Multi-epoch spectroscopic variability of the B supergiant HD 75149

¹ Centro de Astronomía (CITEVA), Universidad de Antofagasta, Av. Angamos 601 Antofagasta, Chile
² Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Av. Gran Bretaña 1111 Valparaíso, Chile
³ Departamento de Computación e Industrias, Universidad Católica del Maule, Avenida San Miguel 3605, Talca, Chile
⁴ Departamento de Espectroscopía, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque S/N, BF1900FWA, La Plata, Buenos Aires, Argentina
⁵ Instituto de Astrofísica de La Plata, CCT La Plata, CONICET-UNLP, Paseo del Bosque S/N, BF1900FWA, La Plata, Buenos Aires, Argentina
⁶ Centro Multidisciplinario de Física, Vicerrectoría de Investigación, Universidad Mayor, 8580745 Santiago, Chile
⁷ Nanjing Institute of Astronomical Optics & Technology, National Astronomical Observatories, Chinese Academy of Sciences, Nanjing 210042, China
⁸ Chinese High Angular Resolution Southern Astronomical Laboratory (CHARSAL)/Astro-Photonics Laboratory/Space and Planetary Exploration Laboratory (SPEL), Dept. of Electrical Engineering, FCFM, Universidad de Chile, Av. Tupper 2007 Santiago, Chile

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Received: 17 November 2025
Accepted: 26 April 2026

Abstract

Context. Massive stars continuously enrich the surrounding interstellar medium by supplying it with stellar material driven by their powerful winds. B supergiant stars (BSGs) in particular are a type of massive star characterized by strong winds and notable photometric and spectroscopic variability.

Aims. We aim to conduct a pilot study of the optical spectroscopic variability of the BSG HD 75149 between 2004 and 2025. Its extended temporal baseline and pronounced variability amplitude make it particularly well suited for investigating the physical origin of the observed short-term variability within a consistent hydrodynamical and radiative-transfer framework.

Methods. We analyzed 25 nightly averaged optical spectra obtained with different instruments and telescopes, some of them with observations over several consecutive days. We measured the radial velocities (RVs) and equivalent widths (EWs) of 17 spectral lines (H, He I, Si III, N II, Mg II, C II). We modeled the Hα emission, absorption, and P-Cygni profiles using the ISOSCELES grid and the δ-slow hydrodynamic regime.

Results. Hα shows variability in intervals of a few days, including P-Cygni changes, while metal lines show small RV amplitudes, consistent with pulsating oscillations. The largest variation in the mass-loss rate corresponds to an increase of a factor of 1.8 within four days. In contrast, the terminal velocity remains barely affected during the same time interval.

Conclusions. The pronounced variation observed in hydrogen lines, in contrast with the variability of other lines, suggests that it is due to mass-loss rate episodes driven by a slow wind occurring on a timescale comparable to photometric variations. We found no evidence of a close binary companion in the sample used, but we cannot completely exclude the possibility of a wide or low-inclination companion.