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Although atmospheric transmission spectroscopy of HD209458b with the Hubble Space Telescope has been very successful, attempts to detect its atmospheric absorption features using ground-based telescopes have so far been fruitless. Here we present a new method for probing the atmospheres of transiting exoplanets which may be more suitable for ground-based observations, making use of the Rossiter effect. During a transit, an exoplanet sequentially blocks off light from the approaching and receding parts of the rotating star, causing an artificial radial velocity wobble. The amplitude of this signal is directly proportional to the effective size of the transiting object, and the wavelength dependence of this effect can reveal atmospheric absorption features, in a similar way as with transmission spectroscopy. The advantage of this method over conventional atmospheric transmission spectroscopy is that it does not rely on accurate photometric comparisons of observations on and off transit, but instead depends on the relative velocity shifts of individual stellar absorption lines within the same on-transit spectra. We used an archival VLT/UVES data set to apply this method to HD209458. The amplitude of the Rossiter effect is shown to be 1.7+-1.2 m/sec higher in the Sodium D lines than in the weighted average of all other absorption lines in the observed wavelength range, corresponding to an increment of 4.3+-3% (1.4 sigma). The uncertainty in this measurement compares to a photometric accuracy of 5e-4 for conventional atmospheric transmission spectroscopy, more than an order of magnitude higher than previous attempts using ground-based telescopes. Observations specifically designed for this method could increase the accuracy further by a factor 2-3.
We report a development of a multi-color simultaneous camera for the 188cm telescope at Okayama Astrophysical Observatory in Japan. The instrument, named MuSCAT, has a capability of 3-color simultaneous imaging in optical wavelength where CCDs are se
Before an exoplanet transit, atmospheric refraction bends light into the line of sight of an observer. The refracted light forms a stellar mirage, a distorted secondary image of the host star. I model this phenomenon and the resultant out-of-transit
Current observations of the atmospheres of close-in exoplanets are predominantly obtained with two techniques: low-resolution spectroscopy with space telescopes and high-resolution spectroscopy from the ground. Although the observables delivered by t
Transit observations of HD209458b in the UV revealed signatures of neutral magnesium escaping the planets upper atmosphere. The absorption detected in the MgI line provides unprecedented information on the physical conditions at the altitude where th
Since 2006 WASP-South has been scanning the Southern sky for transiting exoplanets. Combined with Geneva Observatory radial velocities we have so far found over 30 transiting exoplanets around relatively bright stars of magnitude 9--13. We present a status report for this ongoing survey.