2MASS Seeing and Image Shape Statistics for the First 6 Months of Mt. Hopkins Operations

R. Cutri - IPAC


Atmospheric seeing is one of several key external factors that affect the ability of 2MASS point and extended source data to meet the Level 1 Science Requirements for photometric sensitivity and precision. As seeing degrades, light from point sources is spread over more pixels, resulting in poorer net signal-to-noise and sensitivity to faint sources. This spreading also makes it increasingly difficult to discriminate between fainter extended sources and point sources, and will lead to more contamination by double and triple stars in the extended source candidate lists.

Some of the other factors that will impact the 2MASS sensitivity and accuracy include sky and telescope background levels, atmospheric transmission and telescope and camera stability, etc. 2MASS Quality Assurance will assign quality levels to each survey scan by comparing statistical measures of these factors to empirically determined thresholds relating these factors to achieved point and extended source sensitivity and reliability.   Scan data not meeting minimum thresholds will be assigned low or failed quality levels that will result in reobservation.

As part of the effort to understand the affect of atmospheric seeing (and other factors that degrade image quality) on survey performance, I have compiled image size and shape statistics for all processed 2MASS scans acquired between the dates of 21 May and 19 December 1997.  Data from 125 days and a total of 7470 scans are included in this analysis. The majority of scans processed to date are calibration data, but at least 10% are survey scans. Image size and shape are standard quality assurance output diagnostics from the 2MAPPS system for all scan data.


Last Update 1/24/98