HD 193721
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| 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 (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 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 a 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]
