Chromospheric Activity in Metal-Poor Dwarfs

Details Chromospheric Activity in Metal-Poor Dwarfs Chromospheric Activity in Metal-Poor Dwarfs

2000-05-18

arxiv.org/abs/astro-ph/0005367v1

Astronomy and Astrophysics

Astrophysics

8 pages including 2 figures. To appear in "11th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun," ed. R. J. Gar

Scientific paper

We have obtained echelle spectra with the Hubble Space Telescope (HST) of the MgII 2800A region of ten stars whose metallicities range from 1/300 to 1/3 that of the Sun, and whose space velocities suggest a halo or old thick-disk origin. Spectra of all ten show double-peaked emission in the MgII core, very much like the quiet Sun. A half-dozen non-rotating stars were observed more than once, and show at most a low level of variability in the emission flux, comparable to that of quiet stars of solar metallicity. For four stars, we have obtained Lyman-alpha spectra at 0.2A resolution; all four show emission. The data thus strongly suggest that chromospheric activity at a minimum level is present in all stars of near-solar temperature, regardless of age or metallicity. While this points to non-magnetic sources such as acoustic waves, a contribution from globally-organized magnetic fields is possible at a low level. We plan a longer series of MgII and Lyman alpha observations to constrain this.

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