Delta Arae

Delta Arae is a binary star^[7] in the southern constellation Ara. Its name is a Bayer designation that is Latinized from δ Arae, and abbreviated Delta Ara or δ Ara. This system has an apparent visual magnitude of 3.62^[2] and is visible to the naked eye as a point of light. Based upon an annual parallax of 16.48 mas, it is about 198 light-years (61 parsecs) distant from the Earth.^[1]

Delta Arae

δ Arae (circled) in the Ara Constellation
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Ara
Right ascension	17h 31m 05.91272s[1]
Declination	−60° 41′ 01.8522″[1]
Apparent magnitude (V)	3.62[2]
Characteristics
Spectral type	B8 Vn[3] + G8 V[4]
U−B color index	−0.31[2]
B−V color index	−0.10[2]
Astrometry
Radial velocity (Rv)	+10[5] km/s
Proper motion (μ)	RA: −54.01[1] mas/yr[1] Dec.: −99.25 mas/yr[1]
Parallax (π)	16.48±0.34 mas[1]
Distance	198 ± 4 ly (61 ± 1 pc)
Absolute magnitude (MV)	−0.31[6]
Orbit[7]
Primary	A
Companion	B
Period (P)	2.46697±0.00500 yr
Semi-major axis (a)	52.0±0.2 mas
Eccentricity (e)	0.7380±0.0264
Inclination (i)	90.32±0.97°
Longitude of the node (Ω)	127.13±0.91°
Argument of periastron (ω) (secondary)	347.80±1.05°
Details
δ Ara A
Mass	3.44±0.01[7] M☉
Radius	3.12±0.15[8] R☉
Luminosity	214[6] L☉
Surface gravity (log g)	3.81±0.06[8] cgs
Temperature	12,549[7] K
Rotational velocity (v sin i)	255[9] km/s
Age	125[10] Myr
δ Ara B
Mass	2.03±0.01[7] M☉
Temperature	9,161[7] K
Other designations
δ Ara, CPD−60°6842, FK5 648, GC 23681, HD 158094, HIP 85727, HR 6500, SAO 253945, PPM 362756, WDS J17311-6041A[11]
Database references
SIMBAD	data

Characteristics

This is an astrometric binary system, identified using data from the Gaia spacecraft. The components have an orbital period of about 2.47 years and a high orbital eccentricity of 0.7380. The orbit is nearly edge-on relative to Earth.^[7]

The brighter component is an intermediate-mass B-type main sequence star with a stellar classification of B8 Vn.^[3] The 'n' suffix indicates the absorption lines are spread out broadly because the star is spinning rapidly. It has a projected rotational velocity of 255 km/s, resulting in an equatorial bulge with a radius 13% larger than the polar radius.^[9] The star has 3.44 times the mass^[7] and 3.1 times the radius of the Sun.^[8] It is radiating 214 times the luminosity of the Sun from its photosphere^[6] at an effective temperature of 12,549 K.^[7]

The secondary is 1.27 times fainter than the primary at Gaia's G-band, it has 2.03 times the mass of the Sun and an effective temperature of 9,161 K.^[7]

There is a magnitude 9.5 companion G-type main sequence star that may (17% chance) form a gravitationally bpund system with Delta Arae.^[4] A 12th magnitude optical companion is located 47.4 arcseconds away along a position angle of 313°.^[10]

Etymology

Delta Arae was known as 龜三 (meaning: "the 3rd (star) of Guī") in traditional Chinese astronomy.^[12][13]

Allen erroneously called both Delta and Zeta Arae "Tseen Yin" (天陰).^[14] He probably confused the constellation "Ara" with "Ari", as 天陰 is actually in Aries.^[12][13]

See also

• Ara (Chinese astronomy)
• Aries (Chinese astronomy)