Full Adaptive Optics Images of ADS 9731 and MU Cassiopeiae: Orbits and Masses

The double double ADS 9731 and the nearby Population II astrometric binary μ Cas have been imaged with full adaptive optics employed at the 1.5 m telescope belonging to the USAF Phillips Laboratory's Starfire Optical Range near Albuquerque, New Mexico. On 1994 May 4 at a wavelength of 0.85 μm, the Δmag values and separations for ADS 9731 components AB were observed to be 2.19 and 1".27, 0.90 and 1".55 for CD, and 0.40 and 14".8 between A and C. Combining these observations with earlier ones, we have obtained circular, highly inclined, long-period (834 and 1230 yr) preliminary orbits for both pairs and derived their masses along with other astrophysical quantities. However, consideration of stellar evolutionary models leads to a disagreement in the derived distance to the system (108.1 pc) and/or masses, which will perhaps be resolved by subsequent orbital refinement. The first ever real-time images at short wavelengths (<1 μm) of the faint companion to the astrometric binary μ Cas A component were easily made at 0.85 microns on 1994 August 28 and October 22, with movement noted between the two dates. The Δmag value was determined to be 4.9±0.1, and the separation on the two dates was 0".73 and 0".66. Combining our measurements with astrometric data from both Sproul and Allegheny Observatories, we make a simultaneous fit for a new master orbit and find masses of 0.742±0.059 and 0.173±0.011 Msun for A and B, respectively. From further analysis we derive a presumably primordial helium abundance f6r μ Cas of Y = 0.24±0.07 for an assumed age of 10¹⁰ yr and the latest measured metallicity of Z = 0.0021.