1994A&A...287..843S

We report on non-simultaneous X-ray (with the ROSAT HRI and PSPC) and radio observations (with the VLA) of the visual binary α Gem (= Castor A+B). Each component of this visual binary system is itself spectroscopic, with an A-type star as primary component. In our radio maps we clearly detect a source at the position of Castor A, but not at Castor B. Our X-ray observations confirm the previous detection of X-ray emission from the Castor A+B system, and indicate that Castor A, i.e., the radio source, is also the likely site of the X-ray emission. We examine in detail the hypothesis that both the X-ray and radio emission from Castor A come from the presumably late-type secondary, and show that this hypothesis encounters difficulties. If radio and X-ray emission came from the A-type primary, α Gem A would be one of the nearest X-ray and radio emitting A-type stars.