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29 Cygni

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This article is about b3 Cygni. For other stars with this Bayer designation, see b Cygni.
29 Cygni
Location of 29 Cygni (circled in red)
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension 20h 14m 32.03235s[1]
Declination +36° 48′ 22.7009″[1]
Apparent magnitude (V) 4.94 - 4.97[2]
Characteristics
Evolutionary stage main sequence[3][4]
Spectral type A2 V[5]
B−V color index 0.151±0.018[6]
Variable type δ Sct[7]
Astrometry
Radial velocity (Rv)−17.30±2.80[6] km/s
Proper motion (μ) RA: +68.391[1] mas/yr
Dec.: +70.446[1] mas/yr
Parallax (π)24.5456±0.0724 mas[1]
Distance132.9 ± 0.4 ly
(40.7 ± 0.1 pc)
Absolute magnitude (MV)1.78[6]
Details[8]
Mass1.67–1.75[4] M☉
Radius2.32+0.88
−0.20 (equatorial)
1.50+0.15
−0.08 (polar) R☉
Luminosity10.0+1.7
−0.6 L☉
Surface gravity (log g)3.37+0.36
−0.85 (equatorial)
4.34+0.05
−0.08 (polar) cgs
Temperature6,210+755
−1,083 (equatorial)
8,800+75
−103 (polar) K
Rotational velocity (v sin i)65+6
−7 km/s
Age30–50[9] or 119+37
−10[10] Myr
Other designations
b3 Cygni, 29 Cyg, V1644 Cygni, BD+36°3955, HD 192640, HIP 99770, HR 7736, SAO 69678, WDS J20145+3648A, 2MASS J20143203+3648225[11]
Database references
SIMBADdata
Exoplanet Archivedata

29 Cygni (also known as HIP 99770) is a single[12] star in the northern constellation of Cygnus. It is dimly visible to the naked eye as a white-hued star with an apparent visual magnitude of 4.93.[6] The distance to 29 Cyg, as estimated from an annual parallax shift of 24.5 mas, is 133 light years. The star is moving closer to the Earth with a heliocentric radial velocity of −17 km/s.[6]

Characteristics

[edit]
A yellow-light light curve for V1644 Cygni, adapted from Gies and Percy (1977)[13]

29 Cygni is an A-type main-sequence star with a stellar classification of A2 V.[5] Rodríguez et al. (2000) classify it as a Delta Scuti variable with a frequency of 0.0267 cycles per day.[7] It is a Lambda Boötis class chemically peculiar star[14] and the first such star to be classified as a pulsating variable.[4] 29 Cyg is multi-periodic,[15] small-amplitude variable with a maximum brightness change of about 0.02 magnitudes and a dominant period of 39 minutes.[4] A magnetic field has been detected with an averaged quadratic field of (194.5±230.7)×10−4 T.[16]

This star has a mass 1.67 to 1.75 times the mass of the Sun[4] and is rotating with a projected rotational velocity (v sin i) of 65 km/s.[3] Interferometric observations show that it is being viewed rotating nearly pole-on, with an axial inclination of either 9.1°+3.5°
−1.3° or 170.9°+3.5°
−1.3°,[a] implying that the rotational velocity at the equator is 414+42
−112 km/s, close to the critical (breakup) velocity of the star. As a consequence, it has an oblate shape, with an equatorial radius of roughly 2.3 solar radii (R☉) and a polar radius of roughly 1.50 solar radii. Due to gravity darkening, the effective temperature also varies across latitudes, being of 6,200 K at the poles and 8,800 K at the equator. The star radiates 10 times the Sun's luminosity from its photosphere.[8]

The age of 29 Cygni has been a matter of debate. Its stellar kinematics indicate that it is a member of the Argus Association at 99[9] to 99.7% probability,[17] which would place its age between 30 and 50 million years (Myr).[9] On the other hand, Currie et al. (2022) found that the star's position in the Hertzsprung–Russell diagram indicates an age intermediate between the 115 Myr old Pleiades and the 414 Myr old Ursa Major moving group. They considered a scenario of a 29 Cygni being a rotating rapidly star viewed nearly pole-on, which would imply a lower luminosity, and hence a lower age, to be unlikely based on asteroseismic observations,[17] but this was later found to be the case by Balmer et al. in 2026 with interferometry at the CHARA array.[8] The age of the companion HIP 99770 b has been estimated at either 28+15
−14 Myr or 119+37
−10 Myr by comparing its mass and luminosity to the predictions of substellar evolution models.[10]

