Lambda Ursae Majoris

Lambda Ursae Majoris

Location of λ Ursae Majoris (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Ursa Major
Right ascension	10^h 17^m 05.78287^s[1]
Declination	+42° 54′ 51.6808″[1]
Apparent magnitude (V)	+3.45[2]
Characteristics
Spectral type	A2 IV[3]
U−B color index	+0.06[2]
B−V color index	+0.03[2]
Astrometry
Radial velocity (Rv)	+18.1[4] km/s
Proper motion (μ)	RA: –180.65[1] mas/yr Dec.: –46.07[1] mas/yr
Parallax (π)	23.72 ± 0.78[1] mas
Distance	138 ± 5 ly (42 ± 1 pc)
Details
Mass	2.4[5] M☉
Radius	2.3[5] R☉
Luminosity	37[5] L☉
Surface gravity (log g)	3.90[6] cgs
Temperature	9,280[6] K
Metallicity [Fe/H]	+0.20[6] dex
Rotational velocity (v sin i)	50[7] km/s
Age	410[8] Myr
Other designations
Tania Borealis, λ Ursae Majoris, λ UMa, Lambda UMa, 33 Ursae Majoris, BD+43 2005, FK5 383, GC 14113, HD 89021, HIP 50372, HR 4033, PPM 51795, SAO 43268.[9]
Database references
SIMBAD	data

Lambda Ursae Majoris (Lambda UMa, λ Ursae Majoris, λ UMa) is a star in the northern circumpolar constellation of Ursa Major. It has the proper names Tania Borealis (former Tania borealis^[10]).

This star has an apparent visual magnitude of +3.45,^[2] making it one of the brighter members of the constellation. The distance to this star has been measured directly using the parallax technique, which yields a value of roughly 138 light-years (42 parsecs) with a 4% margin of error. The stellar classification of Lambda Ursae Majoris is A2 IV,^[3] with the luminosity class of 'IV' indicating that, after 410 million years^[8] on the main sequence, this star is in the process of evolving into a giant star as the supply of hydrogen at its core becomes exhausted. Compared to the Sun it has 240% of the mass and 230% of the Sun's radius, but is radiating 37 times as much luminosity.^[5] This energy is being emitted from the star's outer atmosphere at an effective temperature of 9,280 K,^[6] giving it the characteristic white-hot glow of an A-type star.^[11]

Name and etymology

• The traditional name Tania' (share with μ UMa) comes from the Arabic phrase Al Fiḳrah al Thānia "the Second Spring (of the Gazelle)".^[12] The term Borealis meaning "the north side" in Latin.
• In Chinese, 三台 (Sān Tái), meaning Three Steps, refers to an asterism consisting of λ Ursae Majoris, ι Ursae Majoris, κ Ursae Majoris, μ Ursae Majoris, ν Ursae Majoris and ξ Ursae Majoris. Consequently, λ Ursae Majoris itself is known as 三台三 (Sān Tái sān, English: the Third Star of Three Steps) and 中台一 (Zhōng Tái yī, English: Star of First Middle Step).^[13]

References

1. van Leeuwen, F. (November 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
2. Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory 4 (99), Bibcode:1966CoLPL...4...99J
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. Evans, D. S. (June 20–24, 1966), "The Revision of the General Catalogue of Radial Velocities", in Batten, Alan Henry; Heard, John Frederick, Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, University of Toronto: International Astronomical Union, Bibcode:1967IAUS...30...57E
5. Malagnini, M. L.; Morossi, C. (November 1990), "Accurate absolute luminosities, effective temperatures, radii, masses and surface gravities for a selected sample of field stars", Astronomy and Astrophysics Supplement Series 85 (3): 1015–1019, Bibcode:1990A&AS...85.1015M
6. Hill, G. M. (February 1995), "Compositional differences among the A-type stars. 2: Spectrum synthesis up to V sin i = 110 km/s", Astronomy and Astrophysics 294 (2): 536–546, Bibcode:1995A&A...294..536H
7. Royer, F.; Zorec, J.; Gómez, A. E. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics 463 (2): 671–682, arXiv:astro-ph/0610785, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224
8. 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
9. "lam UMa -- High proper-motion Star", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2012-01-20
10. Piazzi, G., The Palermo Catalogue, Palermo, 1814.
11. "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16
12. Richard Hinckley Allen :Star Names — Their Lore and Meaning - Ursa Major, the Greater Bear
13. (Chinese) (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 21 日