NASA Hubble Space Telescope Daily Report #4347

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 # 4347

– Continuing to collect World Class Science

PERIOD COVERED: UT April 23, 2007 (DOY 113)

OBSERVATIONS SCHEDULED

WFPC2 10798

Dark Halos and Substructure from Arcs & Einstein Rings

The surface brightness distribution of extended gravitationally lensed arcs and Einstein rings contains super-resolved information about the lensed object, and, more excitingly, about the smooth and clumpy mass distribution of the lens galaxies. The source and lens information can non-parametrically be separated, resulting in a direct “gravitational image” of the inner mass-distribution of cosmologically-distant galaxies {Koopmans 2005; Koopmans et al. 2006 [astro-ph/0601628]}. With this goal in mind, we propose deep HST ACS-F555W/F814W and NICMOS-F160W WFC imaging of 20 new gravitational-lens systems with spatially resolved lensed sources, of the 35 new lens systems discovered by the Sloan Lens ACS Survey {Bolton et al. 2005} so far, 15 of which are being imaged in Cycle-14. Each system has been selected from the SDSS and confirmed in two time- efficient HST-ACS snapshot programs {cycle 13&14}. High-fidelity multi-color HST images are required {not delivered by the 420s snapshots} to isolate these lensed images {properly cleaned, dithered and extinction-corrected} from the lens galaxy surface brightness distribution, and apply our “gravitational maging” technique. Our sample of 35 early-type lens galaxies to date is by far the largest, still growing, and most uniformly selected. This minimizes selection biases and small-number statistics, compared to smaller, often serendipitously discovered, samples. Moreover, using the WFC provides information on the field around the lens, higher S/N and a better understood PSF, compared with the HRC, and one retains high spatial resolution through drizzling. The sample of galaxy mass distributions – determined through this method from the arcs and Einstein ring HST images – will be studied to: {i} measure the smooth mass distribution of the lens galaxies {dark and luminous mass are separated using the HST images and the stellar M/L values derived from a joint stellar-dynamical analysis of each system}; {ii} quantify statistically and individually the incidence of mass-substructure {with or without obvious luminous counter- parts such as dwarf galaxies}. Since dark-matter substructure could be more prevalent at higher redshift, both results provide a direct test of this prediction of the CDM hierarchical structure-formation model.

ACS/SBC 10815

The Blue Hook Populations of Massive Globular Clusters

Blue hook stars are a class of hot {~35,000 K} subluminous horizontal branch stars that have been recently discovered using HST ultraviolet images of the 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, which suppresses the flux in the far ultraviolet. Although flash mixing is more likely to occur in stars that are born with high helium abundances, a high helium abundance, by itself, does not explain the presence of a blue hook population – flash mixing of the envelope is required. We propose ACS ultraviolet {SBC/F150LP} observations of the five additional globular clusters for which the presence of blue hook stars is suspected from longer wavelength observations. Like omega Cen and NGC 2808, these five targets are also among the most massive globular clusters, because less massive clusters show no evidence for blue hook stars. Because our targets span 1.5 dex in metallicity, we will be able to test our prediction that flash-mixing should be less drastic in metal-rich blue hook stars. In addition, our observations will test the hypothesis that blue hook stars only form in globular clusters massive enough to retain the helium-enriched ejecta from the first stellar generation. If this hypothesis is correct, then our observations will yield important constraints on the chemical evolution and early formation history in globular clusters, as well as the role of helium self-enrichment in producing blue horizontal

branch morphologies and multiple main sequence turnoffs. Finally, our observations will provide new insight into the formation of the hottest horizontal branch stars, with implications for the origin of the hot helium-rich subdwarfs in the Galactic field.

WFPC2 11024

WFPC2 CYCLE 15 INTERNAL MONITOR

This calibration proposal is the Cycle 15 routine internal monitor for WFPC2, to be run weekly to monitor the health of the cameras. A variety of internal exposures are obtained in order to provide a monitor of the integrity of the CCD camera electronics in both bays {both gain 7 and gain 15 — to test stability of gains and bias levels}, a test for quantum efficiency in the CCDs, and a monitor for possible buildup of contaminants on the CCD windows. These also provide raw data for generating annual super-bias reference files for the calibration pipeline.

