SPACE TELESCOPE SCIENCE INSTITUTE Operated for NASA by AURA TIPS: STIS Report Paul Goudfrooij 1.Unusual Target ACQ Failures: Update & Resolution 2.Calibration of CTE loss in Spectroscopic Modes Full story available under Also STIS ISR New “Pseudo-Apertures” (if time available)

TIPS Presentation Paul Goudfrooij 2 May 15, 2003 Recent Target ACQ Failures (with L. Dressel, R. Pitts, T. Wheeler) No Flux in the Lamp Image Two recent ACQs failed (March 2, April 6) due to No Flux in the Lamp Image All mechanisms show nominal telemetry ACQ macro used 3.8 mA setting for HITM1 lamp, much below ‘default’ 10 mA – 3.8 mA setting originally put in place to allow wavecals for the most sensitive MAMA settings, and to save lamp life time Contacted manufacturer + their consultant – Sputtered material forms a ring inside glass envelope around cathode. If set at (too) low current, electrons may flow to sputtered ring rather than to cathode Conclusion: Lamp did not fire Since 5/12/03, ACQs use 10 mA setting. All ACQs taken so far are OK.  

TIPS Presentation Paul Goudfrooij 3 May 15, 2003 Correcting CCD Spectroscopy for CTE Loss (with R. Bohlin) 4 Readout Amps (1 / corner) 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 Sensitive Region (1024x1024 pix)

TIPS Presentation Paul Goudfrooij 4 May 15, 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) should be – Designed to represent “worst–case” point source spectroscopy (should be no background to fill traps)

TIPS Presentation Paul Goudfrooij 5 May 15, 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

TIPS Presentation Paul Goudfrooij 6 May 15, 2003 CTI Parametrization: Imaging vs. Spectroscopy Dependence on signal & background levels to be done separately for imaging and spectroscopy Spectroscopy Imaging CCD Row Number CCD Column Number

TIPS Presentation Paul Goudfrooij 7 May 15, 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 –

TIPS Presentation Paul Goudfrooij 8 May 15, 2003 The Strong Effect of Background: Gain=1 vs. Gain=4 Background level in spectroscopy mode typically low, dominated by dark current – Also need to account for spurious charge of the STIS CCD flush CCD Readout CCD

TIPS Presentation Paul Goudfrooij 9 May 15, 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

TIPS Presentation Paul Goudfrooij 10 May 15, 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 + { [± 0.016] (t – t 0 ) } (with t in yr) CTI data points from Tom Brown 60 e –

TIPS Presentation Paul Goudfrooij 11 May 15, 2003 Final CTI Correction Formula (For Point-Source Spectroscopy) Define background (sky) and epoch parameters: yr = (MJD – ) / (i.e., relative to ) bg = max(BACKGROUND,0) for CCD Gain = for CCD Gain = 4 Functional form producing best fit to the data: CTI = GROSS –  exp –3.85  ( yr) bg GROSS 0.17 ) ( Implementation into the pipeline:  Formula parameters into CCD table reference file (new columns)  1-D extraction step ( x1d ) will correct for CTI by default for CCD data (CTE correction step switchable) For Cycle 12 Phase II, provided downloadable IRAF script to calculate correction factor for a given net & background level.

TIPS Presentation Paul Goudfrooij 12 May 15, 2003 Quality of CTI fit CTI Correction good to  7%  Spectrophotometry good to  1%

TIPS Presentation Paul Goudfrooij 13 May 15, 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 Provide POS TARGs to GOs in Phase-II Update; Apertures to be implemented in next APT build. nominal new