Eta Indi

Eta Indi, Latinised from η Indi, is a single, 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]

η Indi

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]
Characteristics
Spectral type	A9IV[3]
B−V color index	+0.26[2]
Astrometry
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 mas[1]
Distance	78.8 ± 0.5 ly (24.2 ± 0.1 pc)
Absolute magnitude (MV)	2.59[5]
Details
Mass	1.60[6] M☉
Radius	2.27[7] R☉
Luminosity	7.60[5] L☉
Temperature	7,694[6] K
Rotational velocity (v sin i)	75[8] km/s
Age	100±50[7] Myr
Other designations
η Ind, CPD−52° 11752, FK5 776, HD 197157, HIP 102333, HR 7920, SAO 246709[2]
Database references
SIMBAD	data

Measurements with the Hipparcos spacecraft showed the star, which is single,^[9] appears to move against the deep sky backdrop by a mean biannual parallax shift of around 41.37 mas,^[1] which equates to 79 light-years' distance. Its radial vector to our system's own trajectory (radial velocity) shows it to be in a phase of a narrowing of the gap, at a rounded −2 km/s, net.^[4] η Indi appears to be a member of the Octans association, a group of 62 stars that are around 30−50 million years old and have common motion.^[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. The star is estimated 1.6 M_☉ (masses of the Sun),^[6] and 2.27 R_☉ (its radius).^[7] 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] It is very likely to be a hybrid Delta Scuti/Gamma Doradus variable.^[8]

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. S2CID 18759600. Vizier catalog entry
2. "Eta Indi". SIMBAD Astronomical Database. Retrieved 2016-08-23.
3. 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. S2CID 119476992.
4. 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. S2CID 119231169.
5. 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. S2CID 119257644. Vizier catalog entry
6. 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. S2CID 33401607. Vizier catalog entry
7. 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, S2CID 51417657.
8. 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 (1): 122–128, 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. S2CID 16080025.