kepprfphot: fit a PSF model to time series observations within a Target Pixel File

pyke.kepprfphot.kepprfphot(infile, prfdir, columns, rows, fluxes, border=0, background=False, focus=False, ranges='0, 0', xtol=0.0001, ftol=0.01, qualflags=False, outfile=None, plot=False, overwrite=False, verbose=False, logfile='kepprfphot.log')

kepprfphot – Fit a PSF model to time series observations within a Target Pixel File

Parameters:

nfile : str

The name of a MAST standard format FITS file containing Kepler Target Pixel data within the first data extension.

columns : str or list

A starting guess for the CCD column position(s) of the source(s) that are to be fit. The model is unlikely to converge if the guess is too far away from the correct location. A rule of thumb is to provide a guess within 1 CCD pixel of the true position. If more than one source is being modeled then the column positions of each are separated by a comma. The same number of sources in the columns, rows and fluxes field is a requirement of this task.

rows : str or list

A starting guess for the CCD row position(s) of the source(s) that are to be fit. The model is unlikely to converge if the guess is too far away from the correct location. A rule of thumb is to provide a guess within 1 CCD pixel of the true position. If more than one source is being modeled then the row positions of each are separated by a comma. The same number of sources in the columns, rows and fluxes field is a requirement of this task.

fluxes : str or list

A starting guess for the flux(es) of the source(s) that are to be fit. Fit convergence is not particularly reliant on the accuracy of these guesses, but the fit will converge faster the more accurate the guess. If more than one source is being modeled then the row positions of each are separated by a comma. The same number of sources in the columns, rows and fluxes field is a requirement of this task.

prfdir : str

The full or relative directory path to a folder containing the Kepler PSF calibration. Calibration files can be downloaded from the Kepler focal plane characteristics page at the MAST here: http://archive.stsci.edu/missions/kepler/fpc/prf/.

border : int

If a background is included in the fit then it is modeled as a two-dimensional polynomial. This parameter is the polynomial order. A zero-order polynomial is generally recommended.

background : bool

Whether to include a background component in the model. If True the background will be represented by a two-dimensional polynomial of order border. This functionality is somewhat experimental, with one eye upon potential background gradients across large masks or on those detectors more prone to pattern noise. Generally it is recommended to set background as False.

focus : bool

Whether to include pixel scale and focus rotation with the fit parameters of the model. This is also an experimental function. This approach does not attempt to deal with inter- or intra-pixel variations. The recommended use is currently to set focus as False.

ranges : str

The user can choose specific time ranges of data on which to work. This could, for example, avoid removing known stellar flares from a dataset Time ranges are supplied as comma-separated pairs of Barycentric Julian Dates (BJDs). Multiple ranges are separated by a semi-colon. An example containing two time ranges is:

'2455012.48517,2455014.50072;2455022.63487,2455025.08231'

If the user wants to correct the entire time series then providing ranges = ‘0,0’ will tell the task to operate on the whole time series.

xtol : float

The dimensionless, relative model parameter convergence criterion for the fit algorithm.

ftol : float

The dimensionless, relative model residual convergence criterion for the fit algorithm.

qualflags : bool

If qualflags is False, archived observations flagged with any quality issue will not be fit.

outfile : str

kepprfphot creates two types of output file containing fit results and diagnostics. outfile.png contains a time series plot of fit parameters, residuals and chi-squared. outfile.fits contains a table of the same properties, consistent with Kepler archive light curve files. The FITS column PSF_FLUX contains the flux time-series in units of e-/s derived by integrating under the best-fit PRF model. PSF_BKG provides the best-fit background (if calculated) averaged over all mask pixels in units of e-/s/pixel. PSF_CENTR1 provides the best-fit PSF centroid position in the CCD column direction, in CCD pixel units. Similarly, PSF_CENTR2 provides the best-fit PSF centroid position in the CCD row direction, in CCD pixel units. If calculated, PSF_FOCUS1 and PSF_FOCUS2 provide scale factors in the column and row dimensions by which the CCD pixel scale is adjusted to approximate focus variation. PSF_ROTATION provides the angle by which the scaled PSF model was rotated on the focal plane in order to yield a best fit. The table column PSF_RESIDUAL provides the sum of all mask pixels after the best-fit model has been subtracted from the data. PSF_CHI2 delivers the best-fit chi-squred statistic for each observation.

plot : bool

Plot fit results to the screen?

verbose : bool

Print informative messages and warnings to the shell and logfile?

logfile : str

Name of the logfile containing error and warning messages.

Examples

$ kepprfphot kplr012557548-2012004120508_lpd-targ.fits.gz --columns 95
  --rows 1020 --fluxes 1.0 --border 0 --prfdir ../kplr2011265_prf --xtol 1e-7 --ftol 1e-7
  --plot --verbose

  --------------------------------------------------------------
  KEPPRFPHOT --  infile=kplr012557548-2012004120508_lpd-targ.fits.gz
  columns=95 rows=1020 fluxes=1.0 border=0 background=False
  focus=False prfdir=../kplr2011265_prf ranges=0,0 xtol=1e-07 ftol=1e-07
  qualflags=False plot=True overwrite=True verbose=True logfile=kepprfphot.log

  KEPPRFPHOT started at: Wed Jun 14 15:33:30 2017

        KepID: 12557548
   RA (J2000): 290.96622
  Dec (J2000): 51.50472
       KepMag: 15.692
     SkyGroup: 4
       Season: 1
      Channel: 32
       Module: 10
       Output: 4

   19% nrow = 740 t = 0.1 sec
../_images/kepprfphot.png