Wide Field Camera 3
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Posted by John Trauger on June 24, 1999 at 15:05:25:


Here is a strawman filter proposal for the atmospheres of giant planets and brown 
dwarfs -- a set of three quad filters as follows --

(1) UVIS CH4 abs/cntm pairs     619, 619(+/-), 893, 935 nm 
(2) UVIS CH4 narrowband         889, 904, 922, 937 nm (FWHM < 0.01*center wavelength)
(3) NIR CH4 abs/cntm pairs      1080, 1130, 1580, 1710 nm

This selection of planetary science passbands is offered for further discussion by the 
HST user community.  It has been distilled from an informal email survey distributed 
in May 1999 to a number of planetary scientist who are past users of HST data, and 
came from the following tabulation of their preferences.

------------------------------------------------------
 Preferences            Wavelength(nm)      Comments
------------------------------------------------------
   K                    1350 longpass       rings and satellites
   B C K M S W          1710                CH4
   B M S W              1650                cntm
   B C K                1580                cntm
   B M                  1480                NH3, H2O, Galileo/NIMS
   K M S W              1130                CH4     NIC1
   K M S W              1080                cntm    NIC1
   B C K R S W          935                 cntm    ~0.02/km-am
   B K R W              922                 CH4     ~0.3/km-am
   B K R W              904                 CH4     ~3/km-am
   B C H K R S W        893                 CH4     ~30/km-am, WFPC2
   B K                  727                 CH4     WFPC2
   B H K R W            619                 CH4     WFPC2
   W                    619(+/-) dual-passband  continuum, Cassini
   B R                  635                 cntm
                        543                 CH4     WFPC2
   B                    200                 photometry
   B                    350                 photometry
------------------------------------------------------
Voting -- (and thanks to all for communicating your preferences)
   B = Kevin Baines
   C = Nancy Chanover
   H = Heidi Hammel
   K = Erich Karkoschka
   M = Mark Marley (cool brown dwarfs)
   R = Kathy Rages
   S = Amy Simon
   W = Bob West
------------------------------------------------------

There were various opinions on the choice of continuum wavelength companion 
for the 1.71 micron filter, here we have taken Karkoschka's advice and selected 
1.58 microns.  The suggested broadband filters are already accounted in the 
WFC3 set of photometry filters in the UV and NIR.

Bob West suggests a Cassini-style dual-passband continuum filter for the 619 nm 
band.  The 619(+/-) filter simultaneously transmits the continuum wavelengths on 
both sides of the 619 absorption feature, while blocking the 619 absorption band itself.

Since it is likely there will be space for up to two UVIS and one NIR filter for 
methane/planetary science, the list was reduced to 12 passbands distributed into 
three quad filters, each quad element covering an FOV larger than Jupiter. 

Multiple filter elements, four to each (quad) filter, each provide about 70 arcsecond
square fields of view in the UVIS camera, and somewhat smaller (TBD) FOVs in the 
NIR camera.  HST pointing offsets would be used to select among the four filter 
elements, as is done for the WFPC2 quads.  Rapid absorption/continuum exposure 
pairs could be facilitated via filter selection, rather than telescope pointing, by 
placing each CH4 and its corresponding continuum passband in the same quad position 
on two different filters.  Rapid subframe readouts of just one quadrant of the CCD 
can also be used to help keep the absorption/continuum pairs close together in time.

- John Trauger (on behalf of the WFC3 SOC)