STScI Logo

Hubble Space Telescope
WFC3 Grism Resources

Logo WFC3

Spectroscopy

Resource Page

Welcome to the central resource for information related to
Grism Spectroscopy with the WFC3 Instrument.

WFC3 offers slitless spectroscopy with both the ultra-violet/optical (UVIS) and infrared (IR) channels. The UVIS channel is equipped with the G280 grism, which has a resolving power of R~70 in the wavelength range ~ 0.19-0.55 microns. The IR channel includes the G102 and G141 grisms with resolving powers R~210 in the range 0.8-1.15 microns and R~130 in the range 1.1-1.7 microns, respectively.

If you encounter any problems related to the WFC3 Grism, please contact our Help Desk

Table of Contents

I. Proposal Information & Documentation Provides links to Manuals and Web pages to help with preparing your Phase 1 & Phase 2 proposals.
II. Data Analysis Information & Documentation Provides links to Manuals and Web pages for retrieving and analysing WFC3 Grism data. aXe is the Grism reduction software supported by STScI.
III. Calibration Files & Calibration Information Links for obtaining the newest calibration files for the UVIS and IR Grisms.
IV. Grism-related Instrument Science Reports (ISRs) List of ISRs directly relevant to the WFC3/Grism. ISRs are in-house refereed technical papers which address specific topics related to instrument and telescope performance or data analysis techniques. This grouping of ISRs has been compiled to provide additional information to observers beyond what is found in the Instrument Handbook.
V. Frequently Asked Questions (FAQ) List of FAQs related to everything from Proposal Preparation to Data Analysis. This guide is based on questions submitted to the Help Desk as well as feedback from our recent WFC3 Grism survey. The FAQ page will continually evolve over time to include more Q&As as we receive feedback from users.
VI. Other Useful Resources Here you will find links to other useful webpages, including those of the 2010 STScI Slitless Spectroscopy Workshop, and from teams carrying out large surveys with the WFC3 grisms.

I. Proposal Information & Documentation

WFC3 Instrument Handbook Overview of instrument capabilities. Useful for Phase 1 & 2 planning.
PDF version
WFC3 Data Handbook Guide to using the data obtained with WFC3. Useful for post-observations.
PDF version
Phase 2 Proposal Instructions Guide for Preparing Phase 2 proposals. WFC3 information is located in Chapter 14.
Astronomer's Proposal Tool (APT) Training Tools A collection of video tutorials for using APT. See the
APT homepage for obtaining the latest version.
Aladin is the default sky atlas used with APT. See the Aladin homepage for more information on using this software.
aXesim - a WFC3 Grism Simulator A software package which allows you to simulate WFC3/Grism observations.
aXesim on the Web The web-based version of aXesim. This is a more limited version of the standalone aXesim.
Exposure Time Calculator (ETC) User Manual Provides general overview of the ETC for all instruments.
WFC3 Grism Exposure Time Calculator (UVIS) Used for estimating the exposure time for UVIS Grism observations.
WFC3 Grism Exposure Time Calculator (IR) Used for estimating the exposure time for IR Grism observations.
WFC3 Dithering Strategies Web based guide for designing dithering patterns for WFC3.
Activating a Target of Opportunity (ToO) Proposal Describes how an HST observer activates a ToO proposal.

II. Data Analysis Information & Documentation

Retrieving your Data These three links all provide access to proprietary data for PIs as well as publicly available data.
Multimission Archive
Starview
Duplication Checker
WFC3 Pipeline Information Provides a brief description of the WFC3 data pipeline, along with notes on updates.
Do I Need to Recalibrate? Web guide on how to check if calibration files for your datasets have changed recently.
Hubble Observation Problem Reports Guidelines for submitting a Hubble Observation Problem Report (HOPR). This is used for:
1) Problems with implementation, scheduling execution, or data processing of your observations;
2) Requests for failed observations to be repeated
aXe Spectral Extraction Software Detailed information on installation of the Grism data reduction software aXe, including methodology, tasks and parameters. The latest version is 2.3, and is available as part of STSDAS 3.14 (released August 2011).

ASTRODRIZZLE COMPATABILITY:
aXe was originally designed to support Multidrizzle style astrometric information. Current (aXe v2.3) and earlier versions of the software rely on output files from the Multidrizzle process to transform object pixel coordinates between the user supplied "drizzled" direct image and corresponding spectral images. We are currently working on updating aXe to accommodate the use of new Astrodrizzle products, and maintain back-compatability with Multidrizzle.

2013-03-07
A version of aXe, where iolprep and fcubeprep have been modified for compatibility with Astrodrizzle, is available via SSBX (the STSDAS testing environment). Work and testing on both tasks is still on-going. An updated aXe cookbook and manual will be available shortly.

IMPORTANT for SUB-ARRAY MODE: if your data (grism and/or direct image) were taken in this mode, you must embed it in a full-frame before analysing with aXe. A python script to do this is available here along with instructions.
aXe Cookbook (IR) Step-by-step guide to reducing G141 (IR) grism data using aXe. Includes link to download Grism data from the WFC3 ERS Program. This data is used as an example in the guide. A UVIS Cookbook is coming soon.

