The K2 M67 Study: A Curiously Young Star in an Eclipsing Binary in an Old Open Cluster

Journal Article · Sun Apr 01 04:00:00 EDT 2018 · The Astronomical Journal (Online)

DOI:https://doi.org/10.3847/1538-3881/AAB0FF· OSTI ID:22897435

Sandquist, Eric L.; Orosz, Jerome A. ^[1]; Mathieu, Robert D.; Pollack, Maxwell L. ^[2]; Quinn, Samuel N.; Latham, David W.; Vanderburg, Andrew ^[3]; Brown, Timothy M. ^[4]; Esselstein, Rebecca; Aigrain, Suzanne; Parviainen, Hannu ^[5]; Stello, Dennis ^[6]; Somers, Garrett ^[7]; Pinsonneault, Marc H.; Tayar, Jamie ^[8]; Bedin, Luigi R.; Libralato, Mattia; Malavolta, Luca; Nardiello, Domenico ^[9]

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1. San Diego State University, Department of Astronomy, San Diego, CA 92182 (United States)
2. University of Wisconsin—Madison, Department of Astronomy, Madison, WI 53706 (United States)
3. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
4. Las Cumbres Observatory Global Telescope, Goleta, CA 93117 (United States)
5. University of Oxford, Keble Road, Oxford OX3 9UU (United Kingdom)
6. School of Physics, The University of New South Wales, Sydney, NSW 2052 (Australia)
7. Department of Physics and Astronomy, Vanderbilt University, 6301 Stevenson Circle, Nashville, TN 37235 (United States)
8. Department of Astronomy, Ohio State University, 140 W. 18th Avenue, Columbus, OH 43210 (United States)
9. Istituto Nazionale Astrofisica di Padova—Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122 Padova (Italy)

We present an analysis of a slightly eccentric (e = 0.05), partially eclipsing, long-period (P = 69.73 days) main-sequence binary system (WOCS 12009, Sanders 1247) in the benchmark old open cluster M67. Using Kepler K2 and ground-based photometry, along with a large set of new and reanalyzed spectra, we derived highly precise masses (1.111 ± 0.015 and 0.748 ± 0.005 M {sub ⊙}) and radii (1.071 ± 0.008 ± 0.003 and 0.713 ± 0.019 ± 0.026 R {sub ⊙}, with statistical and systematic error estimates) for the stars. The radius of the secondary star is in agreement with theory. The primary, however, is approximately 15% smaller than reasonable isochrones for the cluster predict. Our best explanation is that the primary star was produced from the merger of two stars, as this can also account for the nondetection of photospheric lithium and its higher temperature relative to other cluster main-sequence stars at the same V magnitude. To understand the dynamical characteristics (low measured rotational line broadening of the primary star and low eccentricity of the current binary orbit), we believe that the most probable (but not the only) explanation is the tidal evolution of a close binary within a primordial triple system (possibly after a period of Kozai–Lidov oscillations), leading to merger approximately 1 Gyr ago. This star appears to be a future blue straggler that is being revealed as the cluster ages and the most massive main-sequence stars die out.

• OSTI ID: 22897435
• Journal Information: The Astronomical Journal (Online), Journal Name: The Astronomical Journal (Online) Journal Issue: 4 Vol. 155; ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ECLIPSE
LINE BROADENING
LITHIUM
MAIN SEQUENCE STARS
MASS
ORBITS
OSCILLATIONS
PHOTOMETRY
SPECTRA
TEMPERATURE RANGE 0400-1000 K