Status Report

NASA Hubble Space Telescope Daily Report # 4596

By SpaceRef Editor
April 25, 2008
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NASA Hubble Space Telescope Daily Report # 4596


Continuing to collect World Class Science

PERIOD COVERED: UT April 23, 2008 (DOY 114)


NIC1/NIC2/NIC3 8795

NICMOS Post-SAA calibration – CR Persistence Part 6

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 10852

Coronagraphic Polarimetry with NICMOS: Dust grain evolution in T Tauri stars

The formation of planetary systems is intimately linked to the dust population in circumstellar disks, thus understanding dust grain evolution is essential to advancing our understanding of how planets form. By combining {1} the coronagraphic polarimetry capabilities of NICMOS, {2} powerful 3-D radiative transfer codes, and {3} observations of objects known to span the Class II- III stellar evolutionary phases, we will gain crucial insight into dust grain growth. By observing objects representative of a known evolutionary sequence of YSOs, we will be able to investigate how the dust population evolves in size and distribution during the crucial transition from a star+disk system to a system containing planetesimals. When combine with our previous study on dust grain evolution in the Class I-II phase, the proposed study will help to establish the fundamental time scales for the depletion of ISM-like grains: the first step in understanding the transformation from small submicron sized dust grains, to large millimeter sized grains, and untimely to planetary bodies.

NIC2/WFPC2 11142

Revealing the Physical Nature of Infrared Luminous Galaxies at 0.3< z<2.7 Using HST and Spitzer

We aim to determine physical properties of IR luminous galaxies at 0.3< z<2.7 by requesting coordinated HST/NIC2 and MIPS 70um observations of a unique, 24um flux-limited sample with complete Spitzer mid-IR spectroscopy. The 150 sources investigated in this program have S{24um} > 0.8mJy and their mid-IR spectra have already provided the majority

targets with spectroscopic redshifts {0.3< z<2.7}. The proposed 150~orbits of NIC2 and 66~hours of MIPS 70um will provide the physical measurements of the light distribution at the rest-frame ~8000A and better estimates of the bolometric luminosity. Combining these parameters together with the rich suite of spectral diagnostics from the mid-IR spectra, we will {1} measure how common mergers are among LIRGs and ULIRGs at 0.3< z<2.7, and establish if major mergers are the drivers of z>1 ULIRGs, as in the local Universe. {2} study the co-evolution of star formation and blackhole accretion by investigating the relations between the fraction of starburst/AGN measured from mid-IR spectra vs. HST morphologies, L{bol} and z. {3} obtain the current best estimates of the far-IR emission, thus L{bol} for this sample, and establish if the relative contribution of mid-to-far IR dust emission is correlated with morphology {resolved vs. unresolved}.

NIC3 11120

A Paschen-Alpha Study of Massive Stars and the ISM in the Galactic Center

The Galactic center (GC) is a unique site for a detailed study of a multitude of complex astrophysical phenomena, which may be common to nuclear regions of many galaxies. Observable at resolutions unapproachable in other galaxies, the GC provides an unparalleled opportunity to improve our understanding of the interrelationships of massive stars, young stellar clusters, warm and hot ionized gases, molecular clouds, large scale magnetic fields, and black holes. We propose the first large-scale hydrogen Paschen alpha line survey of the GC using NICMOS on the Hubble Space Telescope. This survey will lead to a high resolution and high sensitivity map of the Paschen alpha line emission in addition to a map of foreground extinction, made by comparing Paschen alpha to radio emission. This survey of the inner 75 pc of the Galaxy will provide an unprecedented and complete search for sites of massive star formation. In particular, we will be able to (1) uncover the distribution of young massive stars in this region, (2) locate the surfaces of adjacent molecular clouds, (3) determine important physical parameters of the ionized gas, (4) identify compact and ultra-compact HII regions throughout the GC. When combined with existing Chandra and Spitzer surveys as well as a wealth of other multi-wavelength observations, the results will allow us to address such questions as where and how massive stars form, how stellar clusters are disrupted, how massive stars shape and heat the surrounding medium, and how various phases of this medium are interspersed.

WFPC2 11113

Binaries in the Kuiper Belt: Probes of Solar System Formation and Evolution

The discovery of binaries in the Kuiper Belt and related small body populations is powering a revolutionary step forward in the study of this remote region. Three quarters of the known binaries in the Kuiper Belt have been discovered with HST, most by our snapshot surveys. The statistics derived from this work are beginning to yield surprising and unexpected results. We have found a strong concentration of binaries among low-inclination Classicals, a possible size cutoff to binaries among the Centaurs, an apparent preference for nearly equal mass binaries, and a strong increase in the number of binaries at small separations. We propose to continue this successful program in Cycle 16; we expect to discover at least 13 new binary systems, targeted to subgroups where these discoveries can have the greatest impact.

