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NASA NTRS1997

Crew Member Interface with Space Station Furnace Facility

The Space Station Furnace Facility (SSFF) is a facility located in the International Space Station United States Laboratory (ISS US Lab) for materials research in the microgravity environment. The SSFF will accommodate basic research, commercial applications, and studies of phenomena of metals and alloys, electronic and photonic materials, and glasses and ceramics. To support this broad base of research requirements, the SSFF will operate, regulate, and support a variety of Experiment Modules (EMs). To meet station requirements concerning the microgravity level needed for experiments, station is providing an active vibration isolation system, and SSFF provides the interface. SSFF physically consists of a Core Rack and two instrument racks (IRs) that occupy three adjacent ISS US Lab rack locations within the International Space Station (ISS). All SSFF racks are modified International Standard Payload Racks (ISPR). SSFF racks will have a 50% larger pass through area on the lower sides than ISPRs to accommodate the many rack to rack interconnections. The Instrument Racks are further modified with lowered floors and an additional removable panel (15" x 22") on top of the rack for access if needed. The Core Rack shall contain all centralized Core subsystems and ISS subsystem equipment. The two Instrument Racks shall contain the distributed Core subsystem equipment, ISS subsystem equipment, and the EMs. The Core System, which includes the Core Rack, the IR structures, and subsystem components located in the IRs serves as the central control and management for the IRs and the EMs. The Core System receives the resources provided by the International Space Station (ISS) and modifies, allocates, and distributes these resources to meet the operational requirements of the furnace. The Core System is able to support a total of four EMs and can control, support, and activate/deactivate the operations of two EMs, simultaneously. The IRs can be configured to house two small EMs or one tall vertical EM, and serve as the interface between the Core and the respective EM. The Core Rack and an adjacent Instrument Rack (containing one or more furnaces) will be delivered to the ISS in one launch. This is Integrated Configuration One (ICI). The Core Rack and IRI will be passive during transport in the Mini Pressurized Logistics Module (MPLM): Any subsequent EMs to operate within IRI are installed on-orbit. The second IR (containing one or more furnaces) is delivered to ISS on a subsequent launch which will establish Integrated Configuration Two (IC2). Additional integrated configurations will be established with the replacement of EMs or Instrument Racks.

Cash, Martha B.↗
NASA NTRS2000

Photodissociation Regions

The interstellar medium of galaxies is the reservoir out of which stars are born and into which stars inject newly created elements as they age. The physical properties of the interstellar medium are governed in part by the radiation emitted by these stars. Far-ultraviolet (6 eV< hNu < 13.6 eV) photons from massive stars dominate the heating and influence the chemistry of the neutral atomic gas and much of the molecular gas in galaxies. Predominantly neutral regions of the interstellar medium in which the heating and chemistry are regulated by far ultraviolet photons are termed Photodissociation Regions (PDRs). These regions are the origin of most of the non-stellar infrared (IR) and the millimeter and submillimeter CO emission from galaxies. The importance of PDRs has become increasingly apparent with the advances in IR and submillimeter astronomy. The IR emission from PDRs includes fine structure lines of C, C(+) and O; rovibrational lines of H2; rotational lines of CO; broad mid-IR features of polycyclic aromatic hydrocarbons; and a luminous underlying IR continuum from interstellar dust. The transition of H to H2 and C(+) to CO occurs within PDRs. Comparison of observations with theoretical models of PDRs enables one to determine the density and temperature structure, the elemental abundances, the level of ionization, and the radiation field. PDR models have been applied to interstellar clouds near massive stars, planetary nebulae, red giant outflows, photoevaporating planetary disks around newly formed stars, diffuse clouds, the neutral intercloud medium, and molecular clouds in the interstellar radiation field-in summary, much of the interstellar medium in galaxies. Theoretical PDR models explain the observed correlations of the [CII] 158, micrometers with the CO J=1-0 emission, the CO J=1-0 luminosity with the interstellar molecular mass, and the [CII] 158 micrometers plus [OI] 63 micrometers luminosity with the IR continuum luminosity. On a more global scale, PDR models predict the existence of two stable neutral phases of the interstellar medium, elucidate the formation and destruction of star-forming molecular clouds, and suggest radiation-induced feedback mechanisms that may regulate star formation rates and the column density of gas through giant molecular clouds.

