VX Sagittarii (VX Sgr)

Image Source    VX Sagittarii is circled

VX Sagittarii (VX Sgr) is a red hypergiant or supergiant located in the constellation of Sagittarius and is located 5,100 light-years away from the Sun. It is a pulsating variable star with a very large magnitude range (6.5 - 14.0). It has a radius of between 1,350 and 1,940 solar radii (radius of the Sun). 

VX Sagittarii is classified as a cool semiregular variable star of type Src and has a pulsating period of 732 days. The brightness of the star is sometimes a long period variable and otherwise, they are much small. The spectral type varies from M9.8e at minimum light to M4e at maximum, and the luminosity class is la which indicates that it is a bright supergiant. The spectrum shows emission lines which means that the star is losing mass through a strong stellar wind. Very-long-baseline interferometry (VLBI) was used to measure the annual parallax of the star and was found to be 0.64″±0.06″, which indicates a distance of about 5,100 ly.

The temperature of the star is highly variable from 2,400K at minimum visibility to 3,300K at the maximum. Such low temperatures are unusual for a massive supergiant. The atmosphere is irregular, highly extended and variable during the pulsation of the star, but the luminosity varies much less than the brightness and is around 195,000 times the luminosity of the Sun. At the higher temperature of 3,300K, the radius is calculated to be somewhere between 1,120 and 1,550 that of the Sun.

Source: Wikipedia

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