The Star Formation Newsletter
A community newsletter on Star and Planet Formation research
No. 349 — 29 January 2022
Editor: João Alveswww.starformation.news

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Cover image caption
A 1.28 GHz image of the inner ∼ 300 pc of the Milky Way from the South African MeerKAT telescope. The Galactic centeris at the center of the image. Networks of about 1000 non-thermal filaments, currently unexplained, are visible. The colors
represent the spectral index, from red (-1.8) to blue (1.0). Credit: Heywood et al. 2022. Color composite by Juan Carlos
Muñoz.
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 or the SFN.

Abstracts
1. Velocity structure of the 50 pc-long NGC 6334 filamentary cloud: Hints of multiple
compressions and their impact on the cloud properties?

Doris Arzoumanian, Delphine Russeil, Annie Zavagno, Michael Chun-Yuan Chen, Philippe André, Shu-ichiro
Inutsuka, Yoshiaki Misugi, Álvaro Sánchez-Monge, Peter Schilke, Alexander Men’shchikov, Mikito Kohno F[Abridged] The interstellar medium is observed to be organised in filamentary structures, as well as neutral (HI) and ionized (HII)
bubbles. The expanding nature of these bubbles makes them shape their surroundings and possibly play a role in the formationand evolution of interstellar filaments. We present APEX 13 CO and C18 O(2-1) observations of the NGC 6334 molecular cloud.
We investigate the gas velocity structure along and across the 50 pc-long cloud and towards 75 identified velocity-coherentfilaments (VCFs). We measure a wealth of velocity gradients along the VCFs. We derive the column density and velocity power
spectra of the VCFs. These power spectra are well represented with power laws showing similar slopes for both quantities(with a mean of about -2), albeit some differ by up to a factor of two. The position velocity diagrams perpendicular to three
VCFs show the V-shaped velocity pattern, corresponding to a bent structure in velocity space with the filament at the tip ofthe V surrounded by an extended structure connected to it with a velocity gradient. This velocity structure is qualitatively
similar to that resulting from numerical simulations of filament formation from large-scale compression from propagating shock
fronts. In addition, the radial profiles perpendicular to these VCFs hint to small-scale internal impacts from neighbouring HII
bubbles. The observed opposite curvature in velocity space towards the VCFs points to various origins of large-scale external
compressions from propagating HI bubbles. This suggests the plausible importance of multiple HI compressions, separated
in space and time, in the formation and evolution of molecular clouds and their star formation history. These latter atomic
compressions due to past and distant star formation events are complemented by the impact of HII bubbles from present timeand local star formation activity.

2. Constraining the cosmic-ray ionization rate and their spectrum with NIR spectroscopyof dense clouds – A test-bed for JWST

Shmuel Bialy, Sirio Belli, Marco Padovani F Low-energy cosmic-rays (CRs) control the thermo-chemical state and thecoupling between gas and magnetic fields in dense molecular clouds, the sites of star-formation. However, current estimates ofthe low-energy CR spectrum (E . 1 GeV) and the associated CR ionization rate are highly uncertain. We apply, for the firsttime, a new method for constraining the CR ionization rate and the CR spectral shape using H2 rovibrational lines from cold
molecular clouds. Using the MMIRS instrument on the MMT, we obtained deep near-infrared (NIR) spectra in six positions
within four dense cores, G150, G157, G163, G198, with column densities NH2 ≈ 1022 cm−2 . We derive 3σ upper limits on
the H2 (1 − 0)S(0) line (2.22 µm) brightness in the range I = 5.9 × 10−8 to 1.2 × 10−7 erg cm−2 s−1 sr−1 for the different2targets. Using both an analytic model and a numerical model of CR propagation, we convert these into upper limits on the CR
ionization rate in the clouds’ interior, ζ = 1.5 to 3.6 × 10−16 s−1 , and lower limits on the low-energy spectral slope of interstellar
CR protons, α = −0.97 to −0.79. We show that while MMT was unable to detect the H2 lines due to high atmospheric noise,
JWST/NIRSpec will be able to efficiently detect the CR-excited H2 lines, making it the ideal method for constraining theotherwise elusive low-energy CRs, shedding light on the sources and propagation modes of CRs.

3. FEEDBACK from the NGC7538 HII region

H. Beuther, N. Schneider, R. Simon, S. Suri, V. Ossenkopf-Okada, S. Kabanovic, M. Roellig, C. Guevara, A.
G. G. M. Tielens, G. Sandell, C. Buchbender, O. Ricken, R. Guesten F Context: How do expanding HII regionsinteract with their environmental cloud? This is one of the central questions driving the SOFIA legacy program FEEDBACK.
Here, we present a case study toward the prototypical Hii region NGC7538. Methods: With SOFIA we mapped an area of
210’2 around NGC7538 in the [CII] line at 1.9THz. Complementary observed atomic carbon [CI] and high-J CO(8-7) data as
well as archival NIR/FIR, cm continuum, CO(3-2) and HI data are folded into the analysis. Results: While the overall [CII]
morphology follows the general ionized gas, the channel maps show multiple bubble-like structures with sizes on the order of
80-100" ( 1.0-1.28pc). While at least one of them may be an individual feedback bubble driven by the main exciting sources of
the region, the other bubble-morphologies may also be due to the intrinsically porous structure of the HII region. An analysisof the expansion velocities around 10 km s−1 indicates that thermal expansion is not sufficient but that wind-driving fromthe central O-stars is required. The most blue-shifted [CII] component has barely any molecular or atomic counterparts. At
the interface to the molecular cloud, we find a typical photon-dominated region (PDR) with a bar-shape. Ionized, atomic
and molecular carbon show a layered structure in this PDR. The carbon in the PDR is dominated by its ionized form withatomic and molecular masses of 0.45+-0.1M and 1.2+-0.1M , respectively, compared to the ionized carbon in the range of
3.6-9.7M . Conclusions: The NGC7538 HII region exhibits a diverse set of sub-structures that interact with each other as wellas with the adjacent cloud. Compared to other recent [CII] observations of HII regions (e.g., Orion Veil, RCW120, RCW49),
bubble-shape morphologies revealed in [CII] emission, indicative of expanding shells, are recurring structures of PDRs.

