The spectroscopic variability of T$_{\rm eff}$ and $\log g$ in $\beta$ Cep

TL;DR

This study investigates the spectroscopic variability of the star $eta$ Cep, measuring changes in temperature, gravity, and elemental abundances over time to understand its pulsational behavior.

Contribution

It provides detailed measurements of temperature, gravity, and elemental abundances, and quantifies pulsational amplitudes and microturbulence variability in $eta$ Cep.

Findings

Effective temperature varies by about 700 K.

Surface gravity varies by approximately 0.2 dex.

Radial velocity amplitude differs between hydrogen and metal lines.

Abstract

Time resolved spectra of $\beta$ Cep yield the following average results: T$_{\rm eff}$ =24000 $\pm$ 250 K, $\log g$ = 3.91 $\pm$ 0.05 and $\xi$ = 8.1 $\pm$ 0.9 km s$^{-1}$. N, O, Ne, Al, Si and S abundances are solar while C, Mg and Fe are slightly under-abundant. Pulsational amplitudes of $\Delta$T$_{\rm eff}$ $\sim$ 700 K and $\Delta$$\log g$ $\sim$ 0.2 dex are found from H$\beta$. The metal lines give similar amplitudes but centred on T$_{\rm eff}$ $\sim$ 25000 K. An upper limit of 1.0 km s$^{-1}$ to the variability of the microturbulence is derived from the Si {\sc iii} triplet at 455 nm. The radial velocity amplitude derived from the core of H$\beta$ is $\sim$ 15% greater than that from the metal lines.