TIPS-JIM Meeting 13 October 2005, 10am, Auditorium

Transcription

1 TIPS-JIM Meeting 13 October 2005, 10am, Auditorium 1. The Mid-Infrared Instrument (MIRI) Martyn Wells Medium Resolution Spectrometer for JWST 2. Temperature changes for ACS CCDs: Marco Sirianni Initial Study on Scientific Performance 3. Projected STIS performance through Paul Groudfrooij 2013 with and without the ASCS Next TIPS Meeting will be held on 17 November 2005.

2 The Mid-Infrared Instrument (MIRI) Medium Resolution Spectrometer for JWST Martyn Wells MIRI EC & UKATC

3 Spectrometer Main Optics Netherlands Spectrometer Pre Optics UKATC Deck (Leicester) Spectrometer Focal Plane Module (USA) Carbon Fibre Hexapod (Denmark) Imager (France) Input Optics and Calibration Unit (Belgium)

4 Summary description

5 Spectrometer block diagram SPO SMO

6 Spectrometer fov

7 Dichroic passbands Exposure C Exposure B Exposure A

8 Spectrometer λ ranges, R, sampling and fov

9

10 Ray-trace diagram of the Channel 1 IFU

11 Diagram of the output slit

12 Integral Field Unit Optical Layout Spectrometer Pre-Optics

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14 Here are the flattened envelopes of the sliced and stacked sky images, heading off to the spectrometer collimator mirrors in the Spectrometer Main Optics (SMO) The position of the Channel 2 collimator mirror

15 Here, the beam from the Channel 2 collimator is shown, heading back to one of Channel 2 s three diffraction gratings. The position of a Channel 2 grating.

16 The light is dispersed by the grating. Dispersion direction

17 ...and heads back to a fold mirror.

18 ...which sends it to the final, camera mirror, which is a common optical element for Channels 1 and 2 (as is the fold mirror)

19 The camera mirror forms the final image...

20 ...on the Focal Plane Module (FPM), shown here as the green cylinder.

21 Here comes the beam from the Channel 1 IFU, collimated and sent to one of Channel 1 s 3 gratings...

22 ...where it is dispersed...

23 ...and sent via this fold mirror to share the last two mirrors on its way to the FPM with the spectrum from Channel 2.

24 Channel 2a spectra Constant wavelength positions

25 Some manufactured components

26 TIPS-JIM Meeting 13 October 2005, 10am, Auditorium 1. The Mid-Infrared Instrument (MIRI) Martyn Wells Medium Resolution Spectrometer for JWST 2. Temperature changes for ACS CCDs: Marco Sirianni Initial Study on Scientific Performance 3. Projected STIS performance through Paul Groudfrooij 2013 with and without the ASCS Next TIPS Meeting will be held on 17 November 2005.

27 Temperature change for ACS CCDs: initial study on scientific performance M. Sirianni, T. Wheeler, C.Cox, M. Mutchler, A. Riess, K. Sembach, R. Doxsey TIPS - Oct 13, 2005 M. Sirianni

28 Introduction We have been asked to predict the impact of variations in operating temperature for WFC and HRC. The current operating temperature is -77 C for WFC -81 C for HRC On average ~ 80% of the ACS usage is with WFC The temperature range investigated is Variation of the CCD temperature can affect the following aspects: 1. Read noise 1. Dark Current 2. Hot pixel population 3. Quantum Efficiency (and Flat Field) 4. Charge Transfer Efficiency TIPS - Oct 13, 2005 M. Sirianni

29 Dark Current Variation Dark Current changes with Temperature: D(T) = C T 1.5 exp(-eg/2kt) Ground Test: Flight build (and similar devices) tested from -100 C to -55 C On-orbit test: Tests at warmer temperature (-71.5 and -66.7C) were executed on March 2003 (Proposal 9097 Cox et al - ISR ) On-orbit, dark current increases with time due to radiation damage : ~ 2.0 e-/pix/hr/yr for WFC1 ~ 1.6 e-/pix/hr/yr for WFC2 ~ 2.1 e-/pix/hr/yr for HRC TIPS - Oct 13, 2005 M. Sirianni

30 Dark variation with temperature variation (%) of dark current Temperature (C) Using -77 C as a reference: At -74 C the dark rate increases by 71% At -81 C the dark rate decreases by 55 % TIPS - Oct 13, 2005 M. Sirianni

31 On-orbit dark variation due to radiation damage Dark Rate WFC (-77 C) e-/pix/hr WFC1_trend WFC2_trend WFC1 WFC Years from launch Mean dark current doubles every ~ 4 years TIPS - Oct 13, 2005 M. Sirianni

32 Dark variation: prediction 1000 Lot 7b e-/pix/hr 10-02_first 10-01_second 10-02_second Flight data at 1 year 100 fit 10-01_1yr 10-02_yr Ground Test data fit_1yr Temperature Radiation Damage Temperature (C) WFC -74 C -77 C -81 C (e-/pix/hr) HRC -77 C -80 C -84 C (e-/pix/hr) A change to -81 C in 2008 would bring back the dark current at the same level after 1 year on orbit. A change to -74 C in 2008 would bring the dark current at the level we would reach after 18 years on orbit at -77 C TIPS - Oct 13, 2005 M. Sirianni

