Deep SWP Spectra of "Marginal" BY Dra Stars
Abstract
Recent optical and UV surveys of M dwarfs have resulted in the discovery of a number of objects with intermediate activity levels (H-alpha in weak emission but strong Ca, II and UV emission). Available data suggest these stars have a level of chromospheric activity (and perhaps an evolutionary status) midway between active BY Dra/dMe stars and quiet dM's. These "marginal" BY Dra (mBY) stars provide us with a class of objects rotating very near a "trigger velocity" (about 5 km s^-1) which appears to divide active BY Dra stars from quiet dM's. Unfortunately, only poor far UV spectra have been obtained to date (<= 5 hours). We propose to take about 20 hour SWP spectra of two mBYs by combining an ESA shift with NASA US1 and US2 (first half). These new spectra will allow us to accurately probe the upper chromospheres and transition regions of these important transitional stars for the first time. Infrared magnetic field measures will be used to explore the connection between fieldstrength/filling-factor and atmospheric heating. Comparison of these data with published information on active dMe and quiet dM stars will yield information on the character of the stellar dynamo as it makes a transition from "high" to "low" activity.
- Publication:
-
IUE Proposal
- Pub Date:
- 1992
- Bibcode:
- 1992iue..prop.4295S