We report time-series photometry for 16 variable stars located in the central part of the globular cluster NGC 6752. The sample includes 13 newly identified objects. The precision of our differential photometry ranges from 1 mmag at V = 14.0 mag to 10 mmag at V = 18.0 mag. We detected four low amplitude variables located on the extended horizontal branch (EHB) of the cluster. They are candidate binary stars harboring sdB subdwarfs. A candidate degenerate binary was detected about 2 mag below the faint end of the EHB. The star is blue and its light curve is modulated with a period of 0.47 d. We argue that some of the identified variable red/blue stragglers are ellipsoidal binaries harboring degenerate stars. They have low amplitude sine-like light curves and periods from a few hours to a few days. Spectroscopic observations of such objects may lead to the detection of detached inactive binaries harboring stellar mass black holes or neutron stars. No binaries of this kind are known so far in globular clusters although their existence is expected based on the common occurrence of accreting LMXBs and millisecond pulsars. An eclipsing SB1 type binary was identified on the upper main sequence of the cluster. We detected variability of optical counterparts to two X-ray sources located in the core region of NGC 6752. The already known cataclysmic variable Bl=CX4 experienced a dwarf nova type outburst. The light curve of an optical counterpart to the X-ray source CX19 exhibited modulation with a period of 0.113 d. The same periodicity was detected in the HST-ACS data. The variable is located on the upper main sequence of the cluster. It is an excellent candidate for a close degenerate binary observed in quiescence.

Aims. Our aims are twofold. First we aim to evaluate the robustness and accuracy of stellar parameters and detailed elemental abundances that can be derived from high-resolution spectroscopic observations of microlensed dwarf and subgiant stars. We then aim to use microlensed dwarf and subgiant stars to investigate the abundance structure and chemical evolution of the Milky Way Bulge. Contrary to the cool giant stars, with their extremely crowded spectra, the dwarf stars are hotter, their spectra are cleaner, and the elemental abundances of the atmospheres of dwarf and subgiant stars are largely untouched by the internal nuclear processes of the star.

We present abundance analyses based on high dispersion and high signal-to-noise ratio Magellan spectra of two highly microlensed Galactic bulge stars in the region of the main-sequence turnoff with T-eff similar to 5650 K. We find that MOA-2008-BLG-310S has [Fe/H](8) = +0.41 +/- 0.09 dex and MOA-2008-BLG-311S has +0.26 +/- 0.09 dex. The abundance ratios for the similar to 20 elements for which features could be detected in the spectra of each of the two stars follow the trends with [Fe/H] found among samples of bulge giants. Combining these two bulge dwarfs with the results from previous abundance analysis of four other Galactic bulge turnoff region stars, all highly magnified by microlensing, gives a mean [Fe/H] of +0.29 dex. This implies that there is an inconsistency between the Fe-metallicity distribution of the microlensed bulge dwarfs and that derived by the many previous estimates based on surveys of cool, luminous bulge giants, which have mean [Fe/H] similar to -0.1 dex. A number of possible mechanisms for producing this difference are discussed. If one ascribes this inconsistency to systematic errors in the abundance analyses, we provide statistical arguments suggesting that a substantial systematic error in the Fe metallicity for one or both of the two cases, bulge dwarfs versus bulge giants, is required which is probably larger than can realistically be accommodated.

We present multi-epoch high-resolution optical spectroscopy, UV/radio/X-ray imaging, and archival Hubble and Spitzer observations of an intermediate luminosity optical transient recently discovered in the nearby galaxy NGC 300. We find that the transient (NGC 300 OT2008-1) has a peak absolute magnitude of M-bol approximate to -11.8 mag, intermediate between novae and supernovae, and similar to the recent events M85 OT2006-1 and SN 2008S. Our high-resolution spectra, the first for this event, are dominated by intermediate velocity (similar to 200-1000 km s(-1)) hydrogen Balmer lines and Ca II emission and absorption lines that point to a complex circumstellar environment, reminiscent of the yellow hypergiant IRC+10420. In particular, we detect asymmetric Ca II H&K absorption with a broad red wing extending to similar to 10(3) km s(-1), indicative of gas inflow at high velocity (possibly the wind of a massive binary companion). The low luminosity, intermediate velocities, and overall similarity to a known eruptive star indicate that the event did not result in a complete disruption of the progenitor. We identify the progenitor in archival Spitzer observations, with deep upper limits from Hubble data. The spectral energy distribution points to a dust-enshrouded star with a luminosity of about 6 x 10(4) L-circle dot, indicative of a similar to 10-20 M-circle dot progenitor (or binary system). This conclusion is in good agreement with our interpretation of the outburst and circumstellar properties. The lack of significant extinction in the transient spectrum indicates that the dust surrounding the progenitor was cleared by the outburst. We thus predict that the progenitor should be eventually visible with Hubble if the transient event marks an evolutionary transition to a dust-free state, or with Spitzer if the event marks a cyclical process of dust formation.

