Showing papers by "Philip W. Lucas published in 2002"

A search for the infrared spectroscopic signature of hot Jupiter planets

Abstract: We present the results of an attempt to detect the hottest 'hot Jupiter' planets directly in the thermal infrared. A simple method based upon high signal-to-noise ratio spectroscopy of the central star at low spectral resolution is described. In the 2-4 μm region the contrast ratio between planet and star is expected to be relatively low and the planetary spectrum should appear as a faint signal on top of the stellar spectrum, distinguished by edges of H 2 O absorption. No water edges were found to 3a limits of one part in a few hundred in each case. These upper limits are compared with the irradiated planetary atmosphere models of Barman, Hauschildt & Allard to derive upper limits on the size of the hot Jupiters, which are expected to be somewhat larger than Jupiter. If reasonably strong H 2 O absorption occurs in these objects then typical upper limits of R < 3 R J u p are derived, the precision being limited by the stability of telluric transmission. Only a modest improvement in precision is needed (e.g. with space-based instruments) to reach the range of greatest interest (1 < R < 2 R J u p ).

Infrared Spectroscopy of Sub-Stellar Objects in Orion

Abstract: Near-infrared spectroscopy of a sample of 21 substellar objects in the Orion Trapezium cluster, with masses in the range 0.008–0.10 M⊙ is presented. Most of the targets are located away from the region of brightest nebulosity and have photometric colours that indicate low extinction (A(v) < 5 mag). All but one, of the low-mass candidates display deep water vapour absorption bands, confirming the low effective temperatures indicated by the (I-J) colours. Interestingly, the profiles of the water bands near 1.6 microns are quite distinct from those of field brown dwarf stars, providing convincing evidence that the Trapezium objects are not foreground or background objects. Furthermore, the 2.3 micron CO absorption bands and the 2.21 micron [NaI] absorption line are significantly weaker than field brown dwarfs with similar water absorption band depths. These spectral characteristics are quite well reproduced by the low surface gravity Ames-Dusty models of Allard et al, providing additional evidence that the Trapezium substellar candidates are young and recently- formed.