Dynamical Masses for the Two Cepheids S Mus and V636 Sco
Abstract
For the Cepheids S Muscae and V636 Scorpii we want to determine the pulsational radial velocities for the spectral lines seen in the LWR region of the IUE Observatory. These measurements are essential for the determination of the dynamical masses for these binaries. On LWR IUE high resolution images of S Mus and V636 Sco the spectrum of the Cepheid can be studied for lambda > 2500 A while the one for the companion can be studied for lambda < 2500 A. This fact permits the measurement of the difference in radial velocity for the two components of the binary system. After subtraction of the pulsational velocity of the Cepheid the difference of the orbital velocities is obtained. With the orbital velocity of the Cepheid known from optical studies the velocity ratio and thereby the mass ratio of the binary components can be determined. So far the pulsational velocities for the Cepheid measured in the optical region have been used in this procedure. Observations show, however, that pulsational velocities are different for different layers of the atmosphere. Subtraction of the pulsational velocities determined for the absorption lines in the optical region, when we should subtract the pulsational velocities for the uv region, may cause large errors in the difference of the orbital velocities and their ratios. We therefore want to determine the pulsational velocities for those high layers in which the lines in the LWR region are formed. This requires measurements for many phases of the pulsational cycle.
- Publication:
-
IUE Proposal
- Pub Date:
- 1988
- Bibcode:
- 1988iue..prop.3065B