T Stars: Definition

Even cooler than the L type brown dwarfs with surface temperatures in the range 700º to 1,300º K, type T brown dwarfs would appear as a dark magenta color. Not surprisingly, they have an abundance of Methane in their spectra.

T Stars: Description

It is thought that there may be a huge number of these, and type L dwarfs, that we are unable to see. Their lifetimes tend to be incredibly long, for the light weight dwarfs, so numbers would continue to increase. The first identified was Gliese 229B, which orbits the red dwarf Gliese 229A. Its surface temperature is estimated to be below 1,000º K, and it weighs only about 2% to 5% the mass of the Sun, or about 20 to 50 times the mass of Jupiter. Remember, a candle flame is between 1,350 and 1,650º K or so! Gliese 229B is the smaller object in the image to the right orbiting its larger companion Gliese 229A. They are about 19 light years away.

Another example is the binary pair Epsilon Indi Ba (T1V) & Bb (T6V) which are in orbit around Epsilon Indi itself. Epsilon Indi Ba, the larger of the pair, weighs about 4.5% of the Sun, while it is about 9% the diameter, with a temperature of 1,280K. Epsilon Indi Bb, meanwhile, weighs about 2.7% of the Sun, while it is about 9.6% the diameter, with a surface temperature of only 850K. Both are similar in size to Jupiter, but much heavier and, therefore, denser.

T Stars: Variability/Peculiarity

T Stars: News

Two new brown dwarf solar neighbors discovered

The two new neighbors attracted attention by the contrast between their strong brightness in the infrared and their almost invisible appearance in optical light.

Scientists from the Leibniz Institute for Astrophysics Potsdam (AIP) have discovered two new brown dwarfs at estimated distances of only 15 and 18 light-years from the Sun. For comparison: The next star to the Sun, Proxima, is located slightly more than 4 light-years from the Sun, whereas the nearest known brown dwarfs, Epsilon Indi Ba and Bb, also found at the AIP several years ago, are about 12 light-years away.

Ralf-Dieter Scholz and his AIP colleagues used the recently published data of the NASA satellite WISE (Wide-field Infrared Survey Explorer) for their discovery. The two new solar neighbors, named WISE J0254+0223 and WISE J1741+2553, attracted attention by the extreme contrast between their strong brightness in the infrared and their almost invisible appearance in optical light. In addition, both objects move at comparably fast speed across the sky, i.e., their positions are remarkably different with respect to earlier observations. This was the first hint of their vicinity that was confirmed by the comparison of their colors and magnitudes with those of other objects. The brighter of the two objects was visible in the night sky at the time of its discovery, so that the AIP team could use the Large Binocular Telescope (LBT) in Arizona for determining the spectral type and distance more accurately. Both objects belong to the coolest representatives of T-type brown dwarfs, just at the boundary to the predicted but not yet well-defined class of Y-type ultra-cool brown dwarfs.