Doppler Imaging of RS CVn and Related Stars

What are RS CVn Stars?

It is believe that convection coupled with high stellar rotation results in a dynamo mechanism which converts the mechanical energy of rotation and convection into magnetic energy. This dynamo is what powers solar and stellar activity. RS CVn are late-type, evolved (spectral type ~ K) stars found in binary systems. The fact that they are cool stars means they have deep convection zone. Also, because they are in binary systems, tidal coupling with the companion forces the star to rotate at high velocity. Consequently, these stars show exhibit magnetic activity in the form of starspots (which we image via Doppler imaging), flares, coronae, X-ray and chromospheric emission, etc. Because of the deeper convection zone and high rotation rates for RS CVn stars, the level of activity is many orders of magnitudes greater than solar activity. For instance, sunspots only cover a few percent of the solar surface even during sunspot maximum. On RS CVn stars starspots can cover 10-20% of the surface. FK Comae stars are single stars late-type stars which are believed to be coaelesced binaries. Once again the high rotation stems from the one-time binary nature of the star.
Starspots, like sunspots are believed to trace the surface magnetic flux. Doppler imaging of these features on stars gives us valuable information about spot morphology, differential rotation, and activity cycles on other stars in much the same way the study of sunspots has yielded much about what we know of solar activity.

Twelve Years of Doppler Imaging of HR 1099

Click on the image to the left to see Doppler images of the RS CVn star HR 1099 from 1981 - 1989.
The image to the right shows images from 1990 - 1993. All the images are shown in a flattened polar projection with latitude lines spaced at equal intervals. The thick heavy circle represents the stellar equator and the other circles represent latitude lines at intervals of 30 degrees. The star rotated counter clockwise with rotation phase 0.0 at the bottom, 0.25 at the left and 0.5 at the top. The radial tick marks around the star indicate the phases of the observations. The hatched spots represent a hot spot for image 1988.79 and 1989.11 and a cool spot in 1989.83. The latter was a feature indicated by photometric measurements but not found in the spectral image.

HD 106225

HD 106225 is a single-lined RS CVn star (K0III) with a 10.4 day rotation period. The Doppler image to the right was derived using the Ca I 6439 Å from data taken in early 1995.