Pi1 Gruis

Pi1 Gruis
Observation data
Epoch J2000      Equinox J2000
Constellation Grus
Right ascension 22h 22m 44.20571s [1]
Declination −45° 56′ 52.6115″ [1]
Apparent magnitude (V) 6.14v
Characteristics
Spectral type S5, G0V[1]
Variable type semi-regular variable[2]
Astrometry
Parallax (π)6.13 ± 0.76 mas
Distanceapprox. 530 ly
(approx. 160 pc)
Absolute magnitude (MV)-
Other designations
HR 8521, HD 212087, SAO 231105, HIP 110478.

Pi1 Gruis is a star in the constellation Grus. It is a semi-regular red giant of spectral type S5, ranging from apparent magnitude 5.31 to 7.01 over a period of 191 days,[2] and is around 532 light-years from Earth.[1] It is one of the brightest stars of a class of stars known as S Stars, and has a companion star of apparent magnitude 10.9 that is sunlike in properties—a yellow main sequence star of spectral type G0V. Separated by 2.71′′, the pair make up a likely binary system. The primary star has a measured diameter of 21 milliarcseconds, corresponding to a diameter 694 times that of the Sun.[3] It is an ageing star, thought be well on its way transitioning from a red giant to a planetary nebula. A shell of material has been detected at a distance of 0.91 light-years (0.28 parsecs), which is estimated to have been ejected 21,000 years ago.[4] Closer to the star, there appears to be a cavity within 200 AU, suggesting a drop off in the ejection of material in the past 90 years. The presence of one companion makes the shape of the shell irregular (rather than spherical), and there may as yet be another undetected companion contributing to this.[3]

The star was catalogued by French explorer and astronomer Nicolas Louis de Lacaille in 1756 but not given a name. Instead, he gave the Bayer designation of "Pi Gruis" to Pi2 Gruis. It was Thomas Brisbane who designated this star as Pi1.[5] Annie Jump Cannon was the first to report its unusual spectrum, sending a plate of its spectrograph made in 1895 to Paul W. Merrill and noting its similarity to R Andromedae. Merrill selected these two stars along with R Cygni to be the three prototypes of the S Star class.[6] Pi1 Gruis was one of the first 17 stars defined as S-stars by Merrill in 1922; the only star not observed from Mount Wilson due to its southerly location in the sky.[7] Analysis of its spectrum showed bands indicating the presence of technetium,[8] as well as oxides of zirconium, lanthanum, cerium and yttrium but not titanium nor barium (which have been recorded in other S stars).[9]

References

  1. 1 2 3 4 "Pi1 Gruis - S Star". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 19 January 2014.
  2. 1 2 Otero, Sebastian Alberto (20 June 2011). "Pi 1 Gruis". AAVSO Website. American Association of Variable Star Observers. Retrieved 19 January 2014.
  3. 1 2 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. ↑ Young, K.; Phillips, T. G.; Knapp, G. R. (1993). "Circumstellar shells resolved in IRAS survey data. II - Analysis" (PDF). Astrophysical Journal 409: 725–38. Bibcode:1993ApJ...409..725Y. doi:10.1086/172702.
  5. ↑ Wagman, Morton (2003). Lost Stars: Lost, Missing and Troublesome Stars from the Catalogues of Johannes Bayer, Nicholas Louis de Lacaille, John Flamsteed, and Sundry Others. Blacksburg, VA: The McDonald & Woodward Publishing Company. pp. 360–62. ISBN 978-0-939923-78-6.
  6. ↑ Merrill, Paul W. (1955). "Red Stars". Publ. Astron. Soc. Pac 67: 199–213. Bibcode:1955PASP...67..199M. doi:10.1086/126804.
  7. ↑ Merrill, Paul W. (1922). "Stellar spectra of class S". Astrophysical Journal 56: 457–82. Bibcode:1922ApJ....56..457M. doi:10.1086/142716.
  8. ↑ 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.
  9. ↑ Murty, P.S. (1983). "Pi Gruis - Molecular identifications and spectral classification" (PDF). Astrophysics and Space Science 94 (2): 295–305. Bibcode:1983Ap&SS..94..295M. doi:10.1007/BF00653719. ISSN 0004-640X.
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