Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995mnras.276..397j&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Vol. 276, NO. 2/SEP15, P. 397, 1995
Astronomy and Astrophysics
Astronomy
25
Stars: Activity - Binaries: Close - Stars: Coronae - Stars: Late-Type - X-Rays: Stars
Scientific paper
We present the results of radial velocity measurements for an EUV-selected sample of 11 new G- and K-type binary systems, discovered in a sample of 22 EUV sources from the ROSAT Wide Field Camera (WFC) all-sky survey. The physical status of each system is reviewed and orbital solutions are obtained for nine of them. All but one show little evidence for any significantly evolved status, have periods of 0.5-5 (1 and low eccentricities, consistent with the idea that tidal locking of the components induces rotationally enhanced dynamo activity. From these results and a consideration of the biases and selection effects inherent in the identification of EUV stellar sources, it is predicted that the remaining unstudied G- and K-type sources in the WFC survey will be evenly split between short-period, main-sequence binary systems and young, rapidly rotating single stars, with few, if any, evolved single or binary systems. We re-examine the `yellow star excess' detected in both the WFC and Einstein Medium Sensitivity (EMSS) surveys, and conclude that in the case of the WFC it is a small statistical effect. The WFC survey number counts would be predicted accurately if just one of the active binaries detailed here were within 25 pc of the Sun and contributed to the local EUV luminosity function. In the EMS S, it may be that main-sequence binaries, which form a large fraction of the X-ray number counts, have not been fully incorporated into the predictive models.
Bertram D.
Jeffries Robin D.
Spurgeon B. R.
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