Differential Rotation of Stars in Spectral Class A
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DIFFERENTIAL ROTATION OF STARS IN SPECTRAL CLASS A
I. S. Savanov,1 E. S. Kalinicheva,1 and E. S. Dmitrienko2
Published data indicate a substantial increase in the differential rotation parameter ': of stars hotter than 6700 K. By analyzing the shape of the light curves and the presence of a specific set of peaks in their power spectra, we have found that 47 of 57 objects with Teff greater than 7500 K that were studied can be identified as pulsating stars and only 10, as stars with brightness variation owing to rotational modulation. After eliminating the pulsating variables, for the stars with Teff greater than 7500 K the average value of ':= 0.051±0.01 rad/day. This conclusion conflicts with our earlier assumption that the peaks in the power spectra for ROTD stars are caused by a possible manifestation of differential rotation. Further independent evidence for a low value of ': for stars in spectral class A has been obtained from Zeeman-Doppler charts for the star J Gem, with an estimate for the differential rotation parameter of the star of 0.0073±0.0023 rad/day. Keywords: stars: activity: spots: photometry: variability: differential rotation
1. Introduction
High precision photometric observations with the Kepler space telescope have opened up the possibility of studying various kinds of stellar variability, including their rotational modulation owing to the presence of spots on their surface. The observational manifestations of differential rotation (DR) of stars can be studied in several ways; these are described and the results from them can be found, for example, in Ref. 1. One of these methods, based on
(1) Institute of Astronomy, Russian Academy of Sciences, Moscow, Russia; e-mail: [email protected] (2) P. K. Shternberg State Institute of Astronomy, M. V. Lomonosov Moscow State University, Moscow, Russia
Original article submitted April 23, 2020; accepted for publication August 26, 2020. Translated from Astrofizika, Vol. 63, No. 4, pp. 573-581 (November 2020) 504
0571-7256/19/6304-0504 ©2020 Springer Science+Business Media, LLC
analyzing the difference in the periods found from splitting of the peaks in the power spectra of the brightness variation of spotted stars has come into widespread use. It has been used [2,3] to establish the DR parameters of representative samples of several tens of thousands of stars. Based on observations with the Kepler telescope, the light curves of 18616 and 12300 objects have been analyzed in Refs. 2 and 3, respectively, and their differential rotation parameters D and ': have been determined. The differential rotation law is described by an equation of
the form : T : eq 1 Dsin 2 T , where T is the latitude and ':
D: eq .
In Ref. 2 the analysis was based on observational data from a limited time interval Q3. The data of Ref. 3 were obtained from a more extensive sample Q1-Q14. These represent more numerous, uniform data for determining D and ':, and permit their statistical analysis. They characterize the variation in the DR parameters for objects within a
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