Upsilon Librae

Upsilon Librae (υ Lib, υ Librae) is the Bayer designation for a double star^[9] in the zodiac constellation Libra. With an apparent visual magnitude of 3.628,^[2] it is visible to the naked eye. The distance to this star, based upon an annual parallax shift of 14.58,^[1] is around 224 light years. It has a magnitude 10.8 companion at an angular separation of 2.0 arc seconds along a position angle of 151°, as of 2002.^[10]

Upsilon Librae

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Libra
Right ascension	15h 37m 01.45020s[1]
Declination	−28° 08′ 06.2926″[1]
Apparent magnitude (V)	3.628[2]
Characteristics
Spectral type	K3 III[3]
U−B color index	+1.586[2]
B−V color index	+1.374[2]
Astrometry
Radial velocity (Rv)	−24.9±0.7[4] km/s
Proper motion (μ)	RA: −12.82[1] mas/yr Dec.: −4.15[1] mas/yr
Parallax (π)	14.58 ± 0.19 mas[1]
Distance	224 ± 3 ly (68.6 ± 0.9 pc)
Absolute magnitude (MV)	−0.28[5]
Details[6]
Mass	1.67 M☉
Radius	31.5[7] R☉
Luminosity	309 L☉
Surface gravity (log g)	1.58 cgs
Temperature	4,135±20 K
Metallicity [Fe/H]	−0.02 dex
Age	3.14 Gyr
Other designations
υ Lib, 39 Lib, CD−27° 10464, FK5 579, HD 139063, HIP 76470, HR 5794, SAO 183619.[8]
Database references
SIMBAD	data

The brighter component is an evolved K-type giant star with a stellar classification of K3 III.^[3] The measured angular diameter, after correction for limb darkening, is 4.27±0.05 mas.^[11] At the estimated distance of the star, this yields a physical size of about 31.5 times the radius of the Sun.^[7] It has 1.67 times the mass of the Sun and radiates 309 times the solar luminosity from its outer atmosphere at an effective temperature of 4,135 K.^[6] The star is about three billion years old.^[6]

Upsilon Librae will be the brightest star in the night sky in about 2.3 million years,^[12] and will peak in brightness with an apparent magnitude of −0.46, or more than 40 times its present-day brightness.^[12]

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. Celis S., L. (October 1975), "Photoelectric photometry of late-type variable stars", Astronomy and Astrophysics Supplement Series, 22: 9–17, Bibcode:1975A&AS...22....9C.
3. Houk, Nancy (1979), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 3, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, Bibcode:1982mcts.book.....H
4. de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, S2CID 59451347, A61.
5. Ryon, Jenna; et al. (August 2009), "Comparing the Ca ii H and K Emission Lines in Red Giant Stars", Publications of the Astronomical Society of the Pacific, 121 (882): 842, arXiv:0907.3346, Bibcode:2009PASP..121..842R, doi:10.1086/605456, S2CID 17821279.
6. Luck, R. Earle (September 2015), "Abundances in the Local Region. I. G and K Giants", The Astronomical Journal, 150 (3): 23, arXiv:1507.01466, Bibcode:2015AJ....150...88L, doi:10.1088/0004-6256/150/3/88, S2CID 118505114, 88.
7. Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, vol. 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R_*) is given by:

   ${\displaystyle {\begin{aligned}2\cdot R_{*}&={\frac {(68.6\cdot 4.27\cdot 10^{-3})\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\\&\approx 63.0\cdot R_{\bigodot }\end{aligned}}}$

8. "ups Lib". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-01-30.
9. 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.
10. Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal, 122 (6): 3466, Bibcode:2001AJ....122.3466M, doi:10.1086/323920
11. Richichi, A.; et al. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431 (2): 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039.
12. Tomkin, Jocelyn (April 1998). "Once and Future Celestial Kings". Sky and Telescope. 95 (4): 59–63. Bibcode:1998S&T....95d..59T. based on computations from HIPPARCOS data. (The calculations exclude stars whose distance or proper motion is uncertain.) PDF^{[permanent dead link]}