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Astron. Astrophys. 345, 583-591 (1999)

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An extremely X-ray luminous proto-Herbig Ae/Be star in the Serpens star forming region *

Thomas Preibisch 1,2

1 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-95121 Bonn, Germany
2 Astronomisches Institut, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany

Received 16 November 1998 / Accepted 2 March 1999

Abstract

We present near-infrared spectra for the highly obscured, optically invisible young stellar object EC 95 in the Serpens molecular cloud, from which we recently could detect strong X-ray emission with ROSAT. Its location in the HR diagram suggests this object to be an extremely young ([FORMULA] yr old) intermediate-mass ([FORMULA]) star, which is most likely the progenitor of a B-type or early A-type main sequence star. The only reasonable explanation for its extremely strong X-ray emission ([FORMULA] erg/sec) seems to be coronal, i.e. magnetic activity; this view is also supported by the strong radio emission of EC 95. This is quite surprising, since one usually does not expect a magnetic field on intermediate-mass stars, which are thought to lack surface convection zones, the prerequisite for a solar-like dynamo effect. A possible explanation might be that EC 95 currently goes through a short period of deuterium shell burning, which causes convection near the stellar surface and might give rise to a dynamo effect and a corona.

Key words: stars: coronae – stars: individual: EC 95: J182958+011247 – stars: individual: EC 95: J182958+011252 – stars: magnetic fields – stars: pre-main sequence – X-rays: stars

* Mainly based on observations collected at the United Kingdom Infrared Telescope, Hawaii, USA

Send offprint requests to: Thomas Preibisch (preib@astro.uni-wuerzburg.de)

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© European Southern Observatory (ESO) 1999

Online publication: April 19, 1999
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