Analysis of chromospheric activity in late type stars

BUCCINO, A. P.; MAUAS, P. J. D.

Pasadena, California, Estados Unidos

Workshop; 14th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun; 2006

Spietzer Science Center y Michelson Science Center

The International Ultraviolet Explorer provides a dense UV spectra database from 1978 to 1995. Moreover, the UV Mg II h and k lines (at 279.6 and 280.3 nm) are, analogous to Ca II H and K lines, good indicators of the thermal structure of stellar atmospheres. Therefore, one of the purposes of this work is to be able to use IUE observations of Mg II and visible observations of Ca II jointly and so extend in time the registry of activity of stars. First, we obtained a colour dependent linear relationship between IUE Mg II h+k line core surface flux and Mount Wilson Ca II H+K index (S) for a set of nearly simultaneous observations of a sample of 21 F5-K3 main sequence stars. From this calibration, we built a catalog of Ca II indexes for all the F, G, K and M main sequence stars with high resolution IUE spectra. Secondly, from these results, we obtained a Mount Wilson index for IUE low resolution spectra. Finally, for the most observed main sequence stars, we anlayzed the stellar activity behaviour using the Mount Wilson index S obtained in this work, together with the one obtained by from CTIO spectra, thus spanning a time interval between 1978 and 1996.