Variable Stars - N Sgr 2015 (PNV J18142514-2554343)
Type Novae Close 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 398/509: February 18, 2015 Nova Sagittarii 2015 = PNV J18142514-2554343 Discovered independently by Hideo Nishimura (Shizuoka-ken, Japan), Koichi Nishiyama (Kurume, Japan) and Fujio Kabashima (Miyaki, Japan) Discovery magnitude: - Nishimura: DSLR magnitude 11.2, using 200-mm f/3.2 lens + digital camera - Nishiyama and Kabashima: unfiltered CCD magnitude 10.9, using a 105-mm f/4 camera lens (+SBIG STL6303E camera) Discovery date: - Nishimura: 2015 February 12.840 UT - Nishiyama and Kabashima: 2015 February    12.87837 UT Spectra: Echelle spectra by Frederick Walter (Stony Brook University) taken on the night of 2015 February 15/16 near maximum light indicate that N Sgr 2015 is a classical Fe II nova. Novae. Close 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. "
Hills Observatory: 1 January 2013 to 14 August 2018
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