Mass Loss in Population I Cepheids
Abstract
It has been proposed by several authors that Cepheids lose mass during their pulsational cycle. due to outwards propagating shockwaves. The S Mus system offers a unique opportunity to check this hypothesis directly. The Cepheid has a main sequence companion with a temperature of about 17,700K. which means a spectral type of B4 V. This star is hot enough that the ultraviolet circumstellar and stellar wind lines can be observed, if present, with high resolution SWP images. On the other hand, it is cool enough that it is not a stellar wind source itself. The apparent visual magnitude of the companion is inferred to be mv ~ 7. The Cepheid has E(B-V) = 0.27. The orbital period is 506 days. so the companion is close enough that circumstellar material and stellar wind material still has high enough densities to be observable in the spectrum of the companion. There is no other known system with such favorable properties. Stellar wind lines can be recognized by their velocities and widths and variations during the orbital cycle. Circurnstellar lines, resting in the binary system, can be distinguished from interstellar lines by means of their velocity difference. We want to search for evidence of mass loss of the Cepheid by studying the companion spectrum during different orbital and pulsational phases, and see whether lines, normally seen in interstellar gas, can be seen to vary, which would show that they are circumstellar. The equivalent widths of the lines will show the amount of circumstellar material. The width or wavelength shift of the lines determines the velocity field.
- Publication:
-
IUE Proposal
- Pub Date:
- 1987
- Bibcode:
- 1987iue..prop.2742B