2003ApJ...585.1007D

The multiple-star system ι Cas was observed as a calibration for our adaptive optics observations in 2001 July with the Advanced Electro-Optical System (AEOS) 3.63 m telescope in Maui, Hawaii, and the first ever image of the faint astrometric component Aa (along with A and B) was obtained at the H-band wavelength. Another image was obtained in 2002 February with the same telescope, but that time in the I band. This wider image includes the C component and is the first to show four components. By combining our images with seven recent speckle interferometry measurements, a 47 yr period relative orbit is derived for the A-Aa components. Comparing the motion of B with respect to the A-Aa system, previous A-B orbits are rejected in favor of simple rectilinear motion of B across the field. Nevertheless, the history of the relative vector separation between B and A reveals the suborbital motion of A around its center of gravity with Aa, leading to a true orbit for A. The masses of A and Aa are thus determined to be 1.99±0.28 and 0.69±0.12 M_☉, respectively. Combining our differential photometry in the I and H bands with B and V information from the Tycho-2 catalog, we derive spectral types for all four from their colors: component A is spectral type A3 with peculiar red colors, Aa is G6, B is F5, and C is K3.