Hollenbach, David J.↗
NASA NTRS2002

Cometary Science After Hale-Bopp

Comets and the chondritic porous interplanetary dust particles (CP IDPs) that they shed in their comae are reservoirs of primitive solar nebula materials. The high porosity and fragility of cometary grains and CP IDPs, and anomalously high deuterium contents of pyroxene-rich CP IDPs imply these aggregate particles contain significant interstellar grain components. Spectrophotometry of comets at thermal IR wavelengths (3-40 microns) reveal the presence of a warm (near-IR) featureless emission modeled by amorphous carbon grains, and mid-IR and far-IR broad and narrow resonances modeled by chondritic (50% Fe and 50% Mg) amorphous and Mg-rich crystalline silicate minerals, respectively. Cometary amorphous silicate resonances are well matched by IR spectra of CP IDPs dominated by 0.1 micron spherules of Glass with Embedded Metal and Sulfides (GEMS) that are thought to be the interstellar Fe-bearing amorphous silicates produced in the cooling outflows of Asymptotic Giant Branch (AGB) stars. Acid-etched microtomed CP IDP samples, however, show that both the carbon phase (aliphatic) and the amorphous silicate phase (Mg-rich) are not optically absorbing while the embedded Fe nanoparticles make the IDPs dark. The CP IDPs suggest either significant processing has occurred in the ISM or that the AGB amorphous silicates have Mg-rich stoichiometry and possibly grew on Fe particle condensates. Cometary crystalline silicate resonances are well matched by IR spectra of laboratory submicron Mg-rich olivine crystals, [Mg(sub y),Fe(sub 1-y)]2SiO4 with y/ge0.85, and in the case of Hale-Bopp at r(sub h) less than or equal to approx. 1.5 AU, by Mg-rich pyroxene crystals, [Mg(sub x),Fe(sub 1-x)]SiO3 with x/ge0.85. While a fraction of AGB stardust (less than or equal to 15%) are Mg-rich crystals, this interstellar star dust component is insufficient to account for the deduced abundance of crystalline minerals in comet dust. An insufficient source of ISM Mg-rich crystals leads to the inference that Mg-rich crystals in comets may be hot, early solar nebula condensates that traveled large radial distances out to the comet-forming zone.

Wooden, Diane H.↗
NASA NTRS1998

Titania and Oberon: Surface Composition from New Near-Infrared Observations and Reflectance Models

Here we report the combination of new near-ir spectra (1.45-2.48 micrometers), of Titania and Oberon obtained in September 1995 at a resolving power of approx. 800, with older near-ir observations (0.5- 1.44 micrometers), and recent UV (0.22-0.48 micrometers) observations obtained with HST. Previous interpretations suggest these surfaces are chiefly composed of water ice and varying amounts of spectrally neutral material. The new near-ir data provide the opportunity to search for absorption bands that could be attributable to surface materials other than water ice and because the combined spectra include such a broad wavelength region, to undertake improved models of water and neutral components on the surface. The calculated near-ir geometric albedos clearly exhibit three broad spectral features. Two (1.52- & 2.05 micrometer) have previously been used to demonstrate the presence of water ice on these satellites. The third (approx. 1.65 micrometer), suggests the presence of hexagonal water ice at low temperatures, and may provide a mechanism of estimating the surface temperature. There is no spectral evidence for ices of CO2, CO, NH3 or CH4. At UV wavelengths there is a broad absorption near 0.27-0.28 micrometer previously attributed to OH formed by magnetospheric-surface interactions and retained at the low surface temperatures of these satellites. Surface components used in a Hapke scattering models include values for a combination of irradiated water ice in the UV and hexagonal water ice at 100k in the near-ir (IR), amorphous carbon (AC), and tholins (T) (produced from gas and solid). Results of these models suggest the surfaces of Titania/Oberon are composed of IW (-77/52%) with AC the next most abundant component (approx. 19/52%) and finally T (approx. 4/7%).

