K2 photometry and HERMES spectroscopy of the blue supergiant ρ Leo: rotational wind modulation and low-frequency waves
We present an 80-d long uninterrupted high-cadence K2 light curve of the B1Iab supergiant ρ Leo (HD 91316), deduced with the method of halo photometry. This light curve reveals a dominant frequency of frot = 0.0373 d-1 and its harmonics. This dominant frequency corresponds with a rotation period of 26.8 d and is subject to amplitude and phase modulation. The K2 photometry additionally reveals multiperiodic low-frequency variability (<1.5 d-1) and is in full agreement with low-cadence high-resolution spectroscopy assembled during 1800 d. The spectroscopy reveals rotational modulation by a dynamic aspherical wind with an amplitude of about 20 km s-1 in the H α line, as well as photospheric velocity variations of a few km s-1 at frequencies in the range 0.2-0.6 d-1 in the Si III 4567 Å line. Given the large macroturbulence needed to explain the spectral line broadening of the star, we interpret the detected photospheric velocity as due to travelling superinertial low-degree large-scale gravity waves with dominant tangential amplitudes and discuss why ρ Leo is an excellent target to study how the observed photospheric variability propagates into the wind.
Publication : Monthly Notices of the Royal Astronomical Society, Volume 476, Issue 1, p.1234-1241
DOI : 10.1093/mnras/sty308
Bibcode : 2018MNRAS.476.1234A
Keywords : asteroseismology; techniques: photometric; techniques: spectroscopic; stars: massive; stars: oscillations; stars: rotation; Astrophysics - Solar and Stellar Astrophysics