STScI

Wide Field Camera 3 Instrument Mini-Handbook for Cycle 16

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1. Overview

1.1 General Information

The Wide Field Camera 3 (WFC3) is a fourth-generation instrument that is designed to be installed in the Hubble Space Telescope (HST) during Servicing Mission 4 (SM4). At this writing in early October 2006, the status of SM4 is uncertain in regard to whether it will occur, and if so when it will take place. Due to this uncertainty, the Space Telescope Science Institute (STScI) will not accept WFC3 observing proposals for Cycle 16 (which nominally covers HST observations to be conducted between July 2007 and June 2008). The purpose of this Mini-Handbook, therefore, is to provide basic information about the planned capabilities of WFC3, at a level that will be helpful to astronomers making long-range plans for future HST observing programs. A full-scale WFC3 Instrument Handbook, giving complete details of the instrument and its use, is planned to be issued at a later time to assist astronomers in preparing actual WFC3 observing proposals for a future Cycle. It should be noted that WFC3 is, at this writing, still under development. Although this Mini-Handbook is as accurate as possible, the information herein is still subject to possible changes.

The WFC3 instrument is designed to occupy HST's radial scientific-instrument bay, where it will obtain on-axis direct images. During SM4, if it occurs, the shuttle astronauts will install WFC3 in place of the currently available Wide Field Planetary Camera 2 (WFPC2). WFPC2, in turn, was installed during SM1 in December 1993, to replace the original Wide Field/Planetary Camera (WF/PC1). WFPC2, like WFC3, contains optics that correct for the spherical aberration discovered in the HST primary mirror following launch of the telescope in April 1990.

WFC3 uses some components of the original WF/PC1, which will thus see service once again onboard Hubble if there is a successful SM4. WFC3 is designed to ensure that HST maintains its unique imaging capabilities until the end of its mission, while at the same time advancing its survey and discovery capability due to its combination of wide wavelength coverage, wide field of view, and high sensitivity. WFC3 would also provide a good degree of redundancy for the aging Advanced Camera for Surveys (ACS) and Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) cameras.

A key feature of WFC3 is its panchromatic wavelength coverage. By combining two optical/ultraviolet CCDs with a near-infrared HgCdTe array, WFC3 will be capable of direct, high-resolution imaging over the entire wavelength range from 200 to 1700 nm. Equipped with a comprehensive range of wide-, intermediate-, and narrow-band filters, WFC3 will have broad applicability to a variety of new astrophysical investigations.

WFC3 is a facility instrument. It is being developed, constructed, characterized, and calibrated by an Integrated Product Team (IPT) led by NASA's Goddard Space Flight Center (GSFC), and composed of staff astronomers and engineers from GSFC, STScI, Ball Aerospace & Technologies Corp., the Jet Propulsion Laboratory (JPL), and other industrial contractors.

A Scientific Oversight Committee (SOC), selected by NASA from the international astronomical community and appointed in 1998, provides scientific advice for the design and development of WFC3. The SOC's activities have been in a variety of areas, including: definition of the key scientific goals and success criteria for WFC3; participation in project reviews; recommending an optimum set of filters and grisms for the instrument and the pixel scale and field of view of the detectors; participation in the selection of flight detectors; and advice on technical trade-off decisions in the light of the scientific goals of the instrument. The SOC continues to provide oversight on all aspects of WFC3 development, with the aim of assuring that the camera will achieve its scientific goals.

1.2 Key Features of Wide Field Camera 3

The optical design of WFC3 features two independent channels, one sensitive at ultraviolet (UV) and optical wavelengths, approximately 200 to 1000 nm (the UVIS channel), and the other sensitive at near-infrared (near-IR) wavelengths, approximately 900 to 1700 nm (the IR channel). A channel-selection mirror will direct on-axis light from the HST Optical Telescope Assembly (OTA) to the IR channel, or can be removed from the beam to allow light to enter the UVIS channel. This means that simultaneous observations with the UVIS and IR detectors are not possible. However, it is anticipated that both UVIS and IR observations can be made sequentially during the same HST orbit.

The extended wavelength range, combined with high sensitivity, high spatial resolution, large field of view, and a wide selection of spectral elements, make WFC3 an extremely versatile instrument. Key features of WFC3 include:

A "white paper," prepared by the SOC and the Science IPT, outlines the scientific areas that will benefit most from the capabilities of WFC3. These include searches for galaxies at redshifts up to z~10; studies of the physics of star formation in distant and nearby galaxies; investigations of resolved stellar populations down to faint levels in the UV, optical, and near-IR; and high-resolution imaging of objects in the solar system. Of particular interest will be programs that fully exploit the panchromatic capability of WFC3 for broad investigations of the assembly and evolution of galaxies; star birth, evolution, and death and its relation to the interstellar medium; and meteorology of the outer planets. The white paper (Stiavelli, M., & O'Connell, R.W., eds., 2000, "Hubble Space Telescope Wide Field Camera 3, Capabilities and Scientific Program") can be found at: 


http://wfc3.gsfc.nasa.gov/white_paper.html
1.3 Current Instrument Status

At present (October 2006), as the editing of this Mini-Handbook was being completed, WFC3 continues to be developed and tested as we await a decision to proceed with SM4.

At the time of the January 2004 decision to cancel SM4, WFC3 was reaching the end of its assembly stage. To characterize the state of the instrument at that time, NASA directed the WFC3 program to conduct a "characterization" system-level thermal-vacuum test of the instrument. The instrument proceeded into this test in the fall of 2004. This was done in spite of a significant number of known issues, which normally would have been resolved prior to a full acceptance/qualification thermal-vacuum test.

The fall 2004 testing successfully demonstrated the overall operation and performance of the instrument, and it informs the performance predictions in this Mini-Handbook. Subsequently, with improving prospects for an SM4, WFC3 has been partially disassembled to resolve both the previously known issues and additional items discovered during testing. In particular, the following problems have been addressed: significant ghost images were discovered in some of the UVIS filters and have been eliminated by replacing the affected filters; various electronics issues have been resolved; and the thermal control system has been improved. A flight UVIS detector has been selected, and a superior infrared detector (FPA 129) has been produced and is a strong candidate for flight.

At this writing, WFC3 is expected to resume thermal-vacuum testing early in 2007, if authority to proceed with SM4 is granted.

1.4 The WFC3 Instrument Team at STScI

STScI maintains a team of Instrument Scientists, Data Analysts, Engineers, and Scientific Programmers, who support the design, development, operation, calibration, and documentation of WFC3. STScI also maintains a Help Desk to provide answers quickly to any WFC3- and HST-related questions. Please send all questions regarding WFC3 and HST to the Help Desk, as follows:

Space Telescope Science Institute
http://www.stsci.edu
Voice: (410) 338-1082
help@stsci.edu
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