Category: Galaxy

Long time readers of this blog will know that from time to time I’ve used remote telescopes for imaging. On occasion, it may be the only way to photograph a particular target e.g. southern hemisphere, or it may provide access to equipment that is out of reach financially or just wouldn’t be practicable to implement at home. I know that this causes problems for some amateur astronomers who may feel that you can’t take ownership of an image if you can’t claim every stage of the process as your own, including actual possession of the equipment used. I take a wider view in that, provided you have identified the sources used, no one is being misled as to the provenance of the images. The individual astronomer still has an input in the collation and presentation of the data.

While attending a meeting of the Webb Society at the Cambridge Institute of Astronomy my eye was caught by one of the pictures on display, an image of a gravitational lens. Such objects were predicted by Albert Einstein and are formed when light from a distant object is bent (or lensed) by gravity around a massive foreground object. In this case the foreground object is a Luminous Red Galaxy (LRG 3-757) and the source is a star forming galaxy. The ring has a diameter of 10″, the LRG has a redshift of 0.44 (or 4.5 billion light years) and the source galaxy has a redshift of 2.379 (10.8 billion light years). Both components are approximately magnitude 20. For anyone interested in the detail the Astrophysical Journal paper is available here. Once home, I did some initial research on this object and went looking for images.

Some time ago I’d become aware of the Hubble Legacy Archive but not had the time to take a detailed look at it. A recent Sky & Telescope article by Robert Gendler rekindled my interest and having found the RA and DEC coordinates for LRG 3-757 I entered them into the search engine on the site (http://hla.stsci.edu). This returned a list of images in the archive for this object and three looked suitable for a colour image; 475nm, 606nm & 814nm corresponding to blue, green and red wavelengths.

Downloading this dataset took some time (each image was 300MB) and each was stretched in FITS Liberator before colour combining using Maxim DL. Once the colour balance looked roughly right I exported the tiff file into Photoshop for fine tuning and noise reduction.

The result is here:

Is this the ultimate in remote imaging? Well, I’ve finally got access to a telescope that’s unaffected by clouds and atmosphere & cost billions of dollars to build, commission and service. It seems a waste not to make full use of it.

I found this galaxy in Sue French’s wonderful Deep Sky Wonders book while looking for a suitable target for the 20″. With the summer twilight we didn’t get started on it until after midnight and got 15 1 minute exposures. Of these, 6 were rejected due either to car headlights or star trailing so the result could use a lot more exposure.

What atracted my attention was that it’s an edge on spiral (as opposed to the Virgo cluster’s usual ellipticals}, it’s fairly bright and it’s also large at 11′ long.

The sharp eyed will notice that the picture’s identification is NGC 4437. This galaxy appears to have two designations.

I finally figured what I was doing wrong with the colour and here’s the final result. In a nutshell, auto-background equalisation coupled with too much contribution from the red channel was resulting in some pretty strange effects.

The Sombrero is never well placed from the UK and only gets to about 25 degreees elevation at the Breckland observatory.

Having just got back from the Kelling Heath star party I would normally be processing images taken there. The weather for the event this spring didn’t co-operate though so while we still had a great trip the actual astronomy time was zero.

So it’s back to an image I took with Dan on the 20″ last sunday of M104. I’m having real trouble adding the colour into this image so while I struggle with that here’s the luminance frames.

Frames: 30x 30 seconds
Bin: 2×2

Galaxy clusters are amongst the largest structures in the observable universe. Local clusters include the Local Group (including the Milky Way and Andromeda galaxies), the M81 group (11 million light years), M101 group (24 million light years) and Virgo Cluster (65 million light years).

Rather further away is the Abell 2065 cluster which is somewhere between 1 and 1.5 billion light years away and located in the constellation Corona Borealis. With the exception of a sprinkling of bright foreground stars most of the objects in this image are galaxies with the brightest members a diminutive magnitude 16.5.

This image is a stack of 10 1 minute exposure on the 20″ taken with the Atik 383L.

Despite a bright moon in the sky last night I was determined to take some images using my QHY9C on the 20″. Things didn’t go exactly to plan and I had some difficulties with guiding; mainly loss of guide star which I put down to some thin, high cloud. To eliminate other effects I slewed to a nearly bright star to see if I could actually guide on anything.

With the SBIG STV producing 26K ADU, Diadem in Coma Berenices at Mag 4.32 provided a good target and guided nicely while I took several 1 minute exposures. After stacking I noticed a faint object near to the star and loaded the image into Aladin (http://aladin.u-strasbg.fr/aladin.gml) to identify it.  The NASA/IPAC Extragalactic Database (NED)  provided a name, KUG 1308+178 and some basic details: Spiral galaxy, Magnitude 16.5, major diameter 0.4′, minor diameter 0.2′.

Other images of this galaxy are few and far between but I did find one taken on the Palomar 48-inch Schmidt in 1950.

The 20″ was working well on Tuesday evening with both tracking and guiding doing a good job of keeping the stars round. Out of 41 images of NGC 891 I only threw 2 away where the stars were less round.

Due to the high altitude of the target exposures were kept short at 30 seconds and binned 2×2. Guide exposures on the STV were 1.5 seconds with the aggressiveness turned down to 70%.

Overall dimentions are 13.1′ x 2.8′ and the dust lane is showing some detail in this picture.

Whilst at the Kelling star party I had a talk with Bernard from Modern Astronomy about cameras and specifically the Kodak KAF-8300 chipped models. I’d been thinking about a single shot colour for the astrotrac setup and the QHY9 looked a good match for a very good price. I placed an order and delivery was via Fedex within 2 days.

I’d had the idea in my head that the cooled colour CCD camera would be a low noise, high sensitivity version of the DSLRs I’ve been using but some test shots revealed that this isn’t entirely true. Initial pictures were a little disappointing and it wasn’t until I was reading an article on setting the offset and gain levels for the camera (http://www.stark-labs.com/blog/files/GainAndOffset.php#unique-entry-id-6) that the pieces fitted together and illumination dawned.

You can get surprisingly good pictures with short exposures on DSLRs by increasing the ISO rating. This is effectively increasing the gain and it’s not a free lunch. Noise is amplified as well and dynamic range is reduced. With the CCD, once you’ve calculated the optimal gain you set it and never alter it again. This level will be a lot lower than the DSLRs value and correspondingly longer exposures are required to fully exploit the increased dynamic range available.

With my Zenithstar 70mm, Astrotrac mounted on a Manfrotto tripod I’m currently limited to 5 minute exposures without trailing so I picked a bright target for a test. M31 is ideally placed for this at the moment and here’s the result resized to about half the original.

12x 5 minute exposures

Zenithstar 70mm

William Optic FFIII field flattener

Friday night was the first opportunity I’ve had to take some pictures of this. Thursday night was also clear but I was busy imaging comet Garradd again, this time passing close to the Coathanger cluster.

Using the club’s ATIK on the 20″ we took 41 30 second exposures binned 3×3 and also 3 each of red, green and blue binned 6×6. This really wasn’t enough colour frames and after a lot of effort I gave up trying to get a colour image and just stacked the luminance frames.

Sn2011fe is a type 1a supernova a mere 21 million light years away.