An imaging survey for extrasolar planets around 45 close, young stars with the simultaneous differential imager at the very large telescope and MMT

We present the results of a survey of 45 young (≲250 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. As part of the survey, we observed 54 objects, consisting of 45 close, young stars; two more distant (<150 pc), extremely young (≤ 10 Myr) stars; three stars with known radial velocity planets; and four older, very nearby (<20 pc) solar analogs. Our SDI devices use a double Wollaston prism and a quad filter to take images simultaneously at three wavelengths surrounding the 1.62 μan methane absorption bandhead found in the spectrum of cool brown dwarfs and gas giant planets. By differencing adaptive optics-corrected images in these filters, speckle noise from the primary star is significantly attenuated, resulting in photon (and flat-field)-noise-limited data. In our VLT data, we achieved H-band contrasts ≳; 10 mag (5 σ) at a separation of 0.5″ from the primary star on 45% of our targets and H-band contrasts ≲; 9 mag at a separation of 0.5″ on 80% of our targets. With these contrasts, we can image (5 σ detection) a 7 M _J planet 15 AU from a 70 Myr Kl star at 15 pc or a 7.8 M _J planet at 2 AU from a 12 Myr M star at 10 pc. We detected no candidates with S/N > 2 σ which behaved consistently like a real object. From our survey null result, we can rule out (with 93% confidence) a model planet population where N(a) ∝ constant out to a distance of 45 AU.