Gas dynamics in the star forming region G18.148−0.283: Is it a manifestation of two

4. colliding molecular clouds?

Jyotirmoy Dey, Jagadheep D. Pandian, Dharam Vir Lal F We report the results obtained from a multi-wavelength studyof the HII region, G18.148−0.283, using the upgraded Giant Metre-wave Radio Telescope (uGMRT) at 1350 MHz along withother archival data. In addition to the radio continuum emission, we have detected the H169α and H170α radio recombinationlines towards G18.148−0.283 using a correlator bandwidth of 100 MHz. The moment-1 map of the ionized gas reveals a velocity
gradient of approximately 10 km s−1 across the radio continuum peaks. The 12 CO (J=3−2) molecular line data from the
COHRS survey also shows the presence of two velocity components that are very close to the velocities detected in the ionizedgas. The spectrum and position-velocity diagram from CO emission reveal molecular gas at an intermediate velocity range
bridging the velocity components. We see mid-infrared absorption and far-infrared emission establishing the presence of afilamentary infrared dark cloud, the extent of which includes the targeted HII region. The magnetic field inferred from dust
polarization is perpendicular to the filament within the HII region. We have also identified two O9 stars and 30 young stellar
objects towards the target using data from the 2MASS, UKIDSS, and GLIMPSE surveys. Cumulatively, this suggests that theregion is the site of a cloud-cloud collision that has triggered massive star formation and subsequent formation of an HII region.

5. A likely flyby of binary protostar Z CMa caught in action

Ruobing Dong, Hauyu Baobab Liu, Nicolas Cuello, Christophe Pinte, Peter Abraham, Eduard Vorobyov, Jun
Hashimoto, Agnes Kospal, Eugene Chiang, Michihiro Takami, Lei Chen, Michael Dunham, Misato Fukagawa,
Joel Green, Yasuhiro Hasegawa, Thomas Henning, Yaroslav Pavlyuchenkov, Tae-Soo Pyo, Motohide Tamura
F Close encounters between young stellar objects in star forming clusters are expected to dramatically perturb circumstellar
disks. Such events are witnessed in numerical simulations of star formation, but few direct observations of ongoing encounters
have been made. Here we report sub-0".1 resolution Atacama Large Millimeter Array (ALMA) and Jansky Very Large Array(JVLA) observations towards the million year old binary protostar Z CMa in dust continuum and molecular line emission. A
point source 4700 au from the binary has been discovered at both millimeter and centimeter wavelengths. It is located along
the extension of a 2000 au streamer structure previously found in scattered light imaging, whose counterpart in dust and gas
emission is also newly identified. Comparison with simulations shows signposts of a rare flyby event in action. Z CMa is a"double burster", as both binary components undergo accretion outbursts, which may be facilitated by perturbations to thehost disk by flybys.

3

ODYSSEUS Survey. Motivation and First Results: Accretion, Ejection, and Disk
6. TheIrradiation of CVSO 109
ODYSSEUS Survey, C. C. Espaillat et al. F The Hubble UV Legacy Library of Young Stars as Essential Standards(ULLYSES) Director’s Discretionary Program of low-mass pre-main-sequence stars, coupled with forthcoming data from ALMA
and JWST, will provide the foundation to revolutionize our understanding of the relationship between young stars and their
protoplanetary disks. A comprehensive evaluation of the physics of disk evolution and planet formation requires understanding
the intricate relationships between mass accretion, mass outflow, and disk structure. Here we describe the Outflows and Disks
around Young Stars: Synergies for the Exploration of ULLYSES Spectra (ODYSSEUS) Survey and present initial results of theclassical T Tauri Star CVSO 109 in Orion OB1b as a demonstration of the science that will result from the survey. ODYSSEUS
will analyze the ULLYSES spectral database, ensuring a uniform and systematic approach in order to (1) measure how theaccretion flow depends on the accretion rate and magnetic structures, (2) determine where winds and jets are launched and how
mass-loss rates compare with accretion, and (3) establish the influence of FUV radiation on the chemistry of the warm inner
regions of planet-forming disks. ODYSSEUS will also acquire and provide contemporaneous observations at X-ray, optical,
NIR, and millimeter wavelengths to enhance the impact of the ULLYSES data. Our goal is to provide a consistent frameworkto accurately measure the level and evolution of mass accretion in protoplanetary disks, the properties and magnitudes of
inner-disk mass loss, and the influence of UV radiation fields that determine ionization levels and drive disk chemistry.

of HC18O+ in a protoplanetary disk: exploring oxygen isotope fractionation
7. Detectionof CO
Kenji Furuya, Takashi Tsukagoshi, Chunhua Qi, Hideko Nomura, L. Ilsedore Cleeves, Seokho Lee, Tomohiro
C. Yoshida F The oxygen isotope fractionation scenario, which has been developed to explain the oxygen isotope anomaly inthe solar system materials, predicts that CO gas is depleted in 18O in protoplanetary disks, where segregation between solids
and gas inside disks had already occurred. Based on ALMA observations, we report the first detection of HC18O+(4-3) in a
Class II protoplanetary disk (TW Hya). This detection allows us to explore the oxygen isotope fractionation of CO in the TW
Hya disk from optically thin HCO+ isotopologues as a proxy of optically thicker CO isotopologues. Using the H13CO+(4-3)
data previously obtained with SMA, we find that the H13CO+/HC18O+ ratio in the central <100 au regions of the disk is10.3 +- 3.2. We construct a chemical model of the TW Hya disk with carbon and oxygen isotope fractionation chemistry, andestimate the conversion factor from H13CO+/HC18O+ to 13CO/C18O. With the conversion factor (= 0.8), the 13CO/C18O
ratio is estimated to be 8.3 +- 2.6, which is consistent with the elemental abundance ratio in the local ISM (8.1 +- 0.8)
within error margin. Then there is no clear evidence of 18O depletion in CO gas of the disk, although we could not draw any
robust conclusion due to large uncertainties. In conclusion, optically thin lines of HCO+ isotopologues are useful tracers of CO
isotopic ratios, which are hardly constrained directly from optically thick lines of CO isotopologues. Future higher sensitivity
observations of H13CO+ and HC18O+ would be able to allow us to better constrain the oxygen fractionation in the disk.

EDR3 distances of the young stellar clusters in the extended Carina Nebula com8. Gaia
plex
C. Göppl, T. Preibisch F Context: The Carina Nebula complex (CNC) is one of the most massive and active star-forming
regions in our Galaxy and it contains several large young star clusters. The distances of the individual clusters and their
physical connection were poorly known up to now, with strongly discrepant results reported in the literature. Aims: We want
to determine reliable distances of the young stellar clusters in the central Carina Nebula region (in particular, Tr 14, 15, and16) and the prominent clusters NGC 3324 and NGC 3293 in the northwestern periphery of the CNC. Methods: We analyzed
the parallaxes in Gaia EDR3 for a comprehensive sample of 237 spectroscopically identified OB stars, as well as for 9562 Xray-selected young stars throughout the complex. We also performed an astrometric analysis to identify members of the young
cluster vdBH 99, which is located in the foreground of the northwestern part of the Carina Nebula. Results: We find that the
distances of the investigated clusters in the CNC are equal within <= 2%, and yield very consistent most likely mean distancevalues of 2.36(+0.05 -0.05) kpc for the OB star sample and 2.34(+0.05 -0.06) kpc for the sample of X-ray-selected young stars.
Conclusions: Our results show that the clusters in the CNC constitute a coherent star-forming region, in particular with regard
to NGC 3324 and NGC 3293 at the northwestern periphery, which are (within <= 2%) at the same distance as the central
Carina Nebula. For the foreground cluster vdBH 99, we find a mean distance of 441(+2 -2) pc and an age of 60 Myr. We
quantified the contamination of X-ray-selected samples of Carina Nebula stars based on members of this foreground cluster.

9. A large catalogue of molecular clouds in the southern sky

Helong Guo, Bingqiu Chen, Xiaowei Liu F We present a large catalogue of molecular clouds with accurate distanceestimates in the southern sky. Based on the three-dimensional (3D) dust extinction map and the best-fit extinction and distanceinformation of over 17 million stars presented in Guo et al., we have identified 250 dust/molecular clouds in the southern sky
using a hierarchical structure identification algorithm. Amongst them, 71 clouds locating at high Galactic latitudes (b < −10◦ ).
We have estimated the distances to the clouds by fitting the extinction versus distance profiles of the lines of sight overlapping4

with the clouds using a simple Gaussian dust distribution model. The typical uncertainties of the distances are less than 7
per cent. We also provide the physical properties of the individual clouds, including the linear radius, mass and surface massdensity.

10. LkHα 225 (V1318 Cyg) South in Outburst
Lynne A. Hillenbrand, Howard Isaacson, Antonio C. Rodriguez, Michael Connelley, Bo Reipurth, Michael A.
Kuhn, Tracy Beck, Diego Rodriguez Perez F Magakian et al. (2019) called attention to the current bright state of LkHa
225 South, which over the past two decades has changed from > 20m to < 13m . We present recent optical photometric monitoringthat shows colorless, non-sinusoidal, periodic brightness variations. The oscillations occur every 43 days, and have amplitude∼0.7 mag with some variation among cycles. We also present new flux-calibrated optical and near-infrared spectroscopy, which
we model in terms of a keplerian disk. Additional high dispersion spectra demonstrate the similarity of the absorption line
pattern to some categories of "mixed temperature" accretion outburst objects. At blue wavelengths, LkHa 225 South has apure absorption spectrum and is a good spectral match to the FU Ori stars V1515 Cyg and V1057 Cyg. At red optical andinfrared wavelengths, however, the spectrum is more similar to Gaia 19ajj, showing emission in TiO, CO, and metals. Sr II lines
indicate a low surface gravity atmosphere. There are also signatures of a strong wind/outflow. LkHa 225 South was moderately
bright in early 1950’s as well as in late 1980’s, with evidence for deep fades during intervening epochs. The body of evidence
suggests that LkHa225 South is another case of a source with episodically enhanced accretion that causes brightening by ordersof magnitude, and development of a hot absorption spectrum and warm wind. It is similar to Gaia 19ajj, but also reminiscentin its long brightening time and brightness oscillation near peak, to the embedded sources L1634 IRS7 and ESO Ha 99.

