Display and study processed images

Start ds9 again, select a dark-subtracted image file, and use the

Zoom -> Invert Y

menu selection to modify the display. Images taken at the focal plane of the 16-inch telescope will typically only require this inversion to have N at the top and W at the right. so the image bottom-to-top will be declination, and right-to-left will be right ascension in just the same sense that a map of the sky is usually displayed.

Adjust the display so that you can see the faintest pixels with a dynamic range that allows you to see gray in regions that are not saturated. This is a difficult adjustment to get right the first time, but once you have some experience it will be easier to come back to a useful setting again. The Scale -> Scale Parameters menu may be helpful since it allows you to set numbers rather than move the mouse to achieve the gray level you prefer. The Color -> Colormap Parameters control allows you to adjust contrast and brightness.

The center of the field of view should be the selected target when the image was taken. You can identify most stars and non-stellar objects by using XEphem. It may be started from the icon on the top menubar of the computer (it's the Egg Nebula and looks like an X), or from the command line:

Open another console window, and type the command xephem. This will start a control panel that allows you to select the date, time, and location. By default on our systems the location will be Louisville.

Change the date and time to match the observation, and select the

View -> Sky View

menu item. This will bring up an interactive sky map. If it has not already been done, you need to configure the field stars to show the faintest stars in the catalogs. Do this with the

Data -> Configure field stars

menu item. Select Local cache for the Guide Star Catalog, and select Hipparcos + Tycho2 for the Proper Motion Catalog. Press Apply and then OK. This selection will be permanent after you exit the program, if you respond to the prompt on exit to save the configuration. These catalogs include all the faint stars, and you have to have this enabled in order to identify most of the stars in your images.

If, for example, you are looking at an image of M1, you should zoom in to Taurus and adjust the display scale on XEphem to match that of the scale on ds9. In the Sky View window click the box on the left that looks like a graph grid to toggle the display from Altitude and Azimuth (as the sky would appear to the eye for a person facing south), to RA and Declination (as the sky will show in ds9). Select a field of view (left slider) to be about 6 degrees. You can right click on M1 in the Sky View window and use the Center and Zoom feature to make an adjustment also. The more you zoom in, the fainter the stars are that will be displayed. The database will go down to about 15th magnitude.

If you cannot identify the object on XEphem, select the Data -> Index menu, and scroll through the list of objects to find the one you want. When you left click on that one, information about the object will appear in the Object Index box and you may center the display on it with Sky Point. With the narrow field of view for these high resolution images, most objects are very easy to identify immediately. Typically a field of view of about 0.2 degrees in XEphem will approximate the scale of the CCD images on the screen.

A set of images for November 6, 2004 are in the directory 20041106. We have these files

 2004-11-07 02:15 c2004q1_100s_01d.fits
 2004-11-06 19:41 dark_100s_01.fits
 2004-11-06 21:19 dark_100s_02.fits
 2004-11-06 22:38 dark_100s_03.fits
 2004-11-07 00:19 dark_1s_01.fits
 2004-11-06 21:55 dark_600s_01.fits
 2004-11-06 19:30 m15_100s_01.fits
 2004-11-06 19:37 m15_100s_02.fits
 2004-11-06 19:52 m15_100s_03.fits
 2004-11-06 19:56 m15_100s_04.fits
 2004-11-06 20:06 m15_100s_05.fits
 2004-11-07 01:26 m15_100s_05d.fits
 2004-11-07 01:35 m1_600s_01d.fits
 2004-11-07 01:34 m1_600s_red_01d.fits
 2004-11-07 01:43 m31_100s_02d.fits
 2004-11-07 01:45 m32_600s_01d.fits
 2004-11-07 02:02 m42_100s_blue_01d.fits
 2004-11-07 02:01 m42_100s_green_01d.fits
 2004-11-07 02:03 m42_100s_neutral_01d.fits
 2004-11-07 02:03 m42_100s_open_01d.fits
 2004-11-07 02:00 m42_100s_red_02d.fits
 2004-11-09 13:22 m42_1s_open_02d.fits
 2004-11-07 01:55 m45_merope_100s_01d.fits
 2004-11-07 01:51 m45_merope_s_600s_01d.fits
 2004-11-07 01:47 n7448_100s_01d.fits
 2004-11-07 01:47 n7465_100s_02d.fits

as well as a notes_20041106.txt that has a list of the images and the conditions for each. All of these files have been dark-subtracted with the best available dark reference image file.

In the event we have more images from later observations there will be other date subdirectories with fits files and notes.