Photometric and spectroscopic variability of the blue supergiant rho Leo

TL;DR

This study analyzes the photometric and spectroscopic variability of the blue supergiant rho Leo to understand its physical properties, variability mechanisms, and evolutionary stage, revealing multiple stable and variable periods linked to rotation and pulsations.

Contribution

It provides a detailed analysis of rho Leo's variability using multi-source data, identifying key periods and their origins, and constrains its evolutionary status as a blue loop post-red supergiant.

Findings

Detection of multiple periods from 0.8 to 35 days.

Identification of the 11-day period as stellar rotation.

Linking the 17-day period to radial pulsations.

Abstract

Context. The post-main-sequence evolution of massive stars remains poorly understood, particularly for blue supergiants. These objects play a crucial role in the dynamical and chemical evolution of galaxies and exhibit pronounced photometric and spectroscopic variability, often quasi-periodic rather than strictly periodic. Aims. We investigate the variability of the evolved B-type star rho Leo to determine its physical properties, identify the underlying mechanisms driving its variability, and constrain its evolutionary stage. Methods. We analyse long-term spectroscopic and photometric datasets obtained from multiple sources, including the TESS and Kepler space missions and observations with the 1.5 m telescope in Estonia. Period analysis is performed using the Generalized Lomb-Scargle periodogram, Lomb-Scargle pre-whitening, and the Weighted Wavelet Z-Transform. Fundamental stellar parameters are derived by fitting synthetic line profiles computed with the FastWind code to the HARPS spectrum, while the stellar rotation inclination is estimated using the ZPEKTR code. Results. The He I 6678.151 A line shows significant radial-velocity and line-profile moment variations. We detect a set of periods and harmonics spanning approximately 0.8 to 35 days. Some periods remain stable over time, whereas others vary between observing seasons. A comparison of spectroscopic and photometric variability, together with phase-curve morphology, allows us to constrain the origin of several signals. In particular, the approximately 11 day period is attributed to stellar rotation, while the approximately 17 day period is linked to radial pulsations. Conclusions. Although the variability is quasi-periodic, most detected periods persist across multiple seasons. The wide range of timescales suggests that rho Leo is likely evolving along a blue loop following the red supergiant phase.