Deep Near-infrared Imaging Of The ρ Oph Cloud Core: Clues To The Origin Of The Lowest-mass Brown Dwarfs

Details Deep Near-infrared Imaging Of The ρ Oph Cloud Core: Clues To The Origin Of The Lowest-mass Brown Dwarfs Deep Near-infrared Imaging Of The ρ Oph Cloud Core: Clues To The Origin Of The Lowest-mass Brown Dwarfs

Jan 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21340602m&link_type=abstract

American Astronomical Society, AAS Meeting #213, #406.02; Bulletin of the American Astronomical Society, Vol. 41, p.198

Astronomy and Astrophysics

Astrophysics

Scientific paper

A search for young substellar objects in the ρ Oph cloud core region has been made with the aid of multiband profile-fitting point-source photometry of the deep-integration Combined Calibration Scan images of the 2MASS extended mission in J, H and K bands, and Spitzer IRAC images at 3.6, 4.5, 5.8 and 8.0 μm. The field of view was 1o x 9.3', and the 5σ limiting magnitude at J was 20.5. Comparison of the observed SEDs with the predictions of the COND and DUSTY models, for an assumed age of 1 Myr, supports the identification of many of the sources with brown dwarfs, and enables the estimation of temperature, T. The brown dwarfs are then readily distinguishable from background stars by their locations on a plot of flux density versus T. The inferred mass function indicates that in this region, low-mass brown dwarfs greatly outnumber normal (hydrogen-burning) stars. Of the former, we have identified 25 methane dwarf candidates with T ≤ 1500 K, and inferred masses of 3 MJ down to 0.6 MJ. In addition, our data show a progressive blueward skew in the distribution of J-H and H-K colors, such that the blue end of the range becomes increasingly bluer with increasing magnitude. This behavior suggests that the faintest sources are seen with the least extinction, consistent with a scenario in which the lowest-mass brown dwarfs (< 0.01 M&sun;) have escaped from their formation sites and are therefore seen nearer to the front edge of the cloud. This result and the form of the mass function are both consistent with the 'ejected stellar embryo' hypothesis which involves fragmentation of a protostellar core and the subsequent ejection of the lowest-mass fragments due to dynamic instability. This work was supported by NASA's Astrophysics Data Analysis Program.

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