The Spectroscopic Orbit of the Evolved Binary HD 197770

We use spectra taken between 1992 and 1997 to derive the spectroscopic orbit of the eclipsing double-lined spectroscopic binary HD 197770. This binary has a period of 99.69 +/- 0.02 days and K amplitudes of 31.2 +/- 0.8 and 47.1 +/- 0.4 km/s for components A and B, respectively. The m sin-cubed i values for A and B are 2.9 and 1.9, respectively, and are close to the actual masses because of the eclipsing nature of this binary. Both components of HD 197770 have spectral types near B2 III. This means that both components are undermassive by about a factor of 5 and, thus, are evolved stars. Additional evidence of the evolved nature of HD 197770 is found in 25-, 60-, and 100-micron IRAS images of HD 197770. These images show two apparent shells centered on HD 197770, a bright 60-micron shell with a 28-arcmin diameter and a larger (0.8-deg diameter) bubble-like feature. At least one of the components of HD 197770 is likely to be a postasymptotic giant branch star. (Author)