zeta Ursae Minoris
{{short description|Star in the constellation Ursa Minor}}
{{Starbox begin
| name = ζ Ursae Minoris
}}
{{Starbox image
| image =
{{Location mark
|image=Ursa Minor constellation map.svg|alt=|float=center|width=240
|label=|position=right
|mark=Red circle.svg|mark_width=10|mark_link=ζ UMi
|x=416|y=500
}}
| caption = Location of ζ Ursae Minoris (circled)
}}
{{Starbox observe
| epoch = J2000
| dec = {{DEC|+77|47|40.1788}}
| constell = Ursa Minor
}}
{{Starbox character
| type =
| variable = Suspected δ Sct
}}
{{Starbox astrometry
| radial_v = {{val|−13.1|4.1}}
| parallax = 8.84
| p_error = 0.12
}}
{{Starbox detail
| metal_fe =
| rotation =
| gravity =
}}
{{Starbox catalog
| names = {{odlist | B=Zeta UMi, ζ UMi | F=16 Ursae Minoris | FK5=590 | HR=5903 | HD=142105 | BD=+78°527 | HIP=77055 | SAO=8328 | GC=21243 | NSV=7263 }}
}}
{{Starbox reference
| Simbad=zet+UMi
}}
{{Starbox end}}
Zeta Ursae Minoris, which is Latinized from ζ Ursae Minoris, is a single star in the northern circumpolar constellation of Ursa Minor, forming the northernmost part of the bowl in this "little dipper" asterism. 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, but is drifting further closer with a radial velocity of about –13 km/s.
File:ZetaUMiLightCurve.png 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.]]
The stellar classification of Zeta UMi is A3Vn, 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. It is a pulsating variable star, with a period of 15.8 hours, and it also undergoes eclipses. 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.
Zeta Ursae Minoris is about 180 million years old with 6.15 times the radius of the Sun. It is radiating 227 times the luminosity of the Sun from its photosphere at an effective temperature of 8,720 K. This anomalously high temperature and an absolute magnitude of –0.98 may indicate it is on the verge of evolving into a giant star. An infrared excess has been detected from an orbiting circumstellar disk. A black body fit to the data yields a mean dust temperature of 160 K and an orbital radius of {{val|42.5|u=AU}}.
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.
References
{{reflist|refs=
| title=zet UMi | access-date=2021-01-08 }}
| title=zet UMi | url=https://www.aavso.org/vsx/index.php?view=detail.top&oid=45887
| website=The International Variable Star Index |publisher=AAVSO |access-date=16 October 2022}}
| title=Cosmic Challenge: The Ultimate Observing List for Amateurs
| first=Philip S. | last=Harrington
| page=38 | date=October 21, 2010
| publisher=Cambridge University Press
| isbn=9781139493680 | url=https://books.google.com/books?id=8mQmvT4wpWQC&pg=PA38 }}
| title=List of Probable Delta Scuti Stars
| last1=Frolov | first1=M. S.
| journal=Information Bulletin on Variable Stars
| volume=427 | page=1 | date=April 1970
| bibcode=1970IBVS..427....1F }}
| display-authors=1 | last1=Su | first1=K. Y. L.
| last2=Rieke | first2=G. H. | last3=Stansberry | first3=J. A.
| last4=Bryden | first4=G. | last5=Stapelfeldt | first5=K. R.
| last6=Trilling | first6=D. E. | last7=Muzerolle | first7=J.
| last8=Beichman | first8=C. A. | last9=Moro-Martin | first9=A.
| title=Debris Disk Evolution around A Stars
| journal=The Astrophysical Journal
| volume=653 | issue=1 | pages=675–689 |date=December 2006
| doi=10.1086/508649 | arxiv=astro-ph/0608563
| bibcode=2006ApJ...653..675S | s2cid=14116473 }}
| last1=Eggleton | first1=P. P. | last2=Tokovinin | first2=A. A.
| title=A catalogue of multiplicity among bright stellar systems
| journal=Monthly Notices of the Royal Astronomical Society
| volume=389 | issue=2 | pages=869–879 | date=September 2008
| doi=10.1111/j.1365-2966.2008.13596.x | doi-access=free | arxiv=0806.2878
| bibcode=2008MNRAS.389..869E | s2cid=14878976 }}
| last=van Belle | first=Gerard T.
| title=Interferometric observations of rapidly rotating stars
| journal=The Astronomy and Astrophysics Review
| volume=20 | issue=1 | page=51 | date=March 2012
| doi=10.1007/s00159-012-0051-2 | s2cid=119273474
| bibcode=2012A&ARv..20...51V | arxiv=1204.2572 }}
| title=Validation of the new Hipparcos reduction
| last=van Leeuwen | first=F.
| journal=Astronomy and Astrophysics
| volume=474 | issue=2 | pages=653–664 | date=2007
| arxiv=0708.1752 | bibcode=2007A&A...474..653V
| doi=10.1051/0004-6361:20078357 | s2cid=18759600 }}
| last=Gontcharov | first=G. A.
| title=Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system
| journal=Astronomy Letters
| volume=32| issue=11| pages=759–771| date=November 2006
| doi=10.1134/S1063773706110065 | arxiv=1606.08053
| bibcode=2006AstL...32..759G | s2cid=119231169 }}
| first=James B. | last=Kaler
| title=Alifa al Farkadain | work=Stars
| publisher=University of Illinois
| url=http://stars.astro.illinois.edu/sow/alifa.html
| access-date=21 June 2014 }}
| title=A study of the bright A stars. I. A catalogue of spectral classifications
| last1=Cowley | first1=A. | last2=Cowley | first2=C.
| last3=Jaschek | first3=M. | last4=Jaschek | first4=C.
| display-authors=1 | journal=Astronomical Journal
| volume=74 | pages=375–406 |date=April 1969
| doi=10.1086/110819 | bibcode=1969AJ.....74..375C }}
| title=A Comprehensive Census of Nearby Infrared Excess Stars
| last1=Cotten | first1=Tara H. | last2=Song | first2=Inseok
| journal=The Astrophysical Journal Supplement Series
| volume=225 | issue=1 | id=15 | pages=24 | date=July 2016
| doi=10.3847/0067-0049/225/1/15 | arxiv=1606.01134
| bibcode=2016ApJS..225...15C | s2cid=118438871 | doi-access=free }}
| last1=Johnson | first1=H. L. | last2=Mitchell | first2=R. I.
| last3=Iriarte | first3=B. | last4=Wisniewski | first4=W. Z.
| display-authors=1 | title=UBVRIJKL photometry of the bright stars
| journal=Communications of the Lunar and Planetary Laboratory
| volume=4 | issue=99 | date=1966 |page=99
| bibcode=1966CoLPL...4...99J }}
| title=XHIP: An extended hipparcos compilation
| last1=Anderson | first1=E. | last2=Francis | first2=Ch.
| journal=Astronomy Letters
| volume=38 | issue=5 | pages=331 | year=2012
| bibcode=2012AstL...38..331A | doi=10.1134/S1063773712050015
| arxiv=1108.4971 | s2cid=119257644 }}
| first=Richard Hinckley | last=Allen
| title=Star-names and Their Meanings
| url=https://archive.org/details/bub_gb_5xQuAAAAIAAJ
| year=1899 | publisher=G. E. Stechert
| pages=[https://archive.org/details/bub_gb_5xQuAAAAIAAJ/page/n469 447]–460}}
}}
{{Stars of Ursa Minor}}
{{DEFAULTSORT:Zeta Ursae Minoris}}
Category:A-type main-sequence stars
Category:Delta Scuti variables