Search

The characterization of a physically-diverse set of transiting exoplanets isan important and necessary step towards establishing the physical propertieslinked to the production of obscuring clouds or hazes. It is those planets withidentifiable spectroscopic features that can most effectively enhance ourunderstanding of atmospheric chemistry and metallicity. The newly-commissionedLDSS-3C instrument on Magellan provides enhanced sensitivity and suppressedfringing in the red optical, thus advancing the search for the spectroscopicsignature of water in exoplanetary atmospheres from the ground. Using dataacquired by LDSS-3C and the Spitzer Space Telescope, we search for evidence ofwater vapor in the transmission spectrum of the Neptune-mass planet HAT-P-26b.Our measured spectrum is best explained by the presence of water vapor, a lackof potassium, and either a high-metallicity, cloud-free atmosphere or asolar-metallicity atmosphere with a cloud deck at ~10 mbar. The emergence ofmulti-scale-height spectral features in our data suggests that futureobservations at higher precision could break this degeneracy and reveal theplanet's atmospheric chemical abundances. We also update HAT-P-26b's transitephemeris, t_0 = 2455304.65218(25) BJD_TDB, and orbital period, p =4.2345023(7) days.

We present ground-based measurements of the transmission and emission spectra of the hot-Jupiter WASP-19b in nine spectroscopic channels from 1.25 to 2.35 μm. The measurements are based on the combined analysis of time-series spectroscopy obtained during two complete transits and two complete secondary eclipses of the planet. The observations were performed with the MMIRS instrument on the Magellan II telescope using the technique of multi-object spectroscopy with wide slits.We compare the transmission and emission data to theoretical models to constrain the composition and thermal structure of the planet's atmosphere. Our measured transmission spectrum exhibits a scatter that corresponds to 1.3 scale heights of the planet's atmosphere, which is consistent with the size of spectral features predicted by theoretical models for a clear atmosphere. We detect the secondary eclipses of the planet at significances ranging from 2.2σ to 14.4σ. The secondary eclipse depths, and the significances of the detections increase toward longer wavelengths. Our measured emission spectrum is consistent with a 2250 K effectively isothermal one-dimensional model for the planet's dayside atmosphere. This model also matches previously published photometric measurements from the Spitzer Space Telescope and ground-based telescopes. These results demonstrate the important role that ground-based observations using multi-object spectroscopy can play in constraining the properties of exoplanet atmospheres, and they also emphasize the need for high-precision measurements based on observations of multiple transits and eclipses. [ABSTRACT FROM AUTHOR]

We present an investigation of the transmission spectrum of the 6.5 M⊕ planet GJ 1214b based on new ground-based observations of transits of the planet in the optical and near-infrared, and on previously published data. Observations with the VLT + FORS and Magellan + MMIRS using the technique of multi-object spectroscopy with wide slits yielded new measurements of the planet's transmission spectrum from 0.61 to 0.85 µm, and in the J, H, and K atmospheric windows. We also present a new measurement based on narrow-band photometry centered at 2.09 µm with the VLT + HAWKI. We combined these data with results from a reanalysis of previously published FORS data from 0.78 to 1.00 µm using an improved data reduction algorithm, and previously reported values based on Spitzer data at 3.6 and 4.5 µm. All of the data are consistent with a featureless transmission spectrum for the planet. Our K-band data are inconsistent with the detection of spectral features at these wavelengths reported by Croll and collaborators at the level of 4.1σ. The planet's atmosphere must either have at least 70% H2O by mass or optically thick high-altitude clouds or haze to be consistent with the data. [ABSTRACT FROM AUTHOR]