Using the new Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST), we obtained moderate-resolution, high signal/noise ultraviolet spectra of HD 209458 and its exoplanet HD 209458b during transit, both orbital quadratures, and secondary eclipse. We compare transit spectra with spectra obtained at non-transit phases to identify spectral features due to the exoplanet's expanding atmosphere. We find that the mean flux decreased by 7.8 ± 1.3% for the C II 1334.5323Å and 1335.6854Å lines and by 8.2 ± 1.4% for the Si III 1206.500Å line during transit compared to non-transit times in the velocity interval -50 to +50 km s −1 . Comparison of the C II and Si III line depths and transit/nontransit line ratios shows deeper absorption features near -10 and +15 km s −1 and less certain features near -40 and +30-70 km s −1 , but future observations are needed to verify this first detection of velocity structure in the expanding atmosphere of an exoplanet. Our results for the C II lines and the non-detection of Si IV 1394.76Å absorption are in agreement with Vidal-Madjar et al. (2004), but we find absorption during transit in the Si III line contrary to the earlier result. The 8 ± 1% obscuration of the star during transit is far larger than the 1.5% obscuration by the exoplanet's disk. Absorption during transit at velocities between -50 and +50 km s −1 in the C II and Si III lines requires high-velocity ion absorbers. Assuming hydrodynamic model values for the gas temperature and outflow velocity at the limb of the outflow as seen in the C II lines, we find mass-loss rates in the range (8-40)×10 10 g s −1 . These rates assume that the carbon abundance is solar, which is not the case for the giant planets in the solar system. Our mass-loss rate estimate is consistent with theoretical hydrodynamic models that include metals in the outflowing gas.Subject headings: planets and satellites: atmospheres -planets and satellites: individual (HD 209458b) -planets and satellites: physical evolution -stars: individual (HD 209458) -ultraviolet: stars

Brown dwarfs are massive analogs of extrasolar giant planets and may host types of atmospheric circulation not seen in the solar system. We analyzed a long-term Spitzer Space Telescope infrared monitoring campaign of brown dwarfs to constrain cloud cover variations over a total of 192 rotations. The infrared brightness evolution is dominated by beat patterns caused by planetary-scale wave pairs and by a small number of bright spots. The beating waves have similar amplitudes but slightly different apparent periods because of differing velocities or directions. The power spectrum of intermediate-temperature brown dwarfs resembles that of Neptune, indicating the presence of zonal temperature and wind speed variations. Our findings explain three previously puzzling behaviors seen in brown dwarf brightness variations.

The formation timescale and final architecture of exoplanetary systems are closely related to the properties of the molecular disks from which they form. Observations of the spatial distribution and lifetime of the molecular gas at planet-forming radii (a < 10 AU) are important for understanding the formation and evolution of exoplanetary systems. Toward this end, we present the largest spectrally resolved survey of H2 emission around low-mass pre-main-sequence stars compiled to date. We use a combination of new and archival far-ultraviolet spectra from the Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph instruments on the Hubble Space Telescope to sample 34 T Tauri stars (27 actively accreting Classical T Tauri Stars and 7 non-accreting Weak-lined T Tauri Stars) with ages ranging from ∼1 to 10 Myr. We observe fluorescent H2 emission, excited by Lyα photons, in 100% of the accreting sources, including all of the transitional disks in our sample (CS Cha, DM Tau, GM Aur, UX Tau A, LkCa 15, HD 135344B, and TW Hya). The spatial distribution of the emitting gas is inferred from spectrally resolved H2 line profiles. Some of the emitting gas is produced in outflowing material, but the majority of H2 emission appears to originate in a rotating disk. For the disk-dominated targets, the H2 emission originates predominately at a ≲ 3 AU. The emission line widths and inner molecular radii are found to be roughly consistent with those measured from mid-IR CO spectra.

We present Spitzer /IRAC Ch1 and Ch2 monitoring of six brown dwarfs during 8 different epochs over the course of 20 months. For four brown dwarfs, we also obtained simulataneous HST /WFC3 G141 Grism spectra during two epochs and derived light curves in five narrow-band filters. Probing different pressure levels in the atmospheres, the multi-wavelength light curves of our six targets all exhibit variations, and the shape of the light curves evolves over the timescale of a rotation period, ranging from 1.4 h to 13 h. We compare the shapes of the light curves and estimate the phase shifts between the light curves observed at different wavelengths by comparing the phase of the primary Fourier components. We use state-of-the-art atmosphere models to determine the flux contribution of different pressure layers to the observed flux in each filter. We find that the light curves that probe higher pressures are similar and in phase, but are offset and often different from the light curves that

We present a far-ultraviolet (FUV) spectral atlas consisting of spectra of 91 pre-main sequence stars. Most stars in this sample were observed with the Space Telescope Imaging Spectrograph (STIS) and Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST ). A few archival spectra from International Ultraviolet Explorer (IUE ) and the Goddard High Resolution Spectrograph (GHRS) on the HST are included for completeness. We find strong correlations among the O I λ1304 triplet, the Si IV λλ1394/1403 doublet, the C IV λ1549 doublet, and the He II λ1640 line luminosities. For classical T Tauri stars (CTTSs), we also find strong correlations between these lines and the accretion luminosity, suggesting that these lines form in processes related to accretion. These FUV line fluxes and X-ray luminosity correlate loosely with large scatters. The FUV emission also correlates well with Hα, Hβ, and Ca II K line luminosities. These correlations between FUV and optical diagostics can be used to obtain rough estimates of FUV line fluxes from optical observations. Molecular hydrogen (H 2 ) emission is generally present in the spectra of actively accreting CTTSs but not the weak-lined T Tauri stars (WTTSs) that are not accreting. The presence of H 2 emission in the spectrum of HD 98800 N suggests that the disk should be classified as actively accreting rather than a debris disk.We discuss the importance of FUV radiation, including the hydrogen Lyα line, on the photoevaporation of exoplanet atmospheres. We find that the Ca II/C IV flux ratios for more evolved stars are lower than those for less evolved accretors, indicating preferential depletion of refactory metals into dust grains. (2003) published the PMS archive of IUE far-and near-UV spectra of 137 TTSs and 97 Herbig Ae/Be (HAeBe) stars, although only 50 of the TTSs were observed in the FUV. Together, this trilogy has laid out the foundation for our understanding of UV radiation fields from young stars, including the strength and the physical processes responsible for such emission. However, the IUE survey of FUV emission from young stars was limited to the FUV-brightest CTTSs and included only three WTTSs, of which the latest spectral type is K0. The survey is also limited by S/N, evident in the low detection rate of H 2 line emission (13/32 CTTSs, Valenti et al. 2000) despite subsequent observations showing that such emission is common to all CTTSs (Herczeg et al. 2006; Ingleby et al. 2009). Analysis of the location and kinematics of the gas that produces the FUV emission lines was also limited by the large aperture (∼ 10 ′′ × 20 ′′ ) and low spectral resolution (6Å) of the IUE SWP camera. Since the launch of the Hubble Space Telescope (HST ) 20 years ago, the Goddard High Resolution Spectrograph (GHRS), Space Telescope Imaging Spectrograph (STIS) and the Advanded Camera for Surveys (ACS) prisms have observed over 80 PMS stars. Analyses of small subsets of these observations (< 10 objects, and often only one) have been used to address specific issues, including ...