Photometric and spectroscopic variability of the blue supergiant ρ Leo

¹ Tartu Observatory, University of Tartu Observatooriumi 1 Tõravere 61602, Estonia
² Centro Multidisciplinario de Física, Vicerrectoría de Investigación, Universidad Mayor 8580745 Santiago, Chile
³ Instituto de Estadística, Universidad de Valparaiso Blanco 951 Valparaíso, Chile
⁴ Division of Physics of stellar atmospheres and magnetism, Shamakhy Astrophysical Observatory Shamakhy 5600, Azerbaijan
⁵ Graduate School of Science, Art and Technology, Khazar University 41 Mahsati Str. AZ 1096 Baku, Azerbaijan
⁶ Departamento de Física, Universidade Federal de S ao Paulo, Rua Prof. Artur Riedel 275 09972-270 Diadema SP, Brazil
⁷ Instituto de Astrofísica La Plata, CCT La Plata, CONICET-UNLP Paseo del Bosque S/N B1900FWA La Plata, Argentina
⁸ Departamento de Espectroscopía, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata (UNLP) Paseo del Bosque S/N B1900FWA La Plata, Argentina

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 20 June 2025
Accepted: 14 December 2025

Abstract

Context. The post-main-sequence evolution of massive stars remains poorly understood, particularly in the case of blue supergiants. As key drivers of the dynamical and chemical evolution of galaxies, massive stars warrant detailed investigation during this complex evolutionary stage. Hot supergiants exhibit pronounced photometric and spectroscopic variability, typically in the form of quasi-periodic rather than strictly periodic variations.

Aims. We investigated the variability patterns of the evolved B-type star ρ Leo to determine its properties, identify the underlying physical processes, and constrain its evolutionary stage. We combined extensive long-term datasets of spectroscopic and photometric observations from various sources. These include data from the TESS and Kepler space telescopes, as well as observations from the 1.5 m telescope in Estonia.

Methods. We analysed the data using the generalized Lomb–Scargle periodogram, the Lomb–Scargle periodogram with pre-whitening, and the weighted wavelet Z-transform. To determine the fundamental parameters of ρ Leo, we fitted synthetic line profiles computed with the FASTWIND code to the HARPS spectrum. We used the ZPEKTR code to infer the stellar rotation inclination angle.

Results. The He I 6678.151 Å line profile exhibits significant changes in radial velocity and, consequently, in its moment values. We identify a set of periods and harmonics ranging from ∼0.8 to ∼35 days. Some periods remain nearly constant, while others appear and disappear from one observing season to another. A comparison of spectroscopic and photometric data, along with the shape of the phase curves, helps to constrain the nature of several periods. In particular, the ∼11-day period is attributed to stellar rotation, while the ∼17-day period is associated with radial pulsations.

Conclusions. Despite their quasi-periodic nature, most periods are observable across multiple observing seasons. Based on the fairly wide range of detected periods, ρ Leo is likely on the blue loop of its evolution, following the red supergiant stage.