analysis using the KOSMA-tau PDR code for one position in the head and one in the tail. The observed FIR lines in
the head can be reproduced with a two-component model: an extended, non-clumpy outer PDR shell and a clumpy,
dense, and thin inner PDR layer, representing the interface between the HII region cavity and the external PDR. The
modelled internal UV field of 2500 Go is similar to what we obtained from the Herschel FIR fluxes, but lower thanwhat we estimated from the census of the embedded stars. External illumination from the 30 pc distant Cyg OB2
cluster, producing an UV field of 150-600 G0 as an upper limit, is responsible for most of the CII emission. For thetail, we modelled the emission with a non-clumpy component, exposed to a UV-field of around 140 Go.

massive dense clumps truly sub-virial? A new analysis using Gould Belt ammonia
37. Aredata
Ayushi Singh, Christopher D. Matzner, Rachel K. Friesen, Peter G. Martin, Jaime E. Pineda, Erik W.
Rosolowsky, Felipe Alves, Ana Chacón-Tanarro, Hope How-Huan Chen, Michael Chun-Yuan Chen, Spandan
Choudhury, James Di Francesco, Jared Keown, Helen Kirk, Anna Punanova, Youngmin Seo, Yancy Shirley,
Adam Ginsburg, Stella S. R. Offner, Héctor G. Arce, Paola Caselli, Alyssa A. Goodman, Philip C. Myers,
Elena Redaelli F Dynamical studies of dense structures within molecular clouds often conclude that the most mas-sive clumps contain too little kinetic energy for virial equilibrium, unless they are magnetized to an unexpected degree.
This raises questions about how such a state might arise, and how it might persist long enough to represent the population of massive clumps. In an effort to re-examine the origins of this conclusion, we use ammonia line data fromthe Green Bank Ammonia Survey and Planck-calibrated dust emission data from Herschel to estimate the masses andkinetic and gravitational energies for dense clumps in the Gould Belt clouds. We show that several types of systematic
error can enhance the appearance of low kinetic-to-gravitational energy ratios: insufficient removal of foreground andbackground material; ignoring the kinetic energy associated with velocity differences across a resolved cloud; andover-correcting for stratification when evaluating the gravitational energy. Using an analysis designed to avoid theseerrors, we find that the most massive Gould Belt clumps harbor virial motions, rather than sub-virial ones. As a
byproduct, we present a catalog of masses, energies, and virial energy ratios for 85 Gould Belt clumps.

temperature of massive star-forming molecular clumps measured with formalde38. Kinetic
hyde IV. The ALMA view of N113 and N159W in the LMC
X. D. Tang, C. Henkel, K. M. Menten, Y. Gong, C. -H. R. Chen, D. L. Li, M. -Y. Lee, J. G. Mangum, Y.
P. Ao, S. Mühle, S. Aalto, S. García-Burillo, S. Martín, S. Viti, S. Muller, F. Costagliola, H. Asiri, S. A.
Levshakov, M. Spaans, J. Ott, C. M. V. Impellizzeri, Y. Fukui, Y. X. He, J. Esimbek, J. J. Zhou, X. W.
Zheng, X. Zhao, J. S. Li F We mapped the kinetic temperature structure of two massive star-forming regions, N113

and N159W, in the Large Magellanic Cloud (LMC). We have used ∼1 00. 6 (∼0.4 pc) resolution measurements of thepara-H2 CO JKa Kc = 303 –202 , 322 –221 , and 321 –220 transitions near 218.5 GHz to constrain RADEX non-LTE modelsof the physical conditions. The gas kinetic temperatures derived from the para-H2 CO line ratios 322 –221 /303 –202 and
321 –220 /303 –202 range from 28 to 105 K in N113 and 29 to 68 K in N159W. Distributions of the dense gas traced bypara-H2 CO agree with those of the 1.3 mm dust and Spitzer 8.0 µm emission, but do not significantly correlate with
the Hα emission. The high kinetic temperatures (Tkin & 50 K) of the dense gas traced by para-H2 CO appear to becorrelated with the embedded infrared sources inside the clouds and/or YSOs in the N113 and N159W regions. The
lower temperatures (Tkin < 50 K) are measured at the outskirts of the H2 CO-bearing distributions of both N113 andN159W. It seems that the kinetic temperatures of the dense gas traced by para-H2 CO are weakly affected by theexternal sources of the Hα emission. The non-thermal velocity dispersions of para-H2 CO are well correlated with thegas kinetic temperatures in the N113 region, implying that the higher kinetic temperature traced by para-H2 CO is
14

