Smoothed Temporal Variance Spectrum: weak line profile variations and NRP diagnostics

Abstract

We describe the version of the Temporal Variance Spectrum (TVS, Fullerton, Gies & Bolton 1996) method with pre-smoothed line profile (smoothed Temporal Variance Spectrum, smTVS). This method introduced by Kholtygin et al. (2003) can be used to detect the ultra weak variations of the line profile even for very noisy stellar spectra. We also describe how to estimate the mode of the non-radial pulsations (NRP) using the TVS and smTVS with different time spans. The influence of the rotational modulation of the line profile on the TVS is considered. The analysis of the contribution of NRP and rotational modulation in the global TVS is studied.

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

“…The tangential velocities associated with convectively-driven gravity waves in the stellar photosphere of massive stars are of order a tenth of a km s −1 for an individual wave (Rogers et al 2013), but the combined effect of hundreds of gravity waves is similar to the effect of a few coherent heat-driven gravity-mode oscillations (Aerts & Rogers 2015). Thus, both travelling gravity waves and coherent gravity modes are feasible explanations for the variability observed in the K2 space photometry and high-resolution HER-MES spectroscopy of ρ Leo, which is similar to the conclusions made recently for other O and B supergiants (Aerts et al 2017a;Simón-Díaz et al 2018) and previously for ρ Leo by Kholtygin & Sudnik (2016).…”

“…Gravity waves have dominant tangential amplitudes, which we observe for ρ Leo in spectroscopy of the photospheric lines, supporting this interpretation. For either the case of travelling gravity waves or coherent gravity modes, our detection of the photospheric variability using both high-quality K2 space photometry combined with high-resolution spectroscopy is in full agreement with the similar detection by Kholtygin & Sudnik (2016).…”

“…In a follow-up study, we will carry out a detailed quantitative analysis of various spectral lines that are formed at different depths in the photosphere and in the wind. This will allow the derivation of the tangential versus vertical velocity structure, as well as how the photospheric variability, concluded to be non-radial gravity-modes oscillations by Kholtygin & Sudnik (2016) and/or travelling gravity waves in this work, propagates into the wind. The wind in ρ Leo is clearly a dynamic and turbulent environment, as indicated by the line profile variability of Hα shown in Fig.…”

“…Furthermore, the variability of other lines formed partially in the wind (i.e., Hβ and Hγ) vary differently with smaller amplitudes than that of Hα but larger than those of pure photospheric lines. Therefore, ρ Leo is a promising target to investigate how photospheric variability propagates into the wind (see e.g., Kholtygin & Sudnik 2016).…”

“…In their sample study of blue supergiants, Crowther et al (2006) obtained the following stellar parameters of ρ Leo: T eff 22 000 K, log g 2.55, M 18 M , R 37 R ,Ṁ 4 × 10 −6 M yr −1 . Recently, Kholtygin & Sudnik (2016) concluded from a 3.5 h highcadence time series of high-precision high-resolution spectroscopy that the star reveals non-radial oscillations. Moreover, these authors deduced that the variability signatures due to these oscillations propagate into the wind of the star.…”