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

2. TIPS Presentation Paul Goudfrooij 2 March 20, 2003 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. TIPS Presentation Paul Goudfrooij 3 March 20, 2003 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. TIPS Presentation Paul Goudfrooij 4 March 20, 2003 Unusual Target ACQ Failure No Flux in the Lamp Image 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   12 3 12 3

5. TIPS Presentation Paul Goudfrooij 5 March 20, 2003 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. TIPS Presentation Paul Goudfrooij 6 March 20, 2003 Correcting CCD Spectroscopy for CTE Loss 4 Readout Amps (1 / corner) Nominal Amp: D (lowest RN) Bi-directional Clocking yields CTI  1 – CTE: CTI =  (flux D / flux B )  Y 1212 STIS CCD: Measured using “Sparse Field Tests” Serial overscan Axis1 (X) Axis2 (Y) Parallel (virtual) overscan Serial overscan Amp A Amp C Amp D Amp B Nominal Clocking Direction Nominal Readout Direction

7. TIPS Presentation Paul Goudfrooij 7 March 20, 2003 “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: (i) “Internal” Sparse Field Test – 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. TIPS Presentation Paul Goudfrooij 8 March 20, 2003 “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. TIPS Presentation Paul Goudfrooij 9 March 20, 2003 External Sparse Field Test: Imaging CTI Analysis Slope systematically flatter with increasing flux “Sky” presumably fills traps in bottoms of potential wells, mostly affecting transfer of small charge packets. Suggests CTI Clear dependence on background level (“sky”) bck signal   exp –

10. TIPS Presentation Paul Goudfrooij 10 March 20, 2003 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 flush CCD Readout CCD

11. TIPS Presentation Paul Goudfrooij 11 March 20, 2003 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 Spectroscopy Imaging CCD Row Number CCD Column Number

12. TIPS Presentation Paul Goudfrooij 12 March 20, 2003 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. TIPS Presentation Paul Goudfrooij 13 March 20, 2003 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 CTI = CTI 0 + { 1 + 0.243 [± 0.016] (t – t 0 ) } (with t in yr) CTI data from Tom Brown 60 e – 120 180 500 3400

14. TIPS Presentation Paul Goudfrooij 14 March 20, 2003 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) bg GROSS 0.17 ) ( 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. TIPS Presentation Paul Goudfrooij 15 March 20, 2003 Quality of CTI fit CTI Correction good to  7%  Spectrophotometry good to  1% @ 2000.6

16. TIPS Presentation Paul Goudfrooij 16 March 20, 2003 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