We report time-series photometry for 55 variable stars located in the central part of the globular cluster M55. The sample includes 28 newly identified objects of which 13 are eclipsing binaries. Three of these are detached systems located in the turn-off region on the cluster color magnitude diagram. Two of them are proper motion (PM) members of M55 and are excellent candidates for a detailed follow-up study aimed at a determination of the cluster age and distance. Other detached binaries are located along the unevolved part of the cluster main sequence. Most of the variable stars are cluster blue straggler stars. This group includes 35 SX Phe stars, two contact binaries, and one semi-detached binary. V60 is a low mass, short period Algol with the less massive and cooler component filling its Roche lobe. The more massive component is an SX Phe variable star. The orbital period of V60 increases at a rate of dP/P = 3.0 x 10(-9). In addition to numerous variable blue stragglers we also report the detection of two red stragglers showing periodic variability. Both of these are PM members of M55. We note and discuss the observed paucity of contact binaries among unevolved main sequence stars in M55 and NGC 6752. This apparent paucity supports an evolution model in which the formation of contact binaries is triggered by stellar evolution at the main-sequence turn off.

We have observed 9 bright metal-poor stars whose kinematics suggest they are members of a stellar stream in the vicinity of the Solar neighborhood. These 9 stars exhibit no star-to-star dispersion in their [X/Fe] ratios for the a and Fe-peak elements, and the neutron-capture elements suggest mild enrichment by the main r-process. The abundance patterns seen in this stream are very similar to those found in the metal-poor globular cluster M15, and the kinematics of M15 are similar to those of the stream, suggesting that these two groups of stars may have shared a common origin.

The Carnegie Planet Finder Spectrograph (PFS) has been commissioned for use with the 6.5 meter Magellan Clay telescope at Las Campanas Observatory in Chile. PFS is optimized for high precision measurements of stellar radial velocities to support an ongoing search for extrasolar planets. PFS uses an R4 echelle grating and a prism cross-disperser in a Littrow arrangement to provide complete wavelength coverage between 388 and 668 nm distributed across 64 orders. The spectral resolution is 38,000 with a 1 arcsecond wide slit. An iodine absorption cell is used to superimpose well-defined absorption features on the stellar spectra, providing a fiducial wavelength reference. Several uncommon features have been implemented in the pursuit of increased velocity stability. These include enclosing the echelle grating in a vacuum tank, actively controlling the temperature of the instrument, providing a time delayed integration mode to improve flatfielding, and actively controlling the telescope guiding and focus using an image of the target star on the slit. Data collected in the first five months of scientific operation indicate that velocity precision better than 1 m s(-1) RMS is being achieved.

We present new radial velocity (RV) measurements of the ultra-cool dwarf VB 10, which was recently announced to host a giant planet detected with astrometry. The new observations were obtained using optical spectrographs (MIKE/Magellan and ESPaDOnS/CFHT) and cover 65% of the reported period of 270 days. The nominal precision of the new Doppler measurements is about 150 m s(-1) while their standard deviation is 250 m s(-1). However, there are indications that such a larger variation is due to uncontrolled systematic errors. We apply least-squares periodograms to identify the most significant signals and evaluate their false alarm probabilities (FAPs). We show that this method is the proper generalization to astrometric data because (1) it mitigates the coupling of the orbital parameters with the parallax and proper motion, and (2) it permits a direct generalization to include nonlinear Keplerian parameters in a combined fit to astrometry and RV data. Our analysis of the astrometry alone uncovers the reported 270 day period and an even stronger signal at similar to 50 days. We estimate the uncertainties in the parameters using a Markov chain Monte Carlo approach. Although the new data alone cannot rule out the presence of a candidate, when combined with published RV measurements, the FAPs of the best solutions grow to unacceptable levels strongly suggesting that the observed astrometric wobble is not due to an unseen companion. The new measurements put an upper limit of m sin i similar to 2.5 m(jup) for a companion with a period shorter than one year and moderate eccentricities.

