J/A+A/639/A87 Complex organic mol. in low-mass protostars (van Gelder+, 2020)
Complex organic molecules in low-mass protostars on Solar System scales.
I. Oxygen-bearing species.
van Gelder M.L., Tabone B., Tychoniec L., van Dishoeck E.F., Beuther H.,
Boogert A.C.A., Caratti o Garatti A., Klaassen P.D., Linnartz H.,
Mueller H.S.P., Taquet V.
<Astron. Astrophys. 639, A87 (2020)>
=2020A&A...639A..87V 2020A&A...639A..87V (SIMBAD/NED BibCode)
ADC_Keywords: Protostars ; YSOs ; Interferometry
Keywords: astrochemistry - stars: formation - stars: protostars -
stars: low-mass - ISM: abundances - techniques: interferometric
Abstract:
Complex organic molecules (COMs) are thought to form on icy dust
grains in the earliest phase of star formation. The evolution of these
COMs from the youngest Class 0/I protostellar phases toward the more
evolved Class II phase is still not fully understood. Since planet
formation seems to start early, and mature disks are too cold for
characteristic COM emission lines, studying the inventory of COMs on
Solar- System scales in the Class 0/I stage is relevant.
Our aim is to determine the abundance ratios of oxygen-bearing COMs in
Class 0 protostellar systems on scales of ∼100AU radius. We aim to
compare these abundances with one another, and to the abundances of
other low-mass protostars such as IRAS16293-2422B and HH 212.
Additionally, using both cold and hot COM lines, the gas-phase
abundances can be tracked from a cold to a hot component, and
ultimately be compared with those in ices to be measured with the
James Webb Space Telescope (JWST). The abundance of deuterated
methanol allows us to probe the ambient temperature during the
formation of this species.
ALMA Band 3 (3mm) and Band 6 (1mm) observations are obtained for seven
Class 0 protostars in the Perseus and Serpens star-forming regions. By
modeling the inner protostellar region using local thermodynamic
equilibrium (LTE) models, the excitation temperature and column
densities are determined for several O-bearing COMs including methanol
(CH3OH), acetaldehyde (CH3CHO), methyl formate (CH3OCHO), and
dimethyl ether (CH3OCH3). Abundance ratios are taken with respect
to CH3OH.
Three out of the seven of the observed sources, B1-c, B1-bS (both
Perseus), and Serpens S68N (Serpens), show COM emission. No clear
correlation seems to exist between the occurrence of COMs and source
luminosity. The abundances of several COMs such as CH3OCHO,
CH3OCH3, acetone (CH3COCH3), and ethylene glycol ((CH2OH)2)
are remarkably similar for the three COM-rich sources; this similarity
also extends to IRAS 16238-2422B and HH 212, even though collectively
these sources originate from four different star-forming regions
(i.e., Perseus, Serpens, Ophiuchus, and Orion). For other COMs like
CH3CHO, ethanol (CH3CH2OH), and glycolaldehyde (CH2OHCHO), the
abundances differ by up to an order of magnitude, indicating that
local source conditions become important. B1-c hosts a cold (Tex=60K),
more extended component of COM emission with a column density of
typically a few percent of the warm/hot (Tex=200K) central component.
A D/H ratio of 1-3% is derived for B1-c, S68N, and B1-bS based on
the CH2DOH/CH3OH ratio (taking into account statistical weighting)
suggesting a temperature of ∼15K during the formation of methanol.
This ratio is consistent with other low-mass protostars, but is lower
than for high-mass star-forming regions.
The abundance ratios of most O-bearing COMs are roughly fixed between
different star-forming regions, and are presumably set at an earlier
cold prestellar phase. For several COMs, local source properties
become important. Future mid-infrared facilities such as JWST/MIRI
will be essential for the direct observation of COM ices. Combining
this with a larger sample of COM-rich sources with ALMA will allow ice
and gas-phase abundances to be directly linked in order to constrain
the routes that produce and maintain chemical complexity during the
star formation process.
Description:
Table E1 describes the main characteristics of the ALMA images
from program 2017.1.01774.S, including data from both Band 3 and Band
6. The images of B1-b include the sources B1-bN and B1-bS within the
field of view, and similarly the images of S68N include Ser-emb 8 (N).
The beam major and minor axis and Largest Angular Separation (LAS) are
given in arcseconds. The velocity resolution is listed in km/s. The
sensitivity of the continuum images is provided in mJy and the
sensitivity of the line images in Kelvin. The absolute flux
calibration uncertainty is present as a percentage.
