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Next: Galaxy Photometry Up: 2MASS Technical Memorandum Previous: Detector Tests

Point Source Photometry Tests

The first three items all concern a concentrated effort using standard stars, therefore they would be most effciently done on 2 to 3 nights devoted more or less exclusively to standard stars. However, these tests can incorporate standard star measurements made during all photometric nights.

Follow good sized set (10 to 12) of standard stars in the K=9-11 range near airmass=1 from night-to-night, to study the stability of color terms. These should have a good range in color, say a range in J-K of 1-2. This test should use the standard scan length since all stars in the scan of appropriate magnitude can be used to improve the statistics.

10 standard stars observed once per night in each band for 3 nights, for a total of 90 observations, will take 11.0 hrs at 442 secs/scan (6 scans with secs/frame), or 3.7 hrs per night.

Follow 2 to 3 standards over 1 or 2 nights at a range of airmasses to check extinction corrections; all 3 bands.

2 standards observed in 3 bands at 5 different airmasses, using short 1 scans: 42 frames per scan 1.7 secs/frame = 71 secs per observation. 30 observations 71 secs = 0.6 hrs.

Check the stability of the zero-point by observing a standard star at airmass 1.0 once per hour.

This test can be done with the observations obtained in 2.1 as long as those are done close enough to X=1. Done independently, one standard observed in a short scan once per hour during one 8 hour night, each of three bands, would require a total of 24 observations, or 0.5 hrs at 71 secs per observation.

Check the uniformity of the photometry across the array with a series of scans across a field with small cross-stepping between scans. Sample the field at 10 to 15 cross-scan positions on array. Carry out for both a standard star as well as a moderately dense region such as the M92 field. To be done in all 3 bands. Randomize the order of the cross-scans to minimize systematic effects.

Repeat this test using a longer reset delay per 1.1.

One standard observed using short scans (12 frames per scan) with 12 cross-stepped positions, repeated twice for better in-scan sampling, requires 490 seconds (12 24 1.7 secs/frame), or 0.4 hrs for all three bands. Repeating 3 times at different reset delays, and once on the denser field, gives a total of 1.6 hrs.

Observe a fairly sparse point source field with at least one bright star through a range in focus to check how the photometry depends on small drifts in focus.

One standard field observed with short 12 frame scans at 5 focus positions will take 0.4 hrs.

Obtain scans in all three bands at a range of source densities, repeated several times, for completeness and reliability tests, confusion processing tests, and bandmerger development.

Three fields (at say , 15 and 25) observed with 6 scans, repeated 5 times in each band require 3 fields 3 bands 5 repeats 442 secs/scan = 5.5 hrs.

next up previous
Next: Galaxy Photometry Up: 2MASS Technical Memorandum Previous: Detector Tests

Gaylin Laughlin
Tue Feb 14 09:11:22 PST 1995