2013-03-11
The cookbook has been updated to reflect changes made thus far to the aXe software to accommodate AstroDrizzle image products. See the cookbook page for more details.

aXe2web Software which produces an html summary of each reduced object which includes:
1) direct image;
2) 2D spectrum;
3) 1D raw extracted spectrum;
4) 1D flux calibrated spectrum.
Documentation and software can be found here.
Space Telescope Analysis Newsletters (STANs) Archive of newsletters sent to observers with updates which may affect observation planning or analysis.
WFC3 Advisories Important advisories regarding the status of the WFC3 instrument.
Publication Guidelines for HST Observations Short summary of what to include in your publications once your data analysis has been completed.

III. Calibration Files and Information

UVIS Grism (G280) G280 configuration & calibration files, primarily for aXe and aXesim. This includes sensitivity, flatfield cube, and trace information.
IR Grism (G102) G102 configuration & calibration files, primarily for aXe and aXesim. This includes sensitivity, flatfield cube, and trace information.
IR Grism (G141) G141 configuration & calibration files, primarily for aXe and aXesim. This includes sensitivity, flatfield cube, and trace information.
WFC3 Reference Files This web page contains the current calibration and reference files used in the CALWF3 pipeline.
Zeropoints for WFC3 Filters This table gives zeropoints for WFC3 UVIS & IR filters. This is important for the *.cat files used with aXe and aXesim. Note: aXe and aXesim only accept ST and AB MAG zeropoints.
Pivot Wavelengths for WFC3 UVIS filters This table gives the pivot wavelengths for the WFC3 UVIS filters. This is important for the *.cat
files used with aXe and aXesim.
Pivot Wavelengths for WFC3 IR filters This table gives the pivot wavelengths for the WFC3 IR filters. This is important for the *.cat
files used with aXe and aXesim.
HST Keyword Dictionary Reference web page for looking up the meanings of all Keywords currently used for HST instruments.

IV. Grism-Related Instrument Science Reports (ISRs)

ISR 2012-06: Flux Calibration Monitoring - WFC3/IR G102 and G141 Grisms Confirms stability in +1 order G102 and G141 flux calibrations to within 1% over WFC3 lifetime.
2011-09: IR Detector Timing & Persistence Information on persistence in the IR detector for full & sub-arrays.
2011-05: Revised Flux Calibration of the WFC3 G102 & G141 Grisms Update of flux calibrations, aperture corrections for the +1 order, and throughput variations across the FOV.
2011-04: WFC3/IR Banding How to deal with background pixels a few DN above of the image in full & sub-array frames, including observing techniques to avoid.
2011-01: Master Sky Images for the WFC3 G102 & G141 Grisms Details regarding construction of new master sky frames for data analysis and discussion of possible time-variations of background sky brightness.
2010-17: WFC3/IR Persistence as Measured in Cycle 17 using Tungsten Lamp Exposures Measurement of persistence from internal Tungsten Lamps to assess impact of bright illumination on observations.
2010-16: IR Channel Subarray Dark Current Behavior Discussion of the effects of, and how to deal with, dark current for sub-arrays.
2010-13: WFC3/IR Bad Pixel Table: Update Using Cycle 17 Data Information regarding updated bad pixel tables, including values assigned to known bad areas (i.e. blob, death star, etc...)
2010-12: Proposal 11913-IR Filter Wedge Check Information on offsets in pixel position for all IR filters. This ISR is important for programs using direct images obtained in filters other than F140W.
2010-09: Dithering Strategies for WFC3 Guidelines for dithering strategies. This ISR is useful for Phase 2 proposal preparation.
2010-07: First On-orbit Measurements of the WFC3-IR Count-rate Non-Linearity Discussion of non-linearity in the WFC3 IR detector and comparison with similar phenomenon in ACS and NICMOS.
2010-06: The WFC3 IR "Blobs" Discussion of blemishes which have appeared in the WFC3 IR detector. This ISR is useful for developing dithering strategies for Phase 2 proposal preparation.
2009-18: WFC3 SMOV proposal 11552: Calibration of the G102 Grism Provides calibration information on the trace, resolution and wavelength solution of the G102 IR Grism.
2009-17: WFC3 SMOV proposal 11552: Calibration of the G141 Grism Provides calibration information on the trace, resolution and wavelength solution of the G141 IR Grism.
2009-01: The ground calibration of the WFC3/UVIS G280 Grism Provides calibration information on the trace, resolution and wavelength solution of the G280 UVIS Grism.
2007-03: Performance of the WFC3 Replacement IR Grisms Summarizes the preformance of the G102 and G141 grisms. This report includes technical specicifications of the grisms, their installation, throughput, and dispersion.
2001-07: WFC3 Data Formats in OPUS & STSDAS Describes content and structure of WFC3 science data files generated by OPUS and used in processing with STSDAS tasks.

VI. Other Useful Resources

2010 STScI Slitless Spectroscopy Workshop The 2010 workshop highlighting scientific results of slitless spectroscopy and tutorials on using and analysing data from the WFC3 Grism. A direct link to the archived videos of the talks can be found here.
WISPS Team Page
WFC3 Infrared Spectroscopic Parallel Survey webpage. Includes access to reduced and drizzled direct near-IR imaging (F110W, F140W, & F160W), direct UVIS imaging (F475X & F600LP), and the near-IR grisms (G102 and G141).
3D-HST Team Page "A Spectroscopic Galaxy Evolution Survey with the Hubble Space Telescope" webpage. Includes access F140W and G141 mosaics. Pipeline used by 3D-HST is available here.