NASA Hubble Space Telescope Daily Report #4111

HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science

DAILY REPORT # 4111

PERIOD COVERED: UT May 10, 2006 (DOY 130)

OBSERVATIONS SCHEDULED

ACS/HRC 10508

Orbits, Masses, and Densities of Three Transneptunian Binaries

The subset of transneptunian objects {TNOs} having natural satellites offers unique opportunities for physical studies of these distant relics from the outer parts of the protoplanetary nebula. HST/ACS is ideally suited to determining orbits of TNO satellites, resulting in the system masses. In conjunction with thermal emission observations by Spitzer, which provides sizes, we can determine the densities of TNOs. Densities offer a powerful window into their bulk compositions and interior structures.

ACS/HRC 10738

Earth Flats

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 in the pipeline and to monitor any changes. Weekly coronagraphic monitoring is required to assess the changing position of the spots.

ACS/HRC/WFC 10758

ACS CCDs daily monitor

This program consists of a set of basic tests to monitor, the read noise, the development of hot pixels and test for any source of noise in ACS CCD detectors. The files, biases and dark will be used to create reference files for science calibration. This programme will be for the entire lifetime of ACS. Changes from cycle 13:- The default gain for WFC is 2 e-/DN. As before bias frames will be collected for both gain 1 and gain 2. Dark frames are acquired using the default gain {2}. This program cover the period May, 31 2006- Oct, 1-2006. The first half of the program has a different proposal number: 10729.

ACS/WFC 10523

The Halo Shape and Metallicity of Massive Spiral Galaxies

We propose to resolve the stellar populations of the halos of seven nearby, massive disk galaxies using a SNAP survey with WFC/ACS. These observations will provide star counts and color-magnitude diagrams 2-3 magnitudes below the tip of the Red Giant Branch along the two principal axes and one intermediate axis of each galaxy. We will measure the metallicity distribution functions and stellar density profiles from star counts down to very low average surface brightnesses, equivalent to ~31 V-mag per square arcsec. This proposal will create a unique sampling of galaxy halo properties, as our targets cover a range in galaxy mass, luminosity, inclination, and morphology. As function of these galaxy properties this survey will provide:- the first systematic measurement of radial light profiles and axial ratios of the diffuse stellar halos and outer disks of spiral galaxies- a comprehensive analysis of halo metallicity distributions as function of galaxy type and position within the galaxy- an unprecedented study of the stellar metallicity and age distribution in the outer disk regions where the disk truncations occur- the first comparative study of globular clusters and their field stellar populations We will use these fossil records of the galaxy assembly process to test halo formation models within the hierarchical galaxy formation scheme.

ACS/WFC 10533

The IMF in NGC6611: the environmental influence on the formation of low-mass stars and brown dwarfs

We propose to use HST with ACS and NICMOS to survey the central area of the young {2 Myr} cluster NGC6611 in the Eagle Nebula, with the goal of constructing the low-mass and substellar Initial Mass Function {IMF}. We plan to obtain deep images in I {F775W} and Z {F850LP} with ACS/WFC, and deep images in J {F110W} and H {F160W} for 25 NICMOS/NIC2 fields within the 202″ x 202″ ACS/WFC field. Using a proven technique based on the use of IZJH color-magnitude and color-color diagrams to identify and determine the masses of the low-mass pre-main sequence cluster members, we are thus able to construct the IMF down to masses of 0.02-0.03 Msun. With an intense ionizing radiation field but a relatively low density, NGC6611 provides a unique laboratory in which to test the importance of photoevaporation and density on the formation of low-mass stars and brown dwarfs, through comparison with the IMFs determined for the different environments in the Orion Nebular Cluster, Taurus and IC348. This will not only offer substantial new insight into the physics of star formation, but also have important ramifications for estimating the global star formation rates at high redshift, the efficiency of galactic chemical evolution and the contribution of sub-stellar mass objects to the baryonic dark matter content of the Universe.

ACS/WFC 10626

A Snapshot Survey of Brightest Cluster Galaxies and Strong Lensing to z = 0.9

We propose an ACS/WFC snapshot survey of the cores of 150 rich galaxy clusters at 0.3 < z < 0.9 from the Red Sequence Cluster Survey {RCS}. An examination of the galaxian light in the brightest cluster galaxies, coupled with a statistical analysis of the strong-lensing properties of the sample, will allow us to contrain the evolution of both the baryonic and dark mass in cluster cores, over an unprecedented redshift range and sample size. In detail, we will use the high- resolution ACS images to measure the metric {10 kpc/h} luminosity and morphological disturbances around the brightest clusters galaxies, in order to calibrate their accretion history in comparison to recent detailed simulations of structure formation in cluster cores. These images will also yield a well-defined sample of arcs formed by strong lensing by these clusters; the frequency and detailed distribution {size, multiplicity, redshifts} of these strong lens systems sets strong constraints on the total mass content {and its structure} in the centers of the clusters. These data will also be invaluable in the study of the morphological evolution and properties of cluster galaxies over a significant redshift range. These analyses will be supported by extensive ongoing optical and near-infrared imaging, and optical spectroscopy at Magellan, VLT and Gemini telescopes, as well as host of smaller facilities.

