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Daily Report #4328
Notice: For the foreseeable future, the daily reports may contain apparent
discrepancies between some proposal descriptions and the listed instrument usage. This is due to the conversion of previously approved ACS WFC or HRC observations into WFPC2, or NICMOS observations subsequent to the loss of ACS CCD science capability in late January. HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science DAILY REPORT # 4328 PERIOD COVERED: UT March 27, 2007 (DOY 086) OBSERVATIONS SCHEDULED FGS 10612 Binary Stars in Cyg OB2: Relics of Massive Star Formation in a Super-Star Cluster We propose to make a high angular resolution SNAP survey of the massive stars in the nearby, super-star cluster Cyg OB2. We will use FGS1r TRANS mode observations to search for astrometric companions in the separation range of 0.01 to 1.00 arcsec and in the magnitude difference range smaller than 4 magnitudes. The observations will test the idea that the formation of very massive stars involves mergers and the presence of nearby companions. Discovery of companions to massive stars in this relatively nearby complex will provide guidance in the interpretation of apparently supermassive stars in distant locations. The search for companions will also be important for verification of fundamental parameters derived from spectroscopy, adjustments to main sequence fitting and distance estimations, determining third light contributions of eclipsing binaries, identifying wide colliding wind binaries, studying the relationship between orbital and spin angular momentum, and discovering binaries amenable to future mass determinations. The massive star environment in Cyg OB2 may be similar to the kinds found in the earliest epoch of star formation, so that a study of the role of binaries in Cyg OB2 will help us understand the formation processes of the first stars in the Universe. FGS 10989 Astrometric Masses of Extrasolar Planets and Brown Dwarfs We propose observations with HST/FGS to estimate the astrometric elements {perturbation orbit semi-major axis and inclination} of extra-solar planets orbiting six stars. These companions were originally detected by radial velocity techniques. We have demonstrated that FGS astrometry of even a short segment of reflex motion, when combined with extensive radial velocity information, can yield useful inclination information {McArthur et al. 2004}, allowing us to determine companion masses. Extrasolar planet masses assist in two ongoing research frontiers. First, they provide useful boundary conditions for models of planetary formation and evolution of planetary systems. Second, knowing that a star in fact has a plantary mass companion, increases the value of that system to future extrasolar planet observation missions such as SIM PlanetQuest, TPF, and GAIA. NIC2 10603 Multiwavelength Imaging of Edge-on Protoplanetary Disks: Quantifying the Growth of Circumstellar Dust Young, edge-on circumstellar disks are uniquely valuable laboratories for the study of planet formation. In these objects, the central star is occulted from direct view, significant PSF artifacts are absent, and the disk is clearly seen as a central dust lane flanked by faint disk reflected light. The detailed morphology of these nebulae and its variation with wavelength provide crucial information on the disk internal structure and the properties of its constituent dust grains. A key observable is the slope defining the wavelength dependence of the dust scattering opacity, which becomes shallower when grain growth has taken place; multiwavelength resolved disk images are the key dataset enabling such measurements. Recent analyses of three different edge-on disks have revealed a diversity in their dust properties that is indicative of different degrees of dust grain evolution having taken place in each system. This characterization of disk grain growth, when applied comparatively to a larger sample of these objects, would enable the construction of an evolutionary sequence of young disks at successive stages on the road to planet formation. In pursuit of this goal, we have identified a sample of 15 edge-on disks previously discovered by HST or groundbased telescopes, but for which high fidelity, high spatial resolution images do not yet exist in both the optical and near-infrared. We propose broad- band multicolor imaging with NICMOS of all these targets, and ACS imaging of nine of these targets In combination with existing data, the proposed images will form a complete database of high resolution optical/near-IR images for these 15 disk systems. Scattered light modeling will be used to derive the disk structure and dust properties, yielding results that will be of fundamental importance for our understanding of grain properties during protoplanetary disk evolution. NIC2 10849 Imaging Scattered Light from Debris Disks Discovered by the Spitzer Space Telescope around 21 Sun-like Stars We propose to use the high-contrast capability of the NICMOS coronagraph to image a sample of newly discovered circumstellar disks associated with Sun-like stars. These systems were identified by their strong thermal infrared {IR} emission with the Spitzer Space Telescope as part of the Spitzer Legacy Science program titled "The Formation and Evolution of Planetary Systems" {FEPS, P.I.: M.Meyer}. Modeling of the thermal excess emission from the spectral energy distributions alone cannot distinguish between narrowly confined high-opacity disks and broadly distributed, low-opacity disks. By resolving light scattered by the circumstellar material, our proposed NICMOS observations can break this degeneracy, thus revealing the conditions under which