NASA Hubble Space Telescope Daily Report #3946

HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science

DAILY REPORT # 3946

PERIOD COVERED: UT September 15, 2005 (DOY 258)

OBSERVATIONS SCHEDULED

ACS/HRC 10377

ACS Earth Flats

High signal sky flats will be obtained by observing the bright Earth with the HRC and WFC. These observations will be used to verify the accuracy of the flats currently used by the pipeline and will provide a comparison with flats derived via other techniques: L-flats from stellar observations, sky flats from stacked GO observations, and internal flats using the calibration lamps. Weekly coronagraphic monitoring is required to assess the changing position of the spots.

ACS/HRC/WFC 10487

A Search for Debris Disks in the Coeval Beta Pictoris Moving Group

Resolved observations of debris disks present us with the opportunity of studying planetary evolution in other solar systems. We propose to search for debris disks in the Beta Pictoris moving group {8-20 Myrs, 10-50 pc away} , which provides a coeval sample of multiple spectral types, and it has already produced two magnificent resolved debris disks: AU Mic and Beta Pic. Such coeval sample will provide us with a snapshop of the crucial time in disk evolution in which the disk makes the transition from optically thick to optically thin, and it will be useful to study the stellar mass dependence of the disk evolution.

ACS/WFC 10505

The Onset of Star Formation in the Universe: Constraints from Nearby Isolated Dwarf Galaxies.

The details of the early star formation histories of tiny dwarf galaxies can shed light on the role in galaxy formation of the reionization which occured at high redshift. Isolated dwarfs are ideal probes since their evolution is not complicated by environmental effects owing to the vicinity of the Milky Way and M31. In addition, dwarf galaxies are the most common type of galaxies, and potentially the building blocks of larger galaxies. Since we can date the oldest stars in them, their study represents a complementary approach to the study of the formation and evolution of galaxies through high-z observations. We propose to use the ACS to obtain a homogeneus dataset of high-quality photometry, down to the old {13 Gyr} main-sequence turnoffs, for a representative sample of 4 isolated Local Group dwarf galaxies. These data are essential to unambiguously determine their early star formation histories, through comparison with synthetic color-magnitude diagrams, and using the constraints provided by their variable stars. Parallel WFPC2 observations of their halos will allow us to reveal the actual nature of their stellar population gradients, providing important aditional constraints on their evolution. The proposed observations are being complemented with ground-based spectroscopy, to obtain metallicity and kinematic information. The observations requested here, which must reach M_I=+3.5 {I=27.5- 28.2} with S/N=10 in crowded systems, can only be achieved with HST using ACS. Based on deep WFPC2 observations and ACS image simulations, our team has designed an observational strategy which carefully considers the optimal filter combination, the necessary photometry depth and the effects of stellar crowding.

ACS/WFC 10524

Blue Stragglers: a key stellar population to probe internal cluster dynamics

This proposal is part of a coordinated project devoted to understand the interplay of globular cluster {GC} dynamics and the formation and evolution of blue straggler stars {BSS}. By using a combination of HST and ground-based observations we are constructing complete BSS surveys in a sample of GCs; complete BSS surveys require mid-UV HST observations in the center and wide field CCD ground based observations under excellent seeing conditions of the exterior. Up to now only four clusters have been surveyed in this way and the results are surprising: in three GCs {M3, 47 Tuc, NGC 6752} we have discovered that the BSS radial distribution is bimodal, highly peaked in the cluster center, rapidly decreasing at intermediate radii and rising again at large radii {Ferraro et al. 1997, 2004, Sabbi et al. 2004}, conversely BSS population in Omega Centauri does not show any signature of the segregation which would be expected for a class of objects arising from either stellar interactions or binarity {Ferraro et al. 2005}. These observational facts are opening a new prospective in the study of the formation processes and evolution of BSS in GCs. By using extensive simulations, we demonstrated that the spatial distribution of BSS observed in 47 Tuc can be only reproduced if a sizable fraction of BSS is generated {via mass transfer in primordial binaries} in the peripheral region of the cluster {Mapelli et al 2004}, thus excluding a purely collisional formation scenario. Here we propose mid-UV imaging of a few clusters suspected of harboring a large population of central BSS and a few known to have many BSS the external region. These are good candidates for determining accurate BSS radial distributions. The modest amount of time proposed here will go far to determine the ubiquity of BSS bimodality and to constrain models of dynamical evolution. Since we believe the proposed observations would be useful to the entire stellar community {for multifold purposes} we waive the propretary period.

