IM Normae (IM Nor) is a

recurrent nova A nova ( novae or novas) is a transient astronomical event that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova", Latin for "new") that slowly fades over weeks or months. All observed novae involve white ...

in the constellation Norma, one of only ten known in the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

. It has been observed to erupt in 1920 and 2002, reaching magnitude 8.5 from a baseline of 18.3. It was poorly monitored after the first eruption, so it is possible that it erupted in between these dates. The 1920 outburst was discovered by Ida Elizabeth Woods when she examined a

Harvard Observatory The Harvard College Observatory (HCO) is an institution managing a complex of buildings and multiple instruments used for astronomical research by the Harvard University Department of Astronomy. It is located in Cambridge, Massachusetts, United St ...

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

taken by the Bruce telescope in

Arequipa Arequipa (; Aymara language, Aymara and ), also known by its nicknames of ''Ciudad Blanca'' (Spanish for "White City") and ''León del Sur'' (Spanish for "South's Lion"), is a city in Peru and the capital of the eponymous Arequipa (province), ...

, Peru, on July 7th of that year. At minimum, IM Normae shows brightness variations of about 0.3 magnitudes. These consist of 0.2 magnitude dips that are interpreted as partial eclipses of the

accretion disk An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is most frequently a star. Friction, uneven irradiance, magnetohydrodynamic effects, and ...

, and continuous variations caused by one side of the secondary star being heated by the

white dwarf A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...

and therefore brighter than the other face. The

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

is 2.462 hours.

References

Recurrent novae Norma (constellation) Normae, IM {{var-star-stub