48 Librae

48 Librae is a single^[6] 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.^[7] 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]

48 Librae

A broad-band optical light curve for FX Librae, adapted from Ozuyar et al. (2018)[1]
Observation data Epoch J2000      Equinox J2000
Constellation	Libra[2]
Right ascension	15h 58m 11.36869s[3]
Declination	−14° 16′ 45.6894″[3]
Apparent magnitude (V)	4.95[2]
Characteristics
Evolutionary stage	main sequence[4]
Spectral type	B3 Vsh[5][6]
B−V color index	−0.08±0.11[2]
Variable type	γ Cas[7]
Astrometry
Radial velocity (Rv)	−7.5±1.8[8] km/s
Proper motion (μ)	RA: −12.44[3] mas/yr Dec.: −16.73[3] mas/yr
Parallax (π)	6.97±0.24 mas[3]
Distance	470 ± 20 ly (143 ± 5 pc)
Absolute magnitude (MV)	−0.83[2]
Details
Mass	6.07[6] M☉
Radius	4.12[6] R☉
Luminosity	1,100[6] L☉
Surface gravity (log g)	3.71±0.04[9] cgs
Temperature	18,000±180[9] K
Rotation	9.6 hours[1]
Rotational velocity (v sin i)	400[6] 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,^[5] 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.^[6] 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^[6] times the Sun's luminosity from its photosphere at an effective temperature of 18,000 K.^[9]

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°.^[6] 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.^[6]

When lettering Bayer designations to Scorpius, Johann Bayer accidently gave the designation Phi Scorpii to what is now known to be 49 Librae and 48 Librae. That designation is no longer in use.^[16]