TypeNovaeClose 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 516: April 2, 2015 Event: Nova Oph 2015 = PNV J17291350-1846120Discovered by: Yukio Sakurai, Ibaraki-ken, JapanDiscovery magnitude: 12.2 unfiltered, using 180-mm f/2.8 lensDiscovery date: 2015 March 29.766 UTSpectra: A spectrum obtained by M. Fujii (Fujii Kurosaki Observatory, Kurashiki, Okayama, Japan) on 2015 Mar 30.758 UT is consistent with PNV J17291350-1846120 being a He/N type nova, and may be seen at http://otobs.org/FBO/fko/nova/pnv_j17291350-1846120_20150330.png. A spectrum by K. Ayani (Bisei Astronomical Observatory, Ibara, Okayama, Japan) on Mar. 30.8 UT confirmed Fujii's findings including N III and O I emission; it may be seen at http://tinyurl.com/kbpoyv6 (CBET 4086).Observing recommendations: Observations of all types (visual, CCD, DSLR, spectroscopy) are strongly encouraged as this nova evolves.
Hills Observatory: 1 January 2013 to 14 August 2018