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 5.3 mas,[2] is around 620 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 25.61909s[2] |
| Declination | +36° 50′ 22.5961″[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: +2.728[2] mas/yr Dec.: +15.562[2] mas/yr |
| Parallax (π) | 5.2947 ± 0.2255 mas[2] |
| Distance | 620 ± 30 ly (189 ± 8 pc) |
| Absolute magnitude (MV) | −2.56[3] |
| Details | |
| Mass | 9.5±0.3[9] M☉ |
| Radius | 5.7[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[9] Myr |
| Other designations | |
| 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 central star is orbited by a secondary companion star, which is a subdwarf O star.[6] After previous failed attempts to find the star,[15] the companion was detected using interferometry, but the orbital parameters are unknown.[6]
References
edit- ^ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.
- ^ a b c d e f Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
- ^ a b c d e Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
- ^ a b Lesh, Janet Rountree (December 1968), "The Kinematics of the Gould Belt: an Expanding Group?", Astrophysical Journal Supplement, 17: 371, Bibcode:1968ApJS...17..371L, doi:10.1086/190179.
- ^ a b Slettebak, A. (1982), "Spectral types and rotational velocities of the brighter Be stars and A-F type shell stars", Astrophysical Journal Supplement Series, 50: 55–83, Bibcode:1982ApJS...50...55S, doi:10.1086/190820, 80
- ^ a b c d Klement, Robert; Schaefer, Gail H.; Gies, Douglas R.; Wang, Luqian; Baade, Dietrich; Rivinius, Thomas; Gallenne, Alexandre; Carciofi, Alex C.; Monnier, John D.; Mérand, Antoine; Anugu, Narsireddy; Kraus, Stefan; Davies, Claire L.; Lanthermann, Cyprien; Gardner, Tyler; Wysocki, Peter; Ennis, Jacob; Labdon, Aaron; Setterholm, Benjamin R.; Le Bouquin, Jean-Baptiste (2022). "Interferometric Detections of sdO Companions Orbiting Three Classical Be Stars". The Astrophysical Journal. 926 (2): 213. arXiv:2112.05073. Bibcode:2022ApJ...926..213K. doi:10.3847/1538-4357/ac4266. S2CID 245005999.
- ^ a b Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
- ^ Becker, Juliette C.; et al. (April 2015), "Extracting Radial Velocities of A- and B-type Stars from Echelle Spectrograph Calibration Spectra", The Astrophysical Journal Supplement Series, 217 (2): 13, arXiv:1503.03874, Bibcode:2015ApJS..217...29B, doi:10.1088/0067-0049/217/2/29, S2CID 33968873, 29.
- ^ a b Tetzlaff, N.; et al. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, arXiv:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x, S2CID 118629873.
- ^ a b c d Baade, D.; et al. (March 2018), "Short-term variability and mass loss in Be stars. III. BRITE and SMEI satellite photometry of 28 Cygni", Astronomy & Astrophysics, 610: 17, arXiv:1708.07360, Bibcode:2018A&A...610A..70B, doi:10.1051/0004-6361/201731187, S2CID 119076967, A70.
- ^ McDonald, I.; et al. (2012), "Fundamental parameters and infrared excesses of Hipparcos stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–357, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x, S2CID 118665352.
- ^ Frémat, Y; et al. (2005), "Effects of gravitational darkening on the determination of fundamental parameters in fast-rotating B-type stars", Astronomy and Astrophysics, 440 (1): 305, arXiv:astro-ph/0503381, Bibcode:2005A&A...440..305F, doi:10.1051/0004-6361:20042229, S2CID 19016751.
- ^ Wang, Luqian; Gies, Douglas R.; Peters, Geraldine J.; Götberg, Ylva; Chojnowski, S. Drew; Lester, Kathryn V.; Howell, Steve B. (2021). "The Detection and Characterization of Be+sdO Binaries from HST/STIS FUV Spectroscopy". The Astronomical Journal. 161 (5): 248. arXiv:2103.13642. Bibcode:2021AJ....161..248W. doi:10.3847/1538-3881/abf144.
- ^ "28 Cyg". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-01-11.
- ^ Wang, Luqian; et al. (February 2018), "Detection of Additional Be+sdO Systems from IUE Spectroscopy", The Astrophysical Journal, 853 (2): 10, arXiv:1801.01066, Bibcode:2018ApJ...853..156W, doi:10.3847/1538-4357/aaa4b8, S2CID 119252820, 156