Zeta Ursae Minoris

Zeta Ursae Minoris, which is Latinized from ζ Ursae Minoris, is a single[12] star in the northern circumpolar constellation of Ursa Minor, forming the northernmost part of the bowl in this "little dipper" asterism.[13] The star has a white hue and is faintly visible to the naked eye with an apparent visual magnitude of +4.28. It is located at a distance of approximately 369 light-years from the Sun based on parallax,[1] but is drifting further closer with a radial velocity of about –13 km/s.[6]

A light curve for Zeta Ursae Minoris, plotted from TESS data. The main plot shows the flux as a function of time, and the inset plot shows the same data (excluding the eclipse) folded with the pulsation period.[14]
ζ Ursae Minoris
Location of ζ Ursae Minoris (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Minor
Right ascension 15h 44m 03.51892s[1]
Declination +77° 47′ 40.1788″[1]
Apparent magnitude (V) +4.29[2]
Characteristics
Spectral type A3Vn[3]
U−B color index +0.05[4]
B−V color index 0.038±0.005[2]
Variable type Suspected δ Sct[5]
Astrometry
Radial velocity (Rv)−13.1±4.1[6] km/s
Proper motion (μ) RA: 19.91[1] mas/yr
Dec.: −1.99[1] mas/yr
Parallax (π)8.84 ± 0.12 mas[1]
Distance369 ± 5 ly
(113 ± 2 pc)
Absolute magnitude (MV)−0.98[2]
Details
Mass~3.4[7] M☉
Radius6.15[8] R☉
Luminosity227[2] L☉
Temperature8,720[8] K
Rotational velocity (v sin i)210[9] km/s
Age180[10] Myr
Other designations
Zeta UMi, ζ UMi, 16 Ursae Minoris, NSV 7263, BD+78°527, FK5 590, GC 21243, HD 142105, HIP 77055, HR 5903, SAO 8328[11]
Database references
SIMBADdata

The stellar classification of Zeta UMi is A3Vn,[3] a notation that indicates this is an A-type main-sequence star with broad "nebulous" absorption lines in its spectrum due to rapid rotation. Based on photometric data, some light variability was suspected by R. A. Baker in 1926, and it may be a Delta Scuti variable.[5] It is a pulsating variable star, with a period of 15.8 hours, and it also undergoes eclipses.[14] The star is spinning with a projected rotational velocity of 210 km/s, which is creating an equatorial bulge that is estimated to be 10% larger than the polar radius.[9]

Zeta Ursae Minoris is about 180[10] million years old with 6.15[8] times the radius of the Sun. It is radiating 227[2] times the luminosity of the Sun from its photosphere at an effective temperature of 8,720 K.[8] This anomalously high temperature and an absolute magnitude of –0.98[2] may indicate it is on the verge of evolving into a giant star.[7] An infrared excess has been detected from an orbiting circumstellar disk.[10] A black body fit to the data yields a mean dust temperature of 160 K and an orbital radius of 42.5 AU.[8]

In some Arabic star charts it is listed as أخفى الفرقدين ʼakhfā al-farqadayn, meaning "the dimmer of the two calves", and paired with η Ursae Minoris as ʼanwar al-farqadayn, "the brighter of the two calves". The names may originally refer to a pair of Ibexes, and are more properly applied to γ UMi and β UMi, respectively, the brighter two stars in the rectangle of Ursa Minor.[15]

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. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
  3. Cowley, A.; et al. (April 1969). "A study of the bright A stars. I. A catalogue of spectral classifications". Astronomical Journal. 74: 375–406. Bibcode:1969AJ.....74..375C. doi:10.1086/110819.
  4. Johnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99): 99. Bibcode:1966CoLPL...4...99J.
  5. Frolov, M. S. (April 1970). "List of Probable Delta Scuti Stars". Information Bulletin on Variable Stars. 427: 1. Bibcode:1970IBVS..427....1F.
  6. Gontcharov, G. A. (November 2006). "Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. S2CID 119231169.
  7. Kaler, James B. "Alifa al Farkadain". Stars. University of Illinois. Retrieved 21 June 2014.
  8. Cotten, Tara H.; Song, Inseok (July 2016). "A Comprehensive Census of Nearby Infrared Excess Stars". The Astrophysical Journal Supplement Series. 225 (1): 24. arXiv:1606.01134. Bibcode:2016ApJS..225...15C. doi:10.3847/0067-0049/225/1/15. S2CID 118438871. 15.
  9. van Belle, Gerard T. (March 2012). "Interferometric observations of rapidly rotating stars". The Astronomy and Astrophysics Review. 20 (1): 51. arXiv:1204.2572. Bibcode:2012A&ARv..20...51V. doi:10.1007/s00159-012-0051-2. S2CID 119273474.
  10. Su, K. Y. L.; et al. (December 2006). "Debris Disk Evolution around A Stars". The Astrophysical Journal. 653 (1): 675–689. arXiv:astro-ph/0608563. Bibcode:2006ApJ...653..675S. doi:10.1086/508649. S2CID 14116473.
  11. "zet UMi". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-01-08.
  12. 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.
  13. Harrington, Philip S. (October 21, 2010). Cosmic Challenge: The Ultimate Observing List for Amateurs. Cambridge University Press. p. 38. ISBN 9781139493680.
  14. "zet UMi". The International Variable Star Index. AAVSO. Retrieved 16 October 2022.
  15. Allen, Richard Hinckley (1899). Star-names and Their Meanings. G. E. Stechert. pp. 447–460.
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