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What are the spectroscopic binaries with high-mass functions near the Gaia DR3 main sequence?

El-Badry, Kareem and Rix, Hans-Walter (2022) What are the spectroscopic binaries with high-mass functions near the Gaia DR3 main sequence? Monthly Notices of the Royal Astronomical Society, 515 (1). pp. 1266-1275. ISSN 0035-8711. doi:10.1093/mnras/stac1797.

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The third data release of the Gaia mission includes orbital solutions for >10⁵ single-lined spectroscopic binaries, representing more than an order of magnitude increase in sample size over all previous studies. This data set is a treasure trove for searches for quiescent black hole + normal star binaries. We investigate one population of black hole candidate binaries highlighted in the data release: sources near the main sequence in the colour–magnitude diagram (CMD) with dynamically inferred companion masses M₂ larger than the CMD-inferred mass of the luminous star. We model light curves, spectral energy distributions, and archival spectra of the 14 such objects in DR3 with high-significance orbital solutions and inferred M₂ > 3 M_⊙⁠. We find that 100 per cent of these sources are mass-transfer binaries containing a highly stripped lower giant donor (0.2 ≲ M/M_⊙ ≲ 0.4) and much more massive (2 ≲ M/M_⊙ ≲ 2.5) main-sequence accretor. The Gaia orbital solutions are for the donors, which contribute about half the light in the Gaia RVS bandpass but only ≲20 per cent in the g band. The accretors’ broad spectral features likely prevented the sources from being classified as double-lined. The donors are all close to Roche lobe filling (⁠R/R_(Roche lobe) > 0.8⁠), but modelling suggests that a majority are detached (⁠R/R_(Roche lobe) < 1⁠). Binary evolution models predict that these systems will soon become detached helium white dwarf + main-sequence ‘EL CVn’ binaries. Our investigation highlights both the power of Gaia data for selecting interesting subpopulations of binaries and the ways in which binary evolution can bamboozle standard CMD-based stellar-mass estimates.

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URLURL TypeDescription
El-Badry, Kareem0000-0002-6871-1752
Rix, Hans-Walter0000-0003-4996-9069
Additional Information:© 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( We thank the referee for constructive comments. This project was developed in part at the Gaia Fête, held at the Flatiron institute Center for Computational Astrophysics in 2022 June. 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. HWR acknowledges the European Research Council for the ERC Advance Grant [101054731]. DATA AVAILABILITY. Data used in this study are available upon request from the corresponding author.
Funding AgencyGrant Number
Gaia Multilateral AgreementUNSPECIFIED
European Research Council (ERC)101054731
Issue or Number:1
Record Number:CaltechAUTHORS:20230105-896018000.57
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:118731
Deposited By: George Porter
Deposited On:06 Jan 2023 22:35
Last Modified:06 Jan 2023 22:35

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