urn:nasa:pds:context:instrument:hst.wfpc2 1.0 1.11.0.0 Product_Context urn:nasa:pds:context:instrument:wfpc2.hst 2021-02-24 1.0 Changed inst LIDs from u:n:p:c:i:instID.scID to u:n:p:c:i:scID.instID And per "Guide toPDS4 Context Products" v1.7, changed all lidvid_reference to lid_reference urn:nasa:pds:context:instrument_host:spacecraft.hst instrument_to_instrument_host Biretta, J.A., S.M. Baggett, J.W. MacKenty, C.E. Ritchie, and W.B. Sparks, 'The WFPC Calibration Pipeline', Proceedings of the HST Calibration Workshop, STScI publication, pp. 8-19, November 1993. reference.BIRETTAETAL1993 Biretta, J.A., C. Burrows, J. Holtzman, I. Heyer, M. Stevens, S. Baggett, S. Casertano, M. Clampin, A. Fruchter, H. Ferguson, R. Gilliland, R. Griffiths, J. Krist, K. Noll, C. O'Dea, M. Stiavelli, A.Suchkov, J. Surdej, and B. Whitmore, The WFPC Instrument Handbook, Version 4.0 (Baltimore: STScI), June, 1996. reference.BIRETTAETAL1996 Burrows, C.J., ed., Wide Field and Planetary Camera 2 Instrument Handbook, Version 2.0, (Baltimore: STScI), May, 1994. reference.BURROWS1994 Burrows, C.J., J.A. Holtzman, S.M. Faber, P.Y. Bely, H. Hasan, C.R. Lynds, and D. Schroeder, 'The imaging Performance of the Hubble Space Telescope', Ap. J. Lett., 369, L21- L25, 1991. reference.BURROWSETAL1991 Holtzman, J., J.J. Hester, S. Casertano, J.T. Trauger, A.M. Watson, G.E. Ballester, C.J. Burrows, J.T. Clarke, D. Crisp, R.W. Evans, J.S. Gallagher III, R.E. Griffiths, J.G. Hoessel, L.D. Matthews, J.R. Mould, P.A. Scowen, K.R. Stapelfeldt, and J.A. Westphal, 'The Performance and Calibration of WFPC2 on the Hubble Space Telescope', Publication of the Astronomical Society of the Pacific, 107, 156-178, 1995. reference.HOLTZMANETAL1995A Holtzman, J.A., C.J. Burrows, S. Casertano, J.J. Hester, J.T. Trauger, A.M. Watson, and G. Worthey, 'The Photometric Performance and Calibration of WFPC2', Publication of the Astronomical Society of the Pacific, 107, 1065-1093, 1995. reference.HOLTZMANETAL1995B WIDE FIELD PLANETARY CAMERA 2 Imager not applicable not applicable Instrument Overview =================== The information in this document is taken from [BURROWS1994]. The original Wide Field and Planetary Camera (WF/PC-1) was a two- dimensional spectrophotometer with rudimentary polarimetric and transmission-grating capabilities. WF/PC-1 was launched aboard the HST in April 1990 and was central to the discovery and characterization of the spherical aberration in HST. It was replaced in December 1993 by a second Wide Field and Planetary Camera (WFPC2) which is described in detail in this document. The original Wide Field and Planetary Camera (WF/PC-1) imaged the center of the field of the Hubble Space Telescope (HST). The instrument was designed to operate from 1150 A to 11000 A with a resolution of 0.1 arcseconds per pixel (Wide Field camera, F/12.9) or 0.043 arcseconds per pixel (Planetary Camera, F/30), each camera mode using an array of four 800 x 800 CCD detectors. The development and construction of the WF/PC-1 was led by Prof. J. A. Westphal, Principal Investigator (PI), of the California Institute of Technology. The Investigation Definition Team (IDT) also included J.E. Gunn (deputy PI), W.A. Baum, A.D. Code, D.G. Currie, G.E. Danielson, T.F. Kelsall, J.A. Kristian, C.R. Lynds, P.K. Seidelmann, and B.A. Smith. The instrument was built at the Jet Propulsion Laboratory, Caltech (JPL). NASA decided to build a second Wide Field and Planetary Camera (WFPC2) at JPL as a backup clone of the WF/PC-1 because of its important role in the overall HST mission. This second version of the WF/PC was in the early stages of construction at JPL at the time of HST launch. A modification of the internal WF/PC optics could correct for the spherical aberration and restore most of the originally expected performance. As a result, it was decided to incorporate the correction within WFPC2 and to accelerate its development. The original Wide Field/Planetary Camera (WF/PC1) was replaced by WFPC2 on the STS-61 shuttle mission in December 1993. Instrument ID : WFPC2 Instrument Host ID : HST Pi PDS User Id : JTRAUGER Instrument Name : Wide Field Planetary Camera 2 Instrument Type : CCD Camera Build Date : 1993-05-01 Instrument Mass : UNK Instrument Length : 2.44 Instrument Width : 1.22 Instrument Height : 0.46 Instrument Manufacturer Name : Jet Propulsion Laboratory Principal Investigator ====================== The Principal Investigator for WFPC2 is Dr. J.T. Trauger of JPL. The IDT members are C.J. Burrows, J. Clarke, D. Crisp, J. Gallagher, R.E. Griffiths, J.J. Hester, J. Hoessel, J. Holtzman, J. Mould, and J.A. Westphal. Scientific Objectives ===================== The scientific objectives of the WFPC2 are to provide photometrically and geometrically accurate, multi-band images of astronomical objects over a relatively wide field-of-view (FOV), with high angular resolution across a broad range of wavelengths. WFPC2 meets or exceeds the photometric performance of WF/PC-1 in most areas. Nominally, the requirement is 1% photometric