DENIS 1048-39

DENIS 1048-39 was discovered in 2000 by Xavier Delfosse (Institute of Astrophysics of the Canary Islands, now Observatoire de Grenoble) and Thierry Forveille (Canada-France-Hawaii Telescope Corporation), with the assistance of nine other astronomers (see the University of Hawaii's Institute for Astronomy news release of 11/21/00). It was found in images collected by the Deep Near-Infrared Survey (DENIS), which is mapping the southern sky with a one-meter telescope at the European Southern Observatory. The object's unusual spectrum was confirmed by Eduardo L. Martin using the 10-meter Keck I telescope (Delfosse et al, 2001).

University of Hawaii's Institute for Astronomy -- larger image
(Apparent motion of DENIS 1048-39 over time -- 11/21/00 press release)

Jean Guibert and Francoise Crifo of the Observatory of Paris used three photographic plates of the object to ascertain that it had moved considerably between 1975 and 1999 indicating its proximity to Sol, with a large proper motion of 1.5 arcseconds per year. The astronomers estimated a distance of about 13 light-years (ly), by relying on comparisons with objects that have similar characteristics (e.g., spectral type), but this estimate will probably change as more is learned about the object. In 2005, a more precise distance estimate of 13.2 +/- 0.1 ly for a star of spectral type M8.5 V was reported by RECONS (Jao et al, 2005).

Robert Hurt, IPAC, NASA

Larger illustration: Sol; M,L,T dwarfs;
and Jupiter.

At one billion years in age, large brown
dwarfs are reddish like the smallest
M-type stars, but cooler, dimmer T-dwarfs
are more magenta in hue (more).

The Object

DENIS 1048-39 (also DENIS 1048-3956 or DENIS-P J104814.7-395606.1) is probably a young brown dwarf (spectral type M7.5) that is less than 20 million years old (Chris Koen, 2010), rather than a very cool and dim, main sequence red dwarf (M8.5 V). It has a surface temperature of only 2,200° Kelvin and only about six to nine percent of Sol's mass, near the 0.075 Solar mass limit for core thermonuclear fusion of hydrogen. The object radiates emits only 0.00015 percent as much visible light as Sol and so look dimmer than the full Moon from Earth if it replaced the Sun in the Solar System Ken Croswell, 2005. Eduardo L. Martin (University of Hawaii) analyzed the object with the Keck I Observatory but failed to detect lithium, a signature of all but the largest brown dwarfs. Hence, the object could be a very low-mass star (75-90 Jupiter masses) or a high-mass brown dwarf (60-75 Jupiter masses). The object spins at 27 kilometers per second (or over 16 miles per second), which would be very fast for a M-type dwarf star. In January 2003, two astronomers (Mary E. Putman and Adam J. Burgasser) reported that quiescent emission and two spectacular radio flares had been detected from the object (AAS 203th Meeting session abstract).

© Anglo-Australian Telescope Board
(Image by Chris Tinney)



Wide field image with satellite trail.



True color image of the brown dwarf
binary DENIS 1228-1547 (more).

Brown Dwarfs or Planets?

When brown dwarfs were just a theoretical concern, astronomers differentiated those hypothetical objects from planets by how they were formed. If a substellar object was formed the way a star does, from a collapsing cloud of interstellar gas and dust, then it would be called a brown dwarf. If it was formed by gradually accumulating gas and dust inside a star's circumstellar disk, however, it was called a planet. Once the first brown dwarf candidates were actually found, however, astronomers realized that it was actually quite difficult to definitely rule on the validity of competing hypotheses about how a substellar object was actually formed without having been there. This problem is particularly difficult to resolve in the case of stellar companions, objects that orbit a star -- or two.

© American Scientist



Artwork by Linda Huff
(for Martin et al, 1997)
used with permission.

University of California at Berkeley astronomer Ben R. Oppenheimer, who helped to discover a nearby brown dwarf, Gliese 229 b, is part of a growing group that would like to define a brown dwarf as an substellar object with the mass of 13 to 80 (or so) Jupiters. While these objects cannot fuse "ordinary" hydrogen (a single proton nucleus) like stars, they have enough mass to briefly fuse deuterium (hydrogen with a proton-neutron nucleus). Therefore, stellar companions with less than 13 Jupiter masses would be defined as planets.

© Estate of John Whatmough
(Artwork from Extrasolar Visions, used with permission from Whatmough)
The brown dwarf companion to Gliese 229 -- with its own dark satellite,
as imagined by Whatmough

Other prominent astronomers, such as San Francisco State University astronomer Geoffrey W. Marcy who also has helped to discover many extrasolar planets, note that there may in fact be many different physical processes that lead to the formation of planets. Similarly, there may also be many different processes that lead to the creation of brown dwarfs, and some of these may also lead to planets. Hence, more observational data may be needed before astronomers can determine how to make justifiable distinctions in the classification of such substellar objects.

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