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Register a new userGround-based NIR emission spectroscopy of HD189733b
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We investigate the K and L band dayside emission of the hot-Jupiter HD 189733b with three nights of secondary eclipse data obtained with the SpeX instrument on the NASA IRTF. The observations for each of these three nights use equivalent instrument settings and the data from one of the nights has previously reported by Swain et al (2010). We describe an improved data analysis method that, in conjunction with the multi-night data set, allows increased spectral resolution (R~175) leading to high-confidence identification of spectral features. We confirm the previously reported strong emission at ~3.3 microns and, by assuming a 5% vibrational temperature excess for methane, we show that non-LTE emission from the methane nu3 branch is a physically plausible source of this emission. We consider two possible energy sources that could power non-LTE emission and additional modelling is needed to obtain a detailed understanding of the physics of the emission mechanism. The validity of the data analysis method and the presence of strong 3.3 microns emission is independently confirmed by simultaneous, long-slit, L band spectroscopy of HD 189733b and a comparison star.
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We attempt to confirm bright non-LTE emission from the exoplanet HD189733b at 3.25 microns, as recently reported by Swain et al. (2010) based on observations at low spectral resolving power (R ~ 30). Non-LTE emission lines from gas in an exoplanet atmosphere will not be significantly broadened by collisions, so the measured emission intensity per resolution element must be substantially brighter when observed at high spectral resolving power. We observed the planet before, during, and after a secondary eclipse event at a resolving power R = 27,000 using the NIRSPEC spectrometer on the Keck II telescope. Our spectra cover a spectral window near the peak found by Swain et al., and we compare emission cases that could account for the magnitude and wavelength dependence of the Swain et al. result with our final spectral residuals. To model the expected line emission, we use a general non-equilibrium formulation to synthesize emission features from all plausible molecules that emit in this spectral region. In every case, we detect no line emission to a high degree of confidence. After considering possible explanations for the Swain et al. results and the disparity with our own data, we conclude that an astrophysical source for the putative non-LTE emission is unlikely. We note that the wavelength dependence of the signal seen by Swain et al. closely matches the 2nu2 band of water vapor at 300K, and we suggest that an imperfect correction for telluric water is the source of the feature claimed by Swain et al.
Exoplanet observations promise one day to unveil the presence of extraterrestrial life. Atmospheric compounds in strong chemical disequilibrium would point to large-scale biological activity just as oxygen and methane do in the Earths atmosphere. The cancellation of both the Terrestrial Planet Finder and Darwin missions means that it is unlikely that a dedicated space telescope to search for biomarker gases in exoplanet atmospheres will be launched within the next 25 years. Here we show that ground-based telescopes provide a strong alternative for finding biomarkers in exoplanet atmospheres through transit observations. Recent results on hot Jupiters show the enormous potential of high-dispersion spectroscopy to separate the extraterrestrial and telluric signals making use of the Doppler shift of the planet. The transmission signal of oxygen from an Earth-twin orbiting a small red dwarf star is only a factor 3 smaller than that of carbon monoxide recently detected in the hot Jupiter tau Bootis b, albeit such a star will be orders of magnitude fainter. We show that if Earth-like planets are common, the planned extremely large telescopes can detect oxygen within a few dozen transits. Ultimately, large arrays of dedicated flux collector telescopes equipped with high-dispersion spectrographs can provide the large collecting area needed to perform a statistical study of life-bearing planets in the solar neighborhood.
We present an occultation of the newly discovered hot Jupiter system WASP-19, observed with the HAWK-I instrument on the VLT, in order to measure thermal emission from the planets dayside at ~2 um. The light curve was analysed using a Markov-Chain Monte-Carlo method to find the eclipse depth and the central transit time. The transit depth was found to be 0.366+-0.072 %, corresponding to a brightness temperature of 2540+-180 K. This is significantly higher than the calculated (zero-albedo) equilibrium temperature, and indicates that the planet shows poor redistribution of heat to the night side, consistent with models of highly irradiated planets. Further observations are needed to confirm the existence of a temperature inversion, and possibly molecular emission lines. The central eclipse time was found to be consistent with a circular orbit.
We report a new detection of the H-band thermal emission of CoRoT-1b and two confirmation detections of the Ks-band thermal emission of WASP-12b at secondary eclipses. The H-band measurement of CoRoT-1b shows an eclipse depth of 0.145%pm0.049% with a 3-{sigma} percentile between 0.033% - 0.235%. This depth is consistent with the previous conclusions that the planet has an isother- mal region with inefficient heat transport from dayside to nightside, and has a dayside thermal inversion layer at high altitude. The two Ks band detections of WASP-12b show a joint eclipse depth of 0.299%pm0.065%. This result agrees with the measurement of Croll & collaborators, providing independent confirmation of their measurement. The repeatability of the WASP-12b measurements also validates our data analysis method. Our measurements, in addition to a number of previous results made with other telescopes, demonstrate that ground-based observations are becoming widely available for characterization of atmospheres of hot Jupiters.
(Abridged) WASP-5b is a highly irradiated dense hot Jupiter orbiting a G4V star every 1.6 days. We observed two secondary eclipses of WASP-5b in the J, H and K bands simultaneously. Thermal emission of WASP-5b is detected in the J and K bands. The retrieved planet-to-star flux ratios in the J and K bands are 0.168 +0.050/-0.052% and 0.269+/-0.062%, corresponding to brightness temperatures of 2996 +212/-261K and 2890 +246/-269K, respectively. No thermal emission is detected in the H band, with a 3-sigma upper limit of 0.166%, corresponding to a maximum temperature of 2779K. On the whole, our J, H, K results can be explained by a roughly isothermal temperature profile of ~2700K in the deep layers of the planetary dayside atmosphere that are probed at these wavelengths. Together with Spitzer observations, which probe higher layers that are found to be at ~1900K, a temperature inversion is ruled out in the range of pressures probed by the combined data set. While an oxygen-rich model is unable to explain all the data, a carbon-rich model provides a reasonable fit but violates energy balance.
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