NASA Hubble Space Telescope Daily Report # 4557
HUBBLE SPACE TELESCOPE DAILY REPORT # 4557
Continuing to collect World Class Science
PERIOD COVERED: UT February 28, 2008 (DOY 059)
OBSERVATIONS SCHEDULED
FGS 11212
Filling the Period Gap for Massive Binaries
The current census of binaries among the massive O-type stars is seriously incomplete for systems in the period range from years to millennia because the radial velocity variations are too small and the angular separations too close for easy detection. Here we propose to discover binaries in this observational gap through a Faint Guidance Sensor SNAP survey of relatively bright targets listed in the Galactic O Star Catalog. Our primary goal is to determine the binary frequency among those in the cluster/association, field, and runaway groups. The results will help us assess the role of binaries in massive star formation and in the processes that lead to the ejection of massive stars from their natal clusters. The program will also lead to the identification of new, close binaries that will be targets of long term spectroscopic and high angular resolution observations to determine their masses and distances. The results will also be important for the interpretation of the spectra of suspected and newly identified binary and multiple systems.
FGS 11301
Dynamical Masses and Radii of Four White Dwarf Stars
This proposal uses the FGS1r in TRANS mode to resolve a pair of double degenerate binary systems {WD1639+153 and WD 1818+26} in order to determine their orbital elements. In addition, the binaries and several nearby field stars are observed by FGS1r in POS mode to establish the local inertial reference frame of each binary, as well as its parallax and proper motion. This will allow for a direct measurement of the distance and radius of each of the four WD stars. When combined with the orbital elements, this leads to a dynamical mass measurement for each WD, and a four calibration points of the WD mass-radius relation.
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=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 i mages. Each observation will need its own CRMAP, as different SAA passages leave different imprints on the NICMOS detectors.
NIC2 11135
Extreme makeovers: Tracing the transformation of massive galaxies at z~2.5
To obtain a full spectroscopic census of the universe at z~2.5 we have conducted a near-infrared spectroscopic survey for K-selected galaxies. We found that, in contrast to the local universe, massive high-redshift galaxies span a wide range of properties, varying from (dusty) star burst to “red and dead” galaxies. This may imply that massive galaxies transform from star-forming to quiescent galaxies in the targeted redshift range. To understand whether the 9 quiescent galaxies in our sample are the progenitors of local elliptical, we are observing them in the current cycle with NIC2. For cycle 16 we propose to complete our sample of massive z~2.5 galaxies and image the remaining 10 galaxies, which all have emission lines. Based on emission-line diagnostics, 6 of these galaxies are identified as star-forming objects and 4 harbor an active galactic nucleus. The goals are to 1) determine whether star formation in massive z~2.5 galaxies takes place in disks or is triggered by merger activity, 2) derive the contribution of AGNs to the rest-frame optical emission, and 3) test whether the morphologies are consistent with the idea that the star-forming galaxies, AGNs, and quiescent galaxies represent subsequent phases of an evolutionary sequence. The combination of both programs will provide the first morphological study of a spectroscopically confirmed massive galaxy sample at z~2.5.
NIC2 11143
NICMOS imaging of submillimeter galaxies with CO and PAH redshifts
We propose to obtain F110W and F160W imaging of 10 z~2.4 submillimeter galaxies {SMGs} whose optical redshifts have been confirmed by the detection of millimeter CO and/or mid- infrared PAH emission. With the 4000A break falling within/between the two imaging filters, we will be able to study these sources’ spatially resolved stellar populations {modulo extinction} in the rest-frame optical. SMGs’ large luminosities appear to be due largely to merger-triggered starbursts; high-resolution NICMOS imaging will help us understand the stellar masses, mass ratios, and other properties of the merger progenitors, valuable information in the effort to model the mass assembly history of the universe.
NIC2 11155
Dust Grain Evolution in Herbig Ae Stars: NICMOS Coronagraphic Imaging and Polarimetry
We propose to take advantage of the sensitive coronagraphic capabilities of NICMOS to obtain multiwavelength coronagraphic imaging and polarimetry of primordial dust disks around young intermediate-mass stars {Herbig Ae stars}, in order to advance our understanding of how dust grains are assembled into larger bodies. Because the polarization of scattered light is strongly dependent on scattering particle size and composition, coronagraphic imaging polarimetry with NICMOS provides a uniquely powerful tool for measuring grain properties in spatially resolved circumstellar disks. It is widely believed that planets form via the gradual accretion of planetesimals in gas-rich, dusty circumstellar disks, but the connection between this suspected process and the circumstellar disks that we can now observe around other stars remains very uncertain. Our proposed observations, together with powerful 3-D radiative transfer codes, will enable us to quantitatively determine dust grain properties as a function of location within disks, and thus to test whether dust grains around young stars are in fact growing in size during the putative planet-formation epoch. HST imaging polarimetry of Herbig Ae stars will complement and extend existing polarimetric studies of disks around lower-mass T Tauri stars and debris disks around older main-sequence stars. When combined with these previous studies, the proposed research will help us establish the influence of stellar mass on the growth of dust grains into larger planetesimals, and ultimately to planets. Our results will also let us calibrate models of the thermal emission from these disks, a critical need for validating the properties of more distant disks inferred on the basis of spectral information alone.