29 Cygni is listed in multiple star catalogs as having several companions within 4′, including the yellow 7th magnitude HD 192661. All are background objects not physically associated with 29 Cygni itself.[18][1] The naked-eye stars b1 Cygni and b2 Cygni, respectively about one and two degrees away, also lie at different distances to 29 Cygni.

Planetary system

[edit]
Direct imaging of HIP 99770 b by the Subaru Telescope.

In 2022, a superjovian planet, HIP 99770 b, was discovered by direct imaging and astrometry. Its spectral class is between L7 and L9.5, corresponding to a surface temperature of 1,400±100 K.[17]

The planet appears to be rotating close to the equatorial plane of the star, with a spin-orbit misaligment of 12°±6°.[8] Together with its low orbital eccentricity[17] and enhanced metallicity compared to that of the host star, it most likely formed in a protoplanetary disk, similar to planets, despite its large mass of (13–15)±5 MJup.[8]

The 29 Cygni planetary system[8]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(years) 		Eccentricity Inclination
(°) 		Radius
b 13±5 or 15±5 MJ 14.7±0.4 47+14
−4[19] 		0.37±0.03 160±5 1.20±0.05 or 1.3±0.1 RJ

Notes

[edit]
  1. ^ The inclination is subject to a 180−i ambiguity, with the prograde value being listed in Table 4.

