Beth Biller
IfA - Hawaii
 

"An Imaging Survey for Extrasolar Planets around 45 Close, Young Stars with SDI at the VLT and MMT"
 

We present the results of a survey of young (<=300 Myr), close (<=50 pc) stars with the Simultaneous Differential Imager (SDI) implemented at the VLT and the MMT for the direct detection of extrasolar planets. Our SDI devices use a double Wollaston prism and a quad filter to take images simultaneously at 3 wavelengths surrounding the 1.62 um methane absorption bandhead found in the spectrum of cool brown dwarfs and gas giant planets. By performing a difference of adaptive optics corrected images in these filters, speckle noise from the primary star can be significantly attenuated, resulting in photon (and flat-field) noise limited data. In our VLT data, we achieved H band contrasts >= 10 mag (5 sigma) at a separation of 0.5 from the primary star on 45% of our targets and H band contrasts of <= 9 mag at a separation of 0.5'' on 80% of our targets. With this degree of attenuation, we should be able to image (5 sigma detection) a 5 MJup planet 15 AU from a 70 Myr K1 star at 15 pc. We have obtained datasets for 54 stars. 45 stars were observed in the southern sky at the VLT and 11 stars were observed in the northern sky at the MMT (2 stars were observed at both telescopes). We believe that our SDI images are the highest contrast astronomical images ever made from ground or space for methane rich companions. We detected no tentative candidates with S/N > 2 sigma. Followup observations were conducted on 8 < 2 sigma candidates (with separations of 3 - 15.5 AU and masses of 2-10 MJup, had they been real) -- none of which were detected at a second epoch. For the best 20 of our survey stars, we attained 50% completeness for 6-10 MJup planets at semi-major axes of 20-40 AU. Thus, our completeness levels are sufficient to significantly test theoretical planet distributions.  We also discuss preliminary results of an experiment at the High Contrast Imaging Testbed at JPL using a similar SDI multiwavelength differential imaging scheme bracketing the Oxygen (A)  telluric absorption feature at 0.762 um.