ACS/WFC 10526

Dynamics of the Polarization Structure of the Crab Nebula

The Crab Nebula is not a free expansion SNR. Rather, it is a pulsar wind nebula expanding from the inside out into a larger remnant of freely expanding ejecta. At the heart of this object is the Crab Pulsar and the region where the pulsar’s highly nonisotropic wind interacts with the larger synchtron nebula. HST and Chandra monitoring has shown this to be one of the most intricately structured and highly dynamical objects ever observed. In Cycle 12 we demonstrated our ability to use the polarization capabilities of the ACS to isolate physically discrete features within the Crab Synchrotron Nebula and accurately measure their polarization characteristics. These data provide a unique look at the physical structure in the heart of the Crab, adding a new dimension to past observations. Polarization provides extensive information about field geometries, the degree of disorder in the field, and particle pitch angle distributions. But one image of the Crab is like a single image of waves at the beach. It necessarily misses the point. In the Crab, the name of the game is “dynamics”. In this proposal we request time to monitor changes in the polarization structure of the Crab. This program will allow us to follow the changing polarization of features including relativistically moving wisps in the Crab Nebula. This is the only place in the sky where a dynamic relativistic plasma can be observed in sufficient detail to make such measurements possible, and the HST/ACS is the only instrument that we are likely to see in our careers capable of making the measurement. These observations will be an important addition to the already rich observational legacy of HST for what is arguably the most important single object in astrophysics.

NIC1/NIC2/NIC3 8793

NICMOS Post-SAA calibration – CR Persistence Part 4

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 10603

Multiwavelength Imaging of Edge-on Protoplanetary Disks: Quantifying the Growth of Circumstellar Dust

Young, edge-on circumstellar disks are uniquely valuable laboratories for the study of planet formation. In these objects, the central star is occulted from direct view, significant PSF artifacts are absent, and the disk is clearly seen as a central dust lane flanked by faint disk reflected light. The detailed morphology of these nebulae and its variation with wavelength provide crucial information on the disk internal structure and the properties of its constituent dust grains. A key observable is the slope defining the wavelength dependence of the dust scattering opacity, which becomes shallower when grain growth has taken place; multiwavelength resolved disk images are the key dataset enabling such measurements. Recent analyses of three different edge-on disks have revealed a diversity in their dust properties that is indicative of different degrees of dust grain evolution having taken place in each system. This characterization of disk grain growth, when applied comparatively to a larger sample of these objects, would enable the construction of an evolutionary sequence of young disks at successive stages on the road to planet formation. In pursuit of this goal, we have identified a sample of 15 edge-on disks previously discovered by HST or groundbased telescopes, but for which high fidelity, high spatial resolution images do not yet exist in both the optical and near-infrared. We propose broad-band multicolor imaging with NICMOS of all these targets, and ACS imaging of nine of these targets In combination with existing data, the proposed images will form a complete database of high resolution optical/near-IR images for these 15 disk systems. Scattered light modeling will be used to derive the disk structure and dust properties, yielding results that will be of fundamental importance for our understanding of grain properties during protoplanetary disk evolution.

FLIGHT OPERATIONS SUMMARY:

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

HSTARS:

9951 – GSAcq(2,3,2) failed to RGA Control (T2GAttHd) @ 258/08:10z The GSAcq(2,3,2) scheduled at 258/08:10:00 – 08:17:18 failed to RGA Control (T2GAttHd) due to search radius limit exceeded on FGS-2. 486 ESB “a05” search rad lmt exc was received at 258/08:14:50.

Prior FHST OBAD1 (with maneuver)scheduled at 258/07:53:21 showed vehicle axis errors: V1=-40.42, V2=-1892.64, V3=2065.24. 3ax-s (RSS) value =2801.62 arcsec.

Prior FHST OBAD2 (with maneuver) scheduled at 258/08:04:44 showed vehicle axis erros: V1=-3.34, V2=32.36, V3=71.60. 3-axis (RSS) value =78.65 arcsec.

Subsequent FHST OBAD (but no maneuver) scheduled at 258/08:17:18 showed vehicle axis errors: V1=115.07, V2=-657.11, V3=-812.71. 3-axis (RSS) value =1051.44 arcsec.

9953 – GSACQ(2,1,2) failed, search radius limit exceeded on FGS 1 @ 258/10:30:25z GSACQ(2,1,2) at 258/10:26:11 failed due to Search Radius Limit Exceeded on FGS 1 at 10:30:25. OBAD prior to GSACQ had total RSS attitude error of 5.14 arcseconds, well within the search radius.

GSACQ(2,1,2) at 12:02:09 with the same guide stars was successful.

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

                             SCHEDULED     SUCCESSFUL    FAILURE TIMES
FGS Gsacq                   08                    06               HSTAR 
9951,9953
FGS Reacq                   06                    06
OBAD with Maneuver     28                    28

SIGNIFICANT EVENTS: (None)