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Astron. Astrophys. 329, 229-232 (1998)

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Research Note

Chromospheric and coronal activity levels in the nearby faint M dwarf Gl 105B

J.G. Doyle , C.I. Short , P.B. Byrne and P.J. Amado

Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland, UK

Received 20 May 1997 / Accepted 20 August 1997


Monitoring with the HRI onboard ROSAT failed to detect the nearby faint M dwarf star Gl 105B (a star of anomalously low chromospheric and coronal activity), implying [FORMULA]. High resolution optical data for Ca II HK indicate a surface flux of [FORMULA], in good agreement with the previously measured Mg II hk flux. Based on chromospheric modelling, both the H [FORMULA] and Ca II K line profiles indicate an atmospheric structure which is intermediate between that of an intermediate dM chromosphere and a basal chromosphere. Also, the modelling indicates that a better fit is obtained using a model atmosphere which has [FORMULA] less than 2650 K, and a thin, steep chromosphere. Furthermore, the Ca II HK radiative losses may only be [FORMULA] 5% of the radiative losses in the UV continuum, implying total chromospheric losses in excess of [FORMULA].

Key words: stars: Gl 105B; activity; chromospheres; late-type

Send offprint requests to: J.G. Doyle

© European Southern Observatory (ESO) 1998

Online publication: November 24, 1997