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

Thomas Preibisch

Astronomy & Astrophysics, 345, 583 (1999)


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 (~ 2 x 10^5 yr old) intermediate-mass (~ 4 M_sun) 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 (L_x ~ 1.2 x 10^33 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.

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