ACS/WFC 10630

The Fine Structure of Elliptical Galaxies in Voids

Elliptical galaxies constitute a remarkably homogeneous class of objects with a tight color- magnitude relation and a well-defined Fundamental Plane. In spite of their bland and symmetrical morphology, they are characterized by a wealth of structural features {such as nuclear disks, dust lanes, shells, blue cores, etc.} which contain important clues to their formation history. Little is known about how and if these sub-structures vary as a function of environment; in fact, due to the morphology density relation, our knowledge of ellipticals is strongly biased towards overdense regions such as clusters. But what of the fine structure of ellipticals in voids? According to theoretical predictions, void galaxies should have different merger histories than those in clusters, which may imply that their fine structure also differs. We address these issues using the exquisite angular resolution of HST/ACS to resolve sub-structures in the most accurately classified sample, to date, of truly isolated ellipticals, identified using the 2dFGRS.

ACS/WFC/HRC 10536

What Are Stalled Preplanetary Nebulae? An ACS SNAPshot Survey

Essentially all planetary nebulae {PNs} are aspherical, whereas the mass-loss envelopes of AGB stars are strikingly spherical. Our previous SNAPshot surveys of a morphologically unbiased sample of pre-planetary nebulae {PPNs} — objects in transition between the AGB and PN evolutionary phases — show that roughly half our observed targets are resolved, with bipolar or multipolar morphologies. Spectroscopic observations of our sample confirm that these objects have not yet evolved into planetary nebulae. Thus, the transformation from spherical to aspherical geometries has already fully developed by the time these dying stars have become PPNs. Although our current studies have yielded exciting results, they are limited in two important ways — {1} the number of well-resolved objects is still small {18}, and the variety of morphologies observed relatively multitudinous, hence no clear trends can yet be established between morphology and other source properties {e.g., near-IR, far-IR colors, stellar spectral type, envelope mass}, and {2} the current samples are strongly biased towards small PPNs, as inferred from their low 60-to-25 micron flux ratios [R{60/25}<1]. However, the prototype of objects with R{60/25}>1, the Frosty Leo Nebula, has a puzzlingly large post-AGB age {almost 10^4 yr} and a fairly cool central star, very different from the expectations of single-star stellar evolutionary models. A proposed, but still speculative, hypothesis for such objects is that the slow evolution of the central star is due to backflow of material onto the mass-losing star, retarding its evolution towards the PN phase. This hypothesis has significant consequences for both stellar and nebular evolution. We therefore propose a survey of PPNs with R{60/25}>1 which is heavily weighted towards the discovery of such “stalled PPNs”. Supporting kinematic observations using long-slit optical spectroscopy {with the Keck}, millimeter and radio interferometric observations {with OVRO, VLA & VLBA} are being undertaken. The results from this survey {together with our previous work} will allow us to draw general conclusions about the complex mass-outflow processes affecting late stellar evolution, and will provide crucial input for theories of post-AGB stellar evolution. Our survey will produce an archival legacy of long-standing value for future studies of dying stars.

ACS/WFC/WFPC2 10594

The Formation of Spiral Spheroids and Their Globular Cluster Systems

The assembly history of spiral galaxies remains one of the most pressing questions in astrophysics today. In particular, we do not have a clear picture of the formation mechanism for bulges of spiral galaxies. Are bulges of spirals simply “small ellipticals”, formed via rapid dissipative collapse during the early universe? Or is bulge building through secular evolution of inner disk stars a more common mechanism? Is there any dependence on bulge mass? A powerful yet relatively simple way to probe these fundamental questions is by studying the properties of globular cluster {GC} systems of spirals. Specifically, bulge formation via secular evolution is expected not to form GCs, whereas bulge formation via dissipative collapse is. We therefore propose to obtain ACS/WFC imaging as well as ground-based, wide-field imaging of five edge-on Sa spirals which cover a factor ~15 in luminosity/mass, and for which spectroscopic follow-up is feasible. This constitutes the first luminosity-selected sample of early-type spirals, which will allow us to directly probe the dependence of GC properties on the bulge luminosity. We will detect a minimum of ~100-200 GCs per galaxy in the ACS images, sufficient to reveal GC subpopulations, their relative numbers, sizes, and radial distributions. This study will more than double the number of well-studied early-type spiral systems.

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:

• 17754-0 – Genslew for proposal 10487 – slot 12 @ 130/1352z
• 17755-0 – Genslew for proposal 10487 – slot 13 @ 130/1530z
• 17756-0 – Genslew for proposal 10487 – slot 14 @ 130/1531z
• 17757-0 – Genslew for proposal 10487 – slot 1 @ 130/1532z

COMPLETED OPS NOTES: (None)

                         SCHEDULED      SUCCESSFUL
FGS GSacq               05                     05
FGS REacq               08                     08
OBAD with Maneuver  24                     24

SIGNIFICANT EVENTS: (None)