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Astron. Astrophys. 331, L5-L8 (1998)

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Letter to the Editor

Pa-beta as a chromospheric diagnostic in M dwarfs

C.I. Short * and J.G. Doyle

Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland (e-mail: cis@star.arm.ac.uk, jgd@star.arm.ac.uk)

Received 7 November 1997 / Accepted 12 December 1997


We have obtained, for the first time, a high resolution near-infrared spectrum in the region of Pa [FORMULA] of a chromospherically active M dwarf (AU Mic). We demonstrate that both Pa [FORMULA] and H [FORMULA] can be fit with a model of large chromospheric pressure, but that the two lines indicate clearly different values of the exact pressure. There are several important types of missing physics that need to be included in the calculations before the importance of this apparent discrepancy can be assessed. Nevertheless, the approximate agreement of the two lines lends support to an earlier theoretical result that the Paschen series is a useful chromospheric diagnostic in M dwarfs.

Key words: stars: late-type – stars: activity – stars: chromospheres – line: formation

* Current address: University of Georgia, Physics and Astronomy, Athens, GA, 30602-2451, USA

Send offprint requests to: C.I. Short, University of Georgia, Physics and Astronomy, Athens, GA, 30602-2451, USA

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© European Southern Observatory (ESO) 1998

Online publication: February 16, 1998