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29 April 2003

HUBBLE SPACE TELESCOPE

DAILY REPORT        # 3351

PERIOD COVERED: DOY 118

Part 2 of 3

ACS/STIS 9451

ACS Imaging and STIS Spectroscopy of Binary Brown Dwarfs

We have compiled a sample of 9 spatially resolved binary brown dwarfs
{18 objects}, and now propose ACS imaging and STIS spectroscopic
follow-up observations. While theoretical models on the interplay of
chemical and physical processes governing brown dwarf atmospheres
have reached a high level of sophistication, interpretation of
observational data remains difficult. As brown dwarfs never stabilize
themselves on the hydrogen main sequence, there is always an
ambiguity between the temperature or luminosity of any brown dwarf
and its mass or age. The individual components of brown dwarf
binaries, however, are expected to be coeval and have the same
underlying chemical composition. This provides crucial constraints on
any model, thus greatly reducing the number of the free parameters.
The aim is to obtain photometric and spectroscopic data to probe the
physical and chemical properties of the brown dwarf atmospheres, as
well as second epoch astrometric data to characterize th e orbital
motion. The study will provide important feedback on theoretical
model atmospheres and evolutionary tracks for brown dwarfs. As such,
it will be an important step towards a better understanding of
objects with spectral properties intermediate between those of giant
planets and late-type stars. 

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 9482

ACS Pure Parallel Lyman-Alpha Emission Survey {APPLES}

Ly-alpha line emission is an efficient tool for identifying young
galaxies at high redshift, because it is strong in galaxies with
young stars and little or no dust --- properties expected in galaxies
undergoing their first burst of star- formation. Slitless
spectroscopy with the ACS Wide-Field Camera and G800L grism allows an
unmatched search efficiency for such objects over the uninterrupted
range 4 <~ z <~ 7. We propose the ACS Pure Parallel Ly-alpha Emission
Survey {``APPLES''}, to exploit this unique HST capability and so
obtain the largest and most uniform sample of high redshift Ly-alpha
emitters yet. Parallel observations will allow this survey to be
conducted with minimal impact on HST resources, and we will place
reduced images and extracted spectra in the public domain within
three months of observation. We aim to find ~ 1000 Ly-alpha emitters,
5 times the biggest current sample of Ly-alpha emitters. This
unprecedented sample will provide robust statistics on the
populations and evolution of Ly-alpha emitters between redshifts
4--7; a robust measurement of the reionization redshift completely
independent of the Gunn-Peterson trough; spatial clustering
information for Ly-alpha emitters which would let us probe their bias
function and hence halo mass as a function of redshift; many galaxies
at redshift exceeding 6; and lower redshift serendipitous
discoveries.

WFPC2 9589

WFPC2 Decontaminations and Associated Observations Pt. 1/3

photometric stability check, focus monitor, pre- and post-decon
internals {bias, intflats, kspots, & darks}, UV throughput check,
VISFLAT sweep, and internal UV flat check.

WFPC2 9594

WFPC2 CYCLE 11 SUPPLEMENTAL DARKS pt2/3

This dark calibration program obtains 3 dark frames every day to
provide data for monitoring and characterizing the evolution of hot
pixels 

STIS 9604

STIS CCD Performance Monitor

This activity measures the baseline performance and commandability of
the CCD subsystem. Only primary amplifier D is used. Bias and Flat
Field exposures are taken in order to measure bias level, read noise,
CTE, and gain. Numerous bias frames are taken to permit construction
of "superbias" frames in which the effects of read noise have been
rendered negligible. Full frame and binned observations are made,
with binning factors of 2 x 1, 1 x 2, 2 x 2, 4 x 1, and 4  x 2. Dark
images are taken in 2x2 binning mode; 1x1 binning darks are being
taken in the nominal CCD Dark Monitor. Bias frames are taken in
subarray readouts to check the bias level for ACQ and ACQ/PEAK
observations. All exposures are internals.

STIS 9606

CCD Dark Monitor-Part 2

Monitor the darks for the STIS CCD.

STIS 9608

CCD Bias Monitor - Part 2

Monitor the bias in the 1x1, 1x2, 2x1, and 2x2 bin settings at
gain=1, and 1x1 at gain = 4, to build up high-S/N superbiases and
track the evolution of hot columns.

STIS/CAL 9609

CCD Read Noise Monitor

This proposal measures the read noise of all the amplifiers {A, B, C,
D} on the STIS CCD using pairs of bias frames. Full frame and binned
observations are made in both Gain 1 and Gain 4, with binning factors
of 1x1, 1x2, 2x1 and 2x2. All exposures are internals. Pairs of
visits are scheduled for monthly execution. 

 - Continued -

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