11. Expected FU Ori Outburst Amplitudes from the Optical to the Mid-Infrared

Lynne A. Hillenbrand, Antonio C. Rodriguez F Disks around young stellar objects (YSOs) consist of material that
thermally emits the energy provided by a combination of passive heating from the central star, and active, viscous heating due
to mass accretion. FU Ori stars are YSOs with substantially enhanced accretion rates in their inner disk regions. As a disk
transitions from standard low-state, to FU Ori-like high-state accretion, the outburst manifests through photometric brightening
over a broad range of wavelengths. We present results for the expected amplitudes of the brightening between ∼4000 Å and 8µm – the wavelength range where FU Ori type outburst events are most commonly detected. Our model consists of an opticallythick passive + active steady-state accretion disk with low and high accretion states.

1.

Self-absorption in [CII], 12 CO, and HI in RCW120. Building up a geometrical and12. physical model of the region
S. Kabanovic, N. Schneider, V. Ossenkopf-Okada, F. Falasca, R. Güsten, J. Stutzki, R. Simon, C. Buchbender,
L. Anderson, L. Bonne, C. Guevara, R. Higgins, B. Koribalski, M. Luisi, M. Mertens, Y. Okada, M. Röllig, D.
Seifried, M. Tiwari, F. Wyrowski, A. Zavagno, A. G. G. M. Tielens F Revealing the 3D dynamics of HII regions andtheir associated molecular clouds is important for understanding the longstanding problem as to how stellar feedback affects
the density structure and kinematics of the interstellar medium. We employed observations of the HII region RCW 120 in[CII], observed within the SOFIA legacy program FEEDBACK, and the 12 CO and 13 CO (3→2) lines, obtained with APEX. In
addition we used HI data from the Southern Galactic Plane Survey. Two radiative transfer models were used to fit the observed
data. A line profile analysis with the 1D non-LTE radiative transfer code SimLine proves that the CO emission cannot stemfrom a spherically symmetric molecular cloud configuration. With a two-layer multicomponent model, we then quantified theamount of warm background and cold foreground gas. There is a deficit of CO emission along the line-of-sight toward thecenter of the HII region which indicates that the HII region is associated with a flattened molecular cloud. Self-absorption in
the CO line may hide signatures of infalling and expanding molecular gas. The [CII] emission arises from an expanding [CII]
bubble and from the PDRs. A significant part of [CII] emission is absorbed in a cool ( 60-100 K), low-density (<500 cm−3 )atomic foreground layer with a thickness of a few parsec. We propose that the RCW 120 HII region formed in a flattenedmolecular cloud and is now bursting out of its parental cloud. The compressed surrounding molecular layer formed a torus
around the spherically expanding HII bubble. This scenario can possibly be generalized for other HII bubbles and would explain
the observed “flat" structure of molecular clouds associated with HII bubbles. We suggest that the [CII] absorption observed inmany star-forming regions is at least partly caused by low-density, cool, HI-envelopes surrounding the molecular clouds.

13. A rich population of free-floating planets in the Upper Scorpius young stellar association

Núria Miret-Roig, Hervé Bouy, Sean N. Raymond, Motohide Tamura, Emmanuel Bertin, David Barrado, Javier
Olivares, Phillip A. B. Galli, Jean-Charles Cuillandre, Luis Manuel Sarro, Angel Berihuete, Nuria Huélamo
F The nature and origin of free-floating planets (FFPs) are still largely unconstrained because of a lack of large homogeneous
samples to enable a statistical analysis of their properties. So far, most FFPs have been discovered using indirect methods;
microlensing surveys have proved particularly successful to detect these objects down to a few Earth masses. However, the5ephemeral nature of microlensing events prevents any follow-up observations and individual characterization. Several studies
have identified FFPs in young stellar clusters and the Galactic field but their samples are small or heterogeneous in age andorigin. Here we report the discovery of between 70 and 170 FFPs (depending on the assumed age) in the region encompassing
Upper Scorpius and Ophiuchus, the closest young OB association to the Sun. We found an excess of FFPs by a factor of up
to seven compared with core-collapse model predictions, demonstrating that other formation mechanisms may be at work. We
estimate that ejection from planetary systems might have a contribution comparable to that of core-collapse in the formation of
FFPs. Therefore, ejections due to dynamical instabilities in giant exoplanet systems must be frequent within the first 10 Myr
of a system’s life.