We report results from a survey of MgII absorbers in the spectra of background quasi-stellar objects (QSOs) that are within close angular distances to a foreground galaxy at z < 0.5, using the Magellan Echellette Spectrograph. We have established a spectroscopic sample of 94 galaxies at a median redshift of < z > = 0.24 in fields around 70 distant background QSOs (z(QSO) > 0.6), 71 of which are in an "isolated" environment with no known companions and located at rho less than or similar to 120 h(-1) kpc from the line of sight of a background QSO. The rest-frame absolute B-band magnitudes span a range from M(B) - 5 log h = -16.4 to M(B) - 5 log h = -21.4 and rest-frame B(AB) - R(AB) colors range from B(AB) - R(AB) approximate to 0 to B(AB) - R(AB) approximate to 1.5. Of these "isolated" galaxies, we find that 47 have corresponding MgII absorbers in the spectra of background QSOs and rest-frame absorption equivalent width W(r)(2796) = 0.1-2.34 angstrom, and 24 do not give rise to MgII absorption to sensitive upper limits. Our analysis shows that (1) W(r) (2796) declines with increasing distance from "isolated" galaxies but shows no clear trend in "group" environments; (2) more luminous galaxies possess more extended MgII absorbing halos with the gaseous radius scaled by B-band luminosity according to R(gas) = 75 x (L(B)/L(B))((0.35 +/- 0.03)) h(-1) kpc; (3) there is little dependence between the observed absorber strength and galaxy intrinsic colors; and (4) within R(gas), we find a mean covering fraction of approximate to 70% for absorbers of W(r)(2796) >= 0.3 angstrom and approximate to 80% for absorbers of W(r) (2796) >= 0.1 angstrom. The results confirm that extended MgII absorbing halos are a common and generic feature around ordinary galaxies and that the gaseous radius is a fixed fraction of the dark matter halo radius. The lack of correlation between W(r) (2796) strength and galaxy colors suggests a lack of physical connection between the origin of extended MgII halos and recent star formation history of the galaxies. Finally, we discuss the total gas mass in galactic halos as traced by MgII absorbers. We also compare our results with previous studies.

We study the connections between ongoing star formation, galaxy mass, and extended halo gas, in order to distinguish between starburst-driven outflows and infalling clouds that produce the majority of observed Mg II absorbers at large galactic radii (greater than or similar to 10 h(-1) kpc) and to gain insights into halo gas contents around galaxies. We present new measurements of total stellar mass (M-star), H alpha emission line strength (EW(H alpha)), and specific starformation rate (sSFR) for the 94 galaxies described by Chen et al.'s 2010 paper. We find that the extent of Mg II absorbing gas, R-Mg (II), scales with M-star and sSFR, following R-Mg (II) alpha M-star(0.28) x sSFR(0.11). The strong dependence of R-MgII on M-star is most naturally explained, if more massive galaxies possess more extended halos of cool gas and the observed Mg II absorbers arise in infalling clouds which will subsequently fuel star formation in the galaxies. The additional scaling relation of R-Mg (II) with sSFR can be understood either as accounting for extra gas supplies due to starburst outflows or as correcting for suppressed cool gas content in high-mass halos. The latter is motivated by the well-known sSFR-M-star inverse correlation in field galaxies. Our analysis shows that a joint study of galaxies and Mg II absorbers along common sight lines provides an empirical characterization of halo gaseous radius versus halo mass. A comparison study of R-Mg (II) around red- and blue-sequence galaxies may provide the first empirical constraint for resolving the physical origin of the observed sSFR-M-star relation in galaxies.