V539 Arae


V539 Arae is a multiple star system in the southern constellation of Ara. It has the Bayer designation Nu Arae, which is Latinized from ν Arae and abbreviated Nu Ara or ν 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. Based upon an annual parallax shift of, this system is at a distance of approximately from Earth. The system is drifting closer to the Sun with a radial velocity of −4 km/s.
File:V539AraLightCurve.png|thumb|left|A visual band light curve for V539 Arae, adapted from Knipe
In 1930, Ferdinand Johannes Neubauer found that the star is a spectroscopic binary. He did not detect any brightness variability. 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. In 1996, the secondary component was found to be a slowly pulsating B-type star with periods of periods of 1.36, 1.78 and possibly 1.08 days.
The core members of this system, ν 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. 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. The eclipse of the primary causes a decrease of 0.52 in magnitude, while the secondary eclipse decreases the magnitude by 0.43.
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. 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 and a mass of. In 2022, a more refined study suggested the influence of two stellar objects with masses of and.
The system is sometimes referred as Upsilon Arae, and more generally unlettered.