V5856 Sagittarii, also known as Nova Sagittarii 2016 Number 4, was the 4th and brightest

nova A nova (plural novae or novas) is a transient astronomical event that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova", which is Latin for "new") that slowly fades over weeks or months. Causes of the dramat ...

that occurred in the constellation Sagittarius during 2016. It was discovered by the

All Sky Automated Survey for SuperNovae The All Sky Automated Survey for SuperNovae (ASAS-SN) is an automated program to search for new supernovae and other astronomical transients, headed by astronomers from the Ohio State University, including Christopher Kochanek and Krzysztof Stane ...

(which assigned to it the name ASASSN-16ma) on 25.02 October 2016, at which time it had an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's lig ...

of 13.7. It was independently discovered by Yukio Sakurai of

Mito, Ibaraki is the capital city of Ibaraki Prefecture, in the northern Kantō region of Japan. , the city had an estimated population of 269,330 in 123,282 households and a population density of 1239 persons per km2. The percentage of the population aged o ...

, Japan on 26.38 October 2016, by which time it had reached magnitude 10.4. It reached its peak brightness of magnitude 5.4, making it visible to the naked eye, on 8 November 2016. The nova occurred within a region of the sky monitored by the OGLE

microlensing Gravitational microlensing is an astronomical phenomenon due to the gravitational lens effect. It can be used to detect objects that range from the mass of a planet to the mass of a star, regardless of the light they emit. Typically, astronomers ...

experiment, and that group reported that no star brighter than magnitude 22 (I band) was seen at the nova's position prior to its eruption. V5856 Sagittarii declined from peak brightness rapidly, fading by 2 magnitudes in 11.3 days, and 3 magnitudes in 14.5 days. It is therefore classified as a "fast" nova in the classification scheme of

Cecilia Payne-Gaposchkin Cecilia Payne-Gaposchkin (born Cecilia Helena Payne; – ) was a British-born American astronomer and astrophysicist who proposed in her 1925 doctoral thesis that stars were composed primarily of hydrogen and helium. Her groundbreaking conclus ...

. The nova showed two peaks: a "fireball" peak corresponding to the freely expanding material ejected from the eruption and, nearly a week later, a second brighter peak coincident in time with the detection of γ-rays from the nova by Fermi-LAT. The fireball peak occurred at different times depending upon the wavelength of light being observed, but the second peak occurred at the same time for all wavelengths. V5856SgrLocation

All novae are binary stars, with a "donor" star orbiting a

white dwarf A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes ...

. The two stars are so close to each other that matter is transferred from the donor to the white dwarf. In the case of V5856 Sagittarii, the absence of a detection of a progenitor in the OGLE images suggests that the donor is a dwarf star.

References

{{DEFAULTSORT:V5856 Sagittarii Novae Sagittarius (constellation) 20161026 Sagittarii, V5856