HUBBLE SPACE TELESCOPE - Continuing to Collect World Class Science

DAILY REPORT #5084

PERIOD COVERED: 5am April 27 - 5am April 28, 2010 (DOY 117/09:00z-118/09:00z)

OBSERVATIONS SCHEDULED

ACS/WFC/WFC3/UV 11578

The Extremely Metal-Poor BCD Galaxy DDO 68: a Young Galaxy in the Local

Universe ?

A long standing question in astrophysics is the existence of young

galaxies, in which stars are now forming for the first time, in the

nearby (i.e., present-day) universe. Such galaxies would be the local

analogs of primordial galaxies observed at high redshift. The most

promising candidates have long been the most metal-poor systems,

including dwarf irregulars (dIrrs) and blue compact dwarfs (BCDs).

However, in many dIrrs and BCDs studied with HST an old (1 Gyr)

underlying stellar population, as traced by red giant branch (RGB)

stars, has been unambiguously detected. Even in I Zw 18, which is the

most-metal poor prototype of the class and long the most controversial

case, our group has recently succeeded in detecting an RGB. Nonetheless,

there remains the possibility that the star formation histories of

BCDs/dIrrs vary from galaxy to galaxy, and that truly young galaxies do

exist in the local universe. A new test of these issues has only

recently become possible with the identification of DDO 68 as an

extremely metal-poor galaxy with an oxygen abundance equal to that of I

Zw 18 (12+(O/H)=7.21). This galaxy is about a factor of 2-3 closer than

I Zw 18, which yields the opportunity to avoid the many ambiguities that

have plagued studies of I Zw 18. Also, DDO 68 resides in a void, making

it more likely that star formation has been suppressed for a very long

time. We will observe DDO 68 with ACS/WFC in F606W and F814W, plus F658N

(Halpha) to correct the broad F606W for gas contamination. We will use

WFC3 in parallel with the same filters to study radial population

gradients. Deep color-magnitude diagrams (CMDs) reaching the depth of

one magnitude below the predicted RGB tip will be constructed and

interpreted based on synthetic CMD fitting. These data will determine

unambiguously whether DDO 68 has an underlying old (RGB) stellar

population or is forming stars for the first time. Finding just a single

nearby ``young'' galaxy would have profound cosmological implications.

COS/NUV/FUV/WFC3/UVIS/IR 11533

COS-GTO: Accretion Flows and Winds of Pre-Main Sequence Stars

COS will obtain spectra of T Tauri stars to study accretion flows and

wind absorption features in ultraviolet emission lines. Observations of

several T Tauri stars with different inclination angles with respect to

the line of sight will determine the temperature distributions, flow

velocities, and column densities of both inflows and outflows for these

stars.

STIS/CC 11845

CCD Dark Monitor Part 2

Monitor the darks for the STIS CCD.

STIS/CC 11847

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/CCD 11852

STIS CCD Spectroscopic Flats C17

The purpose of this proposal is to obtain pixel-to-pixel lamp flat

fields for the STIS CCD in spectroscopic mode.

STIS/CCD/FGS 11848

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 monthly for the first four months and then bi-monthly after

that.

WFC3/ACS/IR 11597

Spectroscopy of IR-Selected Galaxy Clusters at 1 < z < 1.5

We propose to obtain WFC3 G141 and G102 slitless spectroscopy of galaxy

clusters at 1 < z < 1.5 that were selected from the IRAC survey of the

Bootes NDWFS field. Our IRAC survey contains the largest sample of

spectroscopically confirmed clusters at z > 1. The WFC3 grism data will

measure H-alpha to determine SFR, and fit models to the low resolution

continua to determine stellar population histories for the brighter

cluster members, and redshifts for the red galaxies too faint for

ground-based optical spectroscopy.

WFC3/IR 11936

IR Grism Flux Calibration

This program will determine image displacement, spectral trace and flux

calibration for the IR G102 and G141 grisms as a function of spatial

position within the field of view. The HST flux standard GD71 will be

observed in a 9-point pattern in the IR field of view, which will

provide the necessary image displacement, spectral trace, and throughput

measurements.

WFC3/IR/S/C 11929

IR Dark Current Monitor

Analyses of ground test data showed that dark current signals are more

reliably removed from science data using darks taken with the same

exposure sequences as the science data, than with a single dark current

image scaled by desired exposure time. Therefore, dark current images

must be collected using all sample sequences that will be used in

science observations. These observations will be used to monitor changes

in the dark current of the WFC3-IR channel on a day-to-day basis, and to

build calibration dark current ramps for each of the sample sequences to

be used by Gos in Cycle 17. For each sample sequence/array size

combination, a median ramp will be created and delivered to the

calibration database system (CDBS).

WFC3/UV/ACS/WFC 11636

First Resolved Imaging of Escaping Lyman Continuum

The emission from star-forming galaxies appears to be responsible for

reionization of the universe at z > 6. However, the models that attempt

to describe the detailed impact of high-redshift galaxies on the

surrounding inter-galactic medium (IGM) are strongly dependent upon

several uncertain parameters. Perhaps the most uncertain is the fraction

of HI-ionizing photons produced by young stars that escape into the IGM.

