2008BaltA..17..223M

We obtained BVI_C photometry of IRC-10443 on 85 different nights distributed over two years, and low resolution absolute spectrophotometry and high resolution Echelle spectroscopy. Our data show that IRC-10443, which was never studied before in detail, is an SRa variable, characterized by ΔB = 1.27, ΔV = 1.14 and ΔI = 0.70 mag amplitudes and mean values <B> = 13.75, <V> = 11.33 and <I_C> = 6.18 mag. Two strong periodicities are simultaneously present: a principal one of 85.5 (±0.2) days, and a secondary one of 620 (±15) days, both sinusoidal in shape, and with semi-amplitudes ΔV = 0.41 and 0.20 mag, respectively. We find that IRC-10443 is an M7III star, with a mean heliocentric radial velocity -28 km/s and reddened by E_B–V = 0.87, a 1/3 of which of circumstellar origin. The same 0.5 kpc distance is derived from application of the appropriate period-luminosity relations to both the principal and the secondary periods. The long secondary period causes a sinusoidal variation of 0.13 mag semi-amplitude in the V-I_C color, with the star being bluest at maximum and reddest at minimum, and with the associated changes in effective temperature and radius of 85 K and 6%, respectively. This behavior of colors argues in favor of a pulsation nature of the still mysterious long secondary periods in AGB stars.