Trust, O. ; Jurua, E. ; De Cat, P. ; Joshi, S.

published in Proceedings of the International Conference on Stars and their Variability Observed from Space, pp. 353-354 (2020), pp. 433-434 (2020)

Abstract: Using the ``hump and spike'' features, we computed the rotation frequencies and amplitudes. The corresponding equatorial rotational velocity (Vrot) 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 Vrot agrees well with the projected rotational velocity (νsin 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 ∼21±2 and ∼19±2 ppm for the photometric amplitude and of 1.01±0.13 and 1.16±0.12 R_E for the spot radius (where 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±0.2 and 1.5±0.2 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.

Keyword(s): Stars: photometry ; Stars: chemically peculiar ; Stars: rotation ; Stars: starspots
Note: Neiner C., Weiss W.W., Baade D., Griffin R.E., Lovekin C.C., Moffat A.F.J. (eds.)
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