Strömgren four-color photometry of X-ray active late-type stars: Evidence for activity-induced deficiency in the index

Free access article

Issue		Astron. Astrophys. Suppl. Ser. Volume 119, Number 3, November I 1996


Page(s)		403 - 412
DOI		http://dx.doi.org/10.1051/aas:1996255

Strömgren four-color photometry of X-ray active late-type stars: Evidence for activity-induced deficiency in the index DOI: 10.1051/aas:1996255

Astronomy and Astrophysics Supplement Series, Vol. 119, November I 1996, 403-412

Strömgren four-color photometry of X-ray active late-type stars: Evidence for activity-induced deficiency in the index

F. Morale , G. Micela , F. Favata and S. Sciortino
Send offprint requests to: F. Morale

Istituto e Osservatorio Astronomico di Palermo, Palazzo dei Normanni, 90134 Palermo, Italy
Astrophysics Division, European Space Agency -- Postbus 299, 2200 AG Noordwijk, The Netherlands

Received October 30, 1995; accepted February 9, 1996

Abstract:

We present the results of a uvby-

photometric study of a sample of active late-type stars (F--K) selected from the Einstein Extended Medium Sensitivity Survey. Our work shows the presence in the sample of a star population with the photometric index

typical of main sequence stars and an unexpected deficiency in

index. Stars with more anomalous values of

have also very high values of

and X-ray surface fluxes, near the ``saturation'' limit observed in the most active stars and similar to the flux observed in solar active regions. We discuss these results in the light of similar results found in the Sun comparing

indices in quiet and active regions and in other samples of active stars.

Key words: stars: activity --- stars: late-type --- stars: abundances --- X-rays: stars

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