Nature of the oscillating semi-detached eclipsing binary system IO Ursae Majoris

Abstract

This paper presents results from analysing spectroscopic and multicolour photometric observations of the neglected semi-detached eclipsing binary system IO Ursae Majoris (IO UMa). For the first time, the orbital parameters of the system and fundamental physical properties of its components were determined from simultaneous analysis of BVR light curves and radial velocities of the components. The masses and radii of the primary and secondary components were found to be M1 = 2.11 ± 0.07 M⊙, M2 = 0.29 ± 0.02 M⊙ and R1 = 3.00 ± 0.04 R⊙ and R2 = 3.92 ± 0.05 R⊙, respectively. Derived absolute parameters yield the photometric distance of IO UMa as 263 ± 13 pc. The projected rotational velocity of the mass-accreting hotter component was measured as 34.5 ± 2 km s−1, just 1.28 times faster than the synchronous value. The hotter component of the system, located in the region of the instability strip, indicates pulsational variation with short period and small amplitude. Frequency analysis after subtracting the theoretical light curve from photometric data revealed that the more massive component shows δ Scuti type pulsation with four detected frequencies. The total amplitude of the variation in the V filter was found to be 0.03 mag. Mode identification using amplitude ratios and phase differences in different filters suggests that the main pulsation frequency of 22.0148 d−1 is probably a radial mode.