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European astronomers have spotted an unusual outburst activity of a binary star system known as AG Draconis. New observations reveal that the recent changes of brightness of this star are slightly different than the changes that occurred during previous outbursts. The findings were presented October 13 in a paper published on arXiv.org.
Located in a spherical halo around the Milky Way, AG Draconis (AG Dra for short) is a classical symbiotic variable binary of type S. The system consists of a cool red giant with an effective temperature of about 4,300 K and a hot white dwarf with a high temperature of at least 100,000 K. The red giant is about 30 times larger than our sun, however, it has a mass of only 1.5 solar masses. The system's white dwarf is about 40 to 60 percent less massive than the sun. The stars fully orbit each other approximately every 550 days.
AG - Dra - Star - Systems - Variations
AG Dra is one of the most studied symbiotic star systems as its variations in brightness have been observed by astronomers for more than a century. The binary experiences a characteristic symbiotic activity with the alternation of active and quiescent stages. Its apparent magnitude of around 9.8 is known to increase by up to 1.4 when outbursts occur during active stages that take place at intervals of nine to fifteen years.
Previous observations of AG Dra have shown that these active stages consist of several outbursts repeating at about a one-year interval. The observed periods of activity start with a major outburst that is usually cool as the expanding pseudo-atmosphere of the white dwarf cools down. However, the latest phase of activity, which started with an outburst...
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