The field of the metal-rich open cluster NGC 6253 has been surveyed in a search for variable stars. A total of 25 new variables were detected, 14 of which are bright stars with 13 < V < 15 mag. This domain was not covered in an earlier work by de Marchi et al. (2010). Four variables, including three short-period eclipsing binaries, are candidate blue straggler stars. Two new detached eclipsing binaries at the turnoff of the cluster and another one on the subgiant branch were identified. These three systems deserve a detailed follow-up study aimed at a determination of the age and distance of NGC 6253. New photometry for 132 stars from the sample of de Marchi et al. (2010) is provided.

We present the first detailed analysis of the detached eclipsing binary V15 in the super-metal rich open cluster NGC 6253. We obtain the following absolute parameters: M-p = 1.303 +/- 0.006 M-circle dot, R-p = 1.71 +/- 0.03 R-circle dot, L-p = 2.98 +/- 0.10 L-circle dot for the primary, and M-s = 1.225 +/- 0.006 M-circle dot, R-s = 1.44 +/- 0.02 R-circle dot, L-s = 2.13 +/- 0.06 L-circle dot for the secondary. Based on Dartmouth isochrones, the age of NGC 6253 is estimated to be 3.80-4.25 Gyr from the mass radius diagram and 3.9-4.6 Gyr from color magnitude diagram fitting. Both of these estimates are significantly higher than those reported so far. The derived apparent distance modulus of 11.65 mag agrees well with the range of 10.9-12.2 mag derived by other authors; however our estimated reddening (0.113 mag) is lower than the lowest published value (0.15 mag). We confirm earlier observations that model atmospheres are not accurate enough to account for the whole CMD of the cluster, with the largest discrepancies appearing on the subgiant and giant branches. Although age estimation from the mass radius diagram is a relatively safe, distance- and reddening-independent procedure, our results should be verified by photometric and spectroscopic observations of additional detached eclipsing binaries which we have discovered, at least two of which are proper-motion members of NGC 6253.

A recent analysis comparing the [Na/Fe] distributions of red giant branch (RGB) and asymptotic giant branch (AGB) stars in the Galactic globular cluster NGC 6752 found that the ratio of Na-poor to Na-rich stars changes from 30: 70 on the RGB to 100: 0 on the AGB. The surprising paucity of Na-rich stars on the AGB in NGC 6752 warrants additional investigations to determine if the failure of a significant fraction of stars to ascend the AGB is an attribute common to all globular clusters. Therefore, we present radial velocities, [Fe/H], and [Na/Fe] abundances for 35 AGB stars in the Galactic globular cluster 47 Tucanae (47 Tuc; NGC 104), and compare the AGB [Na/Fe] distribution with a similar RGB sample published previously. The abundances and velocities were derived from high-resolution spectra obtained with the Michigan/Magellan Fiber System and MSpec spectrograph on the Magellan-Clay 6.5 m telescope. We find the average heliocentric radial velocity and [Fe/H] values to be < RVhelio.> = -18.56 km s(-1) (sigma = 10.21 km s-1) and <[Fe/H]> = -0.68 (sigma = 0.08), respectively, in agreement with previous literature estimates. The average [Na/Fe] abundance is 0.12 dex lower in the 47 Tuc AGB sample compared to the RGB sample, and the ratio of Na-poor to Na-rich stars is 63: 37 on the AGB and 45: 55 on the RGB. However, in contrast to NGC 6752, the two 47 Tuc populations have nearly identical [Na/Fe] dispersion and interquartile range values. The data presented here suggest that only a small fraction (less than or similar to 20%) of Na-rich stars in 47 Tuc may fail to ascend the AGB, which is a similar result to that observed in M13. Regardless of the cause for the lower average [Na/Fe] abundance in AGB stars, we find that Na-poor stars and at least some Na-rich stars in 47 Tuc evolve through the early AGB phase. The contrasting behavior of Na-rich stars in 47 Tuc and NGC 6752 suggests that the RGB [Na/Fe] abundance alone is insufficient for predicting if a star will ascend the AGB.

