STIS Status Report

1. SPACE TELESCOPE SCIENCE INSTITUTE STIS Status Report Operated for NASA by AURA Paul Goudfrooij • Group News / Reorganization • Unusual Target ACQ Failure • Items for upcoming Phase II Update • Planned New Apertures • Corrections for CTE loss

2. Group Reorganization • Two IS’es on well-deserved sabbatical: • Nolan Walborn (Sep 02) and Kailash Sahu (Mar 03) • Jeff Valenti reassigned to JWST / NIRspec (Jan 03) • But will finish a few STIS assignments • Scott Friedman (COS) helping out with a few tasks • CCD Dispersion Solutions • CCD & MAMA Spectroscopic Sensitivity Monitors • SM4 Backup to Tom Brown • Claus Leitherer (COS) to help out with • Phase-2 reviews of Cycle 12 MAMA programs (if more than we can reasonably handle in Spectrographs Branch)

3. Group Reorganization • “New” ESA Instrument Scientist: Jesús Maíz-Appelániz • User Support Lead IS • ETC & APT oversight • New Pipeline Lead IS: Charles Proffitt • New Calibration Lead IS: Linda Dressel • New Information Lead IS: Bahram Mobasher

4. Unusual Target ACQ Failure • Target ACQ of Spectroscopic Sensitivity Monitor Visit on March 6 failed: No Flux in the Lamp Image •  direct measurement to measure current across lamp • Hint of lower OCLP30VC, but not statistically significant • Slit wheel / MSM resolver counts identical to other ACQs • Shutter closed-open-closed sequence occurred nominally • All other mechanisms in their nominal positions • Preliminary conclusion: Lamp did not fire (HSTAR closed) • ACQs after the problematic one were all OK to date 1 2 1 2 3 3  

5. New “Pseudo-Apertures” • FUV-MAMA first-order spectroscopy at detector location with low dark • ~ 2’’ above bottom of detector • Reduction of dark current by factor of 5 • 52x0.05D1, …, F25QTZD1 • Improvement of Fringe Flats at E1 positions • Important to align fringes in flat with those in target spectrum • 52x0.1 slit (best for defringing) location is offset in dispersion direction from wider slits • New ‘E2’ positions will place target slightly off-center in slits  0.2 arcsec wide • New WEDGEA0.6 position for 50CORON • Will provide POS TARGs to GOs for cycle 12; Apertures to be implemented in next APT build. nominal new

6. Amp D Nominal Readout Direction Axis2 (Y) Nominal Clocking Direction 1 2 (fluxD / fluxB) Y CTI = Parallel (virtual) overscan Amp A Amp B Amp C Axis1 (X) Serial overscan Serial overscan Correcting CCD Spectroscopy for CTE Loss STIS CCD: • 4 Readout Amps (1 / corner) • Nominal Amp: D (lowest RN) • Bi-directional Clocking yields CTI  1 – CTE: Measured using “Sparse Field Tests”

7. (i) “Internal” Sparse Field Test “Sparse Field” Tests • Sparse fields to ensure that sources do not overlap, in which case (e.g.) PSF wings could fill traps for sources along the readout direction • Two varieties: • Annual series of lamp images through narrow slits, projected at 5 positions along columns (or rows) • Designed to represent “worst–case” point source spectroscopy (should be no background to fill traps)

8. “Sparse Field” Tests • (ii) “External” sparse field test (annually) • A. Imaging: • Sparse outer field in NGC 6752 • CVZ target (‘cheap’ observing time; yields range of backgrounds) • 3 exposure times; 50CCD mode • B. Spectroscopy: • Young open cluster NGC 346, in nebulosity • CVZ target • Slitless; 3 exp. times; G430L • [O II] 3727, H, [O III] 5007 lines in nebulosity provide three convenient, ~constant “sky” levels per spectrum

9.  bck signal External Sparse Field Test: Imaging CTIAnalysis Clear dependence on background level (“sky”) • Slope systematically flatter with increasing flux • “Sky” presumably fills traps in bottoms of potential wells, mostly affecting transfer of small charge packets. • Suggests CTI  exp –

10. The Strong Effect of Background:Gain=1 vs. Gain=4 • Background level in spectroscopy mode typically low, dominated by dark current • Need to account for spurious charge of the STIS CCD CCD Readout flush CCD

11. Spectroscopy Imaging CCD Column Number CCD Row Number Functional Dependence on Signal and Background Levels • To be done separately for imaging and spectroscopy • Spectroscopy: • ISF; ESF in slitless mode • CCD Sensitivity monitor data • Imaging (cf. Cal. Workshop ‘02): • ESF & Full-field sens. monitor

12. Functional Dependence on Signal and Background Levels • Iterative Process for Spectroscopy • Parameter space covered by ESF test at a given epoch is limited • Sensitivity monitor: good coverage of signal levels, but not of sky • G230LB data allow suitable cross-comparison with MAMA G230L AGK+81D266,G230LB

13. Time Constant of CTI Evolution • Need several datasets, each with same signal & background level • Need datasets covering long baseline in time  ISF data • Have to correct for signal & background dependence prior to fitting 60 e– CTI = CTI0 + { 1 + 0.243 [± 0.016] (t – t0) } (with t in yr) CTI data from Tom Brown 120 180 500 3400

14. 0.17 bg GROSS Final CTI Correction Formula (For Point-Source Spectroscopy) • Define background (sky) and epoch parameters: yr = (MJD – 51765.25) / 365.25 (i.e., relative to 2000.6) bg = max(BACKGROUND,0) + 0.5 for CCD Gain = 1 + 5.0 for CCD Gain = 4 • Functional form producing best fit to the data: ) ( CTI = 0.0467 GROSS–0.720  exp –3.85  (1 + 0.243 yr) • Implementation into the pipeline: • Formula parameters into CCD table reference file (new columns) • 1-D extraction step (x1d) to correct for CTE by default for CCD data (CTE correction step switchable) • For Cycle 12 Phase II, provide downloadable IRAF script to calculate correction factor for a given net & background level.

15. Quality of CTI fit CTI Correction good to 7%  Spectrophotometry good to 1% @ 2000.6

16. The Strong Effect of Background:Gain=1 vs. Gain=4 Complex behavior at low signal levels • CTE-like behavior obvious, but details not quite understood • Notice somewhat different behavior for B vs. D amps • Renders low-signal CTI values somewhat uncertain