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TOPIC: Ultracool subdwarf

Blobrana

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Posts: 131433

Date: Jun 14 16:31 2009

RE: Ultracool subdwarfs	Permalink

'Ultracool subdwarf' stars speeding through Milky Way A recently discovered family of peculiar wandering stars may include a visitor from another galaxy, scientists believe. The stars, described as "ultracool subdwarfs" follow very unusual paths around our galaxy, the Milky Way. They have low temperatures and are small enough to be close to planet-like objects. Only a few dozen ultracool subdwarfs, which are up to 10,000 times fainter than the Sun, have been identified. One of the oddest aspects of the stars is the rapid speed at which they travel. They have been clocked at more than a million miles per hour. Unlike the majority of nearby stars, most ultracool subdwarfs spent a lot of time thousands of light years above or below the galactic disc. At least one of the objects - a star designated 2MASS 1227-0447 in the constellation Virgo - has an orbit indicating that it might have originated in another galaxy. Read more Orbit of LSR 1610-0040 Ultracool subdwarf Click to Play \| View Details The animation shows the orbits of the 24 subdwarf stars from 500 million years in the past to 500 million years in the future at a rate of 12 million years per second. The animation includes a passage slowed by one-hundredth that rate through the neighbourhood of the sun. Credit: A. Burgasser, B. Abbott __________________

Blobrana

L

Posts: 131433

Date: Jun 14 16:31 2009

2MASS 1227-0447	Permalink

Title: Optical Spectroscopy of 2MASS Colour-selected Ultracool Subdwarfs Authors: Adam J. Burgasser, Kelle L. Cruz and J. Davy Kirkpatrick We present Gemini GMOS and Magellan LDSS-3 optical spectroscopy for seven ultracool subdwarf candidates colour-selected from the Two Micron All Sky Survey. Five are identified as late-type subdwarfs, including the previously reported sdM9.5 SSSPM 1013-1356 and L subdwarf 2MASS 1626+3925, and a new sdM8.5 2MASS 0142+0523. 2MASS 1640+1231 exhibits spectral features intermediate between a late-type M dwarf and subdwarf, similar to the previously identified high proper motion star SSSPM 1444-2019, and we classify both sources as mild subdwarfs, d/sdM9. 2MASS 1227-0447 is a new ultracool extreme subdwarf, spectral type esdM7.5. Spectral model fits yield metallicities that are consistent with these metallicity classifications. Effective temperatures track with numerical subtype within a metallicity class, although they are not equivalent across metallicity classes. As a first attempt to delineate subtypes in the L subdwarf regime we classify 2MASS 1626+3925 and the previously identified 2MASS 0532+8246 as sdL4 and sdL7, respectively, to reflect their similarity to equivalently classified, solar metallicity L-type field dwarfs over the 7300-9000 Å region. We also detail preliminary criteria for distinguishing L subdwarf optical spectra as a road map for defining this new spectral class. The strong TiO bands and Ca I and Ti I lines in the spectrum of 2MASS 1626+3925 provide further evidence that condensate formation may be inhibited in metal-deficient L subdwarfs. We conclude with a compendium of currently known, optically classified ultracool subdwarfs. Source __________________

Blobrana

L

Posts: 131433

Date: Jun 10 12:08 2009

Ultracool subdwarf	Permalink

Astronomers announced today that stars of a recently discovered type, dubbed ultracool subdwarfs, take some pretty wild rides as they orbit around the Milky Way, following paths that are very different from those of typical stars. One of them may actually be a visitor that originated in another galaxy. Adam Burgasser and John Bochanski of the Massachusetts Institute of Technology presented the findings on Tuesday, June 9, in a press conference at the American Astronomical Society's semi-annual meeting in Pasadena, California. The result clarifies the origins of these peculiar, faint stars, and may provide new details on the types of stars the Milky Way has acquired from other galaxies. Ultracool subdwarf Click to Play \| View Details Ultracool subdwarfs were first recognised as a unique class of stars in 2003, and are distinguished by their low temperatures ("ultracool") and low concentrations of elements other than hydrogen and helium ("subdwarf"). They sit at the bottom end of the size range for stars, and some are so small that they are closer to the planet-like objects called brown dwarfs. Only a few dozen ultracool subdwarfs are known today, as they are both very faint - up to 10,000 times fainter than the Sun - and extremely rare. Read more __________________

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