  Credit: Erik Larsen | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cygnus |
| Right ascension | 20h 21m 38.55s [1] |
| Declination | +37° 31′ 58.9″ [1] |
| Apparent magnitude (V) | 9.0 - 10.8 [2] |
| Characteristics | |
| Spectral type | M3.5 Ia [3] (M2 - M5 [4] ) |
| B−V color index | +3.13 - +3.21 [4] |
| Variable type | SRc [3] |
| Astrometry | |
| Radial velocity (Rv) | −20.97 [1] km/s |
| Proper motion (μ) | RA: −3.710 mas/yr [1] Dec.: −6.307 mas/yr [1] |
| Parallax (π) | 0.5760±0.0500 mas [1] |
| Distance | 5,418+470 −430 ly (1,662+144 −132 pc) [5] |
| Absolute magnitude (MV) | −7.71 [6] |
| Details | |
| Mass | 19 [4] [7] M☉ |
| Radius | 1,187 [1] R☉ |
| Luminosity | 150,000 [7] 204,000+159,000 −56,000 [8] L☉ |
| Temperature | 3,535 [7] K |
| Age | >9 [7] [a] Myr |
| Other designations | |
| BC Cyg, HIP 100404, HV 3339, BD+37°3903, IRAS 20197+3722, 2MASS J20213855+3731589 | |
| Database references | |
| SIMBAD | data |
BC Cygni (BC Cyg, HIP 100404, BD + 37 3903) is a red supergiant and pulsating variable star of spectral type M3.5Ia in the constellation Cygnus.
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It is considered a member of the stellar Cygnus OB1 association, and within it the open cluster Berkeley 87, [9] which would place at a distance of 1,673 parsecs (5,000 ly) of the Solar System; [10] it is less than a degree north of another variable red supergiant, BI Cygni. According to its Gaia Data Release 3 parallax, it is at about 1,700 pc. [1]
BC Cygni was found to have a luminosity of 145,000 L☉ and an effective temperature of 2,858 K in the year 1900, and a luminosity of 112,000 L☉ and a temperature of 3,614 K in the year 2000. It is one of largest stars known, at its brightest and coolest calculated to be 1,553 R☉ compared to 856 R☉ at its hottest and faintest. [11] If it were in the place of the Sun, its photosphere would engulf the entire inner Solar System and reach close to the orbit of Jupiter. With a mass of about 19 M☉, it is estimated that the stellar mass loss, as dust, as the atomic and molecular gas could not be evaluators is 3.2×10−9 M☉ per year. [12]
Louisa Wells discovered that the star's brightness varied, based on the examination of 15 photographic plates. That discovery was announced in 1911. [14] It was given its variable star designation, BC Cygni, in 1914. [15] The brightness of BC Cyg varies from visual magnitude +9.0 and +10.8 with a period of 720 ± 40 days. [2] Between around the year 1900 and 2000 appears to have increased its average brightness of 0.5 magnitudes. [4]