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Astron. Astrophys. 346, 811-818 (1999)


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Beppo-SAX observations of AR Lacertae

M. Rodonò 1,2, I. Pagano  *  1, G. Leto 1, F. Walter 3, S. Catalano 1, G. Cutispoto 1 and G. Umana 4

1 Osservatorio Astrofisico di Catania, Viale A. Doria 6, I-95125 Catania, Italy
2 Istituto di Astronomia, Università di Catania, Viale A. Doria 6, I-95125 Catania, Italy
3 Earth and Space Sciences Department, New York State University, Stony Brook, NY 11794-2100, USA
4 Istituto di Radioastronomia C.N.R., Stazione VLBI, I-96017 Noto (SR), Italy

Received 4 January 1999 / Accepted 15 April 1999

Abstract

We present the results of an X-ray observation of the binary system AR Lacertae (HD 210334) obtained with the Low and Medium Energy Concentrator Spectrometers (LECS & MECS) and with the Phoswich Detector System (PDS) on board the Beppo-SAX satellite.

Two flare episodes with comparable peak luminosities were detected, one in each of the two runs into which the observations were split. Several low amplitude flares appear to be superimposed on a rotational modulated light curve. A very tight and shallow primary eclipse was observed, which is different from primary eclipses observed at other epochs by other X-ray telescopes. No sign of secondary eclipse can be inferred from these data.

The PDS data show that the emission in the 15-300 keV range is generally not detectable, but there is convincing evidence of hard photons during the onset of a flare on Nov 4 and during the flare on Nov 11. There was no significant emission in the 15-300 keV range during the major flare on Nov 4.

The AR Lac spectrum between 0.1 and 9 keV is well fit by a two component optical-thin plasma model based on the MEKAL plasma emission code with subsolar metal abundances. We also performed spectral analyses of the two separate segments of data, and found that the plasma temperatures, abundances and emission measures did not significantly change between the two time intervals.

Hints of possible H I absorption in corona or in the circumstellar enviroment are also discussed.

Key words: stars: activity – stars: binaries: general – stars: coronae – stars: individual: AR Lac – stars: late-type – stars: variables: general

* Visiting Member at JILA, University of Colorado, PO BOX 440, 80440 Boulder CO, USA

Present address: CASA, University of Colorado, PO BOX 440, 80440 Boulder CO, USA

Send offprint requests to: ipagano@ct.astro.it

© European Southern Observatory (ESO) 1999

Online publication: June 17, 1999

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