related to turbulence on a ∼0.4 pc scale. The dense gas heating appears to be dominated by internal star formation
activity, radiation, and/or turbulence. It seems that the mechanism heating the dense gas of the star-forming regionsin the LMC is consistent with that in Galactic massive star-forming regions located in the Galactic plane.

39. Chemical compositions in the vicinity of protostars in Ophiuchus
Kotomi Taniguchi, Liton Majumdar, Adele Plunkett, Shigehisa Takakuwa, Dariusz C. Lis, Paul F. Goldsmith,
Fumitaka Nakamura, Masao Saito, Eric Herbst F We have analyzed Atacama Large Millimeter/submillimeter

Array (ALMA) Cycle 4 Band 6 data toward two young stellar objects (YSOs), Oph-emb5 and Oph-emb9, in theOphiuchus star-forming region. The YSO Oph-emb5 is located in a relatively quiescent region, whereas Oph-emb9
is irradiated by a nearby bright Herbig Be star. Molecular lines from cyclic-C3 H2 (c-C3 H2 ), H2 CO, CH3 OH, 13 CO,
C18 O, and DCO+ have been detected from both sources, while DCN is detected only in Oph-emb9. Around Oph-emb5,
c-C3 H2 is enhanced at the west side, relative to the IR source, whereas H2 CO and CH3 OH are abundant at the eastside. In the field of Oph-emb9, moment 0 maps of the c-C3 H2 lines show a peak at the eastern edge of the field ofview, which is irradiated by the Herbig Be star. Moment 0 maps of CH3 OH and H2 CO show peaks farther from thebright star. We derive the N (c-C3 H2 )/N (CH3 OH) column density ratios at the peak positions of c-C3 H2 and CH3 OH
near each YSO, which are identified based on their moment 0 maps. The N (c-C3 H2 )/N (CH3 OH) ratio at the c-C3 H2peak is significantly higher than at the CH3 OH peak by a factor of ∼ 19 in Oph-emb9, while the difference in thiscolumn density ratio between these two positions is a factor of ∼ 2.6 in Oph-emb5. These differences are attributed
to the efficiency of the photon-dominated region (PDR) chemistry in Oph-emb9. The higher DCO+ column density
and the detection of DCN in Oph-emb9 are also discussed in the context of UV irradiation flux.

40. Clump-scale chemistry in the NGC2264-D cluster-forming region

Kotomi Taniguchi, Adele Plunkett, Tomomi Shimoikura, Kazuhito Dobashi, Masao Saito, Fumitaka Nakamura,
Eric Herbst F We have conducted mapping observations toward the n3 and n5 positions in the NGC 2264-D cluster-

forming region with the Atacama Compact Array (ACA) of the Atacama Large Millimeter/submillimeter Array(ALMA) in Band 3. Observations with 10000 au scale beam reveal the chemical composition at the clump scale. The
spatial distributions of the observed low upper-state-energy lines of CH3 OH are similar to those of CS and SO, andthe HC3 N emission seems to be predominantly associated with clumps containing young stellar objects. The turbulent
gas induced by the star formation activities produces large-scale shock regions in NGC 2264-D, which are traced by
the CH3 OH, CS and SO emissions. We derive the HC3 N, CH3 CN, and CH3 CHO abundances with respect to CH3 OH.
Compared to the n5 field, the n3 field is farther (in projected apparent distance) from the neighboring NGC 2264-C, yet
the chemical composition in the n3 field tends to be similar to that of the protostellar candidate CMM3 in NGC 2264C. The HC3 N/CH3 OH ratios in the n3 field are higher than those in the n5 field. We find an anti-correlation between
the HC3 N/CH3 OH ratio and their excitation temperatures. The low HC3 N/CH3 OH abundance ratio at the n5 field
implies that the n5 field is an environment with more active star formation compared with the n3 field.

