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4 Apr 2003

HUBBLE SPACE TELESCOPE

DAILY REPORT        # 3334

PERIOD COVERED: DOY 93

Part 2 of 3

STIS/MA2 9465

The Cosmic Carbon Budget

Gaseous carbon drives the chemistry of, and is an important coolant
in interstellar clouds. In solid form, carbon is the second most
abundant element in interstellar dust, the key element contributing
to interstellar extinction, and the dominant heat source in some
interstellar clouds. Given the fundamental importance of this element
to interstellar cloud physics, it is surprising that only 8
measurements of gas- phase carbon abundances exist for neutral
clouds; 7 are in diffuse clouds where the least amount of chemistry
and dust incorporation are expected. The single measurement in a
translucent cloud suggests a C abundance that differs from the
diffuse clouds, but the measurement uncertainties make this
difference statistically insignificant. We, therefore, have no
information about carbon's behavior in translucent clouds, regions
dense enough for chemistry and dust growth to be important but low
enough extinction so that UV spectroscopy is possible {unlike for
molecular clouds}. We propose to measure total gas-phase C abundances
in 6 translucent clouds with our principal scientific goals being to
1} accurately determine the fraction of carbon in the gas and dust
phases in environments bridging the gap between diffuse and molecular
clouds 2} determine the relative depletions of C and O in neutral
clouds with known O-depletion enhancements and 3} explore how the
interstellar gas-phase C/H is related to extinction variations.

ACS 9480

Cosmic Shear With ACS Pure Parallels

Small distortions in the shapes of background galaxies by foreground
mass provide a powerful method of directly measuring the amount and
distribution of dark matter. Several groups have recently detected
this weak lensing by large-scale structure, also called cosmic shear.
The high resolution and sensitivity of HST/ACS provide a unique
opportunity to measure cosmic shear accurately on small scales. Using
260 parallel orbits in Sloan textiti {F775W} we will measure for the
first time: beginlistosetlength sep0cm setlengthemsep0cm setlength
opsep0cm em the cosmic shear variance on scales <0.7 arcmin, em the
skewness of the shear distribution, and em the magnification effect.
endlist Our measurements will determine the amplitude of the mass
power spectrum sigma_8Omega_m^0.5, with signal-to-noise {s/n} ~ 20,
and the mass density Omega_m with s/n=4. They will be done at small
angular scales where non-linear effects dominate the power spectrum,
providing a test of the gravitational instability paradigm for
structure formation. Measurements on these scales are not possible
from the ground, because of the systematic effects induced by PSF
smearing from seeing. Having many independent lines of sight reduces
the uncertainty due to cosmic variance, making parallel observations
ideal. 

ACS/WFPC2 9481

Pure Parallel Near-UV Observations with WFPC2 within High-Latitude
ACS Survey Fields

In anticipation of the allocation of ACS high-latitude imaging
survey{s}, we request a modification of the default pure parallel
program for those WFPC2 parallels that fall within the ACS survey
field. Rather than duplicate the red bands which will be done much
better with ACS, we propose to observe in the near-ultraviolet F300W
filter. These data will enable study of the rest-frame ultraviolet
morphology of galaxies at 0 * Origin: SpaceBase(tm) Pt 1 -14.4- Van BC Canada 604-473-9358 (1:153/719.1)

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