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)
1
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)
2
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)
3
Rotation rates of the CCD L grating traces
(positive = clockwise)
GRATING
STScI TIPS
20 July 2006
ROTATION
RATE (deg/yr)
G140L, high
0
G140L, low
-0.0030
G230L
+0.0005
G230LB
+0.0030
G430L
+0.0041
G750L
+0.0037
Time-Dependent Spectral Traces for the STIS First Order Modes
Linda Dressel (INS)
4
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)
5
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 01 1996 (for aperture at ~ +3")
G140L, USEAFTER Mar 15 1999 (for aperture at ~ -3"): rotated to compensate
for MSM change
G230L: 2 Sep 1997, CAL/STIS 7667 (o46j01*) NGC346-368 (3 stars, 8 steps)
G230L
G230LB: 13 Feb 1998, CAL/STIS 7665 (o45p02*) HD120315 (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)
6
New Code:
OPUS 2006.4, 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)
7
Comparison of “traces” made from x2d files: G140L (low position)
OLD REDUCTION: EARLY, LATE
STScI TIPS
20 July 2006
NEW REDUCTION: EARLY, LATE
Time-Dependent Spectral Traces for the STIS First Order Modes
Linda Dressel (INS)
8
Comparison of “traces” made from x2d files: G430L (center)
OLD REDUCTION: EARLY, LATE
STScI TIPS
20 July 2006
NEW REDUCTION: EARLY, LATE
Time-Dependent Spectral Traces for the STIS First Order Modes
Linda Dressel (INS)
9
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)
10
• 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)
11
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)
12