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-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s 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 Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...

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-gravity

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

or an atmosphere with

metallicity In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as a ...

. 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

William Herschel Telescope The William Herschel Telescope (WHT) is a optical/near-infrared reflecting telescope located at the Roque de los Muchachos Observatory on the island of La Palma in the Canary Islands, Spain. The telescope, which is named after William Herschel, ...

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 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 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. As of 2009 no direct scientific data have dispelled nor confirmed either conclusion. It could be the first "free floating" non-stellar planet discovered with a mass of 3 M_J, but needs confirmation.

References

{{DEFAULTSORT:S Ori 70 Exoplanets discovered in 2002 Brown dwarfs Orion (constellation) T-type brown dwarfs Rogue planets

Discovery

Argument of the initial study

See also

References