accuracy in all filters, which is essentially a requirement that the relative response in all 800x800 pixels per CCD be known to a precision of 1% in flat-field images taken through each of the 48 science filters. Success in this area is dependent on the stability of all elements in the optical train particularly the CCDs, filters and calibration channel. The recovery of the point spread function is essential to all science programs being conducted with the WFPC2, because it allows one to both go deeper than ground based imagery and to resolve smaller scale structure with higher reliability and dynamic range. Calibration =========== Standard calibration observations are obtained and maintained in the HST archive at the STScI, and can be obtained by external users using StarView. This includes those flat field, dark and bias frames needed to operate the Post Observation Data Processing System (PODPS; usually just called the 'pipeline'), a photometric calibration derived from standard star observations and the measured filter profiles, and derived determinations of the plate scale, distortion, and so on. The first set of these calibrations were provided to the STScI by the WFPC2 IDT from the Servicing Mission Observatory Verification (SMOV) and System Level Thermal Vacuum (SLTV) testing periods, and will be maintained and updated thereafter by the STScI with initial assistance from the IDT as part of the long term calibration program. Operational Considerations ========================== The WFPC2 field of view is divided and distributed into four cameras by a fixed four-faceted pyramid mirror near the HST focal plane. Three of these are F/12.9 Wide Field cameras (WFC), and the remaining one is an F/28.3 Planetary camera (PC). There are thus four sets of relay optics and CCD sensors in WFPC2, rather than the eight in WF/PC-1, which had two independent field formats. The pyramid rotation mechanism has been eliminated, and all four cameras are now in the locations that were occupied in WF/PC-1 by the wide field camera relays. These positions are denoted PC1, WF2, WF3, and WF4. Detectors ========= The WFPC2 CCDs are thick, front-side illuminated devices made by Loral. They support multi-pinned phase (MPP) operation which eliminates quantum efficiency hysteresis. They have a Lumogen phosphor coating to give UV sensitivity. WF/PC-1 CCDs were thinned, backside illuminated devices with a coronene phosphor. The resulting differences may be summarized as follows: Read noise: WFPC2 CCDs have lower read noise (about 5e- rms) than WF/PC-1 CCDs (13 e- rms) which improves their faint object and UV imaging capabilities. Dark noise: Inverted phase operation yields lower dark noise for WFPC2 CCDs. They are presently being operated at -77C and yet the median dark current is about 0.016 electrons/pixel/sec. This is 10C warmer than the WF/PC-1 devices and helps in reducing the build-up of contaminants on the CCD windows. If they end up being operated colder the dark current reduces by a factor of 3 for every 10C temperature drop. Flat field: WFPC2 CCDs have a more uniform pixel to pixel response (<2% pixel to pixel non-uniformity) which will improve the photometric calibration. Pre-Flash: Charge traps are present at the current operating temperature. However, by cooling the devices further, it is expected that they will become negligible for WFPC2 CCDs. Pre-flash exposures will then not be required. This would avoid the increase in background noise, and decrease in operational efficiency that results from a preflash. Gain switch: Two CCD gains are available with WFPC2, a 7e-/DN channel which saturates at about 27000e- (4096 DN with a bias of about 300 DN) and a 14e-/DN channel which saturates at about 53000e-. The Loral devices have a large full well capacity (of 80-100,000 electrons) and are linear up to the saturation level in both channels. DQE: The Loral devices have intrinsically lower QE above 4800A (and up to about 6500A) than thinned, backside illuminated wafers which have no attenuation by frontside electrode structures. On the other hand, the improved phosphorescent coating leads to higher DQE below 4800A. The peak DQE in the optical is 40% at 7000A while in the UV (1100-4000A) the DQE is 10-15%. Image Purge: The residual image resulting from a 100x (or more) full-well over-exposure is well below the read noise within 30 minutes, removing the need for CCD image purging after observations of particularly bright objects. The Loral devices bleed almost exclusively along the columns. Quantization: The systematic Analog to Digital converter errors that were present in the low order bits on WF/PC-1 have been largely eliminated, contributing to a lower effective read noise. QEH: Quantum Efficiency Hysteresis (QEH) is not a significant problem in the Loral CCDs because they are frontside illuminated and use MPP operation. The absence of any significant QEH means that the devices do not need to be UV-flooded and so the chips can be warmed for decontamination purposes without needing to maintain the UV-flood. Detector MTF: The Loral devices do suffer from low detector MTF perhaps caused by scattering in the frontside electrode structure. The effect is to blur images and decrease the limiting magnitude by about 0.5 magnitudes. Electronics =========== The CCD camera electronics system is essentially the same design as that flown on WF/PC-1 with the exception of changes made to implement the different clock pattern for MPP inverted phase operation. Changes in circuit timing have also been made to correct the problem of ADC conversion errors. Filters ======= A set of 48 filters are included in WFPC2, with the following features: 1. It approximately replicates the WF/PC-1 'UBVRI' photometry series. 