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]

References

1. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
2. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
3. Houk, N.; Smith-Moore, M. (1988). Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars. Volume 4, Declinations -26°.0 to -12°.0. Vol. 4. Bibcode:1988mcts.book.....H.
4. Mermilliod, J. -C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data: 0. Bibcode:1986EgUBV........0M.
5. Gontcharov, G. A. (November 2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. ISSN 1063-7737. S2CID 119231169.
6. Anders, F.; Khalatyan, A.; Chiappini, C.; Queiroz, A. B.; Santiago, B. X.; Jordi, C.; Girardi, L.; Brown, A. G. A.; Matijevič, G.; Monari, G.; Cantat-Gaudin, T.; Weiler, M.; Khan, S.; Miglio, A.; Carrillo, I.; Romero-Gómez, M.; Minchev, I.; De Jong, R. S.; Antoja, T.; Ramos, P.; Steinmetz, M.; Enke, H. (2019). "Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18". Astronomy and Astrophysics. 628: A94. arXiv:1904.11302. Bibcode:2019A&A...628A..94A. doi:10.1051/0004-6361/201935765. S2CID 131780028.
7. Stassun, Keivan G.; et al. (September 2018). "The TESS Input Catalog and Candidate Target List". The Astronomical Journal. 156 (3): 102. arXiv:1706.00495. Bibcode:2018AJ....156..102S. doi:10.3847/1538-3881/aad050. ISSN 0004-6256. S2CID 73582386.
8. Radick, R.; Lien, D. (August 1980). "Illinois occultation summary. I - 1977-1978". The Astronomical Journal. 85: 1053. Bibcode:1980AJ.....85.1053R. doi:10.1086/112767. ISSN 0004-6256.