NASA Hubble Space Telescope Daily Report #4100
HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science
DAILY REPORT # 4100
PERIOD COVERED: UT April 25, 2006 (DOY 115)
OBSERVATIONS SCHEDULED
ACS/HRC 10512
Search for Binaries Among Faint Jupiter Trojan Asteroids
We propose an ambitious SNAPSHOT program to survey faint Jupiter Trojan asteroids for binary companions. We target 150 objects, with the expectation of acquiring data on about 50%. These objects span Vmag = 17.5-19.5, a range inaccessible with ground-based adaptive optics. We now have a significant sample from our survey of brighter Trojans to suggest that the binary fraction is similar to that which we find among brighter main-belt asteroids, roughly 2%. However, our observations suggest a higher binary fraction for smaller main-belt asteroids, probably the result of a different formation mechanism {evident also from the physical characteristics of the binaries}. Because the collision environment among the Trojans is similar to that of the Main Belt, while the composition is likely to be very different, sampling the binary fraction among the fainter Trojans should help us understand the collisional and binary formation mechanisms at work in various populations, including the Kuiper Belt, and help us evaluate theories for the origin of the Trojans. Calibration of and constraints on models of binary production and collisional evolution can only be done using these large-scale, real-life physical systems that we are beginning now to find and utilize.
ACS/HRC 10602
A Complete Multiplicity Survey of Galactic O2/O3/O3.5 Stars with ACS
Massive stars are preferentially formed in compact multiple systems and clusters and many of them remain spatially unresolved to date, even in our Galaxy. This has hindered the determination of the stellar upper mass limit. The lack of an accurate knowledge of the multiplicity of massive stars can also introduce biases in the calculation of the IMF at its high-mass end. We have recently used ACS/HRC to resolve HD 93129 A, the earliest O-type star known in the Galaxy, into a 55 mas binary. We propose here to extend that work into a complete multi-filter ACS imaging survey of all {20} known O2/O3/O3.5 Galactic stars to characterize the multiplicity of the most massive stars. The data will be combined with existing FGS observations to explore as large a parameter range as possible and to check for consistency. We will also derive the IMF of each system using a crowded-field photometry package and processing the data with CHORIZOS, a code that can derive stellar temperatures, extinctions, and extinction laws from multicolor photometry.
ACS/HRC/WFC 10514
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 a Snapshot program using the ACS/HRC that has a potential discovery efficiency an order of magnitude higher than the HST observations that have already discovered the majority of known transneptunian binaries. By more than doubling the number of observed objects in dynamically hot and cold subpopulations we will be able to answer, with statistical significance, the question of whether these groups differ in the abundance of binaries as a result 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.
ACS/HRC/WFC 10782
Quit winking: Jupiter opens its other eye
This week {March 6} a new red spot on Jupiter was announced, dubbed “Red Spot Jr.” by the press. It appears to be White Oval BA, the remanant of the three White Ovals that merged during 1998-2000. The new spot is deep red like the Great Red Spot {GRS} rather than bright white as were the ovals. We believe that the color change of the oval from white to red is indicative of a temperature change, as predicted by one of us in a Nature paper in 2004. The goal of our proposed observations is to test our theory of jovian climate change through observations of dynamical features of Red Spot Jr. and its surroundings, which provide indirect measurements of changes in the temperature and stratification of the jovian weather layer.
ACS/WFC 10496
Decelerating and Dustfree: Efficient Dark Energy Studies with Supernovae and Clusters
We propose a novel HST approach to obtain a dramatically more useful “dust free” Type Ia supernovae {SNe Ia} dataset than available with the previous GOODS searches. Moreover, this approach provides a strikingly more efficient search-and-follow-up that is primarily pre- scheduled. The resulting dark energy measurements do not share the major systematic uncertainty at these redshifts, that of the extinction correction with a prior. By targeting massive galaxy clusters at z > 1 we obtain a five-times higher efficiency in detection of Type Ia supernovae in ellipticals, providing a well-understood host galaxy environment. These same deep cluster images then also yield fundamental calibrations required for future weak lensing and Sunyaev-Zel’dovich measurements of dark energy, as well as an entire program of cluster studies. The data will make possible a factor of two improvement on supernova constraints on dark energy time variation, and much larger improvement in systematic uncertainty. They will provide both a cluster dataset and a SN Ia dataset that will be a longstanding scientific resource.
ACS/WFC 10505
The Onset of Star Formation in the Universe: Constraints from Nearby Isolated Dwarf Galaxies.
