CAOSP abstracts, Volume: 34, No.: 1, year: 2004

Abstract: The long-term photometry of the symbiotic nova HM Sge obtained from 1976 to 2003 is presented including new UBV photoelectric and UBVRI CCD data gathered in 1998-2003. The archive photographic plates were used to estimate the brightness of the object after the outburst in 1975. These data together with post-outburst visual observations from international databases are discussed. The outburst of the nova, with a maximum in August 1975, was followed by two minima of brightness which lasted ∼750 days and ∼2100 days, respectively. The descending branch of the minimum I was detected only in photographic data, the ascending branch was also detected in UBV bands. The minimum II was visible only in the U band. The minima were probably caused by the eclipses of the hot component (white dwarf surrounded by an accretion disk) and the hot shocked region formed by colliding winds of the components by a Mira variable. The orbital period of the Mira is certainly longer than the interval of observations of 28 years. Our CCD IR data clearly show the pulsation of the Mira variable. It is shown that the nova-like outburst of HM Sge was triggered by a mass-transfer burst from the Mira variable to the hot component during its periastron passage on an eccentric orbit. These mass-transfer bursts were reponsible also for the postoutburst activity of the system.

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Last update: February 11, 2004