Gamma Lupi

Gamma Lupi
Location of γ Lupi (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Lupus
Right ascension 15h 35m 08.44835s[1]
Declination –41° 10′ 00.3247″[1]
Apparent magnitude (V) 2.77[2]
Characteristics
Spectral type B2 IV[3]
U−B color index –0.82[4]
B−V color index –0.20[4]
Astrometry
Radial velocity (Rv)+2.3[5] km/s
Proper motion (μ) RA: −15.62[1] mas/yr
Dec.: −25.43[1] mas/yr
Parallax (π)7.75 ± 0.50 mas[1]
Distance420 ± 30 ly
(129 ± 8 pc)
Absolute magnitude (MV)–2.4[2]
Orbit[6]
Period (P)190.0 yr
Semi-major axis (a)0.655″
Eccentricity (e)0.51
Inclination (i)95.0°
Longitude of the node (Ω)94.6°
Periastron epoch (T)1885.0
Argument of periastron (ω)
(secondary)		311.5°
Details
γ Lup A
Mass9.5±0.2[3] M☉
Luminosity5,000[2] L☉
Surface gravity (log g)3.96[2] cgs
Temperature20,900[2] K
Rotational velocity (v sin i)270[7] km/s
Age18.6±2.4[3] Myr
Other designations
Thusia[citation needed], γ Lup, CD−40° 9760, HD 138690, HIP 76297, HR 5776, SAO 225938[8]
Database references
SIMBADdata

Gamma Lupi, Latinized from γ Lupi, is a 3rd-magnitude, B-type blue giant star in the constellation of Lupus. It is also known in ancient Chinese astronomy as 騎官一 or "the 1st (star) of the Cavalry Officer". With a telescope, Gamma Lupi can be resolved into a binary star system in close orbit. This is known as the Gamma Lupi AB system, often abbreviated as γ Lupi AB or γ Lup AB.

A light curve for Gamma Lupi, plotted from TESS data[9]

Gamma Lupi A is itself a spectroscopic binary with a period of 2.849769 days.[10] Although the system does not show eclipses, the hotter star of the pair heats the side of the cooler star that faces it, and as they orbit each other the combined starlight varies in brightness by about 0.02 magnitudes, as seen from the Earth.[11]

This star is a proper motion member of the Upper Centaurus–Lupus sub-group in the Scorpius–Centaurus OB association, the nearest such co-moving association of massive stars to the Sun.[2]

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