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S.R. Stolovy (SSC/Caltech), D. Elliott (JPL), D. Makovoz (SSC/Caltech)
The inner few arcseconds of the Galaxy as imaged in NICMOS continuum filters are characterized by a crowded field of many overlapping diffraction-limited PSF's. Images of the ionized gas in Paschen Alpha constructed from the standard technique of taking the difference of two scaled 1% filters (F187N-F190N) do show the complex structure of the ionized ISM in the central parsec. However, the emission line images are also ``contaminated'' by large positive and residual PSF artifacts. These stellar residuals are due to astrophysical processes (e.g. Pa alpha and/or Helium emission or absorption in stellar atmospheres, variable extinction) as well as due to the wavelength difference between the line and continuum filters.
We desire to study both the continuum and ionized emission close to Sgr A*, which is located only 1-3'' from the ``contaminating'' bright IRS16 stars. Point source removal in the F190N filter will allow us to recover the underlying distribution of diffuse continuum emission near Sgr A* due to the combined light of faint stars in the Galactic bulge. In addition, even more stringent limits can be placed on the near-infrared flux at the position of Sgr A*. Removal of strong PSF artifacts from the Pa alpha image will allow imaging of the ionized gas with 0.2'' resolution near Sgr A*; our two epochs of Pa alpha images may show high proper motions due to the gravitational potentional of the purported black hole at Sgr A*.
In order to remove stellar residuals from the NICMOS images, we employ several techniques: First, the PSF is derived from the data directly and by modifying a model PSF (e.g. Tiny Tim) to match the data. We then employ several point source extraction methods, including one developed for the SIRTF pipeline. In order to remove point sources from the emission line images, fluxes and positions derived from the F187N images are correlated with point sources extracted from the F190N ``truth'' image to select only the point sources. Point source removal will be tested using PSF subtraction as well as deconvolution techniques.