A model scenario has recently been introduced by de la Reza and colleagues to explain the presence of very strong Li lines in the spectra of some low-mass K giant stars. In this scenario all ordinary, Li-poor, K giants become Li rich during a short time (~105 yr) when compared to the red giant phase of 5 x 107 yr. In this "Li period," a large

We compare schematic modeling of spots and plage on the surface of cool dwarfs with Pleiades data to assess effects of magnetic activity on the strengths of the LiI and KI resonance lines in Pleiades spectra. Comprehensive LiI and KI NLTE line formation computation is combined with comparatively well-established empirical solar spot and plage

The possible generation of linear polarization in spectral lines due to depopulation-pumping processes in stellar atmospheres is investigated within the framework of a quantum electrodynamic theory for the transfer of polarized radiation based on the atomic density-matrix formalism. It is shown that the radiation field's anisotropy in solar-like

In this work we present spectroscopic observations centered in the spectral lines most widely used as optical indicators of chromospheric activity (Hα, Hβ, Ca ii H & K, and He i D3) in a sample of F, G, K and M chromospherically inactive stars. The spectra have been obtained with the aim of providing a library of high and mid-resolution spectra to

BP Tau is one of the few classical T Tauri stars for which the presence of a hot spot in the surface has been reported without ambiguity. The most likely source of heating is gravitational energy released by the accreting material as it shocks with the stellar surface. This energy is expected to be radiated mainly at UV wavelengths. In this work we

PSR B1951+32 is a γ-ray pulsar detected by the Energetic Gamma Ray Experiment Telescope (EGRET) and identified with the 39.5 ms radio pulsar in the supernova remnant CTB 80. The EGRET data shows no evidence for a spectral turnover. Here we report on the first observations of PSR B1951+32 beyond 30 GeV. The observations were carried out with the 10