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Post Info TOPIC: 2MASS J16262034+3925190


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The Oldest Brown Dwarf: 2MASS 1626+3925
The halo of our Galaxy contains the oldest stars in our home stellar system. These stars are characterised for having considerably fewer metals (in astronomers parlance metals are elements heavier than hydrogen and helium) than our Sun and, also, than most of the stars that populate the Galactic disk. Stars in the Galactic halo represent the second generation of stars formed in our universe, so they are witnesses of a time more than 10 billion years ago, long before our own Solar System had formed. Although we are placed in the Galactic disk, stars from the halo cross the disk (usually at high velocities) and a certain number of them can be found in our immediate neighbourhood.

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Metalpoor and very dim stars are remnants of the early formation history of the Milky Way. Due to their low mass and luminosity, measurements of their physical properties put constrains on theories of the formation of such stars.
However, to derive these properties measuring their true distance is essential. A direct method to measure distances is called "trigonometric parallax measurement". Since Earth moves around the Sun the point of view at the sky is changing. For this reason, stars which are not too far away seem to follow an elliptical path on the sky relative to the far-away galaxies of the Universe. The size of such ellipses is a measure for the distance.

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The Oldest Brown Dwarf
Most of the halo stars previously known are members of stellar aggregates called globular clusters. Recently, however, large deep sky surveys have improved our knowledge on old halo stars living outside those clusters. Halo stars with masses from 10 times to only a few tenths of the mass of our Sun have been detected, proving that the product of star formation 10 billion years ago was not substantially different from the product of ongoing star formation in the Galaxy.
But what about the least massive and coolest stars, those at the border of the brown dwarf regime? And, was the universe producing brown dwarfs, or "failed stars", 10 billion years ago, when it had only one fifth of its current age?

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