This program continues the monthly anneal that has taken place every four weeks for the last three cycles. We now obtain WFC biases and darks before and after the anneal in the same sequence as is done for the ACS daily monitor (now done 4 times per week). So the anneal observation supplements the monitor observation sets during the appropriate week. Extended Pixel Edge Response (EPER) and First Pixel Response (FPR) data will be obtained over a range of signal levels for the Wide Field Channel (WFC). This program emulates the ACS pre-flight ground calibration and post-launch SMOV testing (program 8948), so that results from each epoch can be directly compared. The High Resolution Channel (HRC) visits have been removed since it could not be repaired during SM4.
This program also assesses the read noise, bias structure, and amplifier cross-talk of ACS/WFC using the GAIN=1.4 A/D conversion setting. This investigation serves as a precursor to a more comprehensive study of WFC performance using GAIN=1.4.
COS-GTO: Deep Search for an Oxygen Atmosphere on Callisto
We plan a deep search for 1304? and 1356? O emission from Callisto, to detect or place strong limits on the presence of a hypothesized O2 atmosphere on this moon (Liang et al. 2005). Tenuous oxygen atmospheres on Europa and Ganymede have been detected by HST using these emission lines, but searches for O emission from Callisto have not been successful (Strobel et al. 2002). The Liang et al. models predict O emission at levels comparable to the Strobel et al. upper limit, so the improved sensitivity of COS may be able to detect the emission, and thus Callisto's O2 atmosphere, for the first time.
COS FUV DCE Memory Dump
Whenever the FUV detector high voltage is on, count rate and current draw information is collected, monitored, and saved to DCE memory. Every 10 msec the detector samples the currents from the HV power supplies (HVIA, HVIB) and the AUX power supply (AUXI). The last 1000 samples are saved in memory, along with a histogram of the number of occurrences of each current value.
In the case of a HV transient (known as a "crackle" on FUSE), where one of these currents exceeds a preset threshold for a persistence time, the HV will shut down, and the DCE memory will be dumped and examined as part of the recovery procedure. However, if the current exceeds the threshold for less than the persistence time (a "mini-crackle" in FUSE parlance), there is no way to know without dumping DCE memory. By dumping and examining the histograms regularly, we will be able to monitor any changes in the rate of "mini-crackles" and thus learn something about the state of the detector.
CCD Dark Monitor Part 2
Monitor the darks for the STIS CCD.
CCD Bias Monitor-Part 2
Monitor the bias in the 1x1, 1x2, 2x1, and 2x2 bin settings at gain=1, and 1x1 at gain = 4, to build up high-S/N superbiases and track the evolution of hot columns.
A public SNAPSHOT Survey of Gamma-ray Burst Host Galaxies
We propose to conduct a public infrared survey of the host galaxies of Swift selected gamma-ray bursts (GRBs) at z<3. By obtaining deep, diffraction limited imaging in the IR we will complete detections for the host galaxies, and in concert with our extensive ground based afterglow and host programmes will compile a detailed catalog of the properties of high-z galaxies selected by GRBs. In particular these observations will enable us to study the colours, luminosities and morphologies of the galaxies. This in turn informs studies of the nature of the progenitors and the role of GRBs as probes of star formation across cosmic history. Ultimately it provides a product of legacy value which will greatly complement further studies with next generation facilities such as ALMA and JWST.
IR Dark Current Monitor
Analyses of ground test data showed that dark current signals are more reliably removed from science data using darks taken with the same exposure sequences as the science data, than with a single dark current image scaled by desired exposure time. Therefore, dark current images must be collected using all sample sequences that will be used in science observations. These observations will be used to monitor changes in the dark current of the WFC3-IR channel on a day-to-day basis, and to build calibration dark current ramps for each of the sample sequences to be used by Gos in Cycle 17. For each sample sequence/array size combination, a median ramp will be created and delivered to the calibration database system (CDBS).
