On the possibility of ground-based direct imaging detection of extra-solar planets: The case of TWA-7

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We show that ground-based direct imaging detection of extra-solar planets is possible with current technology. As an example, we present evidence for a possible planetary companion to the young T Tauri star 1RXSJ104230.3-334014 (=TWA-7), discovered by ROSAT as a member of the nearby TW Hya association. In an HST NICMOS F160W image, an object is detected that is more than 9 mag fainter than TWA-7, located 2.445 ± 0.035′ ′ south-east at a position angle of 142.24 ± 1.34∘. One year later using the ESO-NTT with the SHARP speckle camera, we obtained H- and K-band detections of this faint object at a separation of 2.536 ± 0.077′ ′ and a position angle of 139.3 ± 2.1∘. Given the known proper motion of TWA-7, the pair may form a proper motion pair. If the faint object orbits TWA-7, then its apparent magnitudes of H=16.42 ± 0.11 and K=16.34 ± 0.15 mag yield absolute magnitudes consistent with a 10⁶.⁵ yr old 3 M jup mass object according to the non-gray theory by Burrows et al. (1997). At 55 pc, the angular separation of 2.5′ ′ corresponds to 138 AU. However, position angles and separations are slightly more consistent with a background object than with a companion.