Astronomy:28 Cygni
| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| 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[2] mas/yr Dec.: +13.168[2] mas/yr |
| Parallax (π) | 3.8921 ± 0.1129[2] mas |
| 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 |
| Companion | B |
| Period (P) | 359.260±0.041 days |
| Semi-major axis (a) | 1.89±0.06 astronomical unit|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 | |
| Database references | |
| SIMBAD | data |
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.
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]
References
- ↑ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html.
- ↑ 2.0 2.1 2.2 2.3 2.4 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940 Gaia DR3 record for this source at VizieR.
- ↑ 3.0 3.1 3.2 3.3 3.4 Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, doi:10.1134/S1063773712050015, Bibcode: 2012AstL...38..331A.
- ↑ 4.0 4.1 Lesh, Janet Rountree (December 1968), "The Kinematics of the Gould Belt: an Expanding Group?", Astrophysical Journal Supplement 17: 371, doi:10.1086/190179, Bibcode: 1968ApJS...17..371L.
- ↑ 5.0 5.1 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, doi:10.1086/190820, 80, Bibcode: 1982ApJS...50...55S
- ↑ 6.0 6.1 6.2 6.3 Klement, Robert; Schaefer, Gail H.; Gies, Douglas R.; Wang, Luqian; Baade, Dietrich; Rivinius, Thomas; Gallenne, Alexandre; Carciofi, Alex C. et al. (2022). "Interferometric Detections of sdO Companions Orbiting Three Classical Be Stars". The Astrophysical Journal 926 (2): 213. doi:10.3847/1538-4357/ac4266. Bibcode: 2022ApJ...926..213K.
- ↑ 7.0 7.1 Samus, N. N. et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1 61 (1): 80–88, doi:10.1134/S1063772917010085, Bibcode: 2017ARep...61...80S.
- ↑ 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, doi:10.1088/0067-0049/217/2/29, 29, Bibcode: 2015ApJS..217...29B.
- ↑ 9.0 9.1 9.2 9.3 9.4 Klement, Robert; Rivinius, Thomas; Gies, Douglas R.; Baade, Dietrich; Mérand, Antoine; Monnier, John D.; Schaefer, Gail H.; Lanthermann, Cyprien et al. (February 2024), "The CHARA Array Interferometric Program on the Multiplicity of Classical Be Stars: New Detections and Orbits of Stripped Subdwarf Companions" (in en), The Astrophysical Journal 962 (1): 70, doi:10.3847/1538-4357/ad13ec, ISSN 0004-637X, Bibcode: 2024ApJ...962...70K
- ↑ 10.0 10.1 10.2 10.3 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, doi:10.1051/0004-6361/201731187, A70, Bibcode: 2018A&A...610A..70B.
- ↑ McDonald, I. et al. (2012), "Fundamental parameters and infrared excesses of Hipparcos stars", Monthly Notices of the Royal Astronomical Society 427 (1): 343–357, doi:10.1111/j.1365-2966.2012.21873.x, Bibcode: 2012MNRAS.427..343M.
- ↑ 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, doi:10.1051/0004-6361:20042229, Bibcode: 2005A&A...440..305F.
- ↑ 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. doi:10.3847/1538-3881/abf144. Bibcode: 2021AJ....161..248W.
- ↑ 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, doi:10.1111/j.1365-2966.2010.17434.x, Bibcode: 2011MNRAS.410..190T.
- ↑ "28 Cyg". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=28+Cyg.
- ↑ Wang, Luqian et al. (February 2018), "Detection of Additional Be+sdO Systems from IUE Spectroscopy", The Astrophysical Journal 853 (2): 10, doi:10.3847/1538-4357/aaa4b8, 156, Bibcode: 2018ApJ...853..156W
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