NGC 253 'Silver Coin' galaxy in Sculptor (20.7 hours)
The famous galaxy NGC 253, brightest member of the southern Sculptor group. With a visual magnitude of 8.0, it is appears as a long, oval bulge and mottled disk, some 25' x 7' min size (true size of some 70,000 light years across), with complex dust lanes north of the core. It is part of a group of galaxies located 11.4 million light years from the Milky Way, and is viewed by us almost side on spiral (Sc type), giving it the shape of a coin. There is intense starburst activity in its outer arms, and some prominent HII regions, whereas the core is older and redder with a 5 million solar mass black hole at its centre.
The image was captured from my Adelaide surburban backyard, using an Orion ED80T CT apo astrograph (at f/4.8), mounted on an AZ-EQ6. The CCD camera was an Orion StarShoot G3 mono, guided with PHD2 using a think OAG and an ASI120MM-S guide camera. Not much more I can get out of this setup -- it is quite undersampled (4.6 arcsec/pixel), and not ideal for smaller DSOs like this!
The image is composed of the following:
Lum = 62 x 5 min
Ha = 15 x 10 min
R, G & B = 52 x 5 min for each channel
After rejections, this led to a total integration time of 20.7 hours.
I used a synthetic luminance channel by blending an exposure-based weighting of the L, Ha, R, G and B luminances. All subs were unbinned.
Captured over the period 24 Aug to 2 Sept 2014, as weather permitted. Pre-processed with flats (light box), bad pixel map (based on 70 darks) and bias in Nebulosity. Aligned and Drizzled in DSS. Post-processed in StarTools.
Thanks Rick, yes, I'm pretty happy with it. To do better, I really need a longer FL and better image-scale sampling (there is only so much you can drag out of an 80mm refractor and low-rez 'basic' CCD, especially when using them for galaxies!). Still, plenty of time for experimentation.
I have another image of M20 Trifid coming up, using exactly the same setup and about the same integration time. It was captured at the same time (Trifid shots taken in the first hours of the evening, NGC 253 after midnight). But it will take some time to process. After that, I move to my dark sky site and will really start having fun!
Thanks Kevin and Simon. I agree it is surprising how much details can be teased photographically out of an 80mm 'frac via the use of dithering + drizzling. You get resolution of fine structures that should by all rights be impossible to see with this aperture. Almost like magic...
Good image Berry in particular considering the little scope used, you have some nice details of the galaxy. I just find a bit overdone the contrast, I would suggest to reduce it a bit to keep the image more natural..
Marco, I agree re: contrast. One problem I faced in post-processing was elimination of some lighting defects that were not completely removed by the flats. So I 'cheated' a little and forced a slightly darker background than I would have ideally preferred, to hide these. With more work, I may have been able to eliminate these problems more effectively.