WFPC2 11160

Escape fraction and stellar populations in a highly magnified Lyman-Break Galaxy

Understanding how star-forming galaxies contribute to cosmic reionization is one of the frontiers of observational cosmology. A key ingredient in this issue is measuring the escape fraction of Lyman-continuum photons in high redshift galaxies (z>3). Gravitationally lensed Lyman-break galaxies (LBGs) act as important laboratories for studying the resolved physical properties at sub-kpc scales with high signal-to-noise. Correlating the local escape fraction with physical parameters derived from stellar population modeling (such as the star formation rate, age and reddening) will offer new insights into understanding the physical processes involved with the production of ionizing photons. We propose here follow-up observations of the “Cosmic Eye”, a remarkable, highly magnified (x 30), Lyman-break galaxy at z~3.07 using WFPC2 and NICMOS. Deep ultraviolet WFPC2 imaging will provide a detailed study of variations in the escape fraction, while WFPC2 and NICMOS/NIC2 imaging will complement the current broad-band detections to allow a precise modeling of the spatially-dependent spectral energy distribution. This will allow the first comprehensive analysis between the escape fraction, the local SED and the dynamics of a distant galaxy.

WFPC2 11201

Systemic and Internal motions of the Magellanic Clouds: Third Epoch Images

In Cycles 11 and 13 we obtained two epochs of ACS/HRC data for fields in the Magellanic Clouds centered on background quasars. We used these data to determine the proper motions of the LMC and SMC to better than 5% and 15% respectively. These are by far the best determinations of the proper motions of these two galaxies. The results have a number of unexpected implications for the Milky Way-LMC-SMC system. The implied three-dimensional velocities are larger than previously believed, and are not much less than the escape velocity in a standard 10^12 solar mass Milky Way dark halo. Orbit calculations suggest the Clouds may not be bound to the Milky Way or may just be on their first passage, both of which would be unexpected in view of traditional interpretations of the Magellanic Stream. Alternatively, the Milky Way dark halo may be a factor of two more massive than previously believed, which would be surprising in view of other observational constraints. Also, the relative velocity between the LMC and SMC is larger than expected, leaving open the possibility that the Clouds may not be bound to each other. To further verify and refine our results we now request an epoch of WFPC2/PC data for the fields centered on 40 quasars that have at least one epoch of ACS imaging. We request execution in snapshot mode, as in our previous programs, to ensure the most efficient use of HST resources. A third epoch of data of these fields will provide crucial information to verify that there are no residual systematic effects in our previous measurements. More importantly, it will increase the time baseline from 2 to 5 yrs and will increase the number of fields with at least two epochs of data. This will reduce our uncertainties correspondingly, so that we can better address whether the Clouds are indeed bound to each other and to the Milky Way. It will also allow us to constrain the internal motions of various populations within the Clouds, and will allow us to determine a distance to the LMC using rotational parallax.

WFPC2 11231

Calibration of the WFPC2 HeII and [SII] Filters.

Observations of NGC 6720 (the Ring Nebula) will be used to determine the calibration constants for the important emission-line filters that isolate nebular HeII (F469N) and [SII] (F673N) emission. The pre-launch calibrations are inadequate because of possible temporal changes and the fact that these interference filters are used in a different configuration from that of the ground calibration. The Ring Nebula is a nearly ideal reference source as multiple 2.4″x4.0″ samples have been accurately measured spectro-photometrically and five of the six samples can be imaged with one pointing of the HST. The method of derivation of the calibration constants will be the same as previously employed to calibrate the primary emission-line filters for the WFPC2 (F487N, F502N, F656N, F658N) and ACS (F502N, F658N, F660N) using the Orion Nebula as a reference source. However, Orion cannot be used for this calibration because the targeted lines are weak ([SII]) or absent (HeII) and the scattered-light continuum is strong. The Ring Nebula has strong HeII emission in its middle, strong [SII] emission in its main ring, and a weak (atomic only) continuum.

WFPC2 11233

Multiple Generations of Stars in Massive Galactic Globular Clusters

This is a follow-up to recent HST imaging of NGC 2808, which discovered that its main sequence is triple, with three well-separated parallel branches {Fig.~1}. Along with the double MS of Omega Centauri, this challenges the long-held paradigm that globular clusters are simple, single stellar populations. The cause of this main sequence multiplicity in both clusters is likely to be differences in helium abundance, which could play a fundamental role in the understanding of stellar populations. We propose to image seven more of the most massive globular clusters, to examine their main sequences for indications of splitting.


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


11268 – GSACQ(1,2,1) failed, scan step limit exceeded on FGS 1

GSACQ(1,2,1) at 114/18:16:55 failed due to scan step limit exceeded on FGS 1. No ESB messages were received, NICMOS 705 status buffer message (TDF down when a target acquisition SAM request is made) was posted at 18:26:36.



                         SCHEDULED      SUCCESSFUL

FGS GSacq                08                   07
FGS REacq                06                   06
OBAD with Maneuver       28                   28


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