A High Contrast Survey for Extrasolar Giant Planets with the Simultaneous Differential Imager (SDI)

Abstract

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. Our SDI devices use a double Wollaston prism and a quad filter to take images simultaneously at three wavelengths surrounding the 1.62 um methane absorption bandhead found in the spectrum of cool brown dwarfs and extrasolar 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 7 MJup planet 15 AU from a 70 Myr K1 star at 15 pc or a 7.8 MJup planet at 2 AU from a 12 Myr M star at 10 pc. Using the capabilities of the unique SDI device, we also discovered a methane-rich substellar companion to SCR 1845-6357 (a recently discovered (Hambly et al., 2004) M8.5 star just 3.85 pc from the Sun (Henry et al., 2006) at a separation of 4.5 AU (1.170''+-0.003'' on the sky) and fainter by 3.57$\pm$0.057 mag in the 1.575 um SDI filter.We also present high resolution (~0.1''), very high Strehl ratio (0.97+-0.03) mid-infrared (IR) adaptive optics (AO) images of the AGB star RV Boo utilizing the MMT adaptive secondary AO system. RV Boo was observed at a number of wavelengths over two epochs and appeared slightly extended at all wavelengths. With such high Strehls we can achieve super-resolutions of 0.1'' by deconvolving RV Boo with a point-spread function (PSF) derived from an unresolved star.SDI on ground based telescopes provides significant speckle attenuations down to star-planet contrasts of ~1-3x10^4. To test the classical SDI technique at contrasts of 10^6-9, we implemented a similar multiwavelength differential imaging scheme for the JPL High Contrast Imaging Testbed.