Sigma1 Ursae Majoris

Sigma¹ Ursae Majoris (σ¹ UMa) is the Bayer designation for a solitary^[8] star in the northern circumpolar constellation of Ursa Major. With an apparent visual magnitude of 5.14^[2] it is faintly visible to the naked eye on dark nights. Based upon an annual parallax shift of 6.26 mas,^[1] it is located roughly 520 light years from the Sun. At that distance, the visual magnitude of the star is diminished by an extinction factor of 0.06^[3] due to interstellar dust.

For other stars with this Bayer designation, see σ Ursae Majoris.

Sigma¹ Ursae Majoris

Location of σ1 Ursae Majoris (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Ursa Major
Right ascension	09h 08m 23.49946s[1]
Declination	+66° 52′ 23.6492″[1]
Apparent magnitude (V)	5.14[2]
Characteristics
Spectral type	K5 III[3]
U−B color index	+1.80[2]
B−V color index	+1.52[2]
Astrometry
Radial velocity (Rv)	14.60±0.19[4] km/s
Proper motion (μ)	RA: −22.68[1] mas/yr Dec.: −40.11[1] mas/yr
Parallax (π)	6.26 ± 0.30 mas[1]
Distance	520 ± 20 ly (160 ± 8 pc)
Absolute magnitude (MV)	−0.93[3]
Details
Radius	46[5] R☉
Luminosity	560±20[3] L☉
Surface gravity (log g)	1.66[6] cgs
Temperature	3,940[6] K
Metallicity [Fe/H]	−0.23[6] dex
Other designations
σ1 UMa, 11 Ursae Majoris, BD+67°573, HD 77800, HIP 44857, HR 3609, SAO 14769[7]
Database references
SIMBAD	data

This is an evolved K-type giant star with a stellar classification of K5 III.^[3] It is a suspected variable with an amplitude of 0.03 magnitude.^[3] The measured angular diameter of the star after correcting for limb darkening is 2.67±0.04 mas,^[9] which, at the estimated distance of this star, yields a physical size of about 46 times the radius of the Sun.^[5] The star is radiating around 560^[3] times the solar luminosity from its outer atmosphere at an effective temperature of 3,940 K.^[6]

Naming

With π¹, π², σ², ρ, A and d, it composed the Arabic asterism Al Ṭhibā᾽, the Gazelle.^[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, this star (π¹) as Althiba II, π² as Althiba III, ρ as Althiba IV, this star (σ¹) as Althiba V, σ² as Althiba VI, and d as Althiba VII.^[11]

References

1. van Leeuwen, F. (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.
2. Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.
3. Groenewegen, M. A. T. (April 2012), "Infrared excess around nearby red giant branch stars and Reimers law", Astronomy & Astrophysics, 540: 21, Bibcode:2012A&A...540A..32G, doi:10.1051/0004-6361/201118287, A32.
4. de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, S2CID 59451347, A61.
5. Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, vol. 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R_*) is given by:

   ${\displaystyle {\begin{aligned}2\cdot R_{*}&={\frac {(159.7\cdot 2.67\cdot 10^{-3})\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\\&\approx 91.7\cdot R_{\bigodot }\end{aligned}}}$

6. Soubiran, C.; et al. (June 2010), "The PASTEL catalogue of stellar parameters", Astronomy and Astrophysics, 515: A111, arXiv:1004.1069, Bibcode:2010A&A...515A.111S, doi:10.1051/0004-6361/201014247, S2CID 118362423.
7. "sig01 UMa". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-02-25.{{cite web}}: CS1 maint: postscript (link)
8. 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:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
9. Richichi, A.; et al. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431 (2): 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039.
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.