Post-SM4 Sensitivity
Calibration of the STIS
Echelle Modes
Azalee Bostroem
With help from: Ralph Bohlin, Alessandra Aloisi, Charles
Proffitt, Kenneth Hart, Phil Hodge
• Grating disperses light
vertically
• Higher orders are chosen and
dispersed horizontally
• Orders have overlapping
wavelength ranges
• Allows for broadband high
resolution spectroscopy
• STIS has 4 modes medium
and high resolution modes
Increasing Order/ Decreasing Wavelength
Echelle Modes
Increasing Wavelength
Photometric Conversion Table
(PHOTTAB)
 Convert net count rate to flux
 Models the shape of the blaze function of each order
 Shape varies continuously with location on the detector and
time
 Temporal component can experience a discontinuity with
instrument changes (e.g. switch from Side 1 to Side 2
electronics
 Discontinuity expected following SM4
 Program 11866 executed in Cycle 17 to characterize the
echelle blaze function
Status following SM4
Net Counts
Pre-SM4 Flux Calibration on Post-SM4 Data (smoothed)
Making a new PHOTTAB
 Steps:




Divide net counts of each order by a model spectrum
Fit each order with a spline
Smooth splines across orders
Record smoothed nodes for each order of every central
wavelength in a table
But its never that simple…
 First PHOTTAB created using STScI CalSTIS
calibrated data
 Created grating dependent bad pixel tables
 Created new ripple tables
 Look for the E140H flux anomaly
 Data not in current PHOTTAB not extracted
Bad Pixel Tables
 NUV Bad Pixel Table:




NUV corners are vignetted
Vignetting is grating dependent
Previously in flat field
Now in bad pixel table
 FUV Bad Pixel Table:
 Repeller wire across detector
 Previously in flat field
 Location is grating dependent
 Now in bad pixel table
Ripple Tables
 Echelle 2D scattered light background subtraction
 Normalized blaze function
 Only delivered once in
2002, no information on
the creation
 Solve issue in E140H
data background
subtraction
Flux Anomaly
 Decreased throughput directly following SM4 in E140H
and E230M
Flux Anomaly Cont.
 Observed again after MAMA shutdown in fall 2010
 Not observed in next monitoring Observation: April
2010
 Echelle Flux calibration program executed November
28, 2009 - January 6, 2010
Data not affected
 If affected, then flux of new data should be too high
Edge Orders
 When PHOTTAB was created in 2006, the program
was taken at extreme mode select mechanism
positions
 Monthly offsetting turned off for Echelle data
 Some orders are off the detector
 CalSTIS will not extract data not in the PHOTTAB
unless fluxcorr is set to omit
 These orders were evaluated and included on an
individual basis
PHOTTAB Creation
 Find sensitivity for each order:
 Sensitivity = Observed Net Count Rate/Model Flux
 Exclude bad pixels and strong absorption lines
Sensitivity
PHOTTAB Creation
 Find sensitivity for each order:
 Sensitivity = Observed Net Count Rate/Model Flux
 Exclude bad pixels and strong absorption lines
 Fit a 7 (9 for E230M) node spline to sensitivity for
each order
Spline
PHOTTAB Creation
 Find sensitivity for each order:
 Sensitivity = Observed Net Count Rate/Model Flux
 Exclude bad pixels and strong absorption lines
 Fit a 7 (9 for E230M) node spline to sensitivity for each order
 Smooth spline nodes for each order in the cross
dispersion direction
Smooth
PHOTTAB Creation
 Find sensitivity for each order:
 Sensitivity = Observed Net Count Rate/Model Flux
 Fit a 7 (9 for E230M) node spline to sensitivity for each order
 Smooth spline nodes for each order in the cross dispersion direction
 Back out the TDS to reflect sensitivity at Launch
 Extrapolate to infinite aperture and extraction box
height
Final Calibration
Changes in CalSTIS 2.38
Phottab: A DUMMY pedigree will still be extracted
opt_elem
cenwave
sporder
sensitivity
pedigree
E140H
1343
287
DUMMY
E140H
1343
288
DUMMY
E140H
1343
289
DUMMY
E140H
1343
290
INFLIGHT
X1D Table: Add net_err column, set flux, err = 0 for DUMMY pedigree
opt_elem
cenwav
e
sporder
dq
net
net_err
flux
err
E140H
1343
289
dq
array
net
array
net_err
array
0
0
E140H
1343
290
dq
array
net
array
net_err
array
flux
array
err array
Future Work: Blaze Function
Shift Evolution