Observing the Solar System with HST Amy Simon NASA’s Goddard Space Flight Center.

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