Magnetic activity on V889 Herculis ^*,**

Combining photometry and spectroscopy

¹ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: sjarvinen@aip.de
² Tuorla Observatory, University of Turku, 21500 Piikkiö, Finland
³ Astronomy Division, PO Box 3000, 90014 University of Oulu, Finland
⁴ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany
⁵ Institute of Astronomy, ETH Zentrum, 8092 Zürich, Switzerland
⁶ Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland
⁷ Observatory, PO Box 14, 00014 University of Helsinki, Finland

Received: 24 March 2008
Accepted: 17 June 2008

Abstract

Aims. In this paper we analyse photometric and spectroscopic observations of the young active dwarf V889 Her. We present new surface temperature maps, and compare them to earlier published Doppler maps, as well as to the results obtained from long-term photometry.

Methods. The light curve inversions and surface temperature maps were obtained using the Occamian approach inversion technique.

Results. The 12 years of photometric records on V889 Her suggest a possible photometric cycle of approximately 9 years. Variability on this time scale is detected in the maximum, minimum, and mean photometric magnitudes. The spots prefer to concentrate on two active longitudes that are approximately 180° apart. Furthermore, one flip-flop event, i.e., a sudden change of the dominant active longitude by 180°, is detected at the time of the global maximum activity. The wings of the 8662 Å indicate that the quiet photosphere of the V889 Her is similar to the one of the present Sun supporting earlier determined atmospheric parameters, while the chromosphere of V889 Her shows signs of much stronger activity. The temperature maps reveal that the polar regions are covered by spots, which are about 1500 K cooler than the quiet photosphere. The mean spot latitude varies slightly with time. It appears that the spot latitudes from our Doppler images and the spot migration rates revealed by photometry indicate a weaker differential rotation than reported earlier, but in the same (solar-like) direction.