Teegarden's Star
Red dwarfs are by far the most common stars with a share of 75%, but they are difficult to observe because of their low absolute brightness. Indeed, there are only a few
specimens close enough to the Sun to be observed visually with amateur telescopes. The situation with brown dwarfs is even worse - to my knowledge there is not a single
object in the northern firmament that is within the range of telescopes of 50cm aperture.
An exception to this could be "Teegarden's Star". With 0.08 solar masses its mass is just at the border to brown dwarfs. It is officially listed as a red dwarf star, but it could
be possible that it is really a brown dwarf. The absolute brightness of "Teegarden's Star" is only M=17.2mag and with a surface temperature of just 2,370°C it belongs to
the coolest stars which can be observed visually in the sky. Accordingly it belongs to the spectral class M7.0. With a diameter of 180,000 kilometers it is only 35,000
kilometers larger than the planet Jupiter and is orbited at a distance of 4 and 7 million kilometers by two planets, which with a mass of a little more than one earth mass
belong to the group of super earths.
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The observation of "Teegardens Star" in my 50cm telescope was not as easy as thought, but quite feasible.
The position was found quickly. A small star chain of some 12...13mag bright stars can serve as a guide. Because of the high proper motion of 5.05" per year I had to think
about the actual position of Teegarden's star. But in the eyepiece it was quickly identified, because the surrounding field is quite poor in equally bright stars. At 270x it was
a faint point of light with indirect vision. The red color was unfortunately not visible due to the apparent brightness of less than 15mag.
But that doesn't matter either. Just the thought of seeing an extremely low mass red dwarf or possibly even a brown dwarf with my own eyes was totally exciting and thrilling.
