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Observations of the Local Group of Galaxies

IC 10

IC 10 was discovered during the 1890's by Lewis Smith. It was included in the list of nebulae found at the Warner Observatory. Dreyer describes it in the IC catalog of 1895 as "faint star involved in extreamely faint and very large nebula". Though the galaxy was photographed in 1915 it was 20 years later when the galaxies extragalatic nature was revealed by N.U. Mayal.

Hubble considered it a possible local group member as it showed resolution on the plates. But It's place was not secured unitl the 1960's when Morton Roberts in 1962 and Gerard de Vaucouleurs and H.Ables in 1965 determined the galaxies radial velocity and estimated its distance. In the paper "Integrated Magnitudes and colour indices of IC 10" de Vaucouleurs said: "The hight degree of resolution and large size of the HII regions suggest that it is a member of the local group". He also suggested that: "If it were not so heavily obscured, IC 10 would appear as one of the brightest galaxies in the sky and it's over-all optical diameter could be as much as 10'.

IC 10 at this time seems to be going through a period of starburst (see photos below). Parts of the galaxy are very rich in Wolf-Rayet stars which are combined with OB star associations, implying a high star formation rate. Over 140 HII regions have been detected in IC 10. For a galaxy it's size IC 10 as a hihg density of Wolf-Rayet stars. Using the brightest Wolf-Rayet stars as standard candles and compairing them to the LMC stars a distance has been estimated to be 870kpc. The distance to the galaxy has also been estimated using the cepheid variables. The distance value derived was 830kpc.

Observations of variables in the galaxy have revealed a star similar in light curve and in periods to normal cepheid's but are found among the red supergiants. These stars are now being observed in other dawrf galaxies of the local group. The stellar population of IC 10 is very similar to the LMC.

Infrared observations of IC 10 has shown two distinct star froming regions in the central part of the galaxy.

A study of the distribution of HI in IC 10 has shown that the galxy has an extended halo of HI which is interacting with the disc of the galaxy. The distribution of the HI clouds thru the galaxy is dominated by holes and shells created by the intense stellar winds associated with the Wolf-Rayet stars. In fact these stellar wins may be resposible for the new phase of star formation. Estimates of the mass of the HI in the galaxy IC 10 total 270 million solar masses.

The latest observational data show that IC 10 may actually be a Blue compact dwarf and not an Irregular dwarf. The observations show that the galaxy has a high amout of internal reddening due to dust in the galaxy. Once the reddening due to the Milky way is taken into account the galaxy shows many charastics in commom with Blue compatc dwarfs. This idea is consistant with the fact that IC 10 is going through a starburst period which began about 10 million years ago.

I am unable to observe the galaxy from Australia so I have use some of the observations found on the IAAC site. If anyone has any trouble with my using their observing notes please contact me.

Steve Coe observing from Arizona USA using a 13.5" ƒ/5.6 scope

I picked out IC 10 from a dark Arizona site with my 13" ƒ/5.6 but it was tough. I said it was: extremely faint, pretty large, elongated 2X1 in PA 90 with a somewhat brighter middle. At 100X it grows with averted vision. It is in a very rich starfield and there is an 11th mag star on the western tip of the galaxy.

Yann Pothier observing from France with a 17.5" ƒ/4.5

Description: tough target= medium size galaxy extremely faint; irregularly shaped, it has ill defined edges and appears homogeneous; a brighter part about 1.8'x1.4' E-W (PA90/270) includes a mag13 star and 2 mag15 others; a fainter area is extending to the NNW (PA150) and amkes about 2.2x1.6' NE-SO and includes a mag14 star and 2 of mag15; a 8' line of 8 faint stars (mag14-15) crosses the NNW fainter part in a WSW-ENE axis; a triangle of mag12 stars is to be found at 12'SW; UHC and OII filters are somewhat enhancing the overall contrast (without details), because of the numerous HII regions this galaxy shows, but a larger scope (or a better sky) could focus on which part of the galaxy it enhances exactly.

N.J.Martin observing from Scotland using a 20" ƒ/4.4

Description:- IC 10 apears as a faint oval patch of light centred around a faint star. It is best seen by wobbling or moving the telescope. There is a brighter bar like central part, which is the most easily observed part of this difficult object. Finding it. As illustrated in Daivid Eicher's book Galaxies and the universe (p.13). There is a brighter star fairly close to the location of the galaxy with a dog leg line of five brighter than background stars with a sixth froming a right angle triangle at the end of the line.The galaxy is just at the end of the line and the brighter bar runs roughly parallell to the right angle side of the triangle.

Steve Dillinger observing from Colorado USA using a 20" ƒ/3.95

The galaxy was faint and diffuse appearing oval in shape. It has a faint star in the center and several others surrounding the galaxy.

Photos and Maps

Photo from the DSS

H-Alpha image of the Local Group irregular galaxy IC 10 as imaged with the Hubble Space Telescope (HST). This is a mosaic of the four CCDs. (Funded by NASA through grant GO-06406.01-A.)
F555W (=V) image of IC 10 as imaged with HST. This is a mosaic of the four CCDs that make up the WFPC2. (Funded by NASA through grant GO-06406.01-A.)

False-color combination of three images of IC 10 taken with the HST: Red is Halpha, green is F814W (=I), and blue is F555W (=V). This is a mosaic of the four WFPC2 CCDs. (Funded by NASA through grant GO-06423.01-A.)
False-color combination of three images of IC 10 taken with the HST: Red is Halpha, green is F814W (=I), and blue is F555W (=V). This is the WF4 CCD image (bottom, right of the image above). (Funded by NASA through grant GO-06423.01-A.)

H-Alpha image of the Local Group irregular galaxy IC 10 as imaged with the Hubble Space Telescope (HST). This is a mosaic of the four CCDs. (Funded by NASA through grant GO-06406.01-A.)	F555W (=V) image of IC 10 as imaged with HST. This is a mosaic of the four CCDs that make up the WFPC2. (Funded by NASA through grant GO-06406.01-A.)
False-color combination of three images of IC 10 taken with the HST: Red is Halpha, green is F814W (=I), and blue is F555W (=V). This is a mosaic of the four WFPC2 CCDs. (Funded by NASA through grant GO-06423.01-A.)	False-color combination of three images of IC 10 taken with the HST: Red is Halpha, green is F814W (=I), and blue is F555W (=V). This is the WF4 CCD image (bottom, right of the image above). (Funded by NASA through grant GO-06423.01-A.)