15 Eridani

15 Eridani is a binary star[3] system in the equatorial constellation of Eridanus. It is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 4.875.[2] Based upon parallax measurements, the system is located around 260 light years away from the Sun.[1] It is moving further from the Earth with a heliocentric radial velocity of 24 km/s.[6]

15 Eridani
Observation data
Epoch J2000      Equinox J2000
Constellation Eridanus
Right ascension 03h 18m 22.10504s[1]
Declination −22° 30′ 40.0191″[1]
Apparent magnitude (V) 4.875[2]
(6.57 / 5.32)[3]
Characteristics
Evolutionary stage horizontal branch
Spectral type K0III[4]
B−V color index +0.90[5]
Astrometry
Radial velocity (Rv)23.90±0.5[6] km/s
Proper motion (μ) RA: 13.08[1] mas/yr
Dec.: 13.33[1] mas/yr
Parallax (π)12.77 ± 1.17[1] mas
Distance260 ± 20 ly
(78 ± 7 pc)
Absolute magnitude (MV)+0.85[7]
Orbit[3]
Period (P)118.16 yr
Semi-major axis (a)0.340″
Eccentricity (e)0.030
Inclination (i)66.6°
Longitude of the node (Ω)271.6°
Periastron epoch (T)1934.24
Argument of periastron (ω)
(secondary)		333.5°
Details
15 Eri A
Mass2.32[8] M☉
Luminosity72.4[8] L☉
Temperature4,960±31[8] K
Rotational velocity (v sin i)4.5±0.2[7] km/s
Age1.44[8] Gyr
Other designations
15 Eri, CD−22°1146, HD 20610, HIP 15382, HR 994, SAO 168452, WDS J03184-2231
Database references
SIMBADdata

This system has an orbital period of 118.16 years with an eccentricity of 0.030 and a semimajor axis of 0.340″.[3] The primary member, designated component A, is a magnitude 5.32[9] giant star with a stellar classification of K0 III.[4] It is a red clump giant,[10] which means it is on the horizontal branch and is generating energy through helium fusion at its core. This star has 1.44 billion years old with 2.32 times the mass of the Sun. It is radiating 72.4 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 4,960 K.[8] The companion, component B, has a magnitude of 6.57.[9]

References
  1. van Leeuwen, F.; et al. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
  2. Høg, E.; et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H.
  3. "Sixth Catalog of Orbits of Visual Binary Stars". United States Naval Observatory. Retrieved 11 August 2017.
  4. 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". Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars. 4. Bibcode:1988mcts.book.....H.
  5. Johnson, H. L. (1966). "UBVRIJKL Photometry of the Bright Stars". Communications of the Lunar and Planetary Laboratory. 4: 99. Bibcode:1966CoLPL...4...99J.
  6. Kharchenko, N. V.; et al. (2007). "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ~55000 stars and mean radial velocities of 516 Galactic open clusters and associations". Astronomische Nachrichten. 328 (9): 889. arXiv:0705.0878. Bibcode:2007AN....328..889K. doi:10.1002/asna.200710776. S2CID 119323941.
  7. Ammler-von Eiff, M.; Reiners, A. (June 2012), "New measurements of rotation and differential rotation in A-F stars: are there two populations of differentially rotating stars?", Astronomy & Astrophysics, 542: A116, arXiv:1204.2459, Bibcode:2012A&A...542A.116A, doi:10.1051/0004-6361/201118724, S2CID 53666672.
  8. 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.
  9. Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x. S2CID 14878976.
  10. 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
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