V539 Arae

"Nu1 Arae" redirects here. For other star systems with this Bayer designation, see Nu Arae.

V539 Arae is a multiple star system in the southern constellation of Ara. It has the Bayer designation Nu¹ Arae , which is Latinized from ν¹ Arae and abbreviated Nu¹ Ara or ν¹ Ara. This is a variable star system, the brightness of which varies from magnitude 5.71 to 6.24, making it faintly visible to the naked eye under good observing conditions.^[12] Based upon an annual parallax shift of 2.52 mas,^[2] this system is at a distance of approximately 1,290 light-years (400 parsecs) from Earth. The system is drifting closer to the Sun with a radial velocity of −4 km/s.^[5]

A visual band light curve for V539 Arae, adapted from Knipe (1971)^[13]

V539 Arae

The location of V539 Arae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Ara[1]
Right ascension	17h 50m 28.393s[2]
Declination	−53° 36′ 44.66″[2]
Apparent magnitude (V)	5.62[3]
Characteristics
Spectral type	B2 V + B3 V + A1 V[3]
U−B color index	−0.64[citation needed]
B−V color index	−0.099±0.017[1]
Variable type	Algol/SPB[4]
Astrometry
Radial velocity (Rv)	−4.3±2.9[5] km/s
Proper motion (μ)	RA: +2.517 mas/yr[2] Dec.: −12.105 mas/yr[2]
Parallax (π)	2.5208±0.1096 mas[2]
Distance	1,290 ± 60 ly (400 ± 20 pc)
Absolute magnitude (MV)	−1.83/−1.11[6]
Orbit[7]
Period (P)	3.1690854(12) d
Eccentricity (e)	0.0548(15)
Inclination (i)	85.2°
Argument of periastron (ω) (secondary)	118.9(1.2)°
Details[8]
V539 Ara A
Mass	6.239±0.066 M☉
Radius	4.551±0.019 R☉
Luminosity	2,000+240 −210 L☉
Surface gravity (log g)	3.9170±0.0029 cgs
Temperature	18,100±500[6] K
Rotational velocity (v sin i)	100[9] km/s
Age	23.2±2.9[10] Myr
V539 Ara B
Mass	5.313±0.060 M☉
Radius	3.575±0.035 R☉
Luminosity	980+130 −110 L☉
Surface gravity (log g)	4.0570±0.0084 cgs
Temperature	17,100±500[6] K
Rotational velocity (v sin i)	130[9] km/s
Other designations
Boss 4496, ν1 Arae, V539 Ara, CD−53°7423, GC 24187, HD 161783, HIP 87314, HR 6622, SAO 245065, PPM 346351, WDS J17505-5337A[11]
Database references
SIMBAD	AB
	A

In 1930, Ferdinand Johannes Neubauer found that the star (usually called Boss 4496 at the time) is a spectroscopic binary. He did not detect any brightness variability.^[14] Eclipses were first reported by E. Schoeffel and U. Kohler in 1965. The period they reported is 1/2 the currently accepted value, because they did not realize that the light curve has a deep secondary minimum.^[15][16] In 1996, the secondary component was found to be a slowly pulsating B-type star (SPB) with periods of periods of 1.36, 1.78 and possibly 1.08 days.^[17]

The core members of this system, ν¹ Ara AB, consist of a pair of B-type main-sequence stars in a detached orbit with a period of 3.169 days and an eccentricity of 0.055.^[7] Their respective stellar classifications are B2 V and B3 V, and they have a combined visual magnitude of 5.65. Because the orbital plane lies close to the line of sight from the Earth, this pair form a detached eclipsing binary of the Algol type.^[11] The eclipse of the primary causes a decrease of 0.52 in magnitude, while the secondary eclipse decreases the magnitude by 0.43.^[18]

At an angular separation of 12.34 arcseconds, is a possible tertiary component of this system; a magnitude 9.40 A-type main-sequence star with a classification of A1 V.^[3] A 2005 study of the orbit of the main pair demonstrated an apsidal motion, suggesting the influence of a third body. The initial estimate found an orbital period of 42.3±0.8 years and a mass of 1.63 M_☉.^[7] In 2022, a more refined study suggested the influence of two stellar objects with masses of 0.41 M_☉ and 1.74 M_☉.^[19]

The system is sometimes referred as Upsilon¹ Arae (υ¹ Arae), and more generally unlettered.^[20]