Analysis of Lictoria: Mar 27, 2002 EST

At this point, you should have completed the initial steps in reducing our images of asteroid 1107 Lictoria. The goal for today is to measure instrumental magnitudes for the asteroid and two comparison stars, and look for variations in the asteroid's brightness with time.

Recall the 5 groups of images:

  image names    EST start      filter    exptime
--------------------------------------------------
   1107a         10:03:40 PM    none       15       1107a.001, 1107a.002, etc.
   1107b         10:25:50       none       15
   1107c         10:45:40       none       15
   1107d         11:09:00       none       15
   1107e         11:29:30       none       15

You can find copies of all the images at

http://spiff.rit.edu/classes/phys559/lectures/mar27_2002/

Each image has a name like 1107a.001.fit; so the full URL to an individual image would look like:

http://spiff.rit.edu/classes/phys559/lectures/mar27_2002/1107a.001.fit

Using your subset of the images, you should today

Try to find the asteroid. It may help to do this:
- Display the first image in your group on the screen via SIP.
- Open another browser window, start up another SIP process, and load an image from another sequence. For example, if your group is "a", "b", or "c", I suggest you pick 1107e.001; if your group is "d" or "e", choose 1107a.001 The key is to pick an image taken at least an hour before or after your group's images.
- Display the other image, arranging the contrast, etc., so that it looks similar to your own image.
- Try to move the two windows so that the two different images overlap on the screen. Toggle back and forth between the images, shifing them relative to each other so that the stars on one image align with those of the other. This is called blinking. Look for an object which moves.
Once you have found the asteroid, use the Analyze menu item to select Determine Centroid or Instrumental Magnitude.... Follow the instructions on the SIP Photometry page to determine the instrumental magnitudes of three objects in the image:
- the asteroid ("A")
- a bright star close to it ("B")
- a faint star, similar to the asteroid, also nearby ("C")
I will point out the stars "B" and "C" you should use. Choose an aperture box which is 7 pixels on a side, with a fixed 7-pixel background box located off to one side, in the clear sky background.
For each one of your images, record the instrumental magnitudes of the asteroid and stars "B" and "C".

Make a table which shows:

                       instr mag  instr mag    instr mag
      truncated JD      asteroid       B          C
     --------------------------------------------------

Type your table into an Excel spreadsheet. Save the spreadsheet as Excel, and also save it in comma-separated-value format.
Calculate the differential magnitudes between the asteroid and bright star, (A-B), and the faint star and bright star (C-B), for each image.
Make a graph which shows time (in JD) on the x-axis, and the differential magnitudes on the y-axis.

We will combine all the data from all the sets of data together to make a master graph. If the asteroid is really varying as it rotates, then its light curve will wave up and down in a periodic fashion. The faint star serves as a check: if it, too, varies relative to the bright star, then there is probably something wrong with the data or the reductions.