The James Webb Space Telescope (JWST) and its suite of instruments, modes and high contrast capabilities will enable imaging and characterization of faint and dusty astrophysical sources1-3 (exoplanets, proto-planetary and debris disks, dust shells, etc.) in the vicinity of hosts (stars of all sorts, active galactic nuclei, etc.) with an unprecedented combination of sensitivity and angular resolution at wavelengths beyond 2 μm. Two of its four instruments, NIRCam4, 5 and MIRI,6 feature coronagraphs7, 8 for wavelengths from 2 to 23 μm. JWST will stretch the current parameter space (contrast at a given separation) towards the infrared with respect to the Hubble Space Telescope (HST) and in sensitivity with respect to what is currently achievable from the ground with the best adaptive optics (AO) facilities. The Coronagraphs Working Group at the Space Telescope Science Institute (STScI) along with the Instruments Teams and internal/external partners coordinates efforts to provide the community with the best possible preparation tools, documentation, pipelines, etc. Here we give an update on user support and operational aspects related to coronagraphy. We aim at demonstrating an end to end observing strategy and data management chain for a few science use cases involving coronagraphs. This includes the choice of instrument modes as well as the observing and point-spread function (PSF) subtraction strategies (e.g. visibility, reference stars selection tools, small grid dithers), the design of the proposal with the Exposure Time Calculator (ETC), and the Astronomer's Proposal Tool (APT), the generation of realistic simulated data at small working angles and the generation of high level, science-grade data products enabling calibration and state of the art data-processing.
The Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) is fitted with three grisms for slitless spectroscopy.
In the UVIS channel there is one grism, G280, for the near-UV to visible range (200 - 400nm;
1.4nm/pix). The IR channel has two grisms: G102 for the shorter (800-1150nm; 2.45nm/pix) and G141 for the
longer (1100-1700nm; 4.65nm/pix) NIR wavelengths. Using Servicing Mission Observatory Verification (SMOV)
and Cycle 17 calibration data we have assessed the performance of the grisms. We have measured the fielddependent
trace locations and dispersion solutions and determined the throughputs. The trace and wavelength
solutions for the IR grisms were found to be linear functions, varying smoothly across the field of view. The UVIS
grism exhibits a highly bent trace and significantly non-linear dispersion solutions. The maximum throughputs
for the G102 and G141 grisms, including the telescope optics, are 41% at 1100 nm and 48% at 1450 nm, respectively.
Limiting magnitudes at S/N=5 and a 1h exposure are JAB=22.6 and HAB=22.9 for the G102 and G141
grisms, respectively. The calibration results are published in the form of sensitivity and configuration files that
can be used with our dedicated extraction software aXe to reduce WFC3 slitless data.
In ground testing of the Hubble Space Telescope Wide Field Camera 3 (HST/WFC3), the CCDs of its UV/visible channel exhibited an unanticipated quantum efficiency hysteresis (QEH) behavior. The QEH first manifested itself as an occasionally observed contrast in response across the format of the CCDs, with an amplitude of typically 0.1-0.2% or less at the nominal -83°C operating temperature, but with contrasts of up to 3-5% observed at warmer temperatures. The behavior has been replicated in the laboratory using flight spare detectors and has been found to be related to an initial response deficiency of ~5% amplitude when the CCDs
are cooled with no illumination. A visible light flat-field (540nm) with a several times full-well signal level is found to pin the detector response at both optical (600nm) and near-UV (230nm) wavelengths, suppressing the QEH behavior. We have characterized the timescale for the detectors to become unpinned (days for significant
response loss at -83°C and have developed a protocol to stabilize the response in flight by flashing the WFC3 CCDs with the instrument's internal calibration system.
The Wide-field Camera 3 (WFC3) is a fourth-generation instrument planned for installation in Hubble Space Telescope
(HST). Designed as a panchromatic camera, WFC3's UVIS and IR channels will complement the other instruments onboard
HST and enhance the observatory's scientific performance. UVIS images are obtained via two 4096×2051 pixel
e2v CCDs while the IR images are taken with a 1024×1024 pixel HgCdTe focal plane array from Teledyne Imaging
Sensors. Based upon characterization tests performed at NASA/GSFC, the final flight detectors have been chosen and
installed in the instrument. This paper summarizes the performance characteristics of the WFC3 flight detectors based
upon component and instrument-level testing in ambient and thermal vacuum environments.
