Issue |
Astron. Astrophys. Suppl. Ser.
Volume 119, Number 3, November I 1996
|
|
---|---|---|
Page(s) | 403 - 412 | |
DOI | https://doi.org/10.1051/aas:1996255 | |
Published online | 15 November 1996 |
Strömgren four-color photometry of X-ray active late-type
stars: Evidence for activity-induced deficiency in the
index
*
1
Istituto e Osservatorio Astronomico di Palermo, Palazzo dei Normanni, 90134 Palermo, Italy
2
Astrophysics Division, European Space Agency – Postbus 299, 2200 AG Noordwijk, The Netherlands
Send offprint request to: F. Morale
Received:
30
October
1995
Accepted:
9
February
1996
We present the results of a uvby-β 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 c1 typical of main sequence stars and an unexpected
deficiency in m1 index. Stars with more anomalous values of
m1 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 m1 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
© European Southern Observatory (ESO), 1996