We present a calibration of the metallicity and physical parameters (temperature, luminosity, gravity, mass, radius) for RR Lyrae stars using the ugriz SDSS photometric system. Our work is based on calculations of synthetic horizontal branches (HBs),
fully taking into account evolutionary effects for a wide range in metallicities and HB morphologies. We provide analytical fits that are able to provide all quantities mentioned with very high (internal) precision, based solely on mean SDSS magnitudes and colors.
Secondary eclipses are a powerful tool to measure directly the thermal emission from extrasolar planets, and to constrain their type and physical parameters. We started a project to obtain reliable broad-band measurements of the thermal emission of t
ransiting exoplanets. Ground-based high-cadence near-infrared relative photometry was used to obtain sub-millimagnitude precision light curve of a secondary eclipse of WASP-4b -- a 1.12 M_J hot Jupiter on a 1.34 day orbit around G7V star. The data show a clear ~10-sigma detection of the planets thermal emission at 2.2 mu m. The calculated thermal emission corresponds to a fractional eclipse depth of 0.185^{+0.014}_{-0.013}%, with a related brightness temperature in Ks of T_B = 1995 pm 40 K, centered at T_C = 2455102.61162^{+0.00071}_{-0.00077} HJD. We could set a limit on the eccentricity of e cos omega=0.0027 pm 0.0018, compatible with a near-circular orbit. The calculated brightness temperature, as well as the specific models suggest a highly inefficient redistribution of heat from the day-side to the night-side of the planet, and a consequent emission mainly from the day-side. The high-cadence ground-based technique is capable of detecting the faint signal of the secondary eclipse of extrasolar planets, making it a valuable complement to space-based mid-IR observations.
Currently the only technique sensitive to Earth mass planets around nearby stars (that are too close for microlensing) is the monitoring of the transit time variations of the transiting extrasolar planets. We search for additional planets in the syst
ems of the hot Neptune GJ 436b, and the hot-Jupiter XO-1b, using high cadence observations in the J and Ks bands. New high-precision transit timing measurements are reported: GJ 436b Tc = 2454238.47898 pm 0.00046 HJD; XO-1b Tc(A) = 2454218.83331 pm 0.00114 HJD, Tc(B) = 2454222.77539 pm 0.00036 HJD, Tc(C) = 2454222.77597 pm 0.00039 HJD, Tc(D) = 2454226.71769 pm 0.00034 HJD, and they were used to derive new ephemeris. We also determined depths for these transits. No statistically significant timing deviations were detected. We demonstrate that the high cadence ground based near-infrared observations are successful in constraining the mean transit time to ~30 sec., and are a viable alternative to space missions.
