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Magnetic activity in the young solar analog AB Dor. Active longitudes and cycles from long-term photometry.
We analyse photometric observations of the young active dwarf AB Dor,spanning more than 20 years. Similar to the young solar analog LQ Hya,AB Dor shows long-lived, nonaxisymmetric spot distribution- activelongitudes in opposite hemispheres. The active longitudes migratenonlinearly in the fixed reference frame, because of the differentialrotation and changes of the mean spot latitudes. At least two activitycycles are found in the data. One cycle originates from repeatingswitches of the activity between the two active longitudes in about(2-3)-year intervals. This results in the flip-flop cycle of about 5.5years, which includes two consecutive switches. The 5.5-yr cycle alsomodulates variations of the minimum stellar brightness and thepeak-to-peak amplitude, that suggests a periodic redistribution of thespot area between the opposite longitudes and supports the reality ofthe flip-flop cycle. The other cycle is clearly seen in variations ofthe mean and maximum stellar brightness on the time-scale of 20 yearsand is reminiscent of the 11-year sunspot cycle.Tables 2 and 3 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/432/657
| Doppler imaging with a CLEAN -- like approach. 2: A photospheric image of AB Doradus (=HD 36705)
In an application of a new CLEAN-like algorithm for the Doppler imagingof late-type stars we present the first in our series of suface imagesof the young KOV star AB Dor (=HD 36705). This Doppler image resultsfrom our discovery of profile variations in photospheric CaI and FeIabsorption lines. We find star spots concentrated near an activelatitude of +25 deg; one feature also extends towards higher latitudes.The reconstructed photospheric features appear as groups of small spotsrather than as large individual spots. We discuss the reality of thesegroups on the basis of tests carried out on simulated data. We comparethe two-temperature CLEAN image with a maximum entropy reconstruction ofAB Dor's surface performed on the same data set. As an important testfor the derived Doppler image we demonstrate its ability to predict theobserved light curve which we have obtained from contemporaneousphotometry. Furthermore, we demonstrate how Doppler imaging can be usedto determine the stellar inclination.
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