HUBBLE
SPACE TELESCOPE - Continuing to Collect World Class Science
DAILY
REPORT #5174
PERIOD
COVERED: 5am September 2 - 5am September 3, 2010 (DOY 245/09:00z-246/09:00z)
FLIGHT
OPERATIONS SUMMARY:
Significant
Spacecraft Anomalies: (The following are preliminary reports
of
potential non-nominal performance that will be investigated.)
HSTARS:
(None)
COMPLETED
OPS REQUEST: (None)
COMPLETED
OPS NOTES: (None)
SCHEDULED
SUCCESSFUL
FGS
GSAcq
8
8
FGS
REAcq
8
8
OBAD
with Maneuver 6
6
SIGNIFICANT
EVENTS: (None)
OBSERVATIONS
SCHEDULED:
ACS/WFC3
11599
Distances
of Planetary Nebulae from SNAPshots of Resolved Companions
Reliable
distances to individual planetary nebulae (PNe) in the Milky
Way
are needed to advance our understanding of their spatial
distribution,
birthrates, influence on galactic chemistry, and the
luminosities
and evolutionary states of their central stars (CSPN). Few
PNe
have good distances, however. One of the best ways to remedy this
problem
is to find resolved physical companions to the CSPN and measure
their
distances by photometric main- sequence fitting. We have
previously
used HST to identify and measure probable companions to 10
CSPN,
based on angular separations and statistical arguments only. We
now
propose to use HST to re-observe 48 PNe from that program for which
additional
companions are possibly present. We then can use the added
criterion
of common proper motion to confirm our original candidate
companions
and identify new ones in cases that could not confidently be
studied
before. We will image the region around each CSPN in the V and I
bands,
and in some cases in the B band. Field stars that appear close to
the
CSPN by chance will be revealed by their relative proper motion
during
the 13+ years since our original survey, leaving only genuine
physical
companions in our improved and enlarged sample. This study will
increase
the number of Galactic PNe with reliable distances by 50
percent
and improve the distances to PNe with previously known
companions.
STIS/CCD
11845
CCD
Dark Monitor Part 2
Monitor
the darks for the STIS CCD.
STIS/CCD
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/MA/WFC3/UV
11665
The
Formation Mechanisms of Extreme Horizontal Branch Stars
Blue
hook stars are a class of hot (~35, 000 K) subluminous extreme
horizontal
branch (EHB) stars that have been recently discovered using
HST
ultraviolet images of the massive globular clusters omega Cen and
NGC
2808. These stars occupy a region of the HR diagram that is
unexplained
by canonical stellar evolution theory. Using new theoretical
evolutionary
and atmospheric models, we have shown that the blue hook
stars
are very likely the progeny of stars that undergo extensive
internal
mixing during a late helium core flash on the white dwarf
cooling
curve. This "flash mixing" produces an enormous enhancement of
the
surface helium and carbon abundances (relative to the abundance
pattern
that existed on the main sequence), which suppresses the
observed
flux in the far-UV. Because stars born with a high helium
abundance
are more likely to evolve into hot horizontal branch stars,
flash
mixing is more likely to occur in those massive clusters capable
of
helium self-enrichment. However, a high initial helium abundance, by
itself,
is not sufficient to explain the presence of a blue hook
population
- flash mixing of the envelope is also required.
We
propose far-UV spectroscopy of normal and subluminous EHB stars in
NGC
2808 that will unambiguously test this new formation mechanism.
These
observations will easily detect the helium and carbon enhancements
predicted
by flash mixing and will therefore determine if flash mixing
represents
a new evolutionary channel for populating the hot end of the
EHB.
More generally, our observations will help to clarify the role of
helium
self-enrichment in producing blue horizontal branch morphologies
and
multiple main sequences in massive globular clusters. Finally, these
results
will provide new insight into the origin and abundance anomalies
of
the hot helium-rich subdwarf B and O stars in the Galactic field.
WFC3/ACS/IR
11563
Galaxies
at z~7-10 in the Reionization Epoch: Luminosity Functions to
<0.2L*
from Deep IR Imaging of the HUDF and HUDF05 Fields
The
first generations of galaxies were assembled around redshifts
z~7-10+,
just 500-800 Myr after recombination, in the heart of the
reionization
of the universe. We know very little about galaxies in this
period.
