1. Time-Dependent Spectral Traces for the STIS First Order Modes
Time-Dependent Spectral Traces for the STIS First Order Modes Linda Dressel (INS) with Don Lindler, Ralph Bohlin, Phil Hodge, Nadia Dencheva, Sherie Holfeltz
Trace tilt evolution
Trace shape
New traces
New evolution code
Bimodal behavior
Remaining work
STScI TIPS
20 July 2006
Time-Dependent Spectral Traces for the STIS First Order Modes
Linda Dressel (INS)

2. Time-Dependent Spectral Traces for the STIS First Order Modes
A grid of reference file traces is placed on an (flt, crj) image as the framework along which interpolation will be done to produce spectral extractions (x1d), rectified images (x2d)
Problem: x2d images still have some tilt
Row does not come from one location along the slit
 Random changes, systematic changes in traces?
STScI TIPS
20 July 2006
Time-Dependent Spectral Traces for the STIS First Order Modes
Linda Dressel (INS)

3. Time-Dependent Spectral Traces for the STIS First Order Modes
The tilt of the traces has been evolving steadily over time, showing clockwise rotation on the detector
G430L spectral traces at the center of the detector over the lifetime of STIS, along with the reference file trace
STScI TIPS
20 July 2006
Time-Dependent Spectral Traces for the STIS First Order Modes
Linda Dressel (INS)

4. Rotation rates of the CCD L grating traces (positive = clockwise)
ROTATION RATE (deg/yr)
G140L, high
G140L, low
G230L
G230LB
G430L
G750L
STScI TIPS
20 July 2006
Time-Dependent Spectral Traces for the STIS First Order Modes
Linda Dressel (INS)

5. Trace minus linear fit for G230LB, G430L, G750L,
CCD traces have the same shape:
Trace minus linear fit for G230LB, G430L, G750L,
G750M(6581, 6768, 8561)
STScI TIPS
20 July 2006
Time-Dependent Spectral Traces for the STIS First Order Modes
Linda Dressel (INS)

6. Time-Dependent Spectral Traces for the STIS First Order Modes
New traces (rotated as needed)  Improved trace reference files for L modes (delivery imminent) with specified MJD, rotation rate
G140L: 6 feb 1999, CAL/STIS 7937 (o53001*) GD71 (1 star, 20 steps along slit)
G140L, USEAFTER Oct (for aperture at ~ +3")
G140L, USEAFTER Mar (for aperture at ~ -3"): rotated to compensate for MSM change
G230L: 2 Sep 1997, CAL/STIS 7667 (o46j01*) NGC (3 stars, 8 steps)
G230L
G230LB: 13 Feb 1998, CAL/STIS 7665 (o45p02*) HD (1 star, 33 steps)
G230LB
G430L: rotation of G230LB
G750L: rotation of G230LB
STScI TIPS
20 July 2006
Time-Dependent Spectral Traces for the STIS First Order Modes
Linda Dressel (INS)

7. Time-Dependent Spectral Traces for the STIS First Order Modes
New Code: OPUS , including CALSTIS 2.21b (released 28 June 2006) STSDAS, including CALSTIS 2.21b (to be released in fall 2006)
CALSTIS 2.21b reads two new columns in the SPTRCTAB:
MJD
DEGPERYR (rotation rate; 0 if not measured for that grating/cenwave)
It reads the MJD of the science exposure.
It computes the difference in dates and the consequent trace rotation.
It applies that rotation to the traces before applying them to the (flt,crj) image.
STScI TIPS
20 July 2006
Time-Dependent Spectral Traces for the STIS First Order Modes
Linda Dressel (INS)

8. Comparison of “traces” made from x2d files: G140L (low position)
OLD REDUCTION: EARLY, LATE NEW REDUCTION: EARLY, LATE
STScI TIPS
20 July 2006
Time-Dependent Spectral Traces for the STIS First Order Modes
Linda Dressel (INS)

9. Comparison of “traces” made from x2d files: G430L (center)
OLD REDUCTION: EARLY, LATE NEW REDUCTION: EARLY, LATE
STScI TIPS
20 July 2006
Time-Dependent Spectral Traces for the STIS First Order Modes
Linda Dressel (INS)

10. Time-Dependent Spectral Traces for the STIS First Order Modes
COMPLICATION!
In this case, there are two evolutionary tracks of trace tilt vs time, both showing clockwise rotation on the detector
G750M(6768) spectral traces at the center of the detector over the lifetime of STIS, along with the reference file trace
STScI TIPS
20 July 2006
Time-Dependent Spectral Traces for the STIS First Order Modes
Linda Dressel (INS)

11. Time-Dependent Spectral Traces for the STIS First Order Modes
Grating tilt is set by 3 cylinders
Cylinder settings were changed on July 21, 1997
Only one exposure in G750M(6768) plot had the early settings
Virtually all STIS GO data have been taken after the change
Plot: SHIFTA2 vs date
(square: low evolution track, triangle: high evolution track)
Population on the two evolutionary tracks of trace tilt vs time is predicted by SHIFTA2, the measurement of the Y position of the wavecal image on the detector
The higher track is very rarely populated by exposures with central wavelengths 6581, 8561
STScI TIPS
20 July 2006
Time-Dependent Spectral Traces for the STIS First Order Modes
Linda Dressel (INS)

12. Time-Dependent Spectral Traces for the STIS First Order Modes
Remaining Work
Delivery of the new trace reference files for the L modes
Completion and delivery of new trace reference files for G750M(6581), G750M(6768), G750M(8561)
Implementation of a "tweak-trace" post-processing tool that measures the science image to determine the rotation to apply to the reference file traces
Completion of an Instrument Science Report
STScI TIPS
20 July 2006
Time-Dependent Spectral Traces for the STIS First Order Modes
Linda Dressel (INS)