Theta Ursae Majoris

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Theta Ursae Majoris
Diagram showing star positions and boundaries of the Ursa Major constellation and its surroundings
Diagram showing star positions and boundaries of the Ursa Major constellation and its surroundings

Location of θ Ursae Majoris (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Major
Right ascension 09h 32m 51.43390s[1]
Declination +51° 40′ 38.2811″[1]
Apparent magnitude (V) 3.166[2]
Spectral type F6 IV[3]
U−B color index +0.03[4]
B−V color index +0.46[3]
Variable type Suspected
Radial velocity (Rv) +14.6[5] km/s
Proper motion (μ) RA: -947.46[1] mas/yr
Dec.: -535.60[1] mas/yr
Parallax (π) 74.19 ± 0.14[1] mas
Distance 43.96 ± 0.08 ly
(13.48 ± 0.03 pc)
Absolute magnitude (MV) 2.43[2]
Mass 1.41[2] M
Radius 2.365 ± 0.008[6] R
Luminosity 7.871 ± 0.158[6] L
Surface gravity (log g) 3.80 ± 0.10[2] cgs
Temperature 6,300 ± 33[6] K
Metallicity [Fe/H] –0.18 ± 0.07[2] dex
Rotational velocity (v sin i) 6.8[2] km/s
Age 2.2[5] Gyr
Other designations
Al Haud, Sarir, θ Ursae Majoris, θ UMa, Theta UMa, 25 Ursae Majoris, BD+52 1401, CCDM J09329+5141A, FK5 358, GC 13157, HD 82328, HIP 46853, HR 3775, IDS 09262+5208 A, PPM 32203, SAO 27289, WDS J09329+5141A.[7]
Database references

Theta Ursae Majoris (Theta UMa, θ Ursae Majoris, θ UMa) is a suspected spectroscopic binary star system in the northern circumpolar constellation of Ursa Major. It has an apparent visual magnitude of 3.17,[2] placing it among the brighter members of this constellation. The distance to this star has been measured directly using the parallax method, yielding an estimated value of 43.96 light-years (13.48 parsecs).[1]

In 1976, this was reported as a spectroscopic binary system by Helmut A. Abt and Saul G. Levy, giving it an orbital period of 371 days.[8] This has been listed as a spectroscopic binary system with an orbital period of 371 days. However, this was brought into question by Christopher L. Morbey and Roger F. Griffin in 1987, who suggested that the data could be explained by random chance.[9] Further observations in 2009 with observations with the Bok Telescope in Arizona did show changes of 180 m/s in radial velocity, although there was not sufficient evidence to support a Keplerian orbit.[10] There is a 14th-magnitude common proper motion companion to Theta Ursae Majoris at an angular separation of 4.1 arcseconds,[11] so this may potentially be a triple star system.[12]

The primary component of this putative system has a published stellar classification of F6 IV,[3] indicating it is a subgiant star that is evolving away from the main sequence. In 2009, Helmut A. Abt listed it with a stellar classification of F7 V, suggesting that it is still on the main sequence.[13] It is larger than the Sun with 141% of the Sun's mass and 250% of the Sun's radius.[2] Consequently it is shining brighter and evolving more rapidly than the Sun, with a luminosity nearly eight[3] times the Sun's at an age of 2.2 billion years.[5] This energy is being radiated from the star's outer atmosphere at an effective temperature of 6,300 K.[6] At this heat, the star glows with the yellow-white hue of an F-type star.[14]

The McDonald Observatory team has set limits to the hypothetical presence of one or more planets around the primary with masses between 0.24 and 4.6 Jupiter masses and average separations spanning between 0.05 and 5.2 AU.[15]

Naming and etymology[edit]


  1. ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752free to read, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 
  2. ^ a b c d e f g h Fuhrmann, Klaus (February 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 
  3. ^ a b c d Mallik, Sushma V. (December 1999), "Lithium abundance and mass", Astronomy and Astrophysics, 352: 495–507, Bibcode:1999A&A...352..495M 
  4. ^ Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99), Bibcode:1966CoLPL...4...99J 
  5. ^ a b c Nordström, B.; et al. (May 2004), "The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ˜14 000 F and G dwarfs", Astronomy and Astrophysics, 418: 989–1019, arXiv:astro-ph/0405198free to read, Bibcode:2004A&A...418..989N, doi:10.1051/0004-6361:20035959 
  6. ^ a b c d Boyajian, Tabetha S.; et al. (February 2012), "Stellar Diameters and Temperatures. I. Main-sequence A, F, and G Stars", The Astrophysical Journal, 746 (1): 101, arXiv:1112.3316free to read, Bibcode:2012ApJ...746..101B, doi:10.1088/0004-637X/746/1/101 . See Table 10.
  7. ^ "tet UMa -- Spectroscopic binary", SIMBAD Astronomical Object Database, Centre de Données astronomiques de Strasbourg, retrieved 2012-02-04 
  8. ^ Abt, H. A.; Levy, S. G. (March 1976), "Multiplicity among solar-type stars", Astrophysical Journal Supplement Series, 30: 273–306, Bibcode:1976ApJS...30..273A, doi:10.1086/190363 
  9. ^ Morbey, C. L.; Griffin, R. F. (June 1987), "On the reality of certain spectroscopic orbits", Astrophysical Journal, Part 1, 317: 343–352, Bibcode:1987ApJ...317..343M, doi:10.1086/165281 
  10. ^ Behr, Bradford B.; et al. (November 2009), "Stellar Astrophysics with a Dispersed Fourier Transform Spectrograph. I. Instrument Description and Orbits of Single-lined Spectroscopic Binaries", The Astrophysical Journal, 705 (1): 543–553, arXiv:0909.3241free to read, Bibcode:2009ApJ...705..543B, doi:10.1088/0004-637X/705/1/543 
  11. ^ Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv:0806.2878free to read. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x. 
  12. ^ Kaler, James B., "THETA UMA (Theta Ursae Majoris)", Stars, University of Illinois, retrieved 2012-02-25 
  13. ^ Abt, Helmut A. (January 2009), "MK Classifications of Spectroscopic Binaries", The Astrophysical Journal Supplement, 180 (1): 117–118, Bibcode:2009ApJS..180..117A, doi:10.1088/0067-0049/180/1/117 
  14. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16 
  15. ^ Wittenmeyer, R. A.; et al. (2006), "Detection Limits from the McDonald Observatory Planet Search Program", The Astronomical Journal, 132 (1): 177–188, arXiv:astro-ph/0604171free to read, Bibcode:2006AJ....132..177W, doi:10.1086/504942 
  16. ^ Allen, Richard Hinckley (1899), Star-Names and Their Meanings, New York: G. E. Stechert, p. 442 
  17. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 16 日