The details of the early star formation histories of tiny dwarf galaxies can shed light on the role in galaxy formation of the reionization which occured at high redshift. Isolated dwarfs are ideal probes since their evolution is not complicated by environmental effects owing to the vicinity of the Milky Way and M31. In addition, dwarf galaxies are the most common type of galaxies, and potentially the building blocks of larger galaxies. Since we can date the oldest stars in them, their study represents a complementary approach to the study of the formation and evolution of galaxies through high-z observations. We propose to use the ACS to obtain a homogeneus dataset of high-quality photometry, down to the old {13 Gyr} main-sequence turnoffs, for a representative sample of 4 isolated Local Group dwarf galaxies. These data are essential to unambiguously determine their early star formation histories, through comparison with synthetic color-magnitude diagrams, and using the constraints provided by their variable stars. Parallel WFPC2 observations of their halos will allow us to reveal the actual nature of their stellar population gradients, providing important aditional constraints on their evolution. The proposed observations are being complemented with ground-based spectroscopy, to obtain metallicity and kinematic information. The observations requested here, which must reach M_I=+3.5 {I=27.5- 28.2} with S/N=10 in crowded systems, can only be achieved with HST using ACS, and won’t be possible with planned ground- or space-based facilities such as JWST. Based on deep WFPC2 observations and ACS image simulations, our team has designed an observational strategy which carefully considers the optimal filter combination, the necessary photometry depth and the effects of stellar crowding.
ACS/WFC 10524
Blue Stragglers: a key stellar population to probe internal cluster dynamics
This proposal is part of a coordinated project devoted to understand the interplay of globular cluster {GC} dynamics and the formation and evolution of blue straggler stars {BSS}. By using a combination of HST and ground-based observations we are constructing complete BSS surveys in a sample of GCs; complete BSS surveys require mid-UV HST observations in the center and wide field CCD ground based observations under excellent seeing conditions of the exterior. Up to now only four clusters have been surveyed in this way and the results are surprising: in three GCs {M3, 47 Tuc, NGC 6752} we have discovered that the BSS radial distribution is bimodal, highly peaked in the cluster center, rapidly decreasing at intermediate radii and rising again at large radii {Ferraro et al. 1997, 2004, Sabbi et al. 2004}, conversely BSS population in Omega Centauri does not show any signature of the segregation which would be expected for a class of objects arising from either stellar interactions or binarity {Ferraro et al. 2005}. These observational facts are opening a new prospective in the study of the formation processes and evolution of BSS in GCs. By using extensive simulations, we demonstrated that the spatial distribution of BSS observed in 47 Tuc can be only reproduced if a sizable fraction of BSS is generated {via mass transfer in primordial binaries} in the peripheral region of the cluster {Mapelli et al 2004}, thus excluding a purely collisional formation scenario. Here we propose mid-UV imaging of a few clusters suspected of harboring a large population of central BSS and a few known to have many BSS the external region. These are good candidates for determining accurate BSS radial distributions. The modest amount of time proposed here will go far to determine the ubiquity of BSS bimodality and to constrain models of dynamical evolution. Since we believe the proposed observations would be useful to the entire stellar community {for multifold purposes} we waive the propretary period.
ACS/WFC 10587
Measuring the Mass Dependence of Early-Type Galaxy Structure
We propose two-color ACS-WFC Snapshot observations of a sample of 118 candidate early- type gravitational lens galaxies. Our lens-candidate sample is selected to yield {in combination with earlier results} an approximately uniform final distribution of 40 early-type strong lenses across a wide range of masses, with velocity dispersions {a dynamical proxy for mass} ranging from 125 to 300 km/s. The proposed program will deliver the first significant sample of low-mass gravitational lenses. All of our candidates have known lens and source redshifts from Sloan Digital Sky Survey data, and all are bright enough to permit detailed photometric and stellar- dynamical observation. We will constrain the luminous and dark-matter mass profiles of confirmed lenses using lensed-image geometry and lens-galaxy structural/photometric measurements from HST imaging in combination with dynamical measurements from spatially resolved ground-based follow-up spectroscopy. Hence we will determine, in unprecedented detail, the dependence of early-type galaxy mass structure and mass-to-light ratio upon galaxy mass. These results will allow us to directly test theoretical predictions for halo concentration and star-formation efficiency as a function of mass and for the existence of a cuspy inner dark- matter component, and will illuminate the structural explanation behind the fundamental plane of early-type galaxies. The lens-candidate selection and confirmation strategy that we propose has been proven successful for high-mass galaxies by our Cycle 13 Snapshot program {10174}. The program that we propose here will produce a complementary and unprecedented lens sample spanning a wide range of lens-galaxy masses.
ACS/WFC 10753
An Astrometric Calibration Field Near the Ecliptic Pole
This program will obtain deep ACS astrometry of a Large Magellanic Cloud star field lying within the planned continuous viewing zone of the James Webb Space Telescope, which extends to a 5 degree radius from the Ecliptic pole. To allow a full astrometric solution to be calculated, controlling for distortions within ACS that may be time variable over periods of months to years, we will observe our target field at two distinct roll angles separated by approximately 90 degrees. To help control for large scale distortions, we will “chop” the observations in at least one roll angle, using offsets of order one third the ACS field of view.
