Download - Time Dependent Sensitivity
Time Dependent Sensitivity
STIS CCD-Modes
STYS - TIPS ‘04
Currently
Ralph Bohlin
Scott Friedman (PI)
Paul Barrett
Previously
Nolan Walborn
Ed Smith
Ivo Busko
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.
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
G230LB
• 1700-3000 angstroms• 173 sec. exposure• 34 observations
Wavelength (A)
Net
Cou
nt R
ate
AGK+81D266
G430L
• 2900-5700 angstroms• 173 sec. exposure• 35 observations
Wavelength (A)
Net
Cou
nt R
ate
AGK+81D266
G750L
• 5500-9900 angstroms• 432 sec. exposure• 35 observations
Wavelength (A)
Net
Cou
nt R
ate
AGK+81D266
Temperature Dependency
Mode %/C
G230LB 0.34
G430L 0.25
G750L 0.07
The Problem
Net
Cou
nt R
ate
Wavelength (A)
t0 ~ 1997
t1 ~ 2004
G230LB
The Ratio
t 1/t 0
Wavelength (A)
t0 ~ 1997
t1 ~ 2004
Obsn/Reference
0.91
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%
G230LB - all wavelengths
Avg. G430L Trends
Sensitivity loss
0.2%/yr
Avg. G750L Trends
Sensitivity loss
Typically 0%/yr
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
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
G430L
Uncorrected Net Count Rate Corrected FLUX
G750L
Uncorrected Net Count Rate Corrected FLUX
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.