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Astron. Astrophys. 331, 596-600 (1998)

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First VLBI images of a main-sequence star

Arnold O. Benz 1, John Conway 2 and Manuel Güdel 3

1 Institute of Astronomy, ETH-Zentrum, CH-8092 Zürich, Switzerland
2 Onsala Space Observatory, S-43992 Onsala, Sweden
3 Paul Scherrer-Institut, CH-5232 Villigen PSI, Switzerland

Received 15 July 1997 / Accepted 5 November 1997


The binary system UV Cet A and B has been observed with the VLBA/VLA at 3.6 cm wavelength. Both dMe stars have been detected. The stronger, steady radio emitter of the two, UV Cet B, is resolved into at least two spatial components. Their relative intensities change during the 6.3 hours of observing time. One of the components is more stable and resolved, the other is possibly unresolved. The resolved component has a half-power diameter of [FORMULA] cm, exceeding the size of the stellar photosphere. The separation of the two components of UV Cet B is [FORMULA] cm or 4-5 stellar radii. The alignment of the two components is along the axis of the binary orbit and thus parallel and very likely close to the stellar rotation axis. The apparent trapping of the gyrosynchrotron emitting energetic electrons requires large coronal loops extending to several stellar radii. At the more variable source a magnetic field between 15 and 130 G is derived.

Key words: stars: individual: UV Cet – binaries: visual – stars: imaging – stars: coronae – stars: magnetic fields – radio continuum: stars

Send offprint requests to: A.O. Benz

© European Southern Observatory (ESO) 1998

Online publication: February 16, 1998