More Starless Lions!

I'm experimenting with a new tool--Starxterminator. It does a much better job of removing stars than StarNet. Here are a few starless Lion Nebulas to add to the collection :)

 

The Crescent Nebula (NGC 6888)

 The Crescent Nebula's distinctive shape is sculpted by the fast stellar winds from Wolf-Rayet Star WR 136 smashing into the slower moving wind ejected from the star when it was in its red giant phase. The nebula was first observed in 1792 by William Herschel. The images below were created from a total of 90 minutes of exposure with a RASA 8, DS10C and NBZ filter. The starless version was created by Starxterminator.

Gamma Cygni Starless-Another Cut

Here is another starless version of the Gamma Cygni Nebula using the excellent Starxterminator tool. It's a distinct improvement on the (admittedly free) Starnet tool. I'm very pleased with this result.

The Gamma Cygni Nebula

 The Gamma Cygni Nebula--also known as IC 1318, is an extensive cloud of gas and dust close to the star Deneb in the constellation Cygnus. The most prominent star in the nebula is Gamma Cygni, or Sadr, to give it its proper name. The nebula is part of a much larger nebula complex that includes the Butterfly Nebula and the Crescent Nebula.

The images below were taken with the RASA 8 and DS10C camera, with NBZ filter. They are a stack of 50 second integrations, for a total of about 100 minutes. I have included both starred and starless versions of the nebula.

M27 Reprocessed

 I use Siril for stacking images and for steps such as initial histogram adjustment and photometric calibration. Since updating to the latest version, I have noticed that using the Asinh Transformation in the package produces oversaturated and unbalanced images. The image of M27 I posted earlier used this processing step. I decided to reprocess the image stack, skipping the Asinh Transformation. That image is below, followed by the original image. I think the new image shows more detail and is significantly more "natural" looking than the first image. I may play around more with the Asinh function, but for now, I'm leaving it out of my processing workflow.

Processing offers so many options and choices. I've followed these two images with others, just to show a few of the almost infinite number of alternative processing choices there are. It's knowing where to stop that is the difficulty...

The North America Nebula

 The North America Nebula was first observed by William Herschel in 1786. It was catalogued in 1829 by his son, John Herschel. In 1829, Max Wolf took a long exposure photograph of the nebula, noticed its distinctive shape, and named it the North America Nebula.

In 1922, Edwin Hubble proposed that the gas of the nebula was ionized by ultraviolet radiation from the star Deneb. However, it was subsequently discovered that Deneb is not hot enough (Deneb has a surface temperature of 8,500 K, the ionization of the nebula requires a star with a 30,000 K surface temperature. Subsequent work revealed that the star was hidden by the dark central cloud between the North America and Pelican nebulas--L935. Infrared studies indicated the catalogued star, J205551.3+435225 (surface temperature 40,000 K), was responsible for energizing both the North America and Pelican nebulas.

The image of the North America Nebula below consists of about 90 minutes of data captured by a RASA 8, Mallincam DS10C and NBZ filter under Bortle 8/9 skies.

Herbig-Haro Objects in the Pelican Nebula

 Adjacent to the North America Nebula, the Pelican Nebula (IC 5070 and 5067) is a region of active star formation. Of particular interest are several Herbig-Haro objects, which are bright patches of nebulosity associated with newborn stars. Herbig-Haro objects are formed when narrow jets of partially-ionized gas collide with adjacent clouds of gas and dust at speeds of several hundred kilometers an hour.

Images if the Pelican showing these objects typically take more than 10 hours of integration time. I was surprised to see them emerge clearly in the 90-minute total exposure I captured last evening.

The images below are all crops of the Nebula captured with the RASA 8 and DS10C camera.

The images below show: the full scale image of the Pelican and environs; a crop of that image showing more detail of the nebula, and a monochrome image with the Herbig-Haro objects labeled. HH 555 is the most prominent and, if you look closely, you can see the jet shooting out of each side of the tip.

The Lion Nebula

Virtually all the images captured by astrophotographers have scientific value. DSO pictures may be pretty, but they also enable us to see all kinds of things, from the way matter clumps in clouds, to the Bok Globules in which stars are born. Where does science stop and art begin? Are they complimentary, or exclusive?

In this regard, I’ve always felt a little guilty about making starless images. In many cases they look wonderful, but they are a distortion of the original image—information has been subtracted.

Last night, I imaged the Lion Nebula for about 90 minutes, and I combined this data with data from a year ago—again, about 90 minutes of integration time. The result was a fairly decent image of the nebula. But the Lion is in a densely starred region, and the stars made the subtle structures of the nebula hard to see.

Using Starnet GUI, I removed the stars and was astonished at the level of detail revealed. In this case, an “artistic” change enabled the perception of underlying scientific data, including the delicate swirls and eddies of the cloud and the dark condensations where stars are developing.

Here are 3 images—the starless Lion, a severe crop of that frame showing how well the data is preserved by the DS10C camera, and the original, starry image. Click to zoom—the 10C does an impressive job!

The Cygnus Wall Complex

The Cygnus Wall (sometimes called the Waterfall Complex) is a 20 light-year long star forming region in the North America Nebula. Stellar winds sculpt the complex shape of the nebula. This is a cropped image taken with the RASA 8 and DS10C with NBZ filter. The total integration time was 115 minutes of 30-second individual integrations. 

Two Lobster Claws (Sh2-157) and Bubbles (NGC 7635)

 This area of sky is an interesting one for widefield imaging. The RASA 8 did a nice job of capturing some of the interesting DSOs in this area. The images below are an interesting comparison. The first is a 1.7 hour integration (25 second individual frames) processed and with noise reduction applied. For the second image, I added year old data from my last picture on the nebula, for a total of 3.7 hours of integration time (cropped differently due to framing differences in the imaging runs). I processed this image using a similar workflow, but with no noise reduction. I present them for comparison purposes. Is 90 minutes or so integration time the sweet spot, or is the subtle improvement in the second image worth the extra time?

Messier 27

 Messier 27, also known as the Dumbbell Nebula or the Apple Core Nebula, is a bright, planetary nebula. Planetary nebulas form from material ejected from a star at the end of its life, which form a cloud surrounding the white dwarf that remains. It is a bright object visually, and is an easy object for beginning astro imagers. This image is a combination of 200 x 25s individual images, taken with a RASA 8 and a Mallincam DS10C with NBZ filter. Clouds rolled in during imaging, and, although they presented challenges to guiding, M27 was clearly visible and I continued imaging. I'm pleased I was able to capture the subtle nebulosity surrounding the main object, but I'm disappointed at how "blown out" the core appears (and the problem does not appear to be correctable). If I get the opportunity, I will retry with shorter exposure times. The image is heavily cropped from the original frame.