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50BiN

Data pipeline for time-series light curve catalogue for 50BiN

Three tools are provided for analysis and visualization:

  1. mergecat
  2. correctphot
  3. plotcurve

Install

To use this script, virtualenv is highly recommended (but not required). Please check this website for an installation guidance.

$ virtualenv venv
$ . venv/bin/activate
$ pip install -U git+git://github.com/swj1442291549/50BiN

Afterwards, the program should be available:

$ mergecat

Usage

mergecat

This program combines all the frames into a single catalogue, which includes three steps:

  1. Find the reference frame
  2. Merge the frames
  3. Find the non-variable candidate stars for differential photometry

The raw data have four types of files, with different extensions:

  • *.alscat: PSF photometry files
  • *.ap0: original aperture photometry files
  • *.allmag0: the combination of the previous two
  • *.allmag1: similar to *.allmag0, but the aperture photometry is calculated with star center refitted by PSF

phot_flag (default: 0) controls which aperture photometry (apmag) to be used. 0: original aperture photometry; 1: aperture photometry with star center refitted by PSF. It has no interference with PSF photometry (psfmag).

A reference frame, which will be used to match other frames, is selected based on the number of stars and the airmass estimates. Note, the size of the catalogue is determined by that of the reference frame. The number of stars for the reference frame is set to be medframe_factor (default: 1.2) times the mean number. The final selection is taken for the frames which has relatively the same star number but with the least airmass.

Once the reference frame is decided, each star in all other frames is matched by its coordinates. This is controlled by dmatch (default: 1.0 arcsec), setting the maximum matching distance.

The non-variable candidates are selected if their variance of magnitude difference (std(m1-m2)) is smaller than sdev (default: 0.006 mag). If there are too few standard stars, an option of noc is provided to ensure there are adequate number of standard candidates. This value is not exact the same as the final output of standard stars number.

Usage: mergecat.py [OPTIONS]

Options:
  --phot_flag INTEGER      Magnitude type. 0: original aperture photometry; 1:
                           aperture photometry with star center refitted by PSF
  --dmatch FLOAT           Position matching distance in arcsec
  --sdev FLOAT             Standard deviation for none variable selection
  --noc INTEGER            Minimum number of standard candidates. Not the same as Std Stars output
  --medframe_factor FLOAT  A factor on average star number in a frame for reference frame selection
  --obs_flag TEXT          Observatory flag. 'd': Delingha; 'l': Lenghu
  -b, --band TEXT          Passband. If to use more than one
                           bands, list them here without space in between e.g., BV
  --help                   Show this message and exit.

The output files include:

  • stdstar.dat: photometry of non-variable candidates in the reference frame (columns: ra, dec, apmag, apmag_err, psfmag, psfmag_err). Grouped by bands.
  • *.{phot_flag}gcat.pkl: python pickle file that contains all data as a python dictionary

correctphot

This program is to calibrate the instrumental photometry via differential photometry method.

No external standard stars are required. Instead, the brightest noc (default: 5) standard stars from stdstar.dat are used to conduct the ensemble photometry, that is, using the average chaning behavior of these standard stars over frames to correct the photometry of the remaining stars.

A calibration from instrumental magnitudes to standard magnitudes is necessary for many science cases. However, due to different circumstances for users' case, I do not implement this function in this code. The basic idea is to use the stdstar.dat file and cross-match with external catalogues to do your own calibartion. Once its done, its easy to pass the result to correctphot through variable smag_ncs. It should be a 2D-array with the shape of {noc}, nframe.

method option controls which method for differential correction. If left empty, an average magnitude shift (m-m0) among standard stars will be used. This is the fastest one, but only suitable for single-band data. You could also use least-square fitting method. In that case, you need to specify which parameter to fit. The parameters can be the coordinates on the CCD (x, y) and its color (e.g., B-V). They should be joined by the plus sign + with no space. For instance, if you only want to use the coordinate, --method x+y. For multi-band data, you have to include (at least) one color in the method option, e.g., --method BV+VI (which means B-V and V-I).

magtype controls which magnitude to used in this process. a for aperture photometry and p for psf photometry.

Usage: correctphot.py [OPTIONS]

  Calibrate the instrumental photometry

Options:
  -f, --file_name TEXT  Input pkl file name
  --magtype TEXT        magnitude type. a: aperture; p: psf
  --noc INTEGER         Number of selected standard stars
  --method TEXT         Method of correcting photometry (See
                        README for details).
  --help                Show this message and exit.

The output files include:

  • *.{phot_flag}{mag_type}gcat_mmag: average brightness of each star (index, ra, dec, mmag, mmag_err)
  • *.{phot_flag}{mag_type}gcat_cal.pkl: python pickle file that contains all data

bad frames are marked if the standard stars' deviations on those frames are larger than 3 sigma. Those with large fwhm are also suggested to be bad frames, which is left with the user to decide.

plotcurve

This program is to present the data in time-series light curve. It can also show the magnitude versus airmass.

Usage: plotcurve.py [OPTIONS]

  Plot light curves

Options:
  -f, --file_name TEXT           Input pkl file name
  -i, --init_star_index INTEGER  Index of star to plot
  --coord TEXT                   Coordinate of the query star. Example: '0:0:0.0 0:0:0.0' or '0 0 0.0 0 0 0.0' or '0.0 0.0'
  --help                         Show this message and exit.

The default figure is shown in UT horizontal axis with multiple-day data folded into a single frame. The plot_flag controls the output format:

  • l: Light curve (magnitude vs. mjd)
  • a: airmass (raw magnitude vs. airmass)
  • f: FWHM (FWHM vs. mjd)

It can be switched to day mode that expands the data into the MJD axis. The bad frames are indicated as crosses.

You can interact with the plot through the keyboard:

  • n: next star; next day (day mode)
  • N: previous star; previous day (day mode)
  • d: switch on/off day mode
  • l: switch on/off light curve data
  • a: switch on/off airmass data
  • f: switch on/off FWHM data
  • z: zoom out
  • Z: zoom in
  • r: reset scale
  • s: save the data of this star
  • q: quit

The output files include:

  • *.orig: original photometry of one star (index, mjd, ut, mag, mag_err, band)
  • *.dat: corrected photometry of one star (index, mjd, ut, magx, magx_err, band)

TODO

  • [ ] Better implementation of smag_ncs