Gamma Microscopii

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

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).

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]

  1. ^ a b c d Cite error: The named reference aaa474_2_653 was invoked but never defined (see the help page).
  2. ^ a b c d Cite error: The named reference mnras172_667 was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference mnras328_1_45 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference bsc1 was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference gcsrv was invoked but never defined (see the help page).
  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. ^ a b Cite error: The named reference aj125_4_1980 was invoked but never defined (see the help page).
  8. ^ a b c d e f g Cite error: The named reference kaler was invoked but never defined (see the help page).
  9. ^ a b c Cite error: The named reference ajss74_1075 was invoked but never defined (see the help page).
  10. ^ a b Cite error: The named reference aa52_159 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference sb0 was invoked but never defined (see the help page).
  12. ^ a b Cite error: The named reference wds was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference csiro was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference aaa379_2_63 was invoked but never defined (see the help page).
  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. ^ Cite error: The named reference mnras389_2_869 was invoked but never defined (see the help page).
  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.