HD 193721

HD 193721 (HR 7785) is an astrometric binary^[14] in the southern circumpolar constellation Octans. It has an apparent magnitude of 5.77,^[2] allowing it to be faintly seen with the naked eye. Parallax measurements place the system 760 light years^[1] away from the Solar System and it is currently receding with a heliocentric radial velocity 8.6 km/s.^[5]

HD 193721

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Octans
Right ascension	20h 33m 17.6366s[1]
Declination	−80° 57′ 53.5944″[1]
Apparent magnitude (V)	5.77±0.01[2]
Characteristics
Spectral type	G6/8 II[3]
U−B color index	+0.85[4]
B−V color index	+1.14[4]
Astrometry
Radial velocity (Rv)	8.6±0.7[5] km/s
Proper motion (μ)	RA: +9.794 mas/yr[1] Dec.: −16.081 mas/yr[1]
Parallax (π)	4.2823±0.165 mas[1]
Distance	760 ± 30 ly (234 ± 9 pc)
Absolute magnitude (MV)	−0.24[6]
Details
Mass	3.49[7] M☉
Radius	24.38[8] R☉
Luminosity	300±5[9] L☉
Surface gravity (log g)	2.14±0.02[1] cgs
Temperature	4953±122[8] K
Metallicity [Fe/H]	−0.15[10] dex
Rotational velocity (v sin i)	2.7±1.1[11] km/s
Other designations
47 G. Octantis[12], CPD−81°901, FK5 3994, GC 28453, HD 193721, HIP 101427, HR 7785, SAO 258861, WDS J20333-8058A[13]
Database references
SIMBAD	data

HD 193721 has a stellar classification of G6/8 II^[3] — intermediate between a G6 and 8 bright giant. At present it has 3.49 times the mass of the Sun,^[7] but has expanded to 24.4 times its girth.^[8] It shines with a luminosity of 300 L_☉^[9] from its enlarged photosphere at an effective temperature of 4,953 K,^[8] giving a yellow hue. HD 193721 is metal deficient with an iron abundance 71% that of the Sun^[10] and spins leisurely with a projected rotational velocity of 2.7 km/s.^[11]

The system has an companion designated CPD −81°900. The object has a spectral classification of F8^[15] and is located 25.5″ along a position angle of 0° (as of 1998).^[16] CPD −81°900 is a foreground object, having a higher parallax^[17] and different proper motion.^[16]