NML Cygni or V1489 Cygni is a red hypergiant star. It is one of the largest stars known at present. It is about 1,640 times the Sun's radius, However an older study from 2010 says it is 1,183 solar radii. It is one of the extremely luminous supergiant stars. It was discovered in 1965, by Gerry Neugebauer, D.M. Martz and Robert Leighton. The name 'NML' comes from the names of the three discoverers.
NML Cygni's distance from Earth is about 5,250 light-years. This star has dust surrounding it. It has a bean-shaped asymmetric nebula with H2O vapour. It is a semiregular variable star with a period of about 940 days.
This star is a part of the Cygnus OB2 association, which is 1.74 ± 0.2 kpc away. This is one of the nearest massive star groups to the Sun. This group includes some of the most massive and most luminous stars known, including the suspected luminous blue variable Cyg OB2 #12. NML Cyg is a massive oxygen-rich star. Molecules like H2O, SiO, CO, HCN, CS, SO, SO2 and H2S are also present.
NML Cygni has two dense envelopes of dust and molecules. The star has one of the largest mass loss rates at around 2 × 10-4 M☉ per year. These dust envelopes are formed by the high mass emission rate.
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