Pi1 Gruis

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Surface of the red giant star π1 Gruis.[1]

π1 Gruis (or Pi1 Gruis) is an S5[2]-type star in the Grus constellation located near 530 light-years from Earth. It forms a close naked-eye double with the unrelated star π2 Gruis four arc-minutes away. The star is one of the largest known stars, with a diameter 694 times greater than the Sun's own diameter.[3] Giant convention bubbles have been found to occur on Pi1 Gruis's surface (pictured).

Binary Companion

Pi1 Gruis is orbited by a small yellow main sequence star, with the spectral type of G0V.[4]


The star was first discovered by Icons-flag-fr.png French astronomer Nicolas Louis de Lacaille in 1756, but was not given a name. Instead, Lacaille gave the designation of "π Gruis" to π2 Gruis. Later, Icons-flag-uk.png British astronomer Thomas Brisbane who designated this star as π1. Pi1 Gruis was one of the first 17 stars defined as S-stars by the Icons-flag-us.png American astronomer Paul W. Merrill in 1922; the only star not observed from Mount Wilson due to being only visible in the Southern Hemisphere.[5] Analysis of the star's spectrum showed bands indicating the presence of the non-natural radioactive element technetium,[6] as well as oxides of other elements such as zirconium, lanthanum, cerium and yttrium, but strangely not titanium or barium, both of which have been recorded in other S stars.[7]


  1. Lua error in Module:Citation/CS1 at line 379: attempt to call method 'match' (a nil value).
  2. https://doi.org/10.1088/0067-0049/221/2/30
  3. Sacuto, S.; Jorissen, A.; Cruzalèbes, P.; Chesneau, O. et al. (2008). "The close circumstellar environment of the semi-regular S-type star π 1 Gruis". Astronomy & Astrophysics 482 (2): 561–74. arXiv:0803.3077. Bibcode 2008A&A...482..561S. doi:10.1051/0004-6361:20078306.
  4. https://doi.org/10.1051/0004-6361%3A20078306
  5. Merrill, Paul W. (1922). "Stellar spectra of class S". Astrophysical Journal 56: 457–82. Bibcode 1922ApJ....56..457M. doi:10.1086/142716.
  6. Little, Stephen J.; Little-Marenin, Irene R.; Bauer, Wendy Hagen (1987). "Additional late-type stars with technetium". Astronomical Journal 94: 981–995. Bibcode 1987AJ.....94..981L. doi:10.1086/114532.
  7. Murty, P.S. (1983). "Pi Gruis - Molecular identifications and spectral classification". Astrophysics and Space Science 94 (2): 295–305. Bibcode 1983Ap&SS..94..295M. doi:10.1007/BF00653719. ISSN 0004-640X. http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1983Ap%26SS..94..295M&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf.