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Register a new userTwo white dwarfs in ultrashort binaries with detached, eclipsing, likely substellar companions detected by K2
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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 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 $0.39pm0.02$M$_odot$ helium-core white dwarf which is totally eclipsed by a $0.049pm0.006$M$_odot$ ($51pm6$M$_J$) brown dwarf companion, while SDSS J1231+0041 is composed of a $0.56pm0.07$M$_odot$ white dwarf which is partially eclipsed by a companion of mass $lesssim 0.095$M$_odot$. 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.
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Many short-period binary stars have distant orbiting companions that have played a role in driving the binary components into close separation. Indirect detection of a tertiary star is possible by measuring apparent changes in eclipse times of eclipsing binaries as the binary orbits the common center of mass. Here we present an analysis of the eclipse timings of 41 eclipsing binaries observed throughout the NASA Kepler mission of long duration and precise photometry. This subset of binaries is characterized by relatively deep and frequent eclipses of both stellar components. We present preliminary orbital elements for seven probable triple stars among this sample, and we discuss apparent period changes in seven additional eclipsing binaries that may be related to motion about a tertiary in a long period orbit. The results will be used in ongoing investigations of the spectra and light curves of these binaries for further evidence of the presence of third stars.
We present the new results of our long-term observational project to detect the small variations in the orbital periods of low-mass and short-period eclipsing binaries. About 120 new precise mid-eclipse times were obtained for three relatively well-known dwarf eclipsing binaries: SDSS J143547.87+373338.5 (P = 0.126 d), NSVS 07826147 (0.162 d), and NSVS 14256825 (0.110 d). Observed-minus-calculated (O-C) diagrams of these systems were analyzed using all accurate timings, and, where possible, new parameters of the light-time effect were calculated. For the first time, we derive (or improve upon previous findings with regard to) the short orbital periods of 13 and 10 years of possible third bodies for SDSS J143547.87+373338.5 and NSVS 07826147, respectively. In these binaries, our data show that period variations can be modeled simply on the basis of a single circumbinary object. For the first two objects, we calculated the minimum mass of the third components to be 17 MJ, and 1.4 MJ respectively, which corresponds to the mass of a brown dwarf or a giant planet. For NSVS 14256825, the cyclical period changes caused by a single additional body cannot be confirmed by our recent eclipse time measurements. More complex behavior connected with two orbiting bodies, or yet unknown effects, should be taken into account.
Tidal interactions can play an important role as compact white dwarf (WD) binaries are driven together by gravitational waves (GWs). This will modify the strain evolution measured by future space-based GW detectors and impact the potential outcome of the mergers. Surveys now and in the near future will generate an unprecedented population of detached WD binaries to constrain tidal interactions. Motivated by this, I summarize the deviations between a binary evolving under the influence of only GW emission and a binary that is also experiencing some degree of tidal locking. I present analytic relations for the first and second derivative of the orbital period and braking index. Measurements of these quantities will allow the inference of tidal interactions, even when the masses of the component WDs are not well constrained. Finally, I discuss tidal heating and how it can provide complimentary information.
Disks in binary systems can cause exotic eclipsing events. MWC 882 (BD-22 4376, EPIC 225300403) is such a disk-eclipsing system identified from observations during Campaign 11 of the K2 mission. We propose that MWC 882 is a post-Algol system with a B7 donor star of mass $0.542pm0.053,M_odot$ in a 72 day period orbit around an A0 accreting star of mass $3.24pm0.29,M_odot$. The $59.9pm6.2,R_odot$ disk around the accreting star occults the donor star once every orbit, inducing 19 day long, 7% deep eclipses identified by K2, and subsequently found in pre-discovery ASAS and ASAS-SN observations. We coordinated a campaign of photometric and spectroscopic observations for MWC 882 to measure the dynamical masses of the components and to monitor the system during eclipse. We found the photometric eclipse to be gray to $approx 1$%. We found the primary star exhibits spectroscopic signatures of active accretion, and observed gas absorption features from the disk during eclipse. We suggest MWC 882 initially consisted of a $approx 3.6,M_odot$ donor star transferring mass via Roche lobe overflow to a $approx 2.1,M_odot$ accretor in a $approx 7$ day initial orbit. Through angular momentum conservation, the donor star is pushed outward during mass transfer to its current orbit of 72 days. The observed state of the system corresponds with the donor star having left the Red Giant Branch ~0.3 Myr ago, terminating active mass transfer. The present disk is expected to be short-lived ($10^2$ years) without an active feeding mechanism, presenting a challenge to this model.
Detached eclipsing binaries are remarkable systems to provide accurate fundamental stellar parameters. The fundamental stellar parameters and the metallicity values of stellar systems are needed to deeply understand the stellar evolution and formation. In this study, we focus on the detailed spectroscopic and photometric studies of three detached eclipsing binary systems, V372,And, V2080,Cyg, and CF,Lyn to obtain their accurate stellar, atmospheric parameters,and chemical compositions. An analysis of light and radial velocity curves was carried out to derive the orbital and stellar parameters. The disentangled spectra of component stars were obtained for the spectroscopic analysis. Final teff, logg, $xi$, vsini, parameters and the element abundances of component stars were derived by using the spectrum synthesis method. The fundamental stellar parameters were determined with a high certainty for V372,And, V2080,Cyg ($sim$$1-2$%) and with an accuracy for CF,Lyn ($sim$$2-6$%). The evolutionary status of the systems was examined and their ages were obtained. It was found that the component stars of V2080,Cyg have similar iron abundance which is slightly lower than solar iron abundance. Additionally, we showed that the primary component of CF,Lyn exhibits a non-spherical shape with its 80% Roche lobe filling factor. It could be estimated that CF,Lyn will start its first Roche overflow in the next 0.02,Gyr.
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