T Ursae Minoris

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T Ursae Minoris
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Ursa Minor
Right ascension  13h 34m 41.120s[1]
Declination +73° 25′ 52.99″[1]
Apparent magnitude (V) 7.8 - 15[2]
Evolutionary stage M4e-M6e[2]
Variable type SR (previously Mira)[2]
Radial velocity (Rv)-9[3] km/s
Proper motion (μ) RA: −13.031[4] mas/yr
Dec.: +5.948[4] mas/yr
Parallax (π)0.2901 ± 0.0872[4] mas
Distanceapprox. 11,000 ly
(approx. 3,000 pc)
Mass1.66±0.10[5] M
Radius290±15[5] R
Luminosity4080[6] L
Temperature3,200±30[5] K
Metallicity [Fe/H]−0.07[5] dex
Age0.17±0.21[5] Gyr
Other designations
T UMi, HD 118556, TYC 4408-163-1[1]
Database references

T Ursae Minoris (T UMi) is a star in the constellation Ursa Minor, located 2'30" west-southwest of 3 Ursae Minoris toward the western border of the constellation with Draco.[7]


A red giant ranging between spectral types M4e and M6e and with a surface temperature of 3300 K,[8] it is a long period Mira variable ranging from magnitude 7.8 to 15.[2] These are highly evolved ageing stars that are on the asymptotic giant branch, their wide range in magnitude making them ideal targets for monitoring by amateur star observers.

T Ursae Minoris has been monitored closely since 1905. Up until 1979, its brightness had varied over a period of 310 to 315 days. However, from 1979 its period decreased suddenly to 274 days, and appeared to be decreasing by 2.75 days a cycle since. Variable star observers Janet Mattei and Grant Foster proposed that the star had just undergone a shell helium flash – a point at which "the helium shell around the dense core of the star reaches a critical mass and ignites", which "influences the star's pulsation via changes in surface luminosity and radius".[9] By mid 2008, its period had decreased to 230 days (thus removing it by definition from the class of Mira variables), before changing to pulsation as a semiregular variable star, with a dominant period of 113.6 days. This has been the most dramatic change of any Mira variable. The lack of technetium in its spectrum indicates it is not as advanced in age as some other Mira-type stars, as it has either not yet dredged up this sort of material from its core or is of insufficient mass for this to occur.[8]


  1. ^ a b c "V* T UMi". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 18 May 2014.
  2. ^ a b c d Watson, Christopher (4 January 2010). "T Ursae Minoris". AAVSO Website. American Association of Variable Star Observers. Retrieved 18 May 2014.
  3. ^ Feast, Michael W.; Whitelock, Patricia A. (2000). "Mira kinematics from Hipparcos data: A Galactic bar to beyond the Solar circle". Monthly Notices of the Royal Astronomical Society. 317 (2): 460. arXiv:astro-ph/0004107. Bibcode:2000MNRAS.317..460F. doi:10.1046/j.1365-8711.2000.03629.x.
  4. ^ a b c Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  5. ^ a b c d e Molnár, László; Joyce, Meridith; Kiss, László L. (2019). "Stellar Evolution in Real Time: Models Consistent with the Direct Observation of a Thermal Pulse in T Ursae Minoris". The Astrophysical Journal. 879 (1): 62. arXiv:1905.00597. Bibcode:2019ApJ...879...62M. doi:10.3847/1538-4357/ab22a5.
  6. ^ Fadeyev, Yu. A. (2018). "A Model of the Mira–Type Star T UMi". Astronomy Letters. 44 (8–9): 546–553. arXiv:1803.11387. Bibcode:2018AstL...44..546F. doi:10.1134/S1063773718070010.
  7. ^ Simpson, Phil (2012). Guidebook to the Constellations: Telescopic Sights, Tales, and Myths. Springer. pp. 22–23. ISBN 978-1-4419-6941-5.
  8. ^ a b Uttenthaler, S.; van Stiphout, K.; Voet, K.; van Winckel, H.; et al. (2011). "The evolutionary state of Miras with changing pulsation periods". Astronomy & Astrophysics. 531: A88. arXiv:1105.2198. Bibcode:2011A&A...531A..88U. doi:10.1051/0004-6361/201116463.
  9. ^ Mattei, Janet A.; Foster, Grant (1995). "Dramatic Period Decrease in T Ursae Minoris". The Journal of the American Association of Variable Star Observers. 23 (2): 106–16. Bibcode:1995JAVSO..23..106M.