Stellar Properties from VI Photometry Lab

In this lab we will perform photometry on stars in the cluster m36, then we will use this data to ascertain a variety of characteristics of the stars. You will find the information and formula in the Background and Theory section on page 180 of your lab manual useful.

• Finding Charts

  There is a finding chart for m36 on the network drives in the folder H:\observational\clusters\fcharts. You may find it helpful to print this out for easy referral when viewing your images. Do this using your favorite image viewing program. You will find that the images you will perform photometry upon are upside-down when compared to these finding charts.

• Photometry

  Start Maxim and open the V and I filter images in H:\proj-26_Photometry_BVRI\m36. Open the photometry tool by selecting Analyze -> Photometry from the menu. It may make things easier to reduce the zoom of your image to 50% so that it will all fit on the screen. First, you must calibrate the tool as follows:

  1. Find your reference star in the image. Hover the mouse cursor over the reference star and check that the innermost of the three circles completely encloses the star, and that there are no stars between the outer two circles. Right-clicking will bring up a context menu, which will allow you to change the radii of these circles.
  2. Press the Set from FITS button to have Maxim extract this data from the FITS header of the image.
  3. Press the Extract from Image button to prepare Maxim to read intensity data.
  4. Center the cursor on your reference star and left click to measure its intensity.
  5. Finish calibrating the tool by entering the actual magnitude of the star from your finding chart into the box in the photometry tool and pressing Apply. Be sure that you use the V magnitude for the V filter image and so forth.

  You can now measure the magnitude of other stars in the image by merely hovering the cursor over them and reading the magnitude in the photometry tool window. Do this for five stars in the image. You may want to avoid choosing the brightest stars, since they are beyond the range of some of the calculations we will perform later.

  Repeat this process for the same five stars in the image using the other filter.

• Calculations

  Fill in the table on page 184 of your lab manual (or create one in Excel) by using Table 2 on page 184 and the formulae on pages 181-182.