General Data Analysis Facilities

Timeseries

The timeseries package contains tasks for reducing one-dimensional time series data. While these tasks were written to reduce data obtained by the High Speed Photometer (HSP) aboard the Hubble Space Telescope, some tasks may also be used as general photometric reduction tasks. Each timeseries task is described below. Details can be found in the online help files for each task.

coadd: This task will co-add files containing observed count rates as a function of phase (for periodic variable stars, for example). This task is usually used in conjunction with the orderphase task. After sorting a time series observation according to phase (using the orderphase task), you can use coadd to get a smoother light curve.

delaytime: Calculate the difference in light travel time between the space telescope and the solar system barycenter. This task also calculates: (1) Earth to solar system barycenter (maximum of about 500 seconds), (2) geocentric distance to the spacecraft (maximum ~0.023 second), (3) parallax (maximum ~1.2 millisecond per arcsecond of parallax), (4) proper motion of the target (maximum 2.4 milliseconds per arcsecond of proper motion), and (5) relativistic effect due to time dilation caused by Earth's orbital velocity changes and gravitational red shift caused by Earth's orbital heliocentric distance changes (maximum ~1.7 millisecond).

orderphase: Sort the pixels in a file by ascending phase (for periodic variable stars, for example). This task needs input of the variability period and the zero phase epoch. A single-cycle light curve is produced by reordering all points according to their fractional phase. The output from this task can be used as a single-cycle light curve to evaluate the choice of period or to remove discrepant data. Before using this task, you may need to correct the input data for light delay time (using delaytime task), especially if the light delay time is comparable to the variability period.

filterphot: Convert count rates in the input time series to magnitudes and colors, and optionally transform to a standard filter photometry system. Four options are available:

Instrumental magnitudes can be computed from intensity measurements of two time series input files.

Instrumental colors can be computed from intensity measurements of two time series input files.

Standardized magnitudes can be calculated from instrumental magnitudes and appropriate standard colors, by using three transformation coefficients.

Standardized colors can be calculated from instrumental colors and appropriate standard colors by using up to three transformation coefficients.

polarimetry: Reduce count rates obtained from light going through polaroid filters oriented at four different angles to Stokes parameters. The input for this task is four time series files, one for each of the polarizers oriented at 0xfb , 45xfb , 90xfb , and 135xfb of the same bandpass filter. The normalized Stokes parameters are computed from the four measurements and are transformed from the instrumental coordinate system to the equatorial coordinate system. The degree of linear polarization and its position angle are then calculated from the normalized Stokes parameters.

subsky: Subtract background flux from target+background flux. This task can handle several background subtraction schemes: (1) point-by-point subtraction, (2) overall fit of background data by using a low-order polynomial function, (3) background flux calculated by averaging several background points closest to the time of target observation.

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