Prof Patrick Roche

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 H2O absorption. No water edges were found to 3σ 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 H2O absorption occurs in these objects then typical upper limits of R < 3 RJup 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 RJup).

Abstract:

We present 8-13 μm spectropolarimetry, and 12- and 2-μm imaging polarimetry of the southern massive star-forming region G333.6-0.2. Spectropolarimetry measurements show that the polarization observed towards the nebula contains a mixture of both absorptive and emissive polarizations. Model fitting to the spectra indicates that the temperature of the mid-infrared emitting dust grains is generally ∼200 K and the optical depth of the absorbing dust at 9.7 μm is ∼ 1.5. Fits are also made to the polarimetry spectra, which show a reasonably constant peak absorptive polarization (∼3.4 per cent at 43°) across the face of the H II region. This absorptive polarization position angle is consistent with that found by the 2-μm imaging polarimetry (38° ± 6°) and is most likely due to the Galactic magnetic field local to G333.6-0.2. When the absorptive polarization is subtracted from the 12-μm polarization image, the emissive polarization pattern that is intrinsic to the star-forming region is revealed. A probable magnetic field configuration implied by the intrinsic polarization suggests star formation initially influenced by the Galactic magnetic field which is eventually perturbed by the star formation process.