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The dawn of a new era for dustless HdC stars with GAIA eDR3

Tisserand, P. and Crawford, C. L. and Clayton, G. C. and Ruiter, A. J. and Karambelkar, V. and Bessell, M. S. and Seitenzahl, I. R. and Kasliwal, M. M. and Soon, J. and Travouillon, T. (2021) The dawn of a new era for dustless HdC stars with GAIA eDR3. . (Unpublished)

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Context. Decades after their discovery, only four hydrogen-deficient carbon (HdC) stars were known to have no circumstellar dust shell. This is in complete contrast to the  130 known Galactic HdC stars that are notorious for being heavy dust producers, i.e. the R Coronae Borealis (RCB) stars. Together they form a rare class of supergiant stars that are thought to originate from the merger of CO/He white dwarf (WD) binary systems, otherwise known as the double degenerate scenario. Aims. We searched for new dustless HdC (dLHdC) stars to understand their Galactic distribution, to estimate their total number in the Milky Way and to study their evolutionary link with RCB stars and extreme Helium stars, the final phase of HdC stars. Methods. We used primarily the 2MASS and GAIA eDR3 all-sky catalogues to select candidates that were then followed up spectroscopically. We studied the distribution of known and newly discovered stars in the HR diagram. Results.We discovered 27 new dLHdC stars, one new RCB star, and two new EHe stars. Surprisingly, 20 of the new dLHdC stars share a characteristic of the known dLHdC star HD 148839, having lower atmospheric hydrogen deficiencies. The uncovered population of dLHdC stars exhibit a Bulge-like distribution, like the RCB stars, but show multiple differences from those that indicate they are a different population of HdC stars following its own evolutionary sequence with a fainter luminosity and also a narrow range of effective temperatures, between 5000 and 8000 K. Not all the new dLHdC stars belong to that new population, as we found indication of a current low dust production activity around four of them: the warm F75, F152, C526 and the cold A166. Those could in fact be typical RCB stars passing through a transition time, going in or out of the RCB phase. Conclusions. For the first time we have evidence of a large range of absolute magnitude in the overall population of HdC stars, spanning more than 3 mag. In the favoured formation framework, this is explained by a large range in the initial total WD binary mass which leads to a series of evolutionary sequences with distinct maximum brightness and initial temperature. The cold Galactic RCB stars are also noticeably fainter than the Magellanic ones, possibly due to a difrence in metallicity between the original population of stars resulting in different WD mass ratio. The unveiled population of dLHdC stars indicates that the ability to create dust could be linked to the initial total mass. In our Galaxy, there could be as many dLHdC stars as RCB stars.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper ItemJournal Article
Tisserand, P.0000-0003-4237-0520
Clayton, G. C.0000-0002-0141-7436
Ruiter, A. J.0000-0002-4794-6835
Karambelkar, V.0000-0003-2758-159X
Bessell, M. S.0000-0001-7801-1410
Seitenzahl, I. R.0000-0002-5044-2988
Kasliwal, M. M.0000-0002-5619-4938
Travouillon, T.0000-0001-9304-6718
Additional Information:Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). PT is profoundly grateful for the long unconditional support and love from his father, Claude Tisserand (1945-2020), and this paper is dedicated to his memory. He personally thanks Tony Martin-Jones for his usual highly careful reading and comment. PT acknowledge also financial support from "Programme National de Physique Stellaire" (PNPS) of CNRS/INSU, France. AJR is funded through the Australian Research Council under award number FT170100243. We also thank the team located at Siding Spring Observatory that keeps the 2.3m telescope and its instruments in good shape, as well as the engineer, computer and technician teams located at Mount Stromlo Observatory that have facilitated the observations. Palomar Gattini-IR (PGIR) is generously funded by Caltech, the Australian National University, the Mt Cuba Foundation, the Heising Simons Foundation and the Binational Science Foundation. PGIR is a collaborative project among Caltech, the Australian National University, the University of New South Wales, Columbia University and the Weizmann Institute of Science. MMK acknowledges generous support from the David and Lucille Packard Foundation. MMK and EO acknowledge the US-Israel Bi-national Science Foundation Grant 2016227. MMK and JLS acknowledge the Heising-Simons foundation for support via a Scialog fellowship of the Research Corporation. MMK and AMM acknowledge the Mt Cuba foundation. J. Soon is supported by an Australian Government Research Training Program (RTP) Scholarship. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. The DASCH project at Harvard is grateful for partial support from NSF grants AST-0407380, AST-0909073, and AST-1313370.
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
Australian Research CouncilFT170100243
Australian National UniversityUNSPECIFIED
Mt. Cuba Astronomical FoundationUNSPECIFIED
Heising-Simons FoundationUNSPECIFIED
Binational Science Foundation (USA-Israel)2016227
University of New South WalesUNSPECIFIED
Columbia UniversityUNSPECIFIED
Weizmann Institute of ScienceUNSPECIFIED
David and Lucile Packard FoundationUNSPECIFIED
Scialog Fellow of Research CorporationUNSPECIFIED
Gaia Multilateral AgreementUNSPECIFIED
Subject Keywords:Stars: late-type - carbon - AGB and post-AGB - supergiants - circumstellar matter - Infrared: stars
Record Number:CaltechAUTHORS:20220113-234558931
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:112903
Deposited By: George Porter
Deposited On:14 Jan 2022 19:22
Last Modified:02 Jun 2023 01:22

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