Line profiles for the classical Cepheid SV Vulpeculae.

Abstract

The classical cepheid SV Vul is of particular interest because of its long period, 45 days, and large spectral type variation, F7 lab to Ko lab. Curves of growth constructed at phases near maximum light, maximum radius, minimum light and minimum radius gave the damping and Doppler parameters needed to study the line profiles. Values of the ratio of scattering to total absorption, as well as the limb darkening, were assumed, and profiles were calculated for MilneEddington atmospheres using the IBM 650 program of M. H. Wrubel. It was found impossible to fit the line profiles of X4508 of FeII unless some macroscopic motion, formally like rotation, was introduced. An excellent fit to the observed profiles was obtained on the assumption of pure scattering, a limb- darkening coefficient B(0)/B(i) = 2/3, and rotational velocities between 22 and 27 km/sec depending on phase. The profile of X4508 is widest at phases near minimum radius. Using the position of the Cepheids on the H-R diagram given by Sandage (1958) and a set of reasonable evolutionary tracks, these rotational velocities were compared with the velocities to be expected if SV Vul had originally been a BI main sequence star. The agreement was found to be poor. The "evolutionary" rotational velocity was only one-fourth of that obtained from the line profiles if the angular momentum was assumed to be conserved in shells. Similar results were obtained for the two non-variable supergiants p Aqr, Go Ib and 9 Peg, G~ Ib. It is suggested that macroturbulent motions are responsible for the line profiles in SV Vul, p Aqr and 9 Peg. Evolution from the main sequence with angular momentum conserved in shells can explain the line profiles of A and F supergiants (Abt 1958). It is therefore possible that macroturbulence becomes increasingly important relative to rotation with advancing spectral type. In SV Vul, the opacity and atmospheric density vary by large factors during the cycle. The energy bound up in turbulent motions reaches a maximum near minimum radius. Thus we can study the effects produced by changing turbulence in a supergiant atmosphere. Abt, H. A. 1958, Ap. J. 127, 658. Sandage, A. R. 1958, Ap. J. 127, 513. Goethe Link Observatory, Indiana University, Bloomington, Ind.