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R Coronae Borealis and dustless hydrogen-deficient carbon stars likely have different oxygen isotope ratios

Karambelkar, V. and Kasliwal, M. M. and Tisserand, P. and Clayton, G. C. and Crawford, C. L. and Anand, S. G. and Geballe, T. R. and Montiel, E. (2022) R Coronae Borealis and dustless hydrogen-deficient carbon stars likely have different oxygen isotope ratios. Astronomy and Astrophysics, 667 . Art. No. A84. ISSN 0004-6361. doi:10.1051/0004-6361/202142918.

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Context. R 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 ¹⁸O. 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. Aims. It has been suggested that dLHdC stars have lower ¹⁶O/¹⁸O than RCB stars. We aim to compare the ¹⁶O/¹⁸O ratios for a large sample of dLHdC and RCB stars to examine this claim. Methods. 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 49 RCB stars. Due to the several free parameters and assumptions in our fitting strategy, we provide wide range estimates on the ¹⁶O/¹⁸O ratios of seven dLHdC and 33 RCB stars that show ¹²C¹⁶O and ¹²C¹⁸O absorption bands, and present the largest sample of such 16O/18O wide-range values for dLHdC and RCB stars to date. Results. We find that six of the seven dLHdC stars have ¹⁶O/¹⁸O < 0.5, while 28 of the 33 RCB stars have ¹⁶O/¹⁸O > 1. We also confirm that unlike RCB stars, dLHdC stars do not show strong blueshifted (> 200 km s⁻¹) He I 10 833 Å absorption, suggesting the absence of strong, dust-driven winds around them. Conclusions. Although we only can place wide range estimates on the ¹⁶O/¹⁸O and these are more uncertain in cool RCBs, our medium resolution spectra suggest that most dLHdC stars have lower ¹⁶O/¹⁸O than most RCB stars. This confirms one of the first, long-suspected spectroscopic differences between RCB and dLHdC stars. The different oxygen isotope ratios 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. Future high resolution spectroscopic observations will help confirm and more precisely quantify the difference between the oxygen isotope ratios of the two classes.

Item Type:Article
Related URLs:
URLURL TypeDescription
Karambelkar, V.0000-0003-2758-159X
Kasliwal, M. M.0000-0002-5619-4938
Tisserand, P.0000-0003-4237-0520
Clayton, G. C.0000-0002-0141-7436
Crawford, C. L.0000-0002-7654-7438
Anand, S. G.0000-0003-3768-7515
Geballe, T. R.0000-0003-2824-3875
Montiel, E.0000-0003-2553-4474
Additional Information:We thank the anonymous referee for helpful comments that improved the quality of this paper. We thank Bradley Munson for useful comments and discussions. PT acknowledges financial support from “Programme National de Physique Stellaire” (PNPS) of CNRS/INSU, France. MMK acknowledges the Heising-Simons foundation for support via a Scialog fellowship of the Research Corporation. MMK acknowledges generous support from the David and Lucille Packard Foundation. SA acknowledges support from the GROWTH PIRE grant 1545949. GC and CC are grateful for support from National Science Foundation Award 1814967. This research is based in part on observations for programs GS-2005B-Q-20, GN-2011A-Q-112, GS-2015B-FT-1 and GS-2016B-FT-6 obtained at the international Gemini Observatory, a program of NSF’s NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. on behalf of the Gemini Observatory partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea).
Group:Astronomy Department
Funding AgencyGrant Number
Programme National de Physique Stellaire (PNPS)UNSPECIFIED
Centre National de la Recherche Scientifique (CNRS)UNSPECIFIED
Institut national des sciences de l'Univers (INSU)UNSPECIFIED
Heising-Simons FoundationScialog Award
David and Lucile Packard FoundationUNSPECIFIED
Gemini PartnershipUNSPECIFIED
Record Number:CaltechAUTHORS:20221128-494241100.21
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ID Code:118063
Deposited By: Research Services Depository
Deposited On:09 Dec 2022 01:45
Last Modified:13 Dec 2022 17:51

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