J/A+A/667/A84ivo://CDS.VizieR/J/A+A/667/A84doi:10.26093/cds/vizier.36670084CDSKarambelkar V.Kasliwal M.M.Tisserand P.Clayton G.C.Crawford C.L.,Anand S.G.Geballe T.R.Montiel E.2023-11-07T10:42:00Z2022-11-09T07:32:41ZCDS support team

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

cds-question@unistra.frcarbon-starsinfrared-astronomyspectroscopyR Coronae Borealis (RCB) and dustless Hydrogen-deficient Carbon (dLHdC) stars are believed to be remnants of low mass white dwarf mergers. These supergiant stars have peculiar hydrogen-deficient carbon-rich chemistries and stark overabundances of ^18^O. RCB stars undergo dust formation episodes resulting in large-amplitude photometric variations that are not seen in dLHdC stars. Recently, the sample of known dLHdC stars in the Milky Way has more than quintupled with the discovery of 27 new dLHdC stars. It has been suggested that dLHdC stars have lower ^16^O/^18^O than RCB stars. We aim to compare the ^16^O/^18^O ratios for a large sample of dLHdC and RCB stars to conclusively examine this claim. We present medium resolution (R~3000) near-infrared spectra of 20 newly discovered dLHdC stars. We also present medium resolution (R~3000-8000) K-band spectra for 47 RCB stars.We measure the ^16^O/^18^O ratios of 7 dLHdC and 31 RCB stars that show ^12^C^16^O and ^12^C^18^O absorption bands, and present the largest sample of values of ^16^O/^18^O for dLHdC and RCB stars to date. We find that six of the seven dLHdC stars have ^16^O/^18^O<0.5, while 26 of the 31 RCB stars have ^16^O/^18^O>1. We also confirm that unlike RCB stars, dLHdC stars do not show strong blueshifted (>200km/s) HeI 10833{AA} absorption, suggesting the absence of strong, dust-driven winds around them. We conclude that most dLHdC stars have lower ^16^O/^18^O than most RCB stars. This confirms one of the first, longsuspected spectroscopic differences between RCB and dLHdC stars. Our results rule out the existing picture that RCB stars represent an evolved stage of dLHdC stars. Instead, we suggest that whether the white dwarf merger remnant is a dLHdC or RCB star depends on the mass ratios, masses and compositions of the merging white dwarfs.2022A&A...667A..84Khttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/667/A84CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/667/A84https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/667/A84http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/667/A84https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/667/A84https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/667/A84http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/667/A84GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/667/A84/objects (Names and coordinates of RCB and dLHdC star)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/667/A84/objects?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/667/A84/objects?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/667/A84/objects?GETtext/xml+votable180.050000true284.6970417-29.50501940.0055555555555555566/12239 12842 14546 14626 15065 24935 28690 28717 28726 28735 28769 28774 28783 28805 28838 28842 28857 28866 28870 28881 28887 28908 28910-28911 28970 29000 29005 29067 29136 29168 29173 29178 29184 29194 29210 29214 29217 29244 29252 29255 29257 29261 29841 30122 30171 30208 30282 30444 30637 30650 30740 32023 32076 33121 33294 33316 41178 41279 42335 42359 42692 42820 43378 44328 47661 47869 47895 48038 48507 48801https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/667/A84?format=asciiInfrareddefaultJ/A+A/667/A84/objectsNames and coordinates of RCB and dLHdC starSimbadNameSimbad column added by the CDSmeta.idcharnullablerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNameName of starmeta.id;meta.maincharRAJ2000Right Ascension (J2000)pos.eq.ra;meta.mainDEJ2000Declination (J2000)pos.eq.dec;meta.mainClassClassification (RCB or dLHdC)src.classcharInstName and instrument with which the spectra were collectedmeta.id;instr.bandwidthcharspShow the spectrummeta.ref.urlcharFileNameName of the spectrum file in subdirectory spmeta.id;meta.filechar