alan4908

NGC4725 is the brightest member of a galaxy group in the constellation Coma Berenices and is about 40million light years distant and 130,000 light years in diameter. The structure is somewhat unusual, consisting of just one spiral arm which is tightly wound around the core and can be followed for about 1.5 revolutions. The spiral arm consists of dust and gases including bright blue stars and pinkish Ha regions which indicate star forming regions. Towards the center, much older, yellow stars can be seen. The galaxy is classified as a Seyfert Galaxy, indicating that the center contains a supermassive black hole. The smaller galaxy on the right side is NGC4712 is within the galaxy group but is at the much greater distance of about 200million light years. The LRGB image below represents 12 hours integration time and was taken with my Esprit 150.

SH2-115 is a faint emission nebula in the Cygnus constellation about 7500 light years distant. It is normally imaged in narrowband, however, since I prefer natural looking colours, I went for a LRGB composition with an Ha blend into the red and lum channels. The image below represents about 17 hours and was taken with my Esprit 150. I encountered an interesting challenge in the processing stage of the above image in that I discovered that I had also acquired high levels of scattered light from an out of field star. These rays appeared in all the Lum, Red and Green subframes. Having analysed the likely candidates in the direction of the rays, led me to the conclusion that the most likely cause was the star Deneb, reflecting off some surface in my scope. I occasionally encounter this problem, but this was extreme, presumably due to the very high relative brightness of Deneb compared to the nebula. On the good news side, the scattered light was not evident in the Ha captured by my 3nm filter and was only just visible in the red data. So, after Pixsinsight and PS manipulation, I think I've managed to reduce this effect to acceptable levels.

My first attempt at NGC3718 which lies at a distance of about 49 million light years from Earth. It's a very unusually looking galaxy, featuring a twisted dust lane in the central region. To the right you can also see the companion galaxy NGC3729 which, occurring to radio measurements, appears to be interacting with its larger partner. At the top of the image, Hickson 56 can be seen, a grouping of five small galaxies that are estimated to be about 390 million light years away. The LRGB image represents just under 16 hours and was taken with my Esprit 150.

Located in the constellation Bootes, approximately 52000 light years from Earth, lies the globular cluster NGC 5466. It is designated as a class XII cluster, meaning that it has relatively non-concentrated stars towards the core compared to a class I cluster. This last fact starting me wondering if my scope would be able to resolve the "gaps" in the central core...... note also the various background galaxies. The LRGB image below was taken with my Esprit 150 and represents just over 9 hours integration time.

My first attempt at the Tadpole Nebula (IC410). Located in the Auriga constellation, the nebula is about 12000 light years distant and is approx 100 light years across. The red tadpole like objects are believed to be about 10 light years across and consist of dust and gas that have been shaped by stellar winds. The nebula also contains an open cluster (NGC1893) that contains newly born stars that are estimated to be only 4 million years old (in the center of the image and a little to the right). Since I prefer natural looking colours, on the acquisition side, I decided to go for an LRGB image with the details enhanced with some narrowband Ha data. The image was taken with my Esprit 150 and represents 16 hours integration time.

The open cluster M37 contains almost 2000 stars and is spread across 20 light years. Most of the stars are young blue/white but it also contains red giant orange suns which provide considerable colour contrast. I first imaged M37 a couple of years ago but I decided to add to the data since I was never entirely happy about the quality of the some of the sub-frames. I also decided to try out some of my newly learnt stellar processing techniques to improve the data which I describe below for anyone that might be interested. Since I often image in non-ideal conditions, I sometimes find that the red stacked channel has a larger FWHM values than the blue or green channels, if I combine this data to obtain an RGB image. the result is a red fringe around the stars. For blue stars, this is particularly apparent and creates magenta halos. This time, I decided to shrink the red channel via a ring mask using PI's erosion filter. The ring mask protects the star core, minimizing damage and core dimming. The main issue is generating a good ring mask which captures the majority of the red fringing. After watching one of the Adam Block's Pixinsight's tutorials ( https://adamblockstudios.com/) on how to de-emphase stars, I decided to apply a technique he recommends. Basically, you first create a star mask which includes all the stars and all the halos. This mask should be white across the star and halo and slightly feathered around the edges. Having done this, you then subtract from this the Red channel lum information to create the ring mask. The reason this creates an accurate ring mask is that the lum data contains accurate information on how the light profile various from the stars center. So, for example, at the stars core, the star mask will be close to 1 (in PI everything is normalised to 1), whilst the lum information will also be close to 1, so if you subtract one from the other you end up with something that is close to 0 (eg black) at the core. Thus, at the core you will be protecting the star's core almost 100%. Outside of the star mask (eg outside of the halos) you will have 0, whilst in the lum channel you might have 0.2 (say representing a non-stellar structure), if you subtract 0.2 from 0 you get 0, since you cannot have negative values in PI, so outside the star mask the ring mask will be 0 eg black. Within the halo, the ring mask will mimic the stars halo hence generating an accurate ring mask. The LRGB image below was taken with my Esprit 150 and represents just over 15 hours integration time.