Version 1.0 December 2007 Wide Field Camera 3 Instrument Handbook for Cycle 17 Space Telescope Science Institute 3700 San Martin Drive Baltimore, Maryland 21218 [email protected] Operated by the Association of Universities for Research in Astronomy, Inc., for the National Aeronautics and Space Administration User Support For prompt answers to any question, please contact the STScI Help Desk. • E-mail: [email protected] • Phone: (410) 338-1082 (800) 544-8125 (U.S., toll free) World Wide Web Information and other resources are available on the WFC3 World Wide Web sites at STScI and GSFC: • URL: http://www.stsci.edu/hst/wfc3 • URL: http://wfc3.gsfc.nasa.gov WFC3 Instrument Handbook Revision History Version Date Editors 1.0 December 2007 Howard E. Bond and Jessica Kim Quijano Contributors: Sylvia Baggett, Ray Boucarout, Tom Brown, Howard Bushouse, Nicholas Collins, Colin Cox, Ilana Dashevsky, Linda Dressel, Mauro Giavalisco, George Hartig, Bryan Hilbert, Robert J. Hill, Diane Karakla, Jessica Kim Quijano, Randy Kimble, Martin Kümmel, Harald Kuntschner, Matt Lallo, Olivia Lupie, Peter McCullough, John MacKenty, Eliot Malumuth, Andre' Martel, Larry Petro, Elizabeth Polidan, Manuel Quijada, Neill Reid, Massimo Robberto, Massimo Stiavelli, Randal Telfer, Nolan Walborn, Jeremy Walsh and Tom Wheeler. Citation: In publications, refer to this document as: Bond, H. E., and Kim Quijano, J., et al. 2007, “Wide Field Camera 3 Instrument Handbook, Version 1.0” (Baltimore: STScI) Send comments or corrections to: Space Telescope Science Institute 3700 San Martin Drive Baltimore, Maryland 21218 E-mail:[email protected] Table of Contents Acknowledgments.........................................................xi Chapter 1: Introduction to WFC3 ..................... 1 1.1 Overview ......................................................................... 1 1.2 Key Features of WFC3 ................................................ 2 1.3 WFC3 Quick Reference Guide .................................. 3 1.4 Current Instrument Status........................................... 4 1.5 Special Considerations for Cycle 17 ........................ 4 1.5.1 WFC3 is Still Under Development .............................. 4 1.5.2 Return to Three-Gyro Mode in Cycle 17..................... 5 1.6 Sources of Further Information .................................. 5 1.7 The WFC3 Instrument Team at STScI .................... 6 Chapter 2: WFC3 Instrument Description ..................................................................... 7 2.1 Optical Design and Detectors .................................... 7 2.2 Field of View and Geometric Distortions ............... 10 2.3 Spectral Elements....................................................... 11 2.3.1 The Filter Selection Process..................................... 11 2.3.2 Filter and Grism Summaries..................................... 11 2.4 Detector Read-Out Modes and Dithering.............. 12 Chapter 3: Choosing the Optimum HST Instrument......................................................... 13 3.1 Overview ....................................................................... 13 3.2 Choosing Between Instruments............................... 14 iii iv Table of Contents 3.3 Comparison of WFC3 with Other HST Imaging Instruments...................................................... 15 3.3.1 Wavelength Coverage .............................................. 15 3.3.2 Field of View ............................................................. 15 3.3.3 Detector Performance............................................... 17 3.3.4 System Throughputs and Discovery Efficiencies ..... 18 Chapter 4: Designing a Phase I WFC3 Proposal ......................................................... 21 4.1 Phase I and Phase II Proposals .............................. 21 4.2 Preparing a Phase I Proposal .................................. 21 4.2.1 Which WFC3 Channel(s) and Filter(s)?.................... 22 4.2.2 What Exposure Times? ............................................ 22 4.2.3 What Aperture or Subarray?..................................... 23 4.2.4 What Overheads and How Many HST Orbits?......... 24 4.2.5 Any Special Observations? ...................................... 24 4.2.6 What is the Total Orbit Request? ............................. 25 Chapter 5: WFC3 Detector Characteristics and Performance ............ 27 5.1 Overview of this Chapter........................................... 27 5.2 The WFC3 UVIS Channel CCD Detectors ........... 28 5.2.1 Basics of CCD Operation.......................................... 28 5.2.2 The WFC3 CCDs...................................................... 29 5.3 WFC3 CCD Readout Formats ................................. 31 5.3.1 Full-frame Readout................................................... 