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3\12 HST Daily Rpt No 3318
Part 1 of 3

 HUBBLE SPACE TELESCOPE
  DAILY REPORT # 3318

PERIOD COVERED: DOY 71

OBSERVATIONS SCHEDULED

NICMOS 8791

NICMOS Post-SAA calibration - CR Persistence Part 2

A new procedure proposed to alleviate the CR-persistence problem of 
NICMOS. Dark frames will be obtained immediately upon exiting the SAA 
contour 23, and every time a NICMOS exposure is scheduled within 50 
minutes of coming out of the SAA.  The darks will be obtained in 
parallel in all three NICMOS Cameras. The POST-SAA darks will be 
non-standard reference files available to users with a USEAFTER 
date/time mark. The keyword 'USEAFTER=date/time' will also be added to 
the header of each POST-SAA DARK frame. The keyword must be populated 
with the time, in addition to the date, because HST crosses the SAA ~8 
times per day so each POST-SAA DARK will need to have the appropriate 
time specified, for users to identify the ones they need. Both the raw 
and processed images will be archived as POST-SAA DARKSs. Generally we 
expect that all NICMOS science/calibration observations started within 
50 minutes of leaving an SAA will need such maps to remove the CR 
persistence from the science images. Each observation will need its 
own CRMAP, as different SAA passages leave different imprints on the 
NICMOS detectors.

GO 9172

Molecular Hydrogen in the Damped LyAlpha Absorber of Q1331+170

We wish to search for the Lyman and Werner absorption lines of 
molecular hydrogen {rest LambdaLambda = 1104 to 911 Angstrom} 
associated with the well-studied damped LyAlpha and 21-cm absorber at 
z=1.776 in Q1331+170. The rare detection of C I absorption in this 
system make this a promising candidate for a search. After detecting 
H_2, we plan to measure the relative population in the individual 
rotation states. The J = 0, 1, 2, 3 states will yield the kinetic 
temperature of the gas, while the weak J = 4 and higher states will 
measure {or limit} the local UV radiation field and hydrogen density. 
The detection of C I^* has been used to measure the cosmic microwave 
background temperature at z=1.776, and test the validity of the Big 
Bang model. The observed population of the fine structure levels of C 
I can be explained entirely by the expected CMB radiation, with 
surprisingly strong limits on local sources of excitation. The H_2 
spectrum will enable us to check this result, by allowing us to make 
an independent estimate of the rate of UV and collisional pumping of 
the C I^* levels.

ACS 9352

The Deceleration Test from Treasury Type Ia Supernovae at Redshifts 
1.2 to 1.6

Type Ia supernovae {SNe Ia} provide the only direct evidence for an 
accelerating universe, an extraordinary result that needs a rigorous 
test. The case for cosmic acceleration rests on the observation that 
SNe Ia at z ~ 0.5 are ~ 0.25 mag fainter than they would be in a 
universe without acceleration. A powerful and straightforward way to 
assess the reliability of the SN Ia measurement and the conceptual 
framework of its interpretation is to look for cosmic deceleration at 
z >= 1. This would be a clear signature of a mixed dark-matter and 
dark-energy universe. Systematic errors in the SN Ia result attributed 
to grey dust or cosmic evolution of the SN Ia peak luminosity would 
not show this change of sign. We have demonstrated proof of this 
concept with a single SN Ia, SN 1997ff at z = 1.7, found and followed 
by HST. The results suggest an early epoch of deceleration, but this 
is too important a conclusion to rest on just one object. Here we 
propose to use HST for observations of six SNe Ia in the range 1.2 <= 
z <= 1.6, that will be discovered as a byproduct from proposed 
Treasury programs for high-latitude ACS surveys. Six objects will 
provide a much firmer foundation for a conclusion that touches on 
important questions of fundamental physics.

ACS 9381

The Birth of a Dwarf Galaxy: The Star Formation History of the Tidal 
Arm near NGC 3077

The extended tidal arm of neutral gas near NGC 3077 {member of the M 
81 triplet, D~3.8 Mpc} is one of the most dramatic features of its 
kind seen in the local universe; it was created by an interaction with 
M 81 some 3*10^8 yr ago. It is one of the few tidal systems where 
atomic {HI} and molecular {CO} gas as well as low--level star 
formation {HAlpha} is detected over an area of several kpc^2.  This 
tidal complex is believed to be in the process of forming a tidal 
dwarf galaxy. Using the unique resolving capability of the Hubble 
Space Telescope {HST} and the wide--field imaging capabilities of the 
ACS, we propose to perform a stellar population study of this tidally 
created system. By combining various methods to recover the star 
formation history {e.g., using the luminosity function of the core 
Helium burning stars} we will 1} measure the SF history since closest 
encounter with M 81, 2} determine whether older stars are present in 
the tidal feature or not and 3} investigate propagation of star 
formation across the tidal feature. This can be done with F435W, 
F555W, and F814W imaging using HST's ACS with only 8 orbits. We will, 
for the first time, recover the star formation history and the 
distribution of stars within a tidally created system. This study will 
also shed light on the creation and evolution of other tidal dwarf 
galaxies which are typically much further away.

ACS 9454

The Nature of the UV Continuum in LINERs: A Variability Test

LINERs may be the most common AGNs, and the signposts of accretion 
onto the massive black holes present in most galaxies. However, the 
LINER spectrum is the result of UV excitation, and, in at least some 
LINERs, a nuclear cluster of hot stars, rather than an AGN, dominates 
the energetics in the UV. Thus, it is still unknown if the UV 
continuum, or the optical emission lines it excites, have anything to 
do with an AGN. The demographics and accretion physics of 
low-luminosity AGNs hinge on this question. We propose to search for 
variability in a sample of 17 LINERs with compact UV nuclei. 
Variability can reveal an AGN component in the UV continuum, even when 
its light is not dominant. We will test systematically the handful of 
non-definitive reports of UV variability, and potentially quantify the 
AGN contribution to the UV emission. Variability in all or most 
objects will be strong evidence that LINERs mark dormant AGNs in most 
galaxies. Alternatively, a general null detection of variability will 
suggest that, even in LINERs with additional AGN signatures, the UV 
continuum is stellar in origin. Contemporaneous monitoring with the 
VLA/VLBA of 11 objects which have radio cores {five of which we 
already know are radio-variable} will reveal the relations between UV 
and radio variations. The UV-variable objects will be targeted for 
future, better-sampled, monitoring.

(continued)

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