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.
BC Cygni is visible as a red star (circled). The bright star at the centre is γ Cygni and north is to the right. 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[1] mas/yr Dec.: −6.307[1] mas/yr |
Parallax (π) | 0.5760 ± 0.0500 mas[1] |
Distance | 1,710+40 −40[5] pc |
Absolute magnitude (MV) | −7.71[6] |
Details[4] | |
Mass | 19 M☉ |
Radius | 1,031[7] R☉ |
Luminosity | 204,000[5] L☉ |
Temperature | 3,605[8] K |
Minimum (1900) | |
Radius | 1,553 R☉ |
Luminosity | 145,000 L☉ |
Temperature | 2,858 K |
Maximum (2000) | |
Radius | 856 R☉ |
Luminosity | 112,000 L☉ |
Temperature | 3,614 K |
Other designations | |
Database references | |
SIMBAD | data |
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.[citation needed] According to its Gaia Data Release 3 parallax, it is at about 1,700 pc.[1]
BC Cygni was calculated to have an effective temperature of 2,858 to 3,614 K and to vary between 112,000 to 145,000 L☉. The size at its brightest and coolest has been calculated to be 1,553 R☉ compared to 856 R☉ at the hottest and faintest. It is one of largest stars known. If it were in the place of the Sun, its photosphere would engulf the orbit of Jupiter assuming the maximum radius of 1,553 R☉. 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.[11]
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]