Status Report

NASA Hubble Space Telescope Daily Report #4408

By SpaceRef Editor
July 23, 2007
Filed under , ,
NASA Hubble Space Telescope Daily Report #4408

Notice: Due to the conversion of some ACS WFC or HRC observations into WFPC2, or NICMOS observations after the loss of ACS CCD science capability in January, there may be an occasional discrepancy between a proposal’s listed (and correct) instrument usage and the abstract that follows it.


– Continuing to collect World Class Science

PERIOD COVERED: UT July 19, 2007 (DOY 200)


ACS/SBC 10907

New Sightlines for the Study of Intergalactic Helium: A Dozen High-Confidence, UV-Bright Quasars from SDSS/GALEX

The reionization of intergalactic helium is thought to have occurred between redshifts of about 3 and 4. Detailed study of HeII Lyman-alpha absorption toward a handful quasars at 2.73.1 quasars potentially suitable for HeII studies. We have cross-correlated SDSS quasars with GALEX UV sources to obtain a dozen new, very high-confidence, candidate quasars/sightlines {z=3.1 to 4.1} potentially useful for detailed HeII studies even with current HST instruments. We propose brief, 2-orbit per target, reconnaissance spectral exposures with the ACS SBC prism to definitively verify UV flux down to the HeII break. Our combined SDSS/GALEX selection insures a very high- yield of confirmations, as the quasars are already known to be UV-bright from broadband GALEX images. The additional sightlines, extending to very high-redshift, will directly enable ensemble spectral stacks, as well as long exposure follow-up spectra, at high S/N with the ACS/SBC ultraviolet prisms {or perhaps STIS or COS later}, to confidently measure the spectrum and evolution of the ionizing background radiation, the evolution of HeII opacity, and the density of intergalactic baryons.


Star formation in extended UV disk {XUV-disk} galaxies

The Galaxy Evolution Explorer {GALEX} has discovered the existence of extended UV-disk {XUV-disk} galaxies. This class of intriguing spiral galaxies is distinguished by UV-bright regions of star formation located at extreme galactocentric radii, commonly reaching many times the optical extent of each target. XUV-disks represent a population of late-type galaxies still actively building, or significantly augmenting, their stellar disk in the outer, low-density environment. Prior to GALEX, such regions were considered to be far more stable against star formation than now realized. Our work on these targets has led to the recognition of the XUV phenomenon as probing a diverse population of galaxies which, although having certain commonality in terms of their present XUV star formation, have apparently experienced different star formation histories {as judged by their outer disk UV-optical colors and morphology}. In ordinary spirals, disk formation occurred at a much earlier epoch, making today’s XUV-disks useful templates for commonplace, high z galaxies. The diverse XUV-disks in our sample may represent snapshots of different phases in the disk building process. We seek to characterize the demographics of star forming regions occupying this environmental range, especially in contrast to their inner disk counterparts. HST imaging is needed to accurately characterize the massive stars and clusters which have, in fact, managed to form. The GALEX observations are limited by 5″ resolution. Deep ACS FUV, B, V, I, and H-alpha imaging {along with parallel WFPC2 data} will allow: {1} photometric classification of the OB star population, {2} constraint on the cluster mass function and age distribution, {3} critical accounting for possible leakage of Lyman continuum photons in a porous ISM or an IMF change, and {4} population synthesis modeling of the field SFH on Gyr timescales. We benefit from extensive archival HST observations of our target galaxies, although the outer disk has yet to be probed.

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 that 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 10818

Very Young Globular Clusters in M31 ?

We propose to use HST’s unique high spatial resolution imaging capabilities to conclusively confirm or refute the presence of alleged very young globular clusters in M31. Such young globular clusters with ages < 3 Gyr are not present in our galaxy, and, if real, would lead to a striking difference in the age distribution of the GCs between M31 and the Millky Way. If the apparent presence of very young globular clusters in M31 is confirmed through our proposed ACS imaging {now WFPC2 imaging} with HST, this would suggest major differences in the history of assembly of the two galaxies, with probable substantial late accretion into M31 which did not occur in our own galaxy.

WFPC2 11178

Probing Solar System History with Orbits, Masses, and Colors of Transneptunian Binaries

The recent discovery of numerous transneptunian binaries {TNBs} opens a window into dynamical conditions in the protoplanetary disk where they formed as well as the history of subsequent events which sculpted the outer Solar System and emplaced them onto their present day heliocentric orbits. To date, at least 47 TNBs have been discovered, but only about a dozen have had their mutual orbits and separate colors determined, frustrating their use to investigate numerous important scientific questions. The current shortage of data especially cripples scientific investigations requiring statistical comparisons among the ensemble characteristics. We propose to obtain sufficient astrometry and photometry of 23 TNBs to compute their mutual orbits and system masses and to determine separate primary and secondary colors, roughly tripling the sample for which this information is known, as well as extending it to include systems of two near-equal size bodies. To make the most efficient possible use of HST, we will use a Monte Carlo technique to optimally schedule our observations.

