HD 173780

HD 173780 is a single^[9] star in the northern constellation Lyra, near the southern constellation border with Hercules. It is an orange-hued star that is faintly visible to the naked eye with an apparent visual magnitude of +4.84.^[2] This object is located at a distance of approximately 237 light years from the Sun based on parallax, but is drifting closer with a radial velocity of −17 km/s.^[1]

HD 173780

Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Lyra
Right ascension	18h 46m 04.47950s[1]
Declination	+26° 39′ 43.6644″[1]
Apparent magnitude (V)	+4.84[2]
Characteristics
Evolutionary stage	Horizontal-branch[3]
Spectral type	K3III[4]
B−V color index	1.20[2]
Astrometry
Radial velocity (Rv)	−16.92±0.17[1] km/s
Proper motion (μ)	RA: +17.460[1] mas/yr Dec.: +23.819[1] mas/yr
Parallax (π)	13.7599 ± 0.1315 mas[1]
Distance	237 ± 2 ly (72.7 ± 0.7 pc)
Absolute magnitude (MV)	0.37[5]
Details
Mass	1.70[2] M☉
Radius	16.38+0.22 −0.47[1] R☉
Luminosity	91.5±1.0[1] L☉
Surface gravity (log g)	2.42±0.08[6] cgs
Temperature	4,468±19[6] K
Metallicity [Fe/H]	−0.04±0.05[6] dex
Rotational velocity (v sin i)	3.8[7] km/s
Age	2.42[2] Gyr
Other designations
BD+26°3349, HD 173780, HIP 92088, HR 7064, SAO 86418[8]
Database references
SIMBAD	data

This is an aging giant star with a stellar classification of K3III.^[4] It is a red clump giant, indicating it is on the horizontal branch and is generating energy through the fusion of helium at its core.^[3] The star is 2.4 billion years old with 1.7 times the mass of the Sun.^[2] With the supply of hydrogen exhausted at its core, it has expanded to 16 times the radius of the Sun. The star is radiating 92 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 4,468 K.^[1]

References

1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
2. Luck, R. Earle (2015), "Abundances in the Local Region. I. G and K Giants", Astronomical Journal, 150 (3), 88, arXiv:1507.01466, Bibcode:2015AJ....150...88L, doi:10.1088/0004-6256/150/3/88, S2CID 118505114.
3. Alves, David R. (August 2000), "K-Band Calibration of the Red Clump Luminosity", The Astrophysical Journal, 539 (2): 732–741, arXiv:astro-ph/0003329, Bibcode:2000ApJ...539..732A, doi:10.1086/309278, S2CID 16673121.
4. Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245, Bibcode:1989ApJS...71..245K, doi:10.1086/191373.
5. 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.
6. Wu, Yue; et al. (2010), "Coudé-feed stellar spectral library – atmospheric parameters", Astronomy & Astrophysics, 525: A71, arXiv:1009.1491, Bibcode:2011A&A...525A..71W, doi:10.1051/0004-6361/201015014, S2CID 53480665.
7. Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209.
8. "HD 173780". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-02-07.
9. Eggleton, P. P.; Tokovinin, A. A. (2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.