Article Summary #3

A Young Planetary-mass Object in the the ρ Oph Cloud Core

Kenneth A. Marsh et al 2010 ApJ 709 L158-L162
http://www.iop.org/EJ/abstract/2041-8205/709/2/L158/

Stellar clouds are very distant high-density cloud structures where stars are born. A very small object has been found in the ρ Oph cloud core. Cases of planetary-sized objects existing in clusters have been observed before and they are generally only white dwarfs with masses about 13 times that of Jupiter and less.

The big mystery related to the formation of such objects is through what mechanism can there be enough cooling inside a very hot region like a stellar cloud that such a dense and compact object could form (i.e. in order for gravity to overcome the high gas pressure due to the high temperature, strong cooling is needed).

Looking at the near-infrared spectrum, the colors indicate the presence of a low-mass brown dwarf. The region is also very young and it has a high rate of low-mass star formation. Marsh et al. 2010 looked at this cloud also because it is closer than most similar clouds, so the detections are better.

The observational data is in the form of spectroscopic images and it comes from the Two Micron All Sky Survey (2MASS) and from Spitzer IRAC (Infrared Array Camera). The selection was done for brown dwarfs with a relatively low temperature (<2000K) and the objects were found by looking at the K-band continuum images.

The data was fitted with a photospheric model to a grid of synthetic spectra. The spectral morphology is what shows that the brown dwarf is an early T spectral type star, characteristic that is determined from its temperature. It is possible that it might be the youngest star and least massive T-dwarf found so far.