Version 5.0 January, 2002 NICMOS Data Handbook Hubble Division 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 Web site: • URL: http://hst.stsci.edu/nicmos. NICMOS Revision History Version Date Editors 3.0 October 1997 Daniela Calzetti 4.0 December 1999 Mark Dickinson 5.0 January 2002 Mark Dickinson, NICMOS Editor Bahram Mobasher, Chief Editor Contributors STScI NICMOS Group (past & present members), including: Santiago Arribas, Eddie Bergeron, Torsten Boeker, Howard Bushouse, Daniela Calzetti, Luis Colina, Mark Dickinson, Sherie Holfeltz, Lisa Mazzuca, Bahram Mobasher, Keith Noll, Antonella Nota, Erin Roye, Chris Skinner, Al Schultz, Anand Sivaramakrishnan, Megan Sosey, Alex Storrs, Anatoly Suchkov, Chun Xu ST-ECF: Wolfram Freudling. Citation In publications, refer to this document as: Dickinson, M. E. et al. 2002, in HST NICMOS Data Handbook v. 5.0, ed. B. Mobasher, Baltimore, STScI Send comments or corrections to: Hubble Division Space Telescope Science Institute 3700 San Martin Drive Baltimore, Maryland 21218 E-mail:[email protected] Table of Contents Preface .................................................................................... vii Chapter 1: Instrument Overview .................. 1-1 1.1 Instrument Overview ................................................. 1-1 1.2 Detector Readout Modes ......................................... 1-4 1.2.1 MULTIACCUM......................................................... 1-5 1.2.2 ACCUM.................................................................... 1-5 1.2.3 BRIGHTOBJ ............................................................ 1-6 1.2.4 RAMP ...................................................................... 1-6 Chapter 2: Data Structures................................ 2-1 2.1 NICMOS Data Files ................................................... 2-1 2.1.1 File Name Suffixes................................................... 2-2 2.1.2 Science Data Files................................................... 2-3 2.1.3 Auxiliary Data Files.................................................. 2-9 2.2 Header Keywords..................................................... 2-10 2.3 Working with NICMOS Files.................................. 2-16 2.4 From the Phase II Proposal to Your Data .......... 2-20 2.5 Paper Products ......................................................... 2-22 Chapter 3: Calibration............................................ 3-1 3.1 Pipeline Processing, OTFR, and the HST Archive .................................................... 3-1 3.2 NICMOS Calibration Software ................................ 3-3 3.2.1 The Calibration Pipeline .......................................... 3-3 3.2.2 Software for Grism Data Reduction......................... 3-4 3.3 Basic Data Reduction: calnica ................................ 3-5 iii iv Table of Contents 3.4 Mosaicing: calnicb.................................................... 3-16 3.4.1 Input Files .............................................................. 3-17 3.4.2 Output Files ........................................................... 3-18 3.4.3 Processing............................................................. 3-19 3.5 Recalibration ............................................................. 3-23 3.5.1 Why Recalibrate? .................................................. 3-23 3.5.2 Recalibrating the Data ........................................... 3-24 Chapter 4: Anomalies and Error Sources ............................................................ 4-1 4.1 NICMOS Dark Current and Bias ............................ 4-3 4.1.1 Dark Current ............................................................ 4-4 4.1.2 Bias, Shading, and "Pedestal"................................. 4-5 4.1.3 Dark Reference Files............................................. 4-10 4.1.4 What is Removed by Standard Pipeline Processing.................................................... 4-13 4.1.5 Cures: How To Get Rid of What's Left.................. 4-13 4.2 Bars ............................................................................. 4-20 4.3 Detector Nonlinearity Issues ................................. 4-21 4.3.1 New Nonlinearity Calibrations ............................... 4-21 4.3.2 Non-Zero zeroth Read Correction for Bright Sources....................................................... 4-22 4.3.3 Uncorrected Saturation.......................................... 4-23 4.4 Flatfielding.................................................................. 4-24 4.4.1 Characteristics of NICMOS Flatfields .................... 