Nova Search Using ImageJ

The following help pages were put together for use with the RBSE "Search for Novae in M31" research project. They were developed by Linda Stefaniak, Allentown High School, Allentown, NJ.

Open ImageJ on your computer. You can choose to maximize the screen. It will look similar to the image on the left.

From the main menu bar across the top of the screen, choose "File".

From the drop down menu choose "Import" and choose "Image Sequence".

Navigate to where your image files are located in the Nova data directory. A window similar to the one on the left will open on your screen. It shows 16 folders corresponding to the 16 subrasters of the M31 project.

For the remainder of this lesson an image sequence using files from subraster 10 will be used.

The image in the example to the left is from subraster 10.

Notice the file names. These will tell you the following information:

m31e01f10.fits
m31 - image of M31, the Andromeda galaxy
e01 - epoch #1
f10 - field or subraster #10

Open ANY one of these files.

The Sequence Options window will open.

Notice the options you can choose:

Number of images: 89 (for example)
Starting Image: 1 (you may choose to create an image sequence beginning with any epoch from 86 through ...?)
Increment: 1 (allows you to skip through epochs and only build a stack with every fifth or even tenth image). Just leave it at 1.

Choose OK.

When your stack has been created it will pop onto your screen looking similar to the image you see here.

Notice that the information along the top line indicates:

1/89 (m31001f10.fits), 512x512 pixels, 16-bit grayscale

This means that this is image 1 of a stack of 89 images beginning with image number 1 of subraster 10. Image size and file size information follows.

There is also a scroll bar along the bottom that can be used to move through the stack a single image at a time.

Working with a Stack

To begin this research project you will need to put together a stack of subraster images. Blinking or animating the stack will make it possible to see where there is an object that becomes visible over the course of the epoch dates. An object that appears and disappears within a stack of subraster images is an object that you might want to investigate.

You may want to adjust the image sequence so it looks like the images in your Finder Charts for M31. This will make it easier to match up stars on the screen with stars in the Finder Charts.

To do this go to "Image" on the ImageJ toolbar.

Choose "Lookup tables" and "Invert LUT".

Go to "Image" on the toolbar, choose "Adjust" and "Brightness/Contrast".

The B&C control panel will appear. Click on the "Auto" button to adjust the image to the default values.

The window to the left shows what the stack will look like at default image values.

By adjusting the Brightness and Contrast you can bring out dimmer objects that may not otherwise be visible in the stack. This is best done by "bumping" the arrows on either end of the Minimum and Maximum control bars. not by dragging them!

Any changes you make in Brightness and Contrast will be applied to every image in the opened stack.

To animate your stack, go to "Image" on the toolbar, choose "Stacks".

Options include:
Start Animation
Stop Animation
Animation Options (which allows you to adjust the speed with which the stack will flip through pictures in frames per second).

You can also choose to move through the stack a single image at a time by clicking on the scrollbar or using the keyboard keys marked "<" and ">".

Finding the Location and Magnitude of a Nova

It is necessary to know the right ascension and declination of your novae. You will also need to find the magnitude of the nova as it changes over the course of time.

		The animation sequence of subraster 10 indicated that there was a nova that first appeared in epoch 40 and continued until epoch 74. The location of that nova is just to the left of center of the circle in the image to the left. To find the location and brightness of this nova you will need to open each image containing the nova separately.
		To do this, choose "File" and "Open". Navigate to the image file for the first epoch containing the nova and open that file. Note: when the image file opens you will need to invert the image and adjust the Brightness and Contrast before beginning. The image to the left shows epoch 40 in subraster 10 before the image has been adjusted.
When the image has been opened and its brightness adjusted, you will need to activate the nova plugins. To do this choose "Plugins" from the menu bar, "Nova" and "Nova Plugins" from the dropdown boxes that appear. A data table will appear to the right of the image. To find the RA and Dec of any star, simply touch it with the mouse and the values will pop up in the coordinates window to the upper right of the image.

		You can now begin to measure the magnitudes of your nova. Keep a copy of the "Standard Stars in Andromeda" for the subraster you are using on the desk in front of you. You will notice that the finder sheet includes from 2 to 9 index stars, the XY coordinates, RA, Dec and Magnitudes of these stars. Try to choose index stars that are close to where your suspected nova is located Sometimes there are no index stars near to where your nova is found. In that case, use the stars that are available.
		You may find it easier to highlight the standard stars in the image of an epoch if you magnify the section of the image where the star is located.
		Choose the magnifying glass from the ImageJ toolbar and click on the star in the image. This will center the star in the middle of the image as shown here. *Go back to the toolbar and choose the hand-shaped cursor icon before continuing.* To calibrate the photometer, place the cursor over the spot that represents the standard star, click the left mouse button and press the "B" button on the keyboard.
		The Enter Magnitude dialog box will. Type the known magnitude of the standard star you have chosen. Return the image to its original magnification by choosing the magnifying glass from the toolbar and clicking the right mouse button.
The image below shows epoch 40 of subraster 10 after three standard star magnitudes have been entered for the image. To calculate the magnitude of the nova, magnify the spot that is the nova until it is centered in the window. Click on the spot with the left mouse button and hit the space bar. Note that RA and Dec information appears in the Recorded Magnitudes and Measured Magnitudes windows of the data table. Scroll the bar at the bottom of the data window to see the Measured Magnitude of the nova. Close the image window and open the image for the next epoch. Continue logging data for the standard stars and the nova in each of the epochs in which it appears.