SPACE TELESCOPE SCIENCE INSTITUTE Operated for NASA by AURA TIPS: STIS Report Paul Goudfrooij 1. Unusual Target ACQ Failures: Update & Resolution 2. Calibration of CTE loss in Spectroscopic Modes • Full story available under http://www. stsci . edu / hst / stis /training/team/activities/lectures.html • Also STIS ISR 2003-03 3. New “Pseudo-Apertures” (if time available)
SPACE TELESCOPE SCIENCE INSTITUTE. TIPS: STIS Report. Operated for NASA by AURA. Paul Goudfrooij. Unusual Target ACQ Failures: Update & Resolution Calibration of CTE loss in Spectroscopic Modes - PowerPoint PPT Presentation
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nebulosity provide three convenient, ~constant “sky” levels per spectrum
6May 15, 2003TIPS Presentation Paul Goudfrooij
CTI Parametrization:Imaging vs. Spectroscopy
• Dependence on signal & background levels to be done separately for imaging and spectroscopy
Spectroscopy
Imaging
CCD Row NumberCCD Column Number
7May 15, 2003TIPS Presentation Paul Goudfrooij
External Sparse Field Test: Imaging CTI Analysis
• Slope systematically flatter with increasing flux
• “Sky” presumably fills traps in bottoms
of potential wells, mostly affecting transfer of small charge packets.
• Suggests CTI
Clear dependence on background level (“sky”)
bcksignal
exp –
8May 15, 2003TIPS Presentation Paul Goudfrooij
The Strong Effect of Background: Gain=1 vs. Gain=4
• Background level in spectroscopy mode typically low, dominated by dark current– Also need to account for spurious charge of the STIS CCD
flush
CCD ReadoutCCD
9May 15, 2003TIPS Presentation Paul Goudfrooij
Functional Dependence on Signal and Background Levels
• Iterative Process for Spectroscopy – Parameter space covered by ESF test at a given epoch is limited– Sensitivity monitor: good coverage of signal levels, but not of sky
G230LB data allow suitable cross-comparison with MAMA G230L
AGK+81D266,G230LB
10May 15, 2003TIPS Presentation Paul Goudfrooij
Time Constant of CTI Evolution
• Need several datasets, each with same signal & background level• Need datasets covering long baseline in time ISF data
– Have to correct for signal & background dependence prior to fitting
CTI = CTI0 + { 1 + 0.243 [± 0.016] (t – t0) }
(with t in yr)
CTI data points from Tom Brown
60 e
–
120
180
500
3400
11May 15, 2003TIPS Presentation Paul Goudfrooij
Final CTI Correction Formula (For Point-Source Spectroscopy)
• Define background (sky) and epoch parameters: yr = (MJD – 51765.25) / 365.25 (i.e., relative to 2000.6)
bg = max(BACKGROUND,0) + 0.5 for CCD Gain = 1 + 5.0 for CCD Gain = 4
• Functional form producing best fit to the data:
CTI = 0.0467 GROSS –
0.720 exp –3.85 (1 + 0.243 yr)
bgGROSS
0.17
) (• Implementation into the pipeline:
Formula parameters into CCD table reference file (new columns) 1-D extraction step (x1d) will correct for CTI by default for CCD
data(CTE correction step switchable)
• For Cycle 12 Phase II, provided downloadable IRAF script to calculate correction factor for a given net & background level.
12May 15, 2003TIPS Presentation Paul Goudfrooij
Quality of CTI fit
CTI Correction good to CTI Correction good to 7% 7% Spectrophotometry good to Spectrophotometry good to 1% 1%
13May 15, 2003TIPS Presentation Paul Goudfrooij
New “Pseudo-Apertures”
• FUV-MAMA first-order spectroscopy at detector location with low dark
– ~ 2’’ above bottom of detector– Reduction of dark current by factor of 5– 52x0.05D1, …, F25QTZD1
• Improvement of Fringe Flats at E1 positions– Important to align fringes in flat with those in
target spectrum– 52x0.1 slit (best for defringing) location is offset
in dispersion direction from wider slits– New ‘E2’ positions will place target slightly off-
center in slits 0.2 arcsec wide• New WEDGEA0.6 position for 50CORON• Provide POS TARGs to GOs in Phase-II Update;