TypeNovaeClick for lightcurveClose binary systems with orbital periods from 0.05 to 230 days. One of the components of these systems is a hot dwarf star that suddenly, during a time interval from one to several dozen or several hundred days, increases its brightness by 7-19 mag. in V, then returns gradually to its former brightness over several months, years, or decades. Small changes at minimum light may be present. Cool components may be giants, subgiants, or dwarfs of K-M type. The spectra of novae near maximum light resemble A-F absorption spectra of luminous stars at first. Then broad emission lines (bands) of hydrogen, helium, and other elements with absorption components indicating the presence of a rapidly expanding envelope appear in the spectrum. As the light decreases, the composite spectrum begins to show forbidden lines characteristic of the spectra of gas nebulae excited by hot stars. At minimum light, the spectra of novae are generally continuous or resemble the spectra of Wolf-Rayet stars. Only spectra of the most massive systems show traces of cool components. Some novae reveal pulsations of hot components with periods of approximately 100 s. and amplitudes of about 0.05 mag. in V after an outburst. Some novae eventually turn out to be eclipsing systems. According to the features of their light variations, novae are subdivided into fast (NA), slow (NB), very slow (NC), and recurrent (NR) categories. AAVSO Alert 491: December 2, 2013 Event: V556 Serpentis = Nova Ser 2013 = PNV J18090346-1112345. Discovered by: Koichi Itagaki (Teppo-cho, Yamagata, Japan), reported by S. Nakano (Sumoto, Japan), magnitude: unfiltered CCD magnitude mag 12.3, using a 0.21-m reflector: Discovery date: 2013 Nov. 24.384 UT.
Hills Observatory: 1 January 2013 to 4 November 2018