Earth-sized planets in the habitable zones of M dwarfs are good candidates for the study of habitability and detection of biosignatures. To search for these planets, we analyze all available radial velocity data and apply four signal detection criteria to select the optimal candidates. We find 10 strong candidates satisfying these criteria and three weak candidates showing inconsistency over time due to data samplings. We also confirm three previous planet candidates and improve their orbital solutions through combined analyses of updated data sets. Among the strong planet candidates, HIP 38594 b is a temperate super-Earth with a mass of 8.2 1.7M(circle plus)and an orbital period of 60.7 0.1 days, orbiting around an early-type M dwarf. Early-type M dwarfs are less active and thus are better hosts for habitable planets than mid-type and late-type M dwarfs. Moreover, we report the detection of five two-planet systems, including two systems made up of a warm or cold Neptune and a cold Jupiter, consistent with a positive correlation between these two types of planets. We also detect three temperate Neptunes, four cold Neptunes, and four cold Jupiters, contributing to a rarely explored planet population. Due to their proximity to the Sun, these planets on wide orbits are appropriate targets for direct imaging by future facilities such as the Habitable Exoplanet Observatory and the Extremely Large Telescope.

We report the discovery of two transiting Neptunes by the HATSouth survey. The planet HATS-37Ab has a mass of 0.099 +/- 0.042 MJ (31.5.+/-.13.4M(circle dot)) and a radius of 0.606 +/- 0.016 R-J, and is on a P = 4.3315 day orbit around a V = 12.266 +/- 0.030 mag, 0.843(-0.012)(+0.017)M(circle dot) star with a radius of 0.877(-0.012)(+0.019) R-circle dot We also present evidence that the star HATS-37A has an unresolved stellar companion HATS-37B, with a photometrically estimated mass of 0.654 +/- 0.033.M-circle dot The planet HATS-38b has a mass of 0.074. 0.011MJ (23.5 +/- 3.5M(circle dot)) and a radius of 0.614 +/- 0.017 R-J, and is on a P = 4.3750 day orbit around a V = 12.411 +/- 0.030 mag, 0.890(-0.012)(+0.016) M-circle dot star with a radius of 1.105 +/- 0.016.R-circle dot Both systems appear to be old, with isochrone-based ages of 11.46(-1.45)(+0.79) Gyr, and 11.89 +/- 0.60 Gyr, respectively. Both HATS-37Ab and HATS-38b lie in the Neptune desert and are thus examples of a population with a low occurrence rate. They are also among the lowest-mass planets found from ground-based wide-field surveys to date.

We report the detection of 20 new variables in the field of NGC 3201. Among them there are 15 confirmed cluster members. Follow-up observations are desirable for two blue stragglers with variable light curves (probably resulting frommagnetic activity), and for a yellow straggler coinciding with a Chandra X-ray source. Two of the eclipsing binaries, newly detected at the turnoff in cluster's CMD, and an eclipsing binary on the red giant branch, are potentially suitable for the determination of age and distance of NGC 3201.

This paper presents a survey of Mgii absorbing gas in the vicinity of 380 random galaxies, using 156 background quasi-stellar objects (QSOs) as absorption-line probes. The sample comprises 211 isolated (73 quiescent and 138 star-forming galaxies) and 43 non-isolated galaxies with sensitive constraints for both Mgii absorption and H alpha emission. The projected distances span a range from d = 9 to 497 kpc, redshifts of the galaxies range from z = 0.10 to 0.48, and rest-frame absolute B-band magnitudes range from M-B = -16.7 to -22.8. Our analysis shows that the rest-frame equivalent width of Mgii, W-r(2796), depends on halo radius (R-h), B-band luminosity(L-B), and stellar mass (M-star) of the host galaxies, and declines steeply with increasing d for isolated, star-forming galaxies. At the same time, W-r(2796) exhibits no clear trend for either isolated, quiescent galaxies or non-isolated galaxies. In addition, the covering fraction of Mgii absorbing gas kappa is high with kappa greater than or similar to 60 percent at <40 kpc for isolated galaxies and declines rapidly to kappa approximate to 0 at d greater than or similar to 100 kpc. Within the gaseous radius, the incidence of Mgii gas depends sensitively on both M-star and the specific star formation rate inferred from H alpha. Different from what is known for massive quiescent haloes, the observed velocity dispersion of Mgii absorbing gas around star-forming galaxies is consistent with expectations from virial motion, which constrains individual clump mass to and cool gas accretion rate of . Finally, we find no strong azimuthal dependence of Mgii absorption for either star-forming or quiescent galaxies. Our results demonstrate that multiple parameters affect the properties of gaseous haloes around galaxies and highlight the need of a homogeneous, absorption-blind sample for establishing a holistic description of chemically enriched gas in the circumgalactic space.

