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Daily Report #5121
HUBBLE SPACE TELESCOPE - Continuing to Collect World Class Science
DAILY REPORT #5121 PERIOD COVERED: 5am June 18 - 5am June 21, 2010 (DOY 169/09:00z-172/09:00z) FLIGHT OPERATIONS SUMMARY: Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.) HSTARS: 12308 - GSAcq(1,2,1) at 169/23:17:55z acquired fine lock backup on FGS 1 following scan step limit exceeded on FGS 1. Observations possibly affected: ACS 52, proposal ID#11593. COMPLETED OPS REQUEST: (None) COMPLETED OPS NOTES: (None) SCHEDULED SUCCESSFUL FGS GSAcq 24 24 FGS REAcq 23 23 OBAD with Maneuver 18 18 SIGNIFICANT EVENTS: (None) OBSERVATIONS SCHEDULED: ACS/WFC 11995 CCD Daily Monitor (Part 2) 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 320 orbits (20 weeks) from 1 February 2010 to 20 June 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/UVIS 11924 WFC3/UVIS External and Internal CTE Monitor CCD detector Charge Transfer Inefficiency (CTI)-induced losses in photometry and astrometry will be measured using observations of the rich open cluster NGC6791 and with the EPER (Extended Pixel Edge Response) method using tungsten lamp flat field exposures. Although we do not expect to see CTE effects at the outset of Cycle 17, this CTE monitoring program is the first of a multi-cycle program to monitor and establish CTE-induced losses with time. We expect to measure CTE effects with a precision comparable to the ACS measurements. WFC3/UVIS 11912 UVIS Internal Flats This proposal will be used to assess the stability of the flat field structure for the UVIS detector throughout the 15 months of Cycle 17. The data will be used to generate on-orbit updates for the delta-flat field reference files used in the WFC3 calibration pipeline, if significant changes in the flat structure are seen. 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 3x3 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 11907 UVIS Cycle 17 Contamination Monitor The UV throughput of WFC3 during Cycle 17 is monitored via weekly standard star observations in a subset of key filters covering 200-600nm and F606W, F814W as controls on the red end. The data will provide a measure of throughput levels as a function of time and wavelength, allowing for detection of the presence of possible contaminants. 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). STIS/CC 11847 CCD Bias Monitor-Part 2 Monitor the bias in the 1x1, 1x2, 2x1, and 2x2 bin settings at gain=1, and 1x1 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. COS/NUV/FUV 11742 Probing HeII Reionization with GALEX-selected Quasar Sightlines and HST/COS We propose spectroscopic observations with COS of eight z~3 QSOs that we found to be bright in the far ultraviolet. Our aim is to study intergalactic absorption caused by the onset of the He II Lyman forest. Several lines of evidence suggest that helium reionization occurred at z~3. Understanding this process is critical for a complete picture of the intergalactic medium and its evolution; it also gives clues to hydrogen reionization at z6. The only direct means of assessing He II reionization is through far-UV observations of the He II Lyman alpha forest. Only 6 sightlines are known to date where this is feasible, despite extensive surveys. Our program is designed to double the number of available sightlines. To this effect, we cross-correlated all known z2.73 quasars with UV source lists from the GALEX satellite. The selected quasars were all significantly detected in the far UV by GALEX, and their UV colors are similar to those of already known quasars with transparent sightlines. Spectra obtained with COS will allow us to compile the first comprehensive sample of He II absorption spectra probing similar redshifts, enabling a systematic investigation of the He II reionization epoch and the spectral shape of the UV background. COS/NUV/FUV 11720 Detailed Analysis of Carbon Atmosphere White Dwarfs We propose to obtain UV spectra for the newly discovered white dwarf stars with a carbon- dominated atmosphere. Model calculations show that these stars emit most of their light in the UV part of the electromagnetic spectrum and that an accurate determination of the flux in this region is crucial for an accurate determination of the atmospheric parameters. It will also provide a unique opportunity to test the atomic data and broadening theory in stellar conditions never met before. This will play a primordial role in our path to understand the origin of these objects as well to obtain a better understanding of the evolution of stars in general. The principal objective we hope to achieve with these observations are 1) obtain accurate surface gravity/mass for these stars, 2) constrain/determine the abundance of other elements (O, He, Mg, Ne etc.), especially oxygen, 3) verify the accuracy of the various theoretical atomic data used in the model calculations, 4) understand the origin and evolution of carbon atmosphere white dwarfs, in particular whether progenitor stars as massive as 10.5 solar masses can produce white dwarfs, rather than supernovae. We propose to observe 5 objects chosen