Epoch J2000 Equinox J2000
|Right ascension||22h 08m 13.98473s|
|Declination||–46° 57′ 39.5078″|
|Apparent magnitude (V)||+1.74|
|Spectral type||B6 V|
|U−B color index||–0.47|
|B−V color index||–0.13|
|Radial velocity (Rv)||+11.8 km/s|
|Proper motion (μ)||RA: +126.69 mas/yr
Dec.: −147.47 mas/yr
|Parallax (π)||32.29 ± 0.21 mas|
|Distance||101.0 ± 0.7 ly
(31.0 ± 0.2 pc)
|Surface gravity (log g)||3.76 ± 0.11 cgs|
|Metallicity [Fe/H]||–0.13 ± 0.02 dex|
|Rotational velocity (v sin i)||215 km/s|
Alpha Gruis has a stellar classification of B6 V, although some sources give it a classification of B7 IV. The first classification indicates that this is a B-type star on the main sequence of stars that are generating energy through the thermonuclear fusion of hydrogen at the core. However, a luminosity class of 'IV' would suggest that this is a subgiant star; meaning the supply of hydrogen at its core is becoming exhausted and the star has started the process of evolving away from the main sequence. It has no known companions.
The measured angular diameter of this star, after correcting for limb darkening, is 1.02 ± 0.07 mas. At a parallax-measured distance of 101 light-years (31 parsecs) from Earth, this yields a physical size of 3.4 times the radius of the Sun. It is rotating rapidly, with a projected rotational velocity of about 215 km/s providing a lower bound for the rate of azimuthal rotation along the equator. This star has around four times the Sun's mass and is radiating 263 times the luminosity of the Sun.
The effective temperature of Alpha Gruis's outer envelope is 13,920 K, giving it the blue-white hue characteristic of B-type stars. The abundance of elements other than hydrogen and helium, what astronomers term the metallicity, is about 74% of the abundance in the Sun. The Spitzer Space Telescope detected an excess of infrared emission from this star, suggesting that a circumstellar disk of dust may be in orbit around it.
Based on the estimated age and motion, it may be a member of the AB Doradus moving group that share a common motion through space. This group has an age of about 70 million years, which is consistent with α Gruis's 100-million-year estimated age (allowing for a margin of error). The space velocity components of this star in the Galactic coordinate system are [U, V, W] = [–7.0 ± 1.1, –25.6 ± 0.7, –15.5 ± 1.4] km/s.
Alpha Gruis has the proper name Alnair or Al Nair (sometimes Al Na'ir), from the Arabic al-nayyir [an-nai:r], meaning "the bright one". It is derived from its Arabic name, al-Nayyir min Dhanab al-ḥūt (al-Janūbiyy), "the Bright (star) belongs to the Tail of (the constellation of) the (Southern) Fish". Confusingly, "Alnair" is also given as the proper name for Zeta Centauri in an astronomical ephemerides in the middle of the 20th century. With β, δ, θ. ι, and λ Gru, Alnair belonged to Piscis Austrinus in traditional Arabic astronomy.
In Chinese, 鶴 (Hè), meaning Crane, refers to an asterism consisting of α Gruis, β Gruis, ε Gruis, η Gruis, δ Tucanae, ζ Gruis, ι Gruis, θ Gruis, δ2 Gruis and μ1 Gruis. Consequently, α Gruis itself is known as 鶴一 (Hè yī, English: First Star of the Crane). The Chinese name gave rise to another English name, Ke.
- 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.
- Johnson, H. L. et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory 4 (99), Bibcode:1966CoLPL...4...99J
- 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
- Wilson, Ralph Elmer (1953), General catalogue of stellar radial velocities, Carnegie Institution of Washington, Bibcode:1953QB901.W495.....
- Malagnini, M. L.; Morossi, C. (November 1990), "Accurate absolute luminosities, effective temperatures, radii, masses and surface gravities for a selected sample of field stars", Astronomy and Astrophysics Supplement Series 85 (3): 1015–1019, Bibcode:1990A&AS...85.1015M
- Richichi; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics 431: 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039
- Fitzpatrick, Edward L.; Massa, Derck (November 1999), "Determining the Physical Properties of the B Stars. I. Methodology and First Results", The Astrophysical Journal 525 (2): 1011–1023, arXiv:astro-ph/9906257, Bibcode:1999ApJ...525.1011F, doi:10.1086/307944
- Zorec, J. et al. (July 2009), "Fundamental parameters of B supergiants from the BCD system. I. Calibration of the (λ_1, D) parameters into Teff", Astronomy and Astrophysics 501 (1): 297–320, Bibcode:2009A&A...501..297Z, doi:10.1051/0004-6361/200811147
- Niemczura, E. (June 2003), "Metallicities of the SPB stars from the IUE ultraviolet spectra", Astronomy and Astrophysics 404: 689–700, Bibcode:2003A&A...404..689N, doi:10.1051/0004-6361:20030546. The fractional abundance relative to the Sun is given by:
- 10–0.13 = 0.74, or 74%.
- Dachs, J. et al. (March 1981), "Photoelectric scanner measurements of Balmer emission line profiles for southern Be stars. II - A survey for variations", Astronomy and Astrophysics Supplement Series 43: 427–453, Bibcode:1981A&AS...43..427D
- Su, K. Y. L. et al. (December 2006), "Debris Disk Evolution around A Stars", The Astrophysical Journal 653 (1): 675–689, arXiv:astro-ph/0608563, Bibcode:2006ApJ...653..675S, doi:10.1086/508649
- "LTT 8869 -- High proper-motion Star", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2011-12-24
- Scalzi, John (2008), Rough Guide to the Universe, Penguin, p. 306, ISBN 1-4053-8370-4
- 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
- Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library 1 (3 ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R*) is given by:
- "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16
- Zuckerman, B. et al. (May 2011), "The Tucana/Horologium, Columba, AB Doradus, and Argus Associations: New Members and Dusty Debris Disks", The Astrophysical Journal 732 (2): 61, arXiv:1104.0284, Bibcode:2011ApJ...732...61Z, doi:10.1088/0004-637X/732/2/61
- Kunitzsch, P.; Smart, T. (2006), A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd ed.), Cambridge, MA: Sky Publishing, p. 39, ISBN 978-1-931559-44-7
- Kunitzsch,, P. (1959), Arabische Sternnamen in Europa, Wiesbaden: Otto Harrassowitz, p. 128
- Allen, Richard H. (1963). Star Names: Their Lore and Meaning (reprint ed.). New York, NY: Dover Publications Inc. p. 237. ISBN 0-486-21079-0.
- (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
- (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.
- Richard Hinckley Allen: Star Names — Their Lore and Meaning: Grus
- Kaler, James B., "AL NAIR (Alpha Gruis)", Stars (University of Illinois), retrieved 2011-12-26