Distribution of cool starspots on the surface of the red dwarf V647 Her

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Abstract

Photometric observations of the star V647 Her (M3.5V) obtained in 2022 at the 1.25 m telescope of the Crimean Astrophysical Observatory are analyzed. The presence of a low-amplitude variability in brightness of the star with a period of 20.69 d, found from observations in 2019, is confirmed; it is shown that as the brightness decreases, the star becomes redder. The observed nature of photometric variability is due to the presence of cool spots on the surface of the star and manifestation of rotational brightness modulation with a full amplitude of no more than 0m.05. We have performed a comparison of the photometric results obtained in 2019, 2022 and 2004. The zones of starspot concentrations in different epochs were determined from the analysis of phase curves. The distribution of spots has been maintained for 40–100 days. Starspot parameters were estimated in the framework of the zonal model. The temperature of the spots is 2700–2800 K. The area they occupied in 2004 is 15% of the total surface area of the star. According to the 2019 and 2022 data, it increases to 30%. The difference between the spottedness of the hemispheres caused by their seasonal redistribution is less than 2%.

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About the authors

N. I. Bondar

Crimean Astrophysical Observatory of RAS

Author for correspondence.
Email: otbn@mail.ru
Russian Federation, Nauchny

K. A. Antonyuk

Crimean Astrophysical Observatory of RAS; Special Astrophysical Observatory of RAS

Email: otbn@mail.ru
Russian Federation, Nauchny; Nizhnij Arkhyz

N. V. Pit

Crimean Astrophysical Observatory of RAS

Email: otbn@mail.ru
Russian Federation, Nauchny

I. Yu. Alekseev

Crimean Astrophysical Observatory of RAS

Email: otbn@mail.ru
Russian Federation, Nauchny

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Supplementary files

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2. Fig. 1. Changes in the average brightness values ​​of V647 Her in September-October 2022. The brightness values ​​of the control star (triangles) are given with a zero point equal to -0.31, bars indicate the standard errors, dashes indicate the monitoring dates.

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3. Fig. 2. The brightness behavior of V647 Her based on observations in 2019 and 2022. (a) results of observations in 2022, (b) series of ΔV-magnitudes after primary processing of data in 2019 and 2022, ΔV are determined relative to the comparison star TYC 2082-2143-1, the dotted line marks the maximum brightness level.

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4. Fig. 3. Brightness variations of V647 Her with a period of 20.69 days. (a) light curve based on observations in 2022 and errors in the ΔV-magnitudes averaged on the observation date; (b) brightness variations of V647 Her with a period of 20.69 days, inset — the period of 20.69 days based on the results of the Lomb–Scargll frequency analysis; (c) data convolutions on the intervals 05.07–28.09 (crosses) and 1.10–15.11 (filled circles), the lines show the approximating polynomials: (d) a series of residuals after subtracting the contribution of variability with P = 20.69 days and the root mean square error (RMS) of the residuals, the dotted lines mark the ±2σ levels.

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5. Fig. 4. Changes in the V–I color index with a period of 20.69 days. (a) changes in the brightness and color index of V–I and the corresponding scalar values; (b) phase curve — a convolution of the V–I data with a period of 20.69 days and the approximating 4th-order polynomial (solid line); (c) series of residuals Δ(V–I) after taking into account the periodicity of 20.69 days, the value of σ and the ±2σ levels (dashed lines).

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6. Fig. 5. Manifestations of rotational brightness modulation in 2019 and 2022. Phase curves (represented by polynomials) show changes in the amplitude and phase of the minima in 2019 (thin line) and in 2022 (thick line).

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