HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT       #4806

PERIOD COVERED: 5am March 6 - 5am March 9, 2009 (DOY

                           065/1000z-068/1000z)

OBSERVATIONS SCHEDULED

ACS/SBC 11984

Observing Saturn's High Latitude Polar Auroras

Planetary auroral emissions are critical indicators of how the

magnetospheres of the planets work. Recently, a new component of

Saturn's auroral emissions, i.e. high latitude auroras inside the main

auroral oval, have been observed by the Cassini spacecraft during

otherwise quiet auroral conditions. Such high latitude auroras are of

immense interest since they occur on magnetic flux tubes connected to a

region that is key to the overall dynamics of the system, the

magnetotail, and where if conventional theories regarding Saturn's

magnetosphere are correct there should not be any auroras. These faint

auroral emissions have not been previously observed by the Hubble Space

Telescope (HST). However, the unique oblique viewing geometry afforded

during early 2009 due to Saturn's orbital longitude will result in the

apparent brightening of these polar emissions due to the

limb-brightening effect, with the result that they may be observable by

HST for the first ever time. In addition, at this time the Cassini

spacecraft will be in a high latitude orbit, with a trajectory that will

take it through these magnetic flux tubes, providing essential

simultaneous in situ data. This is the last time Cassini will be in such

an orbit during its mission as currently scheduled and HST is the only

instrument capable of obtaining sustained long-term observations of

Saturn's auroras. These observations will address the following:

Does Saturn exhibit high latitude UV auroras observable by HST? Where do

these auroras occur, and at what altitude? How do these auroras behave

over time? How variable are they? Are they periodic? How do they behave

with respect to other auroral components? What processes drive these

auroras?

Are these auroras generated by processes internal to the magnetosphere

or are they driven by the solar wind? How do the infrared (IR) auroras

relate to the ultraviolet (UV) auroras?

WFPC2 11983

An Imaging Survey of Protoplanetary Disks and Brown Dwarfs in the

Chamaeleon I region

We propose to carry out a HST/WFPC2 survey of young brown dwarfs, Class

I and Class II sources in the Chamaelon I region, one of the

best-studied star-forming regions, in order to investigate the link

between disk evolution and the formation of substellar-mass objects. We

will use deep broad-band imaging in the I and z-equivalent HST bands to

unveil the unknown population of substellar binary companions, down to a

few Jupiter masses for separations of a few tens of AU. We will also

perform narrow-band imaging to directly detect accreting circumstellar

disks and jets around brown dwarfs, Class-I and class-II objects.

Chamaelon I is nearly coeaval of Orion (~1-2Myr) but at ~1/3 its

distance, allowing 3x higher resolution and 10x more flux for comparable

objects. Unlike Orion, low-mass objects and protoplanetary disks in

Chamaeleon I have been extensively studied with Spitzer, but not yet

with the HST. The Chamaeleon I region is an ideal HST target, as it lies

in the CVZ of the HST and therefore it is easily accessible any time of

the year with long orbits.

ACS/SBC 11982

Spanning the Reionization History of IGM Helium: a Large and Efficient

HST Spectral Survey of Far-UV-Bright Quasars

The reionization of IGM helium is thought to have occurred at redshifts

of z=3 to 4. Detailed studies of HeII Lyman-alpha absorption toward a

handful of QSOs at 2.7<z<3.3 demonstrated the high potential of such IGM

probes, but the small sample size and redshift range limit confidence in

cosmological inferences. The requisite unobscured sightlines to high-z

are extremely rare, but we've cross-correlated 10, 000 z>2.8 SDSS DR7

(and other) quasars with GALEX GR4 UV sources to obtain 550 new, high

confidence, sightlines potentially useful for HST HeII studies; and in

cycle 15-16 trials we demonstrated the efficacy of our SDSS/GALEX

selection approach identifying 9 new HeII quasars at unprecedented 67%

efficiency. We propose the first far-UV-bright HeII quasar survey that

is both large in scale and also efficient, via 2-orbit reconnaissance

ACS/SBC prism spectra toward a highly select subset of 40 new SDSS/GALEX

quasars at 3.1<z<5.1. These will provide a community resource list that

includes 5 far-UV-bright (restframe) HeII sightlines in each of 8

redshift bins spanning 3.1<z<3.9 (and perhaps several objects at z>4),

enabling superb post-SM4 follow-up spectra with COS or STIS. But

simultaneously and independent of any SM4 uncertainties, we will hereby

directly obtain 10-orbit UV spectral stacks from the 5 HeII quasars in

each of the 8 redshift bins to trace the reionization history of IGM

helium over at least 3.1<z<3.9. These spectral stacks will average over

cosmic variance and individual object pathology. Our new high-yield HeII

sightline sample and spectral stacks, covering a large redshift range,

will allow confident conclusions about the spectrum and evolution of the

ionizing background, the evolution of HeII opacity, the density of IGM

baryons, and the epoch of helium reionization.

