Eta Ursae Minoris

Eta Ursae Minoris
	Location of η Ursae Minoris (circled)
Observation data; Epoch J2000.0 Equinox J2000.0 (ICRS)
Constellation	Ursa Minor
Right ascension	16h 17m 30.27025s
Declination	+75° 45′ 19.2351″
Apparent magnitude (V)	+4.95
Characteristics
Evolutionary stage	main sequence
Spectral type	F5 V
U−B color index	+0.02
B−V color index	+0.35
Astrometry
Radial velocity (Rv)	−11.0±0.9 km/s
Proper motion (μ)	RA: −77.647 mas/yr ; Dec.: +245.726 mas/yr
Parallax (π)	33.4190±0.1103 mas
Distance	97.6 ± 0.3 ly ; (29.92 ± 0.10 pc)
Absolute magnitude (MV)	+2.61
Details
Mass	1.539 M☉
Radius	2.024 R☉
Luminosity	7.725 L☉
Surface gravity (log g)	4.15±0.14 cgs
Temperature	6,764 K
Metallicity [Fe/H]	−0.02 dex
Rotational velocity (v sin i)	84.8 km/s
Age	1.743 Gyr
Other designations
	η UMi, 21 Ursae Minoris, BD+76°596, FK5 612, GC 21999, HD 148048, HIP 79822, HR 6116, SAO 8470, CCDM 16176+7545
Database references
SIMBAD	data

Eta Ursae Minoris (Latinized from η Ursae Minoris) is a yellow-white hued star in the northern circumpolar constellation of Ursa Minor.

This is an F-type main-sequence star of stellar classification F5 V with an apparent magnitude of +4.95, making it faintly visible to the naked eye.^[10] Based upon an annual parallax shift of 33.4 mas as seen from the Earth, it is located 98 light years from the Sun. The star is moving closer to the Sun with a radial velocity of −11 km/s,^[5] and is traversing the sky with a relatively high proper motion of 0.271 arc seconds per year.^[11]

Eta Ursae Minoris is about 1.7 billion years old and has 1.54 times the mass of the Sun.^[1] It has a high rate of spin with a projected rotational velocity of 84.8 km/s.^[3] These coordinates mark a source of X-ray emission with a luminosity of 11.5×10²⁸ erg s⁻¹.^[6] Eta Ursae Minoris may form a wide binary system with a magnitude 15.3 companion star, located at an angular separation of 228.5 arc seconds.^[4]

In some Arabic star charts it is labeled انور الفرقدين ʼanwar al-farqadayn, "the brighter of the two calves", and paired with ζ Ursae Minoris as اخفي الفرقدين akhfā al-farkadain "the dimmer of the two calves". The names may originally refer to a pair of Ibexes, and are more properly applied to β UMi and γ UMi respectively, the brighter two stars in the rectangle of Ursa Minor.^[12]

References

^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
^ ^a ^b ^c Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, Bibcode:1986EgUBV........0M. See the SIMBAD Measurements entry for details.
^ ^a ^b ^c Schröder, C.; Reiners, Ansgar; Schmitt, Jürgen H. M. M. (January 2009), "Ca II HK emission in rapidly rotating stars. Evidence for an onset of the solar-type dynamo", Astronomy and Astrophysics, 493 (3): 1099–1107, Bibcode:2009A&A...493.1099S, doi:10.1051/0004-6361:200810377
^ ^a ^b 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.
^ ^a ^b 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.
^ ^a ^b Pizzolato, N.; et al. (September 2000), "Evolution of X-ray activity of 1-3 Msun late-type stars in early post-main-sequence phases", Astronomy and Astrophysics, 361: 614–628, Bibcode:2000A&A...361..614P.
^ David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146, S2CID 33401607.
^ Casagrande, L.; et al. (June 2011), "New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s). Improved astrophysical parameters for the Geneva-Copenhagen Survey", Astronomy and Astrophysics, 530: A138, arXiv:1103.4651, Bibcode:2011A&A...530A.138C, doi:10.1051/0004-6361/201016276, S2CID 56118016.
^ "eta UMi", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2017-09-14.
^ Kaler, James B., "Anwar al Farkadain", Stars, University of Illinois, retrieved 2014-06-21.
^ Lépine, Sébastien; Shara, Michael M. (March 2005), "A Catalog of Northern Stars with Annual Proper Motions Larger than (LSPM-NORTH Catalog)", The Astronomical Journal, 129 (3): 1483–1522, arXiv:astro-ph/0412070, Bibcode:2005AJ....129.1483L, doi:10.1086/427854, S2CID 2603568.
^ Allen, Richard Hinckley (1899), Star-names and Their Meanings, G. E. Stechert, pp. 447–460.

