Exoplanet atmospheres

Abstract:

The SINFONI1 project combines the MPE cryogenic near-infrared imaging spectrometer SPIFFI2 with an ESO adaptive-optics system on the ESO-VLT to perform high spatial and spectral resolution studies of compact objects. This paper describes the optical design of SPIFFI and the novel techniques used in building its integral-field unit.The image slicer comprises of a bundle of 1024 silica/silica fibers, where each fiber tip is flared to increase the core diameter by a factor of 15. The tapered end is polished to form a spherical microlens with a hexagonal cross-section to couple Light into the optical fiber. This not only yields a high light-coupling efficiency and a high geometrical filling factor but also allows us to use the fiber bundle at a working temperature of 77 K without losing positioning accuracy.

Abstract:

SPIFFI (SPectrometer for Infrared Fibre-fed Field Imaging) is an integral field spectrograph with an HAWAII array that enables us to simultaneously take near infrared spectra of 1024 spatial pixels in an hexagonal field of view on the sky. It can be used on 4 to 8 meter class telescopes with a maximum pixel scale of 0.5 arcsec and with adaptive optics pixel scales, Nyquist sampling the point spread function of the telescope.A fiber bundle of 1024 silica/silica fibers rearranges the two-dimensional field of view into the one-dimensional entrance slit of the spectrometer. A novel technique involving flared fibers is used to achieve a high filling factor and coupling efficiency. Each fiber tip in the bundle is flared to increase the fiber core diameter by a factor of 15. The tapered end is polished to form a spherical micro-lens with a hexagonal cross-section to couple light into the fiber core. Apart from yielding a high coupling efficiency and a high geometrical filling factor, the monolithic micro-lens/fiber system can be used at a working temperature of 77 K without loosing positioning accuracy.The spectrometer optics is achromatic from 1.1 to 2.5 microns and uses four reflection gratings on a wheel as dispersing elements with a resolving power from 2000 to 4500. The fore-optics includes the filter wheel, the cold pupil stop and a scale changing mechanism to switch between three different image scales according to observing and seeing conditions. The spectrometer collimator is a f/4.3 three lens achromat, the spectrometer camera is a f/1.2 folded Schmidt camera. The optical design of the spectrometer is distortion free to get straight, equidistant spectra that match the columns of the detector, thus minimizing cross-talk from adjacent spectra to less than 5%.

Abstract:

Portions of the far-infrared spectra of Jupiter and Saturn measured in grating mode with the ISO Long Wavelength Spectrometer (LWS) are presented. The observed Jovian spectrum between 55 and 90 μm is compared to an atmospheric radiative transfer model using expected values for the constituent vertical concentration profiles. Rotational transitions of ammonia are responsible for the absorption features observed against the hydrogen continuum emission. There is good agreement between the model and data for an ammonia mole fraction of 2×10-4 constrained by saturation up to a 75 mbar cut-off, above which it is assumed all the ammonia is destroyed by ultraviolet radiation. Three sections of the saturnian spectrum are compared to synthetic spectra and absorption features due to methane are identified. The mole fraction of methane is constrained between 0.7-1.5 10-3.

Abstract:

Geomorphic evidence that Mars was warm enough to support flowing water about 3.8 billion years ago presents a continuing enigma that cannot be explained by conventional greenhouse warming mechanisms. Model calculations show that the surface of early Mars could have been warmed through a scattering variant of the greenhouse effect, resulting from the ability of the carbon dioxide ice clouds to reflect the outgoing thermal radiation back to the surface. This process could also explain how Earth avoided an early irreversible glaciation and could extend the size of the habitable zone on extrasolar planets around stars.