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]

Rho¹ Arae

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]
Details
Mass	6.3 ± 0.1[5] M☉
Luminosity	1,418[6] L☉
Surface gravity (log g)	3.75[7] cgs
Temperature	19,800[7] K
Rotational velocity (v sin i)	370 ± 10[8] km/s
Age	18.4 ± 1.5[5] Myr
Other designations
ρ1 Ara, V846 Arae, CD–50 10905, GC 22790, HD 152478, HIP 82868, HR 6274, NSV 8047, SAO 244280[9]
Database references
SIMBAD	data

This is a spectroscopic binary system, which means that the presence of an orbiting companion is indicated by shifts in the spectrum. However, because the primary component is spinning rapidly with a projected rotational velocity of 370 ± 10, it is difficult to obtain reliable orbital elements. The orbital period has been estimated at 0.439 day. The 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, indicating this is a Be star. For Rho¹ Arae, the emission lines are prominent and variable.[8]

Rho¹ Arae has a peculiar velocity of 27.4 ± 4.9 km/s relative to its neighbors,[5] 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.[8]

References

External links

• HR 6274
• HIP 82868
• Image HD 152478