BOSS-Backyard Observatory Supernova Search

Subtitle

            Setting up a Search

Supernova search set up:

Over 20 years ago I read a book about SN called the Supernova Search Charts,  written by Gregg Thompson and James Bryant jr. This book has introduced me to SN and how to observe them. Way back then it was mostly a visual search, CCD cameras and robotic searching were many years away. My interest remained when I purchased a Meade LX200 goto telescope and a Sbig ST7 camera. I was now able to image SN and I did image many previously discovered SN. This ended up being a very good grounding for the start of my own search. There are many ways to begin a SN search programme and my ideas here are only one way, there will be far better ideas out there and everybody has different ways of setting up a system depending on equipment, software and time available to put into the programme.

One of the main things I found critical when I got started was to have good contacts to help with confirmation images if you are clouded out and it is also great to talk over any issues that may arise during your search and it is “fun” to share your discoveries and help with other peoples discoveries. You will find that most people that do similar work are more than happy to help you as everybody knows how hard it is to get a discovery and likes to see people have success.

 

First of all let’s get the numbers right.

If you are considering starting a search then a quote from the book, Supernovae And How To Observe Them written by Martin Mobberley maybe an insight - "You don’t have to be a genius to work out that to discover supernovae you have to be nothing short of obsessed!"

 

You will be imaging thousands upon thousands of galaxies just to find 1 SN. Even if you think you have found something that is when the real fun starts. The new “suspect” could be anything from a cosmic ray hit, hot pixel, variable star,  asteroid  a previously discovered SN or PSN, to a CCD artefact. You have to eliminate all of the above and then and only then you can go to the next step. For every SN I have discovered there would be 10-20 suspects that need to be checked and rechecked either by me or other people if the weather doesn’t allow follow up observations. So there is a lot to do and during this time you also have to control your excitement and focus on what you are doing as time is of the essence, there is also a lot of competition out there.

Some numbers from the searches being done by others -

 

Tim Puckett (one of the largest in the world) ~1 SN every 8000 images (300+ SN)

 

Robert Evens ~ 1 SN every 4000 observations (47 SN)

 

Peter Marples  ~ 1 SN per 5000 images (8 SN)

 

Me ~ 1 SN every 2800 images (57 SN)

 

Equipment needed

 

Mount

To do this amount of observations you need a good mount a really good mount. Even though you won’t be doing a lot of long exposures you will wear out a poor mount really quickly and you need the accuracy that mostly high end mounds provide.

I purchased a Paramount ME robotic mount which is ideal for the job. I t is a very good quality mount that will last for years and years doing 1000s of slews and imaging. Peter Marples uses a Meade LX200R mounted on altaz which he has had success with and Greg Bock used a Losmandy G11 mount.

 

Telescope:

If we are looking for faint 14-18mag stars you need a light bucket and these days they are easily available for a good price. I use a Celestron 14 inch others use Meade 12 and 14 inch scopes one guy I know uses a Celestron 9.25 and has discovered 2 SN. Optics are the key here don’t get a poor quality scope, the better it is the fainter magnitude you will be able to get to while imaging.

 

 Stu Parkers Paramount ME with a Celestron 14" Telescope

 

Shed:

It is very advisable to have a permanent set up for the simple reason that it is far quicker and you can start imaging at a moments notice without the need of tedious setting up and carrying a heavy telescope outside. I do however know of portable setups that work ok but if possible it is highly recommended to have a housed telescope.

 

Small observing shed with a roll back roof

Camera

There many cameras that can be used for SN hunting depending on what your budget is and personal preference is.

I use a Sbig ST8me and a SbigST10  ccd cameras and use different exposures from 30 sec to 1 minute depending if it is good seeing or a new galaxy that I am imaging.

Other cameras that can be used are Starlight Xpress SXVH9. These are dark current cameras and don’t normally need dark farm subtraction.

I have heard of people using Meade deepsky pro ccd cameras which are cheaper but I feel are not sensitive enough to do the job.

 

Sbig ST10 CCD Camera idea for Supernova search work

Software:

Good software for the job is very important as you have to search 1000s of Galaxies per months. The Sky has always been the planetarium package that advanced amateur astronomers have regarded as “the gold standard” it also uses Orchestrate (a scripting program for automated supernova patrols),

This is where basically you create a galaxy list and have Orchestrate slew to each galaxy through CCDsoft or MaxIm DL and take an image and move on to the next galaxy. This allows large amounts of Galaxies to be imaged each night and each script can be save for use again next times that part of the sky needs to be imaged.

This software is used by most SN hunters however even though I am starting to use Orchestrate currently I am using a programme called CCD Auto Pilot. This allow scripts to be imported and is basically does the same thing as Orchestrate however because I search by constellation I find it gives me more flexibility. It does take longer to set up the scripts. I would think I am the only active SN hunter that uses this software for the scripts for searching galaxies.

I highly recommend using maxIm DL for the blinking of the galaxies you have taken. This is a ccd imaging programme that also has a plug in for supernova searching.