WFPC2 11981

FUV Imaging Survey of Galactic Open Clusters

We propose a WFPC2 FUV imaging survey of 6 Galactic open clusters with

ages ranging from 1 Myr to 300 Myr complemented with NUV/optical imaging

of the same fields. No such survey has ever been attempted before in the

FUV at the resolution of WFPC2 (indeed, no WFPC2 FUV images of any

Galactic open cluster exist in the HST archive) and, since WFPC2 will be

retired in SM4 and none of the other HST instruments can do FUV imaging

of bright objects, this is the last chance to do such a survey before

another UV telescope is launched. This survey will provide a new

perspective on young/intermediate age Galactic clusters and a key

template for the study of star formation at high redshift, where the

intensity peak we observe in the optical/NIR from Earth is located in

the FUV in its rest frame. For clusters still associated with an H II

region, UV imaging maps the continuum emission of the ionized gas and

the radiation scattered by background dust and, combined with optical

nebular images, can be used to determine the 3-D structure of the H II

region. For all young clusters, FUV+NUV+optical photometry can be used

to study the UV excesses of T-Tauri stars. For clusters older than ~40

Myr, the same photometric combination is the easiest method to detect

companion white dwarfs which are invisible using only the optical and

NIR. WFPC2 is also an excellent instrument to discover close companions

around bright stars and improve our knowledge of their multiplicity

fraction. Finally, for all clusters, the combination of

high-spatial-resolution UV and optical photometry can be used to

simultaneously measure the temperature, extinction, extinction law,

distance, and existence of companions (resolved and unresolved) and,

thus, produce clean HR diagrams with resolved cluster membership and

much-reduced systematic uncertainties.

WFPC2 11978

Luminous and Dark Matter in Disk Galaxies from Strong Lensing and

Stellar Kinematics

The formation of realistic disk galaxies within the LCDM paradigm is

still an unsolved problem. Theory is only now beginning to make

predictions for how dark matter halos respond to galaxy formation and

for the properties of disk galaxies. Measuring the density profiles of

dark matter halos on galaxy scales is therefore a strong test for the

standard paradigm of galaxy formation, offering great potential for

discovery. However, from an observational point of view, the degeneracy

between the stellar and dark matter contributions to galaxy rotation

curves remains a major road block. Strong gravitational lensing, when

coupled to spatially-resolved kinematics and stellar population models,

can solve this long-standing problem. Unfortunately, this joint

methodology could not be exploited so far due to the paucity of known

edge-on spiral lenses. Exploiting the full SDSS-DR7 archive we have

identified a new sample of exactly these systems. We propose multi-color

HST imaging to confirm and measure a sample of twenty spiral lenses,

covering a range of bulge to disk ratios. By combining dynamical lensing

and stellar population information for this unique sample we will

deliver the first statistical constraints on halos and disk properties,

and a new stringent test of disk galaxy formation theories.

WFPC2 11975

UV Light from Old Stellar Populations: a Census of UV Sources in

Galactic Globular Clusters

In spite of the fact that HST has been the only operative

high-resolution eye in the UV-window over the last 18 years, no

homogeneous UV survey of Galactic globular clusters (GGCs) has been

performed to date. In order to fill this gap in the stellar population

studies, we propose a program that exploits the unique capability of the

WFPC2 and the SBC in the far-/mid- UV for securing deep UV imaging of 46

GGCs. The proposed observations will allow to study with unprecedented

accuracy the hottest GGC stars, comprising the extreme horizontal branch

(HB) stars and their progeny (the so-called AGB-manque', and Post-early

AGB stars), and "exotic stellar populations" like the blue straggler

stars and the interacting binaries. The targets have been selected to

properly sample the GGC metallicity/structural parameter space, thus to

unveil any possible correlation between the properties of the hot

stellar populations and the cluster characteristics. In addition, most

of the targets have extended HB "blue tails", that can be properly

studied only by means of deep UV observations, expecially in the far-UV

filters like the F160BW, that is not foreseen on the WFC3. This data

base is complemented with GALEX observations in the cluster outermost

regions, thus allowing to investigate any possible trend of the

UV-bright stellar types over the entire radial extension of the

clusters. Although the hottest GGC stars are just a small class of

"special" objects, their study has a broad relevance in the context of

structure formation and chemical evolution in the early Universe,

bringing precious information on the basic star formation processes and

the origin of blue light from galaxies. Indeed, the proposed

observations will provide the community with an unprecedented data set

suitable for addressing a number of still open astrophysical questions,

ranging from the main drivers of the HB morphology and the mass loss

processes, to the origin of the UV upturn in elliptical galaxies, the

dating of distant systems from integrated light, and the complex

interplay between stellar evolution and dynamics in dense stellar

aggregates. In the spirit of constructing a community resource, we

entirely waive the proprietary period for these observations.

