New Objects within 20 light-years

On November 14, 2006, a team of astronomers associated with the Cerro Tololo Inter-American Observatory Parallax Investigation (CTIOPI), a research program of the the Research Consortium on Nearby Stars (RECONS), announced their identification of 20 new stars located within 10 parsecs (pc), or 32.6 light-years (ly), of Sol (NOAO press release; and Henry et al, 2006b). This was an update of a July 2006 announcement (Henry et al, 2006a). While some stars were added to the 10-pc list, other stars and brown dwarfs were found to be farther away than previously measured. One red dwarf star was added to the list of stars within 20 ly. While some stars were added to the 10-pc list, other stars and brown dwarfs were found to be farther away than previously measured.

On August 1, 2006, astronomers (led by Edgardo Costa and Rene Mendez of the Universidad de Chile in Santiago) announced that an extremely dim M8.5 red dwarf should be reclassified as the closest known "L-type" brown dwarf in the Solar neighborhood. Originally discovered in 1999 by in images collected by the Deep Near-Infrared Survey (DENIS), the object was designated as DENIS or DEN 0255-4700, Located around 16.2 light-years (4.97 parsecs) from Sol in Constellation Eridanus (02:55:3.7-47:00:52, 2000), the substellar object is 100 million times dimmer than the Sun with a spectral type of L7.5 V, indicative of a cool object with a surface temperature of only 2,600 degrees F (1700 K). Spectral analysis of the object indicated that it has exotic elements such as potassium, rubidium, and cesium in its outer atmosphere, as well as superheated water (NOAO press release). RECONS has provided a preliminary mass estimate of 0.07 Solar-mass.

© European
Southern
Observatory




Larger
illustration.




A cool methane
brown dwarf has
been discovered
around the recently
discovered, nearby
red dwarf star SCR
1845-6357 (more).

On March 22, 2006, a team of astronomers (including Beth Biller, Laird Close, Markus Kasper, Wolfgang Brandner, and Stephan Kellner) using the European Southern Observatory's Very Large Telescope announced the detection of a cool methane brown dwarf (spectral type "T" 5.5 +/- 1) in orbit around the recently discovered, red dwarf star SCR 1845-6357 (ESO press release; and Biller et al, 2006). The object has between nine and 65 Jupiter-masses and a mean orbital distance of about 4.5 AUs from SCR 1845-6357, which was most recently estimated to be located only 12.6 +/- 0.1 light-years from Sol (Henry et al, 2006b; and Henry et al, 2006a). As of March 2006, SCR 1845-6357 may the 36th closest known star to Sol, while its brown dwarf companion "b" is the third closest known brown dwarf.

In late 2004, astronomers (Niall Deacon, Nigel Hambly, and John Cooke of the University of Edinburgh) analyzing data from the Southern Infrared Proper Motion Survey announced the discovery of an extremely dim red dwarf star (M8 V), designated SIPS 1259-4336, that may be located only 11.8 +/- 1.8 light-years from Sol (Deacon et al, 2005). Given its atypical faintness, however, astronomer Todd Henry (Georgia State University and RECONS) suggests that the star may be actually be farther away, although probably located within 5 parsecs or 16.3 light-years (Ken Croswell, 2004). The star's discoverers proposed that the star's dimness could be explained if it was actually an unresolved double star. In February 2005, astronomer Todd Henry reported that RECONS was able to revise the measurement of the star's visual magnitude to 18.0, about a magnitude brighter than originally estimated (Ken Croswell, 2005). Obtaining a more precise parallax for distance estimation will take a year.