Starspots and rotation velocities of normal A- and Am- stars
Abstract
Using the ``hump and spike'' features, we computed the rotation frequencies and amplitudes. The corresponding equatorial rotational velocity ($\rm V_{rot}$) and spot size were estimated. On fitting the autocorrelation functions of the light-curves with the appropriate model, we obtained the starspot decay-time scale. The $\rm V_{rot}$ agrees well with the projected rotational velocity ($\rm \nu sin$ $i$) in the literature. Considering a single circular and black spot, we estimate its radius from the amplitude of the ``spike''. No evidence for a significant difference in the average ``spike'' amplitude and spot radius was found for Am/Fm and normal A stars. Indeed, we derived an average value of $\rm \sim 21\pm2$ and $\rm \sim 19\pm2$\,ppm for the photometric amplitude and of $\rm 1.01\,\pm\,0.13$ and $\rm 1.16\,\pm\,0.12$\,$\rm R_E$ for the spot radius (where $\rm R_E$ is the Earth radius), respectively. We do find a significant difference for the average spot decay-time scale, which amounts to $3.6\pm0.2$ and $1.5\pm0.2$ days for Am/Fm and normal A stars, respectively. In general, spots on normal A stars are similar in size to those on Am/Fm stars, and both are weaker than previously estimated. The existence of the ``spikes'' in the frequency spectra may not be strongly dependent on the appearance of starspots on the stellar surface. In comparison with G, K and M stars, spots in normal A and Am/Fm stars are weak which may indicate the presence of a weak magnetic field.
- Publication:
-
Stars and their Variability Observed from Space
- Pub Date:
- 2020
- Bibcode:
- 2020svos.conf..433T
- Keywords:
-
- stars: photometry;
- stars: chemically peculiar;
- stars: rotation;
- stars: starspots