Image Distortion Correction for STACam Narrow Band Filters

Star formation rates (SFRs) inside of galaxies help constrain models of galaxy formation and the current stage of the Universe. SFRs are determined by accurately calculating the Hα (6563 Å) emission line flux in a star forming region. It is important to remove the continuum emission measured in broad R-band images from the narrow Hα-band images to better constrain emission line fluxes. This is a challenging task when obtaining data with large field-of-view imagers in excellent seeing conditions, like in the case of Mauna Kea. Obtaining data with STACam employed on the UH2.2-meter telescope, varying filter characteristics induce distortions as large as 1.5 arcseconds at the edge of the image field. A distortion solution and correction is necessary to mitigate this effect. 

Mapping the field of a barred irregular galaxy (NGC 6822), a 4th order polynomial is generated to model and transform distorted stellar positions into a common reference frame. Applying this distortion solution, errors in image alignment are reduced to less than 0.2 arcseconds. Presented are the registered images and preliminary results of the continuum-free Hα fluxes in a subset of regions. These regions will be further studied using the SNIFS spectrograph on the UH2.2-meter telescope to determine internal extinction and chemical abundances. Further, the Hα maps will be used to do a census of the properties of star forming regions such as their sizes, luminosities, and SFRs which will be compared to published studies and galaxies we will observe with STACam in the future.