carefully to cover the range of observed properties among carbon atmosphere white dwarfs (effective temperature, surface gravity, abundance of hydrogen/helium and magnetic field). WFC3/IR 11708 Determining the Sub-stellar IMF in the Most Massive Young Milky Way Cluster, Westerlund 1 Despite over 50 years of active research, a key question in galactic astronomy remains unanswered: is the initial mass function (IMF) of stars and sub-stellar objects universal, or does it depend on initial conditions? The answer has profound consequences for the evolution of galaxies as well as a predictive theory of star formation. Work to date suggests that certain environments (high densities, e.g. Elmegreen 2004; low metallicity, e.g. Larson 2005) should produce a top-heavy IMF, and there are hints from unresolved star-bursts that this might be the case. Yet, there is no clear evidence for an IMF that differs from that characterizing the Galactic field stars in a resolved stellar population down to one solar mass. Westerlund 1 is the most massive young star cluster known in the Milky Way. With an estimated mass of 5x10^4 Msun, an age of 3-5 Myr, and located at a distance of 3-4 kpc, it presents a unique opportunity to test whether the IMF in such a cluster deviates from the norm well down into the brown dwarf regime. We propose WFC3 near-IR imaging to probe the IMF down to 40 Jupiter masses. The data will enable use to: 1) provide a stringent test of the universality of the IMF under conditions approximating those of star-bursts; 2) search for primordial or dynamic mass segregation in the clusters; and 3) assess whether the cluster is likely to remain bound (as a massive open cluster) or disperse into the field. We will obtain images in the F125W, F160W, and F139M filters. The F139M filter covers a strong water absorption feature and the color F125W/F139M is a powerful temperature diagnostic in the range 2800-4000 K. This information will enable us to: a) confirm membership for low mass stars suspected on the basis of their position in the color-magnitude diagram; b) place the members in the HR diagram; and c) estimate the masses and ages of cluster members for low-mass stars and sub-stellar objects. This new capability offered with the WFC3 (through a novel combination of filter complement, high spatial resolution, and large field of view) will enable us to make a fundamental test of whether the IMF is universal on a unique resolved stellar population, as well as assess the clusters structure, dynamics, and ultimate fate. WFC3/UVIS/IR 11702 Search for Very High-z Galaxies with WFC3 Pure Parallel WFC3 will provide an unprecedented probe to the early universe beyond the current redshift frontier. Here we propose a pure parallel program using this new instrument to search for Lyman-break galaxies at 6.5z8.8 and to probe the epoch of reionization, a hallmark event in the history of the early universe. We request 200 orbits, spreading over 30 ~ 50 high Galactic latitude visits (|b|20deg) that last for 4 orbits and longer, resulting a total survey area of about 140~230 square arcminute. Based on our understanding of the new HST parallel observation scheduling process, we believe that the total number of long-duration pure parallel visits in Cycle 17 should be sufficient to accommodate our program. We waive all proprietary rights to our data, and will also make the enhanced data products public in a timely manner. (1) We will use both the UVIS and the IR channels, and do not need to seek optical data from elsewhere. (2) Our program will likely triple the size of the probable candidate samples at z~7 and z~8, and will complement other targeted programs aiming at the similar redshift range. (3) Being a pure parallel program, our survey will only make very limited demand on the scarce HST resources. More importantly, as the pure parallel pointings will be at random sight-lines, our program will be least affected by the bias due to the large scale structure ("cosmic variance"). (4) We aim at the most luminous LBG population, and will address the bright-end of the luminosity function at z~8 and z~7. We will constrain the value of L* in particular, which is critical for understanding the star formation process and the stellar mass assembly history in the first few hundred million years of the universe. (5) The candidates from our survey, most of which will be the brightest ones that any surveys would be able to find, will have the best chance to be spectroscopically confirmed at the current 8--10m telescopes. (6) We will also find a large number of extremely red, old galaxies at intermediate redshifts, and the fine spatial resolution offered by the WFC3 will enable us constrain their formation history based on the study of their morphology, and hence shed light on their connection to the very early galaxies in the universe. COS/NUV/FUV 11698 The Structure and Dynamics of Virgo's Multi-Phase Intracluster Medium The dynamical flows of the intracluster medium (ICM) are largely unknown. We propose to map the spatial and kinematic distribution of the warm ICM of the nearby Virgo cluster using the Cosmic Origins Spectrograph. 