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 11030
WFPC2 WF4 Temperature Reduction #3
In the fall of 2005, a serious anomaly was found in images from the WF4 CCD in WFPC2. The WF4 CCD bias level appeared to have become unstable, resulting in sporadic images with either low or zero bias level. The severity and frequency of the problem was rapidly increasing, making it possible that WF4 would soon become unusable if no work-around were found. Examination of bias levels during periods with frequent WFPC2 images showed low and zero bias episodes every 4 to 6 hours. This periodicity is driven by cycling of the WFPC2 Replacement Heater, with the bias anomalies occurring at the temperature peaks. The other three CCDs {PC1, WF2, and WF3} appear to be unaffected and continue to operate properly. Lowering the Replacement Heater temperature set points by a few degrees C effectively eliminates the WF4 anomaly. On 9 January 2006, the upper set point of the WFPC2 Replacement Heater was reduced from 14.9C to 12.2C. On 20 February 2006, the upper set point was reduced from 12.2C to 11.3C, and the lower set point was reduced from 10.9C to 10.0C. These changes restored the WF4 CCD bias level; however, the bias level has begun to trend downwards again, mimicking its behavior in late 2004 and early 2005. A third temperature reduction is planned for March 2007. We will reduce the upper set point of the heater from 11.3C to 10.4C and the lower set point from 10.0C to 9.1C. The observations described in this proposal will test the performance of WFPC2 before and after this temperature reduction. Additional temperature reductions may be needed in the future, depending on the performance of WF4. Orbits: internal 26, external 1
WFPC2 11103
A Snapshot Survey of The Most Massive Clusters of Galaxies
We propose the continuation of our highly successful SNAPshot survey of a sample of 125 very X-ray luminous clusters in the redshift range 0.3-0.7. As demonstrated by the 25 snapshots obtained so far in Cycle14 and Cycle15 these systems frequently exhibit strong gravitational lensing as well as spectacular examples of violent galaxy interactions. The proposed observations will provide important constraints on the cluster mass distributions, the physical nature of galaxy-galaxy and galaxy-gas interactions in cluster cores, and a set of optically bright, lensed galaxies for further 8-10m spectroscopy. All of our primary science goals require only the detection and characterization of high-surface-brightness features and are thus achievable even at the reduced sensitivity of WFPC2. Because of their high redshift and thus compact angular scale our target clusters are less adversely affected by the smaller field of view of WFPC2 than more nearby systems. Acknowledging the broad community interest in this sample we waive our data rights for these observations. Due to a clerical error at STScI our approved Cycle15 SNAP program was barred from execution for 3 months and only 6 observations have been performed to date – reinstating this SNAP at Cycle16 priority is of paramount importance to reach meaningful statistics.
WFPC2 11122
Expanding PNe: Distances and Hydro Models
We propose to obtain repeat narrowband images of a sample of eighteen planetary nebulae {PNe} which have HST/WFPC2 archival data spanning time baselines of a decade. All of these targets have previous high signal-to-noise WFPC2/PC observations and are sufficiently nearby to have readily detectable expansion signatures after a few years. Our main scientific objectives are {a} to determine precise distances to these PNe based on their angular expansions, {b} to test detailed and highly successful hydrodynamic models that predict nebular morphologies and expansions for subsamples of round/elliptical and axisymmetric PNe, and {c} to monitor the proper motions of nebular microstructures in an effort to learn more about their physical nature and formation mechanisms. The proposed observations will result in high-precision distances to a healthy subsample of PNe, and from this their expansion ages, luminosities, CSPN properties, and masses of their ionized cores. With good distances and our hydro models, we will be able to determine fundamental parameters {such as nebular and central star masses, luminosity, age}. The same images allow us to monitor the changing overall ionization state and to search for the surprisingly non-homologous growth patterns to bright elliptical PNe of the same sort seen by Balick & Hajian {2004} in NGC 6543. Non-uniform growth is a sure sign of active pressure imbalances within the nebula that require careful hydro models to understand.
FLIGHT OPERATIONS SUMMARY:
Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.)
HSTARS: 11202 GSAcq(1,2,1) failed to RGA Control while LOS @ 059/21:11:21z No FGS flags were set or 486 ESB messages received. NICMOS 705 status buffer message (TDF down when a target acquisition SAM request is made) with parameter 0 and time 14666 occurred at 21:21:20z. Post-acquisition OBAD map at 21:19:25z had RSS error of 29.45 arcseconds.
COMPLETED OPS REQUEST: (None)
COMPLETED OPS NOTES: (None)
SCHEDULED SUCCESSFUL
FGS GSacq 9 08
FGS REacq 04 04
OBAD with Maneuver 28 28
SIGNIFICANT EVENTS: (None)