Most attempts to measure this "escape fraction" have produced null

results. Recently, a small subset of z~3 Lyman Break Galaxies (LBGs) has

been found exhibiting large escape fractions. It remains unclear

however, what differentiates them from other LBGs. Several models

attempt to explain how such a large fraction of ionizing continuum can

escape through the HI and dust in the ISM (eg. "chimneys" created by SNe

winds, globular cluster formation, etc.), each producing unique

signatures which can be observed with resolved imaging of the escaping

Lyman continuum. To date, there are only six LBGs with individual

detections of escaping Lyman continuum at any redshift. We propose a

single deep, high resolution WFC3/UVIS image of the ionizing continuum

(F336W) and the rest-frame UV/optical (F606W/F814W/F160W) of five of

these six LBGs with large escape fractions. These LBGs have a high

surface density and large escape fractions, and lie at the optimal

redshift for Lyman continuum imaging with UVIS filters, making our

sample especially suitable for follow-up. With these data we will

discern the mechanisms responsible for producing large escape fractions,

and therefore gain insight into the process of reionization.

WFC3/UVIS 11594

A WFC3 Grism Survey for Lyman Limit Absorption at z=2

We propose to conduct a spectroscopic survey of Lyman limit absorbers at

redshifts 1.8 < z < 2.5, using WFC3 and the G280 grism. This proposal

intends to complete an approved Cycle 15 SNAP program (10878), which was

cut short due to the ACS failure. We have selected 64 quasars at 2.3 < z

< 2.6 from the Sloan Digital Sky Survey Spectroscopic Quasar Sample, for

which no BAL signature is found at the QSO redshift and no strong metal

absorption lines are present at z > 2.3 along the lines of sight. The

survey has three main observational goals. First, we will determine the

redshift frequency dn/dz of the LLS over the column density range 16.0 <

log(NHI) < 20.3 cm^-2. Second, we will measure the column density

frequency distribution f(N) for the partial Lyman limit systems (PLLS)

over the column density range 16.0 < log(NHI) < 17.5 cm^-2. Third, we

will identify those sightlines which could provide a measurement of the

primordial D/H ratio. By carrying out this survey, we can also help

place meaningful constraints on two key quantities of cosmological

relevance. First, we will estimate the amount of metals in the LLS using

the f(N), and ground based observations of metal line transitions.

Second, by determining f(N) of the PLLS, we can constrain the amplitude

of the ionizing UV background at z~2 to a greater precision. This survey

is ideal for a snapshot observing program, because the on-object

integration times are all well below 30 minutes, and follow-up

observations from the ground require minimal telescope time due to the

QSO sample being bright.

WFC3/UVIS 11905

WFC3 UVIS CCD Daily Monitor

The behavior of the WFC3 UVIS CCD will be monitored daily with a set of

full-frame, four-amp bias and dark frames. A smaller set of 2Kx4K

subarray biases are acquired at less frequent intervals throughout the

cycle to support subarray science observations. The internals from this

proposal, along with those from the anneal procedure (Proposal 11909),

will be used to generate the necessary superbias and superdark reference

files for the calibration pipeline (CDBS).

WFC3/UVI 11911

UVIS L-Flats and Geometric Distortion

Multiple pointing observations of the globular cluster Omega Centauri (NGC 5139) will be used to

measure the filter-dependent low frequency flat field (L-flat) corrections and stability for a key

set of 10 broadband filters used by GO programs. The selected filters are F225W, F275W, F336W,

F390W, F438W, F555W, F606W, F775W, F814W and F850LP. By measuring relative changes in brightness of

a star over different portions of the detector, we will determine local variations in the UVIS

detector response. The broad wavelength range covered by these observations will allow us to derive

the L-flat correction for the remaining wide, medium and narrow-band UVIS filters. The same data

will also be used to determin and correct the geometric distotrion that affects UVIS data. The broad

wavelength range covered by these observations will allow us to measure the geometric distortion

dependence with wavelength and filters and to provide the most appropriate correction over the

entire wavelength range provided by UVIS.

ACS/WFC 11995

CCD Daily Monitor (Part 2)

This program comprises basic tests for measuring the read noise and dark current of the ACS WFC and

for tracking the growth of hot pixels. The recorded frames are used to create bias and dark

reference images for science data reduction and calibration. This program will be executed four days

per week (Mon, Wed, Fri, Sun) for the duration of Cycle 17. To facilitate scheduling, this program

is split into three proposals. This proposal covers 320 orbits (20 weeks) from 1 February 2010 to 20

June 2010.

FLIGHT OPERATIONS SUMMARY:

Significant Spacecraft Anomalies: (The following are preliminary reports

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

HSTARS:

12255 - Following successful GSAcq(2,3,3), a Loss of Lock occurred while

           guiding with FGS-2, and FGS-3 at 188/04:27:02z. Subsequent REAcqs(2,3,3)

           were successful.

           Observations possibly affected. WFC3 47 Proposal ID#11911, ACS #85,

           Proposal ID#11995.

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

                     SCHEDULED SUCCESSFUL FAILURE TIMES

FGS GSAcq               06           06

FGS REAcq               10           10

OBAD with Maneuver 03           03

LOSS of LOCK                                       118/04:29:57z

SIGNIFICANT EVENTS: (None)