PARSEC · Parallaxes of Southern Extremely Cool Objects

Parallaxes of Southern Extremely Cool Objects

Project context and objectives This project studies L and T dwarfs, commonly known as brown dwarfs, which are sub-stellar objects with masses that are intermediate between stars and planets. Theoretically predicted decades ago, the first brown dwarf was recognised as recently as 1995. Their masses range between 13 (the limit for deuterium thermonuclear fusion) and 80 Jupiter masses, and are therefore below the required mass for hydrogen nuclear fusion. Their radii are however nearly invariant, at the Jovian scale. The temperatures start at stellar level and steadily cool to giant planets standards. The release of thermal energy makes brown dwarfs long lived, emitting mostly in the red and infrared. Like stars, brown dwarfs form as gas collapses and heats up within interstellar clouds, but their masses are too low to generate sufficient heat to ignite hydrogen fusion. Without a central energy source, they cool and dim and never reach the gravitational collapse in the stellar final stage. Low mass, low luminosity and low radius make them very difficult to observe. Once observed, an accurate measurement of the distances to these objects is required to derive their luminosities and temperatures. The objective here was to measure the distance of L and T dwarfs by using observations from the ESO 2.2 m telescope between 2007 and 2010. Here we describe the progress made by Dr Andrei over the last two years, which has led to the publication of over 50 new distances. Work performed The areas addressed by Dr Andrei ranged from completion and checking of the observations to developing an image-cleaning pipeline, including the novel treatment of fringes and testing the pipelines. The fellow also developed a new way of looking at faint objects using a variation of the co-addition of many frames. After this development during the first year, Dr Andrei published the first results which included proper motions of all 192 000 field stars, and parallaxes of ten targets. During the second year, the fellow developed and tested various procedures for the determination of parallaxes, and in collaboration with the University of Hertfordshire published another 40 targets, together with spectra. The astrophysical exploitation of these results was then begun and was the centrepiece of various papers co-authored by the fellow. Main results The results were presented at many meetings, including the IAU in China and CoSpar in India. They are also available via the project website. The fellow has returned to Brazil and is continuing with this research. Project website: http://www.parsec.oato.inaf.it

Data: CORDIS, © European Union