We present a homogeneous chemical abundance analysis of five of the most metal-poor stars in the Sculptor dwarf spheroidal galaxy. We analyze new and archival high resolution spectroscopy from Magellan/MIKE and VLT/UVES and determine stellar parameters and abundances in a consistent way for each star. Two of the stars in our sample, at [Fe/H] = -3.5 and [Fe/H] = -3.8, are new discoveries from our Ca K survey of Sculptor, while the other three were known in the literature. We confirm that Scl 07-50 is the lowest metallicity star identified in an external galaxy, at [Fe/H] = -4.1. The two most metal-poor stars both have very unusual abundance patterns, with striking deficiencies of the a elements, while the other three stars resemble typical extremely metal-poor Milky Way halo stars. We show that the star-to-star scatter for several elements in Sculptor is larger than that for halo stars in the same metallicity range. This scatter and the uncommon abundance patterns of the lowest metallicity stars indicate that the oldest surviving Sculptor stars were enriched by a small number of earlier supernovae, perhaps weighted toward high-mass progenitors from the first generation of stars the galaxy formed.

We report the discovery by the HATSouth survey of HATS-6b, an extrasolar planet transiting a V = 15.2 mag, i = 13.7 mag M1V star with a mass of 0.57 M-circle dot and a radius of 0.57 R-circle dot HATS-6b has a period of P = 3.3253 d, mass of M-p = 0.32 M-J, radius of R-p = 1.00 R-J, and zero-albedo equilibrium temperature of T-eq = 712.8 +/- 5.1 K. HATS-6 is one of the lowest mass stars known to host a close-in gas giant planet, and its transits are among the deepest of any known transiting planet system. We discuss the follow-up opportunities afforded by this system, noting that despite the faintness of the host star, it is expected to have the highest K-band S/N transmission spectrum among known gas giant planets with T-eq < 750 K. In order to characterize the star we present a new set of empirical relations between the density, radius, mass, bolometric magnitude, and V-, J-, H-and K-band bolometric corrections for main sequence stars with M < 0.80 M-circle dot, or spectral types later than K5. These relations are calibrated using eclipsing binary components as well as members of resolved binary systems. We account for intrinsic scatter in the relations in a self-consistent manner. We show that from the transit-based stellar density alone it is possible to measure the mass and radius of a similar to 0.6 M-circle dot star to similar to 7 and similar to 2% precision, respectively. Incorporating additional information, such as the V - K color, or an absolute magnitude, allows the precision to be improved by up to a factor of two.

The field of the globular cluster NGC 6362 was monitored between 1995 and 2009 in a search for variable stars. BV light curves were obtained for 69 periodic variable stars including 34 known RR Lyr stars, 10 known objects of other types and 25 newly detected variable stars. Among the latter we identified 18 proper-motion members of the cluster: seven detached eclipsing binaries (DEBs), six SX Phe stars, two W UMa binaries, two spotted red giants, and a very interesting eclipsing binary composed of two red giants - the first example of such a system found in a globular cluster. Five of the DEBs are located at the turnoff region, and the remaining two are redward of the lower main sequence. Eighty-four objects from the central 9 x 9 arcmin (2) of the cluster were found in the region of cluster blue stragglers. Of these 70 are proper motion (PM) members of NGC 6362 (including all SX Phe and two W UMa stars), and five are field stars. The remaining nine objects lacking PM information are located at the very core of the cluster, and as such they are likely genuine blue stragglers.

Exoplanets of a few Earth masses can be now detected around nearby low-mass stars using Doppler spectroscopy. In this Letter, we investigate the radial velocity variations of Kapteyn's star, which is both a sub-dwarf M-star and the nearest halo object to the Sun. The observations comprise archival and new HARPS (High Accuracy Radial velocity Planet Searcher), High Resolution Echelle Spectrometer (HIRES) and Planet Finder Spectrograph (PFS) Doppler measurements. Two Doppler signals are detected at periods of 48 and 120 d using likelihood periodograms and a Bayesian analysis of the data. Using the same techniques, the activity indices and archival All Sky Automated Survey (ASAS-3) photometry show evidence for low-level activity periodicities of the order of several hundred days. However, there are no significant correlations with the radial velocity variations on the same time-scales. The inclusion of planetary Keplerian signals in the model results in levels of correlated and excess white noise that are remarkably low compared to younger G, K and M dwarfs. We conclude that Kapteyn's star is most probably orbited by two super-Earth mass planets, one of which is orbiting in its circumstellar habitable zone, becoming the oldest potentially habitable planet known to date. The presence and long-term survival of a planetary system seem a remarkable feat given the peculiar origin and kinematic history of Kapteyn's star. The detection of super-Earth mass planets around halo stars provides important insights into planet-formation processes in the early days of the Milky Way.

