The Outer Layers of R Scuti.
George W. Preston · The Astrophysical Journal · 1962
Weak metallic emissions are present between the doubled absorption lines on high-dispersion spectrograms of R Sct obtained during the secondary light-maximum in July, 1961 Apparent doubling of many lines was observed during the subsequent decline in light and at the following deep minimum when TiO bands were present Curves of growth for the absorption lines indicate that during the double-line phases the shortward (V) absorption components are formed in hotter material than are the longward (R) components The half-widths of the V components exceed those of the 1? components; however, the Doppler parameter derived from the curve of growth is larger for the R than for the V components. It is argued that a source of continuous emission overlies the material that produces the V components. The radial velocity-curve for subordinate Fe I lines is similar to those of U Mon and W Vir However, lines arising from levels with x < 0 1 ev have a different velocity variation that can be interpreted as being due to the blending of stationary circumstellar components with moving stellar components The abnormal strength and the profiles of these low4evel lines provide additional evidence for the existence of a circumstellar envelope around R Sct Evidence is presented that the Balmer emission arises below the gas that produces the R components. When allowance is made for the profile distortion introduced by the overlying line absorption, the intrinsic emission profile appears to be approximately symmetrical and undisplaced relative to the time-average velocity of the metallic absorption lines A method is presented for resolving analytically the central maximum of the double lines into (1) a line-emission component and (2) a residual intensity in the wings of the absorption components. Lineemission intensities derived by this method are consistent with the hypothesis that the emission arises in an isothermal layer, optically thin in the emission lines. The excitation temperature of this layer is estimated to be 3500 , a value that does not differ significantly from that obtained for the R absorption components. On the basis of several considerations, it is tentatively proposed that the emission arises within the stellar atmosphere. Unfortunately, the arguments leading to this proposal are not conclusive. Finally, it is suggested that the TiO bands present in the spectrum during the deep light-minima arise in the envelope that produces the abnormally strong low4evel lines.