Sigma Librae
 Location of σ Librae (circled) |
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| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) |
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|---|---|
| Constellation | Libra |
| Right ascension | 15h 04m 04.21608s[1] |
| Declination | –25° 16′ 55.0606″[1] |
| Apparent magnitude (V) | +3.29[2] |
| Characteristics | |
| Spectral type | M3/M4III[3] |
| U−B color index | +1.94[2] |
| B−V color index | +1.70[2] |
| Variable type | Semi-regular[4] |
| Astrometry | |
| Radial velocity (Rv) | –4.2[5] km/s |
| Proper motion (μ) | RA: –71.16[1] mas/yr Dec.: −43.34[1] mas/yr |
| Parallax (π) | 11.31 ± 0.25[1] mas |
| Distance | 288 ± 6 ly (88 ± 2 pc) |
| Absolute magnitude (MV) | –1.5[4] |
| Details | |
| Mass | 2.1[6] M☉ |
| Temperature | 3,600[6] K |
| Other designations | |
Sigma Librae (σ Lib, σ Librae) is a star in the constellation Libra. It has the traditional names Brachium ("Arm"Latin), Cornu ("Horn"Latin), and Zubenalgubi ("Southern Claw"Arabic). The apparent visual magnitude is +3.29,[2] making it a third magnitude star that is visible to the naked eye. Based upon parallax measurements, the distance to this star is roughly 288 light-years (88 parsecs) from Earth.[1]
This star was originally given the Bayer designation "Gamma Scorpii" (γ Sco) despite the fact that it is well within the constellation Libra and far from the boundary with Scorpius. It did not receive its current Bayer designation as Sigma Librae until the 19th century.[citation needed]
Sigma Librae has a spectral class M3/M4III,[3] which places it in the red giant stage of its evolution. This is a semi-regular variable star with a single pulsation period of 20 days.[4] It shows small amplitude variations in magnitude of 0.10–0.15 on time scales as brief as 15–20 minutes, with cycles of repetition over intervals of 2.5–3.0 hours.[8]
[edit] References
- ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, Bibcode 2007A&A...474..653V, doi:10.1051/0004-6361:20078357
- ^ a b c d Nicolet, B. (1978). "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System". Astronomy and Astrophysics Supplement Series 34: 1–49. Bibcode 1978A&AS...34....1N.
- ^ a b Houk, Nancy (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, 4, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode 1988mcts.book.....H
- ^ a b c Yeşilyaprak, C.; Aslan, Z. (December 2004), "Period-luminosity relation for M-type semiregular variables from Hipparcos parallaxes", Monthly Notices of the Royal Astronomical Society 355 (2): 601–607, Bibcode 2004MNRAS.355..601Y, doi:10.1111/j.1365-2966.2004.08344.x
- ^ Wielen, R. et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions, Astronomisches Rechen-Institut Heidelberg, Bibcode 1999VeARI..35....1W
- ^ a b Tsuji, Takashi (May 2007), "Isotopic abundances of Carbon and Oxygen in Oxygen-rich giant stars", in Kupka, F.; Roxburgh, I.; Chan, K., Convection in Astrophysics, Proceedings of IAU Symposium #239 held 21-25 August, 2006 in Prague, Czech Republic, pp. 307–310, arXiv:astro-ph/0610180, Bibcode 2007IAUS..239..307T, doi:10.1017/S1743921307000622
- ^ "sig Lib -- Semi-regular pulsating Star", SIMBAD (Centre de Données astronomiques de Strasbourg), http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Sigma+Librae, retrieved 2012-01-14
- ^ Ruban, E. V.; Arkharov, A. A. (December 2010), "Microvariability and fast variability of stars. II. The semiregular red giants L2 Pup, 2 Cen, η Gem, and σ Lib", Astrophysics 53 (4): 523–535, Bibcode 2010Ap.....53..523R, doi:10.1007/s10511-010-9144-7
[edit] External links
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