AS Leonis Minoris (AS LMi), also known as TYC 2505-672-1, is an

eclipsing binary A binary star or binary star system is a Star system, system of two stars that are gravity, gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved ...

system in the constellation of

Leo Minor Leo Minor is a small and faint constellation in the northern celestial hemisphere. Its name is Latin for "the smaller lion", in contrast to Leo, the larger lion. It lies between the larger and more recognizable Ursa Major to the north and Leo ...

. It has by far the longest period, 69.1 years, of any known eclipsing binary. During its roughly 3.45 year long eclipses, it fades by 4.5 magnitudes (about a factor of 60). AS LMi's variability was first detected in 2013, during a search for "disappearing stars" in the

MASTER Master, master's or masters may refer to: Ranks or titles In education: *Master (college), head of a college *Master's degree, a postgraduate or sometimes undergraduate degree in the specified discipline *Schoolmaster or master, presiding office ...

database. It was initially thought to be an

R Coronae Borealis variable An R Coronae Borealis variable (abbreviated RCB, R CrB) is an eruptive variable star that varies in luminosity in two modes, one low amplitude pulsation (a few tenths of a magnitude), and one irregular, unpredictably-sudden fading by 1 to 9 magni ...

star, although its fading was unusually slow for an R Coronae Borealis variable. Because R Coronae Borealis variables fade repeatedly, the discovery of the star's dramatic brightness decline triggered a search of archival

photographic plates Photographic plates preceded photographic film, film as the primary medium for capturing images in photography. These plates, made of metal or Glass, glass and coated with a light-sensitive Photographic emulsion, emulsion, were integral to early ...

for evidence of earlier dimming events. Tang ''et al.'' used DASCH to search the large collection of Harvard photographic plates, and found that the star had dimmed for three years during the 1940s. They recognized that AS LMi is a very long period eclipsing binary, similar to the ε Aurigae system. The binary system consists of an M-giant primary star orbited by a small hot secondary star that is itself surrounded by an optically thick (large

optical depth In physics, optical depth or optical thickness is the natural logarithm of the ratio of incident to ''transmitted'' radiant power through a material. Thus, the larger the optical depth, the smaller the amount of transmitted radiant power throu ...

) disk.

References

{{DEFAULTSORT:AS Leonis Minoris Algol variables Leo Minor Leonis Minoris, AS