14. FAUST III. Misaligned rotations of the envelope, outflow, and disks in the multiple
protostellar system of VLA 1623−2417

FAUST III, Satoshi Ohashi et al. F We report a study of the low-mass Class-0 multiple system VLA 1623AB in theOphiuchus star-forming region, using H13 CO+ (J = 3 − 2), CS (J = 5 − 4), and CCH (N = 3 − 2) lines as part of the ALMA
Large Program FAUST. The analysis of the velocity fields revealed the rotation motion in the envelope and the velocity gradientsin the outflows (about 2000 au down to 50 au). We further investigated the rotation of the circum-binary VLA 1623A disk aswell as the VLA 1623B disk. We found that the minor axis of the circum-binary disk of VLA 1623A is misaligned by about 12
degrees with respect to the large-scale outflow and the rotation axis of the envelope. In contrast, the minor axis of the circumbinary disk is parallel to the large-scale magnetic field according to previous dust polarization observations, suggesting that themisalignment may be caused by the different directions of the envelope rotation and the magnetic field. If the velocity gradientof the outflow is caused by rotation, the outflow has a constant angular momentum and the launching radius is estimated tobe 5 − 16 au, although it cannot be ruled out that the velocity gradient is driven by entrainments of the two high-velocity
outflows. Furthermore, we detected for the first time a velocity gradient associated with rotation toward the VLA 16293B disk.
The velocity gradient is opposite to the one from the large-scale envelope, outflow, and circum-binary disk. The origin of its
opposite gradient is also discussed.

rays in molecular clouds probed by H2 rovibrational lines – Perspectives for the
15. Cosmic
James Webb Space Telescope
Marco Padovani, Shmuel Bialy, Daniele Galli, Alexei V. Ivlev, Tommaso Grassi, Liam H. Scarlett, Una S.
Rehill, Mark C. Zammit, Dmitry V. Fursa, Igor Bray F Cosmic rays (CRs) at sub-TeV energies play a fundamentalrole in the chemical and dynamical evolution of molecular clouds, as they control the ionisation, dissociation, and excitationof H2 . Their characterisation is important both for the interpretation of observations and for the development of theoreticalmodels. The methods used so far for estimating the CR ionisation rate (ζ) in molecular clouds have several limitations due
to uncertainties in the adopted chemical networks. We refine and extend the method proposed by Bialy (2020) to estimate ζby observing rovibrational transitions of H2 at near-infrared wavelengths, which are mainly excited by secondary CR electrons.
Combining models of interstellar CR propagation and attenuation with the calculation of the expected secondary electron
spectrum and updated H2 excitation cross sections by electron collisions, we derive the intensity of the four H2 rovibrationaltransitions observable in dense, cold gas: (1-0)O(2), (1-0)Q(2), (1-0)S(0), and (1-0)O(4). The proposed method allows theestimation of ζ for a given observed line intensity and H2 column density. We are also able to deduce the shape of the lowenergy CR proton spectrum impinging upon the molecular cloud. We present a look-up plot and a web-based application thatcan be used to constrain the low-energy spectral slope of the interstellar CR proton spectrum. We comment on the capabilityof the James Webb Space Telescope to detect these near-infrared H2 lines, making it possible to derive for the first time spatial
variation of ζ in dense gas. Besides the implications for the interpretation of the chemical-dynamic evolution of a molecular
cloud, it will be possible to test competing models of CR propagation and attenuation in the interstellar medium, as well ascompare CR spectra in different Galactic regions.

Application of a Steady-State Accretion Disk Model to Spectrophotometry and High-

16. Resolution Spectra of Two Recent FU Ori Outbursts

Antonio C. Rodriguez, Lynne A. Hillenbrand F We apply a conventional accretion disk model to the FU Ori-type
objects HBC 722 and Gaia 17bpi. Our base model is a steady-state, thin Keplerian disk featuring a modified ShakuraSunyaev temperature profile, with each annulus radiating as an area-weighted spectrum given by a NextGen atmosphere at
the appropriate temperature. We explore departures from the standard model by altering the temperature distribution in the
innermost region of the disk to account for "boundary region"-like effects. We consider the overall spectral energy distribution(SED) as well as medium- and high-resolution spectra in evaluating best-fit models to the data. Parameter degeneracies arestudied via a Markov Chain Monte Carlo (MCMC) parameter estimation technique. Allowing all parameters to vary, we find
−6.70
accretion rates for HBC 722 of Ṁ = 10−4.90 M yr−1 +0.99
M yr−1 +0.46−0.40 dex and for Gaia 17bpi of Ṁ = 10−0.36 dex; the+900
corresponding maximum disk temperatures are 7100+300
K
and
7900
K,
respectively.
While
the
accretion
rate of HBC 722
−500
−400
is on the same order as other FU Ori-type objects, Gaia 17bpi has a lower rate than previously reported as typical, commensurate

6

with its lower luminosity. Alternate models that fix some disk or stellar parameters are also presented, with tighter confidence
intervals on the remaining fitted parameters. In order to improve upon the somewhat large credible intervals for the Ṁ values,
and make progress on boundary layer characterization, flux-calibrated ultraviolet spectroscopy is needed.

take the square root? An assessment of interstellar magnetic field strength esti17. Why
mation methods
R. Skalidis, J. Sternberg, J. R. Beattie, V. Pavlidou, K. Tassis F The magnetic field strength in interstellar clouds
can be estimated indirectly by using the spread of dust polarization angles (δθ). The method developed by Davis 1951 andby Chandrasekhar and Fermi 1953 (DCF) assumes that incompressible magnetohydrodynamic (MHD) fluctuations induce theobserved dispersion of polarization angles, deriving B ∝ 1/δθ (or, δθ ∝ MA , in terms of the Alfvénic Mach number). However,observations show that the interstellar medium (ISM) is highly
compressible. Recently, Skalidis & Tassis 2021 (ST) relaxed the√2
incompressibility assumption and derived instead B ∝ 1/ δθ (δθ ∝ MA). We explored what the correct scaling is in compressible and magnetized turbulence with numerical simulations. We used 26 magnetized, ideal-MHD numerical simulations withdifferent types of forcing. The range of MA and sonic Mach numbers Ms explored are 0.1 ≤ MA ≤ 2.0 and 0.5 ≤ Ms ≤ 20. We
created synthetic polarization maps and tested the assumptions and accuracy of the two methods. The synthetic data have a2
remarkable consistency with the δθ ∝ MA
scaling, which is inferred by ST, while the DCF scaling fails to follow the data. The
ST method shows an accuracy better than 50% over the entire range of MA explored; DCF performs adequately only in the rangeof MA for which it has been optimized through the use of a "fudge factor". For low MA , DCF is inaccurate by factors of tens.
The assumptions of the ST method reflect better the physical reality in clouds with compressible and magnetized turbulence,and for this reason the method provides a much better estimate of the magnetic field strength over the DCF method.

