Status Report

NASA Hubble Space Telescope Daily Report #5131

By SpaceRef Editor
July 8, 2010
Filed under , ,


Continuing to Collect World Class Science

PERIOD COVERED: 5am July 2 – 5am July 6, 2010 (DOY 183/09:00z-187/09:00z)


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

HSTARS: (None)



FGS GSAcq 27 27
FGS REAcq 32 32
OBAD with Maneuver 20 20



STIS/CCD 11999

JWST Calibration from a Consistent Absolute Calibration of Spitzer & Hubble

Recently, Gordon, Bohlin, et al. submitted a successful Spitzer proposal for cross calibration of HST and Spitzer. The cross-calibration targets are stars in three categories: WDs, A-stars, and G-stars. Traditionally, IR flux standards are extrapolations of stellar models that are tied to absolute fluxes at shorter wavelengths. HST absolute flux standards are among the best available with a solid basis that uses pure hydrogen models of hot WD stars for the SED slopes and is tied to Vega at 5556A via precise Landolt V-band photometry. Consistently matching models to our three categories of HST observations along with Spitzer photometry and the few existing absolute IR flux determinations will provide a solid basis for JWST flux calibration over its 0.8-30micron range. The goal of this proposal is to complete the HST observations of the set of HST/Spitzer cross-calibration stars. Using a variety of standard stars with three different spectral types will ensure that the final calibration is not significantly affected by systematic uncertainties.

ACS/WFC 11996

CCD Daily Monitor (Part 3)

This program comprises basic tests for measuring the read noise and dark current of the ACS WFC and for tracking the growth of hot pixels. The recorded frames are used to create bias and dark reference images for science data reduction and calibration. This program will be executed four days per week (Mon, Wed, Fri, Sun) for the duration of Cycle 17. To facilitate scheduling, this program is split into three proposals. This proposal covers 308 orbits (19.25 weeks) from 21 June 2010 to 1 November 2010.

WFC3/IR/S/C 11929

IR Dark Current Monitor

Analyses of ground test data showed that dark current signals are more reliably removed from science data using darks taken with the same exposure sequences as the science data, than with a single dark current image scaled by desired exposure time. Therefore, dark current images must be collected using all sample sequences that will be used in science observations. These observations will be used to monitor changes in the dark current of the WFC3-IR channel on a day-to-day basis, and to build calibration dark current ramps for each of the sample sequences to be used by Gos in Cycle 17. For each sample sequence/array size combination, a median ramp will be created and delivered to the calibration database system (CDBS).

WFC3/IR 11926

IR Zero Points

We will measure and monitor the zeropoints through the IR filters using observations of the white dwarf standard stars, GD153, GD71 and GD191B2B and the solar analog standard star, P330E. Data will be taken monthly during Cycle 17. Observations of the star cluster, NGC 104, are made twice to check color transformations. We expect an accuracy of 2% in the wide filter zeropoints relative to the HST photometric system, and 5% in the medium- and narrow-band filters.

WFC3/IR 11915

IR Internal Flat Fields

This program is the same as 11433 (SMOV) and depends on the completion of the IR initial alignment (Program 11425). This version contains three instances of 37 internal orbits: to be scheduled early, middle, and near the end of Cycle 17, in order to use the entire 110-orbit allocation.

In this test, we will study the stability and structure of the IR channel flat field images through all filter elements in the WFC3-IR channel. Flats will be monitored, i.e. to capture any temporal trends in the flat fields and delta flats produced. High signal observations will provide a map of the pixel-to-pixel flat field structure, as well as identify the positions of any dust particles.

WFC3/UVIS 11911

UVIS L-Flats and Geometric Distortion

Multiple pointing observations of the globular cluster Omega Centauri (NGC 5139) will be used to measure the filter-dependent low frequency flat field (L-flat) corrections and stability for a key set of 10 broadband filters used by GO programs. The selected filters are F225W, F275W, F336W, F390W, F438W, F555W, F606W, F775W, F814W and F850LP. By measuring relative changes in brightness of a star over different portions of the detector, we will determine local variations in the UVIS detector response.

The broad wavelength range covered by these observations will allow us to derive the L-flat correction for the remaining wide, medium and narrow-band UVIS filters. The same data will also be used to determine and correct the geometric distortion that affects UVIS data. The broad wavelength range covered by these observations will allow us to measure the geometric distortion dependence with wavelength and filters and to provide the most appropriate correction over the entire wavelength range provided by UVIS.

