WY Sagittae, also known as Nova Sagittae 1783, is a star in the constellation Sagitta which had a

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 dramati ...

eruption visible in 1783. It was discovered on 26 July 1783 by the French astronomer Joseph Lepaute D'Agelet. It is usually difficult to precisely identify novae that were discovered hundreds of years ago, because the positions were often vaguely reported (for example the discoverer may have only reported the constellation where the nova occurred) and historically there was not a clear distinction drawn between different sorts of transient astronomical events such as novae and comet apparitions. However D'Agelet observed this nova with a

mural quadrant A mural instrument is an angle measuring instrument mounted on or built into a wall. For astronomical purposes, these walls were oriented so they lie precisely on the meridian. A mural instrument that measured angles from 0 to 90 degrees was cal ...

, which produced coordinates accurate enough to allow modern astronomers to identify the star. D'Agelet reported the

apparent 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 li ...

of the star as 6, but Benjamin Apthorp Gould, who analysed D'Agelet's records, determined that what D'Agelet called magnitude 6 corresponds to magnitude 5.4 ± 0.4 on the modern magnitude scale, so the nova was visible to the naked eye. WYSgeLightCurve

Very little is known about WY Sagittae's post-eruption light curve. D'Agelet reported the star's magnitude as 6, 6 and 6.7 on the 26th, 27th and 29 July 1783, respectively. At least a half dozen observers attempted to find D'Agelet's nova in the late 19th and early 20th centuries, without success. In 1942 a photographic search for the nova was performed using the

60-inch telescope 6 (six) is the natural number following 5 and preceding 7. It is a composite number and the smallest perfect number. In mathematics Six is the smallest positive integer which is neither a square number nor a prime number; it is the second small ...

on Mt. Wilson, and in 1950 Harold Weaver tentatively identified a faint blue star with a photographic magnitude of 18.9 as the quiescent nova. The star was only a few arc seconds away from D'Agelet's reported position, and fluctuations in its brightness added to the confidence that it was indeed the nova. In 1971 Brian Warner observed Weaver's candidate for WY Sagittae with the

Otto Struve Telescope The Otto Struve Telescope was the first major telescope to be built at McDonald Observatory. Located in the Davis Mountains in West Texas, the Otto Struve Telescope was designed by Warner & Swasey Company and constructed between 1933 and 1939 b ...

, and saw rapid brightness variations that are ubiquitous in quiescent novae, which confirmed Weaver's identification of D'Agelet's nova. 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 fro ...

. The two stars are so close together that matter is transferred from the donor star to the white dwarf. Because the distance between the stars is comparable to the radius of the donor star, novae are often eclipsing binaries, and WY Sagittae does show eclipses. The eclipses, which are quite deep (two magnitudes), show that the binary's orbital period is 3 hours and 41 minutes. Christian Knigge classified the donor star's spectral type as M4±1. Somers ''et al.'' estimate the donor star's spectral type to be between M3.5 and M4.5, and the mass of the white dwarf to lie between and . Özdönmez ''et al.'' estimate WY Sagittae's distance to be 4200±400 parsecs, based on reddening. WY Sagittae is sometimes listed as the second oldest "recovered" nova (meaning a historical nova for which modern observations have unambiguously identified the post-nova star), with only

CK Vulpeculae CK Vulpeculae (also Nova Vulpeculae 1670) is an object whose exact nature is unknown. It was once considered to be the oldest reliably-documented nova. It consists of a compact central object surrounded by a bipolar nebula. Models sugge ...

being older. But Naylor ''et al.'' argue that CK Vulpeculae is not a nova, and WY Sagittae is the oldest recovered nova.

References

{{DEFAULTSORT:WY Sagittae Novae Sagitta (constellation) Sagittae, WY