15 sightlines at a range of impact parameters within the virial radius of the cluster (0.2 - 1.7 Mpc) will be probed for Lyman-alpha absorption and the data compared to blind HI, dust and x-ray surveys to create a multi-phase map of the cluster's ICM. Absorption line sightlines are commonly 40-100 kpc from a galaxy, allowing the flow of baryons between galaxies and the ICM to be assessed. The velocity distribution of the absorbers will be directly compared to simulations and used to constrain the turbulent motions of the ICM. This proposal will result in the first map of a cluster's warm ICM and provide important tests for our theoretical understanding of cluster formation and the treatment of gas cooling in cosmological simulations. 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 z6 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 a (1) Detect Lya in ~100 galaxies with z5.6 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 0.5z1.8 to measure the evolution of the extinction-corrected star formation density across the peak epoch of star formation. This is over an order-of-magnitude improvement in the current statistics, from the NICMOS Parallel grism survey. (5) Trace ``cosmic downsizing" from 0.5z2.2; and (6) Estimate the evolution in reddening and metallicty in star- forming galaxies and measure the evolution of the Seyfert population. For hundreds of spectra we will be able to measure one or even two line pair ratios -- in particular, the Balmer decrement and [OII]/[OIII] are sensitive to gas reddening and metallicity. As a bonus, the G102 grism offers the possibility of detecting Lya emission at z=7-8.8. To identify single-line Lya emitters, we will exploit the wide 0.8--1.9um wavelength coverage of the combined G102+G141 spectra. All [OII] and [OIII] interlopers detected in G102 will be reliably separated from true LAEs by the detection of at least one strong line in the G141 spectrum, without the need for any ancillary data. We waive all proprietary rights to our data and will make high-level data products available through the ST/ECF. COS/FUV 11687 SNAPing Coronal Iron This is a Snapshot Survey to explore two forbidden lines of highly ionized iron in late-type coronal sources. Fe XII 1349 (T~ 2 MK) and Fe XXI 1354 (T~ 10 MK) -- well known to Solar Physics -- have been detected in about a dozen cool stars, mainly with HST/STIS. The UV coronal forbidden lines are important because they can be observed with velocity resolution of better than 15 km/s, whereas even the state-of-the-art X-ray spectrometers on Chandra can manage only 300 km/s in the kilovolt band where lines of highly ionized iron more commonly are found. The kinematic properties of hot coronal plasmas, which are of great interest to theorists and modelers, thus only are accessible in the UV at present. The bad news is that the UV coronal forbidden lines are faint, and were captured only in very deep observations with STIS. The good news is that 3rd-generation Cosmic Origins Spectrograph, slated for installation in HST by SM4, in a mere 25 minute exposure with its G130M mode can duplicate the sensitivity of a landmark 25-orbit STIS E140M observation of AD Leo, easily the deepest such exposure of a late-type star so far. Our goal is to build up understanding of the properties of Fe XII and Fe XXI in additional objects beyond the current limited sample: how the lineshapes depend on activity, whether large scale velocity shifts can be detected, and whether the dynamical content of the lines can be inverted to map the spatial morphology of the stellar corona (as in "Doppler Imaging''). In other words, we want to bring to bear in the coronal venue all the powerful tricks of spectroscopic remote sensing, well in advance of the time that this will be possible exploiting the corona's native X-ray radiation. The 1290-1430 band captured by side A of G130M also contains a wide range of key plasma diagnostics that form at temperatures from below 10, 000 K (neutral lines of CNO), to above 200, 000 K (semi-permitted O V 1371), including the important bright multiplets of C II at 1335 and Si IV at 1400; yielding a diagnostic gold mine for the subcoronal atmosphere. Because of the broad value of the SNAP spectra, beyond the coronal iron project, we waive the normal proprietary rights. COS/FUV 11686 The Cosmological Impact of AGN Outflows: Measuring Absolute Abundances and Kinetic Luminosities AGN outflows are increasingly invoked as a major contributor to the formation and evolution of supermassive black holes, their host galaxies, the surrounding IGM, and cluster cooling flows. Our HST/COS proposal will determine reliable absolute chemical abundances in six AGN outflows, which influences several of the processes mentioned above. To date there is only one such determination, done by our team on Mrk 279 using 16 HST/STIS orbits and 100 ksec of FUSE time. The advent of COS and its high sensitivity allows us to choose among fainter objects at redshifts high enough to preclude the need for FUSE. This will allow us to determine the absolute abundances for six AGN (all fainter than Mrk 279) using only 40 HST COS orbits. This