Exoplanets
The main theme of my research is the detection and characterization of extrasolar planetary systems. I enjoy doing research on a wide range of problems in the extrasolar planets field, both in theory and observations.
Planets in binary and multiple star systems
The most massive short period planets (P < 40 days) orbit stars from binary stellar systems. Altogether, among ~200 extrasolar planets discovered with the spectroscopic precision radial velocity (RV) technique close to 30 belong to stars which have also stellar companions. It is quite surprising given that binary stars with separations smaller than ~2 arcsec have been excluded from the surveys. The stars from binary stellar systems known to harbor planets have a distant (widely separated in the sky) and/or faint stellar companion which does not contaminate the primary star spectrum and makes precision RV measurements much easier. The theories of planet formation in binary or multiple stellar systems are still at early stages but such planets once formed would enjoy a wide range of dynamically stable orbits. The subject of planet formation in binary stellar system is an important issue not only because the frequency of binaries among field stars older than 1 Gyr is ~60% and is even higher among pre main-sequence stars. If we believe that the same basic processes lead to the formation of planets around single and components of binary stars, then such processes should be equally feasible regardless of the presence of stellar companions. Therefore planets from close binary stellar systems may supply strong constraints on planet formation scenarios in general.
The molecular iodine (I2) absorption cell technique is the most common way to obtain precision RV observations. In this technique a star is observed through an I2 gas cell which superimposes a dense set of narrow absorption lines onto a stellar spectrum and provides a fiducial wavelength scale against which the Doppler shifts and hence velocities are measured. The I2 technique as is currently practiced fails for spectroscopic binary stars. However, I have developed a novel technique employing an I2 absorption cell that enables me to accurately determine radial velocities of both components of double-lined binaries. With this technique in 2003, I have initiated a survey for planets in binary and multiple stellar systems with the high resolution echelle spectrograph (HIRES) on the Keck I 10-m telescope at the W.M. Keck Observatory (Hawaii). In 2006, I have relocated the survey to the 3.5-m TNG telescope (Canary Islands) equipped with the SARG spectrograph.
My detections of extrasolar planets in binary and multiple star systems:
HD188753Ab, announced on July 14, 2005
Transiting giant planets
The discovery of hot Jupiters and successful detection of the transit of HD 209458b motivated a number of systematic transit monitoring programs. However, the photometric observations alone cannot distinguish between Jupiter size planets, brown dwarfs and late type M dwarfs since they all have similar radii (few tenths of solar radius). Therefore, in order to actually detect a transiting planets one needs to measure radial velocities of the candidates and determine the nature of their companions. To this end, together with my colleagues from Harvard/CfA, Guillermo Torres and Dimitar Sasselov, and collaborators from allover the world I carry out spectroscopic observations of the candidates using various spectrographs and telescopes.
More on our detections of transiting Jupiters:
OGLE-TR-56b, announced on January 6, 2003
OGLE-TR-113b, announced on April 27, 2004
OGLE-TR-10b, announced on December 15, 2004
Pulsar planets
The planetary system around the millisecond pulsar B1257+12 is the first ever discovered (1992) although rarely being mentioned in the professional literature these days. I have been studying this peculiar system since my grad school.
Read more on the PSR B1257+12 planetary system.
