|
|
 |
The Daily Activity Reports are an account of the observations Hubble has
performed in a given day. Each observation is represented by an excerpt
from the scientific proposal that was submitted in order to have the obeservation
reviewed and approved, so the terminology may be somewhat technical.
Also note that although an observation may have been performed, the data
must be be processed and studied, and the finding may not be released for
another few weeks to another few years. |
|  Kuiper Belt Binaries: Probes of Early Solar System Evolution | Instrument:
ACS/HRC/WFC 10514 |
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.
|
|
| Decelerating and Dustfree: Efficient Dark Energy Studies with Supernovae
and Clusters | Instrument:
ACS/WFC 10496 |
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.
|
|
| The Star Formation Histories of Early Type Dwarf Galaxies in Low Density
Environments: Clues from the Sculptor Group | Instrument:
ACS/WFC 10503 |
We seek HST ACS/WFC time to conduct a detailed study of the stellar
populations of 5 early-type {dE, dE/dIrr} dwarf galaxies in the nearby
{~1.5 to 4 Mpc} Sculptor group. Four of these systems have been recently
found to contain modest amounts of HI, and existing ground-based and HST
snapshot data point to the potential presence of small populations of
young {blue} stars in at least three of these systems. Consequently,
they resemble the Local Group 'transition' objects Phoenix and LGS3. The
relative number of such transition systems is thus substantially larger
in the low density environment of the Scl group than for the Local
Group. Detailed stellar populations studies will allow estimation of the
star formation histories, via stellar population modelling of the
color-magnitude diagrams, of the target dwarfs, which in turn will
connect to gas consumption and retention rates. For the two nearer
dwarfs we aim to reach below the horizontal branch {a first for any
system beyond the Local Group} equivalent to a main sequence turnoff age
of ~1 Gyr. The observations of these two systems will also allow
detection of RR Lyrae variables and thus direct confirmation of the
presence of old populations. For the other three dwarfs will we cover
the first 2.5 mags of the red giant branch, equivalent to the main
sequence termination for a ~300 Myr population. The results will have
implications for theories of galaxy formation and evolution,
particularly with regard to the evolutionary relation between low
luminosity dEs and dwarf irregulars.
|
|
| An ACS Survey of a Complete Sample of Luminous Infrared Galaxies in the
Local Universe | Instrument:
ACS/WFC 10592 |
At luminosities above 10^11.4 L_sun, the space density of far-infrared
selected galaxies exceeds that of optically selected galaxies. These
`luminous infrared galaxies' {LIRGs} are primarily interacting or
merging disk galaxies undergoing enhanced star formation and Active
Galactic Nuclei {AGN} activity, possibly triggered as the objects
transform into massive S0 and elliptical merger remnants. We propose
ACS/WFC imaging of a complete sample of 88 L_IR > 10^11.4 L_sun luminous
infrared galaxies in the IRAS Revised Bright Galaxy Sample {RBGS: i.e.,
60 micron flux density > 5.24 Jy}. This sample is ideal not only in its
completeness and sample size, but also in the proximity and brightness
of the galaxies. The superb sensitivity, resolution, and field of view
of ACS/WFC on HST enables a unique opportunity to study the detailed
structure of galaxies that sample all stages of the merger process.
Imaging will be done with the F439W and F814W filters {B and I-band} to
examine as a function of both luminosity and merger state {i} the
evidence at optical wavelengths of star formation and AGN activity and
the manner in which instabilities {bars and bridges} in the galaxies may
funnel material to these active regions, {ii} the relationship between
star formation and AGN activity, and {iii} the structural properties
{AGN, bulge, and disk components} and fundamental parameters {effective
radius and surface brightness} of LIRGs and their similarity with
putative evolutionary byproducts {elliptical, S0 and classical AGN host
galaxies}. This HST survey will also bridge the wavelength gap between a
Spitzer imaging survey {covering seven bands in the 3.6-160 micron
range} and a GALEX UV imaging survey of these galaxies, but will resolve
complexes of star clusters and multiple nuclei at resolutions well
beyond the capabilities of either Spitzer or GALEX. The combined
datasets will result in the most comprehensive multiwavelength study of
interacting and merging galaxies to date.
|
|
| What Are Stalled Preplanetary Nebulae? An ACS SNAPshot Survey | Instrument:
ACS/WFC/HRC 10536 |
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.
|
|
|
