Gamma Leonis

Gamma Leonis (γ Leonis, abbreviated Gamma Leo, γ Leo), also named Algieba /æˈdʒiːbə/,[8][9] is a binary star system in the constellation of Leo. In 2009, a planetary companion around the primary was announced.

γ Leonis
Location of γ Leonis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Leo
Right ascension  10h 19m 58.35056s[1]
Declination +19° 50′ 29.3468″[1]
Apparent magnitude (V) 2.08 (2.37/3.64)[2]
Characteristics
Spectral type K0III[3] + G7IIIb
U−B color index 1.00
B−V color index 1.14
Variable type suspected[4]
Astrometry
Radial velocity (Rv)–36.24 ± 0.18[5] km/s
Proper motion (μ) RA: +304.30[1] mas/yr
Dec.: –154.28[1] mas/yr
Parallax (π)25.07 ± 0.52[1] mas
Distance130 ± 3 ly
(39.9 ± 0.8 pc)
Absolute magnitude (MV)–0.27/+0.98[6]
Orbit[3][7]
Period (P)510.3 yr
Semi-major axis (a)4.24″
Eccentricity (e)0.845
Inclination (i)76.0°
Longitude of the node (Ω)143.4°
Periastron epoch (T)1671.3
Details
γ Leo A
Mass1.23[3] M☉
Radius31.88[3] R☉
Luminosity320[3] L☉
Surface gravity (log g)2.35[6] cgs
Temperature4,470[6] K
Metallicity [Fe/H]–0.49 ± 0.12[6] dex
γ Leo B
Radius10 R☉
Luminosity40 L☉
Surface gravity (log g)2.98[6] cgs
Temperature4,980[6] K
Metallicity [Fe/H]–0.52 ± 0.11[6] dex
Other designations
Algieba, γ Leonis, 41 Leo, BD +20°2467, GCTP 2423.00, HIP 50583, NSV 4823, LTT 12764/12765, WDS 10200+1950.
γ Leo A: γ1 Leonis, HD 89484, HR 4057, SAO 81298
γ Leo B: γ2 Leonis, HD 89485, HR 4058, SAO 81299
Database references
SIMBADdata
Exoplanet Archivedata
Extrasolar Planets
Encyclopaedia		data

Nomenclature
Double star γ Leonis rho(ρ):4.7 arc" Thêta(θ):125,9°
Double star γ Leonis orbit

γ Leonis (Latinised to Gamma Leonis) is the star's Bayer designation. The A and B components of the binary are often referred to as γ1 Leonis and γ2 Leonis respectively.

It also bore the traditional name Algieba or Al Gieba, which originated from the Arabic الجبهة Al-Jabhah, meaning 'the forehead' (despite this meaning, the star actually appears in the mane of Leo). In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[10] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[11] included a table of the first two batches of names approved by the WGSN; which included Algieba for this star.

The star's traditional Latin name was Juba. It is known as 軒轅十二 (the Twelfth Star of Xuanyuan) in Chinese (Xuanyuan is the name of the Yellow Emperor).

Algieba, along with Zeta Leonis, Regulus, Mu Leonis, Epsilon Leonis and Eta Leonis have collectively been called the Sickle, which is an asterism that marks the head of Leo.[12]

Stellar system

The bright binary system in Leo with orange-red and yellow or greenish-yellow components is visible through a modest telescope under good atmospheric conditions. To the naked eye, the Algieba system shines at mid-second magnitude, but a telescope easily splits the pair. The brighter component has an apparent magnitude of +2.28 and is of spectral class K1-IIIbCN-0.5. The giant K star has a surface temperature of 4,470 K, a luminosity 180 times that of the Sun, and a diameter 23 times that of the Sun. The companion star has an apparent magnitude of +3.51 and belongs to the spectral class G7IIICN-I. The giant G star has a temperature of 4,980 K, a luminosity of 50 times that of the Sun, and a diameter 10 times that of the Sun. With angular separation of just over 4", the two stars are at least 170 AU apart (four times the distance between the Sun and Pluto), and have an orbital period of over 500 years.[7] Because the orbital period is so long, only a fraction of the full path has been observed since discovery.

Both stars are almost certainly true giants, meaning that they have stopped fusing hydrogen to helium in their cores and have expanded to great proportions. Although there has been too little observation of their orbit to calculate their masses, comparison with evolutionary calculations suggests that each are about double the mass of the Sun. Originating from the same interstellar cloud some two billion years ago, the stars have iron contents about a third that of the Sun. It is hard to tell how far along they might be in their life cycle. They both may be fusing helium in their cores, or they could be giants in development, with quiet helium cores that are waiting to fire up. The chemical composition at the surface, which is influenced by age, suggests the former.

Variability

γ Leonis is a suspected variable star, with a visual magnitude range of 1.84 to 2.03. It is not known which of the two components is variable.[4] In 1959, the star was mistakenly published as an eclipsing binary due to a typographical error when referring to Y Leonis.[13]

Planetary system

On November 6, 2009, the discovery of a planetary companion around primary star γ1 Leonis (γ Leonis A) was announced.[3] The radial velocity measurements suggest two additional periodicities of 8.5 and 1340 days. The former is likely due to stellar pulsation, whereas the latter could be indicative of the presence of an additional planetary companion with 2.14 Jupiter masses, moderate eccentricity (e=0.13) and located at 2.6 Astronomical Units away from the giant star. Nevertheless, the nature of such a signal is still unclear and further investigations are needed to confirm or rule out an additional substellar companion.

The Gamma Leonis planetary system
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b ≥8.78 MJ 1.19 429 0.14 — —
c (unconfirmed) ≥2.14 MJ 2.6 1340 0.13 — —
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References
  1. van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. 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): 3466–3471. Bibcode:2001AJ....122.3466M. doi:10.1086/323920. ISSN 0004-6256.
  3. Han, Inwoo; Lee, B. C.; Kim, K. M.; Mkrtichian, D. E.; Hatzes, A. P.; Valyavin, G. (2010). "Detection of a Planetary Companion around the giant star γ-1 Leonis". Astronomy and Astrophysics. 509: A24. arXiv:0911.0968. Bibcode:2010A&A...509A..24H. doi:10.1051/0004-6361/200912536.
  4. 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. Bibcode:2009yCat....102025S.
  5. Famaey, B.; et al. (January 2005), "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters", Astronomy and Astrophysics, 430: 165–186, arXiv:astro-ph/0409579, Bibcode:2005A&A...430..165F, doi:10.1051/0004-6361:20041272
  6. McWilliam, Andrew (December 1990), "High-resolution spectroscopic survey of 671 GK giants. I - Stellar atmosphere parameters and abundances", Astrophysical Journal Supplement Series, 74: 1075–1128, Bibcode:1990ApJS...74.1075M, doi:10.1086/191527
  7. Mason; Hartkopf, William I.; Wycoff, Gary L.; Holdenried, Ellis R. (2006). "Speckle Interferometry at the US Naval Observatory. XII". The Astronomical Journal. 132 (5): 2219–2230. Bibcode:2006AJ....132.2219M. doi:10.1086/508231.
  8. Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  9. "IAU Catalog of Star Names". Retrieved 28 July 2016.
  10. "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  11. "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
  12. Proctor, Mary (July 1896), "Evenings with the Stars", Popular Astronomy, 4: 565
  13. "Reports of Observatories". Astronomical Journal. 64: 273. 1959. Bibcode:1959AJ.....64..273.. doi:10.1086/107936.

  • Gamma Leonis Algieba orbite
  • Gamma Leonis Algieba orientation
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