We present radial velocities and metallicities for a sample of 39 open clusters with ages greater than about 700 million years. For 24 clusters new moderate-resolution spectroscopic data obtained with multiobject spectrographs on the Kitt Peak National Observatory and the Cerro Tololo Inter-American Observatory 4 m telescopes are used to determine radial velocities and mean cluster metallicities. These new results are combined with data published previously by Friel & Janes to provide a sample of 459 giants in 39 old open clusters, which are used to investigate radial abundance gradients in the Galactic disk. Based on an updated abundance calibration of spectroscopic indices measuring Fe and Fe-peak element blends, this larger sample yields an abundance gradient of À0.06 AE 0.01 dex kpc À1 over a range in Galactocentric radius of 7 to 16 kpc. There is a slight suggestion of a steepening of the abundance gradient with increasing cluster age in this sample, but the significance of the result is limited by the restricted distance range for the youngest clusters. The clusters show no correlation of metallicity with age in the solar neighborhood. Consistent with the evidence for a steepening of the gradient with age, the clusters in the outer disk beyond 10 kpc show a suggestion at the 1.5 level of a dependence of metallicity on age.

We present a CCD photometric survey of the central one-half degree of the old open cluster, M67, in U, B, V, and I colors to magnitude V=20. Extensive comparison of our photometry with other published datasets shows excellent agreement, indicating that CCD photometry is capable of producing a uniform set of measurements consistent with the photometric system defined primarily by the Landolt standard sequence. The color-magnitude diagram of the cluster shows a well-defined main sequence extending at least to the limit of the photometry at Mv=10.55 and a substantial binary sequence. At least 38% of cluster stars are binaries. The current generation of theoretical isochrones cannot be fit to the observed sequences with the observational errors. We find a tendency for more massive members of the cluster to be more centrally concentrated, along with a turnover in the cluster luminosity function at low masses, which may be due to dynamical relaxation of the cluster. To the limit of our photometry, we find a mass of the cluster of 724 solar masses. In addition, we present a sample of stars of well-determined standard magnitudes that are suitable as photometric standards for further studies of this cluster and for general calibration of UBVI photometry using CCDs.

We present rotation periods for 71 single dwarf members of the open cluster NGC 6811 determined using photometry from NASA's Kepler Mission. The results are the first from The Kepler Cluster Study which combine Kepler's photometry with ground-based spectroscopy for cluster membership and binarity. The rotation periods delineate a tight sequence in the NGC 6811 color-period diagram from ∼1 day at mid-F to ∼11 days at early-K spectral type. This result extends to ∼1 Gyr similar prior results in the ∼600 Myr Hyades and Praesepe clusters, suggesting that rotation periods for cool dwarf stars delineate a welldefined surface in the 3-dimensional space of color (mass), rotation, and age. It implies that reliable ages can be derived for field dwarf stars with measured colors and rotation periods, and it promises to enable further understanding of various aspects of stellar rotation and activity for cool stars.

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We report on a V ¼ 11:2 early K dwarf, , that hosts a R p ¼ 0:98AE 0:03 0:01 R J , M p ¼ 0:57 AE 0:06 M J transiting extrasolar planet, XO-2b, with an orbital period of 2:615857 AE 0:000005 days. XO-2 has high metallicity, ½Fe/H ¼ 0:45 AE 0:02, high proper motion, tot ¼ 157 mas yr À1 , and a common proper motion stellar companion with 31 00 separation. The two stars are nearly identical twins, with very similar spectra and apparent magnitudes. Due to the high metallicity, these early K dwarf stars have a mass and radius close to solar, M ? ¼ 0:98 AE 0:02 M and R ? ¼ 0:97AE 0:02 0:01 R . The high proper motion of XO-2 results from an eccentric orbit (Galactic pericenter, R per < 4 kpc) well confined to the Galactic disk (Z max $ 100 pc). In addition, the phase-space position of XO-2 is near the Hercules dynamical stream, which points to an origin of XO-2 in the metal-rich, inner thin disk and subsequent dynamical scattering into the solar neighborhood. We describe an efficient Markov chain Monte Carlo algorithm for calculating the Bayesian posterior probability of the system parameters from a transit light curve.