IC 10 - Dwarf Galaxy
In the constellation Cassiopeia three companion galaxies of the large Andromeda galaxy can be found. One of them is an irregular dwarf galaxy with the
designation "IC 10".
Although it was discovered back in 1887, it took until 1935 before its extragalactic nature was confirmed. The reason for this was, that the galaxy is
located only 3° from the galactic plane and therefore the emitted light is significantly reddened and attenuated by foreground dust clouds. So accurate
measurements were difficult. The precise distance of 2.15 million light years was determined in 1996 by measurements of the variable brightness of pulsating
stars (the so called Cepheids). This confirmed the affiliation to the local group, to which also our own Milky Way belongs.
IC 10 is quite small with an extent of only 5,000 light-years, but it has a quite high star formation rate, which makes it the closest starburst galaxy to
us. Every year on average 0.06 solar masses are converted to stars, which means that on average every 15 years a star of the size of our sun is formed.
The new stars are primarily born at the edge of the galaxy, because the interior of IC 10 is meanwhile free of available gas masses. Therefore the many
HII-regions are also found in the outskirts, most of them are only 10 million years old. IC 10 has lots of Wolf-Rayet stars - 5 per square parsec. This
indicates that the dwarf galaxy is very young.
----------------------------------------------------------------------------------------------------------------------------------------------
In less than optimal skies, IC 10 appeared relatively faint with a low surface brightness in my 20 inch f/3.2 Dobsonian. However, it was easy to hold
at a magnification of 200x with averted vision. Some structures were also discernible. First, there is the overall elongated but somewhat irregular shape
with two brighter areas. The brightest part of the dwarf galaxy is near the center and east of a star.
The two HII- regions marked on a DSS printout were extremely faint at 270x, but still could be held steady. The dust lane, on the other hand, was only
indicated. It should be more obvious under better sky conditions.