WFC3/UVIS 11908

Cycle 17: UVIS Bowtie Monitor

Ground testing revealed an intermittent hysteresis type effect in the UVIS detector (both CCDs) at the level of ~1%, lasting hours to days. Initially found via an unexpected bowtie-shaped feature in flatfield ratios, subsequent lab tests on similar e2v devices have since shown that it is also present as simply an overall offset across the entire CCD, i.e., a QE offset without any discernable pattern. These lab tests have further revealed that overexposing the detector to count levels several times full well fills the traps and effectively neutralizes the bowtie. Each visit in this proposal acquires a set of three 3×3 binned internal flatfields: the first unsaturated image will be used to detect any bowtie, the second, highly exposed image will neutralize the bowtie if it is present, and the final image will allow for verification that the bowtie is gone.

WFC3/UVIS 11905

WFC3 UVIS CCD Daily Monitor

The behavior of the WFC3 UVIS CCD will be monitored daily with a set of full-frame, four-amp bias and dark frames. A smaller set of 2Kx4K subarray biases are acquired at less frequent intervals throughout the cycle to support subarray science observations. The internals from this proposal, along with those from the anneal procedure (Proposal 11909), will be used to generate the necessary superbias and superdark reference files for the calibration pipeline (CDBS).

COS/FUV 11897

FUV Spectroscopic Sensitivity Monitoring

The purpose of this proposal is to monitor sensitivity in each FUV grating mode to detect any changes due to contamination or other causes.

COS/FUV 11895

FUV Detector Dark Monitor

Monitor the FUV detector dark rate by taking long science exposures without illuminating the detector. The detector dark rate and spatial distribution of counts will be compared to pre-launch and SMOV data in order to verify the nominal operation of the detector. Variations of count rate as a function of orbital position will be analyzed to find dependence of dark rate on proximity to the SAA. Dependence of dark rate as function of time will also be tracked.

COS/NUV 11894

NUV Detector Dark Monitor

The purpose of this proposal is to measure the NUV detector dark rate by taking long science exposures with no light on the detector. The detector dark rate and spatial distribution of counts will be compared to pre-launch and SMOV data in order to verify the nominal operation of the detector. Variations of count rate as a function of orbital position will be analyzed to find dependence of dark rate on proximity to the SAA. Dependence of dark rate as function of time will also be tracked.

ACS/SBC 11886

UV Contamination Monitor

The observations consist of imaging and spectroscopy with SBC and HRC of the cluster NGC 6681 in order to monitor the temporal evolution of the UV sensitivity of the SBC and the HRC.


HST Cycle 17 and Post-SM4 Optical Monitor

This program is the Cycle 17 implementation of the HST Optical Monitoring Program.

The 36 orbits comprising this proposal will utilize ACS (Wide Field Channel) and WFC3 (UVIS Channel) to observe stellar cluster members in parallel with multiple exposures over an orbit. Phase retrieval performed on the PSF in each image will be used to measure primarily focus, with the ability to explore apparent coma, and astigmatism changes in WFC3.

The goals of this program are to: 1) monitor the overall OTA focal length for the purposes of maintaining focus within science tolerances 2) gain experience with the relative effectiveness of phase retrieval on WFC3/UVIS PSFs 3) determine focus offset between the imagers and identify any SI-specific focus behavior and dependencies

If need is determined, future visits will be modified to interleave WFC3/IR channel and STIS/CCD focii measurements.

STIS/CCD 11855

STIS/CCD Spectroscopic Sensitivity Monitor for Cycle 17

Monitor sensitivity of each CCD grating mode to detect any change due to contamination or other causes.

STIS/CC 11847

CCD Bias Monitor-Part 2

Monitor the bias in the 1×1, 1×2, 2×1, and 2×2 bin settings at gain=1, and 1×1 at gain = 4, to build up high-S/N superbiases and track the evolution of hot columns.

STIS/CC 11845

CCD Dark Monitor Part 2

Monitor the darks for the STIS CCD.


