BD+40°4210 is a hot luminous

supergiant star Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram, with absolute magnitude, absolute visual magnitudes between about −3 and −8. The temperatures of supe ...

located in the constellation Cygnus. It is a member of the

Cygnus OB2 Cygnus OB2 is an OB association that is home to some of the most massive and most luminous stars known, including suspected Luminous blue variable Cyg OB2 #12. It also includes one of the largest known stars, NML Cygni. The region is emb ...

association and a candidate

luminous blue variable Luminous blue variables (LBVs) are rare, massive, evolved stars that show unpredictable and sometimes dramatic variations in their spectra and brightness. They are also known as S Doradus variables after S Doradus, one of the brightest stars of th ...

Features

BD+40°4210 is heavily reddened and extinguished by the

interstellar dust Cosmic dustalso called extraterrestrial dust, space dust, or star dustis dust that occurs in outer space or has fallen onto Earth. Most cosmic dust particles measure between a few molecules and , such as micrometeoroids (30 μm). Cosmic dust can ...

of the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

and little studied. It has turned out to be one of the most luminous stars of the Cygnus OB2 association, with an absolute magnitude of −7.66 and a

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

more than 600,000 times that of the Sun. It has been assigned a B1III spectral classification, but with peculiarities including unusually shallow lines and broad emission. Despite the giant luminosity class, the luminosity appears to be extremely high, placing it on or near the

S Doradus S Doradus (also known as S Dor) is one of the brightest stars in the Large Magellanic Cloud (LMC), a satellite galaxy of the Milky Way, located roughly 160,000 light-years away. The star is a luminous blue variable, and one of the List ...

instability strip occupied by quiescent luminous blue variables. Its brightness varies by less than 0.1 magnitudes on a timescale around 100 days. BD+40°4210 is located at a projected 4.8

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (AU), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...

s from the candidate luminous blue variable G79.29+0.46 and probably at a similar distance since both are assumed members of Cygnus OB2; however, unlike the latter which is surrounded by an extensive ring-shaped nebulosity, no nebula has been found around this star.

References

{{DEFAULTSORT:BD 20 2457 Cygnus (constellation) B-type supergiants BD+40 4210 Luminous blue variables J20310464+4030568