@article{02902e8305ee454d80e40c1de3c5d19e,
title = "The Factory and the Beehive. III. PTFEB132.707+19.810, A Low-mass Eclipsing Binary in Praesepe Observed by PTF and K2",
abstract = "Theoretical models of stars constitute the fundamental bedrock upon which much of astrophysics is built, but large swaths of model parameter space remain uncalibrated by observations. The best calibrators are eclipsing binaries in clusters, allowing measurement of masses, radii, luminosities, and temperatures for stars of known metallicity and age. We present the discovery and detailed characterization of PTFEB132.707+19.810, a P = 6.0 day eclipsing binary in the Praesepe cluster (τ ∼ 600-800 Myr; [Fe/H] = 0.14 0.04). The system contains two late-type stars (SpTP = M3.5 0.2; SpTS = M4.3 0.7) with precise masses ( M o; M o) and radii ( R o; R o). Neither star meets the predictions of stellar evolutionary models. The primary has the expected radius but is cooler and less luminous, while the secondary has the expected luminosity but is cooler and substantially larger (by 20%). The system is not tidally locked or circularized. Exploiting a fortuitous 4:5 commensurability between P orb and , we demonstrate that fitting errors from the unknown spot configuration only change the inferred radii by ≲1%-2%. We also analyze subsets of data to test the robustness of radius measurements; the radius sum is more robust to systematic errors and preferable for model comparisons. We also test plausible changes in limb darkening and find corresponding uncertainties of ∼1%. Finally, we validate our pipeline using extant data for GU Boo, finding that our independent results match previous radii to within the mutual uncertainties (2%-3%). We therefore suggest that the substantial discrepancies are astrophysical; since they are larger than those for old field stars, they may be tied to the intermediate age of PTFEB132.707+19.810.",
keywords = "binaries: eclipsing, stars: evolution, stars: fundamental parameters, stars: individual (PTFEB132.707+19.810), stars: low-mass, starspots",
author = "Kraus, {Adam L.} and Douglas, {Stephanie T.} and Mann, {Andrew W.} and Ag{\"u}eros, {Marcel A.} and Law, {Nicholas M.} and Covey, {Kevin R.} and Feiden, {Gregory A.} and Rizzuto, {Aaron C.} and Howard, {Andrew W.} and Howard Isaacson and Eric Gaidos and Guillermo Torres and Gaspar Bakos",
note = "Funding Information: We thank Phil Muirhead and Eunkyu Han for interesting discussions on low-mass eclipsing binaries and comparing results on our respective pipelines, Trent Dupuy for helpful discussions on the fitting of orbits, and Lynne Hillenbrand for contributing to the Keck/HIRES data acquisition. We also thank the referee for providing a helpful and thoughtful critique of our paper that led to a number of valuable additions to the manuscript. AWM was supported through Hubble Fellowship grant 51364 awarded by STScI, which is operated by AURA for NASA, under contract NAS 5-26555. GT acknowledges partial support for this work from NSF grant AST-1509375. MAA acknowledges support provided by the NSF through grants AST-1255419 and AST-1517367. Funding Information: This paper includes data collected by the K2 mission. Funding for the K2 mission is provided by the NASA Science Mission directorate. The K2 data presented in this paper were obtained from the Mikulski Archive for Space Telescopes. Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the Participating Institutions. SDSS-IV acknowledges support and resources from the Center for High-Performance Computing at the University of Utah. The SDSS web site is http://www.sdss.org. SDSS-IV is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS Collaboration. Funding Information: This research has also made use of the Keck Observatory Archive (KOA), which is operated by the W.M. Keck Observatory and the NASA Exoplanet Science Institute (NExScI), under contract with the National Aeronautics and Space Administration. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The observatory was made possible by the generous financial support of the W.M. Keck Foundation.",
year = "2017",
month = aug,
day = "10",
doi = "10.3847/1538-4357/aa7e75",
language = "English (US)",
volume = "845",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "1",
}