Four October Galaxy Images

Dick Steinberg

10/29/2011

October was not an easy month for astrophotography. The very few clear nights occurred during the brightest lunar phases. Nevertheless, we were able to obtain some new color images with the 12.5" Hyperion astrograph and Apogee U16M camera at the Blue Mountain Vista Observatory.

The first of the October images to be presented are those of three NGC galaxies:

NGC891 is a 10th magnitude galaxy located 3 degrees east of Almach in Andromeda. The prominent dust lane is a dramatic feature of this edge-on spiral.

http://www.physics.drexel.edu/~steinberg/astro2/ngc%20galaxies/ngc891-LRGB-150-50-50-50.jpg

NGC6946 is a 9th magnitude spiral often said to be in Cepheus, but which actually lies astride the Cepheus-Cygnus boundary. It is the site of very active star formation, having hosted at least 9 supernova outbursts in the past century. Although only about 22 Mly distant, its position at low galactic latitude leads to significant absorption and reddening of its light by the interstellar matter of our own Milky Way galaxy. The open cluster fortuitously located 38 arc-min away from NGC6946 in the upper right (NW) corner of the image is the object designated NGC 6939.

http://www.physics.drexel.edu/~steinberg/astro2/ngc%20galaxies/ngc6946-LRGB-115-40-40-35.jpg

NGC7479 is a very nice example of a barred spiral galaxy. It is located in Pegasus, about 3 degrees south of  Markab, the bright star marking the neck of the great flying horse.

http://www.physics.drexel.edu/~steinberg/astro2/ngc%20galaxies/ngc7479-LRGB-105-40-50-50.jpg

The fourth image presented here features NGC206, the richest and brightest open cluster in our neighboring galaxy M31. The brighter stars of this cluster are thought to have an absolute magnitude near -3.6.  If this estimate were correct, at the distance of M31 (thought to be 2.5 Mly or about 800 kpc), the apparent brightness of these stars (relative to their brightness at the standard distance of 10 pc) would be lower by a factor of  (800000/10)^2 or about 6.4 billion, leading to an apparent magnitude of -3.6 + 2.5 log (6.4 billion) or about 21. The easy visibility in the image of the blue supergiants of  NGC206 would then imply that the intrinsic luminosity of these objects is somewhat greater than the estimate.

http://www.physics.drexel.edu/~steinberg/astro2/ngc%20galaxies/ngc206-LRGB-30-10-10-10.jpg

We are hoping soon to process and display data from several other interesting objects of the October data set. Let's hope for clearer skies in November.