Wide Field Camera 3 (WFC3), a panchromatic imager developed for the Hubble Space Telescope (HST), is fully
integrated with its flight detectors and has undergone several rounds of ground testing and calibration at Goddard Space
Flight Center (GSFC). The testing processes are highly automated, with WFC3 and the optical stimulus, which is used to
provide external targets and illumination, being commanded by coordinated computer scripts. All test data are captured
and stored in the long-term Hubble Data Archive. A full suite of instrument characterization and calibration tests has
been performed, including the measurement of key detector properties such as dark current, read noise, flat field
response, gain, linearity, and persistence, as well as instrument-level properties like total system throughput, imaging
quality and encircled energy, grism dispersions, IR thermal background, and image stability. Nearly all instrument
characteristics have been shown to meet or exceed expectations and requirements.
Wide Field Camera 3 (WFC3), a panchromatic imager being developed for the Hubble Space Telescope (HST), is now
fully integrated and has undergone extensive ground testing at Goddard Space Flight Center, in both ambient and
thermal-vacuum test environments. The thermal-vacuum testing marks the first time that both of the WFC3 UV/Visible
and IR channels have been operated and characterized in flight-like conditions. The testing processes are completely
automated, with WFC3 and the optical stimulus that is used to provide external targets and sources being commanded
by coordinated computer scripts. All test data are captured and stored in the long-term Hubble Data Archive. A full suite
of instrument calibration tests have been performed, including measurements of detector properties such as dark current,
read noise, flat field response, gain, linearity, and persistence, as well as total system throughput, encircled energy,
grism dispersions, IR thermal background, and image stability tests. Nearly all instrument characteristics have been
shown to meet or exceed expectations and requirements. Solutions to all issues discovered during testing are in the
process of being implemented and will be verified during future ground tests.
The Next Generation Space Telescope (NGST) will be a segmented, deployable, infrared-optimized 6.5m space telescope. Its active primary segments will be aligned, co-phased, and then fine-tuned in order to deliver image quality sufficient for the telescope's intended scientific goals. Wavefront sensing used to drive this tuning will come from the analysis of focussed and defocussed images taken with its near-IR science camera, NIRCAM. There is a pressing need to verify that this will be possible with the near-IR detectors that are still under development for NGST. We create simulated NIRCAM images to test the maintenance phase of this plan. Our simulations incorporate Poisson and electronics read noise, and are designed to be able to include various detector and electronics non-linearities. We present our first such simulation, using known or predicted properties of HAWAII HgCdTe focal plane array detectors. Detector effects characterized by the Independent Detector Testing Laboratory will be included as they become available. Simulating InSb detectors can also be done within this framework in future. We generate Point-Spread Functions (PSF's) for a segmented aperture geometry with various wavefront aberrations, and convolve this with typical galaxy backgrounds and stellar foregrounds. We then simulate up-the-ramp (MULTIACCUM in HST parlance) exposures with cosmic ray hits. We pass these images through the HST NICMOS `CALNICA' calibration task to filter out cosmic ray hits. The final images are to be fed to wavefront sensing software, in order to find the ranges of exposure times, filter bandpass, defocus, and calibration star magnitude required to keep the NGST image within its specifications.
We describe the on-orbit performance of the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) aboard the Hubble Space Telescope (HST) following the installation of the NICMOS Cooling System (NCS). NICMOS is operated at a higher temperature (~77 K) than in the previous observing 1997-1998 period (~62 K). Due to the higher operating temperature, the detector QE is higher, while the well depth is less. The spatial structure of the flat field response remained essentially unchanged. We will show the effects of operating at the higher temperature and present current NICMOS calibration images. In addition, we present an overview of on-orbit testing and report on the re-enabling of NICMOS.
We describe the on-orbit characterization of the HgCdTe detectors aboard NICMOS. The flat-field response is strongly wavelength dependent, and we show the effect of this on the photometric uncertainties in data, as well as the complications it introduces into calibration of slitless grism observations. We present the first rigorous treatment of the dark current as a function of exposure time for HgCdTe array detectors, and show that they consist of three independent components which we have fully characterized - a constant component which is the true dark current, an 'amplifier glow' component which results from operation of the four readout amplifiers situated near the detector corners and injects a spatially dependent signal each time the detector is non-destructively read out, and finally the 'shading', a component well known in HgCdTe detectors which we show is simply a pixel dependent bias change whose amplitude is a function of the time since the detector was last non-destructively read out. We show that with these three components fully characterized, we are able to generate 'synthetic' dark current images for calibration purposes which accurately predict the actual performance of the three flight detectors. In addition, we present linearity curves produced in ground testing before launch. Finally, we report a number of detector related anomalies which we have observed with NICMOS some of which have limited the observed sensitivity of the instrument, and which at the time of writing are still not fully understood.