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 three 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-gravityatmosphere or an atmosphere with metallicity. The object's small proper motion suggests that it is further away than expected if it were a single field T dwarf.
Discovery
The σ Orionis open cluster has been the focus of Osorio's team observations due to the age of the cluster (approximately 3 to 8 million years). The cluster also has low extinction, 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 magnitudes in the J and H Bands[6] 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
Adam J. Burgasser[9][10] 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 Zapatero-Osorio and Martín 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 of the object suggest that the low gravity was not from the field T dwarf but rather a nearby background star.[9] As of 2009 no direct scientific data have dispelled nor confirmed either conclusion.
It could be the first "free floating" non-stellar planet discovered[5] with a mass of 3 MJ, but needs confirmation.
^Zapatero-Osorio, María Rosa; Béjar, V. J. S.; Bihain, G.; Martín, Eduardo L.; Rebolo, Rafael; Villó-Pérez, I.; Díaz-Sánchez, A.; Pérez Garrido, A.; Caballero, J. A.; Henning, T.; Mundt, R.; Barrado y Navascués, D.; Bailer-Jones, C. A. L. (2008). "New constraints on the membership of the T dwarf S Ori 70 in theσ Orionis cluster". Astronomy & Astrophysics. 477 (3): 895–900. arXiv:0710.2776. Bibcode:2008A&A...477..895Z. doi:10.1051/0004-6361:20078600. S2CID15928749.
^ abPeña Ramírez, K.; Zapatero-Osorio, María Rosa; Béjar, V. J. S.; Martin, Eduardo L.; Rebolo, Rafael; Villo-Perez, I.; Diaz-Sanchez, A.; Perez-Garrido, A.; Caballero, J. A.; Henning, T.; Mundt, R.; Barrado y Navascues, D.; Bailer-Jones, C. A. L. (2015). "Characterization of the known T-type dwarfs towards the σ Orionis cluster". Astronomy and Astrophysics. 574: A118. arXiv:1411.3370. Bibcode:2015A&A...574A.118P. doi:10.1051/0004-6361/201424816. S2CID118498007.
