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X-ray emission on hybird stars: ROSAT observations of alpha Trianguli Australis and iota AurigaeWe report on deep ROSAT observations of two Hybrid atmosphere stars, alpha TrA and iota Aur, and our analysis of these observations. We detect high-energy transient phenomena on alpha TrA and consider the implications of this discovery to the atmospheres of Hybrid stars. We detect iota Aur in the high-energy passband of ROSAT, implying the existence of multimillion degree plasma on the star. Our major results include the following: discovery of two large flare events, detected during pointed observations of alpha TrA; the demonstration that the flare emission most likely comes from the giant itself, rather than from a previously unseen low-mass companion star; the demonstration that the plasma characteristics associated with the flares and with the 'quiescent' component are essentially indistinguishable; and that the geometric dimensions of the emitting plasma are considerably smaller than the critical dimension characterizing stable 'hot' coronal loop structures. Our results suggest that alpha TrA does not have any steady X-ray emission consistent with theoretical expectations, and support the argument that Hybrid stars constitute a transitional type of object in which large-scale magnetic dynamo activity ceases, and the dominant spatial scales characterizing coronal structure rapidly decline as such stars evolve across the X-ray 'Dividing Line' in the H-R diagram.
Document ID
Document Type
Reprint (Version printed in journal)
External Source(s)
Kashyap, V. (Univ. of Chicago, Chicago, IL United States)
Rosner, R. (Univ. of Chicago, Chicago, IL United States)
Harnden, F. R., Jr. (Harvard-Smithsonian Center for Astrophysics, Cambridge, MA United States)
Maggio, A. (Osservatorio Astronomico Palermo, Italy)
Micela, G. (Osservatorio Astronomico Palermo, Italy)
Sciortino, S. (Osservatorio Astronomico Palermo, Italy)
Date Acquired
August 16, 2013
Publication Date
August 10, 1994
Publication Information
Publication: The Astrophysical Journal, Part 1
Volume: 431
Issue: 1
ISSN: 0004-637X
Subject Category
Funding Number(s)
Distribution Limits