Sigma2 Ursae Majoris

For other stars with this Bayer designation, see σ Ursae Majoris.
Sigma2 Ursae Majoris
Sigma2 Ursae Majoris is located in 100x100
Sigma2 Ursae Majoris

Location of σ2 Ursae Majoris (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Major
σ2 UMa A
Right ascension 09h 10m 23.538s[1]
Declination +67° 08′ 02.44″[1]
Apparent magnitude (V) +4.813[1]
σ2 UMa B
Right ascension 09h 10m 23.508s[1]
Declination +67° 08′ 06.58″[1]
Apparent magnitude (V) +10.26[1]
Characteristics
Spectral type F6IV-V / K2V[2]
U−B color index +0.01[3]
B−V color index +0.48[3]
Variable type Suspected[4]
Astrometry
σ2 UMa A
Radial velocity (Rv)−2.92 ± 0.12[5] km/s
Proper motion (μ) RA: 7.1[1] mas/yr
Dec.: −95.1[1] mas/yr
Parallax (π)49.07 ± 0.37 mas[6]
Distance66.5 ± 0.5 ly
(20.4 ± 0.2 pc)
Absolute bolometric
magnitude (Mbol)		3.18[7]
σ2 UMa B
Proper motion (μ) RA: 4.1[1] mas/yr
Dec.: −30.0[1] mas/yr
Absolute magnitude (MV)7.16[7]
Orbit[8]
Period (P)970 ± 118 yr
Semi-major axis (a)5.80 ± 0.14″
Eccentricity (e)0.801 ± 0.017
Inclination (i)145.4 ± 1.5°
Longitude of the node (Ω)102.1 ± 1.9°
Periastron epoch (T)B 1917.39 ± 0.12
Argument of periastron (ω)
(secondary)		332.4 ± 1.9°
Details[7]
σ2 UMa A
Mass1.31 M☉
Radius1.75 ± 0.07 R☉
Surface gravity (log g)4.00 ± 0.10 cgs
Temperature6276 ± 80 K
Metallicity [Fe/H]−0.03 ± 0.07 dex
Rotational velocity (v sin i)4.1 ± 0.8 km/s
σ2 UMa B
Mass~0.73 M☉
Temperature~4600 K
Other designations
BD+67°577, Gl 335, HD 78154, HIP 45038, HR 3616, SAO 14788[4]
σ2 UMa A: TYC 4141-1496-1
σ2 UMa B: TYC 4141-1496-2
Database references
SIMBADAB
A
B

Sigma2 Ursae Majoris (σ2 Ursae Majoris, σ2 UMa) is a binary star in the constellation of Ursa Major. Parallax measurements made by the Hipparcos spacecraft put it at a distance of about 66.5 light years (20.4 parsecs) from Earth, making this a fairly nearby system. The primary component has an apparent magnitude of about 4.8,[1] meaning it can be seen with the naked eye (see Bortle scale).

This is a visual binary, meaning that the two components can be resolved, and the orbit is derived from the positions of the two stars. The primary component Sigma2 Ursae Majoris A, is a white-colored F-type subgiant. Its radius is about 1.75 times that of the Sun, and it is 31% more massive.[7] The companion is an orange K-type main-sequence star that is much fainter. The two stars are separated about 4 arcseconds away, and because of their slow orbital motion the orbit is poorly known: estimates of the orbital period range from 970 years[8] to over 1,500 years.[9] There is a third component, designated Sigma2 Ursae Majoris C. Located 205 arcseconds from the primary, it is thought to be a line-of-sight coincidence, and is not related to the system.

Naming

  • With π1, π2, σ1, ρ, A and d, it composed the Arabic asterism الظِّبَاء aẓ-Ẓibāʾ meaning the Gazelles.[10] According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Ṭhibā were the title for seven stars : A as Althiba I, π1 as Althiba II, π2 as Althiba III, ρ as Althiba IV, σ1 as Althiba V, this star (σ2) as Althiba VI, and d as Althiba VII.[11]
  • In Chinese, 三師 (Sān Shī), meaning Three Top Instructors, refers to an asterism consisting of σ2 Ursae Majoris and ρ Ursae Majoris. Consequently, σ2 Ursae Majoris itself is known as 三師三 (Sān Shī sān, English: the Third Star of Three Top Instructors.).[12]

References

  1. ^ a b c d e f g h i j k Høg, E.; et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H.
  2. ^ Edwards, T. W. (1976). "MK classification for visual binary components". Astronomical Journal. 81: 245–249. Bibcode:1976AJ.....81..245E. doi:10.1086/111879.
  3. ^ a b Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
  4. ^ a b "* sig02 UMa". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 27 March 2017.
  5. ^ de Medeiros, J. R.; Mayor, M. (1999). "A catalog of rotational and radial velocities for evolved stars". Astronomy and Astrophysics Supplement. 139 (3): 433–460. arXiv:astro-ph/0608248. Bibcode:1999A&AS..139..433D. doi:10.1051/aas:1999401.
  6. ^ van Leeuwen, F.; et al. (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. S2CID 18759600.
  7. ^ a b c d Fuhrmann, Klaus (2008). "Nearby stars of the Galactic disc and halo - IV". Monthly Notices of the Royal Astronomical Society. 384 (1): 173–224. Bibcode:2008MNRAS.384..173F. doi:10.1111/j.1365-2966.2007.12671.x.
  8. ^ a b "Sixth Catalog of Orbits of Visual Binary Stars". United States Naval Observatory. Archived from the original on 2017-08-01. Retrieved 2017-04-01.
  9. ^ Shklovskii, I. S.; Wenzel, W. (1980). "Book-Review - Stars Their Birth Life and Death". Astronomische Nachrichten. 301: 99. Bibcode:1980AN....301...99S. doi:10.1002/asna.2103010207.
  10. ^ Allen, Richard Hinckley (1899), Star-Names and Their Meanings, New York: G. E. Stechert, p. 444
  11. ^ Rhoads, Jack W. (November 15, 1971), Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars (PDF), Jet Propulsion Laboratory, California Institute of Technology.
  12. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 16 日