Folding RR Lyrae data

In the previous class I introduced the RR Lyrae phenomenon. Briefly, RR Lyrae are pulsating stars of spectral class A. These stars have played a major role in the development of modern astronomy. The periods of RR Lyrae range from 0.2 to 1 day and have a distinct pulse profile shape. The absolute magnitude of RR Lyrae stars is about 0.75 (about 40 times brighter than the Sun). What makes them interesting is that there exists a relation between the pulsation period and the absolute magnitude (see presentation in previous class). Thus merely measuring the pulsation period of an RR Lyrae (when combined with the apparent magnitude) immediately informs you of the distance to the star. RR Lyrae stars allow us to measure the distances to Globular clusters (and thence set the scale of our Galaxy).

PTF data on RR Lyrae stars

A collection of "time series" for a number of RR Lyrae stars (the data is from the Palomar Transient Factory or PTF) can be at RRLyrae. For each RR Lyrae there are two files, the .txt file (data) and a .jpg (pulse profile). The data files have the following structure
54907.843191 16.026 0.022
54907.941112 16.084 0.028
54961.730973 15.881 0.009
54961.788813 15.957 0.009
54961.839863 16.004 0.008
54961.904593 16.049 0.009
The first column is the MJD and is followed by R-band magnitude and error in magnitude. The periods of the objects can be found in periods.txt. You may wish to review my MATLAB output .


  1. The first task in analyzing any time series data is to inspect the data. Read in one file. Plot the data as a function of sample index or MJD (or both). Next, histogram the amplitude and the associated error bars.
  2. Next fold the data at the period and plot the folded curve. Compare your folded light curve with the corresponding .jpg file.
  3. Optional: Repeat this exercise but use "optimal addition" and compute the error bars on the folded light curve.
  4. Optional: Learn how to make downloads of many files (the remaining *.txt files). The file ListOftxtFiles may be useful. [magic: "$ sed 's/^/wget /' ListOftxtFiles | sh -x"]
    Next, set up a program which runs through the entire list of files. Check out bash program.
    $ chmod a+x CombinePeriod
    $ ./CombinePeriod