FGS 11019

Monitoring FGS1r’s Interferometric Response as a Function of Spectral Color

This proosal uses FGS1r in Transfer mode to observe standard single stars of a variety of spectral types to obtain point source interferograms for the Transfer mode calibration library. In specific cases, the calibration star will also be observed in POS mode multiple times with the F583W and F5ND elements to provide the data to verify the stabiligy of the cross filter calibration.

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=3Ddate/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.

WFPC2 10884

The Dynamical Structure of Ellipticals in the Coma and Abell 262 Clusters

We propose to obtain images of 13 relatively luminous early type galaxies in the Coma cluster and Abell 262 for which we have already collected ground based major and minor axis spectra and images. The higher resolution HST images will enable us to study the central regions of these galaxies which is crucial to our dynamical modelling. The complete data set will allow us to perform a full dynamical analysis and to derive the dark matter content and distribution, the stellar orbital structure, and the stellar population properties of these objects, probing the predictions of galaxy formation models. The dynamical analysis will be performed using an up-to-date axi-symmetric orbit superposition code.

WFPC2 11023

WFPC2 CYCLE 15 Standard Darks – part 1

This dark calibration program obtains dark frames every week in order to provide data for the ongoing calibration of the CCD dark current rate, and to monitor and characterize the evolution of hot pixels. Over an extended period these data will also provide a monitor of radiation damage to the CCDs.

WFPC2 11032

CTE Extended Targets Closeout

Measuring the charge transfer efficiency {CTE} of an astronomical CCD camera is crucial to determining the CCD’s photometric fidelity across the field of view. WFPC2’s CTE has degraded steadily over the last 13 years because of continuous exposure to trapped particles in HST’s radiation environment. The fraction of photometric signal lost from WFPC2’s CTI {change transfer inefficiency} is a function of WFPC2’s time in orbit, the integrated signal in the image, the location of the image on the CCD, and the background signal. Routine monitoring of WFPC2’s degrading CTE over the last 13 years has primarily concerned the effects of CTI on point-source photometry. However, most of the sources imaged by WFPC2 are extended rather than point-like. This program aims to characterize the effects of CTI on the photometry and morphology of extended sources near the end of WFPC2’s functional life. Images of a standard field within the rich galaxy cluster Abell 1689 are recorded with each WFPC2 camera using the F606W and F814W filters. These images will be compared with contemporaneous images of Abell 1689 recorded with the field rotated by approximately 180 degrees to assess differences between extended sources imaged near and far from the serial register. The images will also be compared with similar images recorded in Cycle 8 {Program 8456} to characterize the rate of CTE degradation over the lifetime of WFPC2.

WFPC2 11083

The Structure, Formation and Evolution of Galactic Cores and Nuclei

A surprising result has emerged from the ACS Virgo Cluster Survey {ACSVCS}, a program to obtain ACS/WFC gz imaging for a large, unbiased sample of 100 early-type galaxies in the Virgo Cluster. On subarcsecond scales {i.e., <0.1"-1"}, the HST brightness profiles vary systematically from the brightest giants {which have nearly constant surface brightness cores} to the faintest dwarfs {which have compact stellar nuclei}. Remarkably, the fraction of galaxy mass contributed by the nuclei in the faint galaxies is identical to that contributed by supermassive black holes in the bright galaxies {0.2%}. These findings strongly suggest that a single mechanism is responsible for both types of Central Massive Object: most likely internally or externally modulated gas inflows that feed central black holes or lead to the formation of "nuclear star clusters". Understanding the history of gas accretion, star formation and chemical enrichment on subarcsecond scales has thus emerged as the single most pressing question in the study of nearby galactic nuclei, either active or quiescent. We propose an ambitious HST program {199 orbits} that constitutes the next, obvious step forward: high-resolution, ultraviolet {WFPC2/F255W} and infrared {NIC1/F160W} imaging for the complete ACSVCS sample. By capitalizing on HST's unique ability to provide high-resolution images with a sharp and stable PSF at UV and IR wavelengths, we will leverage the existing optical HST data to obtain the most complete picture currently possible for the history of star formation and chemical enrichment on these small scales. Equally important, this program will lead to a significant improvement in the measured structural parameters and density distributions for the stellar nuclei and the underlying galaxies, and provide a sensitive measure of "frosting" by young stars in the galaxy cores. By virtue of its superb image quality and stable PSF, NICMOS is the sole instrument capable of the IR observations proposed here. In the case of the WFPC2 observations, high-resolution UV imaging {< 0.1"} is a capability unique to HST, yet one that could be lost at any any time.

