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.