31 5.3.2 Subarrays ................................................................. 32 5.3.3 On-Chip Binning ....................................................... 32 5.4 WFC3 CCD Characteristics and Performance .... 33 5.4.1 Quantum Efficiency................................................... 33 5.4.2 Multiple-Electron Events at Short Wavelengths ....... 33 5.4.3 Flat Fields ................................................................. 34 5.4.4 Long-Wavelength Fringing ....................................... 36 5.4.5 Linearity and Saturation............................................ 37 5.4.6 Gain .......................................................................... 37 5.4.7 Read Noise............................................................... 37 5.4.8 Dark Current ............................................................. 38 5.4.9 Bad Pixels................................................................. 40 5.4.10 Cosmic Rays........................................................... 41 5.4.11 Charge-Transfer Efficiency..................................... 42 Table of Contents v 5.5 The WFC3 IR Channel Detector ............................. 43 5.5.1 Overview................................................................... 43 5.5.2 IR Detector Basics.................................................... 43 5.6 WFC3 IR Readout Formats and Reference Pixels................................................................................. 46 5.7 WFC3/IR Detector Characteristics and Performance............................................................ 48 5.7.1 Quantum Efficiency................................................... 48 5.7.2 Dark Current ............................................................. 49 5.7.3 Read Noise............................................................... 49 5.7.4 Flat Fields ................................................................. 51 5.7.5 Linearity and Saturation............................................ 51 5.7.6 Detector Cosmetics .................................................. 52 Chapter 6: UVIS Imaging with WFC3 .......... 55 6.1 WFC3 UVIS Imaging .................................................. 55 6.2 Specifying a UVIS Observation ............................... 56 6.3 UVIS Channel Characteristics ................................. 56 6.4 UVIS Field Geometry ................................................. 57 6.4.1 Field of View and Pixel Size ..................................... 57 6.4.2 Geometric Distortion................................................. 57 6.4.3 Coordinate Systems ................................................. 58 6.4.4 Subarrays and On-Chip Binning............................... 59 6.4.5 Apertures .................................................................. 62 6.5 UVIS Spectral Elements............................................ 64 6.5.1 Filter and Grism Summary........................................ 64 6.5.2 Filter Red Leaks........................................................ 74 6.5.3 Ghosts ...................................................................... 75 6.6 UVIS Optical Performance........................................ 76 6.6.1 Model PSF and FWHM............................................. 76 6.6.2 Encircled and Ensquared Energy ............................. 78 6.6.3 Other PSF Behavior and Characteristics.................. 80 6.7 UVIS Exposure and Readout ................................... 83 6.7.1 Exposure Time.......................................................... 83 6.7.2 ACCUM Mode........................................................... 84 6.8 UVIS Sensitivity ........................................................... 87 6.8.1 Limiting Magnitudes.................................................. 87 vi Table of Contents 6.9 Other Considerations for UVIS Imaging ................ 88 6.9.1 Gain and Full-well Saturation ................................... 88 6.9.2 Cosmic Rays and Hot Pixels .................................... 89 6.9.3 Charge-Transfer Efficiency....................................... 90 6.9.4 Image Persistence.................................................... 90 6.9.5 Quantum Yield.......................................................... 90 6.10 UVIS Observing Strategies .................................... 91 6.10.1 Dithering Strategies ................................................ 91 6.10.2 Parallel Observations ............................................. 92 Chapter 7: IR Imaging with WFC3.................. 93 7.1 WFC3 IR Imaging........................................................ 93 7.2 Specifying an IR Observation................................... 94 7.3 IR Channel Characteristics ....................................... 94 7.4 IR Field