WFPC2 11972

Investigating the Early Solar System with Distant Comet Nuclei

We propose 85 orbits of imaging observations with the WFPC2 to get

nucleus size estimates for 8 well observed dynamically new and

long-period comets at large distances from the sun when their activity

levels are low. This will increase the sample of these nucleus sizes by

nearly 50%, but will more than double the selection of comets for which

we can run thermal models. Small icy bodies are the best preserved

remnants of planet formation, and we have recently found that

observationally constrained thermal models can distinguish differences

in microphysical properties of comet nuclei. The new HST data will

enable the first exploration of physical conditions in different regions

of the early solar nebula.

FGS 11788

The Architecture of Exoplanetary Systems

Are all planetary systems coplanar? Concordance cosmogony makes that

prediction. It is, however, a prediction of extrasolar planetary system

architecture as yet untested by direct observation for main sequence

stars other than the Sun. To provide such a test, we propose to carry

out FGS astrometric studies on four stars hosting seven companions. Our

understanding of the planet formation process will grow as we match not

only system architecture, but formed planet mass and true distance from

the primary with host star characteristics for a wide variety of host

stars and exoplanet masses.

We propose that a series of FGS astrometric observations with

demonstrated 1 millisecond of arc per-observation precision can

establish the degree of coplanarity and component true masses for four

extrasolar systems: HD 202206 (brown dwarf+planet); HD 128311

(planet+planet), HD 160691 = mu Arae (planet+planet), and HD 222404AB =

gamma Cephei (planet+star). In each case the companion is identified as

such by assuming that the minimum mass is the actual mass. For the last

target, a known stellar binary system, the companion orbit is stable

only if coplanar with the AB binary orbit.

FGS 11785

Trigonometric Calibration of the Distance Scale for Classical Novae

The distance scale for classical novae is important for understanding

the stellar physics of their thermonuclear runaways, their contribution

to Galactic nucleosynthesis, and their use as extragalactic standard

candles. Although it is known that there is a relationship between their

absolute magnitudes at maximum light and their subsequent rates of

decline--the well-known maximum-magnitude rate-of-decline (MMRD)

relation--it is difficult to set the zero-point for the MMRD because of

the very uncertain distances of Galactic novae.

We propose to measure precise trigonometric parallaxes for the quiescent

remnants of the four nearest classical novae. We will use the Fine

Guidance Sensors, which are proven to be capable of measuring parallaxes

with errors of ~0.2 mas, well below what is possible from the ground.

ACS/SBC 11579

The Difference Between Neutral- and Ionized-Gas Metal Abundances in

Local Star-Forming Galaxies with COS

The metallicity of galaxies and its evolution with redshift is of

paramount importance for understanding galaxy formation. Abundances in

the interstellar medium (ISM) are typically determined using

emission-line spectroscopy of HII regions. However, since HII regions

are associated with recent SF they may not have abundances typical for

the galaxy as a whole. This is true in particular for star-forming

galaxies (SFGs), in which the bulk of the metals may be contained in the

neutral gas. It is therefore important to directly probe the metal

abundances in the neutral gas. This can be done using absorption lines

in the Far UV. We have developed techniques to do this in SFGs, where

the absorption is measured for sightlines toward bright SF regions

within the galaxy itself. We have successfully applied this technique to

a sample of galaxies observed with FUSE. The results have been very

promising, suggesting in I Zw 18 that abundances in the neutral gas may

be up to 0.5 dex lower than in the ionized gas. However, the

interpretation of the FUSE data is complicated by the very large FUSE

aperture (30 arcsec), the modest S/N, and the limited selection of

species available in the FUSE bandpass. The advent of COS on HST now

allows a significant advance in all of these areas. We will therefore

obtain absorption line spectroscopy with G130M in the same sample for

which we already have crude constraints from FUSE. We will obtain

ACS/SBC images to select the few optimal sightlines to target in each

galaxy. The results will be interpreted through line-profile fitting to

determine the metal abundances constrained by the available lines. The

results will provide important new insights into the metallicities of

galaxies, and into outstanding problems at high redshift such as the

observed offset between the metallicities of Lyman Break Galaxies and

Damped Lyman Alpha systems.

FLIGHT OPERATIONS SUMMARY:

Significant Spacecraft Anomalies: (The following are preliminary reports

of potential non-nominal performance that will be investigated.)

HSTARS:

11709 - REAcq (1,2,2) failed due to Scan Step Limit Exceeded on FGS-1 @

           067/01:08:53z

           Observations affected: WFPC 66-70, Proposal ID# 11972

11710 - At 067/02:44:25, REAcq 1,2,2 failed due to QF1STOPF flag on

           FGS-1. The REAcq was scheduled from 067/02:41:24 - 02:48:43.

           Observations affected: WFPC 71 - 74, Proposal ID# 11972

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

                       SCHEDULED      SUCCESSFUL

FGS GSAcq               15                  15                  

FGS REAcq               25                  23    

OBAD with Maneuver 80                  80

SIGNIFICANT EVENTS: (None)