It’s been about a year and a half now since the 16” scope up at Orion’s Belt saw first light. Now, finally, the very first imaging project with that telescope is completed! The “Bubble” nebula, or NGC 7635, it’s official designation in the “New General Catalog” of deep space objects, is a true bubble in space, about 7000 light years from us in the constellation Cassiopeia! Not science fiction! The bubble is created by “stellar wind” or gas ejected from the upper atmosphere of a very hot centrally located star in the nebula. Surrounding the bubble is a huge cloud of hydrogen gas. Since all of you who have been reading these posts are now experts in spectroscopy 😊 you know that hydrogen gas after it absorbs radiation can then emit that radiation back into space in the “hydrogen alpha” wavelength of light which is the visible red portion of the spectrum.
This data was a total bear to process and I almost bailed on the whole thing when I realized that the bubble was hidden in a dense star field! (see below). We forget how many stars are out there. 250 billion in our galaxy alone! It really seemed to me that they were all congregated right there in one frame. The processing challenge was to somehow remove the stars to bring out the nebulosity. Folks, if you are going to image a nebula in a dense star field my suggestion is to use narrow band filters all the way. I felt I could get the natural color of the nebula using just the hydrogen alpha filter, which is narrow band ( in other words just allows the light in the H alpha region to pass through), but only one channel, combined with the regular band width red-green-blue filters. Problem is the regular band width filters do not filter out the stars! The details of the processing are beyond the scope of this one post but I tried to show the essence of what was done in the images shown here. Star removal is still not a perfect “science”. I have yet to see one method that does a complete job with no artifacts, but the method I used seemed to work pretty well. The software Pixinsight has a number of processes that in combination can achieve the desired result. The “star mask process” can be applied repeatedly to “mask” different sized stars which can then be removed by applying the mask back to the image as a “defect map” (another process) to do the actual removal. Anyway it took weeks of trial and error to get it right enough where the residual artifacts were manageable!
If you click on the thumbnail under “My Astro images” on the right side of this blog (scroll down a bit) you will go to the full resolution version.
This is the Hydrogen alpha version. Notice it is black and white. You have to combine this with one or more other channels for color. The detail in the nebula is able to be detected with this filter since it is only letting the narrow 3nm width of light through in the H alpha region of the spectrum. Most of the star field is filtered out however to achieve the red color you have to combine this with another channel, typically red ,but in my case it was the regular band width red channel which is full of stars!
This is the standard “tricolor” RGB image! This is how we obtain color images in general with astroimaging, combining individual red, green and blue filtered images. Amazing to see how the nebula is really hidden in this image behind all of these stars! Also notice the slightly pink color of the nebula which is from the blue channel
Going through the star removal process for the RGB image above, then combining that with the Hydrogen alpha image (first one above) I was able to get to this workable solution which then had to be tweaked some to arrive at the final result many hours later. I did look at trying to sharpen things up a bit as it does get a little soft at full res, but that wasn’t possible due to the processing artifact in the background. Overall I think this was a decent salvage effort!
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After a fairly long course of gremlin battling (since October of last year!) I finally completed a full automated imaging project. Note this is “automated” but not “remote”, meaning I still have to go up there to turn everything on but once that’s done I can go back to the base house to do everything else. That’s the first step. Once we can do that fairly reliably, the next step is total remote operation off site. A lot to do before that!
Still trying to figure out guiding issues with CCD autopilot but we did get this done. It was a relatively short project, just over 7 hours and only 1 channel, Hydrogen alpha ,but a very interesting area that I had not visited before! SH2 249 is an emission nebula visible in the constellation Gemini. Currently March through May/June is really galaxy season and our equipment is not particularly suitable for that…yet! So this was a good initial target. Stewart Sharpless (Hence the designation ‘SH’) back in 1959 published a catalog of HII regions. What is an HII region? Here is the explanation (from Wikipedia):”An H II region or HII region is a region of interstellar atomic hydrogen that is ionized. (H is the chemical symbol for hydrogen, and “II” is the Roman numeral for 2. It is customary in astronomy to use the Roman numeral I for neutral atoms, II for singly-ionised—H II is H+ in other sciences—III for doubly-ionised, e.g. O III is O++, etc. H II, or H+, consists of free protons.) It is typically a cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds of light years, and density from a few to about a million particles per cubic cm. The short-lived blue stars created in these regions emit copious amounts of ultraviolet light that ionize the surrounding gas. H II regions—sometimes several hundred light-years across—are often associated with giant molecular clouds.” Probably the most famous of these is the Orion nebula, but there are many many others! This is one I discovered, never imaged before, designated SH2 249. The object to the upper right has been called by astronomers the “Jellyfish nebula” for obvious reasons. Equipment used is shown here. Right now we have a Tak 130 NFB refractor, SBIG STXL 6303 camera with self guiding filter wheel. 29 exposures with a hydrogen alpha filter, each 15 minutes long.
First operating platform from the new observatory. Takahashi TOA 130 NFB, Moonlite “Nitecrawler” focuser-rotator, SBIG STXL 6303E camera, Paramount MEII mount
HII region in the constellation Gemini (see text above). Taken with 5nm H-alpha filter. March 2017. Orion’s Belt Remote Observatory. See the images link in the right panel for full resolution version!
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Orion the Hunter arrives heralding the start of Winter in the northern hemisphere. He brings with him a host of glorious star-forming regions of our galaxy. Finally I believe I can complete an imaging project on the popular Horsehead nebula which I have been trying for years now. Back on the east coast Orion is fairly low on the horizon and the Horsehead is at the lower end of Orion’s belt so not a particularly favorable target. Here in the Southwest it is better positioned. I have been able to finally test my 3nm HA (hydrogen alpha) filter! It’s a perfect target for that with the broad emission nebula behind the dust.
Constellation Orion which dominates the winter sky in the northern hemisphere. Arrow points to the approximate location of the Horsehead nebula
Single 15 min raw image of the Horsehead taken with SBIG6303E and Astrodon 3nm HA filter!