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V5558 Sagittarii

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V5558 Sgr, or Nova Sagittarii 2007, is a fascinating very slow nova that continues to decline nearly four years after outburst.  After steadily rising for nearly a hundred days, the nova underwent a series of large-amplitude brightenings over the next two hundred days before beginning a more dignified decline.  More than a thousand days after outburst it remains above magnitude 14.  The slow novae are believed to have low-mass white dwarf primaries with masses just over half that of the Sun, and they're probably on the borderline of being able to generate nova eruptions at all.  The slowest of the previously known slow novae, V723 Cas, probably has a mass around 0.6 solar masses.  That star took over a year and a half to go from maximum brightness to the nebular stage of the ejecta, and V5558 Sgr has very similar properties.

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Prepared By: Matthew Templeton
AAVSO 49 Bay State Rd. Cambridge, MA 02138 617-354-0484