CALPRODUCT-VS-001: VIS Absolute Photometric Standards

Parent requirement

R-CAL-B-VS-5100

Scheduling

Once, during PV phase, with high spatial sampling.

Upon request during routine phase, with low spatial sampling, if unexplained discrepancies occur in photometry after processing.

Objective

Obtain absolute flux standard measurements as a function of position for each VIS detector, therefore characterizing the entire optical path. The observations serve as an independent check of the global system response, as well as the impact of persistence and trap filling.

Observations

Fulfilled by

CALBLOCK-PV-002: NISP-P and VIS Absolute Photometric Standards (PV phase)

CALBLOCK-PV-001: Self Calibration

CALBLOCK-F-001: Self Calibration

CALBLOCK-F-006: Wide Survey (spot check, using flux-calibrators in the survey area)

Targets and pointing constraints

Table 10: Spectrophotometric standards in the continuous viewing zones (preliminary). CSV file

# ID

R.A.

Dec

Type

r [AB mag]

J [AB mag]

H [AB mag]

comment

WDJ175318+644502

17:53:18.65

+64:45:02.15

DA

17.45

18.26

18.36

<1% variability; in Self-cal

WDJ174911+643533

17:49:11.78

+64:35:33.54

DA

17.01

17.86

18.26

1% variability

WDJ181144+654916

18:11:44.96

+65:49:16.42

DA

17.76

18.62

19.14

2-3% variability

WDJ040027-502542

04:00:27.30

-50:25:42.04

DA

18.28

19.38

20.00

1-2% variability

WDJ041345-473726

04:13:45.06

-47:37:26.29

DA

17.00

17.71

18.27

<1% variability

WDJ042211-474142

04:22:11.36

-47:41:42.02

DB

15.77

16.66

17.17

5-7% variability

J175300+663151

17:53:00.90

66:31:51.30

Ell

19.30

for validation purposes only

Data volume

NISP: 3*16*16*3 * NP = 202752 MB

VIS: 256*VS = 115712 MB (TBC)

Processing input

Ground Processing Input Data:

Data Description:

NISP: 3*16*16*3 = 2304 photo-MACC images

VIS: 256 images (one VIS image at every dither point)

Processing output

  • Mean and stdev of the photometric zeropoint (conversion factor) per detector

  • Plot of zeropoint as a function of position in the focal plane (with the detector grid overlaid)

Required accuracy, constraints

  • Photometric flux measurement / photometric conversion factor derived from each position are within 1.0% of the mean.

  • Comparison with expectations from the total system throughput, should be within 5%, but may be larger.

Processing tools

L1 science pipeline and absolute calibration pipeline, additional offline trend analysis of flux measurements

Validation

The map of absolute zeropoints should mainly reflect the quantum efficiencies at the respective pixel coordinates. Other effects, such as optical bandpass variations, are negligible (for NISP, but probably not for VIS due to the effective dichroic bandpass for VIS).

The data can be used to directly test the top-level CalCD-A requirements R-CAL-A-VS-4000 (After all calibrations, the relative photometric error of the VIS Instrument shall be < 1.0%), and G-CAL-A-VS-5000 (After all calibrations, the absolute photometric error of the VIS Instrument shall be < 5.0%). After all calibrations, the distribution of measured fluxes at the various detector positions, normalized by the intrinsic (true) fluxes, must have a width of not more than 1.0% of the flux (after correcting for photon noise), and the absolute fluxing should meet the CalCD-A goal.

Recovery

A failure of the validation is critical for the mission success. It must be investigated with high priority. Possible causes are (non-exhaustive)

  • a severe short-coming in the data processing

  • incomplete understanding of the error budget

  • a significant change in hardware properties occurred (electronic, contamination, …)

Quality control parameters

DataModel: https://gitlab.euclid-sgs.uk/

Contact person

VIS instrument scientist