Abstract
Using data from the extended Kepler mission in K2 Campaign 10, we identify two eclipsing binaries containing white dwarfs with cool companions that have extremely short orbital periods of only 71.2 min (SDSS J1205−0242, a.k.a. EPIC 201283111) and 72.5 min (SDSS J1231+0041, a.k.a. EPIC 248368963). Despite their short periods, both systems are detached with small, low-mass companions, in one case a brown dwarf and in the other case either a brown dwarf or a low-mass star. We present follow-up photometry and spectroscopy of both binaries, as well as phase-resolved spectroscopy of the brighter system, and use these data to place preliminary estimates on the physical and binary parameters. SDSS J1205−0242 is composed of a 0.39 ± 0.02 M⊙ helium-core white dwarf that is totally eclipsed by a 0.049 ± 0.006 M⊙ (51 ± 6MJ) brown-dwarf companion, while SDSS J1231+0041 is composed of a 0.56 ± 0.07 M⊙ white dwarf that is partially eclipsed by a companion of mass ≲0.095 M⊙. In the case of SDSS J1205−0242, we look at the combined constraints from common-envelope evolution and brown-dwarf models; the system is compatible with similar constraints from other post-common-envelope binaries, given the current parameter uncertainties, but has potential for future refinement.
Highlights
75 per cent of main-sequence binaries are born wide enough that they evolve essentially as single stars (Willems & Kolb 2004)
In the case of Sloan Digital Sky Survey (SDSS) J1205−0242, we look at the combined constraints from common-envelope evolution and brown-dwarf models; the system is compatible with similar constraints from other post-common-envelope binaries, given the current parameter uncertainties, but has potential for future refinement
As part of a search for transits and variability in white dwarfs observed during K2 Campaign 10, we have discovered two new eclipsing post-common-envelope binary (PCEB) composed of a white dwarf and a likely brown-dwarf companion
Summary
75 per cent of main-sequence binaries are born wide enough that they evolve essentially as single stars (Willems & Kolb 2004). The short orbital periods of PCEBs provide for many deeply eclipsing binaries, which offer a unique opportunity to directly probe the structures of both components by allowing for modelindependent, high-precision mass and radius measurements (e.g. Parsons et al 2012b). This is especially useful for uncommon objects. There is only one double-lined, eclipsing brown-dwarf binary known to date, 2MASS J05352184−0546085 (Stassun, Mathieu & Valenti 2006), another has tentatively been identified (David et al 2016) Both of these systems are young (
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