TSP uses three dimensional datasets to represent time series images. There are two commands which enable such data to be read into TSP.
The DISPLAY command enables time series imaging data to be displayed on an image display device. Once displayed a COMMAND mode enables a number of options to be selected. Any indivdual frame may be displayed. A series of frames may be displayed as a movie. A cursor may be put up to read positions or data values.
The commands described here are used to obtain the light curve of a star from a time series image. First it is necessary to subtract sky using the command SKYSUB which is based on the use of two sky areas on either side of a star.
CCDPHOT can then be used to perform aperture photometry of the star to obtain a light curve. CCDPOL is a similar command that obtains polarimetry from observed through an instrument such as the AAO faint object polarimeter which produces E and O images from a wollaston prism.
As an alternative to CCDPHOT, the commands TSPROFILE and TSEXTRACT can be used to determine a profile which is a smoothly varying function of time, and extract the photometry using an optimal weighted combination of pixels. The procedure is the 3 dimensional analogue of the optimal extraction technique for extracting spectra of stars from long slit data. For the technique to be succesful it is important that the image does not show rapid motion (e.g. due to seeing or tracking problems) that cannot be adequately represented by a low order polynomial fitted through the dataset.
This pair of commands enable the image motion in a time series image to be studied and allow the software analogue of ‘tip-tilt’ correction to be applied to the data. When applied to a time series which consists of very short exposure images, the translational component of seeing can be removed enabling significant reduction in image sizes. This has enabled a FWHM for star images of 0.37 arc seconds to be achieved on data taken with infrared camera IRIS on the AAT.