APEX Large CO Heterodyne Orion Legacy Survey (ALCOHOLS). I. Survey overview
18. TheThomas Stanke, H. G. Arce, J. Bally, P. Bergman, J. Carpenter, C. J. Davis, W. Dent, J. Di Francesco, J. Eislöffel, D. Froebrich, A. Ginsburg, M. Heyer, D. Johnstone, D. Mardones, M. J. McCaughrean, S. T. Megeath,
F. Nakamura, M. D. Smith, A. Stutz, K. Tatematsu, C. Walker, J. P. Williams, H. Zinnecker, B. J. Swift, C.
Kulesa, B. Peters, B. Duffy, J. Kloosterman, U. A. Yıldız, J. L. Pineda, C. De Breuck, Th. Klein F The Orion
molecular cloud complex harbours the nearest GMCs and site of high-mass star formation. Its YSO populations are thoroughly
characterized. The region is therefore a prime target for the study of star formation. Here, we verify the performance of theSuperCAM 64 pixel heterodyne array on APEX. We give a descriptive overview of a set of wide-field CO(3-2) spectral cubes
obtained towards the Orion GMC complex, aimed at characterizing the dynamics and structure of the extended molecular gas
in diverse regions of the clouds, ranging from very active sites of clustered star formation in Orion B to comparatively quiet
regions in southern Orion A. We present a 2.7 square degree (130pc2 ) mapping survey in the CO(3-2) transition, obtained using
SuperCAM on APEX at an angular resolution of 19” (7600AU or 0.037pc at a distance of 400pc), covering L1622, NGC2071,
NGC2068, OriB9, NGC2024, and NGC2023 in Orion B, and the southern part of the L1641 cloud in Orion A. We describe
CO integrated emission and line moment maps and position-velocity diagrams and discuss a few sub-regions in some detail.
Evidence for expanding bubbles is seen with lines splitting into double components, most prominently in NGC2024, where we
argue that the bulk of the molecular gas is in the foreground of the HII region. High CO(3-2)/CO(1-0) line ratios reveal warm
CO along the western edge of Orion B in the NGC2023/NGC2024 region facing the IC434 HII region. Multiple, well separated
radial velocity components seen in L1641-S suggest that it consists of a sequence of clouds at increasingly larger distances.
We find a small, spherical cloud - the ’Cow Nebula’ globule - north of NGC2071. We trace high velocity line wings for the
NGC2071-IR outflow and the NGC2024 CO jet. The protostellar dust core FIR4 (rather than FIR5) is the true driving sourceof the NGC2024 monopolar outflow.

A train of shocks at 3000 au scale? Exploring the clash of an expanding bubble into the

19. NGC 1333 IRAS 4 region. SOLIS XVIMarta De Simone, Claudio Codella, Cecilia Ceccarelli, Ana López-Sepulcre, Roberto Neri, Pedro Ruben RiveraOrtiz, Gemma Busquet, Paola Caselli, Eleonora Bianchi, Francesco Fontani, Bertrand Lefloch, Yoko Oya, Jaime
E. Pineda F There is evidence that the star formation process is linked to the intricate net of filaments in molecular clouds,
which may be also due to gas compression from external triggers. We studied the southern region of the Perseus NGC 1333
molecular cloud, known to be heavily shaped by similar external triggers, to shed light on the process that perturbed thefilament where the Class 0 IRAS4 protostars lie. We use new IRAM-NOEMA observations of SiO and CH3OH, both known totrace violent events as shocks, toward IRAS 4A as part of the Large Program Seeds Of Life in Space (SOLIS). We detected threeparallel elongated (>6000 au) structures, called fingers, with narrow line profiles ( 1.5 kms−1 ) peaked at the cloud systemic
velocity, tracing gas with high density (5-20 105 cm−3 ) and high temperature (80-160 K). They are chemically different, with thenorthern finger traced by both SiO and CH3OH ([CH3OH]/[SiO] 160-300), while the other two only by SiO ([CH3OH]/[SiO]<
40). Among various possibilities, a train of three shocks, distanced by >5000 yr, would be consistent with the observations if asubstantial fraction of silicon, frozen onto the grain mantles, is released by the shocks.We suggest that the shock train is due to7

an expanding gas bubble, coming behind NGC 1333 from the southwest and clashing against the filament, where IRAS 4A lies.
Finally, we propose a solution to the two-decades long debate on the nature and origin of the widespread narrow SiO emission
observed in the south part of NGC 1333, namely that it is due to unresolved trains of shocks.

