Cygnus OB2-8A
Spectroscopic binary star near the center of Cygnus OB2
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Cygnus OB2 #8A is a double-lined spectroscopic binary located near the centre of the Cygnus OB2 association located 5,500 light years away.
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Cygnus[1] |
| Right ascension | 20h 33m 15.07905s[2] |
| Declination | +41° 18′ 50.4762″[2] |
| Apparent magnitude (V) | 9.06[3] |
| Characteristics | |
| Spectral type | O6If + O5.5III(f)[4] |
| U−B color index | +0.15[5] |
| B−V color index | +1.29[5] |
| Astrometry | |
| Radial velocity (Rv) | 125.56[6] km/s |
| Proper motion (μ) | RA: −2.664[6] mas/yr Dec.: −4.895[6] mas/yr |
| Parallax (π) | 0.6058±0.0191 mas[6] |
| Distance | 5,400 ± 200 ly (1,650 ± 50 pc) |
| Absolute magnitude (MV) | −6.78[7] |
| Orbit[8] | |
| Period (P) | 21.9 days |
| Semi-major axis (a) | 71 R☉[9] |
| Eccentricity (e) | 0.24 |
| Semi-amplitude (K1) (primary) | 82.8 km/s |
| Semi-amplitude (K2) (secondary) | 95.8 km/s |
| Details[9] | |
| Cyg OB2 #8A1 | |
| Mass | 44.1 M☉ |
| Radius | 20 R☉ |
| Luminosity | 650,000 L☉ |
| Surface gravity (log g) | 3.48 cgs |
| Temperature | 36,800 K |
| Cyg OB2 #8A2 | |
| Mass | 37.4 M☉ |
| Radius | 14.8 R☉ |
| Luminosity | 468,000 L☉ |
| Surface gravity (log g) | 3.67 cgs |
| Temperature | 39,200 K |
| Age | 2[7] Myr |
| Other designations | |
| Schulte 8A, 1E 203127+4108.5, TYC 3161-1325-1, ADS 14000 A, 2E 4382, HIP 101425, UBV 17839, AG+41°1925, 2E 2031.4+4108, IDS 20297+4058, LS III +41 37, Cyg OB2-8A, 1ES 2031+41.1, 2MASS J20331508+4118504, BD+40 4227, GCRV 20036, PPM 60129, CCDM J20332+4119A, 1RXS J203315.8+411848, CGO 605, GOS G080.22+00.79 01, SAO 49781, CSI+40 4227 1, GSC 03161-01325, Gaia DR2 2067784624247057920 | |
| Database references | |
| SIMBAD | data |
Discovery
Until 1951 Cyg OB2 #8 had been known only as an anonymous catalogue entry in the Bonner Durchmusterung. Then it was identified as one of several highly luminous hot stars close together in Cygnus. Despite being commonly referred to as Schulte #8A, the number 8 was first published in an earlier paper.[10] Schulte identified the grouping as a massive stellar association and split star #8 into four components, including #8A.[11]
System
The Cygnus OB2 #8A system contains two massive luminous O class stars in a 21.9 day orbit. The primary is a 44 M☉ supergiant and the secondary is a 37 M☉ giant star.[8] The two stars are not thought to be exchanging mass and their luminosity classes match the main sequence turnoff in the Cyg OB2 association at around O6.[7] The nearby stars Cyg OB2 #8B, #8C, and #8D, originally thought to be a single star, are all massive and luminous class O stars.