In Search of SNIb/Ic Wolf-Rayet Progenitors and Comparison with Red Supergiants (SNII Progenitors) in the Giant ScI Spiral M101
We propose to test two of the clearest predictions of the theory of evolution of massive-star evolution: 1) The formation of Wolf-Rayet stars depends strongly on these stars' metallicity (Z), with relatively fewer WR stars forming at lower Z, and 2) Wolf-Rayet stars die as Type Ib or Ic supernovae. To carry out these tests we propose a deep, narrowband imaging survey of the massive star populations in the ScI spiral galaxy M101. Just as important, we will test the hypothesis that Superclusters like 30 Doradus are always richly populated with WR stars, and by implication that these complexes are responsible for the spectral signatures of starburst galaxies.
Our previous HST survey of the HII regions in the ScIII galaxy NGC 2403 suggested that the distribution of WR stars and RSG is a sensitive diagnostic of the recent star-forming history of these large complexes: young cores of O and WR stars are surrounded by older halos containing RSG. Theory predicts that this must change with metallicity; relatively fewer WR stars form at lower Z. A key goal of our proposal is to directly test this paradigm in a single galaxy, M101 being the ideal target. The abundance gradient across M101 (a factor of 20) suggests that relatively many more WR will be found in the inner parts of this galaxy than in the outer "suburbs". Second, we note that WR stars are predicted to end their lives as core-collapse or pair-instability supernovae. The WR population in M101 may be abundant enough for one to erupt as a Type Ib or Ic supernova within a generation. The clear a priori identification of a WR progenitor would be a major legacy of HST. Third, we will also determine if "superclusters", heavily populated by WR stars, are common in M101. It is widely claimed that such Superclusters produce the integrated spectral signatures of Starburst galaxies. We will be able to directly measure the numbers and emission-line luminosities of thousands of Wolf Rayet stars located in hundreds of M101 Superclusters, and correlate those numbers against the Supercluster sizes and luminosities. It is likely (but far from certain) that Supercluster sizes and emission-line luminosities are driven by their Wolf-Rayet star content. Our sample will be the largest and best-ever Supercluster/Wolf Rayet sample, an excellent local proxy for characterizing starburst galaxies' Superclusters.
WFC3/UVIS Charge Injection Test
In preparation for making charge injection (CI) available to observers, this proposal will 1) confirm that the CI performs on-orbit as it did on the ground, 2) provide an initial assessment of which CI mode is most effective (10, 17, 25 line or continuous), and 3) obtain a baseline calibration for each mode.
The WFC3 Galactic Bulge Treasury Program: Populations, Formation History, and Planets
Exploiting the full power of the Wide Field Camera 3 (WFC3), we propose deep panchromatic imaging of four fields in the Galactic bulge. These data will enable a sensitive dissection of its stellar populations, using a new set of reddening-free photometric indices we have constructed from broad-band filters across UV, optical, and near-IR wavelengths. These indices will provide accurate temperatures and metallicities for hundreds of thousands of individual bulge stars. Proper motions of these stars derived from multi-epoch observations will allow separation of pure bulge samples from foreground disk contamination. Our catalogs of proper motions and panchromatic photometry will support a wide range of bulge studies.
Using these photometric and astrometric tools, we will reconstruct the detailed star-formation history as a function of position within the bulge, and thus differentiate between rapid- and extended-formation scenarios. We will also measure the dependence of the stellar mass function on metallicity, revealing how the characteristic mass of star formation varies with chemistry. Our sample of bulge stars with accurate metallicities will include 12 candidate hosts of extrasolar planets. Planet frequency is correlated with metallicity in the solar neighborhood; our measurements will extend this knowledge to a remote environment with a very distinct chemistry.
Our proposal also includes observations of six well-studied globular and open star clusters; these observations will serve to calibrate our photometric indices, provide empirical population templates, and transform the theoretical isochrone libraries into the WFC3 filter system. Besides enabling our own program, these products will provide powerful new tools for a host of other stellar-population investigations with HST/WFC3. We will deliver all of the products from this Treasury Program to the community in a timely fashion.
