NASA Hubble Space Telescope Daily Status Report #4392

Notice: For the foreseeable future, the daily reports may contain apparent discrepancies between some proposal descriptions and the listed instrument usage. This is due to the conversion of previously approved ACS WFC or HRC observations into WFPC2, or NICMOS observations subsequent to the loss of ACS CCD science capability in late January.

HUBBLE SPACE TELESCOPE DAILY REPORT # 4392

– Continuing to collect World Class Science

PERIOD COVERED: UT June 26, 2007 (DOY 177)

OBSERVATIONS SCHEDULED

WFPC2 10800

Kuiper Belt Binaries: Probes of Early Solar System Evolution

Binaries in the Kuiper Belt are a scientific windfall: in them we have relatively fragile test particles which can be used as tracers of the early dynamical evolution of the outer Solar System. We propose to continue a Snapshot program using the ACS/HRC that has a demonstrated discovery potential an order of magnitude higher than the HST observations that have already discovered the majority of known transneptunian binaries. With this continuation we seek to reach the original goals of this project: to accumulate a sufficiently large sample in each of the distinct populations collected in the Kuiper Belt to be able to measure, with statistical significance, how the fraction of binaries varies as a function of their particular dynamical paths into the Kuiper Belt. Today’s Kuiper Belt bears the imprints of the final stages of giant-planet building and migration; binaries may offer some of the best preserved evidence of that long-ago era.

ACS/SBC 10872

Lyman Continuum Emission in Galaxies at z=1.2

Lyman continuum photons produced in massive starbursts may have played a dominant role in the reionization of the Universe. Starbursts are important contributors to the ionizing metagalactic background at lower redshifts as well. However, their contribution to the background depends upon the fraction of ionizing radiation that escapes from the intrinsic opacity of galaxies below the Lyman limit. Current surveys suggest escape fractions of a few percent, up to 10%, with very few detections {as opposed to upper limits} having been reported. No detections have been reported in the epochs between z=0.1 and z=2. We propose to measure the fraction of escaping Lyman continuum radiation from 15 luminous z~1.2 galaxies in the GOODS fields. Using the tremendous sensitivity of the ACS Solar- blind Channel, we will reach AB=30 mag., allowing us to detect an escape fraction of 1%. We will correlate the amount of escaping radiation with the photometric and morphological properties of the galaxies. A non-detection in all sources would imply that QSOs provide the overwhelming majority of ionizing radiation at z=1.3, and it would strongly indicate that the properties of galaxies at higher redshift have to be significantly different for galaxies to dominate reionization. The deep FUV images will also be useful for extending the FUV study of other galaxies in the GOODS fields.

NIC1/NIC2/NIC3 8794

NICMOS Post-SAA calibration – CR Persistence Part 5

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.

NIC2 10893

Sweeping Away the Dust: Reliable Dark Energy with an Infrared Hubble Diagram

We propose building a high-z Hubble Diagram using type Ia supernovae observed in the infrared rest-frame J-band. The infrared has a number of exceptional properties. The effect of dust extinction is minimal, reducing a major systematic tha may be biasing dark energy measurements. Also, recent work indicates that type Ia supernovae are true standard candles in the infrared meaning that our Hubble diagram will be resistant to possible evolution in the Phillips relation over cosmic time. High signal-to-noise measurements of 9 type Ia events at z~0.4 will be compared with an independent optical Hubble diagram from the ESSENCE project to test for a shift in the derived dark energy equation of state due to a systematic bias. Because of the bright sky background, H-band photometry of z~0.4 supernovae is not feasible from the ground. Only the superb image quality and dark infrared sky seen by HST makes this test possible. This experiment may also lead to a better, more reliable way of mapping the expansion history of the universe with the Joint Dark Energy Mission.

