C:  PESTphot – produce data products

  1. If it does not already exist, create the directory for the object and observation.  Use this form ‘anything/target_name/obs_date’.  Open Terminal and cd to it – or in Ubuntu Files window, right-click → Open in Terminal.
  2. If you are using a virtual environment, activate it:  source activate pestapps or conda activate pestapps
  3. In Terminal, run the command pestphot.
  4. PESTphot will request some input.  The aperture number is what we noted from B.9.  The magnitude of COMP is used as the reference to place all measured stars on the same scale.  Times of predicted ingress and egress are in terms of HJD or BJD – 2450000.  The expected transit depth is used to calculate how a bright a neighbouring star would need to be to produce the observed signal if it underwent a deep eclipse and was fully blended with the target.  Units accepted are mmag or ppt.  Append the unit to the depth, e.g. in this case ‘3.8ppt’.
  5. Processing may take some time depending on the number of frames, stars and whether some functions or products are switched off in config.  If all goes well it should finally say, e.g. ‘PESTphot completed sucessfully using date type: BJD and aperture no. 6’.
  6. And that’s it!  Most of the data products needed by TESS will now be in the working directory.  The ones in the form ‘target_date_observatory_filter_type’ e.g. TIC259377017-01_20190113_PEST_V_zoomed.png are data products requested by TESS SG1.   The others are either for information, or will be used by MagPy, next in the pipeline.

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A detailed look at the data products

 Star identification

In C-Munipack you will have seen selected stars labelled as ‘var, comp, check #1, check #2, etc’., or ‘V, C, K1, K2, etc.’ in the instrumental magnitudes output file.  We will call these “star labels”.  In the PEST pipeline, however, we will not use these labels.  Instead, only “star ids” will be used.  These are the numbers assigned internally by C-Munipack to all stars detected in the dataset.  For example the id of VAR in the field below is “7”.

Full field with target, COMP and potential ensemble stars marked

There are now many more marked stars than selected in B.6.  PESTphot has added those stars within the constraints set in config.  The stars selected are distributed through the image.  This is important because stars within the same part of the CCD often have the same trends, and a good ensemble will try to neutralise these by including stars with opposite trends.
The coordinate grid shows that the field has been plate-solved.  The numbers in blue are star ids.

Zoomed in area around the target

The circles around stars show the actual size of the photometry aperture used.  The large red circle is drawn at a radius of 2.5′ from the target.  TESS SG1 requests that stars within this radius be checked for NEBs.  The red x’s are stars bright enough to have caused the TESS signal obtained from an interrogation of the Gaia DR2 database.  Where these don’t coincide with a red circle, the observation did not detect those stars so they are not cleared as being potential NEBs.

Scatter vs delta-mag plot

If a star in the field is not variable it will plot onto a straight line.   None of the stars in this field show excess scatter.  If there are any outliers, their light-curves would be plotted with filenames of the form ‘*_outlier_nn.png’ where nn is the star id.


Lightcurves for stars within 2.5′ (‘proximate’ stars)

Lightcurves are plotted for every detected star within 2.5′.  The maroon line with a box transit shows the approximate depth of an eclipse event in this neighbouring star that, if fully blended with the target, could have resulted in the TESS detection.  There is a formal criteria related to scatter vs potential NEB depth that decides if a star is “Cleared” or “Likely Cleared”.  In this case, the formal criteria results in “Not Cleared”, but visual inspection of the lightcurve shows that there is no event deep enough.  So visually cleared.  All these lightcurves, with the exception of stars too faint to have caused the signal, are rolled up into a .zip file to simplify upload to TESS.


Observing conditions

Sometimes changes in observing conditions can result in spurious features or trends in lightcurves.  These charts show how airmass, FWHM, position of the target on the CCD, and actual counts produced on the image, changed during the night.  Some of these parameters are also written to the *_detrend-data.txt file which allows others to de-trend the produced lightcurves to try to clarify any signal.



Other files:

*_WCS.fts:  a plate-solved image (FITS) files with World Coordinate System (WCS) information written to the header so that all objects on it can be mapped to sky coordinates

*_neighbourhood.txt:  details of all detected and Gaia stars within 2.5′, including coordinates, delta-mag, separation from target, and disposition

PESTphot_info.txt:  contains all the information about the observation needed to fill out a new Time Series submission to TESS-ExoFOP, including PSF, max dmag, duration and number of observation.


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