Aims. The energy supply for the radiative losses of the quiet solar chromosphere is studied. On the basis of high spatial resolution data, we investigate the amount of energy flux carried by acoustic waves in the solar photosphere. Methods. Time sequences from quiet Sun disc centre were obtained with the "Göttingen" Fabry-Perot spectrometer at the Vacuum Tower Telescope, Observatorio del Teide/Tenerife, in the non-magnetic Fe i 5576 Å line. The data were reconstructed with speckle methods. The velocity and intensity fluctuations at line minimum were subjected to Fourier and wavelet analyses. The energy fluxes at frequencies higher than the acoustic cutoff frequency (period U ≈ 190 s) were corrected for the transmission of the solar atmosphere, which reduces the signal from short-period waves. Results. Both Fourier and wavelet analysis give an amount of energy flux of ∼3000 W m −2 at a height h = 250 km. Approximately 2/3 of it is carried by waves in the 5−10 mHz range, and 1/3 in the 10−20 mHz band. Extrapolation of the flux spectra gives an energy flux of 230−400 W m −2 at frequencies ν > 20 mHz. We find that the waves occur predominantly above inter-granular areas. Conclusions. We conclude that the acoustic flux in waves with periods shorter than the acoustic cutoff period can contribute to the basal heating of the solar chromosphere, in addition to the atmospheric gravity waves found recently.

Aims. Time series of high-resolution spectra of the late B-type star HD 11753 exhibiting HgMn chemical peculiarity are used to study the surface distribution of different chemical elements and their temporal evolution. Methods. High-resolution and high signal-to-noise ratio spectra were obtained using the CORALIE spectrograph at La Silla in 2000, 2009, and 2010. Surface maps of Y ii, Sr ii, Ti ii, and Cr ii were calculated using the Doppler imaging technique. The results were also compared to equivalent width measurements. The evolution of chemical spots both on short and long time scales were investigated. Results. We determine the binary orbit of HD 11753 and fine-tune the rotation period of the primary. The earlier discovered fast evolution of the chemical spots is confirmed by an analysis using both the chemical spot maps and equivalent width measurements.In addition, a long-term decrease in the overall Y ii and Sr ii abundances is discovered. A detailed analysis of the chemical spot configurations reveals some possible evidence that a very weak differential rotation is operating in HD 11753.

Aims. HD 52265 is the only known exoplanet-host star selected as a main target for the seismology programme of the CoRoT satellite. As such, it will be observed continuously during five months, which is of particular interest when studying planetary systems. This star was misclassified as a giant in the Bright Star Catalog, while it is more probably on the main-sequence or at the beginning of the subgiant branch. We performed an extensive analysis of this star, showing how asteroseismology may lead to a precise determination of its external parameters and internal structure. Methods. We first reviewed the observational constraints on the metallicity, the gravity, and the effective temperature derived from the spectroscopic observations of HD 52265. We also derived its luminosity using the Hipparcos parallax. We computed the evolutionary tracks for models of various metallicities that cross the relevant observational error boxes in the gravity-effective temperature plane. We selected eight different stellar models that satisfy the observational constraints, computed their p-modes frequencies, and analysed specific seismic tests. Results. The possible models for HD 52265, which satisfy the constraints derived from the spectroscopic observations, are different in both their external and internal parameters. They lie either on the main sequence or at the beginning of the subgiant branch. The differences in the models lead to quite different properties of their oscillation frequencies. We give evidence of an interesting specific behaviour of these frequencies in the case of helium-rich cores: the "small separations" may become negative and give constraints on the size of the core. We expect that the observations of this star by the CoRoT satellite will allow a choice between these possible models.

Aims. We present detailed modelling of the exoplanet-host star μ Arae, using a new method for the asteroseismic analysis, and taking into account the new value recently derived for the Hipparcos parallax. The aim is to obtain precise parameters for this star and its internal structure, including constraints on the core overshooting. Methods. We computed new stellar models in a wider range than Bazot et al. (2005, A&A, 440, 615), with various chemical compositions ([Fe/H] and Y), with or without overshooting at the edge of the core. We computed their adiabatic oscillation frequencies and compared them to the seismic observations. For each set of chemical parameters, we kept the model which represented the best fit to the echelle diagram. Then, by comparing the effective temperatures, gravities and luminosities of these models with the spectroscopic error boxes, we were able to derive precise parameters for this star.Results. First we find that all the models which correctly fit the echelle diagram have the same mass and radius, with an uncertainty of the order of one percent. Second, the final comparison with spectroscopic observations leads to the conclusion that besides its high metallicity, μ Arae has a high helium abundance of the order of Y = 0.3. Knowing this allows finding precise values for all the other parameters, mass, radius and age.