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

Abstract

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. 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$\pm$0.6 d, which we interpret to be the rotation period of the G0 component. The BRITE light curve of the F0 supergiant $\epsilon$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 $\hat{I}\P$Aur binary system was covered with BRITE and a precise timing for its eclipse onset derived. $\hat{I}\cdot$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 $\hat{I}¸$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. Photometric rotation periods are also confirmed for the magnetic Ap star $\ddot{I}„$Aur of 2.463 d and for the solar-type star $\hat{I}{º}^1$Cet of 9.065 d, and also for the B7 HgMn giant ${\hat{I}}^2$Tau of 2.74 d. Revised orbital solutions are derived for the eclipsing SB2 binary ${\hat{I}}^2$Aur, for the 27 year eclipsing SB1 $\epsilon$Aur, and for the RS CVn binary HR 1099. The two stars $\hat{I}½$ Aur and ${\hat{I}}^1$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 $\hat{I}½$Aur. The variations of ${\hat{I}}^1$Aur are due to oscillations with a period of $\approx$4 yr.