Tables E2 and E3 contain the main characteristics of the spectral
lines which are analyzed in the paper. The former file lists the
transitions in Band 3, the latter the transitions in Band 6. Provided
are the transition quantum numbers (J, Ka, Kc) of both the upper and
lower state, rest frequency in GHz, Einstein A coefficient in s-1,
and upper energy level in Kelvin.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 84 7 List of protostars discussed in this paper as well
as their main astronomical properties
tablee1.dat 63 8 ALMA image properties from program 2017.1.01774.S
tablee2.dat 51 236 Properties of Band 3 spectral lines
tablee3.dat 51 711 Properties of Band 6 spectral lines
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 --- Source Source name
14 A1 --- n_Source [*] * for objects additionally fell within
the field of view of the ALMA observations
16- 23 A8 --- Cloud Cloud name
24- 25 I2 h RAh Right ascension (J2000)
27- 28 I2 min RAm Right ascension (J2000)
30- 34 F5.2 s RAs Right ascension (J2000)
35 A1 --- DE- Declination sign (J2000)
36- 37 I2 deg DEd Declination (J2000)
39- 40 I2 arcmin DEm Declination (J2000)
42- 45 F4.1 arcsec DEs Declination (J2000)
47- 49 I3 pc d Distance
51 I1 --- r_d Distance reference (1)
53- 57 F5.2 Lsun Lbol ? Bolometric luminosity
59 I1 --- r_Lbol ? Bolometric luminosity reference (1)
61- 63 I3 K Tbol ? Bolometric temperature
65 I1 --- r_Tbol ? Bolometric temperature reference (1)
67- 69 F3.1 Msun Menv ? Envelope mass
71 I1 --- r_Menv ? Envelope mass reference (1)
73 A1 ---- l_CH3OH/H2Oice Limit flag on CH3OH/H2Oice
74- 77 F4.1 % CH3OH/H2Oice ? CH3OH/H2O ice ratio percentage
79 A1 --- r_CH3OH/H2Oice ? CH3OH/H2O ice ratio reference (1)
81 A1 --- B3? [y-n] COMs detected in Band 3 ? (2)
83 A1 --- B6? [y-n] COMs detected in Band 6 ? (2)
84 I1 --- n_B6? ? Note on B6? (3)
--------------------------------------------------------------------------------
Note (1): References as follows:
1 = Ortiz-Leon et al. (2018, Cat. J/ApJ/865/73)
2 = Enoch et al. (2009, Cat. J/ApJ/692/973)
3 = Boogert et al. (2008, Cat. J/ApJ/678/985)
4 = Hirano & Liu (2014ApJ...789...50H 2014ApJ...789...50H)
5 = Karska et al. (2018ApJS..235...30K 2018ApJS..235...30K)
6 = Ortiz-Leon et al. (2017ApJ...834..143O 2017ApJ...834..143O)
7 = Enoch et al. (2011ApJS..195...21E 2011ApJS..195...21E)
Note (2): Flag as follows:
y = (yes) indicates that COMs were detected in this work
n = (no) indicates that the spectra lacked any COM detection
- = indicates that the Band was not observed for the corresponding target
Note (3): Notes as follows:
8 = Only CH3OH emission related to the outflow detected
9 = Based on data from ALMA program 2017.1.01350.S
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablee1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- Source Source name
6- 11 A6 --- Band ALMA Band
13- 17 A5 --- Conf ALMA configuration
19- 24 F6.2 arcsec Bmaj ? Beam major axis
26- 31 F6.2 arcsec Bmin ? Beam minor axis
33- 37 F5.1 arcsec LAS ? Largest angular separation
39- 44 F6.2 km/s DeltaV ? Velocity resolution
46- 50 F5.1 mJy rmscont ? rms level of continuum images
52- 57 F6.2 K rmsline ? rms level of line images
59- 63 F5.1 % e_Fluxcalib ? Unceratinty on absolute flux calibration
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablee2.dat tablee3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Species Species description
12- 13 I2 --- Jup Upper J quantum number
15- 16 I2 --- Kaup Upper Ka quantum number
18- 19 I2 --- Kcup Upper Kc quantum number
21- 22 I2 --- Jlow Lower J quantum number
24- 25 I2 --- Kalow Lower Ka quantum number
27- 28 I2 --- Kclow Lower Kc quantum number
30- 37 F8.4 GHz Freq Transition rest frequency
39- 45 E7.2 1/s Aij Transition Einstein A coefficient
47- 51 F5.1 K Eup Upper energy level
--------------------------------------------------------------------------------
Acknowledgements:
Martijn van Gelder, vgelder(at)strw.leidenuniv.nl
(End) Martijn van Gelder [Leiden Obs.], Patricia Vannier [CDS] 10-Jun-2020