Friday, July 10, 2015

Identification of a Young Planetary-Mass Brown Dwarf

Young, planetary-mass brown dwarfs provide a good proxy for the study of gas giant planets around stars because these objects exist in isolation and are not overwhelmed by the glare of a parent star. Brown dwarfs cool as they age. As a result, young brown dwarfs are hotter and more luminous, making them easier to observe. Brown dwarfs are identified by the spectral types - M, L, T and Y, in order of decreasing effective temperature. The spectral type of a brown dwarf changes as it cools. More massive brown dwarfs take longer to cool.

Planetary-mass brown dwarfs that are younger than ~120 million years old are expected to be T dwarfs (i.e. T-type spectral class). These objects, if located in the Sun's neighbourhood (i.e. nearer than ~65 light years away) are bright enough to be studied by next generation observatories such as the James Webb Space Telescope (JWST) and the Giant Magellan Telescope (GMT). So far, only one isolated planetary-mass T dwarf candidate is known. This object is identified as CFBDSIR J214947.2-040308.9 and it is estimated to have between 4 to 7 times the mass of Jupiter.

Gagné et al. (2015) present the discovery of SDSS J111010.01+011613.1 (hereafter SDSS J1110+0116), a young, planetary-mass T dwarf. Measurements indicate that SDSS J1110+0116 is located at a distance of roughly 60 light years and it is a member of the AB Doradus moving group - a group of objects that formed in the same natal cluster and have since dispersed. J1110+0116 is estimated to have roughly 10 to 12 times the mass and 1.18 ± 0.02 times the radius of Jupiter. The mass of J1110+0116 is well in the planetary-mass regime. J1110+0116 is a young object with an estimated age of only 110 to 130 million years old. It is still glowing hot from the heat acquired during its formation and its effective temperature is estimated to be 940 ± 20 K.

Gagné et al. (2015), "SDSS J111010.01+011613.1: A New Planetary-Mass T Dwarf Member of the AB Doradus Moving Group", arXiv:1506.04195 [astro-ph.SR