Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...283..179p&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 283, no. 1, p. 179-188
Astronomy and Astrophysics
Astrophysics
16
Binary Stars, Chromosphere, Dynamo Theory, Late Stars, Stellar Activity, Atomic Spectra, Calcium, H Alpha Line, Stellar Coronas, Stellar Magnetic Fields
Scientific paper
We analyze Ca II and H-alpha observations for a smaple of 27 Pop II binaries to investigate their degree of chromospheric activity. We find that Pop II binaries having periods shorter than around 10 days possess active chromospheres. On the other hand binaries with longer periods appear to be chromospherically quiet. Only one object clearly deviates from this trend and our high resolution spectroscopic observations reveal that this system contains an evolved star. We interpret these results as a clear sign that the nature of chromospheric activity in Pop II binaries is of magnetic origin, powered by the tidal forces acting in the short period systems. In this context activity can be a powerful tool to investigate the dynamical evolution of binary systems. The rapid decay of chromospheric activity with increasing orbital period may suggest that a minimum rotational velocity is necessary to trigger the onset of a powerful dynamo. Ca II and K observations can also be used to determine more precise orbits, in fact in two systems previously classified as single line spectroscopic binaries, the Ca II emission of the unseen companions is detected. Wilson-Bappu widths are measured for 12 stars which may be used to derive additional information on the components of the system.
Lindgren Harri
Pasquini Luca
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