33 Dark variation: scientific impact In order to assess the impact of the predicted dark current variation on the science with ACS/WFC, we estimated the noise budget for a typical observation: Most used filter : F814W Default gain (2e-/DN) : Read Noise: 5.36 e- Average Sky: 0.1 e-/pix/sec Star A0V magnitude F814W = 26 One single exposure Aperture 3 pixels (76% of light) exposure time: 628 sec average exposure time for WFC observations 339 sec min exposure time for efficient use of WFC Note: potential variations of QE and CTE are not included TIPS - Oct 13, 2005 M. Sirianni

34 T exp= 628s Noise Signal + Dark + Sky + RN Dark variation : scientific impact Temp (C) Signal Dark Sky RN Noise S/N CONCLUSION: When the noise due to dark current D [e-/pix/hr] competes with read noise? For a given aperture and an exposure time EXPTIME (sec) D =3600*Read_Noise^2/Exptime ~ 90000/EXPTIME 1000 sec => D=90e-/pix/hr TIPS - Oct 13, 2005 M. Sirianni

35 Hot pixel variation Dark non uniformity is more serious than the increase in the dark current. Hot pixel threshold: 0.08 e-/pix/sec The number of hot pixels increases with time due to radiation damage. The average signal level of the hot pixels shows the same temperature dependence as normal dark pixels. TIPS - Oct 13, 2005 M. Sirianni

36 Number of hot pixels vs Temp TIPS - Oct 13, 2005 M. Sirianni

37 Hot pixel growth The number of hot pixels changes with time due to radiation damage. In 2008 the number of hot pixels (dark current > 0.08e-/pix/sec) will reach the same level of contamination of cosmic rays in a 1000 sec exposure Hot pixel threshold TIPS - Oct 13, 2005 M. Sirianni

38 Hot pixel growth Percentage of pixels that are hot: C 4.8 % 8.7 % -77C 1.8 % 3.3 % -81C 1.3 % 2.5 % Hot pixels are removed by taking multiple images at offset positions ( dithers ). More hot pixels require more readouts for effective removal. TIPS - Oct 13, 2005 M. Sirianni

39 CRs in 628 sec -81 C C C C C C 2013 Hot pixel Mitigation 8.0 number of frames needed Max number of WFC readouts in 1 orbit pixel contamination (%) For average exposure times, obtaining 3-4 dithered frames is the optimal strategy. The number of readouts needs to be increased only if the temperature changes to -74C. CONCLUSIONS: No impact if increase in temperature can be avoided TIPS - Oct 13, 2005 M. Sirianni

40 QE/Flat Field Variation We do see small variations (< 0.5%) in the flat field at F435W (WFC) when CCDs are warmer We need to investigate variations in the near-ir. Variations in the flat field may require new calibration. QE variations need to be investigated: some impact is expected in the near-ir where WFC is most used. After ~ 3.5 years on orbit we do not observe a significant variation of QE. TENTATIVE CONCLUSION: We do not expect QE or Flat Field variations with temperature to have a serious scientific impact. Better on orbit data can be obtained TIPS - Oct 13, 2005 M. Sirianni

41 CTE variations with Temp difficult to predict without a direct test Temperature and clocking rate are major player Broadly speaking, there are two sort of traps responsible for CTE problems: Shallow Traps Short emission time constant Deep Traps Long emission time constant CTE improves if the emission time is decreased (allowing more time for e- to escape from trap) CTE improves if the emission time is increased (keeping the traps filled) CTE if T CTE if T Given the different clocking rate the effect on Parallel/Serial directions and WFC/HRC can be different. TIPS - Oct 13, 2005 M. Sirianni

42 Summary Lower Temp Higher Temp Scientific impact Notes Read Noise = = none Dark Current - + none Hot Pixels - + low Only if temperature increases to -74C QE +/-? +/-? few % Flat Field =? =? ~ few % CTE +/-? +/-? Unknown Flight test can measure this TIPS - Oct 13, 2005 M. Sirianni

43 WFC Cooling Margin Data from cool down period after anneals indicate that there is additional cooling margin: TEC current is well away from maximum TEC hot side temperatures are well below CARD limits (21 C vs 35 C) Margin should allow: cold test now some mitigation of aft shroud temperature increase in the future. TIPS - Oct 13, 2005 M. Sirianni

44 WFC cool down profile WFC housing temp. WFC TEC current WFC CCD temp. TIPS - Oct 13, 2005 M. Sirianni

45 Previous on-orbit test provided temperature dependence of Read Noise - Dark Current -Hot pixels PROGRAM (Nov-Dec 05) study temperature dependence of QE Flat Field CTE HRC and WFC at three different temperatures WFC [-74,-77,-80] HRC [-77,-80,-84] Tests on orbit Mix of internal and external orbits: total 12 internal + 12 external for CTE and QE : observation of 47 Tuc (or M3) for Flat Field and CTE : internal EPER tests for impact of CTE tails on detection threshold: z band HDFN TIPS - Oct 13, 2005 M. Sirianni

46 TIPS-JIM Meeting 13 October 2005, 10am, Auditorium 1. The Mid-Infrared Instrument (MIRI) Martyn Wells Medium Resolution Spectrometer for JWST 2. Temperature changes for ACS CCDs: Marco Sirianni Initial Study on Scientific Performance 3. Projected STIS performance through Paul Groudfrooij 2013 with and without the ASCS Next TIPS Meeting will be held on 17 November 2005.

