75 Cygni
Star in the constellation Cygnus
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75 Cygni is a binary star[9] system in the northern constellation of Cygnus. It is visible to the naked eye as a dim, reddish-hued point of light with an apparent visual magnitude of 5.09.[2] The system is located at a distance of about 434 light years from the Sun, based on parallax, and is drifting closer with a radial velocity of −29 km/s.[1]
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cygnus |
| Right ascension | 21h 40m 11.10795s[1] |
| Declination | +43° 16′ 25.8161″[1] |
| Apparent magnitude (V) | 5.09[2] |
| Characteristics | |
| Evolutionary stage | asymptotic giant branch[3] |
| Spectral type | M1IIIab[4] |
| B−V color index | 1.601±0.006[2] |
| Variable type | suspected[5] |
| Astrometry | |
| Radial velocity (Rv) | −29.25±0.14[1] km/s |
| Proper motion (μ) | RA: +62.366[1] mas/yr Dec.: +15.488[1] mas/yr |
| Parallax (π) | 7.5210±0.1706 mas[1] |
| Distance | 434 ± 10 ly (133 ± 3 pc) |
| Absolute magnitude (MV) | −0.36[2] |
| Details | |
| Mass | 1.4[6] M☉ |
| Radius | 46[7] R☉ |
| Luminosity | 442[7] L☉ |
| Surface gravity (log g) | 1.69[6] cgs |
| Temperature | 3,906[7] K |
| Metallicity [Fe/H] | −0.24[6] dex |
| Other designations | |
| 75 Cyg, NSV 13834, AAVSO 2136+42, BD+42°4177, GC 30338, HD 206330, HIP 106999, HR 8284, SAO 51167, WDS J21402+4316[8] | |
| Database references | |
| SIMBAD | data |
The pair had an angular separation of 2.7″ as of 2008, with the companion having a visual magnitude of 10.7.[9] The brighter magnitude 5.18[9] primary is an aging red giant star with a stellar classification of M1IIIab.[4] Having exhausted the supply of hydrogen at its core, it has expanded to around 46 times the radius of the Sun.[7] It is a suspected variable star of unknown type and amplitude.[5] The star is radiating 442 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 3,906 K.[7]
It is likely that 75 Cygni is on the asymptotic giant branch, having exhausted its core helium,[3] but there is a chance that it might be a higher-mass star on the red giant branch, before igniting its core helium.[10]
An optical companion, with a spectral type of K, is about an arcminute away and has an apparent magnitude of 10.14.[11]