Stars that are bright enough to be heavily saturated in the R1 exposures (J<4, H<3.5 and Ks<3 mag), can have confusion radii, diffraction spikes and ghost reflections that span more than one scan. An extreme example of this is shown in a montage of several J-band images of Beta Pegasi (Figure 1) from the 2MASS Sampler. The montage covers a region 5 scans in width, clearly showing the large confusion "halo" and extensive diffraction spikes of the Ks~-1.9 star.
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| Figure 1 |
Artifact identification within 2MAPPS requires a good estimate of the parent source brightness, and is currently limited to knowledge of stars that fall within the scan being processing. Heavily saturated objects, such as Beta Pegasi, do not have good photometry, and do affect scans beyond the one in which is lies. Artifacts produced by Beta Pegasi, as well as 4 other bright stars in the Sampler night 2MASSs J0850200+091617 (HD 75432), 2MASSs J0707213+224213 (SAO 79072), 2MASSs J2307067+252806 (HD 218356), 2MASSs J0704065+203413 (HD52973) have been culled from the Catalogs "by-hand", using the geometric relationships from the standard artifact search routines, and infrared brightness estimates from the Catalog of Infrared Observations (Gezari, Schmitz & Meade 1987, NASA Publication 1196).
Users should use caution when examining Point and Extended sources in the vicinity of such bright stars because the reliability of artifact identification is not yet well tested.