X-ray and optical studies of late-type stellar coronae and chromospheres

Thesis/Dissertation · Thu Jan 01 04:00:00 EST 1981

OSTI ID:6049686

Walter, F M

The nature of the coronae of late-type stars is examined through x-ray observations of RS CVn systems, rapidly rotating F, G, and K dwarfs, a small sample of G giants, and some T Tauri and other pre-main sequence stars. X-ray observations of RS CVn systems with HEAO-1 and the EINSTEIN observatory show that these close binary systems exhibit extremely bright coronal soft x-ray surface fluxes which scale linearly with the stellar angular velocity ..cap omega... This linear relation between L/sub x///L/sub bol/ and ..cap omega.. is found to hold as well for late-type dwarfs with rotation periods in excess of Ca 12/sup d/, and for the G giants. Slowly rotating dwarfs have coronal x-ray surface fluxes two orders of magnitude less than predicted from the linear relation. The break in the relation occurs for the same ..cap omega.. as does the gap in the bimodal G dwarf Call K index distribution. This is interpreted within the framework of a simple ..cap alpha omega.. dynamo model, and hypothesize that this is evidence that the convective dynamo changes modes at a crucial ..cap omega... X-ray observations of pre-main sequence stars, including T Tauri stars are discussed. The T Tauri stars exhibit a striking anticorrelation between the H..cap alpha.. equivalent width and the existence of detectable x-ray flux, which is likely attributable to x-ray absorption by the large extended atmospheres of the most active T Tauri stars. Post T Tauri pre-main sequence stars are also found to be strong x-ray sources, as might be expected from rapidly rotating convective stars. The role of the stellar magnetic field in the corona is investigated by considering the correlated variability of the coronal x-ray luminosity and temperature and the magnetic field strength.

• Research Organization: California Univ., Berkeley (USA)
• OSTI ID: 6049686
• Country of Publication: United States
• Language: English

Related Subjects

640103* -- Astrophysics & Cosmology-- Quasi-Stellar
Radio
& X-Ray Sources-- (-1987)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ATMOSPHERES
BALMER LINES
BINARY STARS
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
DWARF STARS
ELECTROMAGNETIC RADIATION
ERUPTIVE VARIABLE STARS
GIANT STARS
IONIZING RADIATIONS
MAGNETIC FIELDS
MAIN SEQUENCE STARS
MASS TRANSFER
MOTION
RADIATION FLUX
RADIATIONS
ROTATION
SATELLITES
SOFT X RADIATION
STARS
STELLAR ATMOSPHERES
T TAURI STARS
VARIABLE STARS
X RADIATION