| Issue |
A&A
Volume 483, Number 3, June I 2008
|
|
|---|---|---|
| Page(s) | 903 - 910 | |
| Section | Stellar atmospheres | |
| DOI | https://doi.org/10.1051/0004-6361:20078925 | |
| Published online | 01 April 2008 | |
Mg II h+k emission lines as stellar activity indicators of main sequence F-K stars *
Instituto de Astronomía y Física del Espacio (CONICET), C.C. 67 Sucursal 28, 1428-Buenos Aires, Argentina e-mail: abuccino@iafe.uba.ar
Received:
25
October
2007
Accepted:
27
March
2008
Context. The largest dataset of stellar
activity measurements available at present is the one obtained at
the Mount Wilson Observatory, where high-precision 
H+K fluxes have been measured from 1966 for about 2200 stars. Since the 
h and k
lines at λ2800 Å are formed in a similar way to the 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 and optical spectroscopy of , 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 h+k lines near λ2800 Å and the line-core surface flux from the IUE
spectra.
Results. We obtained a relation between the mean continuum flux
near the lines with the colour 
of the star. For a
set of 117 nearly simultaneous observations of and fluxes of 21 F5 to K3 main sequence stars, we obtained a
colour dependent relation between the Mount Wilson S-index and the
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
ϵ Eri (HD 22049)
and β Hydri (HD 2151), and we find a magnetic
cycle in α Cen B (HD 128621)
Key words: standards / line: profiles / astronomical data bases: miscellaneous / instrumentation: spectrographs / stars: activity / ultraviolet: stars
© ESO, 2008
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