Over 20-year long series of Doppler images of an active star published

May 01, 2019

Our group has contributed significantly to the collection of a spectroscopic time series of active stars at the Nordic Optical Telescope (NOT) at La Palma, Spain, using the high-resolution spectrographs SOFIN and FIES. The former instrument has served at NOT since 1993, since 2004 including also  a polarimetric mode...

<p>Over 20-year long series of Doppler images of an active star published</p>

Over 20-year long series of Doppler images of an active star published

Our group has contributed significantly to the collection of a spectroscopic time series of active stars at the Nordic Optical Telescope (NOT) at La Palma, Spain, using the high-resolution spectrographs SOFIN and FIES. The former instrument has served at NOT since 1993, since 2004 including also  a polarimetric mode. The NOT observing programmes have resulted in a unique time series of spectroscopy over 24 years, enabling the study of both the long and short-term spot activity of the FK Comae-type star HD199178. These observations were recently published in a study containing the most extensive series of Doppler imaging temperature maps ever published: 41 DI maps covering the years 1994-2017 (Hackman et al., 2019) . The maps were used to extract a time-latitude diagram of the spot activity, i.e. the equivalent to the solar butterfly diagram. The study revealed a persistent cool spot region covering the rotation pole of the star.

The NOT data has also recently been used to study stars that can be regarded as young, rapidly rotating Suns. In V889 Her the spectroscopy reveals a constant polar spot, visible in all 19 data sets between 1999 and 2017, gathered with SOFIN, FIES and HARPSPol at the ESO 3.6m telescope (Willamo et al., 2019). The retrieved average temperature correlates well with photometric brightness variations, and both of these measures indicate that the star has recently entered a higher state of activity. Another young solar analogue monitored with NOT is LQ Hya. In a recently submitted study Doppler imaging temperature maps from 2006-2017 were presented (Cole-Kodikara et al., 2019). During this period, the spot activity of LQ Hya decreased and its luminosity consequently increased. The temperature maps reveal a somewhat erratic behaviour, but the previously reported bimodal latitudinal spot distribution remains.

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