J/A+A/643/A48 Linking ice and gas. Serpens SVS4 (Perotti+, 2020)
Linking ice and gas in the Serpens low-mass star-forming region.
Perotti G., Rocha W.R.M., Jorgensen J.K., Kristensen L.E., Fraser H.J.,
Pontoppidan K.M.
<Astron. Astrophys. 643, A48 (2020)>
=2020A&A...643A..48P 2020A&A...643A..48P (SIMBAD/NED BibCode)
ADC_Keywords: YSOs ; Star Forming Region ; Interstellar medium ;
Spectra, infrared
Keywords: ISM: molecules - stars: protostars - astrochemistry -
molecular processes - stars: low mass -
ISM: individual objects: Serpens
Abstract:
The interaction between dust, ice, and gas during the formation of
stars produces complex organic molecules. While observations indicate
that several species are formed on ice-covered dust grains and are
released into the gas phase, the exact chemical interplay between
solid and gas phases and their relative importance remain unclear.
Our goal is to study the interplay between dust, ice, and gas in
regions of low-mass star formation through ice- and gas- mapping and
by directly measuring gas-to-ice ratios. This provides constraints on
the routes that lead to the chemical complexity that is observed in
solid and gas phases.
We present observations of gas-phase methanol (CH3OH) and carbon
monoxide (13CO and C18O) at 1.3mm towards ten low-mass young
protostars in the Serpens SVS4 cluster from the SubMillimeter Array
(SMA) and the Atacama Pathfinder EXperiment (APEX) telescope. We used
archival data from the Very Large Telescope (VLT) to derive abundances
of ice H2O, CO, and CH3OH towards the same region. Finally, we
constructed gas-ice maps of SVS4 and directly measured CO and CH3OH
gas-to-ice ratios.
The SVS4 cluster is characterised by a global temperature of 15±5K.
At this temperature, the chemical behaviours of CH3OH and CO are
anti-correlated: larger variations are observed for CH3OH gas than
for CH3OH ice, whereas the opposite is seen for CO. The gas-to-ice
ratios (Ngas/Nice) range from 1-6 for CO and
1.4x10-4-3.7x10-3for CH3OH. The CO gas-maps trace an extended
gaseous component that is not sensitive to the effect of freeze-out.
Because of temperature variations and dust heating around 20K, the
frozen CO is efficiently desorbed. The CH3OH gas-maps, in contrast,
probe regions where methanol is predominantly formed and present in
ices and is released into the gas phase through non-thermal desorption
mechanisms.
Combining gas- and ice-mapping techniques, we measure gas-to-ice
ratios of CO and CH3OH in the SVS4 cluster. The CH3OH gas-to-ice
ratio agrees with values that were previously reported for embedded
Class 0/I low-mass protostars. We find that there is no
straightforward correlation between CO and CH3OH gas with their ice
counterparts in the cluster. This is likely related to the complex
morphology of SVS4: the Class 0 protostar SMM4 and its envelope lie in
the vicinity, and the outflow associated with SMM4 intersects the
cluster. This study serves as a pathfinder for future observations
with ALMA and the James Webb Space Telescope (JWST) that will provide
high-sensitivity gas-ice maps of molecules more complex than methanol.
Such comparative maps will be essential to constrain the chemical
routes that regulate the chemical complexity in star-forming regions.
Description:
The observations of the Serpens SVS 4 cluster were done with the
Submillimeter Array (SMA), Mauna Kea, Hawaii, program code:
2016B-S022; with the Atacama Pathfinder EXperiment (APEX), Llano
Chajnantor, Chile, program code: 099.F-9316(A) and with the Very Large
Telescope (VLT), Paranal, Chile, under European Southern Observatory
(ESO) programmes 075.C-0384(A) and 077.C-0363(A).
The calibration and imaging were done in CASA and CLASS. The datacubes
are 6 FITS files that correspond to 4 spectral windows for each
sideband (lower and upper) and each receiver (230 and 240GHz). The VLT
spectra are 20 ascii files.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
sources.dat 59 10 Observed sources
sp/* . 20 Individual spectra
list.dat 157 6 List of fits datacubes
fits/* . 6 Individual fits datacubes
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Byte-by-byte Description of file: sources.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Name Source name, SVS 4-NN
10- 11 I2 h RAh Right Ascension (J2000)
13- 14 I2 min RAm Right Ascension (J2000)
16- 20 F5.2 s RAs Right Ascension (J2000)
22 A1 --- DE- Declination sign (J2000)
23- 24 I2 deg DEd Declination (J2000)
26- 27 I2 arcmin DEm Declination (J2000)
29- 33 F5.2 arcsec DEs Declination (J2000)
34- 45 A12 --- SpL Name of the spectrum in L band, in subdirectory sp
47- 59 A13 --- SpM Name of the spectrum in M band, in subdirectory sp
--------------------------------------------------------------------------------
Byte-by-byte Description of file: sp/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 24 E24.19 um lambda Wavelength
26- 50 E25.20 --- tau ? Optical depth
52- 64 F13.11 --- e_tau ? rms uncertainty on tau (only for M-type spectra)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
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- 26 I3 --- Ny Number of pixels along Y-axis
28- 30 I3 --- Nz Number of pixels along Z-axis
32- 57 A26 "datime" Obs.date Observation date
59- 62 I4 km/s bVRAD ? Lower value of VRAD interval for
APEX datacubes
64- 66 I3 km/s BVRAD ? Upper value of VRAD interval for
APEX datacubes
68 I1 km/s dVRAD ? VRAD resolution for APEX datacubes
69- 75 F7.3 GHz bFreq ? Lower value of frequency interval for
SMA datacubes
77- 83 F7.3 GHz BFreq ? Upper value of frequency interval for
SMA datacubes
85- 90 I6 Hz dFreq ? Frequency resolution for SMA datacubes
92- 97 I6 Kibyte size Size of FITS file
99-113 A15 --- FileName Name of FITS file, in subdirectory fits
115-157 A43 --- Title Title of the FITS file
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Acknowledgements:
Giulia Perotti, Giulia.perotti(at)nbi.ku.dk
(End) Patricia Vannier [CDS] 08-Oct-2020