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

Kraus, Adam L. and Douglas, Stephanie T. and Mann, Andrew W. and Agüeros, Marcel A. and Law, Nicholas M. and Covey, Kevin R. and Feiden, Gregory A. and Rizzuto, Aaron C. and Howard, Andrew W. and Isaacson, Howard and Gaidos, Eric and Torres, Guillermo and Bakos, Gaspar (2017) The Factory and the Beehive. III. PTFEB132.707+19.810, A Low-mass Eclipsing Binary in Praesepe Observed by PTF and K2. Astrophysical Journal, 845 (1). Art. No. 72. ISSN 1538-4357.

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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 (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_⊙) and radii (R_p = 0.363 ± 0.008 R_⊙; R_s = 0.272 ± 0.012 R_⊙). 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 P_(rot,prim), 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Kraus, Adam L.0000-0001-9811-568X
Douglas, Stephanie T.0000-0001-7371-2832
Mann, Andrew W.0000-0003-3654-1602
Agüeros, Marcel A.0000-0001-7077-3664
Law, Nicholas M.0000-0001-9380-6457
Covey, Kevin R.0000-0001-6914-7797
Feiden, Gregory A.0000-0002-2012-7215
Rizzuto, Aaron C.0000-0001-9982-1332
Howard, Andrew W.0000-0001-8638-0320
Isaacson, Howard0000-0002-0531-1073
Gaidos, Eric0000-0002-5258-6846
Torres, Guillermo0000-0002-5286-0251
Bakos, Gaspar0000-0001-7204-6727
Additional Information:© 2017 American Astronomical Society. Received 2017 March 23. Accepted 2017 June 28. Published 2017 August 11. 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. 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 SDSS-IV is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS Collaboration. 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. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Software: CPS pipeline (Howard et al. 2010), gatspy (Press & Rybicki 1989; Vanderplas et al. 2016), lsf_rotate (Gray 1992; Hubeny & Lanz 2011), MAKEE (, supersmoother (Friedman 1984; Vanderplas & Willmer 2015).
Funding AgencyGrant Number
NASA Hubble Fellowship51364
NASANAS 5-26555
Alfred P. Sloan FoundationUNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
University of UtahUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:binaries: eclipsing; stars: evolution; stars: fundamental parameters; stars: individual (PTFEB132.707+19.810) ; stars: low-mass; starspots
Issue or Number:1
Record Number:CaltechAUTHORS:20170814-084009189
Persistent URL:
Official Citation:Adam L. Kraus et al 2017 ApJ 845 72
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:80346
Deposited By: Ruth Sustaita
Deposited On:14 Aug 2017 16:25
Last Modified:29 Nov 2019 02:56

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