The optical transmission spectrum of the hot Jupiter HAT-P-32b: Clouds explain the absence of broad spectral features?
Monthly Notices of the Royal Astronomical Society 436:4 (2013) 2974-2988
Abstract:
We report Gemini-North Gemini Multi-Object Spectrograph observations of the inflated hot Jupiter HAT-P-32b during two primary transits. We simultaneously observed two comparison stars and used differential spectrophotometry to produce multiwavelength light curves. 'White' light curves and 29 'spectral' light curves were extracted for each transit and analysed to refine the system parameters and produce transmission spectra from 520 to 930 nm in ̃ 14 nm bins. The light curves contain time-varyingwhite noise as well as time-correlated noise, and we used a Gaussian process model to fit this complex noise model. Common mode corrections derived from the white light-curve fits were applied to the spectral light curves which significantly improved our precision, reaching typical uncertainties in the transit depth of ̃ 2 × 10-4, corresponding to about half a pressure scale height. The low-resolution transmission spectra are consistent with a featureless model, and we can confidently rule out broad features larger than about one scale height. The absence of Na/K wings or prominent TiO/VO features is most easily explained by grey absorption from clouds in the upper atmosphere, masking the spectral features. However, we cannot confidently rule out clear atmosphere models with low abundances (̃ 10-3 solar) of TiO, VO or even metal hydrides masking the Na and K wings. A smaller scale height or ionization could also contribute to muted spectral features, but alone are unable to account for the absence of features reported here ©2013 The Authors.The prevalence of dust on the exoplanet HD 189733b from Hubble and Spitzer observations
Monthly Notices of the Royal Astronomical Society 432:4 (2013) 2917-2944
Abstract:
The hot jupiter hd 189733b is the most extensively observed exoplanet. its atmosphere has been detected and characterized in transmission and eclipse spectroscopy, and its phase curve measured at several wavelengths. this paper brings together the results of our campaign to obtain the complete transmission spectrum of the atmosphere of this planet from uv to infrared with the hubble space telescope, using the stis, acs and wfc3 instruments. we provide a new tabulation of the transmission spectrum across the entire visible and infrared range. the radius ratio in each wavelength band was re-derived, where necessary, to ensure a consistent treatment of the bulk transit parameters and stellar limb darkening. special care was taken to correct for, and derive realistic estimates of the uncertainties due to, both occulted and unocculted star spots. the combined spectrum is very different from the predictions of cloud-free models for hot jupiters: it is dominated by rayleigh scattering over the whole visible and near-infrared range, the only detected features being narrow sodium and potassium lines. we interpret this as the signature of a haze of condensate grains extending over at least five scaleheights. we show that a dust-dominated atmosphere could also explain several puzzling features of the emission spectrum and phase curves, including the large amplitude of the phase curve at 3.6 μm, the small hotspot longitude shift and the hot mid-infrared emission spectrum. we discuss possible compositions and derive some first-order estimates for the properties of the putative condensate haze/clouds. we finish by speculating that the dichotomy between the two observationally defined classes of hot jupiter atmospheres, of which hd 189733b and hd 209458b are the prototypes, might not be whether they possess a temperature inversion, but whether they are clear or dusty. we also consider the possibility of a continuum of cloud properties between hot jupiters, young jupiters and l-type brown dwarfs. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.The secondary eclipses of WASP-19b as seen by the ASTEP 400 telescope from Antarctica
Astronomy and Astrophysics 553 (2013)
Abstract:
Aims. The Antarctica Search for Transiting ExoPlanets (ASTEP) program was originally aimed at probing the quality of the Dome C, Antarctica for the discovery and characterization of exoplanets by photometry. In the first year of operation of the 40 cm ASTEP 400 telescope (austral winter 2010), we targeted the known transiting planet WASP-19b in order to try to detect its secondary transits in the visible. This is made possible by the excellent sub-millimagnitude precision of the binned data. Methods. The WASP-19 system was observed during 24 nights in May 2010. Once brought back from Antarctica, the data were processed using various methods, and the best results were with an implementation of the optimal image subtraction (OIS) algorithm. Results. The photometric variability level due to starspots is about 1.8% (peak-to-peak), in line with the SuperWASP data from 2007 (1.4%) and higher than in 2008 (0.07%). We find a rotation period of WASP-19 of 10.7 ± 0.5 days, in agreement with the SuperWASP determination of 10.5 ± 0.2 days. Theoretical models show that this can only be explained if tidal dissipation in the star is weak, i.e. the tidal dissipation factor Q'ẫ... > 3×107. Separately, we find evidence of a secondary eclipse of depth 390 ± 190 ppm with a 2.0σ significance, a phase that is consistent with a circular orbit and a 3% false positive probability. Given the wavelength range of the observations (420 to 950 nm), the secondary transit depth translates into a day-side brightness temperature of 2690 -220+150 K, in line with measurements in the z′ and K bands. The day-side emission observed in the visible could be due either to thermal emission of an extremely hot day side with very little redistribution of heat to the night side or to direct reflection of stellar light with a maximum geometrical albedo Ag = 0.27 ± 0.13. We also report a low-frequency oscillation in phase at the planet orbital period, but with a lower limit amplitude that could not be attributed to the planet phase alone and that was possibly contaminated with residual lightcurve trends. Conclusions. This first evidence of a secondary eclipse in the visible from the ground demonstrates the high potential of Dome C, Antarctica, for continuous photometric observations of stars with exoplanets. These continuous observations are required to understand star-planet interactions and the dynamical properties of exoplanetary atmospheres. © 2013 ESO.On the potential of the EChO mission to characterise gas giant atmospheres
(2012)
Detection of Neptune-size planetary candidates with CoRoT data: Comparison with the planet occurrence rate derived from Kepler
Astronomy and Astrophysics 547 (2012)