K2 photometry and HERMES spectroscopy of the blue supergiant ρLeo: rotational wind modulation and low-frequency waves

Journal article

We present an 80-d long uninterrupted high-cadence K2 light curve of the B1Iab supergiant rho Leo (HD 91316), deduced with the method of halo photometry. This light curve reveals a dominant frequency of $f_{\rmrot}=0.0373$d$^{-1}$ and its harmonics. This dominant frequency corresponds with a rotation period of 26.8d and is subject to amplitude and phase modulation. The K2 photometry additionally reveals multiperiodic low-frequency variability ($<1.5 $d$^{-1}$) and is in full agreement with low-cadence high-resolution spectroscopy assembled during 1800 days. The spectroscopy reveals rotational modulation by a dynamic aspherical wind with an amplitude of about 20km s$^{-1}$ in the H$\alpha$ line, as well as photospheric velocity variations of a few km s$^{-1}$ at frequencies in the range 0.2 to 0.6 d$^{-1}$ in the SiIII 4567\AA\ 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 super-inertial low-degree large-scale gravity waves with dominant tangential amplitudes and discuss why $\rho$~Leo is an excellent target to study how the observed photospheric variability propagates into the wind.

Authors: Aerts, C; Bowman, DM; Simon-Diaz, S; Buysschaert, B; Johnston, CC

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 476
• Issue: 1
• Pages: 1234–1241
• Publication date: 2018-02-09
• Acceptance date: 2018-02-02
• DOI: 10.1093/mnras/sty308
• EISSN: 1365-2966
• ISSN: 0035-8711
• Keywords: stars: rotation; stars: oscillations (including pulsations); asteroseismology; stars: massive; techniques: spectroscopy; techniques: photometry