IRC +10420
IRC +10420, also known as V1302 Aquilae, is a yellow hypergiant star located in the constellation of Aquila at a distance of 4-6 kiloparsecs of the Sun.
Discovery
IRC +10420 was first identified in the 1969 Infrared Catalogue of 2.2 micron sources. It was quickly noted as a very unusual object after being detected at 20 microns as one of the brightest sources in the sky with a large infrared excess, and was compared to Eta Carinae during one of its outbursts. It was also discovered to be a strong source of OH maser emission.It was formally catalogued as variable star V1302 Aquilae. Identification on historical photographic plates showed possible irregular variations of about a magnitude before 1925, followed by a smooth gradual increase in brightness from magnitude 15 to brighter than magnitude 14 by 1976.
Some authors had grouped IRC +10420 with the proto-planetary nebulae because of the surrounding nebulosity, but it was widely recognised as a highly luminous supergiant.
Physical properties
Despite being one of the most luminous stars known, 513,000 times brighter than the Sun, IRC +10420 cannot be seen with the naked eye and needs a telescope to be observed.IRC +10420's spectrum has changed from late F to early A in recent decades without experiencing changes in its luminosity. This suggests IRC +10420 is a former red supergiant that is evolving blueward on the Hertzsprung-Russell diagram to become a luminous blue variable, or Wolf–Rayet star. Models suggest it started its life as a 40-50 solar masses star that lost most of its mass due to strong stellar winds leaving it with just 10 solar masses and that the star - which actually has a high surface temperature - is totally enshrouded in the matter it has expelled appearing as a fake photosphere, so IRC +10420 appears with a later spectral type as humans see just the expelled dust and gas it has blown out during its life and not the star itself.