2. The broad-band filter series is extended into the far UV. 3. There is a new Stromgren series. 4. A Wood's filter is included for far-UV imaging without a red leak. 5. There is a 1% bandpass linear ramp filter series covering 3700-9800A. 6. The narrow-band series is more uniformly specified and better calibrated. The filters are mounted in the Selectable Optical Filter Assembly (SOFA) between the shutter and the reflecting pyramid. The SOFA contains 12 filter wheels, each of which has 4 filters and a clear 'home' position. Wheel number 1 is located closest to the shutter. The categories of simple filters (F) are long-pass (LP), wide (W), medium (M), and narrow (N). Most of these filters are either flat single substrates or sandwiches. The filter complement includes two solar blind Wood's filters F160AW and F160BW. F160BW will be used in all science observations because the other filter has some large pinholes that lead to significant red leak. In addition to the above complement of broad and narrow band filters WFPC2 features a set of three specialized quadrant (quad or Q) filters in which each quadrant corresponds to a facet of the pyramid, and therefore to a distinct camera relay. There is one quad containing four narrow-band, redshifted [OII] filters with central wavelengths from 3763-3986A, one quad with four polarizing elements (POL) with polarization angles, 0, 45, 90 and 135 degrees, and one quad with four methane (CH4) band filters with central wavelengths from 5433-8929A. The polarizer quad filter, can be crossed with any other filter over the wavelength range from 2800A to 8000A, with the exception of the Methane Quad and Redshifted [OII] Quad which share the same wheel. Optics ====== The central portion of the OTA F/24 beam is intercepted by a steerable pick-off mirror attached to the WFPC2 and is diverted through an open entry port into the instrument. The entry port is not sealed with an afocal MgF2 window as it was in WF/PC-1. The beam then passes through a shutter and filters. A total of 48 spectral elements and polarizers are contained in an assembly of 12 filter wheels. Then the light falls onto a shallow-angle, four-faceted pyramid located at the aberrated OTA focus, each face of the pyramid being a concave spherical surface. The pyramid divides the OTA image of the sky into four parts. After leaving the pyramid, each quarter of the full field-of-view is relayed by an optical flat to a cassegrain relay that forms a second field image on a charge-coupled device (CCD) of 800x800 pixels. Each detector is housed in a cell that is sealed by a MgF2 window. This window is figured to serve as a field flattener. The aberrated HST wavefront is corrected by introducing an equal but opposite error in each of the four cassegrain relays. An image of the HST primary mirror is formed on the secondary mirrors in the cassegrain relays. The previously flat fold mirror in the PC channel has a small curvature to ensure this, and this is why the magnification is changed from F/30 to F/28.3 in the PC. The spherical aberration from the telescope's primary mirror is corrected on these secondary mirrors, which are extremely aspheric. The point spread function is then close to that originally expected for WF/PC-1. Operational Modes ================= The CCDs and their associated signal chains have read-out noise levels (in the absence of signal shot noise or interference) of approximately 5 e-. The WF/PC-1 CCD read noise was effectively 15-20 e-, since there were additional contributions above the nominal 13 e- resulting from 'missing codes' in the ADC and the preflash exposure. The conversion factors from detected electrons (QE * number of incident photons) to data numbers (DN) are tabulated below, as are read noise and linearity. Note that all calculations of sensitivity in this manual assume gains of 7 and 14 for two gain channels, choices very close to the measured gains. Gain PC1 WF3 ====================================== Noise '7' 5.24+-0.30 5.22+-0.28 '14' 7.02+-0.41 6.99+-0.38 -------------------------------------- Gain '7' 7.12+-0.41 6.90+-0.32 '14' 13.99+-0.63 13.95+-0.63 -------------------------------------- Gamma '7' 1.0015+-0.0006 1.0020+-0.0006 '14' 1.0004+-0.0001 1.0032+-0.0006 --------------------------------------