Nov 25 2009
The "Laboratorio de Astrofísica Estelar y Exoplanetas", part of the Center of Astrobiology (INTA-CSIC), and led by David Barrado, presents the discovery of the best proto brown dwarf candidate found so far, in collaboration with several internationl research centers.
Brown dwarfs are sometimes called "failed stars". They are born from interstellar clouds following processes closely related to the formation of normal stars. But brown dwarfs lack mass enough to light up nuclear reactions in their interiors. Thus, they cannot be considered true stars and in fact some properties reassemble those shown by giant planets. Uncovering proto-brown dwarfs, i.e., brown dwarfs in their very first evolutionary stages, is a long-sought hit. A recent study has found the best proto-brown dwarf candidate known to date.
The first brown dwarfs were discovered in 1995. A lot has been learned about them since that date, but the formation mechanism (or mechanisms) is a hotly debated issue. The processes leading to the birth of a brown dwarf are, no doubt, related to those forming normal stars, but many details are lacking. Stars and brown dwarfs evolve very rapidly during their first stages, what makes quite difficult to catch them in the very process of birth. This challenge is even more difficult due to the fact that extremely young objects are still embedded into the gas and dust clouds from which they condense. This is the "Class 0/I stage", in the classical evolutionary scheme of young stellar objects.
A recent international study leaded by David Barrado y Navascués (LAEX-CAB, INTA-CSIC) has identified the best proto-brown dwarf candidate known to date. Their search begun analysing data obtained with the Spitzer infra-red space telescope. They were looking for low-luminosity bodies (dimmer than one tenth of the solar energy output) still embedded within dense nebular cores. A preliminary list of candidates resulted from this search. As stated by Barrado y Navascués, "we acknowledge the fact that we are exploring uncharted water, and that the contamination by extragalactic sources and very extincted stars can mimic the properties of a potential sub-stellar object". For this reason they "carried out an exhaustive follow-up at different spectral ranges".
The multi-band analysis was carried out retrieving data from public data bases and, also, making new observations at different observatories. Spitzer, 2MASS and CFHT archive data were used, and observing campaigns were performed with the IRAM 30m radiotelescope (Granada, Spain), ESO's Very Large Telescope (Chile), Caltech Submillimetre Observatory (Hawaii, USA), Very Large Array (New Mexico, USA) and Calar Alto Observatory (Almería, Spain). The starting point of the work was data acquired with the Spitzer Space Telescope. Based on these data, the team selected a very faint and red object with mid-infrarred excess, a signpost of youth. Calar Alto data were obtained in 2007 with the Zeiss 3.5 m telescope equipped with Omega 2000 infrared camera. According to the researchers "CAHA data were key to confirm the nature of the object", by providing near-infrared high spatial resolution imaging, that turned out to be the best proto-brown dwarf candidate yet known.
This object, known as SSTB213 J041757, is placed in Taurus constellation, inside the dark cloud Barnard 213, at a distance of 450 light-years (140 parsecs). CAHA imaging has shown that it is a double object, with both components being compatible with the status of Class I proto-brown dwarfs.
Some conclusions can be drawn from this work. In relation to the formation mechanism, the researchers state that "if the source is really associated with a proto-brown dwarf, our observations strongly suggest that it was not formed through the ejection scenario, but rather in a similar way to low-mass stars".
More observations and work will be needed to find more proto-brown dwarf candidates, and to definitely clarify the nature of these first examples. No doubt this research team will offer new and exciting results in this field, in a near future.