Multiple Stellar Generations in the Unique Globular Clusters NGC 6388 and NGC 6441

Over the last few years HST observations have resulted in one of the most exciting and unexpected developments in stellar population studies: the discovery of multiple generations of stars in several globular clusters. The finding of multiple main sequences in the massive clusters NGC 2808 and Omega Centauri, and multiple subgiant branches in NGC 1851, M54, and NGC 6388 has challenged the long-held paradigm that globular clusters are simple stellar populations. Even more surprising, given the spectroscopic and photometric constraints, the only viable explanation for the main sequence splitting appears to be Helium enrichment, up to an astonishingly high Y=0.4. The conditions under which certain globulars experience the formation of multiple stellar generations remain mysterious, and even more so the helium-enrichment phenomenon. Such an enrichment has important implications for chemical-enrichment, star-formation, and stellar-evolution scenarios, in star clusters and likely elsewhere. To properly constrain the multiple main sequence phenomenon, it is important to determine its extent among GCs: is it limited to Omega Cen and NGC2808, or is it more common? We propose deep WFC3 optical/IR imaging of NGC 6388 and 6441, the two globular clusters that are most likely to host multiple, helium-enriched populations. Our simulations of WFC3 performance suggest that we will be able to detect even the main sequence splittings caused by small He differences (Delta Y <0.03). WFC3/UVIS 11732 The Temperature Profiles of Quasar Accretion Disks We can now routinely measure the size of quasar accretion disks using gravitational microlensing of lensed quasars. At optical wavelengths we observe a size and scaling with black hole mass roughly consistent with thin disk theory but the sizes are larger than expected from the observed optical fluxes. One solution would be to use a flatter temperature profile, which we can study by measuring the wavelength dependence of the disk size over the largest possible wavelength baseline. Thus, to understand the size discrepancy and to probe closer to the inner edge of the disk we need to extend our measurements to UV wavelengths, and this can only be done with HST. For example, in the UV we should see significant changes in the optical/UV size ratio with black hole mass. We propose monitoring 5 lenses spanning a broad range of black hole masses with well-sampled ground based light curves, optical disk size measurements and known GALEX UV fluxes during Cycles 17 and 18 to expand from our current sample of two lenses. We would obtain 5 observations of each target in each Cycle, similar to our successful strategy for the first two targets. WFC3/UV/ACS/WFC 11710 The Extreme Globular Cluster System of Abell 1689: The Ultimate Test of Universal Formation Efficiency The stellar masses of the most luminous galaxies poorly represent the masses of the halos in which they reside. However, recent studies of the very rich globular cluster (GC) populations in the centers of galaxy clusters point toward an apparently linear scaling of the number of GCs with the total core mass of the galaxy cluster. Thus, unlike for the stars in cD galaxies, GC formation in these systems appears to have proceeded with a roughly universal mass conversion efficiency. GCs are also distinct in that their spatial distributions are more extended than the starlight, and recent simulations suggest that they follow the mass density profile of the merged dark matter halos that formed stars at high redshift. To provide a definitive test of the universal efficiency hypothesis requires measuring the number of GCs in the most massive galaxy clusters, where the number should be a factor of 5 or more greater than seen in M87. Likewise, the relationship between GCs and mass density can only be tested in systems where the total mass and mass density are well-determined. Fortunately, the imaging power of HST brings the GC population of Abell 1689, the most extreme high-mass lensing cluster, into range. Estimates of the size of the A1689 GC population from available data suggest an unprecedented 100, 000 GCs, but this number is based on the tip of the iceberg and is extremely uncertain. We propose to obtain the first accurate measurement of the number of GCs and their density profile in this extraordinary system – the most massive and most distant GC system ever studied – and thus make the ultimate test of the universal GC formation hypothesis. Our deep I-band image will also provide a stringent “null-detection” test of several known z>7 galaxy candidates and improve the mass model of the system by increasing the number of usable lensed background galaxies. Finally, we will take deep multi-band parallel observations with WFC3/IR to help in quantifying the abundance of rare faint red objects.

WFC3/IR 11696

Infrared Survey of Star Formation Across Cosmic Time

We propose to use the unique power of WFC3 slitless spectroscopy to measure the evolution of cosmic star formation from the end of the reionization epoch at z>6 to the close of the galaxy- building era at z~0.3.Pure parallel observations with the grisms have proven to be efficient for identifying line emission from galaxies across a broad range of redshifts. The G102 grism on WFC3 was designed to extend this capability to search for Ly-alpha emission from the first galaxies. Using up to 250 orbits of pure parallel WFC3 spectroscopy, we will observe about 40 deep (4-5 orbit) fields with the combination of G102 and G141, and about 20 shallow (2-3 orbit) fields with G141 alone.

