The ultraviolet variations of Delta Scuti

Abstract

This paper reports on low resolution observations of the pulsating star Delta Scuti (F2IIIp) obtained with the International Ultraviolet Explorer (IUE) at different phases of the 4 hr and 40 min pulsation cycle. The ultraviolet flux varies in phase with the optical flux measured with the Fine Error Sensor (FES). The amplitude of the ultraviolet variations increases toward shorter wavelengths from 20 percent at 3000 A to 50 percent around 1900 A. Most likely, the ultraviolet variations are caused by the alteration of the effective temperature over the pulsation cycle. A comparison of the spectra of Delta Scuti at maximum and minimum light with low resolution IUE spectra of nonvariable stars indicates that the effective temperature does not vary by more than 400 K over a cycle, in agreement with Trodahl and Sullivan's (1977) result based on optical spectrophotometry. Two high-resolution spectra covering the range 1900-3200 A are also presented. A line identification was presented showing that the mid-UV spectrum of Delta Scuti is crowded with lines of neutral and singly ionized iron-peak elements, in particular those of Fe II, Cr II, Mn II, and Ti II. 18 refs.