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A New Class of Roche Lobe–filling Hot Subdwarf Binaries

Kupfer, Thomas and Bauer, Evan B. and Burdge, Kevin B. and van Roestel, Jan and Bellm, Eric C. and Fuller, Jim and Hermes, JJ and Marsh, Thomas R. and Bildsten, Lars and Kulkarni, Shrinivas R. and Phinney, E. S. and Prince, Thomas A. and Szkody, Paula and Yao, Yuhan and Irrgang, Andreas and Heber, Ulrich and Schneider, David and Dhillon, Vik S. and Murawski, Gabriel and Drake, Andrew J. and Duev, Dmitry A. and Feeney, Michael and Graham, Matthew J. and Laher, Russ R. and Littlefair, S. P. and Mahabal, A. A. and Masci, Frank J. and Porter, Michael and Reiley, Dan and Rodriguez, Hector and Rusholme, Ben and Shupe, David L. and Soumagnac, Maayane T. (2020) A New Class of Roche Lobe–filling Hot Subdwarf Binaries. Astrophysical Journal Letters, 898 (1). Art. No. L25. ISSN 2041-8213.

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We present the discovery of the second binary with a Roche lobe–filling hot subdwarf transferring mass to a white dwarf (WD) companion. This 56 minute binary was discovered using data from the Zwicky Transient Facility. Spectroscopic observations reveal an He-sdOB star with an effective temperature of T_(eff) = 33,700 ± 1000 K and a surface gravity of log(g) = 5.54 ± 0.11. The GTC+HiPERCAM light curve is dominated by the ellipsoidal deformation of the He-sdOB star and shows an eclipse of the He-sdOB by an accretion disk as well as a weak eclipse of the WD. We infer a He-sdOB mass of M_(sdOB) = 0.41 ± 0.04 M_⊙ and a WD mass of M WD = 0.68 ± 0.05 M_⊙. The weak eclipses imply a WD blackbody temperature of 63,000 ± 10,000 K and a radius R_(WD) = 0.0148 ± 0.0020 R_⊙ as expected for a WD of such high temperature. The He-sdOB star is likely undergoing hydrogen shell burning and will continue transferring mass for ≈1 Myr at a rate of 10⁻⁹ M_⊙ yr⁻¹, which is consistent with the high WD temperature. The hot subdwarf will then turn into a WD and the system will merge in ≈30 Myr. We suggest that Galactic reddening could bias discoveries toward preferentially finding Roche lobe–filling systems during the short-lived shell-burning phase. Studies using reddening-corrected samples should reveal a large population of helium core–burning hot subdwarfs with T_(eff) ≈ 25,000 K in binaries of 60–90 minutes with WDs. Though not yet in contact, these binaries would eventually come into contact through gravitational-wave emission and explode as a subluminous thermonuclear supernova or evolve into a massive single WD.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Kupfer, Thomas0000-0002-6540-1484
Bauer, Evan B.0000-0002-4791-6724
Burdge, Kevin B.0000-0002-7226-836X
van Roestel, Jan0000-0002-2626-2872
Bellm, Eric C.0000-0001-8018-5348
Fuller, Jim0000-0002-4544-0750
Hermes, JJ0000-0001-5941-2286
Marsh, Thomas R.0000-0002-2498-7589
Kulkarni, Shrinivas R.0000-0001-5390-8563
Phinney, E. S.0000-0002-9656-4032
Prince, Thomas A.0000-0002-8850-3627
Szkody, Paula0000-0003-4373-7777
Yao, Yuhan0000-0001-6747-8509
Irrgang, Andreas0000-0002-0465-3725
Heber, Ulrich0000-0001-7798-6769
Dhillon, Vik S.0000-0003-4236-9642
Murawski, Gabriel0000-0001-7809-1457
Duev, Dmitry A.0000-0001-5060-8733
Graham, Matthew J.0000-0002-3168-0139
Laher, Russ R.0000-0003-2451-5482
Littlefair, S. P.0000-0001-7221-855X
Mahabal, A. A.0000-0003-2242-0244
Masci, Frank J.0000-0002-8532-9395
Rusholme, Ben0000-0001-7648-4142
Shupe, David L.0000-0003-4401-0430
Soumagnac, Maayane T.0000-0001-6753-1488
