Hydrogen column density evaluations toward Capella: consequences on the interstellar deuterium abundance

The deuterium abundance evaluation in the direction of Capella has for a long time been used as a reference for the local interstellar medium (ISM) within our Galaxy. We show here that broad and weak HI components could be present on the Capella line of sight, leading to a large new additional systematic uncertainty on the N(HI) evaluation. The D/H ratio toward Capella is found to be equal to 1.67 (+/-0.3)x10^-5 with almost identical chi^2 for all the fits (this range includes only the systematic error; the 2 sigma statistical one is almost negligible in comparison). It is concluded that D/H evaluations over HI column densities below 10^19 cm^-2 (even perhaps below 10^20 cm^-2 if demonstrated by additional observations) may present larger uncertainties than previously anticipated. It is mentionned that the D/O ratio might be a better tracer for DI variations in the ISM as recently measured by the Far Ultraviolet Spectroscopic Explorer (FUSE).Comment: Accepted for publication in the Astrophysical Journal Letter

Atmospheric Escape from Hot Jupiters

The extra-solar planet HD209458b has been found to have an extended atmosphere of escaping atomic hydrogen (Vidal-Madjar et al. 2003), suggesting that ``hot Jupiters'' closer to their parent stars could evaporate. Here we estimate the atmospheric escape (so called evaporation rate) from hot Jupiters and their corresponding life time against evaporation. The calculated evaporation rate of HD209458b is in excellent agreement with the HI Lyman-alpha observations. We find that the tidal forces and high temperatures in the upper atmosphere must be taken into account to obtain reliable estimate of the atmospheric escape. Because of the tidal forces, we show that there is a new escape mechanism at intermediate temperatures at which the exobase reaches the Roche lobe. From an energy balance, we can estimate plausible values for the planetary exospheric temperatures, and thus obtain typical life times of planets as a function of their mass and orbital distance.Comment: A&A Letters, in pres

Detection of deuterium Balmer lines in the Orion Nebula

The detection and first identification of the deuterium Balmer emission lines, D-alpha and D-beta, in the core of the Orion Nebula is reported. Observations were conducted at the 3.6m Canada-France-Hawaii Telescope, using the Echelle spectrograph Gecko. These lines are very narrow and have identical 11 km/s velocity shifts with respect to H-alpha and H-beta. They are probably excited by UV continuum fluorescence from the Lyman (DI) lines and arise from the interface between the HII region and the molecular cloud.Comment: 4 pages, latex, 1 figure, 1 table, accepted for publication in Astronomy & Astrophysics, Letter

GTC OSIRIS transiting exoplanet atmospheric survey: detection of sodium in XO-2b from differential long-slit spectroscopy

We present two transits of the hot-Jupiter exoplanet XO-2b using the Gran Telescopio Canarias (GTC). The time series observations were performed using long-slit spectroscopy of XO-2 and a nearby reference star with the OSIRIS instrument, enabling differential specrophotometric transit lightcurves capable of measuring the exoplanet's transmission spectrum. Two optical low-resolution grisms were used to cover the optical wavelength range from 3800 to 9300{\AA}. We find that sub-mmag level slit losses between the target and reference star prevent full optical transmission spectra from being constructed, limiting our analysis to differential absorption depths over ~1000{\AA} regions. Wider long slits or multi-object grism spectroscopy with wide masks will likely prove effective in minimising the observed slit-loss trends. During both transits, we detect significant absorption in the planetary atmosphere of XO-2b using a 50{\AA} bandpass centred on the Na I doublet, with absorption depths of Delta(R_pl/R_star)^2=0.049+/-0.017 % using the R500R grism and 0.047+/-0.011 % using the R500B grism (combined 5.2-sigma significance from both transits). The sodium feature is unresolved in our low-resolution spectra, with detailed modelling also likely ruling out significant line-wing absorption over an ~800{\AA} region surrounding the doublet. Combined with narrowband photometric measurements, XO-2b is the first hot Jupiter with evidence for both sodium and potassium present in the planet's atmosphere.Comment: 9 pages, 10 figures, 1 table, accepted for publication in MNRA

New observations of the extended hydrogen exosphere of the extrasolar planet HD209458b

Atomic hydrogen escaping from the planet HD209458b provides the largest observational signature ever detected for an extrasolar planet atmosphere. However, the Space Telescope Imaging Spectrograph (STIS) used in previous observational studies is no longer available, whereas additional observations are still needed to better constrain the mechanisms subtending the evaporation process, and determine the evaporation state of other `hot Jupiters'. Here, we aim to detect the extended hydrogen exosphere of HD209458b with the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope (HST) and to find evidence for a hydrogen comet-like tail trailing the planet, which size would depend on the escape rate and the amount of ionizing radiation emitted by the star. These observations also provide a benchmark for other transiting planets, in the frame of a comparative study of the evaporation state of close-in giant planets. Eight HST orbits are used to observe two transits of HD209458b. Transit light curves are obtained by performing photometry of the unresolved stellar Lyman-alpha emission line during both transits. Absorption signatures of exospheric hydrogen during the transit are compared to light curve models predicting a hydrogen tail. Transit depths of (9.6 +/- 7.0)% and (5.3 +/- 10.0)% are measured on the whole Lyman-alpha line in visits 1 and 2, respectively. Averaging data from both visits, we find an absorption depth of (8.0 +/- 5.7)%, in good agreement with previous studies. The extended size of the exosphere confirms that the planet is likely loosing hydrogen to space. Yet, the photometric precision achieved does not allow us to better constrain the hydrogen mass loss rate.Comment: Accepted for publication in Astronomy & Astrophysics. 5 pages, 3 figure

FUSE Observations of the HD Molecule toward HD 73882

The Lyman and Werner band systems of deuterated molecular hydrogen (HD) occur in the far UV range below 1200 A. The high sensitivity of the FUSE mission can give access, at moderate resolution, to hot stars shining through translucent clouds, in the hope of observing molecular cores in which deuterium is essentially in the form of HD. Thus, the measurement of the HD/H2 ratio may become a new powerful tool to evaluate the deuterium abundance, D/H, in the interstellar medium. We report here on the detection of HD toward the high extinction star HD 73882 [E(B-V)=0.72]. A preliminary analysis is presented.Comment: 4 pages + 4 .ps figures. This paper will appear in a special issue of Astrophysical Journal Letters devoted to the first scientific results from the FUSE missio