will put abundances studies in AGN on a firm footing, an elusive goal for the past four decades. In addition, prior FUSE observations of four of these targets indicate that it is probable that the COS observations will detect troughs from excited levels of C III. These will allow us to measure the distances of the outflows and thereby determine their kinetic luminosity, a major goal in AGN feedback research. We will use our state of the art column density extraction methods and velocity-dependent photoionization models to determine the abundances and kinetic luminosity. Previous AGN outflow projects suffered from the constraints of deciding what science we could do using ONE of the handful of bright targets that were observable. With COS we can choose the best sample for our experiment. As an added bonus, most of the spectral range of our targets has not been observed previously, greatly increasing the discovery phase space. WFC3/ACS/IR 11677 Is 47 Tuc Young? Measuring its White Dwarf Cooling Age and Completing a Hubble Legacy With this proposal we will firmly establish the age of 47 Tuc from its cooling white dwarfs. 47 Tuc is the nearest and least reddened of the metal-rich disk globular clusters. It is also the template used for studying the giant branches of nearby resolved galaxies. In addition, the age sensitive magnitude spread between the main sequence turnoff and horizontal branch is identical for 47 Tuc, two bulge globular clusters and the bulge field population. A precise relative age constraint for 47 Tuc, compared to the halo clusters M4 and NGC 6397, both of which we recently dated via white dwarf cooling, would therefore constrain when the bulge formed relative to the old halo globular clusters. Of particular interest is that with the higher quality ACS data on NGC 6397, we are now capable with the technique of white dwarf cooling of determining ages to an accuracy of +/-0.4 Gyrs at the 95% confidence level. Ages derived from the cluster turnoff are not currently capable of reaching this precision. The important role that 47 Tuc plays in galaxy formation studies, and as the metal-rich template for the globular clusters, makes the case for a white dwarf cooling age for this metal-rich cluster compelling. Several recent analyses have suggested that 47 Tuc is more than 2 Gyrs younger than the Galactic halo. Others have suggested an age similar to that of the most metal poor globular clusters. The current situation is clearly uncertain and obviously a new approach to age dating this important cluster is required. With the observations of 47 Tuc, this project will complete a legacy for HST. It will be the third globular cluster observed for white dwarf cooling; the three covering almost the full metallicity range of the cluster system. Unless JWST has its proposed bluer filters (700 and 900 nm) this science will not be possible perhaps for decades until a large optical telescope is again in space. Ages for globular clusters from the main sequence turnoff are less precise than those from white dwarf cooling making the science with the current proposal truly urgent. ACS/WFC3 11670 The Host Environments of Type Ia Supernovae in the SDSS Survey The Sloan Digital Sky Survey Supernova Survey has discovered nearly 500 type Ia supernovae and created a large, unique, and uniform sample of these cosmological tools. As part of a comprehensive study of the supernova hosts, we propose to obtain Hubble ACS images of a large fraction of these galaxies. Integrated colors and spectra will be measured from the ground, but we require high-resolution HST imaging to provide accurate morphologies and color information at the site of the explosion. This information is essential in determining the systematic effects of population age on type Ia supernova luminosities and improving their reliability in measuring dark energy. Recent studies suggest two populations of type Ia supernovae: a class that explodes promptly after star-formation and one that is delayed by billions of years. Measuring the star-formation rate at the site of the supernova from colors in the HST images may be the best way to differentiate between these classes. WFC3/UVIS 11657 The Population of Compact Planetary Nebulae in the Galactic Disk We propose to secure narrow- and broad-band images of compact planetary nebulae (PNe) in the Galactic Disk to study the missing link of the early phases of post-AGB evolution. Ejected AGB envelopes become PNe when the gas is ionized. PNe expand, and, when large enough, can be studied in detail from the ground. In the interim, only the HST capabilities can resolve their size, morphology, and central stars. Our proposed observations will be the basis for a systematic study of the onset of morphology. Dust properties of the proposed targets will be available through approved Spitzer/IRS spectra, and so will the abundances of the alpha- elements. We will be able thus to explore the interconnection of morphology, dust grains, stellar evolution, and populations. The target selection is suitable to explore the nebular and stellar properties across the galactic disk, and to set constraints on the