4-24 4.4.2 Temperature-dependent Flatfields ........................ 4-25 4.4.3 Color Dependence of Flatfields ............................. 4-25 4.5 Pixel Defects and Bad Imaging Regions............ 4-26 4.5.1 Hot Pixels, Cold Pixels, and Grot .......................... 4-26 4.5.2 Erratic Middle Column/Row. .................................. 4-28 4.5.3 Coronagraphic Hole............................................... 4-28 4.5.4 Vignetting............................................................... 4-29 4.6 Effects of Overexposure......................................... 4-30 4.6.1 Photon Persistence ............................................... 4-30 4.6.2 Cosmic Ray Persistence........................................ 4-31 4.6.3 Amplifier Ringing (The "Mr. Staypuft" Anomaly)..................................... 4-34 4.6.4 Optical Ghost Images ............................................ 4-36 4.7 Cosmic Rays of Unusual Size............................... 4-37 4.8 Scattered Earthlight ................................................. 4-39 Table of Contents v Chapter 5: Data Analysis .................................... 5-1 5.1 STSDAS Software ..................................................... 5-1 5.2 The NICMOS History Tool ....................................... 5-5 5.3 Photometric Calibrations .......................................... 5-6 5.3.1 Units for NICMOS Photometry................................. 5-6 5.3.2 Fluxes and Magnitude Zeropoints ........................... 5-6 5.3.3 Photometric Corrections ........................................ 5-12 5.3.4 Absolute Photometry for Emission Line Filters .................................................. 5-17 5.3.5 Absolute Spectrophotometry with NICMOS Grisms......................................................... 5-18 5.4 Astrometry, Pixel scales, and Geometric Distortion .................................................. 5-19 5.4.1 Pixel Scale Time Dependence ............................. 5-19 5.4.2 X and Y Pixel Scale Differences........................... 5-20 5.4.3 Geometric Distortion............................................. 5-20 5.4.4 Drizzling................................................................ 5-22 5.4.5 Absolute Astrometry ............................................. 5-22 5.5 PSF Subtraction ....................................................... 5-23 5.5.1 Impact of Instrumental Effects on PSF Subtraction ......................................................... 5-25 5.6 Coronagraphic Reductions .................................... 5-29 5.6.1 Data Products and File Structures......................... 5-29 5.6.2 Coronagraphic Acquisitions................................... 5-29 5.6.3 Positions of the Hole and Target ........................... 5-32 5.6.4 Recalibrating Coronagraphic Images .................... 5-35 5.6.5 Reducing and Co-adding Coronagraphic Images............................................... 5-38 5.7 Analysis of Polarization Images............................ 5-43 5.7.1 Introduction............................................................ 5-43 5.7.2 Theory.................................................................... 5-44 5.7.3 A Useful Script for Polarization Analysis ............... 5-46 5.8 Grism Data Reduction............................................. 5-47 5.8.1 Extraction Software................................................ 5-48 5.8.2 Processing............................................................. 5-49 Index .......................................................................................... 1 vi Table of Contents Preface How to Use this Handbook This handbook is designed to help you manipulate, process and analyze data from the Near-Infrared Camera and MultiObject Spectrograph (NICMOS) on board the Hubble Space Telescope (HST). This is presented as an independent and self-contained document, extensively built on the contents of an older edition (version 3.0) of the HST Data Handbook. The old HST Data Handbook has now been subdivided into separate volumes for each instrument. Users who wish to find more general information about details of acquiring HST data from archive, their file formats, and general purpose software for displaying and processing these data, are referred to a companion volume, the Introduction to the HST Data Handbook. The current edition of the NICMOS Data Handbook is being written in late 2001, as we approach servicing mission 3b (SM3b) and the installation of the NICMOS Cooling System (NCS). Therefore, the material presented in this volume are based on the experience gained in