EPIC 220204960: A Quadruple Star System Containing Two Strongly Interacting Eclipsing Binaries

Creators: Rappaport, S.; Vanderburg, A.; Borkovits, T.; Kalomeni, B.; Halpern, J. P.; Ngo, H.; Mace, G. N.; Fulton, B. J.; Howard, A. W.; Isaacson, H.; Petigura, E. A.; Mawet, D.; Kristiansen, M. H.; Jacobs, T. L.; LaCourse, D.; Bieryla, A.; Forgács-Dajka, E.; Nelson, L.

Abstract

We present a strongly interacting quadruple system associated with the K2 target EPIC 220204960. The K2 target itself is a Kp = 12.7-mag star at Teff ≃ 6100 K, which we designate as 'B-N' (blue northerly image). The host of the quadruple system, however, is a Kp ≃ 17-mag star with a composite M-star spectrum, which we designate as 'R-S' (red southerly image). With a 3.2-arcsec separation and similar radial velocities and photometric distances, 'B-N' is likely physically associated with 'R-S', making this a quintuple system, but that is incidental to our main claim of a strongly interacting quadruple system in 'R-S'. The two binaries in 'R-S' have orbital periods of 13.27 and 14.41 d, respectively, and each has an inclination angle of ≳89°. From our analysis of radial-velocity (RV) measurements, and of the photometric light curve, we conclude that all four stars are very similar with masses close to 0.4 M_⊙. Both of the binaries exhibit significant eclipse-timing variations where those of the primary and secondary eclipses 'diverge' by 0.05 d over the course of the 80-d observations. Via a systematic set of numerical simulations of quadruple systems consisting of two interacting binaries, we conclude that the outer orbital period is very likely to be between 300 and 500 d. If sufficient time is devoted to RV studies of this faint target, the outer orbit should be measurable within a year.

Additional Information

© 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2017 January 16. Received 2017 January 16; in original form 2016 December 15. AV is supported by the National Science Foundation Graduate Research Fellowship, Grant no. DGE 1144152. BK gratefully acknowledges the support provided by the Turkish Scientific and Technical Research Council (TÜBİTAK-112T766 and TÜBİTAK-BİDEP 2219). TB and EF-D acknowledge the financial support of the Hungarian National Research, Development and Innovation Office – NKFIH Grant OTKA K-113117. MHK, DL and TLJ acknowledge Allan R. Schmitt for making his light-curve examining software 'lctools' freely available. LN thanks Natural Sciences and Engineering Research Council (Canada) for financial support and F. Maisonneuve for his work on the stellar models. Some of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc., under National Aeronautics and Space Administration (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. The MDM Observatory is operated by Dartmouth College, Columbia University, Ohio State University, Ohio University and the University of Michigan. A portion of this work was based on observations at the W. M. Keck Observatory granted by the California Institute of Technology. We thank the observers who contributed to the measurements reported here and acknowledge the efforts of the Keck Observatory staff. We extend special thanks to those of Hawaiian ancestry on whose sacred mountain of Mauna Kea we are privileged to be guests. Some of these results made use of the Discovery Channel Telescope at Lowell Observatory. Lowell is a private, non-profit institution dedicated to astrophysical research and public appreciation of astronomy and operates the Discovery Channel Telescope in partnership with Boston University, the University of Maryland, the University of Toledo, Northern Arizona University and Yale University. This latter work used the Immersion Grating Infrared Spectrometer (IGRINS) that was developed under a collaboration between the University of Texas at Austin and the Korea Astronomy and Space Science Institute (KASI) with the financial support of the US National Science Foundation under grant AST-1229522, of the University of Texas at Austin, and of the Korean GMT Project of KASI. Some results are based on data from the Carlsberg Meridian Catalogue 15 Data Access Service at Centro de Astrobiología (CAB, INTA-CSIC) (INTA-CSIC).

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