J/A+A/621/A122 G351.77-0.54 ALMA observations (Beuther+, 2019)
High-mass star formation at sub-50AU scales.
Beuther H., Ahmadi A., Mottram J.C., Linz H., Maud L.T., Henning T.,
Walsh A.J., Kuiper R., Johnston K.G., Longmore S.N.
<Astron. Astrophys. 621, A122 (2019)>
=2019A&A...621A.122B 2019A&A...621A.122B (SIMBAD/NED BibCode)
ADC_Keywords: H II regions ; Interferometry
Keywords: stars: formation - stars: massive - stars: individual: G351.77-0.54 -
stars: winds, outflows - instrumentation: interferometers
Abstract:
The hierarchical process of star formation has so far mostly been
studied on scales from thousands of au to parsecs, but the smaller
sub-1000 au scales of high-mass star formation are still largely
unexplored in the submm regime.
We aim to resolve the dust and gas emission at the highest spatial
resolution to study the physical properties of the densest structures
during high-mass star formation.
We observed the high-mass hot core region G351.77-0.54 with the
Atacama Large Millimeter Array with baselines extending out to more
than 16 km. This allowed us to dissect the region at sub-50 au spatial
scales.
At a spatial resolution of 18/40au (depending on the distance), we
identify twelve sub-structures within the inner few thousand au of the
region. The brightness temperatures are high, reaching values greater
1000K, signposting high optical depth toward the peak positions. Core
separations vary between sub-100 au to several 100 and 1000au. The
core separations and approximate masses are largely consistent with
thermal Jeans fragmentation of a dense gas core. Due to the high
continuum optical depth, most spectral lines are seen in absorption.
However, a few exceptional emission lines are found that most likely
stem from transitions with excitation conditions above 1000K. Toward
the main continuum source, these emission lines exhibit a velocity
gradient across scales of 100-200au aligned with the molecular
outflow and perpendicular to the previously inferred disk
orientation.While we cannot exclude that these observational features
stem from an inner hot accretion disk, the alignment with the outflow
rather suggests that it stems from the inner jet and outflow region.
The highest-velocity features are found toward the peak position, and
no Hubble-like velocity structure can be identified. Therefore, these
data are consistent with steady-state turbulent entrainment of the hot
molecular gas via Kelvin-Helmholtz instabilities at the interface
between the jet and the outflow.
Resolving this high-mass star-forming region at sub-50au scales
indicates that the hierarchical fragmentation process in the framework
of thermal Jeans fragmentation can continue down to the smallest
accessible spatial scales. Velocity gradients on these small scales
have to be treated cautiously and do not necessarily stem from disks,
but may be better explained with outflow emission. Studying these
small scales is very powerful, but covering all spatial scales and
deriving a global picture from large to small scales are the next
steps to investigate.
Description:
The target high-mass star-forming region G351.77-0.54 was observed
with ALMA as a cycle 3 project (id 2015.1.00496) in four separate
observing blocks between Nov. 5 and Dec. 2, 2015. The duration of the
four scheduling blocks varied between 1 and 1.6 hours with on-source
target observing times between 24 and 45 minutes. Between 33 and 43
antennas were in the array and baselines between 17m and more than 16
km were covered. The phase center of our observations was R.A.
(J2000.0) 17:26:42.568 and Dec. (J2000.0) -36:09:17.60.
Objects:
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RA (2000) DE Designation(s)
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17 26 42.8 -36 09 17 G351.78-00.54 = GAL 351.78-00.54
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
splist.dat 143 4 List of fits spectra
sp/* . 4 Individual fits spectra
list.dat 144 6 List of fits images and datacube
fits/* . 6 Individual images and datacube
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See also:
J/A+A/603/A10 : ALMA view of G351.77-0.54 (Beuther+, 2017)
Byte-by-byte Description of file: splist.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 22 I3 --- Nx Number of pixels along X-axis
24- 46 A23 "datime" Obs.date Observation date
48- 63 E16.11 Hz RestFreq Rest-frequency
65- 76 E12.6 Hz bFreq Lower value of relative frequency interval
78- 88 E11.6 Hz BFreq Upper value of relative frequency interval
90-100 E11.6 Hz dFreq Referency resolution
102-103 I2 Kibyte size Size of FITS spectrum
105-113 A9 --- FileName Name of FITS spectrum, in subdirectory sp
115-143 A29 --- Title Title of the FITS spectrum
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg ? Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg ? Declination of center (J2000)
20- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 31 I2 --- Nz ? Number of slices for the datacube
33- 54 A22 "datime" Obs.date Observation date (YYYY-MM-DDThh:mm:ss.ss)
56- 61 I6 Kibyte size Size of FITS file
63- 83 A21 --- FileName Name of FITS file, in subdirectory fits
85-144 A60 --- Title Title of the FITS file
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Acknowledgements:
Henrik Beuther, beuther(at)mpia.de
(End) Patricia Vannier [CDS] 30-Nov-2018