Eta Microscopii

η Microscopii, Latinised as Eta Microscopii, is a solitary[7] star in the constellation Microscopium. It is visible to the naked eye as a dim, orange-hued star with an apparent visual magnitude of 5.53.[2] The star is located around 910 light-years distant from the Sun based on parallax, and is drifting further away with a radial velocity of +22 km/s.[1]

Eta Microscopii
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Microscopium
Right ascension 21h 06m 25.51950s[1]
Declination −41° 23′ 09.4805″[1]
Apparent magnitude (V) 5.53[2]
Characteristics
Spectral type K3 III[3]
U−B color index +1.50[2]
B−V color index +1.35[2]
Astrometry
Radial velocity (Rv)+22.29±0.13[1] km/s
Proper motion (μ) RA: +28.760[1] mas/yr
Dec.: −11.548[1] mas/yr
Parallax (π)3.5657 ± 0.1149 mas[1]
Distance910 ± 30 ly
(280 ± 9 pc)
Absolute magnitude (MV)−1.13[4]
Details
Mass1.2[5] M☉
Radius47.41+0.95
−5.67[1] R☉
Luminosity735±28[1] L☉
Surface gravity (log g)1.1[5] cgs
Temperature4,365+287
−43[1] K
Metallicity [Fe/H]−0.31[5] dex
Other designations
η Mic, CD−41°14379, FK5 3684, GC 29461, HD 200702, HIP 104177, HR 8069, SAO 230523[6]
Database references
SIMBADdata

This is an aging giant star with a stellar classification of K3 III,[3] indicating that it has exhausted the supply of hydrogen at its core then cooled and expanded. At present it has around 47[1] times the girth of the Sun. The star is radiating 735 times the luminosity of the Sun from its swollen photosphere at an effective temperature of 4,365 K.[1]

Multiple star catalogues list two optical companions.[8] Two arc-minutes away, the 8th magnitude HD 200733 is a main sequence star much closer to Earth than η Microscopii.[9] A 14th-magnitude star one arc-minute from η Microscopii is a background object.[10]

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. Drilling, J. S. (February 1973), "Photoelectric UBV photometry of late-type stars in two regions at high galactic latitude", Astronomical Journal, 78: 44–46, Bibcode:1973AJ.....78...44D, doi:10.1086/111370.
  3. Houk, Nancy (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 2, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode:1978mcts.book.....H.
  4. 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.
  5. Anders, F.; Khalatyan, A.; Chiappini, C.; Queiroz, A. B.; Santiago, B. X.; Jordi, C.; Girardi, L.; Brown, A. G. A.; Matijevič, G.; Monari, G.; Cantat-Gaudin, T.; Weiler, M.; Khan, S.; Miglio, A.; Carrillo, I.; Romero-Gómez, M.; Minchev, I.; De Jong, R. S.; Antoja, T.; Ramos, P.; Steinmetz, M.; Enke, H. (2019), "Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18", Astronomy and Astrophysics, 628: A94, arXiv:1904.11302, Bibcode:2019A&A...628A..94A, doi:10.1051/0004-6361/201935765, S2CID 131780028.
  6. "eta Mic", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2017-08-12.
  7. 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.
  8. Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001), "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog", The Astronomical Journal, 122 (6): 3466, Bibcode:2001AJ....122.3466M, doi:10.1086/323920.
  9. 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.
  10. 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.
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