Spectroscopic Study of β Cephei in the Hα Region

Volume 53 number 2 (2025)

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J. Elías

Agrupación Astronómica de Madrid, Madrid-Spain, javierdeelias@gmail.com

S. Díaz

Agrupación Astronómica de Madrid, Madrid-Spain, samueldl@gmail.com

Abstract

We present a spectroscopic study of the star β Cephei in the Hα region, based on more than 1100 high-resolution spectra obtained during two observing campaigns (2023 and 2024). The data were reduced and analyzed with an automated pipeline including wavelength calibration with neon lamps and telluric lines and robust continuum normalization. Comparison of the observed profiles with NLTE synthetic models of the primary component shows that in 2023 the Hα line was dominated by photospheric absorption, while in 2024 the observed spectrum exhibits a residual excess over the model. The morphology of this residual, when compared to the expected Be–type contribution, is consistent with a double–peaked emission attributable to the secondary. A variability analysis using the moment method confirms the main pulsation frequency at 5.25 cd–1, together with several secondary terms already reported in the literature. The equivalent width (EW) and the first moment (M1) display nearly antiphased variations, with a phase shift of ~0.3 cycle, consistent with a non-adiabatic response of the stellar atmosphere. These results confirm the stability of the pulsation modes of β Cephei and highlight the variable influence of the Be companion on the morphology of the Hα line.