Evidence of asymmetry in Mira variable U Ori

Abstract

Near simultaneous, two high angular resolution observations by lunar occultation technique at the same wavelength (2.2mu m) but at different position angles (PA) result in two unique Uniform Disk (UD) angular diameters of Mira variable U Ori. UD angular diameter obtained from observations at Mt. Abu observatory is 11.9(+/-)0.3 milliarcsecond (mas) at PA 136o while from observations at TIRGO observatory UD value obtained is 15.14(+/-)0.05 mas at PA 75o. The source brightness profile derived from a model independent analysis shows an asymmetric spatial structure in both cases. Asymmetric structure of the source at higher spatial scale was also reported by several authors from OH and H2O maser distribution at radio wavelengths; the source is more extended at PA of 30 - 60o. Furthermore, moderate level maximum optical intrinsic polarization of ~1-2% at PA approx 20o - 40o is also detected. All the evidences bring out the spatial asymmetry in U Ori.