galactic evolutionary models through the analysis of metallicity and population gradients. ACS/WFC 11655 Dynamics of the Galactic Bulge/bar We request second-epoch ACS observations of four star fields in the Galactic bar. These will allow us to measure proper motions for tens of thousands of stars well below the turnoff, to construct a dynamical model for the bulge/bar (in combination with data already in hand from other HST fields, and from VLT spectroscopy), and hence to take a unique look at the internal dynamical structure of the central regions of our Galaxy. By relating the kinematics with stellar population we can elucidate the formation history of the bulge and bar, and their relation to the surrounding Galactic disk. This is a resubmission of an approved Cycle 15 proposal that was hit by the ACS malfunction. STIS/CC/MA 11609 NGC 6266: The Smoking Gun of Intermediate-Mass Black Holes in Galactic Globular Clusters? The existence of intermediate-mass black holes (IMBHs) in star clusters has been predicted by a variety of theoretical arguments and, more recently, by several large, realistic sets of collisional N-body simulations. Establishing their presence or absence at the centers of globular clusters would profoundly impact our understanding of problems ranging from the formation and long-term dynamical evolution of stellar systems, to the nature of the seeds and the growth mechanisms of the supermassive black holes (BHs) that inhabit the centers of most large, luminous galaxies. Observationally, the unambiguous signature of a massive central BH would be the discovery of central, unresolved X-ray or radio emission that is not consistent with more common stellar-mass accreting objects or pulsars. Yet, due to the largely uncertain details of accretion modeling, a precise mass determination of a central BH must necessarily come from stellar dynamics. This goal has not been achieved to date at the centers of Galactic globular clusters because of lack of adequate data as well as the use of too simplified methods of analysis. This situation can be overcome today through the combination of HST proper-motion measurements and state-of-the-art dynamical models specifically designed to take full advantage of this type of dataset. In this project, we will use two HST orbits to obtain another epoch of observations of NGC 6266. This cluster has photometric and structural properties that are consistent with current theoretical expectations for a cluster harboring an IMBH. Even more importantly, it is the only Galactic globular cluster for which there exists a detection of radio emission coincident with the cluster's core, and with a flux density that appears to rule out a stellar or binary origin. The goal of our project is to obtain proper motion measurements to either confirm an IMBH in this cluster and measure its mass, or to set limits to its mass and existence. ACS/WFC3 11593 Dynamical Masses of the Coolest Brown Dwarfs T dwarfs are excellent laboratories to study the evolution and the atmospheric physics of both brown dwarfs and extrasolar planets. To date, only a single T dwarf binary has a dynamical mass determination, and more are sorely needed. The prospects of measuring more dynamical masses over the next decade are limited to 6 known short-period T dwarf binaries. We propose here to obtain Long-Term HST/ACS monitoring for the 3 of the 6 binaries which cannot be resolved with AO from the ground. Upon completion, our program will substantially increase the number of T dwarf dynamical mass measurements and thereby provide key benchmarks for testing theoretical models of ultracool objects. COS/FUV/STIS/CCD/MA1 11592 Testing the Origin(s) of the Highly Ionized High-Velocity Clouds: A Survey of Galactic Halo Stars at z3 kpc Cosmological simulation predicts that highly ionized gas plays an important role in the formation and evolution of galaxies and their interplay with the intergalactic medium. The NASA HST and FUSE missions have revealed high-velocity CIV and OVI absorption along extragalactic sightlines through the Galactic halo. These highly ionized high-velocity clouds (HVCs) could cover 85% of the sky and have a detection rate higher than the HI HVCs. Two competing, equally exciting, theories may explain the origin of these highly ionized HVCs: 1) the "Galactic" theory, where the HVCs are the result of feedback processes and trace the disk-halo mass exchange, perhaps including the accretion of matter condensing from an extended corona; 2) the "Local Group" theory, where they are part of the local warm-hot intergalactic medium, representing some of the missing baryonic matter of the Universe. Only direct distance determinations can discriminate between these models. Our group has found that some of these highly ionized HVCs have a Galactic origin, based on STIS observations of one star at z5.3 kpc. We propose an HST FUV spectral survey to search for and characterize the high velocity NV, CIV, and SiIV interstellar absorption toward 24 stars at much larger distances than any previous searches (4d21 kpc, 3|z|13 kpc). COS will provide atomic to highly ionized species (e.g.,OI, CII, CIV, SiIV) that