Researchers from NPF studied brown dwarfs formation process

A group of international astronomers, lead by researchers from the Millenium Nucleus of Planet Formation, carried out a detailed study of a brown dwarf orbiting a binary system. This allowed them to infer properties of the unknown formation process of these objects.

Lead by the PhD student from the NPF, Alejandro Santamaría-Miranda, a group of experts studied with the highest detail to date a sub-stellar object orbiting a binary system, which allowed them to make progress in the research of their formation process. Within this group, Matthias R.  Schreiber, sub-director of the Nucleus and thesis supervisor of Santamaría-Miranda, stands out, along with NPF director Amelia Bayo and the M. Sc. Student Aurora Aguayo. This work was published in the prestigious scientific journal Monthly Notices of the Royal Astronomical Society, MNRAS.

“How these objects form is still not entirely clear to date, but there are several theories. The latest results point out that in principle, they could form as an escalated version of very low-mass stars”, explains Alejandro Santamaría-Miranda, who is also a PhD student from the Faculty of Sciences of Universidad de Valparaíso, and is currently doing an internship at the European Southern Observatory, ESO.

To study this process, the researchers took spectra – that cover near ultraviolet to near infrared, including the visible wavelength – of the brown dwarf SR 12 C, using an instrument called X-Shooter, installed in the ESO VLT, in Chile.

SR 12 C orbits the binary system SR 12 AV, formed by two stars that have masses similar to that of the Sun. The distance between the brown dwarf and the central system is greater than 1000 AU, which allowed the astronomers to study its spectrum without suffering from contamination coming from the presence of nearby objects.

One of the results of the research was that SR 12 C is accreting matter. “This means that it is still in the process of formation, and therefore there is material in the form of gas that is falling towards the object”, comments Santamaría-Miranda. Moreover, the student explains that this accretion rate was compared to other isolated brown dwarfs, and also to other low-mass stars, concluding that all of them are more or less similar. This is a useful result to calibrate theoretical models about the formation of these objects.

From these results, the authors concluded that the whole system formed as a triple one, and that SR 12 C must have been previously ejected to the position in which it is now. Nevertheless, Santamaría- Miranda stresses that it is necessary to study other similar objects to reaffirm these conclusions.


Image: Kuzuhara et al. 2011, figure 1.

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