Gamma Microscopii

Gamma Microscopii (γ Microscopii, γ Mic) is the brightest star in the faint southern constellation of Microscopium.[8] It has an apparent visual magnitude of 4.68,[2] which is too dim to be viewed from city skies. The distance to this star has been determined using parallax measurements made with the Gaia telescope, which place it at 223 ± 8 light-years (68.4 ± 2.5 parsecs).

Gamma Microscopii
Diagram showing star positions and boundaries of the Microscopium constellation and its surroundings
Location of γ Microscopii (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Microscopium
Right ascension 21h 01m 17.46047s[1]
Declination −32° 15′ 27.9574″[1]
Apparent magnitude (V) 4.680[2]
Characteristics
Spectral type G6 III[3]
U−B color index +0.575[2]
B−V color index +0.882[2]
R−I color index +0.32[4]
Astrometry
Radial velocity (Rv)+17.6[5] km/s
Proper motion (μ) RA: −1.73[1] mas/yr
Dec.: +0.41[1] mas/yr
Parallax (π)14.6428 ± 0.4966 mas[6]
Distance223 ± 8 ly
(68 ± 2 pc)
Absolute magnitude (MV)0.49[7]
Details
Mass2.5[8] M☉
Radius10[8] R☉
Luminosity64[8] L☉
Surface gravity (log g)3.34[9] cgs
Temperature5,050[9] K
Metallicity [Fe/H]–0.22 ± 0.11[10] dex
Age620[8] Myr
Other designations
Gamma Microscopii, Gamma Mic, γ Mic, CD−32 16353, CPD−32 6269, FK5 1550, GC 29331, HD 199951, HIP 103738, HR 8039, SAO 212636, WDS 21013-3215A.[11][12]
Database references
SIMBADdata

Based upon a stellar classification of G6 III,[3] this is a G-type giant star. It is a core helium fusing star that is classified as a member of the red clump evolutionary branch, although the metallicity of this star—meaning the abundance of elements other than hydrogen and helium—is anomalously low for a member of this group.[10] The effective temperature of the star's outer envelope is 5,050 K,[9] giving it the yellow-hued glow typical of G-type stars.[13]

In the galactic coordinate system, this star has space velocity components of [U, V, W] = [+13.75, +3.47, –10.50] km s−1. The peculiar velocity of this star, relative to its neighbors, is 1.2 km s−1. It has been listed as likely member of the Ursa Major Moving Group of stars that share a similar location and a common trajectory through space.[7] Backwards extrapolation of the motion of γ Microscopii has shown that approximately 3.8 million years ago, it was only around 6 light-years from the Sun.[14] It would then have had an apparent magnitude of −3 and have been brighter than Sirius is now.[8] Shortly before that, around 3.9 million years ago, it likely passed within 1.14 to 3.45 light-years of the Sun, possibly massive enough and close enough to disturb the Oort cloud.[15] The same authors looked at Proper Motion Data collected with Gaia DR2 and didn't confirm the close encounter based on that dataset. Additional information is needed to identify the root cause for the mismatch between Hipparcos and Gaia datasets in that case.[16]

Gamma Microscopii has a visual companion, CCDM J21013-3215B at an angular separation of 26 arcseconds along a position angle of 94°, with an apparent visual magnitude of approximately 13.7.[12] Most likely this star is not gravitationally bound to γ Microscopii, but is merely a line of sight companion.[8][17]

The Bayer designation γ Microscopii was not assigned by Bayer himself. It was given the Flamsteed designation of 1 Piscis Austrini before Lacaille created the constellation of Microscopium in 1756.[18]

References
  1. van Leeuwen, F. (November 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. Jennens, P. A.; Helfer, H. L. (September 1975), "A new photometric metal abundance and luminosity calibration for field G and K giants.", Monthly Notices of the Royal Astronomical Society, 172 (3): 667–679, Bibcode:1975MNRAS.172..667J, doi:10.1093/mnras/172.3.667
  3. Montes, D.; et al. (November 2001), "Late-type members of young stellar kinematic groups - I. Single stars" (PDF), Monthly Notices of the Royal Astronomical Society, 328 (1): 45–63, arXiv:astro-ph/0106537, Bibcode:2001MNRAS.328...45M, doi:10.1046/j.1365-8711.2001.04781.x, S2CID 55727428, archived from the original (PDF) on 2017-09-22, retrieved 2018-11-04
  4. HR 8039, database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDS ID V/50. Accessed on line November 20, 2008.
  5. 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.
  6. 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.
  7. King, Jeremy R.; et al. (April 2003), "Stellar Kinematic Groups. II. A Reexamination of the Membership, Activity, and Age of the Ursa Major Group", The Astronomical Journal, 125 (4): 1980–2017, Bibcode:2003AJ....125.1980K, doi:10.1086/368241
  8. Gamma Mic, Stars, Jim Kaler. Accessed on line March 19, 2015.
  9. McWilliam, Andrew (December 1990), "High-resolution spectroscopic survey of 671 GK giants. I - Stellar atmosphere parameters and abundances", Astrophysical Journal Supplement Series, 74: 1075–1128, Bibcode:1990ApJS...74.1075M, doi:10.1086/191527
  10. Kubiak, M.; et al. (June 2002), "Metal Abundance of Red Clump Stars in Baade's Window", Acta Astronomica, 52: 159–175, Bibcode:2002AcA....52..159K
  11. * gam Mic -- Star in double system, database entry, SIMBAD. Accessed on line November 20, 2008.
  12. Entry 21013-3215, The Washington Double Star Catalog Archived 2009-01-31 at the Wayback Machine, United States Naval Observatory. Accessed on line November 20, 2008.
  13. "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-18, retrieved 2012-01-16
  14. García-Sánchez, J.; Weissman, P. R.; Preston, R. A.; Jones, D. L.; Lestrade, J.-F.; Latham, D. W.; Stefanik, R. P.; Paredes, J. M. (2001), "Stellar encounters with the solar system" (PDF), Astronomy and Astrophysics, 379 (2): 634–659, Bibcode:2001A&A...379..634G, doi:10.1051/0004-6361:20011330
  15. Bailer-Jones, C. A. L. (2015). "Close encounters of the stellar kind". Astronomy & Astrophysics. 575: 13. arXiv:1412.3648. Bibcode:2015A&A...575A..35B. doi:10.1051/0004-6361/201425221. S2CID 59039482. A35.
  16. Bailer-Jones, C. A. L.; Rybizki, J.; Andrae, R.; Fouesneau, M. (19 May 2018). "New stellar encounters discovered in the second Gaia data release". Astronomy & Astrophysics. 616 (37): A37. arXiv:1805.07581. Bibcode:2018A&A...616A..37B. doi:10.1051/0004-6361/201833456. S2CID 56269929.
  17. 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.
  18. Wagman, M. (August 1987). "Flamsteed's Missing Stars". Journal for the History of Astronomy. 18 (3): 220. Bibcode:1987JHA....18..209W. doi:10.1177/002182868701800305. S2CID 118445625.
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