NASA Hubble Space Telescope Daily Report #4363
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 DAILY REPORT # 4363
– Continuing to collect World Class Science
PERIOD COVERED: UT May 15, 2007 (DOY 135)
OBSERVATIONS SCHEDULED
WFPC2 10800
Kuiper Belt Binaries: Probes of Early Solar System Evolution
Binaries in the Kuiper Belt are a scientific windfall: in them we have relatively fragile test particles which can be used as tracers of the early dynamical evolution of the outer Solar System. We propose to continue a Snapshot program using the ACS/HRC that has a demonstrated discovery potential an order of magnitude higher than the HST observations that have already discovered the majority of known transneptunian binaries. With this continuation we seek to reach the original goals of this project: to accumulate a sufficiently large sample in each of the distinct populations collected in the Kuiper Belt to be able to measure, with statistical significance, how the fraction of binaries varies as a function of their particular dynamical paths into the Kuiper Belt. Today’s Kuiper Belt bears the imprints of the final stages of giant-planet building and migration; binaries may offer some of the best preserved evidence of that long-ago era.
WFPC2 10832
Solving the microlensing puzzle: An HST high-resolution imaging approach
We propose to use the HST Advanced Camera for Surveys High Resolution Channel to obtain high resolution imaging data for 10 bona-fide LMC microlensing events seen in the original MACHO survey. The purpose of this survey will be to assess whether or not the lens and source stars have separated enough to be resolved since the original microlensing event took place – about a decade has passed since the original MACHO survey and the HST WFPC2 follow-up observations of the microlensing events. If the components of the lensing event are resolved, we will determine the apparent magnitude and color of both the lens and the source stars. These data, in combination with Spitzer/IRAC data and Magellan near-IR JHK data, will be used to ascertain the basic properties of the lens stars. With the majority of the microlensing events in the original MACHO survey observed at the highest spatial resolution currently possible, we will be able to draw important conclusions as to what fraction of these events have lenses which belong to some population of dwarf stars in the disk and what fraction must be due to lenses in the halo or beyond. These data will greatly increase our understanding of the structure of the Galaxy by characterizing the stellar population responsible for the gravitational microlensing.
ACS/SBC 10862
Comprehensive Auroral Imaging of Jupiter and Saturn during the International Heliophysical Year
A comprehensive set of observations of the auroral emissions from Jupiter and Saturn is proposed for the International Heliophysical Year in 2007, a unique period of especially concentrated measurements of space physics phenomena throughout the solar system. We propose to determine the physical relationship of the various auroral processes at Jupiter and Saturn with conditions in the solar wind at each planet. This can be accomplished with campaigns of observations, with a sampling interval not to exceed one day, covering at least one solar rotation. The solar wind plasma density approaching Jupiter will be measured by the New Horizons spacecraft, and a separate campaign near opposition in May 2007 will determine the effect of large-scale variations in the interplanetary magnetic field {IMF} on the Jovian aurora by extrapolation from near-Earth solar wind measurements. A similar Saturn campaign near opposition in Jan. 2007 will combine extrapolated solar wind data with measurements from a wide range of locations within the Saturn magnetosphere by Cassini. In the course of making these observations, it will be possible to fully map the auroral footprints of Io and the other satellites to determine both the local magnetic field geometry and the controlling factors in the electromagnetic interaction of each satellite with the corotating magnetic field and plasma density. Also in the course of making these observations, the auroral emission properties will be compared with the properties of the near-IR ionospheric emissions {from ground-based observations} and non thermal radio emissions, from ground-based observations for Jupiter?s decametric radiation and Cassini plasma wave measurements of the Saturn Kilometric Radiation {SKR}.
