J/A+A/617/A132 Abundances and distributions of CS and SiS (Danilovich+, 2018)
Sulphur-bearing molecules in AGB stars.
II. Abundances and distributions of CS and SiS.
Danilovich T., Ramstedt S., Gobrecht D., Decin L., De Beck E., Olofsson H.
<Astron. Astrophys. 617, A132 (2018)>
=2018A&A...617A.132D 2018A&A...617A.132D (SIMBAD/NED BibCode)
ADC_Keywords: Stars, giant ; Spectroscopy
Keywords: stars: AGB and post-AGB - circumstellar matter - stars: mass-loss -
stars: evolution
Abstract:
Sulphur has long been known to form different molecules depending on
the chemical composition of its environment. More recently, the
sulphur-bearing molecules SO and H2S have been shown to behave
differently in oxygen-rich asymptotic giant branch (AGB) circumstellar
envelopes of different densities.
By surveying a diverse sample of AGB stars for CS and SiS emission, we
aim to determine in which environments these sulphur-bearing molecules
most readily occur. We include sources with a range of mass-loss rates
and carbon-rich, oxygen-rich, and mixed S-type chemistries. Where
these molecules are detected, we aim to determine their CS and SiS
abundances.
We surveyed 20 AGB stars of different chemical types using the APEX
telescope, and combined this with an IRAM 30m and APEX survey of CS
and SiS emission towards over 30 S-type stars. For those stars with
detections, we performed radiative transfer modelling to determine
abundances and abundance distributions.
We detect CS towards all the surveyed carbon stars, some S-type stars,
and the highest mass-loss rate oxygen-rich stars,
(dM/dt≥5x10-6M[sun/yr). SiS is detected towards the highest
mass-loss rate sources of all chemical types
(dM/dt≥8x10-7M☉/yr). We find CS peak fractional abundances
ranging from ∼4x10-7 to ∼2x10-5 for the carbon stars, from
∼3x10-8 to ∼1x10-7 for the oxygen-rich stars, and from ∼1x10-7
to ∼8x10-6 for the S-type stars. We find SiS peak fractional
abundances ranging from ∼9x10-6 to ∼2x10-5 for the carbon stars,
from ∼5x10-7 to ∼2x10-6 for the oxygen-rich stars, and from
∼2x10-7 to ∼2x10-6 for the S-type stars.
Overall, we find that wind density plays an important role in
determining the chemical composition of AGB circumstellar envelopes.
It is seen that for oxygen-rich AGB stars both CS and SiS are detected
only in the highest density circumstellar envelopes and their
abundances are generally lower than for carbon-rich AGB stars by
around an order of magnitude. For carbon-rich and S-type stars SiS was
also only detected in the highest density circumstellar envelopes,
while CS was detected consistently in all surveyed carbon stars and
sporadically among the S-type stars.
Description:
This CS and SiS spectral line catalogue is based on observations
carried out by the APEX telescope in Chile.
The stars observed are listed in the Objects table below and are noted
in the corresponding .fits file names with the individual transitions
saved in each file. Observations were carried out in March-April and
August- December in 2016.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 104 56 List of fits spectra
fits/* . 56 Individual fits spectra
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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- 2 I2 h RAh Right ascension (J2000)
4- 5 I2 min RAm Right ascension (J2000)
7- 11 F5.2 s RAs Right ascension (J2000)
13 A1 --- DE- Declination sign (J2000)
14- 15 I2 deg DEd Declination (J2000)
17- 18 I2 arcmin DEm Declination (J2000)
20- 23 F4.1 arcsec DEs Declination (J2000)
25- 28 I4 --- Nx Number of points
30- 38 F9.1 m/s bVel Lower value of velocity interval
40- 47 F8.1 m/s BVel Upper value of velocity interval
49- 56 F8.3 m/s dVel Velocity resolution
58 I1 Kibyte size Size of FITS file
60- 68 A9 --- Star Star name
70- 79 A10 --- Line Observed line
81-104 A24 --- FileName Name of FITS file, in subdirectory fits
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Acknowledgements:
Taissa Danilovich, taissa.danilovich(at)kuleuven.be
References:
Danilovich et al., Paper I 2017A&A...606A.124D 2017A&A...606A.124D
(End) Taissa Danilovich [KU Leuven], Patricia Vannier [CDS] 26-Jul-2018