Despite great effort with HST and other telescopes, less than
~15
galaxies have been reliably detected so far at z>7, contrasting with
the
~1000 galaxies detected to date at z~6, just 200-400 Myr later, near
the
end of the reionization epoch. WFC3 IR can dramatically change this
situation,
enabling derivation of the galaxy luminosity function and its
shape
at z~7-8 to well below L*, measurement of the UV luminosity
density
at z~7-8 and z~8-9, and estimates of the contribution of
galaxies
to reionization at these epochs, as well as characterization of
their
properties (sizes, structure, colors). A quantitative leap in our
understanding
of early galaxies, and the timescales of their buildup,
requires
a total sample of ~100 galaxies at z~7-8 to ~29 AB mag. We can
achieve
this with 192 WFC3 IR orbits on three disjoint fields
(minimizing
cosmic variance): the HUDF and the two nearby deep fields of
the
HUDF05. Our program uses three WFC3 IR filters, and leverages over
600
orbits of existing ACS data, to identify, with low contamination, a
large
sample of over 100 objects at z~7-8, a very useful sample of ~23
at
z~8-9, and limits at z~10. By careful placement of the WFC3 IR and
parallel
ACS pointings, we also enhance the optical ACS imaging on the
HUDF
and a HUDF05 field. We stress (1) the need to go deep, which is
paramount
to define L*, the shape, and the slope alpha of the luminosity
function
(LF) at these high redshifts; and (2) the far superior
performance
of our strategy, compared with the use of strong lensing
clusters,
in detecting significant samples of faint z~7-8 galaxies to
derive
their luminosity function and UV ionizing flux. Our recent z~7.4
NICMOS
results show that wide-area IR surveys, even of GOODS-like depth,
simply
do not reach faint enough at z~7-9 to meet the LF and UV flux
objectives.
In the spirit of the HDF and the HUDF, we will waive any
proprietary
period, and will also deliver the reduced data to STScI. The
proposed
data will provide a Legacy resource of great value for a wide
range
of archival science investigations of galaxies at redshifts z~2-
9.
The data are likely to remain the deepest IR/optical images until
JWST
is launched, and will provide sources for spectroscopic follow up
by
JWST, ALMA and EVLA.
WFC3/ACS/IR
11840
Identifying
the Host Galaxies for Optically Dark Gamma-Ray Bursts
We
propose to use the high spatial resolution of Chandra to obtain
precise
positions for a sample of Gamma-Ray Bursts (GRBs) with no
optical
afterglows, where the optical light is suppressed relative to
the
X-ray flux. These bursts are likely to be highly obscured and may
have
different environments from the optically bright GRBs. Our Chandra
observations
will (unlike Swift XRT positions) allow for the unique
identification
of a host galaxy. To locate these host galaxies we will
follow
up our Chandra positions with deep optical and IR observations
with
HST. The ultimate aim is to understand any differences between the
host
galaxies of optically dark and bright GRBs, and how these affect
the
use of GRBs as tracers of starformation and galaxy evolution at high
redshift.
WFC3/ACS/UVIS
11877
HST
Cycle 17 and Post-SM4 Optical Monitor
This
program is the Cycle 17 implementation of the HST Optical
Monitoring
Program.
The
36 orbits comprising this proposal will utilize ACS (Wide Field
Channel)
and WFC3 (UVIS Channel) to observe stellar cluster members in
parallel
with multiple exposures over an orbit. Phase retrieval
performed
on the PSF in each image will be used to measure primarily
focus,
with the ability to explore apparent coma, and astigmatism
changes
in WFC3.
The
goals of this program are to: 1) monitor the overall OTA focal
length
for the purposes of maintaining focus within science tolerances
2)
gain experience with the relative effectiveness of phase retrieval on
WFC3/UVIS
PSFs 3) determine focus offset between the imagers and
identify
any SI-specific focus behavior and dependencies
If
need is determined, future visits will be modified to interleave
WFC3/IR
channel and STIS/CCD focii measurements.
WFC3/IR
11678
Resolved
H alpha star formation in two lensed galaxies at z=0.9
We
will obtain H alpha narrow-band images of two galaxies at z=0.912
that
have been gravitationally lensed by the galaxy cluster Abell 2390.
H
alpha falls squarely into the F126N filter, and both galaxies fit in a
single
WFC3 field of view. Because these two galaxies are magnified by
factors
of 6.7 (+-0.4) and 12.6 (+-0.8), WFC3 IR pixels probe spatial
scales
of 150 and 80 pc. (Without lensing, the WFC3 pixels probe 1 kpc
scales
at these redshifts.) Thus, these two galaxies provide a rare
chance
to examine, in detail and at high S/N, the spatial distribution
of
star formation in average galaxies at z=1.
After
lensing deprojection, we will study the spatial distribution of
star
formation, the star-forming disk properties and nuclear
contribution,
as well as the distribution of extinction (from the
archival
F55W to H-alpha ratio map). We will also compare integrated
extinction--corrected
H alpha to Spitzer-derived diagnostics of star
formation
rate.
