Astronomy:9 Equulei

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9 Equulei
Observation data
Epoch J2000      Equinox J2000
Constellation Equuleus
Right ascension  21h 21m 04.825s[1]
Declination 07° 21′ 16.21″[1]
Apparent magnitude (V) 5.798[2]
Spectral type M2IIIa[3]
U−B color index +1.97[4]
B−V color index +1.66[4]
Variable type suspected[5]
Radial velocity (Rv)−21.82±0.30[1] km/s
Proper motion (μ) RA: 43.871±0.274[1] mas/yr
Dec.: −17.822±0.261[1] mas/yr
Parallax (π)4.3895 ± 0.1647[1] mas
Distance740 ± 30 ly
(228 ± 9 pc)
Absolute magnitude (MV)−0.69[6]
Radius58[1] R
Luminosity720[1] L
Temperature3,920[1] K
Other designations
HIP 105413, HD 203291, HR 8163, SAO 126719
Database references

9 Equulei is an M-type star in the constellation Equuleus. It is an asymptotic giant branch (AGB) star, a star that has exhausted its core helium and is now fusing both hydrogen and helium in shells outside the core.[7] It is also a suspected variable star with an amplitude of about 0.05 magnitudes.[5]

The spectral type is M2IIIa, meaning it is a relatively cool giant star. As an AGB star, it is burning hydrogen and helium in shells around an inert carbon-oxygen core. It has expanded to 58 times the radius of the Sun, and it radiates 720 times as much electromagnetic radiation from a photosphere with an effective temperature of 3,920 K.


  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode2018A&A...616A...1G.  Gaia DR2 record for this source at VizieR.
  2. Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P. et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics 355: L27. Bibcode2000A&A...355L..27H. 
  3. Yamashita, Y. (1967). "MK Spectral Types of Bright M-Type Stars". Publications of the Dominion Astrophysical Observatory Victoria 13: 47. Bibcode1967PDAO...13...47Y. 
  4. 4.0 4.1 Hoffleit, Dorrit; Jaschek, Carlos (1991). "The Bright star catalogue". New Haven, Conn.: Yale University Observatory, 5th rev.ed.. 
  5. 5.0 5.1 Samus, N. N. 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. Bibcode2009yCat....102025S. 
  6. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331. doi:10.1134/S1063773712050015. Bibcode2012AstL...38..331A. 
  7. Eggen, Olin J. (1992). "Asymptotic Giant Branch Stars Near the Sun". The Astronomical Journal 104: 275. doi:10.1086/116239. Bibcode1992AJ....104..275E.