48 Librae
Star in the constellation Libra
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48 Librae is a single[5] 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.[6] Based upon an annual parallax shift of 6.97±0.24 mas as seen from Earth's orbit, it is located approximately 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.[12]
  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Libra[1] |
| Right ascension | 15h 58m 11.36869s[2] |
| Declination | −14° 16′ 45.6894″[2] |
| Apparent magnitude (V) | 4.95[1] |
| Characteristics | |
| Evolutionary stage | main sequence[3] |
| Spectral type | B3 Vsh[4][5] |
| B−V color index | −0.08±0.11[1] |
| Variable type | γ Cas[6] |
| Astrometry | |
| Radial velocity (Rv) | −7.5±1.8[7] km/s |
| Proper motion (μ) | RA: −12.44[2] mas/yr Dec.: −16.73[2] mas/yr |
| Parallax (π) | 6.97±0.24 mas[2] |
| Distance | 470 ± 20 ly (143 ± 5 pc) |
| Absolute magnitude (MV) | −0.83[1] |
| Details | |
| Mass | 6.07[5] M☉ |
| Radius | 4.12[5] R☉ |
| Luminosity | 1,100[5] L☉ |
| Surface gravity (log g) | 3.71±0.04[8] cgs |
| Temperature | 18,000±180[8] K |
| Rotation | 9.6 hours[9] |
| Rotational velocity (v sin i) | 400[5] km/s |
| Age | 10[10] Myr |
| Other designations | |
| 48 Lib, FX Lib, AAVSO 1552-14, BD−13°4302, FK5 1417, HD 142983, HIP 78207, HR 5941, SAO 159607[11] | |
| Database references | |
| SIMBAD | data |
This is a main sequence Be star with a stellar classification of B3 Vsh,[4] 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.[5] This is giving the star a pronounced oblate shape with an equatorial bulge that is estimated to be 43% larger than the polar radius.[13] It has six times the mass of the Sun and four times the Sun's radius. The star is radiating 1,100[5] times the Sun's luminosity from its photosphere at an effective temperature of 18,000 K.[8]
The surrounding gaseous disk stretches out to at least 15[14] times the star's radius and is nearly aligned with the line of sight from the Earth, having an estimated inclination of 85°±3°.[5] Some time between 1931 and 1935, the disk became active and has remained so since that time, becoming the subject of multiple studies.[15] 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.[5]
The Bayer designation Phi Scorpii has been associated with this star. No star is found at the position marked φ Scorpii in Johann Bayer's Uranometria.[16] The closest stars to that position are 48 and 49 Librae; 48 Librae is clearly shown but not given a designation while no star is shown at the position of 49 Librae. In his Uranographia Bode assigned the designation φ Scorpii to the star now known as 49 Librae.[17] The designation is no longer in use.[18]