Context. Recently, unanticipated magnetic activity in ultracool dwarfs (UCDs, spectral classes later than M7) has emerged from a number of radio observations. The highly (up to 100%) circularly polarized nature and high brightness temperature of the emission have been interpreted as requiring an effective amplification mechanism of the high

We analyze more than 5000 days of Sun-as-a-star radial velocity GOLF and intensity VIRGO observations to measure the visibilities of the I = 0, 1, 2, and 3 modes and the m-amplitude ratios of the I = 2 and 3 modes in the solar acoustic spectrum. We provide observational values that we compare to theoretical predictions.

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The stellar parameters were determined using an LTE analysis based on equivalent widths (EW) of iron lines and by imposing excitation and ionization equilibrium. The ARES code (that can be downloaded at http://www.astro.up.pt/~sousasag/ares ) was used to allow automatic and systematic derivation of the stellar parameters. Precise stellar parameters

The iodine gas cell is replaced by the telluric O2 and water vapor lines to calibrate observations of RV stable M dwarfs made with the High Resolution Spectrograph of the Hobby-Eberly Telescope. Radial velocities are to be measured with both iodine lines in the visible and the atmospheric lines in the 6000-8800A region, as a first step in

We study the propagation of waves from the photosphere to the chromosphere of sunspots. From time series of cospatial Ca II H (including its line blends) intensity spectra and polarimetric spectra of Si I λ 1082.7 nm and He I λ 1083.0 nm we retrieve the line-of-sight velocity at several heights. The analysis of the phase difference and