Photometric vs. Non-photometric Scans in the 6x Science Data

1. Introduction

In an effort to salvage as much of the 6x data as possible, all 6x lsc and lca scans will be run through the 6x pipeline whether or not a nightly CALMON photometric solution can be applied during processing. For 6x scans in which no CALMON solution is possible, a future user of the 6x catalog could potentially determine a bootstrap calibration using photometry from the 1x ADR as the calibration source, if that piece of sky were crucial to his/her science. This page describes the breakdown of photometric vs. non-photometric data that will be run during 6x processing.

Table 1 gives the breakdown by date/hemisphere (column 1) of all 6x data. Column 2 gives the calibration method for the night, as described in detail below. Column 3 lists the non-photometric 6x scans followed by the photometric scans in column 4.

2. Breakdown of Photometric vs. Non-photometric Scans

In total, there are 1482 6x scans of which 54 (3.6%) are non-photometric. Of these, 44 scans fall in a part of the night where no cal scans were obtained (as can happen if the night was cut short because of clouds) or in a part of the night where clouds so badly effected the zero-points that a meaningful CALMON solution could not be obtained. The remaining 10 scans, denoted by a trailing "*" in Table 1, were calibrated by CALMON in v3 but were found to contain clouds. Table 2 gives a breakdown of all 54 scans, along with a listing of whether or not repeat scans were taken of the same tiles. As Table 2 shows, 23 of them have no repeats, and this includes 2 Virgo tiles, 9 M33 tiles, 4 Lupus tiles, 7 LMC tiles, and 1 test tile. The other 31 have one or multiple repeats, all of which appear (for now) as photometric.

The Notes section at the bottom of Table 1 lists an additional 9 scans as possibly being non-photometric, and another 2 scans that are part of a two-cal-only interval in which the CALMON solution is not very robust.

Variability in cloud cover during the course of these scans will make some of them unsalvagable. A user of the 2MASS Extended Mission data products could, however, bootstrap a calibration to those scans in which clouds are not a problem by using 1x data in the 2MASS All-Sky Data Release.

3. Calibration Methods for the 6x Data

There are several methods needed to run these data through the 6x pipeline, as listed in column 2 of Table 1. These are --

v3 -- The CALMON solution used in v3 can be applied
v3rerun -- The v3 CALMON solution needs to be rerun to include more standard cal sets than the original v3 run
new -- The v3 CALMON solution needs to be run to include special cal fields set up for the Magellanic Cloud campaign
none -- No CALMON solution can be applied to these data, but they should be run far enough through the pipeline so that .bfpts and .gals files are created
(wrong exp.) -- No processing will be attempted on southern data from 001025s to 001109s since the exposure time was incorrectly set to 1x instead of 6x.

Five nights need to have some of their scans calibrated and others not, and these are listed as "v3rerun/none" or "new/none" in Table 1. We need to discuss how best to process these nights, whether it be in a single pass or broken into two separate runs.

[Last Updated: 2003 Jul 23; Davy Kirkpatrick]