OPEN CLUSTERS IN THEKEPLERFIELD. II. NGC 6866

Abstract

We have developed a maximum-likelihood procedure to fit theoretical isochrones to the observed cluster color-magnitude diagrams of NGC 6866, an open cluster in the Kepler Spacecraft field of view. The Markov-Chain Monte Carlo algorithm permits exploration of the entire parameter space of a set of isochrones to find both the best solution and the statistical uncertainties. For clusters in the age range of NGC 6866, with few if any red giant members, a purely photometric determination of the cluster properties is not well-constrained. Nevertheless, based on our UBVRI photometry alone, we have derived the distance, reddening, age and metallicity of the cluster and established estimates for the binary nature and membership probability of individual stars. We derive the following values for the cluster properties: (m − M ) V = 10.98 ± 0.24, E(B − V ) = 0.16 ± 0.04 (so the distance = 1250 pc), age = 705 ± 170 Myr and Z = 0.014 ± 0.005.

THE AGE AND DISTANCE OF THE KEPLER OPEN CLUSTER NGC 6811 FROM AN ECLIPSING BINARY, TURNOFF STAR PULSATION, AND GIANT ASTEROSEISMOLOGY∗

“…Figure 14. Differences between the BV I C photometry of Janes et al (2013) and the present paper in the sense of (ours -theirs).…”

“…G99: Glushkova et al (1999). J13: Janes et al (2013). Hectoechelle, we find mean offsets of less than 0.1 km s −1 .…”

“…The authors found that the primary star implied a slightly Figure 15. Color-magnitude diagrams for stars in the NGC 6811 field in BV (top row) and V I C (bottom row) from Janes et al (2013) and this work. Stars with proper motion memberships Pµ > 50% in any of the three studies (Sanders 1971;Dias et al 2002;Kharchenko et al 2013) are shown with circles, and if proper motion membership is corroborated by radial velocities (Frinchaboy & Majewski 2008;Mermilliod & Mayor 1990;Molenda-Żakowicz et al 2014;Meibom et al 2011) the circle is filled.…”

“…We have attempted to use a uniform set of photometry covering as much of the field as possible, using the Janes et al (2013) dataset supplemented for a few stars with Glushkova et al (1999) photometry as well as our own. (The comparisons in §2.2 show that these datasets are have the same photometric zeropoints to within 0.02 mag.)…”

Strong evidences for a nonextensive behavior of the rotation period in open clusters

“…Accordingly, it can be stated that the minimum age for subextensivity falls within the range of the probable ages of NCG2516, namely between 60 and 270 Myr. On the other hand, if we consider the age of 1 Gyr for NGC6811, as determined by Janes et al [34], instead of 575 Myr, the age for the extensivity of rotation period distributions changes to only 560 Myr. Figure 2 shows how the inverse of the median rotation period changes over cluster ages, as well as the nonextensive model proposed by de Freitas & De Medeiros [15].…”