There are people that compare the galaxies by eye however I much prefer Maxim than this how I have discovered all my SN to date. Once going it is very easy to use. There are some other software packages but I have had no success with them. A programme called Grepnova seems to be able to blink a lot of images however I have had little experience with it.

 

Imaging:

You will need a set of reference images to compare your nightly images taken. This library is very important and is constantly changing as you image better ref images and adding galaxies you your lists. I currently have a reference library of about 10000 images. I use the DSS images as reference images until I have take a better image with my own system.

 

Once you are set up and have got your galaxies lists and reference images and you want to start to image there are a couple of things to remember.

It is a good idea to use a focal reducer it simply speeds up you scope so you can take short exposures per galaxy and this also helps with seeing conditions .I am now imaging at F/5.0 not F/10.Imaging at F/10 is not possible very often because of the seeing conditions and the field of view is small so unless you mount is very well set up you images may not be on the ccd chip. Also a wider field of views gives you the chance to image other galaxies in the same field of view increasing the chances of finding a SN.

I normally bin at 1x1 but have used 2x2 and discovered 2 Sn using Bin 2x2.But you have to which your pixel scale using bin 2x2 as the stars can stars to look like hot pixels on good nights of seeing. However the binning 2x2 speeds up the down load and therefore allows more galaxies to be imaged

 

It is also a good idea with Sbig cameras to calibrate Darks and flats it makes the image easier to work with the files when blinking.

Here is an example of a 30 second exposure of IC5231.No processing has been done to this image

 

 

 

A 30 second image of NGC5128

 

Processing images

You have just spent a night collecting images and you want to process them. There are 3 ways of checking them for SN

 

1-     Automated software that checks each image and alerts if there is a suspect. This sounds really good however the software currently can miss a suspect if it is close to the galaxy centre. However this method is used by people that image 1000s of galaxies per night 

2-     Visually  compare each image with a ref image and the image taken

3-     Blink the reference image with the nights image to see if a “new Star”pops into view

 

I use a mixture of both visual and blinking. Here is an example

A New Supernova will look like a new point of light as in the above image.

 

Once you spot something that’s when the fun begins. There are many things that can confuse the issue which must be checked out before any report can be sent to CBAT. Here are some of them.

The new suspect could be the following

 

1-     Hot Pixel

2-     Cosmic ray hit

3-     A known or unknown asteroid in the same field of view

4-     A known or unknown variable star

5-     Photon leaking from previous images from a bright star causing RBI (Residual Bulk Image or Blinker as we at BOSS call them)

6-     Seeing a fainter star that previously hadn't been in your images as the seeing conditions are better

7-     A previously known SN or PSN (Possible SuperNova)

 

All of this has to be checked out if all if this is done and you still think it is a new object then you reimage the galaxy again to make sure it is not an asteroid.

You should image every hour for 2-3 hours to make sure the suspect doesn’t move. While you are doing this you can check the asteroid lists PSN and  SN lists. You should also get someone else to image the galaxy to make sure it is a new object.

Time is critical as if you take too long you can miss out on the discovery if someone else has put in a report before you.

 

Reporting

 

Once you have done all your checks and you have got multiply images you will want to send a report to Dan Green at the Central Bureau for Astronomical Telegrams (CBAT) in Boston, Massachusetts, the world clearinghouse for astronomical discoveries,is not something to be considered unless you are absolutely 110% sure that you have made a discovery.

 

You will need To include in the report:

 

Information You Should Include In A Discovery Report

All discovery reports should include the following:

- your name

- your address and contact details (preferably e-mail address, otherwise telephone/fax number)

- date and UT time of observation

- observation method (e.g., naked eye, visual telescopic observation, photographic, or telescopic CCD)

- specific details on instrumentation (aperture size, f/-ratio, etc.) and exposures (type of film or CCD, length of exposure, etc.)

- observation site (name of location, giving either city/town and state/province/country, or some other geographical name nearby); longitude and latitude and elevation above sea level can be useful.

 DO NOT submit  images in any fashion, because they don’t generally have sufficient staff resources to analyze many such images. If you wish to submit CCD images in support of your discovery claim, please ask first

 

What not to include in your report: any html encoding or any binary text (as with images; They prefer that you place images at your own website and send them the URL).

If you are a new contributor to the CBAT, please provide some background information regarding your observing experience. It is recommended that observations be made of a suspected object more than once -- separated by at least an hour and preferably a day.

. Discovery report submitted without sufficient information will not be acted upon.

 

To Get the precise mag and position we use a piece of software called Astrometrica by Herbert Raab

To measure an image in Astrometrica, what you have to do is load the FITS format image with north at the top, go to “Astrometry/Data Reduction” and click “OK”. The software will then use the FITS RA and Dec information to compare the stars in the image with whatever stars are in the catalogue you have specified for it to look in. It can be a little more tricky than this if the image scale is wrong and the data calalogue  cannot find a match. One of our team members of BOSS is a real wiz at using this software even though I am able to use it I tend to use his measurements as they are more accurate.

 

 

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