New Low-mass Eclipsing Binary Systems in Praesepe Discovered by K2

Abstract

We present the discovery and characterization of four low-mass ( < M 0.6  M ) eclipsing binary (EB) systems in the sub-Gyr old Praesepe open cluster using Kepler/K2 time series photometry and Keck/HIRES spectroscopy. We present a new Gaussian process EB model, GP-EBOP, as well as a method of simultaneously determining effective temperatures and distances for EBs. Three of the reported systems (AD 3814, AD 2615 and AD 1508) are detached and double-lined, and precise solutions are presented for the first two. We determine masses and radii to 1%-3% precision for AD 3814 and to 5%-6% for AD 2615. Together with effective temperatures determined to ∼50 K precision, we test the PARSEC v1.2 and BHAC15 stellar evolution models. Our EB parameters are more consistent with the PARSEC models, primarily because the BHAC15 temperature scale is hotter than our data over the mid-M-dwarf mass range probed. Both ADs 3814 and 2615, which have orbital periods of 6.0 and 11.6 days, are circularized but not synchronized. This suggests that either synchronization proceeds more slowly in fully convective stars than the theory of equilibrium tides predicts, or magnetic braking is currently playing a more important role than tidal forces in the spin evolution of these binaries. The fourth system (AD 3116) comprises a brown dwarf transiting a mid-M-dwarf, which is the first such system discovered in a sub-Gyr open cluster. Finally, these new discoveries increase the number of characterized EBs in sub-Gyr open clusters by 20% (40%) below < M 1.5 M e ( < M 0.6 M e ).

Planetary Candidates from K2 Campaign 16

“…Dressing et al (2017) validated two of our high-quality C16 candidates, 212069861.01 (K2-123b) and 212154564.01 (K2-124b); another candidate 212110888.01 is a previously known hot Jupiter K2-34b (Hirano et al 2016;Lillo-Box et al 2016); and our lower-priority candidate 211969807.01 was validated as K2-104b (Mann et al 2017). One more low-quality candidate, 211946007.01, was confirmed to be a transiting brown dwarf (Gillen et al 2017). Our derived system parameters are in approximate agreement with those in the discovery papers.…”

The Factory and the Beehive. III. PTFEB132.707+19.810, A Low-mass Eclipsing Binary in Praesepe Observed by PTF and K2

“…Given the HIPPARCOS distance, we find that the corresponding space velocity for PTFEB132.707+19.810 is v 33.8 UVW =  ( 1.7, 8.5 2.2, 2.5 2.1 - - )kms −1 . Finally, we note that while this paper was under review, PTFEB132.707+19.810 was also reported as an eclipsing binary by Rebull et al (2017), Douglas et al (2017), and Gillen et al (2017). The latter group analyzed eight RV measurements and the K2 light curve to compute system parameters.…”

“…As we describe below, PTFEB132.707+19.810 also was identified to be an eclipsing binary with an orbital period of P 6.0 orb = days that has not locked its stars into synchronous rotation. The star has otherwise remained anonymous in the literature until this year, when its eclipsing nature was recognized by others studying K2 data in Praesepe (Douglas et al 2017;Gillen et al 2017;Rebull et al 2017). In this paper, we analyze our discovery light curve from PTF, follow-up spectroscopic observations, and the newly released K2 light curve of PTFEB132.707+19.810 in order to measure the stellar properties of this mid-M-type eclipsing binary system and test the predictions of stellar evolutionary models.…”

NGTS J214358.5−380102 – NGTS discovery of the most eccentric known eclipsing M-dwarf binary system

“…In order to determine the effective temperatures of both stars we fitted their Spectral Energy Distributions (SEDs), following a method similar to Gillen et al (2017). We fit both stars simultaneously using the PHOENIX v2 models (Husser et al 2013).…”