observing the solar system with hst amy simon nasa’s goddard space flight center
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Observing the Solar System with HSTAmy SimonNASA’s Goddard Space Flight Center
Observation Planning for PlanetsLocation, location, location
◦ Planets move! Need accurate ephemerides, tracking
Timing◦ Planets rotate
Need to track longitude, and satellites/shadows
◦ Planets change Sudden, rapid response events
Orientation◦ Planets have varying obliquities, preferred axes for slits◦ Problem for HST, will be worse for JWST
Ideally, want to observe at opposition◦ Used to be a problem for HST◦ Will be a problem for JWST
PhotometryNeed accurate photometric
calibration for many studies◦PHOTFLAM is used extensively to
calculated the solar flux in each filter passband
◦DN converted to “I/F”Filters/instrument performance
should be monitored.WFPC2 CTE changes, etc.
Jupiter Spectrum May 2008
Jupiter Spectrum May 2008
Cross calibration & time variabilityHubble’s long life has led to studies
of time variability◦Need accurate long-term calibration◦Need accurate cross-calibration
WPFC2 focal planes ◦PC vs WF3 show some mismatches
WFPC2, ACS, WFC3 ◦Some similar filters◦Even with different central wavelengths
and pass bands, can get reasonably good agreement
WFPC2 PC only
WFPC2 PC & WF3
Long term trends in CTE, etc.
Oh, the games we play
Normalized to 13° N
WFPC2 vs WFC3
Fringing and VignettingExtended bright objects cause
interesting effects in filtersWFPC2 CH4 quad filters suffer
from vignetting◦Can get saturation in the vignetted
areasWFC3 long wavelength filters
show fringing◦Correctable, with patience
WFPC2 CH4 quad vignetting
WFC3 Fringing
Lessons for the Future Most planetary observers don’t use IRAF!
◦ Helpful to have instrument throughput tables as text file – needed for calculating solar flux (even more helpful to have solar flux in each filter!)
Keywords ◦ V3 PA not particularly helpful, but can be used with a
planetary ephemeris to determine north angle ◦ PHOTFLAM – don’t change the units! ◦ CTE – helpful to have performance keywords
Filter and performance monitoring Full frame bright object characterization
◦ Fringe flats Archive is actually set up reasonably well (though
planet names are not NED resolvable!). ◦ New Planets Pipeline looks promising
archive.stsci.edu/prepds/planetpipeline