planet formation processes are occuring or have occured. For three of our IR-excess stars that have known radial-velocity planets, resolved imaging of the circumstellar debris disks may further offer an unprecedented view of planet-disk interactions in an extrasolar planetary system. Even non-detections of the light scattered by the circumstellar material will place strong constraints on the disk geometries, ruling out disk models with high optical depth. Unlike previous disk imaging programs, our program contains a well-defined sample of ~1 solar mass stars covering a range of ages from 3 Myr to 3 Gyr, thus allowing us to study the evolution of disks from primordial to debris for the first time. The results from our program will greatly improve our understanding of the architecture of debris disks around Sun-like stars, and will create a morphological context for the existence of our own solar system. This proposal is for a continuation of an approved Cycle 14 program {GO/10527, P.I.: D. Hines}. WFPC2 11030 WFPC2 WF4 Temperature Reduction #3 In the fall of 2005, a serious anomaly was found in images from the WF4 CCD in WFPC2. The WF4 CCD bias level appeared to have become unstable, resulting in sporadic images with either low or zero bias level. The severity and frequency of the problem was rapidly increasing, making it possible that WF4 would soon become unusable if no work-around were found. Examination of bias levels during periods with frequent WFPC2 images showed low and zero bias episodes every 4 to 6 hours. This periodicity is driven by cycling of the WFPC2 Replacement Heater, with the bias anomalies occurring at the temperature peaks. The other three CCDs {PC1, WF2, and WF3} appear to be unaffected and continue to operate properly. Lowering the Replacement Heater temperature set points by a few degrees C effectively eliminates the WF4 anomaly. On 9 January 2006, the upper set point of the WFPC2 Replacement Heater was reduced from 14.9C to 12.2C. On 20 February 2006, the upper set point was reduced from 12.2C to 11.3C, and the lower set point was reduced from 10.9C to 10.0C. These changes restored the WF4 CCD bias level; however, the bias level has begun to trend downwards again, mimicking its behavior in late 2004 and early 2005. A third temperature reduction is planned for March 2007. We will reduce the upper set point of the heater from 11.3C to 10.4C and the lower set point from 10.0C to 9.1C. The observations described in this proposal will test the performance of WFPC2 before and after this temperature reduction. Additional temperature reductions may be needed in the future, depending on the performance of WF4. Orbits: internal 26, external 1 FLIGHT OPERATIONS SUMMARY: Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.) HSTARS: 10757 - GSAcq(2.3.2) results in Fine Lock Back-up (2,0,2) using FGS-1 At 087/02:13:56 GSAcq (2,3,2) scheduled from 02:10:10-02:17:24 resulted in Fine Lock Back-up (2,0,2) using FGS 1. OBAD #1 RSS: 1783.55 OBAD #2 RSS: 8.39 COMPLETED OPS REQUEST: 18024-2 - ACS Bus C On-Orbit Test, Phase I - Part 1 18025-2 - ACS Bus C On-Orbit Test, Phase I - Part 2 18026-6 - ACS Bus C On-Orbit Test, Phase I - Part 3 18027-3 - ACS Bus C On-Orbit Test, Phase I - Part 4 18029-0 - Patch WF2 UIDLE replacement htr set point, adjustment #3 COMPLETED OPS NOTES: 1585-1 - Update WF-2 Temp Limits 1582-0 - Change JERRCNT Limit after Replacement Heater adj#3 SCHEDULED SUCCESSFUL FGS GSacq 06 06 FGS REacq 00 00 OBAD with Maneuver 12 12 SIGNIFICANT EVENTS: Flash Report: ACS Main Bus C On-orbit Test As of 086/14:05:20 UTC, all commanding for the ACS Main Bus C on-orbit test has been successfully completed through execution of Ops Requests 18024 - 18028. During the course of execution of Macro 3 to close the ACS Side 2 Hold relay for 50 ms, the PDU2 fuse was observed to clear, indicating the likely location for the short circuit is in the Hold bus. The engineering team is now reviewing the high-rate T-Prime telemetry data collected during the test for a detailed analysis of the results. The primary Main Bus C relay has been successfully re-opened, the FHSTs have been powered on, and the remaining vehicle configuration has been restored to normal as part of the post-test clean-up. Flash Report: ACS Bus C Test, Post-Test Monitoring The Fixed-Head Star Trackers are performing nominally following their power cycle as part of the ACS Main Bus C test. OBAD corrections of approximately 0.5 and 0.005 degrees RSS were performed prior to the successful guide star acquisition at 086/20:58. Flash Report: WF/PC-II CCD4 replacement Heater In-Flight Temperature Adjustment #3 The 3rd in-flight adjustment of the WF/PC-II replacement heater temperature control was successfully completed with the execution of Ops Request 18029-0 at 086/18:20. All activities proceeded nominally. The NSSC-1 executive limit table action value for the pyramid bulkhead temperature was changed from 8.13 to 2.38 degC in accordance with the updates to CARD item 2.4.6.1, and the UIDLE dead band control range was shifted from 9.99 - 11.3 to 8.7 to 9.99 degC. The behavior of the replacement heaters under the control of UIDLE and the optical bench temperatures will continue to be monitored in real-time until such time as the new settings can be functionally verified, likely within the next hour. Another Flash Report will be sent following this verification. Flash Report: Post WF/PC-II CCD4 Replacement Heater In-Flight Temperature Adjustment #3 Monitoring At 86/23:08 the replacement heaters were observed turning on when Bay1 fell to 8.74 degs, ~ 7 minutes later they were disables when Bay1 reached 9.99 deg as expected, functionally verifying the patch. |
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