Magnetic activity in the young solar analog AB Dor^*

Active longitudes and cycles from long-term photometry

¹ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
² Nordic Optical Telescope, Apartado 474, 38700 Santa Cruz de La Palma, Spain
³ Astronomy Division, PO Box 3000, 90014 University of Oulu, Finland e-mail: silva.jarvinen@iki.fi
⁴ Institute of Astronomy, ETH Zentrum, 8092 Zürich, Switzerland
⁵ INAF - Catania Astrophysical Observatory, v. S. Sofia 78, 95123 Catania, Italy
⁶ Molehill Astronomical Observatory, 54 McDowell Crescent, Glenfield, North Shore City, New Zealand

Received: 13 September 2004
Accepted: 5 November 2004

Abstract

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 – active longitudes in opposite hemispheres. The active longitudes migrate nonlinearly in the fixed reference frame, because of the differential rotation and changes of the mean spot latitudes. At least two activity cycles are found in the data. One cycle originates from repeating switches of the activity between the two active longitudes in about (2–3)-year intervals. This results in the flip-flop cycle of about 5.5 years, which includes two consecutive switches. The 5.5-yr cycle also modulates variations of the minimum stellar brightness and the peak-to-peak amplitude, that suggests a periodic redistribution of the spot area between the opposite longitudes and supports the reality of the flip-flop cycle. The other cycle is clearly seen in variations of the mean and maximum stellar brightness on the time-scale of 20 years and is reminiscent of the 11-year sunspot cycle.