Additional Information:© 2020. The American Astronomical Society. Received 2020 June 9; revised 2020 July 6; accepted 2020 July 8; published 2020 July 23. Based on observations obtained with the Samuel Oschin Telescope 48-inch at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations are conducted by COO, IPAC, and UW. Based on observations obtained at the international Gemini Observatory, proposal ID GN-2019B-FT-102, a program of NSF's OIR Lab, 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). The authors thank the staff at the Gemini-North observatory for performing the observations in service mode. Some results presented in this Letter are based on observations made with the Shane telescope. Research at Lick Observatory is partially supported by a generous gift from Google. Based on observations made with the Gran Telescopio Canarias (GTC), installed at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, in the island of La Palma. This research was supported in part by the National Science Foundation through grant ACI-1663688, and at the KITP by grant PHY-1748958. This research benefited from interactions that were funded by the Gordon and Betty Moore Foundation through grant GBMF5076. We acknowledge the use of the Center for Scientific Computing supported by the California NanoSystems Institute and the Materials Research Science and Engineering Center (MRSEC) at UC Santa Barbara through NSF DMR 1720256 and NSF CNS 1725797. HiPERCAM and VSD are funded by the European Research Council under the European Union's Seventh Framework Programme (FP/2007–2013) under ERC-2013-ADG grant agreement No. 340040 (HiPERCAM). T.R.M. was supported by a grant from the United Kingdom's Science and Technology Facilities Council. P.S. acknowledges support from NSF grant AST-1514737. E.S.P.'s research was funded in part by the Gordon and Betty Moore Foundation through grant GBMF5076. D.S. acknowledges support by the Deutsche Forschungsgemeinschaft through grant HE1356/70-1. 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 work benefited from a workshop held at DARK in 2019 July that was funded by the Danish National Research Foundation (DNRF132). We thank Josiah Schwab for his efforts in organizing this. Facilities: PO:1.2 m (ZTF) - , Gemini:Gillett (GMOS) - , Shane (KAST) - , GTC (HiPERCAM). - Software: Lpipe (Perley 2019), Gatspy (VanderPlas & Ivezić 2015; Vanderplas 2015), FITSB2 (Napiwotzki et al. 2004), LCURVE (Copperwheat et al. 2010), emcee (Foreman-Mackey et al. 2013), MESA (Paxton et al. 2011, 2013, 2015, 2018, 2019), Matplotlib (Hunter 2007), Astropy (Astropy Collaboration et al. 2013, 2018), Numpy (Oliphant 2015), ISIS (Houck & Denicola 2000), TLUSTY (Hubeny & Lanz 1995).
Group:Astronomy Department, Infrared Processing and Analysis Center (IPAC), TAPIR, Zwicky Transient Facility
Funding AgencyGrant Number
ZTF partner institutionsUNSPECIFIED
Gordon and Betty Moore FoundationGBMF5076
European Research Council (ERC)340040
Science and Technology Facilities Council (STFC)UNSPECIFIED
Deutsche Forschungsgemeinschaft (DFG)HE1356/70-1
Gaia Multilateral AgreementUNSPECIFIED
Danish National Research FoundationDNRF132
Subject Keywords:B subdwarf stars ; Stellar evolution ; White dwarf stars ; Compact binary stars ; Stellar accretion
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: B subdwarf stars (129); Stellar evolution (1599); White dwarf stars (1799); Compact binary stars (283); Stellar accretion (1578)
Record Number:CaltechAUTHORS:20200724-100653916
Persistent URL:
Official Citation:Thomas Kupfer et al 2020 ApJL 898 L25
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:104560
Deposited By: George Porter
Deposited On:24 Jul 2020 20:49
Last Modified:24 Jul 2020 20:49

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