The Companion of the Classical Cepheid Z Lacertae

Abstract

A deep IUE exposure of the Cepheid Z Lac from 1200 to 2000 A has been taken in order to search for light from the radial velocity companion. A faint signal of approximately 1.0 X 10^-14 ergs A^-1 sec^-1 cm^-2 has been detected in the dereddened spectrum. Because this is approximately the flux expected due to "camera artifacts," we consider that at least part of this signal does not come from Z Lac B. We use this flux as an upper limit to the flux of the companion. This corresponds to a spectral type later than A5 V at the distance of the Cepheid. We have also obtained new radial velocity observations of Z Lac. Although only limited velocity data are available, an orbital velocity variation of 16 km sec^-1 has been observed. Combining this with even the shortest period compatible with the data (approximately 14 years) implies a much more massive companion than is seen in the IUE spectrum. It is likely that the companion is itself a binary. (SECTION: Stars)