Homework #5

Due October 29, 2009

Download the file day0.txt to your IDL directory.

It contains simulated data of the absorption line from a star with a planet going around it. There is an absorption line in this part of the spectrum.

The file contains two columns. The first column is the wavelength.  The second column is the counts per bin.  The first column actually contains the value dl where lam=6520.+dl.  This keeps the number of digits in the wavelength column from getting out of hand.

You can model each data set as m=i*(1.-exp(-(dl-L0)*(dl-L0)/2./w/w))+b

Here, i is the intensity of the continuum.  b is the detector background. L0 is the center of the line. w is the width of the line.

Write an IDL procedure to read in the two arrays of wavelength and intensity. Plot them vs each other. Overplot a the model above. Fiddle around until you get a good agreement between the model and the data. What are your best-fit values for i, b, L0 and w?

Submit the plot showing the data with the overplotted model and the values of the best guess parameters to Will.

In the next exercise we will learn to find the actual best fit and estimate error bars!