Our primary science goals at the highest redshifts are: (1) Detect Lya in ~100 galaxies with z>5.6 and measure the evolution of the Lya luminosity function, independent of of cosmic variance; 2) Determine the connection between emission line selected and continuum-break selected galaxies at these high redshifts, and 3) Search for the proposed signature of neutral hydrogen absorption at re-ionization. At intermediate redshifts we will (4) Detect more than 1000 galaxies in Halpha at 0.55) galaxies.


How Galaxies Acquire their Gas: A Map of Multiphase Accretion and Feedback in Gaseous Galaxy Halos

We propose to address two of the biggest open questions in galaxy formation – how galaxies acquire their gas and how they return it to the IGM – with a concentrated COS survey of diffuse multiphase gas in the halos of SDSS galaxies at z = 0.15 – 0.35. Our chief science goal is to establish a basic set of observational facts about the physical state, metallicity, and kinematics of halo gas, including the sky covering fraction of hot and cold material, the metallicity of infall and outflow, and correlations with galaxy stellar mass, type, and color – all as a function of impact parameter from 10 – 150 kpc. Theory suggests that the bimodality of galaxy colors, the shape of the luminosity function, and the mass-metallicity relation are all influenced at a fundamental level by accretion and feedback, yet these gas processes are poorly understood and cannot be predicted robustly from first principles. We lack even a basic observational assessment of the multiphase gaseous content of galaxy halos on 100 kpc scales, and we do not know how these processes vary with galaxy properties. This ignorance is presently one of the key impediments to understanding galaxy formation in general. We propose to use the high-resolution gratings G130M and G160M on the Cosmic Origins Spectrograph to obtain sensitive column density measurements of a comprehensive suite of multiphase ions in the spectra of 43 z < 1 QSOs lying behind 43 galaxies selected from the Sloan Digital Sky Survey. In aggregate, these sightlines will constitute a statistically sound map of the physical state and metallicity of gaseous halos, and subsets of the data with cuts on galaxy mass, color, and SFR will seek out predicted variations of gas properties with galaxy properties. Our interpretation of these data will be aided by state-of-the-art hydrodynamic simulations of accretion and feedback, in turn providing information to refine and test such models. We will also use Keck, MMT, and Magellan (as needed) to obtain optical spectra of the QSOs to measure cold gas with Mg II, and optical spectra of the galaxies to measure SFRs and to look for outflows. In addition to our other science goals, these observations will help place the Milky Way's population of multiphase, accreting High Velocity Clouds (HVCs) into a global context by identifying analogous structures around other galaxies. Our program is designed to make optimal use of the unique capabilities of COS to address our science goals and also generate a rich dataset of other absorption-line systems. WFC3/ACS/IR 11597 Spectroscopy of IR-Selected Galaxy Clusters at 1 < z < 1.5 We propose to obtain WFC3 G141 and G102 slitless spectroscopy of galaxy clusters at 1 < z < 1.5 that were selected from the IRAC survey of the Bootes NDWFS field. Our IRAC survey contains the largest sample of spectroscopically confirmed clusters at z > 1. The WFC3 grism data will measure H-alpha to determine SFR, and fit models to the low resolution continua to determine stellar population histories for the brighter cluster members, and redshifts for the red galaxies too faint for ground-based optical spectroscopy.

ACS/WFC3 11586

Exceptional Galactic Halo Globular Clusters and the Second Parameter

We propose to obtain deep ACS-WFC images of six globular clusters (five of which have no previous HST photometry) that reside in the Galactic halo, where the second parameter effect is most pronounced. These globular clusters are among the least studied in the Galaxy and yet, from the perspective of the second parameter phenomenon, the most intriguing.

With the best available CMDs only reaching the vicinity of the main sequence turn off at present, the unique sensitivity and resolution of ACS-WFC will yield ages of unprecedented precision for these clusters. These data will provide us with new insight into the stellar populations present in the outer Galactic halo and the nature of the second parameter. The second parameter plays a critical role in our understanding of the formation and evolution of the Galaxy and the proposed observations will shed new light on this problem and these exceptional clusters.