Observations of Molecular Complexity in the Large Magellanic Cloud: The N105
20. ALMA
Star-Forming Region
Marta Sewiło, Martin Cordiner, Steven B. Charnley, Joana M. Oliveira, Emmanuel Garcia Berrios, Peter
Schilke, Jacob L. Ward, Jennifer Wiseman, Remy Indebetouw, Kazuki Tokuda, Jacco Th. van Loon, Álvaro
Sánchez-Monge, Veronica Allen, C. -H. Rosie Chen, Roya Hamedani Golshan, Agata Karska, Lars E. Kristensen, Stan E. Kurtz, Toshikazu Onishi, Sarolta Zahorecz F The Large Magellanic Cloud (LMC) is the nearest
laboratory for detailed studies on the formation and survival of complex organic molecules (COMs), including biologically important ones, in low-metallicity environments–typical for earlier cosmological epochs. We report the results of 1.2 mm continuum
and molecular line observations of three fields in the star-forming region N105 with the Atacama Large Millimeter/submillimeter
Array (ALMA). N105 lies at the western edge of the LMC bar with on-going star formation traced by H2 O, OH, and CH3 OH
masers, ultracompact H II regions, and young stellar objects. Based on the spectral line modeling, we estimated rotational temperatures, column densities, and fractional molecular abundances for twelve 1.2 mm continuum sources. We identified sources
with a range of chemical make-ups, including two bona fide hot cores and four hot core candidates. The CH3 OH emission is
widespread and associated with all the continuum sources. COMs CH3 CN and CH3 OCH3 are detected toward two hot coresin N105 together with smaller molecules typically found in Galactic hot cores (e.g., SO2 , SO, and HNCO) with the molecular abundances roughly scaling with metallicity. We report a tentative detection of the astrobiologically relevant formamide
molecule (NH2 CHO) toward one of the hot cores; if confirmed, this would be the first detection of NH2 CHO in an extragalactic
sub-solar metallicity environment. We suggest that metallicity inhomogeneities resulting from the tidal interactions between
the LMC and the Small Magellanic Cloud (SMC) might have led to the observed large variations in COM abundances in LMC
hot cores.

21. Revisiting the formaldehyde masers
D. J. van der Walt, L. L. Mfulwane F The 4.8 GHz formaldehyde masers are one of a number of rare types of molecularmasers in the Galaxy. The aim of the present calculations is to explore a larger region of parameter space to improve on ourprevious calculations, thereby to better understand the range of physical conditions under which an inversion of the 4.8 GHztransition occurs. We solve the rate equations of the first 40 rotational levels of o-formaldehyde using a fourth-order RungeKutta method. We consider gas kinetic temperatures between 10 K and 300 K, H2 densities between 104 and 106 per cc, and anumber of different dust temperatures and grey-body spectral energy density distributions. Using a grey-body dust radiation
field appropriate for Arp 220 we find that none of 4.8 GHz, 14 GHz, and 28 GHz transitions are inverted for kinetic temperaturesless than 100 K. Our calculations also show that in theory the 4.8 GHz transition can be inverted over a large region of exploredparameter space in the presence of an external far-infrared radiation field. Limiting the abundance of o-formaldehyde to lessthan 10−5 , however, reduces the region where an inversion occurs to H2 densities > 105 per cc and kinetic temperatures >100
K. We propose a pumping scheme for the formaldehyde masers which can explain why collisions play a central role in invertingthe 4.8 GHz transition, and therefore why an external radiation field alone does not lead to an inversion. Collisions are an
essential mechanism for the inversion of the 4.8 GHz transition. Our results suggest that 4.8 GHz formaldehyde megamasers
are associated with hot and dense gas typical of high mass star forming regions rather than with cold material.

Discovery of ammonia (9,6) masers in two high-mass star-forming regions

22. Y. T. Yan, C. Henkel, K. M. Menten, Y. Gong, J. Ott, T. L. Wilson, A. Wootten, A. Brunthaler, J. S. Zhang,
J. L. Chen, K. Yang F Molecular maser lines are signposts of high-mass star formation, probing excitation and kinematics
of very compact regions in the close environment of young stellar objects and providing useful targets for trigonometric parallax
measurements. Only a few NH3 (9,6) masers were known so far, and their origin is still poorly understood. Here we aim to find
new NH3 (9,6) masers to provide a better observational basis to study their role in high-mass star-forming regions. We carriedout NH3 (9,6) observations toward Cepheus A and G34.26+0.15 with the Effelsberg-100 m telescope and the Karl G. Janksy
Very Large Array. We discovered new NH3 (9,6) masers in Cep A and G34.26+0.25, which increases the number of high-massstar-forming regions hosting NH3 (9,6) masers from five to seven. Long term monitoring (20 months) at Effelsberg showsthat the intensity of the (9,6) maser in G34.26+0.25 is decreasing, while the Cep A maser remains stable. Compared to the
Effelsberg data and assuming linear variations between the epochs of observation, the JVLA data indicate no missing flux. Thissuggests that the NH3 (9,6) emission arises from single compact emission regions that are not resolved by the interferometricmeasurements. As JVLA imaging shows, the NH3 (9,6) emission in Cep A originates from a sub-arcsecond sized region, slightly
to the west of the peak position of the 1.36 cm continuum object, HW2. In G34.26+0.25, three NH3 (9,6) maser spots areobserved: one is close to the head of the cometary ultracompact HII region C and the other two are emitted from a compact
region to the west of the hypercompact HII region A. The newly found (9,6) masers appear to be related to outflows. Higher

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angular resolution of JVLA and VLBI observations are needed to provide more accurate positions and constraints for pumping
scenarios.

