48 Librae

48 Librae is a single[4] shell star in the constellation Libra. It is a variable star with the designation FX Lib, ranging in magnitude from 4.74 to 4.96.[5] Based upon an annual parallax shift of 6.97±0.24 mas as seen from Earth's orbit, it is located around 470 light years from the Sun. It is a candidate member of the Upper Scorpius group of the Scorpius-Centaurus Association, with the former having an age of about 11 million years.[9]

48 Librae
Observation data
Epoch J2000      Equinox J2000
Constellation Libra
Right ascension 15h 58m 11.36869s[1]
Declination −14° 16′ 45.6894″[1]
Apparent magnitude (V) 4.95[2]
Characteristics
Spectral type B3 Vsh[3][4]
B−V color index −0.08±0.11[2]
Variable type γ Cas[5]
Astrometry
Radial velocity (Rv)−7.5±1.8[6] km/s
Proper motion (μ) RA: −12.44[1] mas/yr
Dec.: −16.73[1] mas/yr
Parallax (π)6.97 ± 0.24[1] mas
Distance470 ± 20 ly
(143 ± 5 pc)
Absolute magnitude (MV)−0.83[2]
Details[4]
Mass6.07 M☉
Radius4.12 R☉
Luminosity1,100 L☉
Temperature7,612[7] K
Rotational velocity (v sin i)400 km/s
Other designations
48 Lib, FX Lib, BD−13° 4302, FK5 1417, HD 142983, HIP 78207, HR 5941, SAO 159607[8]
Database references
SIMBADdata

This is a main sequence Be star with a stellar classification of B3 Vsh,[3] although it has been variously classed as B3V, B5IIIp shell He-n, B6p shell, B4III, B3IV:e-shell, and B3 shell by different sources. As is the norm for a shell star, it is spinning very rapidly with a projected rotational velocity of 400 km/s − matching or exceeding 80% of the critical velocity.[4] This is giving the star a pronounced oblate shape with an equatorial bulge that is estimated to be 43% larger than the polar radius.[10] It has six times the mass of the Sun and four times the Sun's radius. The star is radiating 1,100[4] times the Sun's luminosity from its photosphere at an effective temperature of 7,612 K.[7]

The surrounding gaseous disk stretches out to at least 15[11] times the star's radius and is nearly aligned with the line of sight from the Earth, having an estimated inclination of 85°±3°.[4] Some time between 1931 and 1935, the disk became active and has remained so since that time, becoming the subject of multiple studies.[12] The unusual asymmetry in its emission lines have led to it being misclassified as a supergiant of type B8 Ia/Ib by SIMBAD and others. This asymmetry displays quasi-periodic behavior of the type found in about a third of all Be stars, with a period of about 10 to 17 years. This variation may arise from the precession of a one-armed density wave in the disk.[4]

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. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
  3. Rivinius, Thomas; et al. (2013), "Classical Be stars. Rapidly rotating B stars with viscous Keplerian decretion disks", The Astronomy and Astrophysics Review, 21: 69, arXiv:1310.3962, Bibcode:2013A&ARv..21...69R, doi:10.1007/s00159-013-0069-0, S2CID 118652497.
  4. Silaj, J.; et al. (July 2016), "Investigating the Circumstellar Disk of the Be Shell Star 48 Librae", The Astrophysical Journal, 826 (1): 11, arXiv:1608.00943, Bibcode:2016ApJ...826...81S, doi:10.3847/0004-637X/826/1/81, S2CID 119112873, 81.
  5. Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, GCVS 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
  6. 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.
  7. McDonald, I.; et al. (2012), "Fundamental parameters and infrared excesses of Hipparcos stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–357, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x, S2CID 118665352.
  8. "48 Lib". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-03-04.
  9. Jang-Condell, Hannah; et al. (August 2015), "Spitzer IRS Spectra of Debris Disks in the Scorpius-Centaurus OB Association", The Astrophysical Journal, 808 (2): 19, arXiv:1506.05428, Bibcode:2015ApJ...808..167J, doi:10.1088/0004-637X/808/2/167, S2CID 118549483, 167.
  10. van Belle, Gerard T. (March 2012), "Interferometric observations of rapidly rotating stars", The Astronomy and Astrophysics Review, 20 (1): 51, arXiv:1204.2572, Bibcode:2012A&ARv..20...51V, doi:10.1007/s00159-012-0051-2, S2CID 119273474.
  11. Štefl, S.; et al. (April 2012), "New activity in the large circumstellar disk of the Be-shell star 48 Librae", Astronomy & Astrophysics, 540: 12, arXiv:1202.4523, Bibcode:2012A&A...540A..76S, doi:10.1051/0004-6361/201118054, S2CID 54663995, A76
  12. Faraggiana, R. (June 1969), "A study of 48 Librae in the period 1950 - 1962", Astronomy and Astrophysics, 2: 162, Bibcode:1969A&A.....2..162F.
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