1998A&A...329..229D

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 log L_x<26.1. High resolution optical data for CaII HK indicate a surface flux of ∼6.5x10³erg/cm²/s, in good agreement with the previously measured Mg II hk flux. Based on chromospheric modelling, both the Hα and CaII 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 T_min less than 2650K, and a thin, steep chromosphere. Furthermore, the CaII HK radiative losses may only be ∼5% of the radiative losses in the UV continuum, implying total chromospheric losses in excess of 10⁵erg/cm²/s.