Epsilon Lupi

ε Lupi
Location of ε Lupi (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Lupus
Right ascension 15h 22m 40.86826s[1]
Declination –44° 41′ 22.6146″[1]
Apparent magnitude (V) 3.41[2]
Characteristics
Spectral type B2 IV-V[3]
U−B color index –0.778[2]
B−V color index –0.195[2]
Astrometry
Radial velocity (Rv)+7.9[4] km/s
Proper motion (μ) RA: −22.86[1] mas/yr
Dec.: −18.87[1] mas/yr
Parallax (π)6.37 ± 0.70 mas[1]
Distanceapprox. 510 ly
(approx. 160 pc)
Absolute magnitude (MV)−2.55[5]
Orbit[3]
PrimaryAa
CompanionAb
Period (P)4.55970 d
Semi-major axis (a)29.2 R☉
Eccentricity (e)0.277
Inclination (i)20.5°
Periastron epoch (T)2452790.33
Argument of periastron (ω)
(secondary)		17°
Semi-amplitude (K1)
(primary)		53.8 km/s
Semi-amplitude (K2)
(secondary)		64.7 km/s
Details
ε Lup Aa
Mass13.24[3] M☉
Radius4.7[3] R☉
Luminosity (bolometric)3,200[3] L☉
Surface gravity (log g)3.89 ± 0.17[3] cgs
Temperature19,275 ± 1800[3] K
Rotational velocity (v sin i)133[3] km/s
ε Lup Ab
Radius3.8[3] R☉
Other designations
ε Lup, CPD−44° 7342, HD 136504, HIP 75264, HR 5708, SAO 225712 .[6]
Database references
SIMBADdata

Epsilon Lupi, Latinized from ε Lup, is a multiple star system in the southern constellation of Lupus. At an apparent visual magnitude of 3.41, Epsilon Lupi can be readily viewed from the southern hemisphere with sufficiently dark skies. It is the fifth-brightest star or star system in the constellation.[2] Parallax measurements give a distance to this system of roughly 510 light-years (160 parsecs).[1]

This system is what astronomers term a double-lined spectroscopic binary. When the spectrum is examined, the absorption line features of both stars can be viewed. As a result of the Doppler effect, these lines shift back and forth in frequency as the two stars orbit around each other. This allows some of their orbital elements to be deduced, even though the individual stars have not been resolved with a telescope. The pair share a close, elliptical orbit with a period of 4.55970 days. The orbital eccentricity is 0.277,[3] which means that at the separation at closest approach, or periapsis, is only 57% of the distance at their greatest separation, or apoapsis.[7] There is a third, more distant companion at an angular separation of around 1 arcsecond that may be orbiting the pair with a period of about 64 years.[3]

The pair that share the close orbit, Epsilon Lupi Aa and Epsilon Lupi Ab, have estimated masses of 13.24 and 11.46 times the mass of the Sun, respectively. The more distant component, Epsilon Lupi B, has a mass of about 7.64 times the Sun. The combined stellar classification of the system is B2 IV-V, while the individual components may have spectral classes of B3 IV, B3 V, and A5 V, in order of decreasing mass. The inner A-a pair appear to have their rate of spin synchronized with their orbit, so that the same face of each star always faces its partner. The secondary, Epsilon Lupi a, shows regular variation in luminosity of the type that occurs with Beta Cephei variables, at a periodicity of 10.36 cycles per day.[3]

This star system is a probable member of the Scorpius–Centaurus association, a moving group of stars that originated together and share a similar trajectory through space.[2]

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  2. ^ a b c d e Cite error: The named reference apjs15_459 was invoked but never defined (see the help page).
  3. ^ a b c d e f g h i j k l Cite error: The named reference aaa440_1_249 was invoked but never defined (see the help page).
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  5. ^ Cite error: The named reference Anderson2012 was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference ratio was invoked but never defined (see the help page).