kepfold: phase-fold light curve data on linear ephemeris

pyke.kepfold.kepfold(infile, period, bjd0, outfile=None, bindata=False, binmethod='median', threshold=1.0, niter=5, nbins=1000, rejqual=False, plottype='det', overwrite=False, verbose=False, logfile='kepfold.log')

kepfold: Phase-fold light curve data on linear ephemeris.

kepfold calculates the phase of all time-tagged data points relative to a user-supplied linear ephemeris. The relation is:

\[TIME_i = bjd0 + period \cdot PHASE_i\]

\(TIME\) is the column within the FITS light curve file containing barycenter-corrected time stamps. \(bjd0\) is a user-supplied BJD for zero phase. period is a user-supplied period in units of days. PHASE is the calculated phase for each time stamp; these results are written to a new float column in the LIGHT CURVE extension of the input file before being exported as a new file with name defined by the user. Optionally, kepfold will plot the data folded on the ephemeris and store it within a new FITS extension of the output file called FOLDED. Both the SAP and PDC fluxes are binned and stored in the new extension. There are a number of binning algorithms, mean, median and sigma clipping. The user has options to adapt bin size, binning method and the rejection of outliers.

Parameters:

inile : str

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

outfile : str

The name of the output FITS file with a new extension containing a phased light curve.

period : str

Period over which to fold the light curve, in units of days.

bjd0 : float

Time of zero phase for the folded data, in units of BJD.

bindata: bool

Collect the data into discrete bins during the fold?

binmethod : str

Binning method.

  • mean calculates the mean of all data points contained within a bin.
  • median calculates the median of all data points within a bin.
  • sigclip calculates a mean iteratively. Each iteration rejects data lying further than a threshold number of standard deviations from the mean before recalculating the result.

threshold : float

The sigma clipping threshold in units of the standard deviation about the calculated mean within a phase bin. A typical outlier lies > 3.0:math:sigma from the mean.

niter : int

The maximum number of iterations over which to reject outliers before accepting the sigclip result.

nbins : int

The number of phase bins to calculate.

rejqual : bool

If True, timestamps with quality issues recorded as a finite quality flag in the input file will be thrown away before folding the data.

plottype : str

The type of data to plot. The choices refer to the types of photometry stored in the input file.

  • sap is Simple Aperture Photometry, stored in the column, SAP_FLUX. SAP data is generated by the Kepler pipeline but it can also be generated from a target pixel file using the kepextract tool.
  • pdc is Pre-search Data Conditioning photometry, stored in the column PDCSAP_FLUX. PDC data is a Kepler pipeline product.
  • cbv Cotrending Basis Vector is SAP photometry corrected manually by the user using the tool kepcotrend. CBV data is stored in the column CBVSAP_FLUX.
  • det data has been detrended using piecemeal polynomials with the kepflatten tool. DET data is stored in the column DETSAP_FLUX.

overwrite : bool

Overwrite the output file?

verbose : bool

Print informative messages and warnings to the shell and logfile?

logfile : str

Name of the logfile containing error and warning messages.

Examples

$ kepfold kplr010544976-2009201121230_slc.fits
  0.350471 2455002.825 --bindata --binmethod median --threshold 3.0
  --niter 1000 --plottype sap --verbose
../_images/kepfold.png