EVIDENCE FROM MICHELSON INTERFEROMETRY FOR SMALL-SCALE STRUCTURE IN THE SOURCE GEOMETRY OF THE M0 GIANT BETA-ANDROMEDAE

We report near-infrared measurements of the amplitude visibility function of the nearby MO giant β And which shows evidence for a complex source structure discovered by ground-based Michelson optical interferometry. The one-dimensional spatial power spectrum of the star has been measured at selected frequencies in the range 60-120 arcsec-1 with accuracy good enough to reveal a spectral flattening between ∼80 and 120 arcsec-1, where the zero point and the secondary maximum should be yielded. The observations do not indicate any time evolution over a 4 yr period. The spectral distortion can be readily accounted for by a two-component source model, assuming the secondary to be a faint small-scale structure. The set of the model-fitting solutions for the free parameters is combined with available information from empirical effective temperature scales for achieving the most likely values: φ ≃ 13.7 mas, S ≃ 0.07, and p ≃ ±8.1 mas of the primary angular size, the contribution of the secondary to the total flux and the projected north-south separation between the sources, respectively. With no other information now available, the structure is merely interpreted as an infrared companion.