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Figure 6.

z = 0.97. From the deepest late-time observations, they

The mass of Wolf 940b is probably between 20 and

infer evidence for an optical jet break and a luminous

30 times that of Jupiter. This places it directly in the

supernova. The object was measured to be as bright as

regime of “brown dwarfs”–objects that are too large

J ~ 4.5 by the PAIRITEL 1.3-meter telescope.

to be considered planets but are too small (and cool)

Rest frame comparison of the most luminous optical/infrared probes of the distant universe, showing the absolute magnitude vs. time of GRB 080319B, of the most luminous QSO known, and of supernova SN 2006gy, one of the most energetic supernovae recorded (From Bloom, et al. 2009, ApJ 691, 723-737).

to be classified as stars. With a surface temperature of approximately 570K Wolf 940b is the coolest brown dwarf measured to date. Burningham says that free floating objects with temperatures similar to this have been suspected before, but this is the first time he and his team were able to confirm it. The fact that it is orbiting a star makes it extra special. Due to such low surface temperatures, objects like Wolf 940b do not emit much visible light. However, they glow brightly in the infrared. Because of its infrared glow, Wolf 940b was initially discovered as part of the UKIRT Infrared Deep Sky Survey (UKIDSS), a large survey project being carried out at the United Kingdom Infrared Telescope (UKIRT) on Mauna Kea. The object was found as part of a wider effort to discover and characterize the least luminous objects in the solar neighborhood. When its proper motion revealed it as

This event was absolutely extraordinary. For 30

a companion to Wolf 940 follow-up observations to

minutes in the rest frame, GRB 080319B was brighter

determine its nature were initialized.

than the brightest known quasi-stellar object (QSO)

Figure 7.

NIRI spectrum (black line) compared to models of a cool brown dwarf atmosphere with different temperatures and effective gravities. In addition to the JHK spectroscopy, L-band photometry (with error bar) from NIRI is shown as the dark blue line between 3.4 – 4.2 microns (μm).

in the universe (Figure 6). At z = 0.17, the distance of the nearest GRB with a typical luminosity, this event would peak at R ~ 1 magnitude, nearly as bright as the brightest star in the sky. The authors estimate that such events could be detected out to very high redshifts and would remain visible even if placed well into the epoch of reionization. If an event such as GRB 080319B were to occur in own galaxy, at a distance of one kiloparsec (around 3,200 light-years), the optical flash would peak at magnitude about -28.5, several times the brightness of the Sun. Spectroscopy using the Near-infrared Imager and

A Cool Dwarf in Aquarius

Spectrometer (NIRI) on Gemini North allowed the team to determine the surface temperature of

An international team led by Ben Burningham

this record-setting brown dwarf (see Figure 7). By

(University of Hertfordshire) has discovered a brown

comparing the data collected by Gemini to complex

dwarf that will likely set the record as the coolest body

atmospheric models, the team was able to assign a

ever detected outside our solar system. The object,

surface temperature and a spectral type of T8.5 to the

named Wolf 940b, and its companion star, a red dwarf


named Wolf 940, lie in the constellation Aquarius at a distance of about 40 light-years from Earth. Wolf 940b

This object is going to continue to provide insights

orbits its star at a distance of around 440 astronomical

into the processes of cool brown dwarfs and warm

units, more than ten times farther out than Neptune

planetary atmospheres for some time to come, and

orbits the Sun. At this distance, it takes Wolf 940b

finding it was just the first step.

approximately 18,000 years to complete a single orbit.



Issue 38 - June 2009