Spectroscopy of low mass pre-main sequence stars: photospheric spots and chromospheric activity

We present high resolution spectra in the 6532-6745 Angstrom wavelength range of 9 rapidly rotating (v sini > 25 km/s) T Tauri stars. Among these stars, V410 Tau and HD 283572 have been monitored in more detail, covering 2.2 and 3.2 rotational periods, respectively. The data allow us to study the changes of the profiles of the H-alpha, and several absorption lines. These changes are supposed to be related to the chromospheric emission and to the cold spots, respectively. From the absorption line profiles of some lines of V410 Tau, the presence of several spots can be inferred. We have found that the equivalent width of some absorption lines varies according to the rotational period. There is a range for the amplitude of these variations, the maximum value corresponding to the Li I 6708 line (0.53-0.65 Angstrom). Maximum equivalent widths are observed near the minimum of the light curve. The fact that these variations have not been previously detected may be partially due to the large amplitude of the continuum variability at the time of our observations. The H-alpha emission profile in V410 Tau also varies according to the rotational period. The data indicate a coincidence in longitude between the largest spot and the region in which the narrow emission component of the H-alpha line arises. For HD 283572, some metallic absorption lines indicate the presence of a polar spot but the equivalent widths of all the observed lines present constant values, except for H-alpha. Variable emission contributes to the H-alpha absorption line and, due to the position of its maximum on the light curve, the region responsible for this emission could be related to the polar spot. For the other stars of our sample the spectra present new information about their variability. HP Tau/G2 and, probably, VSB 78, show asymmetries in the Li I 6708 line, as expected from cold spots.