K2 Discovery of Young Eclipsing Binaries in Upper Scorpius: Direct Mass and Radius Determinations for the Lowest Mass Stars and Initial Characterization of an Eclipsing Brown Dwarf Binary

Creators: David, Trevor J.; Hillenbrand, Lynne A.; Cody, Ann Marie; Carpenter, John M.; Howard, Andrew W.

Abstract

We report the discovery of three low-mass double-lined eclipsing binaries in the pre-main sequence Upper Scorpius association, revealed by K2 photometric monitoring of the region over ~78 days. The orbital periods of all three systems are <5 days. We use the K2 photometry plus multiple Keck/HIRES radial velocities (RVs) and spectroscopic flux ratios to determine fundamental stellar parameters for both the primary and secondary components of each system, along with the orbital parameters. We present tentative evidence that EPIC 203868608 is a hierarchical triple system comprised of an eclipsing pair of ~25 MJup brown dwarfs with a wide M-type companion. If confirmed, it would constitute only the second double-lined eclipsing brown dwarf binary system discovered to date. The double-lined system EPIC 203710387 is composed of nearly identical M4.5-M5 stars with fundamentally determined masses and radii measured to better than 3% precision M_1 = 0.1183 ± 0.0028M_⊙, M_2 = 0.1076 ± 0.0031{M}_⊙ and R_1 = 0.417 ± 0.010R_⊙, R_2 = 0.450 ± 0.012R_⊙) from combination of the light curve and RV time series. These stars have the lowest masses of any stellar mass double-lined eclipsing binary to date. Comparing our derived stellar parameters with evolutionary models, we suggest an age of ~10–11 Myr for this system, in contrast to the canonical age of 3–5 Myr for the association. Finally, EPIC 203476597 is a compact single-lined system with a G8-K0 primary and a likely mid-K secondary whose lines are revealed in spectral ratios. Continued measurement of RVs and spectroscopic flux ratios will better constrain fundamental parameters and should elevate the objects to benchmark status. We also present revised parameters for the double-lined eclipsing binary UScoCTIO 5 (M_1 = 0.3336 ± 0.0022M_⊙, M_2 = 0.3200 ± 0.0022M_⊙ and R_1 = 0.862 ± 0.012, R_2 = 0.852 ± 0.013R_⊙), which are suggestive of a system age younger than previously reported. We discuss the implications of our results on these ~0.1–1.5 M_⊙ stars for pre-main-sequence evolutionary models.

Additional Information

© 2016. The American Astronomical Society. Received 2015 May 29; accepted 2015 November 11; published 2015 December 23. We thank the referee for many helpful comments, which greatly improved the quality and rigor of this work. We thank Ian Crossfield for lending his Python MCMC wrapper for the jktebop orbit fitting code and for consultation regarding its use, which aided our analysis. We thank Erik Petigura for helpful discussions regarding eclipse model fitting practices. We thank Howard Isaacson, Geoff Marcy, Erik Petigura and the CPS group for acquiring additional HIRES spectra and providing MAGIQ snapshots for the three systems. We thank Christoph Baranec for acquiring Keck/NIRC2 images of EPIC 203476597 and EPIC 203868608, and Brendan Bowler for performing the reductions of these data. We thank Jessie Christiansen for early advice regarding Kepler telescope data products, photometry techniques, and detrending strategies. We thank Avi Shporer for suggesting the possibility of measuring the direction of orbital motion for EPIC 203476597. We thank Jonathan Swift for lending his transit analysis routines, which aided our analysis. We thank Ross Fredella for his assistance in creating Figure 1. The material presented herein is based upon work supported in 2015 by the National Science Foundation Graduate Research Fellowship under Grant No. DGE1144469. T. J. D. gratefully acknowledges research activities support from France Córdova through the Neugebauer Scholarship. This research was partially supported by an appointment to the NASA Postdoctoral Program at the Ames Research Center, administered by Oak Ridge Associated Universities through a contract with NASA. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. This research has also made use of the SIMBAD database and VizieR catalog access tool, operated at CDS, Strasbourg, France, and NASA's ADS and IPAC/IRSA services. Some of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts. This paper includes data collected by the Kepler mission. Funding for the Kepler mission is provided by the NASA Science Mission directorate. 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 Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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