WFC3/UV
12296
HST
Observations of Astrophysically Important Visual Binaries
We
propose to continue three long-term programs. All three consist of
astrometry
of close visual binaries, with the primary goal of
determining
dynamical masses for 3 important main-sequence stars and 6
white
dwarfs (WDs). A secondary aim is to set limits on third bodies in
the
systems down to planetary mass. Since all 3 programs needed to be
proposed
for Cycle 18 continuation, we are simplifying the review
process
by combining them into a single proposal. Three of our 5 targets
are
naked-eye stars with much fainter companions that are very difficult
to
image from the ground. Our other 2 targets are double WDs, whose
small
separations and faintness likewise make them difficult to measure
using
ground-based techniques.
The
bright stars, to be imaged with WFC3, are: (1) Procyon (P = 40.9
yr),
for which our first HST images yielded an accurate angular
separation
of the bright F star and its much fainter WD companion.
Combined
with ground-based astrometry of the bright star, our
observation
significantly revised downward the derived masses, and
brought
Procyon A into much better agreement with theoretical
evolutionary
masses. With the continued monitoring proposed here, we
will
obtain masses to an accuracy of better than 1%, providing a testbed
for
theories of both Sun-like stars and WDs. (2) Sirius (P = 50.1 yr),
an
A-type star also having a faint WD companion, Sirius B, the nearest
and
brightest of all WDs. (3) Mu Cas (P = 21.0 yr), a nearby
metal-deficient
G dwarf for which accurate masses will lead to the
stars'
helium contents, with cosmological implications.
The
faint double WDs, to be observed with FGS, are: (1) G 107-70 (P =
18.8
yr), and (2) WD 1818+126 (P = 12.7 yr). Our astrometry of these
systems
will add 4 accurate masses to the handful of WD masses that are
directly
known from dynamical measurements. The FGS measurements will
also
provide precise parallaxes for the systems, a necessary ingredient
in
the mass determinations.
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/UVIS
11914
UVIS
Earth Flats
This
program is an experimental path finder for Cycle 18 calibration.
Visible-wavelength
flat fields will be obtained by observing the dark
side
of the Earth during periods of full moon illumination. The
observations
will consist of full-frame streaked WFC3 UVIS imagery: per
22-
min total exposure time in a single "dark-sky" orbit, we anticipate
collecting
7000 e/pix in F606W or 4500 e/pix in F814W. To achieve
Poisson
S/N > 100 per pixel, we require at least 2 orbits of F606W and 3
orbits
of F814W.
For
UVIS narrowband filters, exposures of 1 sec typically do not
saturate
on the sunlit Earth, so we will take sunlit Earth flats for
three
of the more-commonly used narrowband filters in Cycle 17 plus the
also-popular
long-wavelength quad filters, for which we get four filters
at
once.
Why
not use the Sunlit Earth for the wideband visible-light filters? It
is
too bright in the visible for WFC3 UVIS minimum exposure time of 0.5
sec.
Similarly, for NICMOS the sunlit-Earth is too bright which
saturates
the detector too quickly and/or induces abnormal behaviors
such
as super-shading (Gilmore 1998, NIC 098-011). In the narrowband
visible
and broadband near- UV its not too bright (predictions in Cox et
al.
1987 "Standard Astronomical Sources for HST: 6. Spatially Flat
Fields."
and observations in ACS Program 10050).
Other
possibilities? Cox et al.'s Section II.D addresses many other
possible
sources for flat fields, rejecting them for a variety of
reasons.
A remaining possibility would be the totally eclipsed moon.
Such
eclipses provide approximately 2 hours (1 HST orbit) of opportunity
per
year, so they are too rare to be generically useful. An advantage of
the
moon over the Earth is that the moon subtends less than 0.25 square
degree,
whereas the Earth subtends a steradian or more, so scattered
light
and light potentially leaking around the shutter presents
additional
problems for the Earth. Also, we're unsure if HST can point
180
deg from the Sun.
WFC3/UVIS
11924
WFC3/UVIS
External and Internal CTE Monitor
CCD
detector Charge Transfer Inefficiency (CTI)-induced losses in
photometry
and astrometry will be measured using observations of the
rich
open cluster NGC6791 and with the EPER (Extended Pixel Edge
Response)
method using tungsten lamp flat field exposures. Although we
do
not expect to see CTE effects at the outset of Cycle 17, this CTE
monitoring
program is the first of a multi-cycle program to monitor and
establish
CTE-induced losses with time. We expect to measure CTE effects
with
a precision comparable to the ACS measurements.