References

[edit]
  1. ^ a b c d e f Vallenari, A.; et al. (Gaia collaboration) (2023), "Gaia Data Release 3. Summary of the content and survey properties", Astronomy and Astrophysics, 674: A1, arXiv:2208.00211, Bibcode:2023A&A...674A...1G, doi:10.1051/0004-6361/202243940, S2CID 244398875 Gaia DR3 record for this source at VizieR.
  2. ^ Samus, N. N.; Durlevich, O. V.; et al. (2009), "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)", VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S, 1: B/GCVS, Bibcode:2009yCat....102025S.
  3. ^ a b Zorec, J.; Royer, F. (2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics, 537: A120, arXiv:1201.2052, Bibcode:2012A&A...537A.120Z, doi:10.1051/0004-6361/201117691, S2CID 55586789, A120.
  4. ^ a b c d e Casas, R.; et al. (May 2009), "Asteroseismological Modeling of the Multiperiodic λ Bootis Star 29 Cygni", The Astrophysical Journal, 697 (1): 52–534, Bibcode:2009ApJ...697..522C, doi:10.1088/0004-637X/697/1/522, hdl:10481/41210, S2CID 120924176.
  5. ^ a b Cowley, A.; et al. (April 1969), "A study of the bright A stars. I. A catalogue of spectral classifications", Astronomical Journal, 74: 375–406, Bibcode:1969AJ.....74..375C, doi:10.1086/110819.
  6. ^ 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.
  7. ^ a b Rodríguez, E.; et al. (June 2000), "A revised catalogue of delta Sct stars", Astronomy and Astrophysics Supplement, 144 (3): 469–474, Bibcode:2000A&AS..144..469R, doi:10.1051/aas:2000221, hdl:10261/226673.
  8. ^ a b c d e f Balmer, William O.; Pueyo, Laurent; Messier, Ashley; Bruinsma, Evelyn; Jones, Jeremy; Matuszewska, Klara; Perrin, Marshall D.; Girard, Julien H.; Leisenring, Jarron M.; Lawson, Kellen; van der Marel, Roeland P.; Kammerer, Jens; Carter, Aarynn; Mâlin, Mathilde; Ward-Duong, Kimberly (April 2026), "Direct Images of CO2 Absorption in the Atmosphere of a Super-Jupiter: Enhanced Metallicity Suggestive of Formation in a Disk", The Astrophysical Journal, 1001 (2): L26, arXiv:2604.09785, Bibcode:2026ApJ..1001L..26B, doi:10.3847/2041-8213/ae374a, ISSN 0004-637X.
  9. ^ a b c Malo, Lison; et al. (January 2013), "Bayesian Analysis to Identify New Star Candidates in Nearby Young Stellar Kinematic Groups", The Astrophysical Journal, 762 (2): 50, arXiv:1209.2077, Bibcode:2013ApJ...762...88M, doi:10.1088/0004-637X/762/2/88, S2CID 118497872, 88.
  10. ^ a b Winterhalder, T. O.; Kammerer, J.; Lacour, S.; Mérand, A.; Nowak, M.; Stolker, T.; Balmer, W. O.; Marleau, G.-D.; Abuter, R.; Amorim, A.; Asensio-Torres, R.; Berger, J.-P.; Beust, H.; Blunt, S.; Bonnefoy, M. (2025-06-27), "Orbit and atmosphere of HIP 99770 b through the eyes of VLTI/GRAVITY", Astronomy & Astrophysics, 700: A4, arXiv:2507.00117, Bibcode:2025A&A...700A...4W, doi:10.1051/0004-6361/202554766, ISSN 0004-6361.
  11. ^ "29 Cyg", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2019-01-13.
  12. ^ De Rosa, R. J.; et al. (2014), "The VAST Survey - III. The multiplicity of A-type stars within 75 pc", Monthly Notices of the Royal Astronomical Society, 437 (2): 1216, arXiv:1311.7141, Bibcode:2014MNRAS.437.1216D, doi:10.1093/mnras/stt1932, S2CID 88503488.
  13. ^ Gies, Douglas R.; Percy, John R. (February 1977), "Photometric variability of 29 Cygni", The Astronomical Journal, 82 (2): 166–168, Bibcode:1977AJ.....82..166G, doi:10.1086/112023.
  14. ^ Murphy, Simon J.; et al. (October 2015), "An Evaluation of the Membership Probability of 212 λ Boo Stars. I. A Catalogue", Publications of the Astronomical Society of Australia, 32 e036: 43, arXiv:1508.03633, Bibcode:2015PASA...32...36M, doi:10.1017/pasa.2015.34, S2CID 59405545, e036.
  15. ^ Mkrtichian, D. E.; et al. (October 2007), "Multimode Pulsations of the λ Bootis Star 29 Cygni: The 1995 and 1996 Multisite Campaigns", The Astronomical Journal, 134 (4): 1713, Bibcode:2007AJ....134.1713M, doi:10.1086/521434.
  16. ^ Bychkov, V. D.; et al. (August 2003), "Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars", Astronomy and Astrophysics, 407 (2): 631–642, arXiv:astro-ph/0307356, Bibcode:2003A&A...407..631B, doi:10.1051/0004-6361:20030741, S2CID 14184105.
  17. ^ a b c d Currie, Thayne; Brandt, G. Mirek; Brandt, Timothy D.; et al. (2023-04-14), "Direct imaging and astrometric detection of a gas giant planet orbiting an accelerating star", Science, 380 (6641): 198–203, arXiv:2212.00034, Bibcode:2023Sci...380..198C, doi:10.1126/science.abo6192, ISSN 0036-8075, PMID 37053312.
  18. ^ Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001), "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog", The Astronomical Journal, 122 (6): 3466, Bibcode:2001AJ....122.3466M, doi:10.1086/323920.
  19. ^ Bovie, Danielle; Currie, Thayne; El Morsy, Mona; Lacy, Brianna; Kuzuhara, Masayuki; Chilcote, Jeffrey; Tobin, Taylor L.; Guyon, Olivier; Groff, Tyler D.; Lozi, Julien; Vievard, Sebastien; Deo, Vincent; Martinache, Frantz; Li, Yiting; Tamura, Motohide (2025-11-03), "Multi-band Spectral and Astrometric Characterization of the HIP 99770 b Planet with SCExAO/CHARIS and Gaia", The Astronomical Journal, 170 (5): 254, arXiv:2509.02665, doi:10.3847/1538-3881/ae0195, ISSN 0004-6256.