Alpha Mensae

Coordinates: Sky map 6h 10m 14.4s, −74° 45′ 11″
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α Mensae
Mensa IAU.svg
Red circle.svg
Location of α Mensae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Mensa
Right ascension 06h 10m 14.47353s[1]
Declination –74° 45′ 10.9583″[1]
Apparent magnitude (V) 5.09[2]
Spectral type G7 V[3] + M3.5-6.5 V[4]
U−B color index 0.33[5]
B−V color index 0.72[5]
V−R color index 0.38
R−I color index 0.32
Radial velocity (Rv)+34.9[6] km/s
Proper motion (μ) RA: 121.80[1] mas/yr
Dec.: −212.34[1] mas/yr
Parallax (π)97.8983 ± 0.0719 mas[7]
Distance33.32 ± 0.02 ly
(10.215 ± 0.008 pc)
Absolute magnitude (MV)5.03[8]
α Men A
Mass0.964 ± 0.037 M
Radius0.960 ± 0.013 R
Luminosity0.81 ± 0.02 L
Surface gravity (log g)4.459 ± 0.006 cgs
Temperature5569 ± 50 K
Metallicity [Fe/H]0.11 ± 0.05 dex
Rotational velocity (v sin i)0.6 ± 0.6 km/s
Age6.2 ± 1.4 Gyr
α Men B
Mass0.169 ± 0.006 M
Radius0.19 ± 0.01 R
Temperature3054 ± 44 K
Other designations
Alf Men, Alp Men, CD−74° 294, FK5 239, GJ 231, HD 43834, HIP 29271, HR 2261, SAO 256274, LTT 2490[9]
Database references

α Mensae (Latinised as Alpha Mensae, abbreviated to α Men or Alpha Men) is the brightest star in the constellation Mensa. At a magnitude of 5.09, it is the dimmest lucida (a constellation's brightest star) in the sky. Due to its declination, on Earth it is best visible from higher latitudes of the southern hemisphere, yet can also be seen, though low in the sky, from just north of the Equator when near its daily arc's highest point, the culmination.

This star has a stellar classification of G7 V,[9] indicating that it is a G-type main sequence star that is generating energy by fusing hydrogen into helium at its core. It is of similar size but slightly cooler than the Sun, with 96.4% of the mass, 96% of the radius, and 81% of the Sun's luminosity.[4] The effective temperature of the stellar atmosphere is 5,569 K, and it has a slightly higher (129%) proportion of elements other than hydrogen and helium—what astronomers call the star's metallicity—compared to the Sun.[4] The estimated age of this star is 6.2 billion years, and is rotating at a relatively leisurely projected rotational velocity of 0.6 km/s.[4]

Located about 33 light years distant from the Sun, Alpha Mensae has a relatively high proper motion across the sky. It has already made its closest approach to the Sun, coming within about 10 ly (3.2 pc) around 250,000 years ago.[10] A candidate infrared excess has been detected around this star, most which would indicate the presence of a circumstellar disk at a radius of over 147 AU. The derived temperature of this dust is below 22 K.[11] However, data from Herschel Space Observatory failed to confirm this excess, leaving the finding in doubt.[12] No planetary companions have yet been discovered around it. It has a red dwarf companion star at an angular separation of 3.05 arcseconds; equivalent to a projected separation of roughly 30 AU.[9][13][14] With a mass just 16.9% that of the Sun, the companion is fully convective.[4]


  1. ^ a b c d 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. ^ Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. SIMBAD. Bibcode:1986EgUBV........0M.
  3. ^ Gray, R. O.; et al. (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): 161–70, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637, S2CID 119476992.
  4. ^ a b c d e f Chontos, Ashley; et al. (2021). "TESS Asteroseismology of α Mensae: Benchmark Ages for a G7 Dwarf and its M-dwarf Companion". The Astrophysical Journal. 922 (2): 229. arXiv:2012.10797. Bibcode:2021ApJ...922..229C. doi:10.3847/1538-4357/ac1269. S2CID 229340231.
  5. ^ a b Johnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99): 99. Bibcode:1966CoLPL...4...99J.
  6. ^ Evans, D. S. (June 20–24, 1966). "The Revision of the General Catalogue of Radial Velocities". In Batten, Alan Henry; Heard, John Frederick (eds.). Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30. University of Toronto: International Astronomical Union. Bibcode:1967IAUS...30...57E.
  7. ^ 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.
  8. ^ Holmberg, J.; et al. (July 2009), "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics", Astronomy and Astrophysics, 501 (3): 941–947, arXiv:0811.3982, Bibcode:2009A&A...501..941H, doi:10.1051/0004-6361/200811191, S2CID 118577511.
  9. ^ a b c "LTT 2490 -- High proper-motion star". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2010-09-11.
  10. ^ Bailer-Jones, C. A. L. (March 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.
  11. ^ Eiroa, C.; et al. (July 2013). "DUst around NEarby Stars. The survey observational results". Astronomy & Astrophysics. 555: A11. arXiv:1305.0155. Bibcode:2013A&A...555A..11E. doi:10.1051/0004-6361/201321050. S2CID 377244.
  12. ^ Sibthorpe, B.; et al. (April 2018), "Analysis of the Herschel DEBRIS Sun-like star sample", Monthly Notices of the Royal Astronomical Society, 475 (3): 3046–3064, arXiv:1803.00072, Bibcode:2018MNRAS.475.3046S, doi:10.1093/mnras/stx3188.
  13. ^ Eggenberger, A.; et al. (2007). "The impact of stellar duplicity on planet occurrence and properties. I. Observational results of a VLT/NACO search for stellar companions to 130 nearby stars with and without planets". Astronomy and Astrophysics. 474 (1): 273–291. Bibcode:2007A&A...474..273E. doi:10.1051/0004-6361:20077447.
  14. ^ "HD 43834B – Star". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2010-03-26. (details on the stellar properties of the companion star)

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