ACS/WFC/HRC 10536
What Are Stalled Preplanetary Nebulae? An ACS SNAPshot Survey
Essentially all planetary nebulae {PNs} are aspherical, whereas the mass-loss envelopes of AGB stars are strikingly spherical. Our previous SNAPshot surveys of a morphologically unbiased sample of pre-planetary nebulae {PPNs} — objects in transition between the AGB and PN evolutionary phases — show that roughly half our observed targets are resolved, with bipolar or multipolar morphologies. Spectroscopic observations of our sample confirm that these objects have not yet evolved into planetary nebulae. Thus, the transformation from spherical to aspherical geometries has already fully developed by the time these dying stars have become PPNs. Although our current studies have yielded exciting results, they are limited in two important ways — {1} the number of well-resolved objects is still small {18}, and the variety of morphologies observed relatively multitudinous, hence no clear trends can yet be established between morphology and other source properties {e.g., near-IR, far-IR colors, stellar spectral type, envelope mass}, and {2} the current samples are strongly biased towards small PPNs, as inferred from their low 60-to-25 micron flux ratios [R{60/25}<1]. However, the prototype of objects with R{60/25}>1, the Frosty Leo Nebula, has a puzzlingly large post-AGB age {almost 10^4 yr} and a fairly cool central star, very different from the expectations of single-star stellar evolutionary models. A proposed, but still speculative, hypothesis for such objects is that the slow evolution of the central star is due to backflow of material onto the mass-losing star, retarding its evolution towards the PN phase. This hypothesis has significant consequences for both stellar and nebular evolution. We therefore propose a survey of PPNs with R{60/25}>1 which is heavily weighted towards the discovery of such “stalled PPNs”. Supporting kinematic observations using long-slit optical spectroscopy {with the Keck}, millimeter and radio interferometric observations {with OVRO, VLA & VLBA} are being undertaken. The results from this survey {together with our previous work} will allow us to draw general conclusions about the complex mass-outflow processes affecting late stellar evolution, and will provide crucial input for theories of post-AGB stellar evolution. Our survey will produce an archival legacy of long-standing value for future studies of dying stars.
WFPC2 10745
WFPC2 CYCLE 14 INTERNAL MONITOR
This calibration proposal is the Cycle 14 routine internal monitor for WFPC2, to be run weekly to monitor the health of the cameras. A variety of internal exposures are obtained in order to provide a monitor of the integrity of the CCD camera electronics in both bays {both gain 7 and gain 15 — to test stability of gains and bias levels}, a test for quantum efficiency in the CCDs, and a monitor for possible buildup of contaminants on the CCD windows. These also provide raw data for generating annual super-bias reference files for the calibration pipeline.
WFPC2 10751
WFPC2 CYCLE 14 Intflat Linearity Check and Filter Rotation Anomaly Monitor
Intflat observations will be taken to provide a linearity check: the linearity test consists of a series of intflats in F555W, in each gain and each shutter. A combination of intflats, visflats, and earthflats will be used to check the repeatability of filter wheel motions. {Intflat sequences tied to decons, visits 1-18 in prop 10363, have been moved to the cycle 14 decon proposal 10744 for easier scheduling.} Note: long-exposure WFPC2 intflats must be scheduled during ACS anneals to prevent stray light from the WFPC2 lamps from contaminating long ACS external exposures.
FLIGHT OPERATIONS SUMMARY:
Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.)
HSTARS:
10241 – GSacq(1,3,1) failed@116/0823z GSacq(1,3,1)scheduled at 116/08:20:18 failed. At 08:23:30 the GSacq returned to default following FL-DV on both FGSs. OBAD2 showed errors of V1=-79.41, V2=43.13, V3=-64.30, RSS=110.91. The Map at 08:34:07 showed errors of V1=1.37, V2=15.94, V3=4.07, RSS=16.51 .
COMPLETED OPS REQUEST:
17736-1 – Adjust VTFE to K1L4-50mV @115/1755z
COMPLETED OPS NOTES:
1458-2 – Battery Temperature Limits @114/1317z
SCHEDULED SUCCESSFUL FAILURE TIMES
FGS GSacq 11 10 (HSTAR 10241)
FGS REacq 03 03
OBAD with Maneuver 28 28
SIGNIFICANT EVENTS:
VTFE Curve Adjustment Flash Report
As the battery temperatures have decreased and are now cycling below 0 DegC, EPS SEs raised the VTFE curves by 50mV to K1L4-50mV in preparation for the upcoming Battery 2 Capacity test (scheduled to commence on 05/02/06). This commanding was successfully executed via Ops Request 17736-1 on DOY 2006/115 at 17:55 GMT. The system was monitored for 2 full orbits and nominal system performance was observed. EPS SEs will continue to monitor the system.