[dr3-1] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.

[eggen1986-2] Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, Bibcode:1986EgUBV........0M. See the SIMBAD Measurements entry for details.

[Schroeder2009-3] Schröder, C.; Reiners, Ansgar; Schmitt, Jürgen H. M. M. (January 2009), "Ca II HK emission in rapidly rotating stars. Evidence for an onset of the solar-type dynamo", Astronomy and Astrophysics, 493 (3): 1099–1107, Bibcode:2009A&A...493.1099S, doi:10.1051/0004-6361:200810377

[Eggleton2008-4] 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.

[Gontcharov2006-5] 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.

[aaa361_614-6] Pizzolato, N.; et al. (September 2000), "Evolution of X-ray activity of 1-3 Msun late-type stars in early post-main-sequence phases", Astronomy and Astrophysics, 361: 614–628, Bibcode:2000A&A...361..614P.

[David2015-7] David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146, S2CID 33401607.

[Casagrande2011-8] Casagrande, L.; et al. (June 2011), "New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s). Improved astrophysical parameters for the Geneva-Copenhagen Survey", Astronomy and Astrophysics, 530: A138, arXiv:1103.4651, Bibcode:2011A&A...530A.138C, doi:10.1051/0004-6361/201016276, S2CID 56118016.

[SIMBAD-9] "eta UMi", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2017-09-14.

[kalereta-10] Kaler, James B., "Anwar al Farkadain", Stars, University of Illinois, retrieved 2014-06-21.

[Lepine2005-11] Lépine, Sébastien; Shara, Michael M. (March 2005), "A Catalog of Northern Stars with Annual Proper Motions Larger than (LSPM-NORTH Catalog)", The Astronomical Journal, 129 (3): 1483–1522, arXiv:astro-ph/0412070, Bibcode:2005AJ....129.1483L, doi:10.1086/427854, S2CID 2603568.

[allen-12] Allen, Richard Hinckley (1899), Star-names and Their Meanings, G. E. Stechert, pp. 447–460.

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Observation data Epoch J2000.0 Equinox J2000.0 (ICRS)
Location of η Ursae Minoris (circled)
Constellation	Ursa Minor
Right ascension	16^h 17^m 30.27025^s^[1]
Declination	+75° 45′ 19.2351″^[1]
Apparent magnitude (V)	+4.95^[2]
Characteristics
Evolutionary stage	main sequence^[3]
Spectral type	F5 V^[4]
U−B color index	+0.02^[2]
B−V color index	+0.35^[2]
Astrometry

Radial velocity (R_v)	−11.0±0.9^[5] km/s
Proper motion (μ)	RA: −77.647^[1] mas/yr Dec.: +245.726^[1] mas/yr
Parallax (π)	33.4190±0.1103 mas^[1]
Distance	97.6 ± 0.3 ly (29.92 ± 0.10 pc)
Absolute magnitude (M_V)	+2.61^[6]

Details

Mass	1.539^[1] `M`_☉
Radius	2.024^[1] `R`_☉
Luminosity	7.725^[1] `L`_☉
Surface gravity (log g)	4.15±0.14^[7] cgs
Temperature	6,764^[1] K
Metallicity [Fe/H]	−0.02^[8] dex
Rotational velocity (v sin i)	84.8^[3] km/s
Age	1.743^[1] Gyr

Other designations
η UMi, 21 Ursae Minoris, BD+76°596, FK5 612, GC 21999, HD 148048, HIP 79822, HR 6116, SAO 8470, CCDM 16176+7545^[9]
Database references
SIMBAD	data

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