Eta Indi

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η Indi
Indus constellation map.svg
Red circle.svg
Location of η Indi (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Indus
Right ascension  20h 44m 02.33404s[1]
Declination −51° 55′ 15.4970″[1]
Apparent magnitude (V) 4.52[2]
Spectral type A9IV[3]
B−V color index +0.26[2]
Radial velocity (Rv)−1.6±0.8[4] km/s
Proper motion (μ) RA: +155.80[1] mas/yr
Dec.: −53.86[1] mas/yr
Parallax (π)41.37 ± 0.25[1] mas
Distance78.8 ± 0.5 ly
(24.2 ± 0.1 pc)
Absolute magnitude (MV)2.59[5]
Mass1.60[6] M
Radius2.27[7] R
Luminosity7.60[5] L
Temperature7,694[6] K
Rotational velocity (v sin i)75[8] km/s
Age100±50[7] Myr
Other designations
η Ind, CPD−52° 11752, FK5 776, HD 197157, HIP 102333, HR 7920, SAO 246709[2]
Database references

Eta Indi, Latinized from η Indi, is a single,[9] white-hued star in the southern constellation Indus. It is a faint star but visible to the naked eye with an apparent visual magnitude of 4.52.[2] Measurements with the Hipparcos spacecraft showed an annual parallax shift of 41.37 mas,[1] which provides a distance estimate of 79 light years. It is moving closer to the Sun with a radial velocity of −2 km/s.[4] Eta Indi appears to be a member of the Octans association, which is a group of 62 stars that are around 30−50 million years old and following a common motion through space.[10]

The spectrum of this star matches a stellar classification of A9 IV[3] which suggests it is an evolving subgiant star of type A. In 2017, it was found to be a possible hybrid Delta Scuti/Gamma Doradus variable.[8] The star has an estimated 1.6[6] times the mass of the Sun and 2.27[7] times the Sun's radius. It is shines with 7.60[5] times the Sun's luminosity, which is radiated from its photosphere at an effective temperature of 7,694 K.[6] The star is spinning with a projected rotational velocity of 75 km/s.[8]


  1. ^ a b c d e f 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. ^ a b c d "Eta Indi". SIMBAD Astronomical Database. Retrieved 2016-08-23.
  3. ^ a b Gray, R. O.; et al. (July 2006). "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample". The Astronomical Journal. 132 (1): 161–170. arXiv:astro-ph/0603770. Bibcode:2006AJ....132..161G. doi:10.1086/504637.
  4. ^ a b 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.
  5. ^ a b c Anderson, E.; Francis, Ch. (May 2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331–346. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. Vizier catalog entry
  6. ^ a b c d David, Trevor J.; Hillenbrand, Lynne A. (May 2015). "The Ages of Early-type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets". The Astrophysical Journal. 804 (2): 146–184. arXiv:1501.03154. Bibcode:2015ApJ...804..146D. doi:10.1088/0004-637X/804/2/146. Vizier catalog entry
  7. ^ a b c Plavchan, Peter; et al. (June 2009), "New Debris Disks Around Young, Low-Mass Stars Discovered with the Spitzer Space Telescope", The Astrophysical Journal, 698 (2): 1068–1094, arXiv:0904.0819, Bibcode:2009ApJ...698.1068P, doi:10.1088/0004-637X/698/2/1068.
  8. ^ a b c Koen, C.; van, Wyk F.; Laney, C. D.; Kilkenny, D. (2017), "HR 7920: a very bright new Delta Scuti star with possible Gamma Doradus variations", MNRAS, 466: 122, Bibcode:2017MNRAS.466..122K, doi:10.1093/mnras/stw3062
  9. ^ Rodriguez, David R.; et al. (May 2015), "Stellar multiplicity and debris discs: an unbiased sample", Monthly Notices of the Royal Astronomical Society, 449 (3): 3160–3170, arXiv:1503.01320, Bibcode:2015MNRAS.449.3160R, doi:10.1093/mnras/stv483.
  10. ^ Torres, C. A. O.; Quast, G. R.; da Silva, L .; de la Reza, R.; Melo, C. H. F.; Sterzik, M. (2006). "Search for associations containing young stars (SACY)". Astronomy and Astrophysics. 460 (3): 695–708. arXiv:astro-ph/0609258. Bibcode:2006A&A...460..695T. doi:10.1051/0004-6361:20065602. ISSN 0004-6361.