Epsilon Reticuli

Epsilon Reticuli (Epsilon Ret, ε Reticuli, ε Ret) is a double star approximately 59 light-years away in the constellation of Reticulum. The primary component is an orange subgiant, while the secondary is a white dwarf. The two stars share a common motion through space and hence most likely form a binary star system.[10] The brighter star should be easily visible without optical aid under dark skies in the southern hemisphere. In 2000, an extrasolar planet was confirmed to be orbiting the primary star in the system.

Epsilon Reticuli
Location of ε Reticuli (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Reticulum
Right ascension 4h 16m 29.029s[1]
Declination –59° 18′ 07.76″[1]
Apparent magnitude (V) 4.44[2] / 12.5
Characteristics
Spectral type K2 III-IV + DA3.3[3]
U−B color index +1.07[2]
B−V color index +1.08[2]
Astrometry
Radial velocity (Rv)+29.3[4] km/s
Proper motion (μ) RA: –47.53 ± 0.17[1] mas/yr
Dec.: –167.58 ± 0.17[1] mas/yr
Parallax (π)54.83 ± 0.15[1] mas
Distance59.5 ± 0.2 ly
(18.24 ± 0.05 pc)
Absolute magnitude (MV)0.87[5]
Details
ε Reticuli A
Mass1.46 ± 0.01[6] M☉
Radius3.18 ± 0.08[6] R☉
Luminosity6.2 ± 0.6[6] L☉
Surface gravity (log g)3.76 ± 0.05[6] cgs
Temperature4961 ± 28[6] K
Metallicity [Fe/H]0.26 ± 0.07[6] dex
Rotational velocity (v sin i)2.07 ± 0.42[6] km/s
Age2.89 ± 0.06[6] Gyr
ε Reticuli B
Mass0.60 ± 0.02[3] M☉
Radius0.0132 ± 0.0002[3] R☉
Surface gravity (log g)7.98 ± 0.02[3] cgs
Temperature15310 ± 350[3] K
Age1.5[3] Gyr
Other designations
JSP 56, CCDM J04165-5918AB, WDS J04165-5918AB[7]
Epsilon Reticuli A: ε Reticuli, CPD−59°324, GJ 9153, HD 27442, HIP 19921, HR 1355, WDS J04165-5918A[8]
Epsilon Reticuli B: ε Reticuli B, CPD−59°324B, HD 27442B, WDS J04165-5918B, WD 0415-594[9]
Database references
SIMBADdata

Star system

The primary component, Epsilon Reticuli A, is a subgiant star with a stellar classification of K2IV, indicating that the fusing of hydrogen in its core is coming to an end and it is in the process of expanding to a red giant. With an estimated mass of about 1.5 times the solar mass, it was probably an F0 star while in the main sequence.[3] It has a radius of 3.18 times the solar radius, a luminosity of 6.2 the solar luminosity and an effective temperature of 4,961 K. As is typical of stars with giant planets, it has a high metallicity, with an iron abundance 82% larger than the Sun's.[6]

The secondary star, Epsilon Reticuli B, is known as a visual companion since 1930, and in 2006 was confirmed as a physical companion on the basis of its common proper motion.[11][12] It was noted that its color indices are incompatible with a main sequence object, but are consistent with a white dwarf.[12] This was confirmed in 2007 by spectroscopic observations, that showed the absorption spectrum typical of a hydrogen-rich white dwarf (spectral type DA).[10][13] This star has a visual apparent magnitude of 12.5 and is located at a separation of 13 arcseconds, corresponding to a projected physical separation of 240 AU and an orbital period of more than 2,700 years.[3]

It is estimated that Epsilon Reticuli B has a mass of 0.60 M☉ and a radius of 0.0132 R☉. Originally, when it was in the main sequence, it probably had a spectral type of A5 and a mass of 1.9 M☉, and spent 1.3 billion years on this phase. From a measured effective temperature of 15,310 K, it has a cooling age (time spent as a white dwarf) of 200 million years, corresponding to a total age of 1.5 billion years. This age is inconsistent with the primary estimated age of 2.8 billion years, which suggests a smaller mass for the white dwarf or a larger mass for the primary.[3]

Planetary system
The inner solar system superimposed behind the orbits of the planet Epsilon Reticuli b (and several others)

On December 11, 2000, a team of astronomers announced the discovery of a planet Epsilon Reticuli b.[14] With a minimum mass of 1.17 that of Jupiter, the planet moves around Epsilon Reticuli with an average separation of 1.16 AU. The eccentricity of the planet is extremely low (at 0.06), and it completes an orbit every 418 days (or 1.13 years).

