Rho1 Arae

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ρ1 Arae
Ara IAU.svg
Cercle rouge 100%25.svg
The location of ρ1 Arae (circled)
Observation data
Epoch J2000       Equinox J2000
Constellation Ara
Right ascension 16h 56m 08.8405s [1]
Declination –50° 40 29.244 [1]
Apparent magnitude  (V)6.275 [2]
Characteristics
Spectral type B3 Vnpe
U−B color index –0.691 [2]
B−V color index +0.008 [2]
Astrometry
Radial velocity (Rv)+19 [3]  km/s
Proper motion (μ)RA: –7.66 [1]   mas/yr
Dec.: –9.79 [1]   mas/yr
Parallax (π)5.06 ± 0.39  mas [1]
Distance 640 ± 50  ly
(200 ± 20  pc)
Absolute magnitude  (MV)−0.16 [4]
Orbit [5]
Period (P)236.50 ± 0.18 d
Inclination (i)60 ± 7°
Periastron epoch (T)HJD 2458672.10 ± 0.72
Semi-amplitude (K1)
(primary)
4.33 ± 0.05 km/s
Semi-amplitude (K2)
(secondary)
52.83 ± 1.49 km/s
Details
ρ1 Ara A
Mass 6.5 ± 1.3 [5]   M
Radius 4.21 ± 0.20 [6]   R
Luminosity 1,418 [7]   L
Surface gravity (log g)3.75 [8]   cgs
Temperature 19,800 [8]   K
Rotational velocity (v sin i)370 ± 10 [9]  km/s
Age 18.4 ± 1.5 [10]   Myr
ρ1 Ara B
Mass 0.53 ± 0.11 [5]   M
Radius 0.27 ± 0.04 [6]   R
Luminosity204 [6]   L
Temperature 42,000 [6]   K
Other designations
ρ1 Ara, V846 Arae, CD–50 10905, GC 22790, HD  152478, HIP 82868, HR 6274, NSV 8047, SAO 244280 [11]
Database references
SIMBAD data

Rho1 Arae is the Bayer designation for a star in the southern constellation of Ara. Unusually for a star with a Bayer designation, it was not catalogued by Bayer in his Uranometria . It was instead first catalogued by Nicolas Lacaille, in his Coelum Australe Stelliferum published in 1763. This star gained the Bayer designation of Rho1 Arae in Bode's Uranographia , published in 1801. Rho1 Arae is one of the dimmest stars with a Bayer designation, having an apparent visual magnitude of just +6.275 [2] According to the Bortle Dark-Sky Scale, this means the star is just barely visible to the naked eye in dark rural skies. Based upon parallax measurements, it is about 640 light-years (200 parsecs ) distant from the Sun, give or take a 50-light-year margin of error. [1]

A light curve for V846 Arae, plotted from TESS data V846AraLightCurve.png
A light curve for V846 Arae, plotted from TESS data

The Hipparcos data revealed that Rho1 Arae is a variable star. It was given its variable star designation, V846 Arae, in 1999. [13] This is a spectroscopic binary system, which means that the presence of an orbiting companion is indicated by shifts in the spectrum. The primary star is a Be star, while the secondary star is a subdwarf O star; they orbit each other with a period of about 236.50 days. [5] The combined spectrum of this system matches a stellar classification of B3 Vnpe, which may indicate the primary is a B-type main-sequence star. The 'e' suffix indicates the presence of emission lines from the primary Be star. For Rho1 Arae, the emission lines are prominent and variable. [9] The primary star is spinning rapidly with a projected rotational velocity of 370 ± 10, which makes it difficult to obtain reliable orbital elements. [9]

Rho1 Arae has a peculiar velocity of 27.4 ± 4.9 km/s relative to its neighbors, [10] making it a runaway star system. A scenario that it was ejected from the Scorpius–Centaurus OB association as a result of a past supernova explosion seems unlikely because of its binarity. [9]

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−1.9
 km/s
, making it a runaway star.

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References

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