STEREO HI Post-Launch Support Chris Davis October 2009

HI-1 flatfield and photometric calibrations Have taken into account all available instrument response data – Instrument-level and optics unit-level calibrations at CSL Optics manufacturer’s (ICOS) filter response data CCD manufacturer’s (e2v) QE data Optical glass manufacturer’s (Schott) transmission data Response to source spectrum S(λ) predicted as – C pred = (A/G) ∫ (λ/hc)S(λ)T(λ)QE(λ)dλ (in DN s –1 ) where A is aperture and G is CEB readout gain (e – per DN) Note: The term (λ /hc) is required because CEB response is determined by number of photoelectrons and not by energy flux. Some authors (other instruments) have neglected this!

Measured stellar responses vs predicted (1) Measured response determined by aperture photometry Many100’s of stars of various spectral types & with known spectra used Note: The outliers with large intensities lie below the fitted line due to saturation effects. Including/excluding these has negligible effect on fits.

Measured stellar responses vs predicted (2) If our model for instrument response were perfect, slope of measured vs predicted intensity would be 1.0 Actually 0.93 for HI-1A and 0.98 for HI-1B Residual error likely to be some combination of the following systematics (but we have determined it): Absolute value of optics/filter transmissions Absolute value of CCD QE Value of CEB readout gain G Size of optics entrance aperture Agreement for HI-1B (2% error) regarded as excellent, HI-1A (7% error) still very good

Results: Large-scale flatfield Surface plots of pre-launch & optimised large- scale flatfield for HI-1A (top left & right) and HI-1B (bottom left & right)

Results: HI-1 photometry Defined HI-1 magnitude scale for stellar-type objects – Also conversion factors from DN s –1 pixel –1 to B 0 (mean solar brightness) and S10 units for diffuse emission regions.

On-going and future work “Determination of the photometric calibration and large-scale flatfield of the STEREO Heliospheric Imagers: I. HI-1” just being submitted to Solar Physics Large-scale flatfield and photometric calibrations of HI-2 Instrument response less uncertain because no filter But tracking of stars and aperture photometry more challenging because of much larger and variable PSFs Small-scale flatfields for HI-1 and HI-2 Not so crucial as large-scale but still important for maximising the data quality

Accurate alignment using the starfield results in improved background subtraction in HI1B

Davis et al, 2009

Williams et al, 2009 (submitted)

New data products J-maps (elongation vs time) C-maps (latitude vs time)

Rouillard et al, 2009 (in preparation)

Savani et al, Observational evidence of a CME distortion directly attributable to a structured solar wind, Submitted to GRL, Savani et al, 2009 (in preparation)

Pearson et al, 2009 (in preparation)

The Pleiades Mercury Mars Vesta Uranus Astraea Earth and Moon

Outreach project with a local school to produce light-curves for asteroids such as for Vega (below)

Solar Stormwatch – Outreach project with the Royal Greenwich Observatory

HI data has been used by UK artists Semiconductor in a film that is being exhibited in galleries world-wide and on the web – bringing STEREO to the attention of the arts community