Infrared imaging of M Cas B using rapid image motion compensation

The orbital parameters and component masses of the μ Cas binary system can provide a measure of the helium abundance in the early Galaxy. In a continuing effort to measure these characteristics, we have obtained the first direct images of the low mass companion to μ Cas A using techniques for high speed correction of image motion at 1.25 and 1.65 μm. These techniques include real-time tracking of the brightest infrared speckle at 75 Hz and of the visible centroid at 500 Hz. Mu Cas B is easily detected with a magnitude difference relative to the primary of > 4 at a separation of ∼1.4 arcsec. Its energy distribution from 0.55 to 3.4 μm yields an effective temperature (3034±160 K), stellar diameter (0.26 R_⊙), and luminosity (0.0051±0.0011 L_⊙). A direct mass measurement using two photocentric orbits yields 0.15±0.0013 script M_⊙. Significant improvements in these parameters can result from astrometric, spectroscopic, and imaging observations of the upcoming periastron passage.