A Simple Time-Dependent Method for Calculating Spirals: Applications to Eccentric

23. Planets in Protoplanetary discs

Zhaohuan Zhu, Raymond M. Zhang F Spirals in protoplanetary discs have been used to locate the potential planet indiscs. Since only the spiral shape from a circularly orbiting perturber is known, most previous works assume that the planet isin a circular orbit. We develop a simple semi-analytical method to calculate the shape of the spirals launched by an eccentric
planet. We assume that the planet emits wavelets during its orbit, and the wave fronts of these propagating wavelets form thespirals. The resulting spiral shape from this simple method agrees with numerical simulations exceptionally well. The spirals
excited by an eccentric planet can detach from the planet, bifurcate, or even cross each other, which are all reproduced by thissimple method. The spiral’s bifurcation point corresponds to the wavelet that is emitted when the planet’s radial speed reaches
the disc’s sound speed. Multiple spirals can be excited by an eccentric planet (more than 5 spirals when e & 0.2). The pitch
angle and pattern speed are different between different spirals and can vary significantly across one spiral. The spiral wakes
launched by high-mass eccentric planets steepen to spiral shocks and the crossing of spiral shocks leads to distorted or broken
spirals. With the same mass, a more eccentric planet launches weaker spirals and induces a shallower gap over a long period oftime. The observed unusually large/small pitch angles of some spirals, the irregular multiple spirals, and the different pattern
speeds between different spirals may suggest the existence of eccentric perturbers in protoplanetary discs.

Accretion variability from minutes to decade timescales in the classical T Tauri star CR

24. ChaG. Zsidi, C. F. Manara, Á. Kóspál, G. A. J. Hussain, P. Ábrahám, E. Alecian, A. Bódi, A. Pál, P. Sarkis F
Classical T Tauri stars are surrounded by a circumstellar disk from which they are accreting material. This process is essential
in the formation of Sun-like stars. Although often described with simple and static models, the accretion process is inherently
time variable. Our aim is to examine the accretion process of the low-mass young stellar object CR Cha on a wide rangeof timescales from minutes to a decade by analyzing both photometric and spectroscopic observations from 2006, 2018, and2019. We carried out period analysis on the light curves of CR Cha from the TESS mission and the ASAS-SN and the ASAS-3
databases. We studied the color variations of the system using I, J, H, K-band photometry obtained contemporaneously with the
TESS observing window. We analyzed the amplitude, timescale, and the morphology of the accretion tracers found in a seriesof high-resolution spectra obtained in 2006 with the AAT/UCLES, in 2018 with the HARPS, and in 2019 with the ESPRESSO
and the FEROS spectrographs. All photometric data reveal periodic variations compatible with a 2.327 days rotational period,
which is stable in the system over decades. Moreover, the ASAS-SN and ASAS-3 data hint at a long-term brightening by 0.2
mag, between 2001 and 2008, and of slightly less than 0.1 mag in the 2015 - 2018 period. The near-infrared color variations
can be explained by either changing accretion rate or changes in the inner disk structure. Our results show that the amplitudeof the variations in the Hα emission increases on timescales from hours to days/weeks, after which it stays similar even whenlooking at decadal timescales. On the other hand, we found significant morphological variations on yearly/decadal timescales,
indicating that the different physical mechanisms responsible for the line profile changes, such as accretion or wind, are present
to varying degrees at different times.

25. The Rate, Amplitude and Duration of Outbursts from Class 0 Protostars in Orion

W. Zakri, S. T. Megeath, W. J. Fischer, Robert Gutermuth, Elise Furlan, Lee Hartmann, Nicole Karnath,
Mayra Osorio, Emily Safron, Thomas Stanke, Amelia M. Stutz, John J. Tobin, Thomas S. Allen, Sam Federman,
Nolan Habel, P. Manoj, Mayank Narang, Riwaj Pokhrel, Luisa Rebull, Patrick D. Sheehan, Dan M. Watson
F At least half of a protostar’s mass is accreted in the Class 0 phase, when the central protostar is deeply embedded in adense, infalling envelope. We present the first systematic search for outbursts from Class 0 protostars in the Orion clouds.
Using photometry from Spitzer/IRAC spanning 2004 to 2017, we detect three outbursts from Class 0 protostars with ≥ 2 magchanges at 3.6 or 4.5 µm. This is comparable to the magnitude change of a known protostellar FU Ori outburst. Two are newly
detected bursts from the protostars HOPS 12 and 124. The number of detections implies that Class 0 protostars burst every
438 yr, with a 95% confidence interval of 161 to 1884 yr. Combining Spitzer and WISE/NEOWISE data spanning 2004-2019,
we show that the bursts persist for more than nine years with significant variability during each burst. Finally, we use 19 − 100µm photometry from SOFIA, Spitzer and Herschel to measure the amplitudes of the bursts. Based on the burst interval, aduration of 15 yr, and the range of observed amplitudes, 3-100accretion during the Class 0 phase occurs during bursts. In total,
we show that bursts from Class 0 protostars are as frequent, or even more frequent, than those from more evolved protostars.
This is consistent with bursts being driven by instabilities in disks triggered by rapid mass infall. Furthermore, we find thatbursts may be a significant, if not dominant, mode of mass accretion during the Class 0 phase.

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