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

Abstract

We present an analysis of a slightly eccentric ($e=0.05$), partially eclipsing long-period ($P=69.73$ d) 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 ($1.111\pm 0.015$ and $0.748\pm 0.005M_{\odot }$) and radii ($1.071\pm 0.008\pm 0.003$ and $0.713\pm 0.019\pm 0.026R_{\odot }$, 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 non-detection 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 the 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 1Gyr 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.

arXiv comment33 pages, 11 figures, accepted to AJ, photometry files will be available with the electronic journal article

References in corpus (63)

• emcee: The MCMC Hammer
• The chemical composition of the Sun
• PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
• MESA Isochrones and Stellar Tracks (MIST). I: Solar-Scaled Models
• MESA Isochrones and Stellar Tracks (MIST) 0: Methods for the construction of stellar isochrones
• A Survey of Stellar Families: Multiplicity of Solar-Type Stars
• A large stellar evolution database for population synthesis studies. I. Scaled solar models and isochrones
• Accurate masses and radii of normal stars: modern results and applications
• Shrinking binary and planetary orbits by Kozai cycles with tidal friction
• Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics
• Efficient, uninformative sampling of limb darkening coefficients for two-parameter laws
• Solar Chemical Abundances Determined with a CO5BOLD 3D Model Atmosphere
• An absolutely calibrated effective temperature scale from the InfraRed Flux Method
• A Technique for Extracting Highly Precise Photometry for the Two-Wheeled Kepler Mission
• Element Diffusion in the Solar Interior
• A library of high resolution synthetic stellar spectra from 300nm to 1.8 micron with solar and alpha-enhanced composition
• The Victoria-Regina Stellar Models: Evolutionary Tracks and Isochrones for a Wide Range in Mass and Metallicity that Allow for Empirically Constrained Amounts of Convective Core Overshooting
• Abundances, Stellar Parameters, and Spectra From the SDSS-III/APOGEE Survey
• Evolution of low-mass star and brown dwarf eclipsing binaries
• Stellar Collisions During Binary-Binary and Binary-Single Star Interactions
• Synthetic Stellar Photometry - I. General considerations and new transformations for broad-band systems
• Parallel Implementation of the PHOENIX Generalized Stellar Atmosphere Program
• The Kepler Cluster Study: Stellar Rotation in NGC6811
• Planetary Candidates from the First Year of the K2 Mission
• K2SC: Flexible systematics correction and detrending of K2 light curves using Gaussian Process regression
• Radial Velocity Studies of Close Binary Stars.VII. Methods and Uncertainties
• Stellar Collisions and the Interior Structure of Blue Stragglers
• New H-band Stellar Spectral Libraries for the SDSS-III/APOGEE survey
• Ground-based CCD astrometry with wide field imagers. II. A star catalogue for M67: [email protected] MPG/ESO astrometry, FLAMES@VLT radial velocities
• The Yale-Potsdam Stellar Isochrones (YaPSI)
• Stellar Radial Velocities in the Old Open Cluster M67 (NGC 2682) I. Memberships, Binaries, and Kinematics
• Abundances and possible diffusion of elements in M67 stars
• Models for Solar Abundance Stars with Gravitational Settling and Radiative Accelerations: Application to M67 and NGC188
• Solar twins in M67
• A High Relative-Precision Color-Magnitude Diagram of M67
• Abundances of four open clusters from solar stars
• M67-1194, an unusually Sun-like solar twin in M67
• Deep 2MASS Photometry of M67 and Calibration of the Main Sequence J-Ks Color Difference as an Age Indicator
• On using the CMD morphology of M67 to test solar abundances
• The chemical compositions of solar twins in the open cluster M67
• Metallicities for 13 nearby open clusters from high-resolution spectroscopy of dwarf and giant stars. Stellar metallicity, stellar mass, and giant planets
• WIYN Open Cluster Study. LX. Spectroscopic Binary Orbits in NGC 6819
• The K2 M67 Study: Revisiting old friends with K2 reveals oscillating red giants in the open cluster M67
• Dynamical formation & scattering of hierarchical triples: Cross sections, Kozai-Lidov oscillations, and collisions
• Mergers of close primordial binaries
• A Survey of Chromospheric Activity in the Solar-Type Stars in the Open Cluster M67
• A PSF-based approach to Kepler/K2 data. I. Variability within the K2 Campaign 0 star clusters M 35 and NGC 2158
• Time-Series Photometry of M67: W UMa Systems, Blue Stragglers, and Related Systems
• The Blue Straggler RS CVn Star S1082 in M67: A Detailed Light Curve and the Possibility of a Triple
• Lithium in M67: From the main sequence to the red giant branch
• WIYN Open Cluster Study. XXXVI. Spectroscopic Binary Orbits in NGC 188
• A Constraint on Z_\odot from Fits of Isochrones to the Color-Magnitude Diagram of M67
• Variable stars in one open cluster within the Kepler/K2-Campaign-5 field: M 67 (NGC 2682)
• Lithium depletion is a strong test of core-envelope recoupling
• Close binary stars in the solar-age Galactic open cluster M67
• Photometric variability in the old open cluster M 67. II. General Survey
• A PSF-based approach to Kepler/K2 data - III. Search for exoplanets and variable stars within the open cluster M 67 (NGC 2682)
• Kinematic parameters and membership probabilities of open clusters in the Bordeaux PM2000 catalogue
• $uvby-H_{\beta }$ CCD photometry and membership segregation of the open cluster NGC2682 (M67)
• MOST satellite photometry of stars in the M67 field: Eclipsing binaries, blue stragglers and delta-Scuti variables
• Orbital and physical parameters of eclipsing binaries from the ASAS catalogue -- II. Two spotted M < 1 M${}_{\odot }$ systems at different evolutionary stages
• No "Maunder minimum" candidates in M67: mitigating interstellar contamination of chromospheric emission lines
• Multi-site campaign on the open cluster M67. I. Observations and photometric reductions

Cited by in corpus (8)

• MINESweeper: Spectrophotometric Modeling of Stars in the Gaia Era
• A 4 Gyr M-dwarf Gyrochrone from CFHT/MegaPrime Monitoring of the Open Cluster M67
• Testing systematics of Gaia DR2 parallaxes with empirical surface brightness -- color relations applied to eclipsing binaries
• Testing Models of Stellar Structure and Evolution I. Comparison with Detached Eclipsing Binaries
• WIYN Open Cluster Study. LXXVII. Radial-Velocity Measurements and Spectroscopic Binary Orbits in the Open Cluster NGC 7789
• Discovery and characterisation of long-period eclipsing binary stars from Kepler K2 campaigns 1, 2 and 3
• The K2 M67 Study: Precise Mass for a Turnoff Star in the Old Open Cluster M67
• Rotation of Kepler field dwarfs and sub giants: Spectroscopic $v\sin I$ from APOGEE