Doppler Imaging of the Hertzsprung gap star OU Andromedae
Abstract
OU And (HD 223460, HR 9024) is a moderately fast-rotating early G-type giant star, located in the Hertzsprung gap; potentially it was an Ap-star during its main sequence phase.
Our data intermittently cover the years 2008 to 2017 with a few single spectra and four observing campaigns, each lasting several weeks. Using high-resolution spectra from two sites (NARVAL and TIGRE), we create photospheric Doppler images (DI) and, furthermore, analyze the evolution of OU And's chromospheric emission. We compare our DI to simultaneous Zeeman DI (ZDI) from an earlier study and include a detailed discussion of fundamental Doppler imaging limitations. During all our observations OU And has shown only feeble surface features apart from a pronounced polar spot, which is thus present in all DI and ZDI of OU And made so far. Furthermore, we find that in several instances weak features move, evolve or disappear during less than one stellar rotation. Combining our results with findings of earlier photometric campaigns, we summarize that the activity of OU And has changed from a few epochs of obvious rotational modulation in the 1980s and 90s to several epochs after 2002 without such modulation. We perform a systematic error analysis of the chromospheric activity indices on our densely sampled 2015 TIGRE data. Thus covering almost three stellar rotations, we find OU And's chromospheric emissions to be nearly constant down to a level of a few percent.- Publication:
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Bulgarian Astronomical Journal
- Pub Date:
- July 2019
- Bibcode:
- 2019BlgAJ..31...76B
- Keywords:
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- stars: individual: OU And;
- stars: late-type;
- stars: activiy;
- stars: starspots