WFPC2 10834

The Shell of the Recurrent Nova T Pyx

T Pyx is the only known recurrent nova with a shell. This ‘shell’ is mysterious because it has been resolved into thousands of knots that apparently aren’t expanding. We propose to take a deep F658N image of T Pyx during one orbit to serve as a 12 year baseline from the previous HST WFPC2 images in 1994 and 1995. This much longer baseline will allow us to push down the limits on expansion velocities to ~10 km/s and will allow us to measure the lifetimes of the knots. Also, we expect to discover the expanding inner shell from the last eruption in 1966 which should now have expanded to ~0.9″ in radius. Detailed modeling of the observed line fluxes will give the mass of the individual knots and the shells. The details of the expansion velocities, lifetimes, and masses of the knots will determine the nature of the T Pyx shell; with alternatives being a nova shell, a planetary nebula, stalled shocks in a pre-existing shell, or a cloud ionized by the high luminosity and temperature of the white dwarf. If we can separate out the mass ejected during the 1966 eruption, then we can compare it to the total mass accreted between the 1944 and 1966 eruptions {6.0×10^-6 solar mass} so as to determine whether the white dwarf is gaining or losing mass on average. If the white dwarf is gaining mass, then it must inevitably exceed the Chandrasekhar mass and collapse as a Type Ia supernova, and thus recurrent novae would be shown to be an important component of the solution to the Type Ia progenitor problem.

WFPC2 11112

The Collisional Ring Galaxy NGC922

We request WFPC2 images of the newly recognized collisional ring galaxy NGC922 which will become the nearest such system observed by HST. These will be used to get a clear understanding of the geometry of the interaction and the induced star formation in this system. Quantitive modeling of the colors of the star clusters and stellar populations will be used to constrain the star formation history of the system. They will also be used to test the “infant mortality” scenario for star cluster evolution. The derived population ages will test predictions of how star formation evolves in the various components {ring, core, spokes} of collisional rings, and will improve our own simulations of this system. These will be used to determine the final fate of the stars formed in the present burst – some will end up in a central bar or bulge while others will become part of a thickened disk. By analogy this will tell us how similar collisions enrich stellar populations in the early universe. This is especially relevant since the number density of collisional rings increases rapidly with redshift.

WFPC2 11140

Can mass-ejections from late He-shell flash stars constrain convective/reactive flow modeling of stellar interiors?

The existence of H-deficient knots around the central stars of the planetary nebulae Abell 30 and Abell 78 is still unexplained. We hypothesize that these knots were ejected during a very late helium-shell flash {= very late thermal pulse, VLTP} suffered by the precursor white dwarf stars. If this is true, then the characteristics of these knots {mass, velocity, density, spatial distribution} allow to draw conclusions on the course of the hydrogen- ingestion flash detonation that is triggered by the He-shell flash. This provides important, otherwise inaccessible constraints for the hydrodynamical modeling of convective/reactive flows in stellar interiors. Understanding the physics of these flows is not only important for the understanding of these particular central stars, but also for the frequent, very similar convective/reactive events that determine the nucleosynthesis in Pop. III stars. With this proposal we want to proof or discard the idea that the H-deficient knots are resulting from a VLTP. If true, then they can be exploited for flash-physics diagnostics. We propose a simple test. We search for such knots around five H-deficient central stars {PG1159 stars}. Our models predict, that only those stars with residual nitrogen in the atmosphere have suffered a VLTP and, hence, should have expelled knots. We therefore want to take [O III] images of stars which have photospheric N and those which do not.

FLIGHT OPERATIONS SUMMARY:

Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.)

HSTARS:

10871 – OBAD Failed Identification

OBAD2 scheduled at 177/09:42:35 failed. Status Buffer message 1902 “OBAD Failed Identification” was received. GSacq was successful. OBAD1 RSS error was 10957.43 arcseconds

COMPLETED OPS REQUEST:

18111-0 – Modify Magnitude Threshold Values in SOB Macros

COMPLETED OPS NOTES: (None)

                       SCHEDULED      SUCCESSFUL 
FGS GSacq               04                 04 
FGS REacq               09                 09 
OBAD with Maneuver      24                 23 

SIGNIFICANT EVENTS:

Flash Report: FHST Stuck-on-Bottom (SOB) Macro Visual-Magnitude Threshold Modification: Operations Request 18111-0 to modify the magnitude threshold values in the SOB macros to a magnitude value of 3 was completed at 177/14:39:24.