Stability analysis shows that the planet's Lagrangian points would be stable enough to host Earth-sized planets, though as yet no trojan planets have been detected in this system.[15]

The Epsilon Reticuli planetary system[16]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b ≥1.55±0.07 MJ 1.269±0.001 429.1±0.7 0.057±0.037 — —

References
  1. van Leeuwen, F. (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.Vizier catalog entry
  2. Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J.
  3. Farihi, J.; Burleigh, M. R.; Holberg, J. B.; Casewell, S. L.; Barstow, M. A. (November 2011). "Evolutionary constraints on the planet-hosting subgiant ε Reticulum from its white dwarf companion". Monthly Notices of the Royal Astronomical Society. 417 (3): 1735–1741. arXiv:1104.0925. Bibcode:2011MNRAS.417.1735F. doi:10.1111/j.1365-2966.2011.19354.x.
  4. Wilson, Ralph Elmer (1953), "General Catalogue of Stellar Radial Velocities", Carnegie Institute Washington D.C. Publication, Washington: Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W.
  5. Elgarøy, Øystein; Engvold, Oddbjørn; Lund, Niels (March 1999), "The Wilson-Bappu effect of the MgII K line - dependence on stellar temperature, activity and metallicity", Astronomy and Astrophysics, 343: 222–228, Bibcode:1999A&A...343..222E.
  6. Jofré, E.; et al. (February 2015), "Stellar parameters and chemical abundances of 223 evolved stars with and without planets", Astronomy & Astrophysics, 574: 46, arXiv:1410.6422, Bibcode:2015A&A...574A..50J, doi:10.1051/0004-6361/201424474, A50.
  7. "** JSP 56". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-08-22.
  8. "Epsilon Reticuli". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-08-22.
  9. "Epsilon Reticuli B". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-08-22.
  10. Chauvin, G.; Lagrange, A.-M.; Udry, S.; Mayor, M. (2007), "Characterization of the long-period companions of the exoplanet host stars: HD 196885, HD 1237 and HD 27442", Astronomy and Astrophysics, 475 (2): 723–727, arXiv:0710.5918, Bibcode:2007A&A...475..723C, doi:10.1051/0004-6361:20067046.
  11. Raghavan; et al. (2006). "Two Suns in The Sky: Stellar Multiplicity in Exoplanet Systems". The Astrophysical Journal. 646 (1): 523–542. arXiv:astro-ph/0603836. Bibcode:2006ApJ...646..523R. doi:10.1086/504823.
  12. Chauvin, G.; Lagrange, A.-M.; Udry, S.; Fusco, T.; Galland, F.; Naef, D.; Beuzit, J.-L.; Mayor, M. (2006). "Probing long-period companions to planetary hosts. VLT and CFHT near infrared coronographic imaging surveys". Astronomy and Astrophysics. 456 (3): 1165–1172. arXiv:astro-ph/0606166. Bibcode:2006A&A...456.1165C. doi:10.1051/0004-6361:20054709.
  13. Mugrauer, M.; Neuhäuser, R.; Mazeh, T. (2007). "The multiplicity of exoplanet host stars. Spectroscopic confirmation of the companions GJ 3021 B and HD 27442 B, one new planet host triple-star system, and global statistics". Astronomy and Astrophysics. 469 (2): 755–770. arXiv:astro-ph/0703795. Bibcode:2007A&A...469..755M. doi:10.1051/0004-6361:20065883.
  14. Butler, R. P.; et al. (2001). "Two New Planets from the Anglo-Australian Planet Search". The Astrophysical Journal. 555 (1): 410–417. Bibcode:2001ApJ...555..410B. doi:10.1086/321467. hdl:2299/137.
  15. Schwarz; Dvorak, R.; Süli, Á.; Érdi, B. (2007). "Survey of the stability region of hypothetical habitable Trojan planets" (PDF). Astronomy and Astrophysics. 474 (3): 1023–1029. Bibcode:2007A&A...474.1023S. doi:10.1051/0004-6361:20077994.
  16. Wittenmyer, Robert A.; et al. (2020). "Cool Jupiters greatly outnumber their toasty siblings: occurrence rates from the Anglo-Australian Planet Search". Monthly Notices of the Royal Astronomical Society. 492 (1): 377–383. arXiv:1912.01821. Bibcode:2020MNRAS.492..377W. doi:10.1093/mnras/stz3436.

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