aXeTwoZero: The Next Generation of aXe

The aXe spectral extraction software was designed to extract spectra from slitless data such as taken with the Advanced Camera for Surveys (ACS) on board of HST. Wide Field Camera 3 (WFC3), which was installed on HST during Service Mission 4 in May 2009, also contains slitless spectroscopic modes on both, the IR and the UVIS arms, and aXe is the recommended tool for reducing its slitless data. Rather than adjusting the previous version aXe-1.71 to WFC3, we have chosen to re-factorize the current aXe to build aXeTwoZero (aXeTZ), the next generation of the aXe software. We explain the structure and the properties of aXeTZ. The reduction of WFC3 slitless data with aXeTZ is demonstrated using early in-orbit calibration data. aXeTZ is scheduled to be released as part of STSDAS in November 2009. A brief outlook of further developments is given. 1 Slitless Spectroscopy with aXe Slitless spectroscopy has some special features and properties which require a dedicated extraction package such as aXe (Kummel et al. 2009a; Freudling et al. 2008). A slitless dataset such as the WFC3 example shown in Figure 1 usually consists of a slitless image (upper left panel) and a corresponding direct image (lower left panel, here F098M) taken at the same position in order to derive the zeropoint of the wavelength calibration. Due to the low spectral resolving power, there are multiple spectral orders of the same object visible in a single image. The absence of slits makes contamination, which is the mutual overlap of spectra, a ubiquitous phenomenon in both the spatial direction and in dispersion direction, even across different spectral orders and at distances of many hundred pixels. Table 1 lists all slitless spectroscopic modes to which aXe has been applied. 2 aXeTZ (aXeTwoZero) The structure of aXeTZ is depicted in Figure 2. As compared to previous versions, aXeTZ contains a python interface layer which is capable to fully replace the PyRAF layer and would allow an easy transformation of aXeTZ into a pure 305