Far-Ultraviolet light curves of the δ Scuti variable: β Cassiopeiae

Abstract

Ultraviolet spectra of β Cas (Sp F2 III–IV) were acquired with the International Ultraviolet Explorer (IUE) satellite. The observed flux level changes rapidly from F λ ≈ 2.5 · 10 −13 to 2.0 · 10 −10 erg/cm 2/s/Å at λ = 1280 A ̊ and 3000 Å, respectively. Chromospheric emission in UV spectra is seen both in spectral lines (e.g. SiIV 1400, CIV 1550, MgII 2800 Å) and continuum (for λ < 1700 A ̊ ). To obtain the basic photospheric parameters of this star we took the mean IUE spectrum only for λ > 2300 A ̊ as well as the ground based observations in the spectral range of 3200–10800 Å. We found log T eff = 3.85, log g = 3.40, log L/ L ⊙ = 1.43 and θ = 2.0 mas. β Cas is a δ Scuti variable and time sequences of the low resolution SWP (1150–1950 Å) spectra and high resolution LWP (1900–3200 Å) spectra made in the large aperture allowed us to construct the light curves at selected wavelength passbands. In general, the amplitude grows with decreasing wavelength. Our results also indicate pulsational variability of the lower chromosphere, as seen at λ < 1700 A ̊ .