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               11                  11          

FGS REacq               04                  04               

OBAD with Maneuver      25                  25

SIGNIFICANT EVENTS:

Evaluation of Universal Kalman Filter performance continued. Multiple
text

segments were executed, all of them successfully. Details follow.

The Kalman Filter was restarted at 113/13:17 (OR 18046-0) during orbit day and during an M2G guiding interval. The filter was activated with the MSS, CSS and Gyro-1 sensor inputs enabled. All UKF parameters showed nominal convergence and steady-state operation. The test was an MSS/CSS/Gyro-1 Initialization Test Case with the spacecraft inertially fixed during a fast changing B-field in orbit day (MC_G1_INF, Test #17). The KF was halted at 14:10 and reconfigured back to the default MSS/CSS configuration.

The Gyro-1 sensor input was added to the KF at 113/15:00 (OR 18047-0) during orbit day and during a T2G guiding interval. The filter was running with the MSS and CSS sensor inputs enabled and converged. All UKF parameters showed nominal operation. The test was an MSS/CSS Test Case with the Gyro-1 sensor input added to an already converged filter. The spacecraft was inertially fixed during a fast changing B-field in orbit day (MC_G1_RNF, Test #29). The Gyro-1 input was removed at 16:10 during an F2G period in orbit day to reconfigure the KF back to default MSS/CSS configuration.

The Kalman Filter was restarted at 113/18:44 (OR 18045-0) just prior to orbit night entry (approx. 1 minute) and during an F2G guiding interval and with the spacecraft inertially fixed (M_C_INP, Test #10). The filter was activated with the default configuration of MSS and CSS sensor inputs enabled. The test was executed to monitor the initial nominal convergence of the filter as it crossed the EON penumbra. The filter began to converge initially, paused and two minutes after EON it continued toward convergence. All UKF parameters showed nominal steady-state operation.

The Kalman Filter was restarted at 113/20:01 (OR 18046-0) during orbit day and during an M2G guiding interval. The filter was activated with the MSS, CSS and Gyro-1 sensor inputs enabled. All UKF parameters showed nominal convergence and steady-state operation. The test was an MSS/CSS/Gyro-1 Initialization Test Case with the spacecraft inertially fixed during a slow changing B-field in orbit day (M_G1_INS, Test #18). The KF was halted at 20:35 and reconfigured back to the default MSS/CSS configuration.

The Gyro-1 sensor input was added to the KF at 113/21:46 (OR 18047-0) during orbit day and during a M2G guiding interval. The filter was running with the MSS and CSS sensor inputs enabled and converged. All UKF parameters showed nominal operation. The test was an MSS/CSS Test Case with the Gyro-1 sensor input added to an already converged filter. The spacecraft was inertially fixed during a slow changing B-field in orbit day (M_G1_RNS, Test #30). The KF was halted at 23:20 and reconfigured back to the default MSS/CSS configuration.

The Kalman Filter was restarted at 113/23:34 (OR 18045-0) during orbit night and during an T2G guiding interval. The filter was activated with the MSS and CSS sensor inputs enabled. The KF was restarted as the OBAD-1 correction maneuver was occurring and all the UKF parameters showed nominal convergence and steady-state operation. The test was an MSS/CSS Initialization Test Case with the spacecraft inertially fixed during a slow changing B-field in orbit night (M_0_INS, Test #4). The test may be re-executed as the intent was to execute with the spacecraft inertially fixed.

The Gyro-1 sensor input was added to the KF at 113/23:55 (OR 18048-2) during orbit night and during an F2G guiding interval. The filter was running with the MSS and CSS sensor inputs enabled and converged. The Gyro-1 sensor input was later removed at 114/01:18 to monitor the response of the filter when the gyro input is removed during orbit night with a slow changing B-field and no vehicle maneuver occurring (M_G1_HNS, Test #26). All UKF parameters showed nominal operation.

The test above completed testing for the day and left the KF configured in the default MSS/CSS mode