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WFPC2 Filter Wavelengths in the HST Archive

April 16, 2003: WFPC2 Filter Wavelengths in the HST Archive

-Anton Koekemoer and Gabe Brammer

The HST Archive/CDBS catalog contains a number of different quantities that characterize the properties of each filter in the WFPC2 filter set. These quantities include the "Central Wavelength", which appears as a default output column in archive searches, as well as the "Pivot Wavelength" and other related quantities that are used to calculate photometric keywords such as PHOTFLAM, which can be used to define the zeropoints for WFPC2 photometry.

The CDBS keyword referring to "Central Wavelength" was populated with a value for each filter before the launch of WFPC2, based on ground-based measurements of the filters. This quantity is not used in determining any other keywords, but appears as a default output column when archive searches are performed. There are a number of issues related to this quantity, which include the following:

Therefore, the WFPC2 group, in conjunction with personnel in charge of CDBS, have chosen to replace the use of "Central Wavelength" with the use of "Pivot Wavelength" instead. The only effect that this will have is that, when archive searches are performed, the column that used to list "Central Wavelength" will now contain values populated from the "Pivot Wavelength" instead. No other quantities are affected by this change; in particular, photometric keywords within the WFPC2 dataset headers will remain unchanged, since they are already calculated based on the Pivot Wavelength.

For reference, we are providing here a table that lists the old values, representing "Central Wavelength", together with the new values that are based on "Pivot Wavelength".

Table 1: 'Central Wavelength' lookup table showing both the old and updated table values. Cases where the central wavelength changed substantially (>15%) relative to the filter bandwidth are italicized.
Postscript version
Old Archive Values New Archive Values
Filter name Central Wavelength(A) Bandwidth(A) Pivot Wavelength(A) Bandwidth(A)
F122M 1368 340 1322 239
F160BW 1523 483 1522 449
F160AW 1523 483 1523 483
F160AN15 1523 483 1523 483
F160AP15 1523 483 1523 483
F160BN15 1523 483 1523 483
F160BP15 1523 483 1523 483
F170W 1730 500 1770 545
F185W 1933 308 1962 334
F218W 2159 358 2203 395
F255W 2553 393 2599 395
F300W 2911 745 2987 740
F336W 3344 381 3344 374
F343N 3424 25 3427 24
F375N 3737 27 3732 24
FQUVN33 3765 73 3765 73
FQUVN 3880 63 3913 60
F390N 3889 45 3888 45
F380W 3960 675 3983 682
F410M 4090 146 4088 147
FR418N 4200 40 4200 40
FR418N33 4200 40 4200 40
FR418N18 4200 40 4200 40
F439W 4300 475 4311 473
F437N 4369 25 4369 25
F450W 4520 958 4556 951
F467M 4669 166 4670 167
F469N 4694 25 4694 25
F130LP 4796 5365 5815 4755
F487N 4866 26 4865 26
F165LP 5002 5036 5853 4529
F502N 5013 27 5012 27
FR533N 5400 55 5400 55
FR533N33 5400 55 5400 55
FR533N18 5400 55 5400 55
F555W 5407 1236 5439 1228
F547M 5479 486 5483 483
F569W 5623 974 5642 966
F588N 5893 49 5894 49
F606W 5957 1508 5997 1502
F622W 6170 917 6186 917
FQCH4N33 6211 44 6199 34
FQCH4N15 6211 44 6199 34
F631N 6283 31 6306 31
F656N 6563 21 6564 22
F658N 6590 28 6591 29
F675W 6714 877 6717 867
F673N 6732 47 6732 47
FR680N 6800 70 6800 70
FR680N33 6800 70 6800 70
FR680N18 6800 70 6800 70
F702W 6895 1389 6919 1385
FQCH4N 7200 46 7279 38
F791W 7829 1218 7881 1231
F814W 7940 1531 8012 1539
F785LP 8674 1407 8707 1381
FR868N 8700 90 8700 90
FR868N33 8700 90 8700 90
FR868N18 8700 90 8700 90
FQCH4P15 8922 60 8930 55
F850LP 9124 1051 9129 1038
F953N 9534 61 9545 53
F1042M 10201 382 10228 449
POLQ NULL NULL NULL NULL
POLQN33 NULL NULL NULL NULL
LRF NULL NULL NULL NULL
DEF NULL NULL NULL NULL
NONE NULL NULL NULL NULL