BRITE photometry and STELLA spectroscopy of bright stars in Auriga: Rotation, pulsation, orbits, and eclipses

Abstract

Context. Knowing rotational and pulsational periods across the Hertzsprung-Russell diagram is of top priority for understanding stellar activity as a function of time. Aims. We aim to determine periods for bright stars in the Auriga field that are otherwise not easily accessible for ground-based photometry. Methods. Continuous photometry with up to three BRITE satellites was obtained for 12 targets and subjected to a period search. Contemporaneous high-resolution optical spectroscopy with STELLA was used to obtain radial velocities through cross correlation with template spectra as well as to determine astrophysical parameters through a comparison with model spectra. Results. The Capella red light curve was found to be constant over 176 days with a root mean square of 1 mmag, but the blue light curve showed a period of 10.1 ± 0.6 d, which we interpret to be the rotation period of the G0 component. From STELLA we obtained an improved orbital solution based on 9600 spectra from the previous 12.9 yr. We derive masses precise to ≈0.3% but 1% smaller than previously published. The BRITE light curve of the F0 supergiant ε Aur suggests 152 d as its main pulsation period, while the STELLA radial velocities reveal a clear 68 d period. An ingress of an eclipse of the ζ Aur binary system was covered with BRITE and a precise timing for its eclipse onset derived. A possible 70 d period fits the proposed tidal-induced, nonradial pulsations of this ellipsoidal K4 supergiant. η Aur is identified as a slowly pulsating B (SPB) star with a main period of 1.29 d and is among the brightest SPB stars discovered so far. The rotation period of the magnetic Ap star θ Aur is detected from photometry and spectroscopy with a period of 3.6189 d and 3.6177 d, respectively, likely the same within the errors. The radial velocities of this star show a striking non-sinusoidal shape with a large amplitude of 7 km s−1. Photometric rotation periods are also confirmed for the magnetic Ap star IQ Aur of 2.463 d and for the solar-type star κ1 Cet of 9.065 d, and also for the B7 HgMn giant β Tau of 2.74 d. Revised orbital solutions are derived for the eclipsing SB2 binary β Aur, which replaces the initial orbit dating from 1948 for the 27-year eclipsing SB1 ε Aur, and for the RS CVn binary V711 Tau, for which a spot-corrected orbital solution was achieved. The two stars ν Aur and ι Aur are found to be long-term, low-amplitude RV and brightness variables, but provisional orbital elements based on a period of 20 yr and an eccentricity of 0.7 could only be extracted for ν Aur. The variations of ι Aur are due to oscillations with a period of ≈4 yr.

TESS survey of rotational and pulsational variability of mercury-manganese stars

“…High-precision photometric observations from space opened another avenue for finding variable HgMn stars. Detection of variability with periods of a few days was reported for individual HgMn stars using CoRoT (Morel et al 2014;Strassmeier et al 2017), Kepler (Balona et al 2011(Balona et al , 2015, K2 (White et al 2017;Krtička et al 2020), the BRITE nanosat constellation (Strassmeier et al 2020), and TESS González et al 2021). In some of these cases, interpretation of photometric variability in terms of rotational modulation was supported by the detection of line profile variations in follow-up time-resolved spectroscopy.…”

Space-Based Photometry of Binary Stars: From Voyager to TESS

“…The crucial finding is that the system shows a small eccentricity (e = 0.10 ± 0.01) and an extraordinarily fast apsidal period of U = 100 ± 5 d. The latter causes changes in the effects of binarity over timescales of months, confounding studies based on data covering a longer timespan. BRITE has also been used to observe other binary systems such as the eclipsers β Lyr, β Aur, ζ Aur and Aur and the non-eclipsing RS CVn-type system V711 Tau, ν Cen and γ Lup [123][124][125][126].…”

Space Photometry with Brite-Constellation

“…Rotation and pulsation periods across the Hertzsprung-Russell diagram are of top priority for understanding stellar activity as a function of time. Continuous photometry with up to three BRITE satellites was obtained for 12 targets, primarily in the Aur/Per I field, and subjected to a period search (Strassmeier et al [115]). The bright active star, Capella, was found to be constant in the red bandpass with an rms of just 1 mmag over 176 d, but showed a 10.1 ± 0.6 d periodicity in the blue, which is interpreted to be the rotation period of its active and hotter secondary star (Figure 21).…”