A: Set up C-Munipack
C-Munipack has a comprehensive manual accessed through ‘Help’ → ‘User’s manual’. The steps here are a guide through the pipeline but is not a detailed how-to for the software.
- Install C-Munipack from: http://c-munipack.sourceforge.net/
- Set up ‘Projects’ for Bias, Flats, Darks and Photometry. It’s important to set the ADUs for the limit of linearity, as well as other CCD parameters.
- Make sure you know where the Project directories are. That’s where C-Munipack will put the photometry files (.pht) as well, and PESTphot will look for them there.
- Set the radii for the range of photometry apertures to be used. Make sure the range covers everything you are likely to use. For PEST I keep it simple by setting the radius the same as the aperture number. To avoid confusion, once these are set keep them the same for all future runs!
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B: C-Munipack image reduction and photometry
Prepare calibration frames. You may want to use frames prepared using other software, but C-Munipack does a very good job. Refer to the manual.
- Reduce the science frames. I usually use ‘Express reduction’, which does Fetch (copies images to the working directory), Darks, Flats and Photometry.
- ‘Matching’ or registration of images is the next step. This can be using a frame from the current project, or, on a future run for the same target, a Catalog file prepared in B.11. Choose the best image – the software helps by ordering images by quality as indicated by no. of stars detected.
- After matching, light-curves for any star can be viewed using Tools → Find Variables. Remove outlier points at this stage (Shift & hold mouse left button to select points, Right click, ‘Remove frames from project’).
- After outlier removal it becomes clearer if there is any signal in the LC. In the example below there is no obvious variability except perhaps an couple of suspicious shallow dips. We will try to get a clearer indication of any signal when we run MagPy.
- Click Plot → Light curve. Make sure ‘Compute heliocentric correction’, Compute air mass coefficients’, and Show raw instrumental magnitudes’ are all ticked.
- Select stars. The convention that must be used is that ‘var’ is the target, ‘comp’ is the star that will be used as the mag scale reference, and ‘check #x’ are either other stars of interest, or just those that we want to be available for the ensemble. There must be only one ‘var’ and one ‘comp’. Select just enough stars to be able to get an idea of scatter vs photometry aperture (see B.9). It is not necessary to choose many check stars, because PESTphot later will automatically add stars to the catalog. Specific behaviour is defined in config. We will check later if these are good, well-behaved, ensemble stars. N.B. choose a ‘comp’ that has high S/N and that does not result in strong systematics/ trends in the target and surrounding stars. This is because all the ‘proximate’ and ‘outlier’ lightcurves will be plotted as differential magnitudes against comp.
- Click ‘Save as…’ and enter the name of the target. This saves the selection. PESTphot expects there to be only one selection and will throw an error if e.g. you saved one selection, made a change to the stars and then clicked save again with either another selection name, or no name.
- Click ‘OK’.
- The ‘Choose aperture’ window opens. Clearly Aperture #6 gives the least scatter. Select that. Click ‘OK’. Remember the aperture number that gives the best result, because PESTphot will request this as input.
- A plot of instrumental mags for the target opens. This screen is for information only because we will use PESTphot to write the mags to file and do date conversion to BJD.
- Close the ‘Light curve’ window. On the main window click ‘Tools’ → ‘Make catalog file’. The filename must be exactly the same as the target name. The save folder should be the catalog directory as specified in config. The catalog file will be used by PESTphot as well as for subsequent observations of the same target. Matching to the same catalog file will keep star selections consistent. IMPORTANT – save the catalog at this point. Going to a different screen (eg Find Variables) can sometimes cause the star selection to disappear from this screen when you come back to it. The selection can always be recalled, but it’s yet another step.
- For data archiving, locate the directory where the Munipack project is. Open the subdirectory project_name.cmpack-files. Inside, the files tmpxxx.fts are the flat-fielded, dark-subtracted science frames. Copy these files to an archive location for record/ future use.
Behind the scenes
As a result of these steps:
- A set of C-Munipack photometry files named tmpxxx.pht have been created in the same directory as the .fts files in B.12 above. There is one for each science image and it contains photometric data for every star found in that image, calculated using each aperture specified in A.4, so it’s a lot of data.
- A Catalog file has been created for this target with star selections. This is actually 2 files, an XML and a FITS file. The XML contains the star selection and data. At this stage there may be fewer stars selected than ideal for the ensemble. But in the next step PESTphot will add stars to the catalog XML file.
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