New algorithms have been implemented in the 2MAPPS V3 processing to photometer stars saturated in the Read1 exposures (stars brighter than mag ~5). In the 2MAPPS V2 processing, no special processing was done for these objects and they often had very poor positions and were given fiducial magnitudes, complicating the clean up process around bright stars. Methods have been developed and implemented for 2MAPPS V3 to determine the positions to a few tenths of an arcsecond and the magnitudes to 0.2 mag for even the brightest (mag -4) objects in the sky by centroiding the r1 exposures over a threshold, and fitting a radial profile to the combined unsaturated data from all the overlapping frames.
Processing
Saturated sources are identified in each of the Read1 frames, the position in the frame is determined from the centroid of the central area, the radial profile data is collected from all the frames containing the star, and a template is fitted to the non-saturated wings of the radial profile data. The profile development and fitting methods are described in the following pages:
Photometry of Bright Stars - Methods developed by Cong Xu In particular, see Report 4 detailing the implemented profiles and results vs the photometric reference set.
Results for data taken in the southern hemisphere are excellent, showing ~0.1 mag scatter relative to the photometric reference set in all 3 bands. Results in the north are somewhat problematic, showing more scatter relative to the photometric reference set, and also offsets in the colors in the analysis below.
Preliminary Processing Results
Roc Cutri has analyzed the colors of the saturated Read 1 photometry from test processing using the implementation of the above methods in the 2MAPPS V3 pipeline. Offsets are seen in the J-H vs H-Ks plots for the nothern hemisphere sources saturated in all three bands which are not understood at this time.
Colors of Saturated Read 1 Stars from V3 Test Processing
[Last updated: 2000 April 5, by E. Kopan]