47 Space Telescope Imaging Spectrograph: Projected Performance through 2013 Paul Goudfrooij STScI Part of procedure to address necessity of ASCS installation CCD and MAMA Performance Estimates with/without ASCS Science Impact example TIPS meeting October 13, 2005 Paul Goudfrooij 47

48 CCD Performance after SM4 Main contributor of effective throughput loss is increase of Charge Transfer Inefficiency (CTI = 1 CTE) with time (due to accumulated radiation damage) Performance degradation continues in current Safe mode Functional dependence of CTI on source counts, background level, and elapsed on-orbit time determined in 2003 (Goudfrooij & Bohlin) CCD spectroscopy mode unique to STIS and hence deemed most relevant for current exercise Issues related to growth of number of hot pixels similar to those for ACS CCDs (cf. Marco s talk), but can be mitigated by dithering On-orbit increase of dark current typically has less impact than that of CTI for faint sources No positive impact of ASCS/STIK expected on CCD performance Effect of higher temp s on CTI would need to be calibrated in flight TIPS meeting October 13, 2005 Paul Goudfrooij 48

49 Science Impact of CTI Increase Example of popular use of STIS CCD: Measurement of Black Hole Mass in center of typical bulge in low-mass galaxy (plenty of mediumand high-mass galaxies already done). SETUP: G750M/8561 Å 52x0.2 slit CCD binning 2x1 galaxy with μ V = 16 mag/arcsec 2 TIPS meeting October 13, 2005 Paul Goudfrooij 49

50 FUV-MAMA Performance after SM4 Dark Current Limited: Exp time needed Dark Counts FUV-MAMA dark in glow region generally increasing with tube temp, but no clear relation between the two. relation between dark in glow region and time since HV turn-on If tube temp will rise significantly after SM4, might consider Echelle data constraining use to only few hours after every HV turn-on F1 apertures NUV-MAMA on NUV-MAMA off TIPS meeting October 13, 2005 Paul Goudfrooij 50

51 FUV-MAMA Performance after SM4 Past Long-term Evolution of FUV-MAMA Temperature Overall increase with time, but rate of increase declining Temp stayed ~ constant with time since 2002 SM3A SM3B Solar Max Note: Tube Temp is ~ 4 ºC lower than Charge Amp Temp (latter shown on left) TIPS meeting October 13, 2005 Paul Goudfrooij 51

52 NUV-MAMA Performance after SM4 NUV-MAMA Dark Current Due to phosphorescence in impurity sites in MgF 2 window, where e can be in metastable level just below level decaying to emit γ Dark level strongly dependent on thermal environment Long-term history of dark current (and temp) shows leveling off Plot by James Davies SM3A SM3B Solar Max TIPS meeting October 13, 2005 Paul Goudfrooij 52

53 NUV-MAMA Performance after SM4 Dark can be substantially reduced with ASCS/STIK Temp s (and hence dark and exp time for darklimited obs.) down by nearly factor of 2 Dark down extra factor ~2 if cooling campaigns established Would open up whole new field of applications Echelle spectroscopy of absorption lines in faint, distant QSOs NUV imaging of distant, low surface brightness galaxies Approx. current dark level Model of dark during cooling campaign TIPS meeting October 13, 2005 Paul Goudfrooij 53

54 Summary of potential impact of ASCS on STIS performance Detector Impacted by ASCS? How? Science Impact What if NO ASCS? FUV-MAMA YES Positive: Able to run colder than lately Somewhat lower dark and better performance If temps higher than now, may find operational workaround NUV-MAMA YES Positive: Able to run colder than lately Significantly lower dark and better performance If temps higher than now, somewhat lower performance CCD NO Performance dependent on post- SM4 thermal environment impact of CTE degradation at current temp not substantial Need recalibration if temp TIPS meeting October 13, 2005 Paul Goudfrooij 54

55 TIPS-JIM Meeting 13 October 2005, 10am, Auditorium 1. The Mid-Infrared Instrument (MIRI) Martyn Wells Medium Resolution Spectrometer for JWST 2. Temperature changes for ACS CCDs: Marco Sirianni Initial Study on Scientific Performance 3. Projected STIS performance through Paul Groudfrooij 2013 with and without the ASCS Next TIPS Meeting will be held on 17 November 2005.