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

We present the discovery 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 eclipsing binary 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 $\sim $50 K p r e c i s i o n, w e t e s t t h e P A R S E C v 1.2 a n d B H A C 15 s t e l l a r e v o l u t i o n m o d e l s . O u r E B p a r a m e t e r s a r e m o r e c o n s i s t e n t w i t h t h e P A R S E C m o d e l s, p r i m a r i l y b e c a u s e t h e B H A C 15 t e m p e r a t u r e s c a l e i s h o t t e r t h a n o u r d a t a o v e r t h e m i d M − d w a r f m a s s r a n g e p r o b e d . B o t h A D s 3814 a n d 2615, w h i c h h a v e o r b i t a l p e r i o d s o f 6.0 a n d 11.6 d a y s, a r e c i r c u l a r i z e d b u t n o t s y n c h r o n i z e d . T h i s s u g g e s t s t h a t e i t h e r s y n c h r o n i z a t i o n p r o c e e d s m o r e s l o w l y i n f u l l y c o n v e c t i v e s t a r s t h a n t h e t h e o r y o f e q u i l i b r i u m t i d e s p r e d i c t s o r m a g n e t i c b r a k i n g i s c u r r e n t l y p l a y i n g a m o r e i m p o r t a n t r o l e t h a n t i d a l f o r c e s i n t h e s p i n e v o l u t i o n o f t h e s e b i n a r i e s . T h e f o u r t h s y s t e m (A D 3116) c o m p r i s e s a b r o w n d w a r f t r a n s i t i n g a m i d M − d w a r f, w h i c h i s t h e f i r s t s u c h s y s t e m d i s c o v e r e d i n a s u b − G y r o p e n c l u s t e r . F i n a l l y, t h e s e n e w d i s c o v e r i e s i n c r e a s e t h e n u m b e r o f c h a r a c t e r i z e d E B s i n s u b − G y r o p e n c l u s t e r s b y 20$ M<1.5$ $M ⊙$ ( $M <0.6$ $M ⊙$ ).

Keywords

binaries: eclipsing, binaries: spectroscopic, brown dwarfs, stars: evolution, stars: fundamental parameters, stars: low-mass

Journal Title

Astrophysical Journal

Journal ISSN

0004-637X
1538-4357

Volume Title

849

Publisher

American Astronomical Society

Publisher DOI

https://doi.org/10.3847/1538-4357/aa84b3

Rights

Publisher's own licence

Sponsorship

The Royal Society (wm120055)

Collections

University of Cambridge Research Outputs (Articles and Conferences)