WFPC2 10798
Dark Halos and Substructure from Arcs & Einstein Rings
The surface brightness distribution of extended gravitationally lensed arcs and Einstein rings contains super-resolved information about the lensed object, and, more excitingly, about the smooth and clumpy mass distribution of the lens galaxies. The source and lens information can non-parametrically be separated, resulting in a direct “gravitational image” of the inner mass-distribution of cosmologically-distant galaxies {Koopmans 2005; Koopmans et al. 2006 [astro-ph/0601628]}. With this goal in mind, we propose deep HST ACS-F555W/F814W and NICMOS-F160W WFC imaging of 20 new gravitational-lens systems with spatially resolved lensed sources, of the 35 new lens systems discovered by the Sloan Lens ACS Survey {Bolton et al. 2005} so far, 15 of which are being imaged in Cycle-14. Each system has been selected from the SDSS and confirmed in two time- efficient HST-ACS snapshot programs {cycle 13&14}. High-fidelity multi-color HST images are required {not delivered by the 420s snapshots} to isolate these lensed images {properly cleaned, dithered and extinction-corrected} from the lens galaxy surface brightness distribution, and apply our “gravitational maging” technique. Our sample of 35 early-type lens galaxies to date is by far the largest, still growing, and most uniformly selected. This minimizes selection biases and small-number statistics, compared to smaller, often serendipitously discovered, samples. Moreover, using the WFC provides information on the field around the lens, higher S/N and a better understood PSF, compared with the HRC, and one retains high spatial resolution through drizzling. The sample of galaxy mass distributions – determined through this method from the arcs and Einstein ring HST images – will be studied to: {i} measure the smooth mass distribution of the lens galaxies {dark and luminous mass are separated using the HST images and the stellar M/L values derived from a joint stellar-dynamical analysis of each system}; {ii} quantify statistically and individually the incidence of mass-substructure {with or without obvious luminous counter- parts such as dwarf galaxies}. Since dark-matter substructure could be more prevalent at higher redshift, both results provide a direct test of this prediction of the CDM hierarchical structure-formation model.
WFPC2 10888
Complexity in the Smallest Galaxies: Star Formation History of the Sculptor Dwarf Spheroidal
The Sculptor dwarf spheroidal galaxy {Scl dSph} is one of the most luminous of the Milky Way dSph satellites, suffers virtually no foreground confusion or reddening because of its high galactic latitude, and is nearby at 80 kpc from the Sun. It is of great interest to astronomy to understand the detailed histories of dSph galaxies because they may be survivors of the hierarchical merging process that created giant galaxies like our own. Despite this, the age distribution of stars in Scl dSph remains remarkably poorly constrained because of a dearth of high-quality color-magnitude diagrams {CMDs} of its central regions. Scl dSph is known to be complex on the basis of shallower photometry, radial velocity studies, and investigations of the metallicity; however, the age range of significant star-formation and the proportion of stars older and younger than 10 Gyr is still completely unknown. The age of the centrally concentrated, metal-rich population has never been measured. We propose to obtain deep optical images of the core of Scl dSph with WFPC2 in order to measure the temporal evolution of its star-formation rate over its entire lifetime. The ONLY way to reliably measure the variation in star-formation rate on Gyr timescales at ages of 10-13 Gyr is with photometry of a large number of stars at and below the oldest main-sequence turnoffs to magnitudes of {B,I} = {25.1, 24.5}. Because of the high stellar density and resulting image crowding, it is impossible to achieve the required level of photometric precision except with diffraction-limited imaging. These data will permit the first reliable measurement of the star-formation history of the main body of Scl dSph; limited inferences from WFPC2 data in an outer field have been made, but they were hindered not only by small number statistics but by the subsequent revelation of extremely strong population gradients in Scl dSph, such that the stars in the existing WFPC2 field are not representative of the galaxy as a whole. Our proposed program will shed strong new light on the formation processes of the smallest galaxies. Only by measuring the detailed early histories of galaxies like Scl dSph can we evaluate the impact of outside influences like ram-pressure stripping, tidal stirring, and photoionization feedback on the evolution of small galaxies.
WFPC2 10903
Resolving the LMC Microlensing Puzzle: Where are the Lensing Objects?
We are requesting 12 HST orbits to continue to investigate the nature of the population that gives rise to the microlensing seen towards the LMC. This proposal builds on the cycle 14 HST program {10583} and will complement the study with 12 yet-to-be discovered microlensing candidates from Fall 2006. Our SuperMacho project is an ongoing ground- based survey on the CTIO 4m that has demonstrated the ability to detect LMC microlensing events via frame subtraction. The combination of high angular resolution and photometric accuracy with HST will allow us to 1} confrim that the detected flux excursions arise from LMC stars, rather than background supernovae or AGN, and 2} obtain reliable baseline flux measurements for the objects in their unlensed state. This latter measurement in important in determining the microlensing optical depth towards the LMC.
FLIGHT OPERATIONS SUMMARY:
Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.)
HSTARS:
10811 – REACQ(1,2,1) failed, Search Radius Limit Exceeded on FGS 1 Upon acquisition of signal at 136/00:53:48, vehicle was in gyro control with FGS 1 search radius limit flag set. REACQ(1,2,1) at 135/23:32:53 failed with search radius limit exceeded on FGS 1. OBAD map after GSACQ failure showed RSS error of 45.81 arcseconds.
COMPLETED OPS REQUEST: (None)
COMPLETED OPS NOTES: (None)
SCHEDULED SUCCESSFUL FGS GSacq 06 06 FGS REacq 04 03 OBAD with Maneuver 20 20
SIGNIFICANT EVENTS: (None)
