trace tilt evolution trace shape new traces new evolution code bimodal behavior remaining work

STScI TIPS20 July 2006

Time-Dependent Spectral Traces for the STIS First Order ModesLinda Dressel (INS)

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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



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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?



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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



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Rotation rates of the CCD L grating traces(positive = clockwise)

GRATING ROTATION RATE (deg/yr)

G140L, high 0

G140L, low -0.0030

G230L +0.0005

G230LB +0.0030

G430L +0.0041

G750L +0.0037



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CCD traces have the same shape:

Trace minus linear fit for G230LB, G430L, G750L, G750M(6581, 6768, 8561)



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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)

G230LBG430L: rotation of G230LBG750L: rotation of G230LB



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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.



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Comparison of “traces” made from x2d files: G140L (low position)OLD REDUCTION: EARLY, LATE NEW REDUCTION: EARLY, LATE



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Comparison of “traces” made from x2d files: G430L (center)OLD REDUCTION: EARLY, LATE NEW REDUCTION: EARLY, LATE



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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



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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

• 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



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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

trace tilt evolution trace shape new traces new evolution code bimodal behavior remaining work

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