Xi Lupi

Xi Lupi is a triple star system^[7] in the southern constellation of Lupus. Its main identifier is a Bayer designation that is Latinized from ξ Lupi, and abbreviated Xi Lup or ξ Lup. The combined apparent magnitude is 4.56, making it faintly visible to the naked eye.^[a] The system is located at 210 light-years (64 parsecs) from Earth, and is a member of the Upper Scorpius sub-group of the nearby Sco OB2 association.^[12]

Xi Lupi

The location of Xi Lupi (ξ Lup) in the constellation of Lupus, close to Chi Lupi and Eta Lupi.
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Lupus
ξ1 Lup
Right ascension	15h 56m 53.48964s[1]
Declination	−33° 57′ 58.0131″[1]
Apparent magnitude (V)	5.114[2]
ξ2 Lup
Right ascension	15h 56m 54.11281s[3]
Declination	−33° 57′ 51.3380″[3]
Apparent magnitude (V)	5.55[4]
Characteristics
ξ1 Lup
Spectral type	A3 V[5]
U−B color index	0.069[2]
B−V color index	0.116[2]
ξ2 Lup
Spectral type	B9 V[5]
B−V color index	+0.06[4]
Astrometry
ξ1 Lup
Radial velocity (Rv)	−10.0±4.2[6] km/s
Proper motion (μ)	RA: +11.963 mas/yr[1] Dec.: −37.94 mas/yr[1]
Parallax (π)	15.0230±0.1787 mas[1]
Distance	217 ± 3 ly (66.6 ± 0.8 pc)
ξ2 Lup
Radial velocity (Rv)	−12.20±1.78[6] km/s
Proper motion (μ)	RA: +10.663 mas/yr[3] Dec.: −41.073 mas/yr[3]
Parallax (π)	15.5015±0.0722 mas[3]
Distance	210.4 ± 1.0 ly (64.5 ± 0.3 pc)
Details
ξ1 Lup A
Mass	2.0[7] M☉
Radius	2.0[7] R☉
Surface gravity (log g)	4.14±0.14[8] cgs
Temperature	8,650[7] K
Rotational velocity (v sin i)	78[8] km/s
Age	450[7] Myr
ξ1 Lup B
Mass	1.65[7] M☉
Radius	1.6[7] R☉
Temperature	7,800[7] K
Age	450[7] Myr
ξ2 Lup
Mass	2[7] M☉
Radius	1.74±0.04[9] R☉
Luminosity	22.7±1.0[9] L☉
Surface gravity (log g)	4.34±0.06[9] cgs
Temperature	9,550±120[9] K
Rotational velocity (v sin i)	184[8] km/s
Age	500[7] Myr
Other designations
CCDM J15569-3358, WDS J15569-3358
A: ξ1 Lup, CD−33°10826A, HD 142629, HIP 78105, HR 5925, SAO 207144[10]
B: ξ2 Lup, CD−33°10826B, HD 142630, HIP 78106, HR 5926, SAO 207145[11]
Database references
SIMBAD	ξ1 Lup
	ξ2 Lup

Characteristics

This is a hierarchical triple system. It consists on the binary star ξ¹ Lup and the star ξ² Lup; both form a visual binary separated by 10.2" in the sky, or 660 astronomical units at their distance. The components of ξ¹ Lup, named ξ¹ Lup A and B, are separated by about the same distance Earth is from Sun (1 au), the orbital period is an estimated 200 days, although the observed separation is merely a projected separation and the whole orbit has not been observed.^[7]

ξ¹ Lup has a combined stellar classification of A3 V,^[5] and its primary and secondary components have, respectively, 2.0 and 1.65 times the mass of the Sun, radii 2.0 and 1.6 times solar and effective temperatures of 8,650 and 7,850 K.^[7]

ξ² Lup has a stellar classification of B9 V,^[5] matching a B-type main-sequence star. It has twice the mass of the Sun,^[7] 1.74 times the Sun's radius, is 23 times more luminous and has an effective temperature of 9,550 K.^[9] It spins rapidly with a projected rotational velocity of 184 km/s.^[8] The star has a peculiar velocity of 14.3±1.9 km/s relative to its neighbors, and is probably (86% chance) a runaway star.^[13]

The system is currently about 500 million years old. When ξ¹ Lup A evolves into an AGB star, it will likely engulf component Ab, but given the orbit of the system is unknown, it may be more distant, and survive its companion's AGB phase. Assuming the Aa-Ab separation is correct, the system will likely end as a triple white dwarf system; few of such system have been observed so far.^[7]

Notes

1. Calculated from components' individual magnitudes using the equation given in Apparent magnitude § Magnitude addition.