WFPC2 11202

The Structure of Early-type Galaxies: 0.1-100 Effective Radii

The structure, formation and evolution of early-type galaxies is still largely an open problem in cosmology: how does the Universe evolve from large linear scales dominated by dark matter to the highly non-linear scales of galaxies, where baryons and dark matter both play important, interacting, roles? To understand the complex physical processes involved in their formation scenario, and why they have the tight scaling relations that we observe today {e.g. the Fundamental Plane}, it is critically important not only to understand their stellar structure, but also their dark-matter distribution from the smallest to the largest scales. Over the last three years the SLACS collaboration has developed a toolbox to tackle these issues in a unique and encompassing way by combining new non-parametric strong lensing techniques, stellar dynamics, and most recently weak gravitational lensing, with high-quality Hubble Space Telescope imaging and VLT/Keck spectroscopic data of early-type lens systems. This allows us to break degeneracies that are inherent to each of these techniques separately and probe the mass structure of early-type galaxies from 0.1 to 100 effective radii. The large dynamic range to which lensing is sensitive allows us both to probe the clumpy substructure of these galaxies, as well as their low-density outer haloes. These methods have convincingly been demonstrated, by our team, using smaller pilot-samples of SLACS lens systems with HST data. In this proposal, we request observing time with WFPC2 and NICMOS to observe 53 strong lens systems from SLACS, to obtain complete multi-color imaging for each system. This would bring the total number of SLACS lens systems to 87 with completed HST imaging and effectively doubles the known number of galaxy-scale strong lenses. The deep HST images enable us to fully exploit our new techniques, beat down low-number statistics, and probe the structure and evolution of early- type galaxies, not only with a uniform data-set an order of magnitude larger than what is available now, but also with a fully coherent and self-consistent methodological approach!

WFPC2 11218

Snapshot Survey for Planetary Nebulae in Globular Clusters of the Local Group

Planetary nebulae {PNe} in globular clusters {GCs} raise a number of interesting issues related to stellar and galactic evolution. The number of PNe known in Milky Way GCs, 4, is surprisingly low if one assumes that all stars pass through a PN stage. However, it is likely that the remnants of stars now evolving in Galactic GCs leave the AGB so slowly that any ejected nebula dissipates long before the star becomes hot enough to ionize it. Thus there should not be ANY PNe in Milky Way GCs–but there are four! It has been suggested that these PNe are the result of mergers of binary stars within GCs, i.e., that they are descendants of blue stragglers. The frequency of occurrence of PNe in external galaxies poses more questions, because it shows a range of almost an order of magnitude. I propose a Snapshot survey aimed at discovering PNe in the GC systems of Local Group galaxies more distant than the Magellanic Clouds. These clusters, some of which may be much younger than their counterparts in the Milky Way, might contain many more PNe than those of our own galaxy. I will use the standard technique of emission-line and continuum imaging, which easily discloses PNe.


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


#10901 MNDRDT1 & MNDRDT2 out of limits for 1 minute.

At 200/15:03:03 the mnemonics MNDRDT1 & MNDRDT2 (NCS CPL RES-RAD B DELTA T) flagged out of limits – red low at 5.3725 & 6.46859 respectively. They returned back in bounds at 200/15:04:02. the red lower limit is set at 7.0.

#10902 OBAD Failed Identification (ESB 1902), GSAcq not attempted. At 200/15:33:26z “OBAD failed”. The second OBAD failed during LOS scheduled 15:33:38-15;46;00z. Other data included: Mnemonic GOBSTAT = 255, GCHACL09 = 1, TGS Mode = T2G. GSAcq (1,3,1) scheduled from 15:43:55-15:50:59 was not attempted.

OBAD #1: V1 5.77, V2 -3.06, V3 -9.55, RSS 11.57

OBAD #2: V1 -33466.27, V2 -13497.54, V3 24133.27, RSS 43411.86

OBAD MAP: V1 -131.31, V2 131.93, V3 -105.57, RSS 213.99 REAcq (1,3,1) scheduled for 17:21:35-17:28:56 failed. No data available due to LOS. #10903 GSACQ(1,3,1) failed.

GSACQ(1,3,1) at 200/20:36:06 failed to RGA control. No FGS flags were seen. Vehicle was LOS at time of failure. At acquisition of signal vehicle had OBAD RSS error of 11020.84 arcseconds. COMPLETED OPS REQUEST: (None)

                                SCHEDULED  SUCCESSFUL 
FGS GSacq                       08               06 
FGS REacq                       07               06 
OBAD with Maneuver              30                27 



SpaceRef staff editor.