Planetary Nebula- NGC 7026


This is a view in the Cygnus, the swan, constellation. The view here is almost 9*9 arc minutes, 3.5 times smaller than the full moon in the sky. This is the field of view of Celestron C14 telescope and SBIG ST9XE CCD camera; TCF focuser and a SBIG CFW8 filter wheel is placed in between them.

At one o clock in the image, there is a seemingly double star like object with some very faint nebulosity around it. Let me introduce:

Friends meet dead star.. dead star meet friends!

NGC 7026 is the closest astronomers could get to name it as poetically as they could (NGC stands for 'New General Catalogue'). This designation is of a star who died a thousand or a bit more years ago (exact date is uncertain) and lost its out layers into the interstellar space. These objects are called 'Planetary Nebulae'. The gas a star loses in its last stage of its death, keeps on becoming thinner and harder to see and in about 10,000 years or so, it becomes invisible mixing up with the interstellar medium.

The location of NGC 7026 is already in a bad place for us to observe. It is in the milkyway (most Planetary Nebula (PN) are because there the most stars live) so light loss (interstellar extinction) must be happening severely. And talk about my beloved city, Lahore, where i reach my sky-limit even before i open the telescope! (okay... that is not so true.. it takes a few minutes). When it comes to deep sky imaging, i am up against all the odds. But nevertheless, i did try to image this PN with a luminance filter. It has two bright lobes, very bright.. so capturing the nebulosity in the surroundings seemed harder. With a few test exposures, i settled on 4 minutes of sub-exposures. It seemed to give me enough light for capturing the nebulosity and not overexposing the bright lobes, i did however got a little bit of bloom in the neighboring star but that was not an issue for me.

Two nights and a total of 4.8 hours of luminance data. Calibrated carefully with a lot of Bias, Dark and Flat frames. Here is the magnified and resized image of this PN:

This PN has a complex lobed structure and many studies have shown a lot of intricate pattern in the nebulosity. See here and here and this talks about the central star in NGC 7026.

I found an image from H D Curtis of Shapley-Curtis Great Debate fame; this image is some 100 years old. Now compare it with my image:

okay so my image is not so clear.. remember: i live in Lahore!

So after a 100 years, we must expect some changes in the nebula's extending nebulosity... hmm.. what has changed here.. want to take a minute to compare?

Maxim DL provides a nice tool in 'Graph Window', called 'Area Plot'. This shows a 3D view of a particular user selected area in terms of brightness indication and the location.

See the two bright lobes are peaking in the intensity, changing colour from blue (sky background which is supposed to be dark but here the value is in a few thousands!) to red the brightest. Notice the nebulosity is also visible as small bumps in the background sky. Actually the dimmest nebulosity here in my image is just about 1.3 times the brightness of the background sky. Yes i was using LP filter, Hutech LPS2.

What else can i do with this image? hmm.. oh yes.. let's measure the size of this PN. So my image scale with my current setup is 1.045 arcseconds per pixel. I again used Maxim DL to show me the size of the nebulosity in pixel counts.

The line graph shown the intensity at each individual pixel and the total pixels the line has covered. They are about 40. So the line is covering 40 * 1.045 = 41.8 arcseconds.

If the distance of the nebula is 2000 parsac then using the ABC formula in astronomy, the small angle formula, the size of the nebula is 1.3 light years, which is a typical size of a planetary nebula.

Oh and this is what hubble space telescope could image in this PN.