Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998a%26a...330..685s&link_type=abstract
Astronomy and Astrophysics, v.330, p.685-695 (1998)
Astronomy and Astrophysics
Astrophysics
62
Stars: Activity Of, Stars: Imaging, Stars: Individual: Ek Dra, Stars: Late-Type, Starspots
Scientific paper
We present the first Doppler images of the single G1.5V-star EK Draconis from high-resolution CFHT spectra obtained in 1995. EK Dra is an important target for investigating the evolution of stellar magnetism because it resembles the rapidly-rotating young Sun. From the inversion of a total of 12 spectral lines we reconstruct several cool spots at low and medium latitudes but the dominating feature is located consistently at a latitude of ~70-80° , thus, at far higher latitudes than where our Sun shows spots. In fact, our data indicate that this feature could be an appendage of a larger polar cap-like spot as seen on other rapidly-rotating stars, however, due to the small vsin i of just 17.3+/-0.4 kms(-1) \ the cap's existence remains inconclusive. Spot temperatures between Delta T~1200 K and 400 K are recovered. We have used the non-parametrized convective-flux description of Canuto & Mazzitelli for our input model atmospheres and found good agreement with local line profiles computed from standard mixing-length atmospheres. New phase-resolved UBVRI data spanning the 1996/97 observing season indicate a surprisingly short photometric period of 2.599+/-0.001 days, which is different by 7% from the longest seasonal period found so far but in good agreement with the long-term photometric period of 2.605 days. We interpret these differences as being due to differential surface rotation and adopt the long-term photometric period to be the rotation period of EK Dra. Our data also confirms the continuing decline of the mean brightness seen since 1994 and we suspect the high-latitude feature to be the cause.
Rice John B.
Strassmeier Klaus G.
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