NML Cygni Star - A red Supergiant star from Cygnus Constellation.
“NML Cygni” is a red hypergiant (or red Supergiant) star from Cygnus Constellation. It is also known as V1489 Cygni. It is one of the largest and luminous known star.
This massive cool hypergiant is also one of the most luminous star in the Milky way galaxy.
It was 1965 when this(NML Cygni) hypergiant was firstly detected by a team of astronomers (Neugebauer, Martz, and Leighton) along with NLM Tauri ( also known as IK Tauri is a M9 Mira variable Type red hypergiant star).
The name NML Cygni is named after its discoverer (Neugebauer, Martz, and Leighton in short (NML)). As I have mentioned above that the another name of NML Cygni is V1489 Cygni this is because of its semi-regular brightness variations. That means the brightness of this star varies from time to time.
Like typical stars the composition of this star is also same. So, far astronomers are able detect H
2O, SiO, CO, HCN, CS, SO, SO
2, and H2S molecules on this red Supergiant.
Because of its long distance from earth, it was very difficult for astronomers to calculate its accurate radius. This is why we its radius in range. So, as per approx estimation the radius of NML Cygni is calculated to be between 1183 to 2770 times that of the Sun’s radius.
Distance from Earth
The distance between NML Cygni and Earth is around 5300 Light-years (1.6 kpc). it is located in
Cygnus Constellation and in Cygnus Constellation it is part of Cygnus OB2 association.
(Cygnus OB2 association : Cygnus OB2 association is one of the closest associations to the Sun, Covering approximately 2° on the Sky.)
Characteristics of NML Cygni
It is an extremely large and luminous cool red hypergiant with parameters similar to that of another notable but more extreme cool hypergiant star, like VY Canis Majoris.
It is also a semi-regular variable star with a period of either 1,280 or 940 days. It lies in the upper-right hand corner of the Hertzsprung–Russell diagram although most of the properties of the star depend directly on its distance.
Originally the bolometric brightness for NML Cygni was calculated to be 500,000 L☉ at an estimated distance of 2 kpc, while the radius was calculated to be 3,700 R☉ based on an 8.6 8.6 angular diameter and distance. A 2006 study, similar to studies on VY Canis Majoris, suggests that NML Cygni is a common red supergiant resulting in very low brightness and radius values.
Modern and accurate measurements give a distance of about 1.6 kpc, which gives a brightness of about 200,000 L☉. A radio angular diameter of 44 mas was given depending on the distance, suggesting that the optical angular diameter may be around 22 mas.
This distance and luminosity of 270,000 L☉ were combined with assumptions of the star’s effective temperature, giving a radius of 1,640 R for a temperature of 3,250 K, or possibly 2,770 R for a temperature of 2,500 K. range was given.
However, another paper gives a much smaller radius of 1,183 R☉ based on an estimated effective temperature of 3,834 K and a shorter distance of 1.22 kpc.
The Gaia Data Release 2 for NML Cygni of 1.5259 ± 0.5677 mas is parallax, but the underlying measurements show a considerable level of noise and the parallax is considered unreliable.
NML Cygni is closer to the expected state that a 25 M☉ star would evolve after eight million years. Its current mass is difficult to estimate. A research measures its mass as 50 M☉.
NML Cygni has evolved and many heavy elements and molecules have been detected in its atmosphere, especially oxygen, hydroxyl and water.
It is surrounded by dusty material and exhibits a bean-shaped asymmetric nebula that coincides with the distribution of its H2O vapor masers.
NML Cygni has an estimated mass loss rate of 4.2 to 4.8×10−4 M☉ per year, the highest known for any star. The annual parallax of NML Cygni is measured to be about 0.62 milliarseconds.
From observations, it has been inferred that NML Cygni consists of two discrete optically thick envelopes of dust and molecules. The optical depth of the inner shell is found to be 1.9, while that of the outer is 0.33.
These dust envelopes are formed by strong post-main-sequence wind, which has a velocity of 23 km/s.
Because of the star’s position on the outskirts of the giant Cygnus OB2 union, NML Cygni’s radiation detectable effects on the surrounding dust and gas are limited to the region far from the union’s central hot stars.
This Particular part is taken from Wikipedia Article