An Unbiased CO Survey Toward the Northern Region of the Small Magellanic Cloudwith the Atacama Compact Array. I. Overview: CO Cloud Distributions
Kazuki Tokuda, Hiroshi Kondo, Takahiro Ohno, Ayu Konishi, Hidetoshi Sano, Kisetsu Tsuge, Sarolta Zahorecz,
Nao Goto, Naslim Neelamkodan, Tony Wong, Marta Sewiło, Hajime Fukushima, Tatsuya Takekoshi, Kazuyuki
Muraoka, Akiko Kawamura, Kengo Tachihara, Yasuo Fukui, Toshikazu Onishi F We have analyzed the data froma large-scale CO survey toward the northern region of the Small Magellanic Cloud (SMC) obtained with the Atacama
Compact Array (ACA) stand-alone mode of ALMA. The primary aim of this study is to comprehensively understandthe behavior of CO as an H2 tracer in a low-metallicity environment (Z ∼ 0.2 Z ). The total number of mosaic fields
is ∼8000, which results in a field coverage of 0.26 degree2 (∼2.9 ×105 pc2 ), corresponding to ∼10% area of the galaxy.
The sensitive ∼2 pc resolution observations reveal the detailed structure of the molecular clouds previously detected in
the single-dish NANTEN survey. We have detected a number of compact CO clouds within lower H2 column density(∼1020 cm−2 ) regions whose angular scale is similar to the ACA beam size. Most of the clouds in this survey also show
peak brightness temperature as low as <1 K, which for optically thick CO emission implies an emission size muchsmaller than the beam size, leading to beam dilution. The comparison between an available estimation of the total
molecular material traced by thermal dust emission and the present CO survey demonstrates that more than ∼90%
H2 gas cannot be traced by the low-J CO emission. Our processed data cubes and 2-D images are publicly available.

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Protostellar Interferometric Line Survey of the Cygnus X region (PILS-Cygnus) – First

42. results: observations of CygX-N30

S. J. van der Walt, L. E. Kristensen, J. K. Jørgensen, H. Calcutt, S. Manigand, M. el Akel, R. T. Garrod,
K. Qiu F (Abridged) Complex organic molecules (COMs) are commonly detected in and near star-forming regions.

However, the dominant process in the release of these COMs from the icy grains - where they predominately form
- to the gas phase is still an open question. We investigate the origin of COM emission in a protostellar source,
CygX-N30, through high-angular-resolution interferometric observations over a continuous broad frequency range. We
used 32 GHz Submillimeter Array observations with continuous frequency coverage from 329 to 361 GHz at an angularresolution of 1" to do a line survey and obtain a chemical inventory of the source. The line emission was used todetermine column densities and excitation temperatures for the COMs. We mapped out the intensity distribution of
the different species and identified approximately 400 lines that can be attributed to 29 different molecular species
and their isotopologues. We find that the molecular peak emission is along a linear gradient, coinciding with the axisof red- and blueshifted H2CO and CS emission. Chemical differentiation is detected along this gradient, with the
O-bearing molecular species peaking towards one component of the system and the N- and S-bearing species peaking
towards the other. The inferred column densities and excitation temperatures are compared to other sources whereCOMs are abundant. The origin of the observed COM emission is probably a combination of the young stellar sourcesalong with accretion of infalling material onto a disc-like structure surrounding a young protostar. The low D/H ratio
observed (<0.1%) likely reflects a pre-stellar phase where COMs formed on the ices at warm temperatures ( 30 K),
with inefficient deuterium fractionation. The observations and results presented here demonstrate the importance ofgood frequency coverage and high angular resolution when disentangling the origin of COM emission.

