VHK 83 (Var 83 in the VHK survey) is a luminous blue variable (LBV) in the constellation

Triangulum Triangulum is a small constellation in the northern sky. Its name is Latin for "triangle", derived from its three brightest stars, which form a long and narrow triangle. Known to the ancient Babylonians and Greeks, Triangulum was one of the 48 ...

, in the

Triangulum Galaxy The Triangulum Galaxy is a spiral galaxy 2.73 million light-years (ly) from Earth in the constellation Triangulum. It is catalogued as Messier 33 or NGC (''New General Catalogue)'' 598. With the D25 isophotal diameter of , the Triangulum Ga ...

. With its

bolometric luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a ...

of at least 2,240,000 times that of the Sun (4,500,000 in some estimates), it was described as "the brightest nonstable star in M33" and is one of the

most luminous stars This is a list of stars arranged by their absolute magnitude – their intrinsic stellar luminosity. This cannot be observed directly, so instead must be calculated from the apparent magnitude (the brightness as seen from Earth), the distance t ...

known. The brightness varies slowly and unpredictably over a 1-2 magnitude visual range and can remain approximately constant for many years. These variations, combined with the high luminosity and temperature of the star, caused it to be grouped with the Hubble-Sandage variables even before the term "Luminous blue variable" was more than a simple description. Despite widespread agreement that it is an LBV, it has yet to be observed in outburst, although the temperature has been observed to change in tandem with the brightness variations. Temperature estimates for the star range from around 18,000K to well over 30,000K. The hotter temperatures found from fitting the spectral energy distribution (SED) are consistent with the calculated luminosity of an LBV in the quiescent stage, but the spectrum is that of a cooler star.

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