We present 87 candidates for RR Lyrae variable stars in binary systems, based on our new search using the light-travel time effect (LTTE) and observed - calculated (O - C) diagrams in the Galactic bulge time-series photometry of the Optical Gravitational Lensing Experiment. Out of these, 61 are new candidates, while 26 have been announced previously. Furthermore, 12 stars considered as binary candidates in earlier works are discarded from the list, either because they were found to have O - C diagrams incompatible with the LTTE or because their long-term periodicity is definitely caused by the Blazhko effect. This sample of RR Lyrae binary candidates allows us to draw the first firm conclusions about the population of such objects: no candidate has an orbital period below 1000 days, while their occurrence rate steadily increases with increasing period, and peaks between 3000 and 4000 days; however, the decrease in the number of stars toward even longer periods is probably the result of observational biases. The eccentricities show a very significant concentration between 0.25 and 0.3, with a quarter of candidates found in this single bin, overlaid on an otherwise flat distribution between 0.05 and 0.6. Only six stars have inferred eccentricities above 0.6. Lastly, the distribution of the mass functions is highly peculiar, exhibiting strong trimodality. We interpret these modes as the presence of three distinct groups of companions, with typical inferred masses of similar to 0.6, similar to 0.2, and similar to 0.067 M (circle dot), which can be associated with populations of white dwarf and main sequence, red dwarf, and brown dwarf companions, respectively.

The results of 23 km s-1 resolution echelle spectroscopy of the Lyman forest region of the z = 3.38 QSO 0014 + 813 are described. Voigt profile fits to the Lyman series absorption lines yield H i column density and Doppler parameter distributions similar to those obtained in three previous studies of other objects. There is no evidence so far of significant changes of the behavior of these distributions with redshift, except for the number of systems per unit redshift which, for log N(H I) > 13.75 (cgs), is proportional to (1 + Z)2.1 +/- 0.5. We find no evidence for a correlation between the Doppler parameter and column density and show that an apparent correlation is due entirely to selection effects of line detection and fitting. While the Lyman forest systems as a whole show no clustering, there appears to be a population of weak, narrow-lined systems which show clustering on scales of less than or similar to 1000 km s-1. It is not clear if these are unidentified heavy element lines or a genuine Lyman forest component. A simple test for voids along the sight line to 0014 + 813 proved negative. However, applying the same test to the spectrum of 0420-388 reveals a 24 Mpc region where the line number density is significantly below the mean. The depletion is unlikely to be due to a single nearby ionization source.

We attempt to resolve the controversy concerning the minimum temperature of Ly alpha clouds. The results by Pettini et al. are scrutinized, namely that Ly alpha absorption lines have Doppler parameters with a median of about 17 km s-1, values below 10 km s-1, and that there is a strong intrinsic correlation between Doppler parameter and column density.

The H I column density distribution function of QSO absorption line systems is investigated using recent data with high spectral resolution, and extensive surveys of the Lyman limit systems and damped Ly alpha systems.

We present high spectral resolution (R similar to 15 000) and high signal to noise ratio (20-50) of two z(em) similar to 2 quasars PKS 0424-131 and Q 0450-131 in the wavelength range 370-510 nm.

We discuss a method to detect or put upper limits on our motion relative to a rest frame provided by point sources at high redshift, and we apply the technique to real and artificial redshift surveys of intergalactic gas clouds (Lyman alpha absorption systems). The redshift regime that can be sampled this way extends from z approximately 0 (UV observations) right up to the redshifts of the most distant QSO (z approximately 5 at present). The detection of our motion with respect to this high-z frame is based on the direction-dependent changes in the number of objects per redshift interval, as induced by the Doppler effect. The presently available data samples (not optimal for our purpose) enable us to establish an upper limit upsilon/c < 0.05 for the motion of the Solar system relative to the Ly alpha forest at mean redshift = 2.9.