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Astron. Astrophys. 341, 751-767 (1999)

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Deep ROSAT HRI observations of the Pleiades *

G. Micela 1, S. Sciortino 1, F.R. Harnden Jr. 2, V. Kashyap 2, R. Rosner 3, C.F. Prosser  ** 4, F. Damiani 1, J. Stauffer 2 and J.-P. Caillault 5

1 Osservatorio Astronomico di Palermo, Palazzo dei Normanni, I-90134 Palermo, Italy
(e-mail: gmicela@oapa.astropa.unipa.it; ssciortino@oapa.astropa.unipa.it; fdamiani@oapa.astropa.unipa.it)
2 Smithsonian Astrophysical Observatory-Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
(e-mail: frh@cfa.harvard.edu; kashyap@cfa.harvard.edu; stauffer@cfa.harvard.edu)
3 Department of Astronomy and Astrophysics and Enrico Fermi Institute, The University of Chicago, 5640 South Ellis Avenue, Chicago,
IL 60637, USA (e-mail: rrosner@oddjob.uchicago.edu)
4 NOAO, P.O. Box 26732, Tucson, AZ 85726-6732, USA
5 Department of Physics and Astronomy, University of Georgia, Athens, GA 30602-24551, USA (e-mail: jpc@akbar.physast.uga.edu)

Received 23 June 1998 / Accepted 30 September 1998

Abstract

In a deep X-ray survey of the Pleiades open cluster, we use the ROSAT High Resolution Imager to explore a region of the cluster formerly surveyed with the PSPC. These new observations substantially improve upon both the sensitivity and the spatial resolution for this region of the Pleiades, allowing us to detect 18 cluster members not detected before and 16 members not included in the catalogs used in previous surveys. The high sensitivity of the present observations permits us to obtain more stringent upper limits for 72 additional members and also provides sufficient numbers of stars to enable us to explore the dependence of [FORMULA] on stellar rotation for the slow rotators of the Pleiades. Using the new high sensitivity X-ray observations and the recent rotational measurements we discuss the activity-rotation relationship in the Pleiades solar type stars.

We also present new photometric observations of optical counterparts of a number of X-ray sources detected in previous surveys but not yet identified.

Key words: X-rays: stars – stars: coronae – open clusters and associations: individual: Pleiades

* Table 2 is available in electronic form at CDS via ftp 130.79.128.5
** Deceased, Aug. 16, 1998

Send offprint requests to: G. Micela

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© European Southern Observatory (ESO) 1999

Online publication: December 16, 1998
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