Delta Indi

Delta Indi, Latinized from δ Indi, is a binary star^[4] system in the southern constellation of Indus. It is visible to the naked eye with a combined apparent visual magnitude of +4.40.^[2] The brighter primary, designated component A, is magnitude 4.80 while the companion, component B, is magnitude 5.96.^[3] Based upon an annual parallax shift of 17.34 mas as measured from Earth,^[1] the system is located about 188 light years from the Sun.

Delta Indi

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Indus
Right ascension	21h 57m 55.07353s[1]
Declination	−54° 59′ 33.2740″[1]
Apparent magnitude (V)	+4.40[2] (4.80 + 5.96)[3]
Characteristics
Spectral type	F0 IV[4]
U−B color index	+0.10[2]
B−V color index	+0.28[2]
Astrometry
Proper motion (μ)	RA: +41.94[1] mas/yr Dec.: −3.93[1] mas/yr
Parallax (π)	17.34±0.48 mas[1]
Distance	188 ± 5 ly (58 ± 2 pc)
Absolute magnitude (MV)	+0.60[5]
Orbit[4]
Period (P)	12.237±0.080 yr
Semi-major axis (a)	0.176±0.004″
Eccentricity (e)	0.032±0.032
Inclination (i)	76.3±2.0°
Longitude of the node (Ω)	90.8±2.0°
Periastron epoch (T)	2007.518±0.480
Argument of periastron (ω) (secondary)	64.9±11.0°
Details
δ Ind A
Mass	1.78±0.21[4] M☉
Luminosity	48[5] L☉
Surface gravity (log g)	3.85[6] cgs
Temperature	7,445±253[6] K
Metallicity [Fe/H]	−0.21[5] dex
Rotational velocity (v sin i)	130[7] km/s
Age	462[6] Myr
δ Ind B
Mass	1.33±0.16[4] M☉
Other designations
δ Ind, CPD−55°9733, FK5 824, HD 208450, HIP 108431, HR 8368, SAO 247244, WDS J21579-5500AB[8]
Database references
SIMBAD	data

The binary nature of this system was discovered by South African astronomer William Stephen Finsen from 1936 onward,^[4] with his published orbital elements appearing in 1956.^[9] The pair have an orbital period of 12.2 years, a semimajor axis of 0.176 arc seconds, and an eccentricity of around 0.03. They have been listed with a stellar classification of F0 IV by multiple authors, suggesting they are yellow-white hued F-type subgiant stars. However, their estimated masses don't match this classification, so Docobo and Andrade (2013) suggest the Hipparcos parallax may have been underestimated.^[4] One paper has published separate spectral classes of A8(V) and F3(V) respectively for the two components.^[10]