10.1 Analysis of Scanned Data

Spatial scans enable high-fidelity observations of bright sources such as host stars of exoplanets. In the case of photometry of bright, isolated sources, spatial scans have two key advantages, leading to higher photometric precision, over staring mode observations. First, the ability to collect of millions source photons per exposure without saturating is enabled by spreading the light over hundreds of pixels, yielding much higher signal to noise ratios than conventional staring-mode observations. Second, illuminating hundreds of pixels averages out spatially-dependent sources of noise such as flat-field errors and enables sampling of different pixel phases along the direction of the scan. Spatial scans also enable high precision astrometry of bright sources.

The analysis of spatially scanned data obtained with HST WFC3, however, is different from that of the nominal, standard pipeline (calwf3, see Chapter 3) calibrated, staring-mode observations. The observers are sometimes required to customize, depending on the usage, a large fraction of their analysis of spatially scanned data.

In this chapter, we give a general overview of the custom analysis flows for scanned A) IR spectroscopy, especially of exoplanet transits or eclipses, and B) UVIS and IR imaging. Please note that UVIS scanned spectroscopy is not recommended due to order overlap.

We recommend the observers use the following pipeline generated files as the starting point of their own custom analysis:

  • IR: *_ima.fits

  • UVIS: *_flt.fits or *_flc.fits