Spot and flare activity of single G5 III IV giant HD 199178 from TESS observations

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Abstract

The aim of our work is to study the activity of the FK Com type star rapidly rotating G5 III IV giant HD 199178 (V1794 Cyg) on the base of available photometric data from TESS mission in five sectors. The light curves of the star characterized the variability caused by rotational modulation due to the presence of cool spots on the surface, power spectra and phase diagrams are studied. The dominant peak corresponds to the photometric period P = 3.28d ± 0.12d. It is suggested that the value of P decreases over time (over an interval of about 40 years) from 3.337d up to 3.28d may be due to the long-term evolution of the positions of the active areas (spots) on the surface of a differentially rotating star. The changes in the amplitude of the brightness variability and the shape of the phase curves of HD 199178 were analyzed and it was found that the fraction of the star’s surface occupied by spots varied from 7 to 12% of its surface area. The flare activity of the star has been studied. The parameters of the amplitude, duration and energy of the flares are determined for two of them. One of the considered flares is the strongest during the observations in five sectors (5.1 × 1035 erg) and in magnitude can characterize the upper limit of the flare energies in a given state of star activity. Maps of the surface temperature inhomogeneities of the star are constructed.

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About the authors

I. S. Savanov

Institute of Astronomy of the Russian Academy of Sciences

Author for correspondence.
Email: isavanov@inasan.rssi.ru
Russian Federation, Moscow

A. N. Tarasenkov

Lomonosov Moscow State University, Sternberg Astronomical Institute

Email: isavanov@inasan.rssi.ru
Russian Federation, Moscow

E. S. Dmitrienko

Lomonosov Moscow State University, Sternberg Astronomical Institute

Email: isavanov@inasan.rssi.ru
Russian Federation, Moscow

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Supplementary files

Supplementary Files
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2. Fig. 1. On the left are the light curves for HD 199178, in the center are the power spectra of the brightness variability, on the right are the phase diagrams of the brightness variability (the horizontal lines characterize the magnitude of the amplitude of the brightness variability). The data are given for observations in 5 sets.

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3. Fig. 2. The upper panel is the power spectrum of the brightness variability of HD 199178, the lower panel is the phase diagram.

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4. Fig. 3. Section of the light curve of HD 199178 in the interval 1726.0 — 1731.0 days. The abscissa scale corresponds to the TESS format, BJD —245 4833.

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5. Fig. 4. Results of reconstructing temperature inhomogeneities on the surface of HD 199178. Sector numbers are indicated above the maps and light curves.

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