1995A&A...298..505M

We present X-ray and optical observations of G102-21, a newly discovered dMe flare star in the solar neighborhood. The star, which falls serendipitously in a pointed PSPC ROSAT observation, shows an intense X-ray flare as well as other, lower-amplitude variations on time scales of around 10⁴ seconds. The decay time of about 1000sec, the characteristics of its X-ray spectrum, and the derived physical parameters, make the observed flare similar to compact solar flares and to many other flares observed on dMe stars, by previous missions. Low resolution spectroscopic observations show the whole Balmer series and the CaII H&K lines strongly in emission. Monitoring of the equivalent width of the Hα, Hβ and CaII H&K lines shows sizable night to night variations, with flaring-like behavior. Both Hα and H β lines show the presence of two components, which are very clearly separated at high resolution. The relative radial velocity changes from night to night, indicating a binary system. Based on simple assumptions we estimate that the system has a period of less than 1 day. The rotational broadening of the photospheric absorption lines observable in the high resolution spectra allows us to measure the stellar rotational velocity. The observed value (about 20km/s) is compatible with a tidally-locked system with a period between 0.5 and 1 day. The X-ray observations are consistent with a period in the range of 14-15 hours and with an inclination of the rotation axis near 50^o.