Time Dependent Sensitivity
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Transcript of Time Dependent Sensitivity
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Time Dependent Sensitivity
STIS CCD-Modes
STYS - TIPS ‘04
Currently
Ralph Bohlin
Scott Friedman (PI)
Paul Barrett
Previously
Nolan Walborn
Ed Smith
Ivo Busko
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TDS: Time Dependent Sensitivity
• Monitor the sensitivity of each CCD grating mode to detect any changes due to contamination or other causes.
• Prior to analysis we first account for temperature dependencies as well as losses due to CTE.
• Create reference files for use in the STIS data-reduction pipeline to correct extracted 1D spectra for time dependent sensitivity losses.
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Observations
• AGK+81D266 is a flux standard sub-dwarf whose position allows for observations throughout the year.
• CRSPLIT = 2 for cosmic ray rejection; CCDGAIN=1 (default)
• G750L and G750M observations have contemporaneous fringe flat exposures for fringe removal.
Cycle Proposal Frequency
7 7672 Every two months8 8418
9 8856Every three
months10 8914
11 9627
12 10030 1.5 months
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G230LB
• 1700-3000 angstroms• 173 sec. exposure• 34 observations
Wavelength (A)
Net
Cou
nt R
ate
AGK+81D266
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G430L
• 2900-5700 angstroms• 173 sec. exposure• 35 observations
Wavelength (A)
Net
Cou
nt R
ate
AGK+81D266
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G750L
• 5500-9900 angstroms• 432 sec. exposure• 35 observations
Wavelength (A)
Net
Cou
nt R
ate
AGK+81D266
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Temperature Dependency
Mode %/C
G230LB 0.34
G430L 0.25
G750L 0.07
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The Problem
Net
Cou
nt R
ate
Wavelength (A)
t0 ~ 1997
t1 ~ 2004
G230LB
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The Ratio
t 1/t 0
Wavelength (A)
t0 ~ 1997
t1 ~ 2004
Obsn/Reference
0.91
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Avg. G230LB Trends
Sensitivity loss
1%/yr - 3%/yr
1.10%/yr +/- 0.19 sig = 0.23%
-1.79%/yr +/- 0.10 sig = 0.59%
-0.43%/yr +/- 0.43 sig=0.59%
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G230LB - all wavelengths
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Avg. G430L Trends
Sensitivity loss
0.2%/yr
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Avg. G750L Trends
Sensitivity loss
Typically 0%/yr
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Pipeline Implementation
• A TDS reference file contains MJDs and slopes at each wavelength bin.
• calSTIS uses linear interpolation to correct each observation based on wavelength and epoch.
• The result is an extracted 1D flux spectrum corrected for both TDS and CTE.
Flu
x
t0 ~ 1997
t1 ~ 2004mean(ratio)
0.995
G230LB
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G230LB
1.10%/yr +/- 0.19 sig = 0.23%
-1.79%/yr +/- 0.10 sig = 0.59%
-0.43%/yr +/- 0.43 sig=0.59%
Uncorrected Net Count Rate Corrected FLUX
Side 2Electronics
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G430L
Uncorrected Net Count Rate Corrected FLUX
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G750L
Uncorrected Net Count Rate Corrected FLUX
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Summary• STIS sensitivity has been monitored since activation and is
dependent on time, temperature and wavelength.
• Sensitivity losses in the CCD modes range from 0%/yr (G750L) to ~3%/yr (G230LB)
• M-mode sensitivities mimic the trends found in the L-modes. We apply the L-mode corrections to the M-modes since we only observe medium dispersion modes at selected wavelengths.
• TDS reference files are available for first-order MAMA and CCD modes. In the future, imaging and echelle modes will also be corrected for TDS.