Parameters Used in the 2MASS 24-Hour Monitor -------------- pointing summary -------------- PctNpm = Percent of scans which failed position reconstruction because no pattern match could be found. Pointing: AvDraN = Average difference of the adjusted* observatory estimate of RA at start of scan minus the reconstructed value for northgoing (N) scans. AvDraS = Average difference of the adjusted* observatory estimate of RA at start of scan minus the reconstructed value for southgoing (S) scans. AvDdec = Average difference of the reconstructed Dec at start of scan minus the adjusted observatory estimate. *Note- 1) "adjusted" means that average offsets determined from a large sample of previously processed scans have been applied. RA values are adjusted separately for northgoing and southgoing scans. Dec values are not. 2) All differences were generated using vectors and the units are real arcseconds on the sky. SigDraN = RMS on above RA values for northgoing scans.. SigDraS = RMS on above RA values for southgoing scans. SigDdec = RMS on above Dec values.
AVXSDif = Average cross-scan difference between equatormost 6-deep frame center (3-band average) and the corresponding tile/cal endpoints**. A positive value implies the scan is too far east. The units are real arcseconds on the sky. SigXSDif = RMS on above. AvISMS = Average in-scan coverage margin at south/north (S/N) end AvISMN of tiles. Compares Dec of southmost/northmost 6-deep frame center (3-band average) with Dec of tile/cal south/north endpoint**. A positive value implies excess coverage and a negative value missing coverage. SigISMS = RMS on above for the south end. SigISMN = RMS on above for the north end. **Note- The tile/cal endpoints reflect where the two 6-deep end-frame centers would need be to exactly cover the tile with the required overlap. -------------- scanning summary -------------- Array Rotation: dtheta (J,H,Ks) = Average for the night of the rotation angle of the three arrays with respect to scan direction. J and H are corrected to Ks rotation with a constant offset. Just the one value is quoted. (Current conversions are J'=J-0.0433 and H'=H-0.0989) Optimal value for the current frame-frame step size of 82.6" is 0.27. sigthet (J,H,Ks) = RMS on above. Test for >2-sigma excursions in the rotation as evidence for flexure in the camera. Offsets: avyoff (N,S) = Average frame-to-frame in-scan step size, reported separately for northgoing (N) and southgoing (S) scans. sigyoff (N,S) = RMS on above.
avxoff (N,S) = Average frame-to-frame cross-scan step size, reported separately for northgoing (N) and southgoing (S) scans. sigxoff (N,S) = RMS on above.
Tracking: maxdra = Magnitude of the mean maximum deviation of reconstructed frame- center RA's from the of-date RA of the first frame in the scan. rmsdra_first = RMS on above. -------------- seeing/focus summary -------------- Avshape (J,H,Ks) = Average seeing shape parameter for night in each of the three bands. Shape is defined as the "radial shape discriminant", which is computed by fitting (least-squares algorighm; see GALWORKS SDS) the three-parameter function fu*exp[(-r/alpha)**(1/beta)] to the coadd pixels centered on each object, where r is the radial distance from the object centroid or peak pixel and fu is the central surface brightness. The quantity (alpha*beta) is the "radial shape discriminant" or simply "shape." sigshape (J,H,Ks) = RMS on above.
AvFWHM (J,H,Ks) = Average image full-width at half-maximum.
AvAspct (J,H,Ks) = Average composite second image moment ratio - cross-scan/in-scan. MnAspct (J,H,Ks) = Minimum image moment ratio. MxAspct (J,H,Ks) = Maximum image moment ratio. -------------- photometric summary -------------- AvZP (J,H,Ks) = Average photometric zero point offset - Minst'-Mcat for each band. sigZP (J,H,Ks) = RMS on above. ---------- dark/responsivity summary ------------ Dark and responsivity values are shown for both Read 1 (only) and for Read 2 (Read 2 - Read 1) extractions, however, quality tests are not performed on the Read 1 (only) values.
diffdark (J,H,Ks) = Average pixel difference between nightly and canonical dark frames in J,H,Ks. sigdark (J,H,Ks) = RMS on above. Ndrkmask (J,H,Ks) = Number of pixels masked in DARKS. diffresp (J,H,Ks) = Average pixel difference between nightly and canonical J, H, Ks responsivity images. sigresp (J,H,Ks) = RMS on above.
Note that dark and twilight sky flat field images may not be acquired every night during the survey. Therefore, the 24hr Q/A analysis derives the above parameters only if the dark and twilight sky flats are known to exist. In the absence of darks and/or flats, these parameters are assigned the value "not taken." 99/03/02 ldf