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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. (2022) The dawn of a new era for dustless HdC stars with Gaia eDR3. Astronomy and Astrophysics, 667 . Art. No. A83. ISSN 0004-6361. doi:10.1051/0004-6361/202142916.

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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, that is 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 (EHe) stars, the final phase of HdC stars. Methods. We primarily used 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 Hertzsprung-Russell 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 exhibits a bulge-like distribution, like the RCB stars, but show multiple differences from RCB stars that indicate that they are a different population of HdC stars. This population follows 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 this new population, as we found an indication of a current low dust production activity around 4 of them: the warm F75, F152, and C526, and the cold A166. They might be typical RCB stars passing through a transition time, entering or leaving the RCB phase. Conclusions. For the first time, we have evidence of a wide range of absolute magnitudes in the overall population of HdC stars, spanning more than 3 mag. In the favoured formation framework, this is explained by a wide 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 RCB stars, possibly due to a difference in metallicity between the original population of stars, resulting in a different WD mass ratio. The unveiled population of dLHdC stars indicates that the ability to create dust might be linked to the initial total mass. In our Galaxy, there could be as many dLHdC stars as RCB stars.

Item Type:Article
Related URLs:
URLURL TypeDescription ItemDiscussion Paper
Tisserand, P.0000-0003-4237-0520
Crawford, C. L.0000-0002-7654-7438
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
Soon, J.0000-0001-9226-4043
Travouillon, T.0000-0001-9304-6718
Additional Information:P.T. 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. P.T. acknowledges also financial support from “Programme National de Physique Stellaire” (PNPS) of CNRS/INSU, France. A.J.R. is funded through the Australian Research Council under award number FT170100243. We also thank the team located at Siding Spring Observatory that keeps the 2.3 m 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. M.M.K. acknowledges generous support from the David and Lucille Packard Foundation. M.M.K. and E.O. acknowledge the US-Israel Bi-national Science Foundation Grant 2016227. M.M.K. and J.L.S. acknowledge the Heising-Simons foundation for support via a Scialog fellowship of the Research Corporation. M.M.K. and A.M.M. 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)UNSPECIFIED
University of New South WalesUNSPECIFIED
Weizmann Institute of ScienceUNSPECIFIED
David and Lucile Packard FoundationUNSPECIFIED
Scialog Fellow of Research CorporationUNSPECIFIED
Gaia Multilateral AgreementUNSPECIFIED
Record Number:CaltechAUTHORS:20221128-494241100.35
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ID Code:118074
Deposited By: Research Services Depository
Deposited On:20 Dec 2022 18:23
Last Modified:20 Dec 2022 18:23

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