Norberts's Cool Stars Page

Overview

RS CVn stars are spectroscopic binaries with periods between about a day and one month with enhanced chromospheric and coronal activity. They distinct themselves because their optical Ca II emission is too strong for their luminosity class. They also show dark distortion waves in their light curves. Although those lightcurve distortions were originally thought to be the result of circumstellar matter in the binary, it is now clear that they are more closely related to dark spots on the surface of the star. In general RS CVn systems are close binaries with stellar rotation rates that are higher than field stars of the same spectral type, because of tidal interaction between the components. The optical primaries have spectral types between late G and late K, mostly subgiants. The mass ratio in these binary system is often very close to unity. All of them show dark waves moving in retrograde through the light curves. many times it is observed that chromospheric lines like Ca II, but also Mg II and C II, vary in antiphase with the optical light, a fact that has been well established for the eclipsing binary AR Lac as well a s the non-eclipsing system II Peg.

Many RS CVn binaries are strong X-ray and radio sources with X-ray luminosities in the range between 10^30 < Lx < 10^32 erg/s. They possess strong, hotter than normal coronae with temperatures up to 10^8 K and up to now are the best examples of active large scale dynamo activity in stars. Spectroscopy with the HETGS allows us for the first time to determine coronal parameters such as temperatures and densities through various phases of the binary orbit in the X-ray domain. Line ratios deduced from the emission line spectra at different phases during the eclipse can be used to map the coronal geometry.

Resolve Emission Line Spectra of Coronal Sources
Determine Temperature and Density of Stellar Coronae
Determine Geometry and Temporal Structures
Refine Models of the Underlying Heating Mechanisms

TITLE: HETGS Observations of the Eclipsing Binary AR Lac.

AR Lac is an eclipsing binary (G2 IV + K0 IV). With an orbital period of 1.98 days and a mass ratio of almost 1 it is the prototype of its kind. It will be observed through primary eclipse to map the extent of the emitting structures on the primary star. It will also be observed at quadratures to determine the relative contributions from each stellar component.

TITLE: HETGS Observations of the Single-lined Binary II Peg.

II Peg is a single-lined binary (K2-3 IV-V) with an orbital period of 6.72 days and a mass function of f = 0.004 Msun. It is very active, and is known to flare frequently. It's spectrum will be studied for temporal variability due to flaring, as well as for temperature structure.

Norbert's Chandra Science page