A Method for Reducing single filter (V) CCD data using MaxIm and SPSS

  1. In MaxIm tag object of interest and as many comp stars (refs) as possible - don't do check stars. [Caution: comp stars must be similar in mag to the object star or SNR factors will make this method inaccurate.] Adjust aperature and sky annuli and throw away really bad (badly tracked or too much cloud) frames until the plot of the comp stars is as flat as possible.
  2. Save data from MaxIm photometry tool as a csv file.
  3. Load csv file into SPSS. Change name of obj to the name of the var and the names of ref1, ref2 etc to C12.23, C13.46 etc to designate comp 12.23, comp 13.46, etc. Adjust decimal place display to 4 places for JD and 2 places for mag. Save as an SPSS (.sav) file.
  4. Transpose data, excluding JD and var mags. Change the first column to numerical data to represent the known chart values for the comps. Save as comps.sav.
  5. Set up the first linear regression from Analyze -> Regression -> Linear.. Put the actual mag value as the independent variable, put the first frame comp data (var001) as the dependent variable. In the statistics box click everything off except the Regression Coefficients -> Estimates box. In the Save box click off everything except the Predicted Values -> S.E. of mean predictions box. In the options box, click off the Include constant in equation box. If there are many frames, create a script by hitting the Paste button. Copy and paste multiple times, change only the var001 name each time. Run the script (which you may want to save) from the Run menu. New columns will be created in the data sheet labeled SEP_1 etc. These are the standard error of the mean predictions - use the largest value as the error for the variable mag measurement associated with the corresponding frame. In the output sheet, which you should save as comps.spo, the value of Unstandardized B is the transformation coefficient from instrurmental v to standardized V, Cv so that V = Cv * v. MaxIm usually does it's math so that Cv =1, so this is normally just a check. Note that no correction is done or can be done with this method to factor in the star color in the transformation equation. So the comps and the var should be of similar color when using this method.
  6. Transpose the error data in SPSS and save as a spreadsheet. Save the mag SPSS file as a spreadsheet. Merge the mag and error spreadsheets.