Supernova Searching

Supernova searching is an activity I started in 2010 and ramped up in 2011 after a good bit of discussion with experienced amateurs such as Peter Marples from the BOSS team (Backyard Observatory Supernova Search). The type of supernova searching I am referring to here is taking images of galaxies and blinking those images to see if a supernova has appeared since the last image was taken. Supernova searching was a natural progression from my previous “Project NGC” where I imaged over 2500 NGC objects, doing 10 x 30 second exposures of each object. The Supernova search was nearly identical except only taking 1 x 30 second exposure for each galaxy, and the selection criteria on what objects to image was refined for supernova candidate galaxies rather than NGC objects. I have now increased the exposure time to 60 seconds, still sticking to one exposure per galaxy.

A typical night of Supernova Searching

A night of supernova searching typically goes something like this. At some time prior to the night I will prepare a CCD Commander script file containing all the instructions for the night (instructions such as: cool camera, focus on a mag ~6.5 star every hour, move to and photograph each galaxy, and then at the end of the night take reduction frames and shut down the equipment). Around sunset time I will turn on the equipment, open the roof and start the script running. Timing is not critical as the script will have commands to wait until appropriate times to cool the camera and then another time for starting the focusing and imaging, once it is dark. If the script is already built getting the setup running is a 3 minute job. I then leave the telescope to run overnight. In the morning I will close the roof, turn off the equipment and start the image reduction and pressing running before I leave for work. I then need to blink the images to detect any changes. Sometimes I fit this in before work, or while on the train to work, or some time later at home, but either way this is the most time consuming task and sometimes hard to achieve in an appropriate timeframe. I am keen to automate this last detection/analysis phase.

Selecting Candidate Galaxies

The selection process for candidate galaxies is interesting. I initially had over 96,000 galaxies in my list of candidates but (partly thanks to Peter’s advise) quickly realised there were several criteria such as declination, magnitude, apparent size and type of galaxy that make narrowing this a must. The need to blink images the next day meant that blinking 500 per night is quite an arduous task and so narrowing the list is a requirement. In general my scripts contain galaxies matching these criteria:

  • -30 degrees south through -85 degrees south
  • Magnitude 15 or brighter
  • Major axis being 1 arc minutes or larger

Building Automation Scripts

Building of the script has often been a time consuming process, but has now been refined to a set of pre-prepared scripts, one for each RA on the night sky. There is a set number of galaxies that can be photographed every hour to keep the telescope in the perfect area of the sky (one RA hour east of the meridian). For my current setup this works out to 38 objects per hour. So, the script file for each RA starts with a focus on a star, then has 38 move-to and image command sets. At the moment it is always the same 38 galaxies I image in each RA. My best images of each object I retain as a reference image to blink future images of that object against.

[Picture: SN – action list sample – startup.jpg] Caption: A small snippet showing an example of the start of a night’s script.
[Picture: SN – action list sample – take image.jpg] Caption: For each RA in the script it slews and takes images.

Processing and Blinking Supernova Images

Having a set of galaxy images from a night the images must be processed and then blinked. For supernova images where I am only capturing one image of each object the processing done is to reduce Dark, Bias and Flat frames from the Light frames. This is done using CCDSoft’s reduction facility. To blink the images they must first be named appropriately. Ordinarily an acquired image would be named such as “IC_1615.00014421.IC_1615.REDUCED.FIT” and needs to be renamed to match the name of the reference image. I have a custom built little application which runs through the night’s images renaming them “IC 1615.FIT” for this purpose. Once renamed, the images can easily be blinked using various software packages. I have found Maxim DL’s supernova plugin the best, and only requires you to buy the cheaper Maxim DL suite. Given the directory of reference images and directory of new images it will let you simply click a next button to move through the blinking pairs of images (no pun intended!). Blinking 500 images takes me a little while. If I am able to take time over this it is very enjoyable to see what interesting galaxies have been photographed. There’s usually something new, as the RA move overhead throughout the year. Looking through the varied and unique galaxies often takes me back to days flicking through books such as the “Colour Atlas of Galaxies” from the 80’s.

Software used for Supernova Searching

I use a combination of software for the Supernova searching, I will try to summarise it here as the list is a good starting point for anyone interested. TheSky6 control the telescope and is where I extract galaxy data from. It has a “Data Query Wizard” which makes it easy to extract in your chosen format a list of objects such as galaxies. TPoint is used with TheSky6 to control the telescope. CCDSoft is used to control the camera and filter wheel. FocusMax together with RoboFocus is used to control the focus motor (attached to a JMI NGF-C). CCD Commander ties all of the above together as an automation/scripting engine, controlling each component of the setup through the above software packages. Maxim DL with a Supernova Blink plugin is used for blinking. On top of this I have several custom built MS Access databases and Visual Basic 6 applications I have written to aid the automation – things like refining the list of objects and exporting a list for the night, and reducing taken images, grouping them in to sub-folders and renaming image files ready for blinking.

Supernova Searching is a Team Sport

An aspect of supernova searching I enjoy is being involved with others who are actively hunting also. Through the BOSS team I am finding more and more that there are regular alerts of candidate galaxies requiring urgent imaging for confirmation, and the like. This adds excitement, and the team aspect adds significantly to the process also. There is plenty of room for others to become involved, especially locally where in WA we are uniquely positioned compared to the eastern states participants who often suffer similar weather conditions at the same and inconvenient times.

Where to from here…

While I have had many tens of nights of supernova runs I am still in the “ramping up” phase, still refining the list of galaxies selected, building up my reference image library (for blink comparison), and working out what is achievable. The only galaxy I have imaged with a supernova so far, was, believe it or not, the very first I tried – NGC 1954. I thought “I’ll just check it out in case” and blow me down a supernova had been discovered in it only a short time earlier!

[image: NGC 1954 supernova]. the way the odds are, it will be a long time before I discover my own supernova, if ever.

[Picture of NGC 1954 with supernova: ngc1954.jpg] Caption: NGC 1954 with supernova 2010ko.