Photometric Metallicity Calibration with WFC3 Specialty Filters
The community has chosen to include several filters in the WFC3 filter complement that have been designed to allow fairly precise estimates of stellar metallicities, and many science programs are enabled by this capability. Since these filters do not exactly match those used for this purpose on the ground, however, the mapping of stellar colors to stellar metallicities needs to be calibrated. We propose to achieve this calibration through observations of five stellar clusters with well known metallicities. We will calibrate several different filter calibrations which will allow future users to determine what filter combination best meets their science needs.
WFC3 UVIS CCD Daily Monitor
The behavior of the WFC3 UVIS CCD will be monitored daily with a set of full-frame, four-amp bias and dark frames. A smaller set of 2Kx4K subarray biases are acquired at less frequent intervals throughout the cycle to support subarray science observations. The internals from this proposal, along with those from the anneal procedure (Proposal 11909), will be used to generate the necessary superbias and superdark reference files for the calibration pipeline (CDBS).
Cycle 17: UVIS Bowtie Monitor
Ground testing revealed an intermittent hysteresis type effect in the UVIS detector (both CCDs) at the level of ~1%, lasting hours to days. Initially found via an unexpected bowtie- shaped feature in flatfield ratios, subsequent lab tests on similar e2v devices have since shown that it is also present as simply an overall offset across the entire CCD, i.e., a QE offset without any discernable pattern. These lab tests have further revealed that overexposing the detector to count levels several times full well fills the traps and effectively neutralizes the bowtie. Each visit in this proposal acquires a set of three 3x3 binned internal flatfields: the first unsaturated image will be used to detect any bowtie, the second, highly exposed image will neutralize the bowtie if it is present, and the final image will allow for verification that the bowtie is gone.
A Dynamical-Compositional Survey of the Kuiper Belt: A New Window Into the Formation of the Outer Solar System
The eight planets overwhelmingly dominate the solar system by mass, but their small numbers, coupled with their stochastic pasts, make it impossible to construct a unique formation history from the dynamical or compositional characteristics of them alone. In contrast, the huge numbers of small bodies scattered throughout and even beyond the planets, while insignificant by mass, provide an almost unlimited number of probes of the statistical conditions, history, and interactions in the solar system. To date, attempts to understand the formation and evolution of the Kuiper Belt have largely been dynamical simulations where a hypothesized starting condition is evolved under the gravitational influence of the early giant planets and an attempt is made to reproduce the current observed populations. With little compositional information known for the real Kuiper Belt, the test particles in the simulation are free to have any formation location and history as long as they end at the correct point. Allowing compositional information to guide and constrain the formation, thermal, and collisional histories of these objects would add an entire new dimension to our understanding of the evolution of the outer solar system. While ground based compositional studies have hit their flux limits already with only a few objects sampled, we propose to exploit the new capabilities of WFC3 to perform the first ever large-scale dynamical-compositional study of Kuiper Belt Objects (KBOs) and their progeny to study the chemical, dynamical, and collisional history of the region of the giant planets. The sensitivity of the WFC3 observations will allow us to go up to two magnitudes deeper than our ground based studies, allowing us the capability of optimally selecting a target list for a large survey rather than simply taking the few objects that can be measured, as we have had to do to date. We have carefully constructed a sample of 120 objects which provides both overall breadth, for a general understanding of these objects, plus a large enough number of objects in the individual dynamical subclass to allow detailed comparison between and within these groups. These objects will likely define the core Kuiper Belt compositional sample for years to come. While we have many specific results anticipated to come from this survey, as with any project where the field is rich, our current knowledge level is low, and a new instrument suddenly appears which can exploit vastly larger segments of the population, the potential for discovery -- both anticipated and not -- is extraordinary.