Alvio Renzini

Transiting extrasolar planetary candidates in the Galactic bulge

More than 200 extrasolar planets have been discovered around relatively nearby stars, primarily through the Doppler line shifts owing to reflex motions of their host stars, and more recently through transits of some planets across the faces of the host stars. The detection of planets with the shortest known periods, 1.2–2.5 days, has mainly resulted from transit surveys which have generally targeted stars more massive than 0.75u2009M[circdot], where M[circdot] is the mass of the Sun. Here we report the results from a planetary transit search performed in a rich stellar field towards the Galactic bulge. We discovered 16 candidates with orbital periods between 0.4 and 4.2 days, five of which orbit stars of masses in the range 0.44–0.75u2009M[circdot]. In two cases, radial-velocity measurements support the planetary nature of the companions. Five candidates have orbital periods below 1.0 day, constituting a new class of ultra-short-period planets, which occur only around stars of less than 0.88u2009M[circdot]. This indicates that those orbiting very close to more-luminous stars might be evaporatively destroyed or that jovian planets around stars of lower mass might migrate to smaller radii.

The Distance and Age of the Globular Cluster NGC6752 Measured by HST Observations of Cluster and Field White Dwarfs

We present first results of a new method for finding distances, hence ages, of Galactic Globular Clusters with a precision of about 10%. We measured the White Dwarfs cooling sequence in NGC6752 with the Hubble Space Telescope and, comparing it to a fiducial cooling sequence of field WDs we derive a distance modulus (m-M)0=13.05 ±0.10, and an age of about 15 Gyr (±1.5 Gyr).