A. Wyttenbach

Grids of stellar models with rotation III. Models from 0.8 to 120 M at a metallicity Z = 0.002 ?

Aims. Many topical astrophysical research areas, such as the properties of planet host stars, the nature of the progenitors of different types of supernovae and gamma ray bursts, and the evolution of galaxies, require complete and homogeneous sets of stellar models at different metallicities in order to be studied during the whole of cosmic history. We present here a first set of models for solar metallicity, where the effects of rotation are accounted for in a homogeneous way. Methods. We computed a grid of 48 different stellar evolutionary tracks, both rotating and non-rotating, at Z = 0.014, spanning a wide mass range from 0.8 to 120 M� . For each of the stellar masses considered, electronic tables provide data for 400 stages along the evolutionary track and at each stage, a set of 43 physical data are given. These grids thus provide an extensive and detailed data basis for comparisons with the observations. The rotating models start on the zero-age main sequence (ZAMS) with a rotation rate υini/υcrit = 0.4. The evolution is computed until the end of the central carbon-burning phase, the early asymptotic giant branch (AGB) phase, or the core helium-flash for, respectively, the massive, intermediate, and both low and very low mass stars. The initial abundances are those deduced by Asplund and collaborators, which best fit the observed abundances of massive stars in the solar neighbourhood. We update both the opacities and nuclear reaction rates, and introduce new prescriptions for the mass-loss rates as stars approach the Eddington and/or the critical velocity. We account for both atomic diffusion and magnetic braking in our low-mass star models. Results. The present rotating models provide a good description of the average evolution of non-interacting stars. In particular, they reproduce the observed main-sequence width, the positions of the red giant and supergiant stars in the Hertzsprung-Russell (HR) diagram, the observed surface compositions and rotational velocities. Very interestingly, the enhancement of the mass loss during

Spectrally resolved detection of sodium in the atmosphere of HD 189733b with the HARPS spectrograph

Context. Atmospheric properties of exoplanets can be constrained with transit spectroscopy. At low spectral resolution, this technique is limited by the presence of clouds. The signature of atomic sodium (Nai), known to be present above the clouds, is a powerful probe of the upper atmosphere, where it can be best detected and characterized at high spectral resolution. Aims. Our goal is to obtain a high-resolution transit spectrum of HD 189733b in the region around the resonance doublet of Nai at 589 nm, to characterize the absorption signature that was previously detected from space at low resolution. Methods. We analyzed archival transit data of HD 189733b obtained with the HARPS spectrograph (R = 115 000) at the ESO 3.6-m telescope. We performed di erential spectroscopy to retrieve the transit spectrum and light curve of the planet, implementing corrections for telluric contamination and planetary orbital motion. We compared our results to synthetic transit spectra calculated from isothermal models of the planetary atmosphere. Results. We spectrally resolve the Nai D doublet and measure line contrasts of 0:64 0:07% (D2) and 0:40 0:07% (D1) and FWHMs of 0:52 0:08 A. This corresponds to a detection at the 10 level of excess of absorption of 0:32 0:03% in a passband of 2 0:75 A centered on each line. We derive temperatures of 2600 600 K and 3270 330 K at altitudes of 9800 2800 and 12 700 2600 km in the Nai D1 and D2 line cores, respectively. We measure a temperature gradient of 0.2 K km 1 in the region where the sodium absorption dominates the haze absorption from a comparison with theoretical models. We also detect a blueshift of 0:16 0:04 A (4 ) in the line positions. This blueshift may be the result of winds blowing at 8 2 km s 1 in the upper layers of the atmosphere. Conclusions. We demonstrate the relevance of studying exoplanet atmospheres with high-resolution spectrographs mounted on 4-m-class telescopes. Our results pave the way for an in-depth characterization of physical conditions in the atmospheres of many exoplanetary systems with future spectrographs such as ESPRESSO on the VLT or HiReS and METIS on the E-ELT.

Populations of rotating stars III. SYCLIST, the new Geneva population synthesis code

Context. Constraints on stellar models can be obtained from observations of stellar populations, provided the population results from a well defined star formation history. Aims. We present a new tool for building synthetic colour‐magnitude diagrams of coeval stellar populations. We study, from a theoretical point of view, the impact of axial rotation of stars on various observed properties of single-aged stellar populations: magnitude at the turno , photometric properties of evolved stars, surface velocities, surface abundances, and the impact of rotation on the age determination of clusters by an isochrone fitting. One application to the cluster NGC 663 is performed. Methods. Stellar models for di erent initial masses, metallicities, and zero-age main sequence (ZAMS) rotational velocities are used for building interpolated stellar tracks, isochrones, and synthetic clusters for various ages and metallicities. The synthetic populations account for the e ects of the initial distribution of the rotational velocities on the ZAMS, the impact of the inclination angle and the e ects of gravity and limb darkening, unresolved binaries, and photometric errors. Interpolated tracks, isochrones, and synthetic clusters can be computed through a public web interface. Results. For clusters with a metallicity in the range [0:002; 0:014] and an age between 30 Myr and 1 Gyr, the fraction of fast rotators on the main sequence (MS) band is the largest just below the turno . This remains true for two di erent published distributions of the rotational velocities on the ZAMS. This is a natural consequence of the increase in the MS lifetime due to rotation. The fraction of fast rotators one magnitude below the turno also increases with the age of the cluster between 30 Myr and 1 Gyr. The most nitrogen-rich stars are found just below the turno . There is an increase in the fraction of enriched stars when the metallicity decreases. We show that the use of isochrones computed from rotating stellar models with an initial rotation that is representative of the average initial rotation of the stars in clusters provides a reasonable estimate of the age, even though stars in a real cluster did not start their evolution with an identical initial rotation.

Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS)

High-resolution optical spectroscopy during the transit of HD 189733b, a prototypical hot Jupiter, allowed the resolution of the Na i D sodium lines in the planet, giving access to the extreme conditions of the planet upper atmosphere. We have undertaken HEARTS, a spectroscopic survey of exoplanet upper atmospheres, to perform a comparative study of hot gas giants and determine how stellar irradiation affect them. Here, we report on the first HEARTS observations of the hot Saturn-mass planet WASP-49b. We observed the planet with the HARPS high-resolution spectrograph at ESO 3.6 m telescope. We collected 126 spectra of WASP-49, covering three transits of WASP-49b. We analyzed and modeled the planet transit spectrum, while paying particular attention to the treatment of potentially spurious signals of stellar origin. We spectrally resolve the Na i D lines in the planet atmosphere and show that these signatures are unlikely to arise from stellar contamination. The large contrasts of 2.0 ± 0.5% (D 2 ) and 1.8 ± 0.7% (D 1 ) require the presence of hot neutral sodium (2950 +400 -500 K) at high altitudes (~1.5 planet radius or ~45 000 km). From estimating the cloudiness index of WASP-49b, we determine its atmosphere to be cloud free at the altitudes probed by the sodium lines. WASP-49b is close to the border of the evaporation desert and exhibits an enhanced thermospheric signature with respect to a farther-away planet such as HD 189733b.

Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) - I. Detection of hot neutral sodium at high altitudes on WASP-49b

High-resolution optical spectroscopy during the transit of HD 189733b, a prototypical hot Jupiter, allowed the resolution of the Na i D sodium lines in the planet, giving access to the extreme conditions of the planet upper atmosphere. We have undertaken HEARTS, a spectroscopic survey of exoplanet upper atmospheres, to perform a comparative study of hot gas giants and determine how stellar irradiation affect them. Here, we report on the first HEARTS observations of the hot Saturn-mass planet WASP-49b. We observed the planet with the HARPS high-resolution spectrograph at ESO 3.6 m telescope. We collected 126 spectra of WASP-49, covering three transits of WASP-49b. We analyzed and modeled the planet transit spectrum, while paying particular attention to the treatment of potentially spurious signals of stellar origin. We spectrally resolve the Na i D lines in the planet atmosphere and show that these signatures are unlikely to arise from stellar contamination. The large contrasts of 2.0 ± 0.5% (D 2 ) and 1.8 ± 0.7% (D 1 ) require the presence of hot neutral sodium (2950 +400 -500 K) at high altitudes (~1.5 planet radius or ~45 000 km). From estimating the cloudiness index of WASP-49b, we determine its atmosphere to be cloud free at the altitudes probed by the sodium lines. WASP-49b is close to the border of the evaporation desert and exhibits an enhanced thermospheric signature with respect to a farther-away planet such as HD 189733b.

A Non-isothermal Theory for Interpreting Sodium Lines in Transmission Spectra of Exoplanets

We present a theory for interpreting the sodium lines detected in transmission spectra of exoplanetary atmospheres. Previous analyses employed the isothermal approximation and dealt only with the transit radius. By recognising the absorption depth and the transit radius as being independent observables, we develop a theory for jointly interpreting both quantities, which allows us to infer the temperatures and number densities associated with the sodium lines. We are able to treat a non-isothermal situation with a constant temperature gradient. Our novel diagnostics take the form of simple-to-use algebraic formulae and require measurements of the transit radii (and their corresponding absorption depths) at line center and in the line wing for both sodium lines. We apply our diagnostics to the HARPS data of HD 189733b, confirm the upper atmospheric heating reported by Huitson et al. (2012), derive a temperature gradient of

Helium in the eroding atmosphere of an exoplanet

0.4376 \pm 0.0154

Search for water vapor in the high-resolution transmission spectrum of HD 189733b in the visible

K km

Orbital misalignment of the Neptune-mass exoplanet GJ 436b with the spin of its cool star

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Strong H i Lyman-α variations from an 11 Gyr-old host star: a planetary origin?

and find densities