IAFE   05512
INSTITUTO DE ASTRONOMIA Y FISICA DEL ESPACIO
Unidad Ejecutora - UE
artículos
Título:
Mg II h+k emission lines as stellar activity indicators of main sequence F-K stars
Autor/es:
BUCCINO, A. P.; MAUAS, P. J. D.
Revista:
ASTRONOMY AND ASTROPHYSICS
Referencias:
Año: 2008 vol. 483 p. 903 - 910
ISSN:
0004-6361
Resumen:
Context: The largest dataset of stellar activity measurements available at present is the one obtained at the Mount Wilson Observatory, where high-precision Ca II H+K fluxes have been measured from 1966 for about 2200 stars. Since the Mg II h and k lines at 2800 Å are formed in a similar way to the Ca II H+K emission lines, they are also good indicators of chromospheric structure. The International Ultraviolet Explorer (IUE) provides a large database of UV spectra in the band 1150-3350 Å from 1978 to 1995, which can also be used to study stellar activity. Aims: The main purpose of this study is to use the IUE spectra in the analysis of magnetic activity of main sequence F-K stars. Combining IUE observations of Mg II and optical spectroscopy of Ca II, the registry of activity of stars can be extended in time. Methods: We retrieved all the high-resolution spectra of F, G, and K main sequence stars observed by IUE (i.e. 1623 spectra of 259 F to K dwarf stars). We obtained the continuum surface flux near the Mg II h+k lines near 2800 Å and the Mg II line-core surface flux from the IUE spectra. Results: We obtained a relation between the mean continuum flux near the Mg II lines with the colour B-V of the star. For a set of 117 nearly simultaneous observations of Mg II and Ca II fluxes of 21 F5 to K3 main sequence stars, we obtained a colour dependent relation between the Mount Wilson Ca II S-index and the Mg II emission line-core flux. As an application of this calibration, we computed the Mount Wilson index for all the dF to dK stars which have high resolution IUE spectra. For some of the most frequently observed main sequence stars, we analysed the Mount Wilson index S from the IUE spectra, together with the ones derived from visible spectra. We confirm the cyclic chromospheric activity of Epsilon Eridani (HD 22049) and Beta Hydri (HD 2151), and we find a magnetic cycle in Alpha Cen B (HD 128621).