S Ori 70

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S Ori J053810.1-023626
Observation data
Epoch J2000      Equinox J2000
Constellation Orion
Right ascension 05h 38m 10.10s[1]
Declination −02° 36′ 00.0″[1]
Apparent magnitude (V) 4.2/5.1/8.79/6.62/6.66
Distance 1,150[2] ly
Spectral type T6[3][4]
Other designations
Mayrit 520267, S Orionis 70, S Ori 70, S Ori J053810.1-023626, S Orionis J053810.1-023626[5][6]
Database references

S Ori 70 or S Ori J053810.1-023626 is a mid-T type astronomical object in the foreground of the σ Orionis cluster, which is approximately 1,150 light-years from Earth. It was discovered on November 24, 2002 by M. R. Zapatero Osorio and E. L. Martin's team at the Roque de los Muchachos Observatory. It has yet to be determined if it is a field brown dwarf or a 3-million-year-old planet that is part of a cluster. Near-infrared spectroscopy images taken 3 years after its discovery led to the first motion measurements for the object. Its behavior is significantly different from what may be expected; it was further described as either a low-gravity atmosphere or an atmosphere with metallicity. The object’s small proper motion suggests that it is farther away than expected if it were a single field T dwarf.


The Sigma Ori open cluster has been the focus of Osorio’s team observations[7] due to the age of the cluster (approximately 3 to 8 million years). The cluster also has few extinctions, its distance is convenient, and it is observed to be rich and dense. Using the 4.2-meter (170-inch) William Herschel Telescope in a pencil-beam deep mini-survey measuring 55 square minutes of arc at a sensitivity of 21 J and H Bands[8] allowed the team to find S Ori 70. The raw data collected was reduced to IRAF (an acronym for Image Reduction and Analysis Facility), a standard technique used with near-infrared images; after subtracting the sky background and dark current, an extracted object spectrum was derived. It was the faintest and coolest member found in the cluster and was named S Ori 70.

Argument of the initial study[edit]

Adam J. Burgasser[9][10][11] examined the claims of Osorio’s T-type brown dwarf discovery and its spectroscopically verified low-mass. A comparison of the J band spectrum between S Ori 70 and other field objects was done. The J band spectrum revealed a distinct triangular-shaped spectral morphology which was previously explained by Osorio and Martin was due to the surface’s low gravity. In order to see if similar discrepancies occurred in the T dwarf's behavior, Burgasser’s team compared data from the claims of Osorio to that of standard COND models. Identical wavelength scales interpolated through both empirical and model spectra were Gaussian smoothed; this showed that best-fit spectral models can yield skewed gravities for late-type field T dwarfs which resulted in the underestimation of age and mass. Burgasser concluded that S Ori 70 is not a member of the Sigma Ori cluster but is rather a foreground field brown dwarf. Further study[12] of the object suggest that the low gravity was not from the field T dwarf but rather a nearby background star. As of 2009 no direct scientific data have dispelled nor confirmed either conclusion.


  1. ^ a b "[BMZ2001] S Ori J053810.1-023626". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 24 March 2017. 
  2. ^ "Mysterious Object Might be First Extrasolar Planet Photographed". Silver Star Academy. Retrieved 2010-02-08. 
  3. ^ "New constraints on the membership of the T dwarf S Ori 70 in the Sigma Orionis cluster". DOI 10.1051/0004-6361:20078600. Retrieved 2010-02-08. 
  4. ^ "Spectroscopic Estimate of Surface Gravity for a Planetary Member in the Orionis Cluster". The Astrophysical Journal, 593:L113-L116, 20 August 2003. Retrieved 2010-02-08. 
  5. ^ "Membership, binarity and accretion among very low mass stars and brown dwarfs of the Sigma Orionis cluster". Kenyon M.J. Retrieved 2010-02-08. 
  6. ^ "Unified Near Infrared Spectral Classification Scheme for T Dwarfs". Burgasser A.J., Geballe T.R., Legget S.K., Kirkpatrick J.D., Golimowski D.A. Retrieved 2010-02-08. 
  7. ^ "S Ori 70, Still a Strong Cluster Planet Candidate" (PDF). E.L. Martin. Retrieved 2010-02-08. 
  8. ^ "OBSERVATIONS AND DATA REDUCTION". The American Astronomical Society. Retrieved 2010-02-08. 
  9. ^ "S Orionis 70: Just a Foreground Field Brown Dwarf?". The Astrophysical Journal, 604:827-831, 1 April 2004. Retrieved 2010-02-08. 
  10. ^ "T dwarfs". MIT.edu. Retrieved 2010-02-08. 
  11. ^ "2MASS Science Publications". Caltech.edu. Retrieved 2010-02-08. 
  12. ^ "S Orionis 70: Just a Foreground Field Brown Dwarf?". Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, CA 90095-1562. Retrieved 2010-02-08.