ngc 2768 and ngc 2742 in Ursa Major

[wimvb]

A lenticular galaxy (ngc 2768) and a spiral galaxy (ngc 2742, or ngc 2816). One which is all but dead (as far as star creation goes), and one which is very active.

Both these galaxies are located in Ursa Major, at a distance of 65 - 70 million light years.

Towards the left there are two colliding galaxies, pgc 25980 and pgc 25982. These are only small galaxies, they are closer to us than ngc 2768 / ngc 2742.

Also in the field are numerous background galaxies. In fact, most of the reddish "gnats" are galaxies and not stars. There are so many, that I have only indicated the galaxy clusters to which they belong. These galaxies are between 2.5 and 5.5 billion light years away.

What peaked my interest was a small blue dot at the top of the image. According to Simbad, this is a Seyfert 1 galaxy. It has a red shift of 0.763, which puts it at a (Hubble-) distance of 10 billion light years. Despite this large red shift, the light that we receive is still in the blue part of the optical spectrum. This means that the light that is transmitted lies well within the UV part of the spectrum.

Technical details:

16 hours and 48 minutes exposures with Ha and RGB filters under a 67% moon (on average), using the SkyWatcher 190MN and ZWO ASI294MM

[Stargazer33]

Lovely detail in 2742! The bright star nearby has been controlled very well too.

[wimvb]

8 hours ago, Stargazer33 said:

Lovely detail in 2742! The bright star nearby has been controlled very well too.

Thanks, Bryan. Star control in galaxy images is always a bit tricky. Star removal and then reinsertion destroys the very small, redshifted background galaxies, and usually isn't an option. Most of the time I just reduce only the largest stars with a star mask and careful erosion.

[Rodd]

Beautiful.  Background is Devine. It feels like I am peering out a spaceport window. 

[wimvb]

4 hours ago, Rodd said:

Beautiful.  Background is Devine.

Thank you, Rodd. I don't know if it's devine, but I have a computer screen that is absolutely unforgiving; it shows every small blemish. Even images by a well known astrophotographer and YouTuber can show an unflattering background sometimes.

[Adreneline]

Nice image Wim and interesting write up - as always.

Looking at your image at 1:1 what is causing this to happen to the stars on the r.h.s.?

The l.h.s. of the image shows nothing similar.

Adrian

[wimvb]

4 hours ago, Adreneline said:

Nice image Wim and interesting write up - as always.

Looking at your image at 1:1 what is causing this to happen to the stars on the r.h.s.?

The l.h.s. of the image shows nothing similar.

Adrian

Thanks, Adrian. I'm not sure about the exact cause. At first I suspected the focuser extension tube. But since I have more vignetting at the same side, I now suspect that it's caused by the edge of the secondary mirror. Light that hits that edge is diffracted, and that could cause such a flare. Collimation is otherwise very good, as slightly defocused stars show round, symmetrical doughnuts across most of the field. 

When astro season ends by the end of the month, I will try to get to the bottom of this, but for now, I live with it.

[Adreneline]

4 hours ago, wimvb said:

Thanks, Adrian. I'm not sure about the exact cause. At first I suspected the focuser extension tube. But since I have more vignetting at the same side, I now suspect that it's caused by the edge of the secondary mirror. Light that hits that edge is diffracted, and that could cause such a flare. Collimation is otherwise very good, as slightly defocused stars show round, symmetrical doughnuts across most of the field. 

When astro season ends by the end of the month, I will try to get to the bottom of this, but for now, I live with it.

These things are so frustrating to track down so I wish you good luck in finding the source of the problem; whatever it does not detract from the excellent image.

Adrian

[wimvb]

2 hours ago, Adreneline said:

whatever it does not detract

My thoughts too.

Thanks.