28 Cygni
Star in the constellation Cygnus
From Wikipedia, the free encyclopedia
28 Cygni is a binary[6] star in the northern constellation of Cygnus. It is a faint blue-white hued star but visible to the naked eye with an apparent visual magnitude of 4.93.[3] The distance to 28 Cyg, as estimated from its annual parallax shift of 3.9 mas,[2] is around 840 light years. It has an absolute magnitude of −2.56,[3] which means that if the star were just 10 parsecs (33 light-years) away it would be brighter than Sirius, the brightest star in the night sky.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cygnus |
| Right ascension | 20h 09m 25.61906s[2] |
| Declination | +36° 50′ 22.6340″[2] |
| Apparent magnitude (V) | 4.93[3] |
| Characteristics | |
| Spectral type | B2.5 V[4] or B2 IV(e)[5] + sdO[6] |
| B−V color index | −0.139±0.004[3] |
| Variable type | SX Ari[7] |
| Astrometry | |
| Radial velocity (Rv) | −0.36±2.59[8] km/s |
| Proper motion (μ) | RA: +2.739 mas/yr[2] Dec.: +13.168 mas/yr[2] |
| Parallax (π) | 3.8921±0.1129 mas[2] |
| Distance | 840 ± 20 ly (257 ± 7 pc) |
| Absolute magnitude (MV) | −2.56[3] |
| Details | |
| A | |
| Mass | 6.26±0.28[9] M☉ |
| Radius | 6.5 (equator) 5.7 (polar)[10] R☉ |
| Luminosity | 1,353.22[11] L☉ |
| Surface gravity (log g) | 3.983[12] cgs |
| Temperature | 20,470[13] K |
| Rotational velocity (v sin i) | 320[10] km/s |
| Age | 22.1±2.8[14] Myr |
| B | |
| Mass | 0.76±0.28[9] M☉ |
| Orbit[9] | |
| Primary | A |
| Name | B |
| Period (P) | 359.260±0.041 days |
| Semi-major axis (a) | 1.89±0.06 AU |
| Eccentricity (e) | 0 |
| Inclination (i) | 118.7±0.2° |
| Longitude of the node (Ω) | 146.0±0.3° |
| Argument of periastron (ω) (secondary) | 90° |
| Semi-amplitude (K1) (primary) | 5.4±1.7 km/s |
| Semi-amplitude (K2) (secondary) | 44.9±1.0 km/s |
| Other designations | |
| b2 Cygni, 28 Cygni, V1624 Cygni, BD+36°3907, HD 191610, HIP 99303, HR 7708, SAO 69518[15] | |
| Database references | |
| SIMBAD | data |
This primary object is a B-type main-sequence star with a stellar classification of B2.5 V, per Lesh (1968).[4] Slettebak (1982) found a class of B2 IV(e),[5] which would suggest this is a more evolved subgiant star. It is a Be star, which means the spectrum displays emission lines due a disk of ejected gas in a Keplerian orbit around the star. The star displays short-term variability with two or more periods,[10] and is classified as an SX Arietis variable by Samus et al. (2017).[7] It is spinning rapidly with a projected rotational velocity of 320 km/s; estimated at round 80% of the critical rotation rate. This is giving the star an oblate shape with an equatorial bulge out to 6.5 times the Sun's radius, compared to 5.7 at the poles.[10]
The companion is a subdwarf O star.[6] After previous failed attempts to find the star,[16] the companion was detected using interferometry.[6][9] It has an orbital period of nearly a year and is separated by 1.9 astronomical units from its host.[9]