The field of the globular cluster M12 (NGC 6218) was monitored between 1995 and 2009 in a search for variable stars. BV light curves were obtained for thirty-six periodic or likely periodic variable stars. Thirty-four of these are new detections. Among the latter we identified twenty propermotion members of the cluster: six detached or semi-detached eclipsing binaries, five contact binaries, five SX Phe pulsators, and three yellow stragglers. Two of the eclipsing binaries are located in the turnoff region, one on the lower main sequence and the remaining three among the blue stragglers. Two contact systems are blue stragglers, and the remaining three reside in the turnoff region. In the blue straggler region a total of 103 objects were found, of which 42 are proper motion members of M12, and another four are field stars. 55 of the remaining objects are located within two core radii from the center of the cluster, and as such they are likely genuine blue stragglers. We also report the discoveries of a radial color gradient of M12, and the shortest period among contact systems in globular clusters in general.

We present precise Doppler observations of WASP-47, a transiting planetary system featuring a hot Jupiter with both inner and outer planetary companions. This system has an unusual architecture and also provides a rare opportunity to measure planet masses in two different ways: the Doppler method, and the analysis of transit-timing variations (TTV). Based on the new Doppler data, obtained with the Planet Finder Spectrograph on the Magellan/Clay 6.5 m telescope, the mass of the hot Jupiter is 370 +/- 29 M-circle plus. This is consistent with the previous Doppler determination as well as the TTV determination. For the inner planet WASP-47e, the Doppler data lead to a mass of 12.2 +/- 3.7 M-circle plus, in agreement with the TTV-based upper limit of < 22 M-circle plus (95% confidence). For the outer planet WASP-47d, the Doppler mass constraint of 10.4 +/- 8.4 M-circle plus is consistent with the TTV-based measurement of 15.2(-7.6)(+6.7) M-circle plus.

We use photometric and spectroscopic observations of the detached eclipsing binaries V40 and V41 in the globular cluster NGC 6362 to derive masses, radii, and luminosities of the component stars. The orbital periods of these systems are 5.30 and 17.89 days, respectively. The measured masses of the primary and secondary components (M-p, M-s) are (0.8337 +/- 0.0063, 0.7947 +/- 0.0048) M-circle dot for V40 and (0.8215 +/- 0.0058, 0.7280 +/- 0.0047) M-circle dot for V41. The measured radii (R-p, R-s) are (1.3253 +/- 0.0075, 0.997 +/- 0.013) R-circle dot for V40 and (1.0739 +/- 0.0048, 0.7307 +/- 0.0046) R-circle dot for V41. Based on the derived luminosities, we find that the distance modulus of the cluster is 14.74 +/- 0.04 mag-in good agreement with 14.72 mag obtained from color-magnitude diagram (CMD) fitting. We compare the absolute parameters of component stars with theoretical isochrones in mass-radius and mass-luminosity diagrams. For assumed abundances [Fe/H] = -1.07, [alpha/Fe] = 0.4, and Y = 0.25 we find the most probable age of V40 to be 11.7 +/- 0.2 Gyr, compatible with the age of the cluster derived from CMD fitting (12.5 +/- 0.5 Gyr). V41 seems to be markedly younger than V40. If independently confirmed, this result will suggest that V41 belongs to the younger of the two stellar populations recently discovered in NGC 6362. The orbits of both systems are eccentric. Given the orbital period and age of V40, its orbit should have been tidally circularized some +/- 7 Gyr ago. The observed eccentricity is most likely the result of a relatively recent close stellar encounter.