Tau1 Capricorni

Tau¹ Capricorni (τ¹ Cap, τ¹ Capricorni) is a star in the constellation Capricornus. It has an apparent magnitude of 6.76,^[2] making it readily visible in binoculars, but not to the naked eye. Located approximately 750 light years from Earth,^[1] the star is receding with a heliocentric radial velocity of 18.5 km/s.^[5] Due to its location near the ecliptic, τ¹ Cap can be occulted by the Moon and rarely planets.^[8]

For other stars with this Bayer designation, see τ Capricorni.

τ¹ Capricorni

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Capricornus
Right ascension	20h 37m 21.20s[1]
Declination	−15° 08′ 50.4″[1]
Apparent magnitude (V)	+6.76[2]
Characteristics
Spectral type	K1 III[3]
U−B color index	+1.23[4]
B−V color index	+1.26[4]
Astrometry
Radial velocity (Rv)	18.5 ± 3[5] km/s
Proper motion (μ)	RA: 61.508[1] mas/yr Dec.: −47.081[1] mas/yr
Parallax (π)	4.3504±0.0229 mas[1]
Distance	750 ± 4 ly (230 ± 1 pc)
Absolute magnitude (MV)	−0.27[2]
Details
Mass	1.18[6] M☉
Radius	25[7] R☉
Luminosity	191[7] L☉
Surface gravity (log g)	1.81[6] cgs
Temperature	4,272[6] K
Metallicity [Fe/H]	−0.02[6] dex
Other designations
τ1 Cap, 13 Capricorni, 34 G. Capricorni, BD−15°5732, GC 28694, HD 196348, HIP 101751, SAO 163740
Database references
SIMBAD	data

τ¹ Capricorni has a stellar classification of K1 III, indicating that it is an ageing K-type giant.^[3] At present it has 118% the mass of the Sun^[6] and an enlarged radius of 25 solar radii.^[7] It shines at 191 times the luminosity of the Sun^[7] from its photosphere at an effective temperature of 4272 K.^[6] τ¹ Cap's metallicity – elements heavier than helium – is at solar level.^[6]