CFBDSIR J1458+1013 ab

Davide de Martin,
Digitized Sky Survey-2, ESO





Larger and jumbo images.





Although the brown dwarf binary
is located at the center of this
visible light field image, it is
too faint to be visible (more).

The system was first detected as an ultra-cool object in near infrared as part of the Canada-France Brown Dwarfs Survey - InfraRed. It was originally designated as CFBDSIR J154829+101343. Subsequently, various shorter designations have been used, including: CFBDSIR J1548+1013, CFBDSIR 1458+10, and even CFBDS 1548 in some references (Delorme et al, 2010).

Michael Liu, IFA, LGS, Keck




Larger and jumbo infrared (H-band) images.



The binary system probably has an orbital
period of 20 to 35 years, at a projected
separation of around 2.6 AUs (more).

The binarity of the object was soon determined from images taken in May and December 2010 (Liu et al, 2011). The two substellar objects have a projected separation of around 2.6 +/- 0.3 AUs (0.11") and would have an orbital period of 20 to 35 years if the system is between one and five billion years old (Liu et al, 2011, Table 3). CFBDSIR J1548+1013 "b" is extremely cool, possibly cooler than UGPS-0722-05, but its estimated mass has a large uncertainty and could place it in the realm of Jupiter-class planets -- roughly as cool as WD 0806-661 b (Luhman et al, 2011), another potential Y-dwarf discovered in 2010 (ESO Science release; Liu et al, 2011; Ian O'Neill, Discover, March 9, 2011; and Patrick Morgan, Discover, March 10, 2011).

Brown Dwarf "a"

This substellar object was detected in near infrared as part of the Canada-France Brown Dwarfs Survey - InfraRed (Delorme et al, 2010). The object may have 12 to 42 Jupiter-masses, and it probably has a spectral class of T9.5. Object "a" may be as cool as UGPS-0722-05, if older and higher mass (Liu et al, 2011). CFBDSIR J1458+1013 a probably has an estimated effective temperature of of only 540 to 660 Kelvins (267 to 387 Celsius or 512 to 729 Fahrenheit). Its bolometric luminosity is estimated at only 1.1 +/- 0.4 times 10^-6 of Sol's, and the object is probably one to five billion years old (Liu et al, 2011).

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).

Brown Dwarf or Planet "b"

Substellar object "b" has an estimated mass of only six to 15 Jupiter-masses. It has a bolometric luminosity estimated at only 2.0 +/- 0.9 times 10^-7 of Sol's (Liu et al, 2011). By comparing to evolutionary models and T9-T10 objects, the discovery team estimated an effective temperature of only 370 +/-40 Kelvins (97 Celsius or 206 Fahrenheit) and so may be a member of the proposed "Y" spectral class for brown dwarfs (Kirkpatrick et al, 1999). Atmospheric models predict the presence of clouds of water as well as methane (Liu et al, 2011).

Luis Calçada, ESO



Larger and jumbo illustrations.



Spectral class "Y" brown dwarfs
are even more bluish than T-dwarfs
(from methane absorption of
green and red light) but also
much cooler and so are less
red, and like Jupiter may have
high clouds of water ice (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.

© 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

University of California at Berkeley astronomer Ben R. Oppenheimer, who helped to discover the other 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.

WISE, UC-Boulder,
CalTech, JPL, NASA




Larger composite image.




Large planets and brown dwarfs that have multiples
of Jupiter's mass do not increase in diameter at
the same rate due to gravitational compression,
but they may become redder as they get hotter
and radiate more visible as well as infrared light.

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.

© American Scientist



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