The age and distance of the Kepler open cluster NGC 6811 from an eclipsing binary, turnoff star pulsation, and giant asteroseismology. (2016)
Keywords :
asteroseismology; binaries eclipsing; binaries: spectroscopic; open clusters and associations: individual: NGC 6811; stars: distances; stars: variables: delta Scuti
Abstract:We present the analysis of an eccentric, partially eclipsing long-period (P=19.23 days) binary system KIC 9777062 that contains main-sequence stars near the turnoff of the intermediate-age open cluster NGC 6811. The primary is a metal-lined Am star with a possible convective blueshift to its radial velocities, and one star (probably the secondary) is likely to be a {gamma} Dor pulsator. The component masses are 1.603+/-0.006(stat.)+/-0.016(sys.) and 1.419+/-0.003+/-0.008M_{sun}_, and the radii are 1.744+/-0.004+/-0.002 and 1.544+/-0.002+/-0.002R_{sun}_. The isochrone ages of the stars are mildly inconsistent: the age from the mass-radius combination for the primary (1.05+/-0.05+/-0.09Gyr, where the last quote was systematic
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Long-cadence (30 minutes of exposure time) data were recorded for
KIC9777062 during the entire 17-quarter duration of the main Kepler
mission. In addition, short-cadence (1 minute of exposure time)
observations were taken during six different month-long periods within
quarters 4 (Dec 2009), 10 (June 2011), and 14 (June 2012).
In order to obtain color information for the binary, we obtained
eclipse photometry in BVIc using the Mount Laguna Observatory (MLO) 1m
telescope spanning 2012 Jun 2 to 2014 Aug 11.
Spectroscopic observations for KIC 9777062 were obtained at the
Hobby-Eberly Telescope (HET) with the High Resolution Spectrograph
(HRS) (R=60000; 4825-6750{AA}), the Nordic Optical Telescope (NOT)
Fibre-fed Echelle Spectrograph (FIES) (R=67000; 3700-7300{AA}), and
the MMT Hectoechelle (R=45000; 5150-5300{AA}).
To make the most effective use of the information in the CMD, we have
vetted cluster members using proper motions and radial velocities from
the literature where possible. We have attempted to use a uniform set
of photometry covering as much of the field as possible, using the
Janes+ (2013, J/AJ/145/7) data set supplemented for a few stars with
Glushkova+ (1999, J/PAZh/25/115) photometry as well as our own.
See section 4 for further explanations.
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