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

Deuterium toward the WD0621-376 sight line: Results from the Far Ultraviolet Spectroscopic Explorer (FUSE) Mission

Far Ultraviolet Spectroscopic Explorer observations are presented for WD0621-376, a DA white dwarf star in the local interstellar medium (LISM) at a distance of about 78 pc. The data have a signal-to-noise ratio of about 20-40 per 20 km/s resolution element and cover the wavelength range 905-1187 \AA. LISM absorption is detected in the lines of D I, C II, C II*, C III, N I, N II, N III, O I, Ar I, and Fe II. This sight line is partially ionized, with an ionized nitrogen fraction of > 0.23. We determine the ratio $D/O = (3.9 \pm ^{1.3}_{1.0})\times 10^{-2}$ (2$\sigma$). Assuming a standard interstellar oxygen abundance, we derive ${\rm D/H} \approx 1. 3 \times 10^{-5}$. Using the value of N(H I) derived from EUVE data gives a similar D/H ratio. The D I/N I ratio is $(3.3 \pm ^{1.0}_{0.8})\times 10^{-1}$ (2$\sigma$).Comment: accepted for publication in the ApJ

Exoplanet HD 209458b : Evaporation strengthened

Following re-analysis of Hubble Space Telescope observations of primary transits of the extrasolar planet HD209458b at Lyman-alpha, Ben-Jaffel (2007, BJ007) claims that no sign of evaporation is observed. Here we show that, in fact, this new analysis is consistent with the one of Vidal-Madjar et al. (2003, VM003) and supports the detection of evaporation. The apparent disagreement is mainly due to the disparate wavelength ranges that are used to derive the transit absorption depth. VM003 derives a (15+/-4)% absorption depth during transit over the core of the stellar Lyman-alpha line (from -130 km/s to +100 km/s), and this result agrees with the (8.9+/-2.1)% absorption depth reported by BJ007 from a slightly expanded dataset but over a larger wavelength range (+/-200 km/s). These measurements agree also with the (5+/-2)% absorption reported by Vidal-Madjar et al. (2004) over the whole Lyman-alpha line from independent, lower-resolution data. We show that stellar Lyman-alpha variability is unlikely to significantly affect those detections. The HI atoms must necessarily have velocities above the escape velocities and/or be outside the Roche lobe, given the lobe shape and orientation. Absorption by HI in HD209458b's atmosphere has thus been detected with different datasets, and now with independent analyses. All these results strengthen the concept of evaporating hot-Jupiters, as well as the modelization of this phenomenon.Comment: To be published in ApJ

Osteochondral transfer using a transmalleolar approach for arthroscopic management of talus posteromedial lesions

SummaryCharacterizing osteochondral lesions of the talus has enabled the strategies of surgical management to be better specified. The main technical problem is one of access for arthroscopy instruments to posteromedial lesions. A range of techniques and approaches has been described in ankle arthroscopy in general, and a transmalleolar approach provides reliable and efficient access in these cases. It is frequently used for transchondral drilling, but also enables satisfactory implant positioning in autologous osteochondral mosaicplasty procedures. We report our technique and results on five cases with a minimum 1.2 years’ follow-up