HD 40307 explained

HD 40307 is an orange (K-type) main-sequence star located approximately 42 light-years away in the constellation of Pictor (the Easel), taking its primary name from its Henry Draper Catalogue designation. It is calculated to be slightly less massive than the Sun. The star has six known planets, three discovered in 2008[1] and three more in 2012. One of them, HD 40307 g, is a potential super-Earth in the habitable zone, with an orbital period of about 200 days. This object might be capable of supporting liquid water on its surface, although much more information must be acquired before its habitability can be assessed.[2] [3] [4] [5]

No stellar companions to HD 40307 were detected as in 2018.[6]

History and nomenclature

HD 40307 was observed during or before 1900 as part of the Cape Photographic Durchmusterung.[7] The designation HD 40307 is from the Henry Draper Catalogue, which is based on spectral classifications made between 1911 and 1915 by Annie Jump Cannon and her co-workers, and was published between 1918 and 1924.[8] [9]

Characteristics

As a K-type star, HD 40307 emits orange-tinted light. It has only about three-quarters of the Sun's radius and mass. Its temperature is measured at slightly under .

The astronomers who discovered the planets orbiting HD 40307 suggested that the metallicities of stars determine whether or not the planetary bodies that orbit them will be terrestrial, like Earth, or gaseous, like Jupiter and Saturn.

Distance and visibility

Despite its relative proximity to the Sun at 42 light-years, HD 40307 is not visible to the naked eye, given its apparent magnitude of 7.17.[10] It came within 6.4 light-years of the Sun about 413,000 years ago.[11]

Planetary system

A planetary system around HD 40307 contains four confirmed planets and two other possible planets, all within of the star.

After spending five years observing the star,[12] the European Organisation for Astronomical Research in the Southern Hemisphere (ESO) announced that they had discovered three super-Earths in orbit around HD 40307 in June 2008. All three planets were detected by the radial velocity method, using the HARPS spectrograph system.[13]

In 2012, an independent analysis carried out by a team of astronomers led by Mikko Tuomi of the University of Hertfordshire confirmed the existence of these planets and found an additional three planets in the systems. The planet HD 40307 f on 51.6-day orbit was confirmed in 2015, with inconclusive evidence for the planets HD 40307 e and HD 40307 g.[14]

Five of the planets orbit very close to the star, with the farthest of them located twice as close to HD 40307 than is the planet Mercury is to the Sun.[15] [16] The outermost planet orbits at a distance similar to the distance of Venus to the Sun and is situated well in the system's liquid water habitable zone.

The minimum masses of the planets in the system ranges from three to ten times the mass of the Earth, placing them somewhere between Earth and gas giants like Uranus and Neptune. Dynamical analysis of the innermost planets suggests that planet b is unstable at its age unless it is an ice giant, having migrated from further away. That implies similar for the other planets, even further out.[17] The most recent discovery also indicates via dynamical analysis that the true planetary masses can not be much higher than their minimum masses.

See also

Notes

  1. Web site: Three super-Earths found around one star . https://web.archive.org/web/20131213170111/http://www.nbcnews.com/id/25191635/ . dead . December 13, 2013 . Jeanna Bryner . NBC News . June 16, 2008 . June 18, 2008 .
  2. Web site: Possible Earth-like planet could hold water; scientists cautious . Amina Khan . Los Angeles Times . November 7, 2012 . November 8, 2012 .
  3. 10.1051/0004-6361/201220268 . Tuomi . Mikko . Anglada-Escudé . Guillem . Gerlach . Enrico . Jones . Hugh R. A. . Reiners . Ansgar . Rivera . Eugenio J. . Vogt . Steven S. . Butler . R. Paul . Habitable-zone super-Earth candidate in a six-planet system around the K2.5V star HD 40307 . Astronomy & Astrophysics . 17 December 2012 . 549 . A48 . 1211.1617 . 2013A&A...549A..48T . 7424216 .
  4. Web site: Wall . Mike . 'Super-Earth' Alien Planet May Be Habitable for Life . November 7, 2012 . . November 8, 2012 .
  5. Web site: Tate . Karl . Super-Earth Planet: Potentially Habitable Alien World Explained (Infographic) . November 7, 2012 . . November 8, 2012 .
  6. 1811.09666 . 10.1051/0004-6361/201731341 . Archival VLT/Na Co multiplicity investigation of exoplanet host stars . 2018 . Dietrich . J. . Ginski . C. . Astronomy & Astrophysics . 620 . A102 . 2018A&A...620A.102D . 119294338 .
  7. http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=I/108/cpd&recno=379090 CPD−60 508
  8. pp. 214–215 in The Henry Draper Memorial, Annie J. Cannon, Journal of the Royal Astronomical Society of Canada 9, #5 (May–June 1915), pp. 203–215, .
  9. The Henry Draper Catalogue, Annie J. Cannon and Edward C. Pickering, Annals of Harvard College Observatory;
    hours 0 to 3, 91 (1918), ;
    hours 4 to 6, 92 (1918), ;
    hours 7 to 8, 93 (1919), ;
    hours 9 to 11, 94 (1919), ;
    hours 12 to 14, 95 (1920), ;
    hours 15 to 16, 96 (1921), ;
    hours 17 to 18, 97 (1922), ;
    hours 19 to 20, 98 (1923), ;
    hours 21 to 23, 99 (1924), .
  10. Web site: Stellar Magnitudes. 20 November 2008 . Astrophysics 162 Unit. University of Tennessee. 2008.
  11. Bobylev . Vadim V. . March 2010 . Searching for Stars Closely Encountering with the Solar System . Astronomy Letters . 36 . 3 . 220–226 . 10.1134/S1063773710030060 . 1003.2160 . 2010AstL...36..220B. 118374161.
  12. Web site: HD 40307 / CD-60 1303. 27 November 2008 . SolStation . Sol Company . 2008 .
  13. News: Trio of 'super-Earths' discovered . Mayor. etal. 2008-06-16. BBC News. 2008-06-16.
  14. The HARPS search for southern extra-solar planets. XXXVIII. Bayesian re-analysis of three systems. New super-Earths, unconfirmed signals, and magnetic cycles . Díaz . R. F. . Ségransan . D. . Udry . S. . Lovis . C. . Pepe . F. . Dumusque . X. . Marmier . M. . Alonso . R. . Benz . W. . Bouchy . F. . Coffinet . A. . Collier Cameron . A. . Deleuil . M. . Figueira . P. . Gillon . M. . Lo Curto . G. . Mayor . M. . Mordasini . C. . Motalebi . F. . Moutou . C. . Pollacco . D. . Pompei . E. . Queloz . D. . Santos . N. . Wyttenbach . A. . 1 . Astronomy and Astrophysics . 585 . A134 . 2016 . 1510.06446 . 2016A&A...585A.134D . 10.1051/0004-6361/201526729 . 118531921 .
  15. Web site: Mercury Fact Sheet. NASA Goddard Space Flight Center . November 30, 2007 . 2008-11-12.
  16. Mercury orbits at approx. 0.39 AU
  17. Barnes. Rory. January 13, 2009. The HD 40307 Planetary System: Super-Earths or Mini-Neptunes?. The Astrophysical Journal. 0901.1698. 2009ApJ...695.1006B . 10.1088/0004-637X/695/2/1006. Jackson. Brian. Raymond. Sean N.. West. Andrew A.. Greenberg. Richard. 695. 2. 1006–1011 . 18849636.

External links

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