The impact of massive stars and black holes on the fate of open star clusters and their

43. tidal streams

Long Wang, Tereza Jerabkova F Context: To investigate how the content of massive OB stars affects the long-term
evolution of young open clusters and their tidal streams, and how such an effect influences the constraint of initialconditions by looking at the present-day observations. Aims: OB stars are typically in binaries, have a strong windmass loss during the first few Myr, and many become black holes. These affect the dynamical evolution of an open
star cluster and impact its dissolution in a given Galactic potential. We investigate the correlation between the massof OB stars and the observational properties of open clusters. Hyades-like star clusters are well represented in the
Solar neighborhood and thus allow comparisons with observational data. Methods: We perform a large number ofstar-by-star numerical N -body simulations of Hyades-like star clusters by using the high-performance N -body code
petar combined with galpy. We also developed the tool to transfer the simulation data to mock observations ofGaia. Results: We find that OB stars and black holes have a major effect on star cluster evolution. Star clusters withthe same initial conditions, but a different initial content of OB stars, follow very different evolutionary paths. Thus,
the initial total mass and radius of an observed star cluster cannot be unambiguously determined unless the initial
content of OB stars is known. We show that the stellar counts in the corresponding tidal tails, that can be identified
in the Gaia data, help to resolve this issues. We thus emphasise the importance of exploring not only star-clusters,
but also their corresponding tidal tails. These findings are relevant for studies of the formation of massive stars.

In search of infall motion in molecular clumps III: HCO+ (1-0) and H13CO+ (1-0)

44. mapping observations toward the confirmed infall sources

Yang Yang, Zhibo Jiang, Zhiwei Chen, Yiping Ao, Shuling Yu F The study of infall motion helps us to understandthe initial stages of star formation. In this paper, we use the IRAM 30-m telescope to make mapping observations of 24
infall sources confirmed in previous work. The lines we use to track gas infall motions are HCO+ (1-0) and H13CO+(1-0). All 24 sources show HCO+ emissions, while 18 sources show H13CO+ emissions. The HCO+ integrated
intensity maps of 17 sources show clear clumpy structures; for the H13CO+ line, 15 sources show clumpy structures.
We estimated the column density of HCO+ and H13CO+ using the RADEX radiation transfer code, and the obtained[HCO+]/[H2] and [H13CO+]/[HCO+] of these sources are about 10− 11 10− 7 and 10− 3 1, respectively. Based on theasymmetry of the line profile of the HCO+, we distinguish these sources: 19 sources show blue asymmetric profiles,
and the other sources show red profiles or symmetric peak profiles. For eight sources that have double-peaked blue line
profiles and signal-to-noise ratios greater than 10, the RATRAN model is used to fit their HCO+ (1-0) lines, and to
estimate their infall parameters. The mean Vin of these sources are 0.3 1.3 km/s, and the Min are about 10− 3 10− 4
Msun/yr , which are consistent with the results of intermediate or massive star formation in previous studies. The
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Vin estimated from the Myers model are 0.1 1.6 km/s, and the Min are within 10− 3 10− 5 Msun/yr. In addition,some identified infall sources show other star-forming activities, such as outflows and maser emissions. Especially for
those sources with a double-peaked blue asymmetric profile, most of them have both infall and outflow evidence.

A Morphological Classification of 18190 Molecular Clouds Identified in 12 CO Data from

45. the MWISP Survey

Lixia Yuan, Ji Yang, Fujun Du, Xunchuan Liu, Shaobo Zhang, Zehao Lin, Jingfei Sun, Qing-Zeng Yan, Yuehui
Ma, Yang Su, Yan Sun, Xin Zhou F We attempt to visually classify the morphologies of 18190 molecular clouds,

which are identified in the 12 CO(1-0) spectral line data over ∼ 450 deg2 of the second Galactic quadrant from theMilky Way Imaging Scroll Painting project (MWISP). Using the velocity-integrated intensity maps of the 12 CO(1-0)
emission, molecular clouds are first divided into unresolved and resolved ones. The resolved clouds are further classified
as non-filaments or filaments. Among the 18190 molecular clouds, ∼ 25 % are unresolved, ∼ 64% are non-filaments,and ∼ 11% are filaments. In the terms of the integrated flux of 12 CO(1-0) spectra of the whole 18190 molecular clouds,∼ 90% are from filaments, ∼ 9% are from non-filaments, and the rest ∼ 1% are from unresolved sources. Although
non-filaments are dominant in the number of the discrete molecular clouds, filaments are the main contributor of
12
CO emission flux. We also present the number distributions of physical parameters of the molecular clouds in ourcatalog, including their angular sizes, velocity spans, peak intensities of 12 CO(1-0) emission, and 12 CO(1-0) total
fluxes. We find that there is a systematic difference between the angular sizes of the non-filaments and filaments, withthe filaments tending to have larger angular scales. The H2 column densities of them are not significantly different.
We also discuss the observational effects, such as those induced by the finite spatial resolution, beam dilution andline-of-sight projection, on the morphological classification of molecular clouds in our sample.

46. Global 3D Radiation Hydrodynamic Simulations of Proto-Jupiter’s Convective Envelope
Zhaohuan Zhu, Yan-Fei Jiang, Hans Baehr, Andrew N. Youdin, Philip J. Armitage, Rebecca G. Martin F The

core accretion model of giant planet formation has been challenged by the discovery of recycling flows between theplanetary envelope and the disc that can slow or stall envelope accretion. We carry out 3D radiation hydrodynamic
simulations with an updated opacity compilation to model the proto-Jupiter’s envelope. To isolate the 3D effectsof convection and recycling, we simulate both isolated spherical envelopes and envelopes embedded in discs. The
envelopes are heated at given rates to achieve steady states, enabling comparisons with 1D models. We vary envelope
properties to obtain both radiative and convective solutions. Using a passive scalar, we observe significant mass
recycling on the orbital timescale. For a radiative envelope, recycling can only penetrate from the disc surface until∼0.1-0.2 planetary Hill radii, while for a convective envelope, the convective motion can "dredge up" the deeper partof the envelope so that the entire convective envelope is recycled efficiently. This recycling, however, has only limited
effects on the envelopes’ thermal structure. The radiative envelope embedded in the disc has identical structure as theisolated envelope. The convective envelope has a slightly higher density when it is embedded in the disc. We introduce
a modified 1D approach which can fully reproduce our 3D simulations. With our updated opacity and 1D model, we
recompute Jupiter’s envelope accretion with a 10 M⊕ core, and the timescale to runaway accretion is shorter than thedisc lifetime as in prior studies. Finally, we discuss the implications of the efficient recycling on the observed chemical
abundances of the planetary atmosphere (especially for super-Earths and mini-Neptunes).

The HD 98800 quadruple pre-main sequence system. Towards full orbital characterisa-

47. tion using long-baseline infrared interferometry

S. Zúñiga-Fernández, J. Olofsson, A. Bayo, X. Haubois, J. M. Corral-Santana, A. Lopera-Mejía, M. P. Ronco,
A. Tokovinin, A. Gallenne, G. M. Kennedy, J. -P. Berger F HD 98800 is a young (∼ 10 Myr old) and nearby(∼ 45 pc) quadruple system, composed of two spectroscopic binaries orbiting around each other (AaAb and BaBb),
with a gas-rich disk in polar configuration around BaBb. While the orbital parameters of BaBb and AB are relatively
well constrained, this is not the case for AaAb. A full characterisation of this quadruple system can provide insights
on the formation of such a complex system. The goal of this work is to determine the orbit of the AaAb subsystem
and refine the orbital solution of BaBb using multi-epoch interferometric observations with the VLTI/PIONIER andradial velocities. The PIONIER observations provide relative astrometric positions and flux ratios for both AaAa and
BaBb subsystems. Combining the astrometric points with radial velocity measurements, we determine the orbitalparameters of both subsystems. We refined the orbital solution of BaBb and derived, for the first time, the full orbital

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solution of AaAb. We confirmed the polar configuration of the circumbinary disk around BaBb. From our solutions,
we also inferred the dynamical masses of AaAb (MAa = 0.93 ± 0.09 and MAb = 0.29 ± 0.02 M ). We also revisitedthe parameters of the AB outer orbit. Using the N-body simulation, we show that the system should be dynamicallystable over thousands of orbital periods and that it made preliminary predictions for the transit of the disk in front of
AaAb which is estimated to start around 2026. We discuss the lack of a disk around AaAb, which can be explainedby the larger X-ray luminosity of AaAb, promoting faster photo-evaporation of the disk. High-resolution infrared
spectroscopic observations would provide radial velocities of Aa and Ab (blended lines in contemporary observations),
which would allow us to calculate the dynamical masses of Aa and Ab independently of the parallax of BaBb.

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