J/A+A/310/933ivo://CDS.VizieR/J/A+A/310/933doi:10.26093/cds/vizier.33100933CDSOhnaka K.Tsuji T.1997-12-09T16:42:59Z1997-12-09T17:42:55ZCDS support team

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

cds-question@unistra.frcarbon-starsccd-photometryWe present a result of quantitative analysis of ^12^C/^13^C ratios in 62 N-type and 15 SC-type carbon stars. By the use of CCD as a detector we can obtain spectra of resolution ~20,000 with enough signal-to-noise ratios for a large number of carbon stars, for which ^12^C/^13^C ratios have not yet been derived. Carbon isotopic ratios are determined from lines of the CN red system around 8000A, based on the iso-intensity method and line-blanketed model atmospheres. The average of ^12^C/^13^C ratios in 62 N-type carbon stars is found to be 27+/-11 (standard deviation). The majority of the N-type carbon stars studied (about 85%) are found to have ^12^C/^13^C ratios less than 40, and the number of stars which have ^12^C/^13^C ratios larger than 40 is found to be relatively small. This result shows a marked contrast to some of the previous results that have shown the opposite distribution, namely, ^12^C/^13^C ratios mostly larger than 40 in N-type carbon stars. The average of ^12^C/^13^C ratios in 15 SC-type carbon stars is found to be 22+/-14 (standard deviation). Most of the SC-type carbon stars studied are found to have ^12^C/^13^C ratios larger than 10, while only three of them turn out to be ^13^C-rich. This is in contrast with the earlier classification based on low resolution spectra which classified them as J-type, that is, ^13^C-rich. The earlier temperature scale which classified SC-type carbon stars as the latest (C8-9) based on their strong NaI D lines can not be necessarily justified. The strong NaI D lines of SC stars should be attributed to the peculiar atmospheric structure due to C/O ratios very near to unity. The resulting ^12^C/^13^C ratios are partly consistent with the scenario in which M giants evolve through SC-type to N-type carbon stars, as ^12^C produced during the helium shell flash is added to the envelope.1996A&A...310..933Ohttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/310/933CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/310/933https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/310/933http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/310/933https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/310/933https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/310/933http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/310/933GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticaldefaultJ/A+A/310/933/table1Summary of the observations of 66 N-type carbon starsS/NSignal-to-noise ratiostat.snrintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintGCCGCS? Designation in "A General Catalogue of Cool Galactic Carbon Stars", Stephenson (1989) (Catalogue <III/156>)meta.idintCCCS? Designation in "A General Catalogue of Cool Carbon Stars", Stephenson (1973)meta.id;meta.mainintn_CCCS[)] A ')' indicates that the designation is in "A General Catalog of S stars", Stephenson (1976) (Catalogue <III/168>)meta.notecharNameStar Namemeta.idcharC-ClassC-Classification, Yamashita (1972, 1975)src.classcharVmagV magnitude or lowest V magnitude if intervalmagphot.mag;em.opt.Vfloatn_Vmag[-] A '-' indicates an interval of magnitudesmeta.notecharl_Vmag2Limit flag on Vmag2meta.code.errorcharVmag2? Upper V magnitude if intervalmagphot.mag;em.opt.V;stat.maxfloatObsDate of observations for two wavelengthtime.epochcharJ/A+A/310/933/table2Summary of the observations of 19 SC-type carbon starsS/NSignal-to-noise ratiostat.snrintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintGCCGCS? Designation in "A General Catalogue of Cool Galactic Carbon Stars", Stephenson (1989) (Catalogue <III/156>)meta.idintCCCS? Designation in "A General Catalogue of Cool Carbon Stars", Stephenson (1973)meta.idintn_CCCS[)] A ')' indicates that the designation is in "A General Catalog of S stars", Stephenson (1976) (Catalogue <III/168>)meta.notecharNameStar Namemeta.id;meta.maincharC-ClassC-Classification, Yamashita (1972, 1975)src.classcharVmagV magnitude or lowest V magnitude if intervalmagphot.mag;em.opt.Vfloatn_Vmag[-] A '-' indicates an interval of magnitudesmeta.notecharl_Vmag2Limit flag on Vmag2meta.code.errorcharVmag2? Upper V magnitude if intervalmagphot.mag;em.opt.V;stat.maxfloatObsDate of observations for two wavelengthtime.epochchar