[en] The extraordinary brightness of supernova 1987A in the Large Magellanic Cloud (LMC) allowed the authors to obtain high-resolution spectra with high signal-to-noise ratios, sampling the galactic disk and halo, interstellar gas in the LMC, and the intervening medium. Thirty-five distinct components have been clearly identified, probably located between the Galaxy and the LMC, and showing low dust content. (author)

[en] The supernova 1987A offers a unique opportunity to probe the visible interstellar absorption spectrum towards the Large Magellanic Cloud at high resolution and high signal-to-noise ratio. The authors report the first results of these observations. A Ca II 'forest' is detected through all the velocity range between the Galaxy and the Large Magellanic Cloud and in particular, a component is seen at a velocity of approx. 215 km s^-1 which may correspond to cooler gas in a halo. A preliminary abundance study is also presented. (author)

[en] Water, methane, and carbon monoxide are expected to be among the most abundant molecules besides molecular hydrogen in the hot atmosphere of close-in extrasolar giant planets. Atmospheric models for these planets predict that the strongest spectrophotometric features of those molecules are located at wavelengths ranging from 1 to 10 μm making this region of particular interest. Consequently, transit observations in the mid-infrared (mid-IR) allow the atmospheric content of transiting planets to be determined. We present new primary transit observations of the hot-Jupiter HD 189733b, obtained simultaneously at 4.5 and 8 μm with the Infrared Array Camera onboard the Spitzer Space Telescope. Together with a new refined analysis of previous observations at 3.6 and 5.8 μm using the same instrument, we are able to derive the system parameters, including planet-to-star radius ratio, impact parameter, scale of the system, and central time of the transit from fits of the transit light curves at these four wavelengths. We measure the four planet-to-star radius ratios, to be (R_p /R _*)_3.6μm = 0.1545 ± 0.0003, (R_p /R_*)_4.5μm = 0.1557 ± 0.0003, (R_p /R _*)_5.8μm = 0.1547 ± 0.0005, and (R_p/R_*)_8μm = 0.1544 ± 0.0004. The high accuracy of the planet radii measurement allows the search for atmospheric molecular absorbers. Contrary to a previous analysis of the same data set, our study is robust against systematics and reveals that water vapor absorption at 5.8 μm is not detected in this photometric data set. Furthermore, in the band centered around 4.5 μm we find a hint of excess absorption with an apparent planetary radius ΔR_p /R _* = 0.00128 ± 0.00056 larger (2.3σ) than the one measured simultaneously at 8 μm. This value is 4σ above what would be expected for an atmosphere where water vapor is the only absorbing species in the near-IR. This shows that an additional species absorbing around 4.5 μm could be present in the atmosphere. Carbon monoxide (CO) being a strong absorber at this wavelength is a possible candidate and this may suggest a large CO/H₂O ratio between 5 and 60.

[en] We present the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) optical transmission spectroscopy of the cool Saturn-mass exoplanet WASP-39b from 0.29-1.025 μ m, along with complementary transit observations from Spitzer IRAC at 3.6 and 4.5 μ m. The low density and large atmospheric pressure scale height of WASP-39b make it particularly amenable to atmospheric characterization using this technique. We detect a Rayleigh scattering slope as well as sodium and potassium absorption features; this is the first exoplanet in which both alkali features are clearly detected with the extended wings predicted by cloud-free atmosphere models. The full transmission spectrum is well matched by a clear H₂-dominated atmosphere, or one containing a weak contribution from haze, in good agreement with the preliminary reduction of these data presented in Sing et al. WASP-39b is predicted to have a pressure-temperature profile comparable to that of HD 189733b and WASP-6b, making it one of the coolest transiting gas giants observed in our HST STIS survey. Despite this similarity, WASP-39b appears to be largely cloud-free, while the transmission spectra of HD 189733b and WASP-6b both indicate the presence of high altitude clouds or hazes. These observations further emphasize the surprising diversity of cloudy and cloud-free gas giant planets in short-period orbits and the corresponding challenges associated with developing predictive cloud models for these atmospheres.