ACS/WFC 11582

The Spatial Distribution of Radiation in the Complex ISM of Distant Ultraluminous Galaxies

A significant fraction of energy emitted by galaxies at redshifts when their stars were forming most vigorously, and when their blackholes were growing most powerfully emerges at far-infrared (IR) wavelengths. The fraction of this energy generated by the most extreme and luminous objects is also much larger than the equivalent fraction at optical wavelengths. Many of the most luminous far-IR sources have been located precisely and unambiguously using deep radio, Spitzer and optical observations, and have spectroscopic identifications using the largest ground-based telescopes. Surprisingly, however, the spectra of most of these heavily dust-enshrouded galaxies show prominent Lyman-alpha emission. We propose to observe five of the brightest examples at z~2-3 in re-activated ACS ramp filters, to resolve the spatial distribution of this line emission on fine kpc scales, in order to contrast and compare with the underlying ultraviolet (UV) continuum. Precise spectroscopic redshifts and the unique rest-UV resolution of HST are both essential to reveal the escape and generation of Lyman-alpha photons in the dusty ISM of these extreme galaxies. There is no other way to trace the detailed spatial distirbution of the most excited gas in a galactic wind, along with emission from less-massive star-forming galaxies in associated groups. The targets have available HST-resolution ground-based near-IR AO imaging and arcsec-scale images in CO from ground-based mm-wave interferometers, which provide context for spatial structure of evolved stars and the ISM. The interplay between restframe UV emission and the ISM in these galaxies has important consequences for understanding the origin of the prodigous luminosity of these systems, and for future observations with JWST and ALMA.


The Difference Between Neutral- and Ionized-Gas Metal Abundances in Local Star-Forming Galaxies with COS

The metallicity of galaxies and its evolution with redshift is of paramount importance for understanding galaxy formation. Abundances in the interstellar medium (ISM) are typically determined using emission-line spectroscopy of HII regions. However, since HII regions are associated with recent SF they may not have abundances typical for the galaxy as a whole. This is true in particular for star-forming galaxies (SFGs), in which the bulk of the metals may be contained in the neutral gas. It is therefore important to directly probe the metal abundances in the neutral gas. This can be done using absorption lines in the Far UV. We have developed techniques to do this in SFGs, where the absorption is measured for sightlines toward bright SF regions within the galaxy itself. We have successfully applied this technique to a sample of galaxies observed with FUSE. The results have been very promising, suggesting in I Zw 18 that abundances in the neutral gas may be up to 0.5 dex lower than in the ionized gas. However, the interpretation of the FUSE data is complicated by the very large FUSE aperture (30 arcsec), the modest S/N, and the limited selection of species available in the FUSE bandpass. The advent of COS on HST now allows a significant advance in all of these areas. We will therefore obtain absorption line spectroscopy with G130M in the same sample for which we already have crude constraints from FUSE. We will obtain ACS/SBC images to select the few optimal sightlines to target in each galaxy. The results will be interpreted through line-profile fitting to determine the metal abundances constrained by the available lines. The results will provide important new insights into the metallicities of galaxies, and into outstanding problems at high redshift such as the observed offset between the metallicities of Lyman Break Galaxies and Damped Lyman Alpha systems.

WFC3/UV 11556

Investigations of the Pluto System

We propose a set of high SNR observations of the Pluto system that will provide improved lightcurves, orbits, and photometric properties of Nix and Hydra. The key photometric result for Nix and Hydra will be a vastly improved lightcurve shape and rotation period to test if the objects are in synchronous rotation or not. A second goal of this program will be to retrieve a new epoch of albedo map for the surface of Pluto. These observations will also improve masses and in some case densities for the bodies in the Pluto system.


Star Formation in Nearby Galaxies

Star formation is a fundamental astrophysical process; it controls phenomena ranging from the evolution of galaxies and nucleosynthesis to the origins of planetary systems and abodes for life. The WFC3, optimized at both UV and IR wavelengths and equipped with an extensive array of narrow-band filters, brings unique capabilities to this area of study. The WFC3 Scientific Oversight Committee (SOC) proposes an integrated program on star formation in the nearby universe which will fully exploit these new abilities. Our targets range from the well-resolved R136 in 30 Dor in the LMC (the nearest super star cluster) and M82 (the nearest starbursting galaxy) to about half a dozen other nearby galaxies that sample a wide range of star-formation rates and environments. Our program consists of broad band multiwavelength imaging over the entire range from the UV to the near-IR, aimed at studying the ages and metallicities of stellar populations, revealing young stars that are still hidden by dust at optical wavelengths, and showing the integrated properties of star clusters. Narrow-band imaging of the same environments will allow us to measure star-formation rates, gas pressure, chemical abundances, extinction, and shock morphologies. The primary scientific issues to be addressed are: (1) What triggers star formation? (2) How do the properties of star-forming regions vary among different types of galaxies and environments of different gas densities and compositions? (3) How do these different environments affect the history of star formation? (4) Is the stellar initial mass function universal or determined by local conditions?

SpaceRef staff editor.