J/A+A/628/A62ivo://CDS.VizieR/J/A+A/628/A62doi:10.26093/cds/vizier.36280062CDSMassalkhi S.Agundez M.Cernicharo J.2019-08-21T11:12:36Z2019-08-07T08:16:37ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frcarbon-starschemical-abundancesradio-spectroscopyWe aim to determine the abundances of CS, SiO, and SiS in a large sample of carbon star envelopes covering a wide range of mass loss rates to investigate the potential role that these molecules could play in the formation of dust in the surroundings of the central AGB star. We surveyed a sample of 25 carbon-rich AGB stars in the {lambda}2mm band, more concretely in the J=3-2 line of CS and SiO and in the J=7-6 and J=8-7 lines of SiS, using the IRAM 30m telescope. We performed excitation and radiative transfer calculations based on the LVG method to model the observed lines of the molecules and to derive their fractional abundances in the observed envelopes. We also assessed the effect of infrared pumping in the excitation of the molecules. We detected CS in all 25 targeted envelopes, SiO in 24 of them, and SiS in 17 sources. Remarkably, SiS is not detected in any envelope with a mass loss rate below 10^-6^M_{sun}_/yr while it is detected in all envelopes with mass loss rates above that threshold. We found that CS and SiS have similar abundances in carbon stars envelopes, while SiO is present with a lower abundance. We also found a strong correlation in which the denser the envelope, the less abundant CS and SiO are. The trend is however only tentatively seen for SiS in the high mass loss rate range. Furthermore, we found a relation in which the integrated flux of the MgS dust feature at 30um increases as the fractional abundance of CS decreases. The decline in the fractional abundance of CS with increasing density could be due to gas phase chemistry in the inner envelope or to adsorption onto dust grains. The latter possibility is favored by a correlation between the CS fractional abundance and the 30um feature, which suggests that CS is efficiently incorporated onto MgS dust around C-rich AGB stars. In the case of SiO, the observed abundance depletion with increasing density is most likely caused by an efficient incorporation onto dust grains. The latter possibility is favored by a correlation between the CS fractional abundance and the 30um feature, which suggests that CS is efficiently incorporated onto MgS dust around C-rich AGB stars. In the case of SiO, the observed abundance depletion with increasing density is most likely caused by an efficient incorporation onto dust grains. We conclude that CS and SiO (very likely) and SiS (tentatively) are good candidates to act as gas-phase precursors of dust in C-rich AGB envelopes.2019A&A...628A..62Mhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/628/A62CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/628/A62https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/628/A62http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/628/A62https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/628/A62https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/628/A62http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/628/A62GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/628/A62/list (List of spectra)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/628/A62/list?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/628/A62/list?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/628/A62/list?GETtext/xml+votable180.050000true146.9893513.278850.0055555555555555566/1297 1727 3359 3438 3459 3735 3766 4365 5273 6714 10960 13677 14391 14427 14600 14738 15401 16233 19112 20022 21224 21338 22941 29886 32062https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/628/A62?format=asciiRadiodefaultJ/A+A/628/A62/listList of spectrarecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintLineObserved linemeta.id;spect.linecharObjectObject namemeta.id;meta.maincharRAJ2000Right ascension (J2000)degpos.eq.ra;meta.mainDEJ2000Declination (J2000)degpos.eq.dec;meta.mainRestFreqRest frequencyHzem.freqdoubleImgFreqImage frequencyHzem.freq;obs.imagedoubleVelVelocitym/sphys.velocintDVelVelocity resolutionm/sspect.resolutiondoubleObs.DateObservation datetime.epoch;obscharspShow the spectrm curvesmeta.ref.urlcharSimbadSimbad column added by the CDSmeta.ref.urlchar