can be observed at sufficient resolution (R~22, 000) to not only detect these highly ionized HVCs but also to model their properties and understand their physics and origins. This survey is only possible because of the high sensitivity of COS in the FUV spectral range. WFC3/IR 11591 Are Low-Luminosity Galaxies Responsible for Cosmic Reionization? Our group has demonstrated that massive clusters, acting as powerful cosmic lenses, can constrain the abundance and properties of low-luminosity star-forming sources beyond z~6; such sources are thought to be responsible for ending cosmic reionization. The large magnification possible in the critical regions of well-constrained clusters brings sources into view that lie at or beyond the limits of conventional exposures such as the UDF. We have shown that the combination of HST and Spitzer is particularly effective in delivering the physical properties of these distant sources, constraining their mass, age and past star formation history. Indirectly, we therefore gain a valuable glimpse to yet earlier epochs. Recognizing the result (and limitations) of blank field surveys, we propose a systematic search through 10 lensing clusters with ACS/F814W and WFC3/[F110W+F160W] (in conjunction with existing deep IRAC data). Our goal is to measure with great accuracy the luminosity function at z~7 over a range of at least 3 magnitude, based on the identification of about 50 lensed galaxies at 6.5z8. Our survey will mitigate cosmic variance and extend the search both to lower luminosities and, by virtue of the WFC3/IRAC combination, to higher redshift. Thanks to the lensing amplification spectroscopic follow-up will be possible and make our findings the most robust prior to the era of JWST and the ELTs. STIS/CCD/MA2 11568 A SNAPSHOT Survey of the Local Interstellar Medium: New NUV Observations of Stars with Archived FUV Observations We propose to obtain high-resolution STIS E230H SNAP observations of MgII and FeII interstellar absorption lines toward stars within 100 parsecs that already have moderate or high-resolution far-UV (FUV), 900-1700 A, observations available in the MAST Archive. Fundamental properties, such as temperature, turbulence, ionization, abundances, and depletions of gas in the local interstellar medium (LISM) can be measured by coupling such observations. Due to the wide spectral range of STIS, observations to study nearby stars also contain important data about the LISM embedded within their spectra. However, unlocking this information from the intrinsically broad and often saturated FUV absorption lines of low-mass ions, (DI, CII, NI, OI), requires first understanding the kinematic structure of the gas along the line of sight. This can be achieved with high resolution spectra of high-mass ions, (FeII, MgII), which have narrow absorption lines, and can resolve each individual velocity component (interstellar cloud). By obtaining short (~10 minute) E230H observations of FeII and MgII, for stars that already have moderate or high- resolution FUV spectra, we can increase the sample of LISM measurements, and thereby expand our knowledge of the physical properties of the gas in our galactic neighborhood. STIS is the only instrument capable of obtaining the required high resolution data now or in the foreseeable future. WFC3/UVIS 11565 A Search for Astrometric Companions to Very Low-Mass, Population II Stars We propose to carry out a Snapshot search for astrometric companions in a subsample of very low-mass, halo subdwarfs identified within 120 parsecs of the Sun. These ultra-cool M subdwarfs are local representatives of the lowest-mass H burning objects from the Galactic Population II. The expected 3-4 astrometric doubles that will be discovered will be invaluable in that they will be the first systems from which gravitational masses of metal-poor stars at the bottom of the main sequence can be directly measured. COS/NUV/FUV 11555 Transition Region and Chromospheric Activity on Low Metallicity Arcturus Moving Group `Alien' Dwarfs How does low metallicity affect the heating and resultant temperature structure of the chromospheres, transition regions, and coronae of old solar-like dwarf stars? The Arcturus Moving Group is very likely a remnant of the merger of a dwarf galaxy with the Milky Way Galaxy in the distant (~ 7- 8 Gyr) past. This kinematically distinct group has members that are located very close to the Sun, allowing study of stellar activity on very old, low metallicity stars that typically would not be possible. We propose to obtain COS G140L spectra of four dwarf star members of the Arcturus Moving Group to measure the fluxes of their transition region and upper chromospheric emission lines and to investigate the effects of low metallicity on the outer atmospheric radiative losses and temperature structure. Our targets have metallicities of ~ 20% solar or less, spectral types F9 - M4, and are at distances less than 25 pc from the Sun. COS is the only UV spectrograph that is capable of registering the FUV spectra of these stars in a reasonable number of HST orbits. |
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