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

摘要: Theoretical models of stars constitute the fundamental bedrock upon which much astrophysics is built, but large swaths model parameter space remain uncalibrated by observations. The best calibrators are eclipsing binaries in clusters, allowing measurement masses, radii, luminosities, and temperatures for known metallicity age. We present discovery detailed characterization PTFEB132.707+19.810, a P = 6.0 day binary Praesepe cluster (τ ~ 600–800 Myr; [Fe/H] 0.14 ± 0.04). system contains two late-type (SpT_P M3.5 0.2; SpT_S M4.3 0.7) with precise masses (M_p 0.3953 0.0020 M_⊙; M_s 0.2098 0.0014 M_⊙) radii (R_p 0.363 0.008 R_⊙; R_s 0.272 0.012 R_⊙). Neither star meets predictions stellar evolutionary models. primary has expected radius cooler less luminous, while secondary luminosity substantially larger (by 20%). not tidally locked or circularized. Exploiting fortuitous 4:5 commensurability between P_(orb) P_(rot,prim), we demonstrate that fitting errors from unknown spot configuration only change inferred ≾1%–2%. also analyze subsets data to test robustness measurements; sum more robust systematic preferable comparisons. plausible changes limb darkening find corresponding uncertainties ~1%. Finally, validate our pipeline using extant GU Boo, finding independent results match previous within mutual (2%–3%). therefore suggest substantial discrepancies astrophysical; since they than those old field stars, may be tied intermediate age PTFEB132.707+19.810.