Sudden Dimming of the Symbiotic Mira HM Sge

Abstract

Abstract The Symbiotic Mira HM Sge has dimmed considerably over the last year, beyond what is expected of its pulsation-related variability. HM Sge is composed of a cool oxygen-rich AGB star accreting onto a hotter white dwarf companion. The system brightened 6 mag in the optical in 1975 as a result of a Nova-like outburst. It has since dimmed and plateaued in the visible, while gradually growing in brightness in the near-IR over the past 15 yr (0.092 mag yr−1). Within the last year, however, the brightness has dropped by 1.52 mag in the I-band. While the system is expected to be near its pulsation minimum, the brightness is below the values expected of the last three pulsation cycles, and appears independent of the system’s fundamental mode pulsations. We suspect this may be the result of a change in the orientation of the system or episodic mass loss.