Bøger af Stanimir A Metchev

We present results from an adaptive optics survey conducted with thePalomar and Keck telescopes over 3 years, which measured the frequency ofstellar and sub-stellar companions to Sun-like stars. The survey samplecontains 266 stars in the 3-10000 million year age range atheliocentric distances between 8 and 200 parsecs and with spectral typesbetween F5-K5. A sub-sample of 101 stars, between3-500 million years old, were observed in deep exposures with acoronagraph to search for faint sub-stellar companions. A total of 288candidate companions were discovered around the sample stars, which werere-imaged at subsequent epochs to determine physical association with thecandidate host stars by checking for common proper motion. Benefitting froma highly accurate astrometric calibration of the observations, we wereable to successfully apply the common proper motion test in the majorityof the cases, including stars with proper motions as small as20 milli-arcseconds/year.The results from the survey include the discovery of three new brown dwarfcompanions (HD 49197B, HD 203030B, and ScoPMS 214B), 43 new stellar binaries,and a triple system. The physical association of an additional, apriori-suspected, candidate sub-stellar companion to the star HII 1348 isastrometrically confirmed. The newly-discovered and confirmed young browndwarf companions span a range of spectral types between M5 and T0.5, andwill be of prime significance for constraining evolutionary models ofyoung brown dwarfs and extra-solar planets.Based on the 3 new detections of sub-stellar companions in the 101 starsub-sample and following a careful estimate of the survey incompleteness,a Bayesian statistical analysis shows that the frequency of 0.012-0.072solar-mass brown dwarfs in 30-1600 AU orbits around young solar analogsis 6.8% (-4.9%, +8.3%; 2-sigma limits). While this is a factor of 3lower than the frequency of stellar companions to G-dwarfs in the sameorbital range, it is significantly higher than the frequency of browndwarfs in 0-3 AU orbits discovered through precision radial velocitysurveys. It is also fully consistent with the observed frequency of0-3 AU extra-solar planets. Thus, the result demonstrates that theradial-velocity "brown dwarf desert" does not extend to wideseparations, contrary to previous belief.