Roush, Ted L.↗
NASA NTRS2002

Infrared Emission From Interstellar PAHs, New Probes of the Interstellar Medium

Tremendous strides have been made in the understanding of interstellar material over the past twenty years thanks to significant, parallel developments in two closely related areas: observational IR astronomy and laboratory astrophysics. Twenty years ago the composition of interstellar dust was largely unknown and the notion of abundant, gas phase, polycyclic aromatic hydrocarbons (PAHs) anywhere in the interstellar medium (ISM) considered impossible. Today the dust composition of the diffuse and dense ISM is reasonably well constrained and the spectroscopic case for interstellar PAHs, impossibly large molecules by early interstellar chemistry standards, is very strong. PAH spectral features are now being used as new probes of the ISM. PAH ionization states reflect the ionization balance of the medium while PAH size and structure reflect the energetic and chemical history of the medium. Aromatic carbon-rich materials ranging in size from PAHs and PAH nanoclusters, to sub-micron and micron-sized dust grains represent an important component of the ISM. These species: (1) dominate the heating and cooling of interstellar clouds via energetic photoelectron ejection and infrared (IR) emission; (2) moderate the ionization balance in photodissociation regions and molecular clouds; (3) moderate the composition of the gas phase and play an important role in determining the chemistry of the ISM; (4) contribute to the interstellar extinction in the near IR, visible, and UV spectral regions; and (5) convert UV, visible, and near-IR radiation to mid- and far-IR radiation in the ISM and, as such, are responsible for the well known, widespread family of mid-IR emission features with major components near 3.3, 6.2, 7.7, 8.6, and 11.3 microns.

Hudgins, D. M.↗
NASA NTRS2003

MGS/TES-Odyssey/THEMIS-IR Analysis of Localized Low Albedo Regions in Valles Marineris

We are conducting a systematic analysis of small (approximately 10's of km), localized regions in Valles Marineris that display significant albedo differences relative to their surroundings. This analysis is based on a finding that the locations of the hematite deposits identified by [1] in the interior layered deposits of Valles Marineris typically coincide with regions having a low MGS/TES visible bolometric albedo [1,2]. Until recently, it was difficult to identify the morphology or geologic context of the regions containing the hematite deposits. However, with the recent advent of high-resolution (1/128 /pixel) MOLA grided topography and Mars Odyssey s THEMIS-IR instrument, it has been possible to better understand the morphologic context of TES observations. This analysis combines the use of PDS-released data from the MGS/TES visible bolometer and infrared spectrometer, the Odyssey/THEMIS Infrared imager, and MOLA grided topography. First, the TES infrared bolometer is used to identify regions of interesting albedo variability, and is overlaid on Viking controlled photomosaics for context. THEMIS-IR data, in conjunction with MOLA topography, is then used to: 1) identify the context and morphology of the area; and 2) identify spectrally unique regions at the km scale. In preparation for the latter, all the THEMIS planes are coregistered using an autocorrelation routine, the data are converted to brightness temperature and then each plane is normalized to the brightness temperature of the third plane (1261 cm-1). We then perform a 3-band search for color variations and a Principle Components Analysis (PCA) of the 8 unique bands in the THEMIS-IR dataset. Any variability is then investigated using both THEMIS-IR and TES spectra of the same regions. In both cases, the spectra are ratioed to near-simultaneously acquired spectra of adjacent or "average" regions that do not show this albedo variation, therefore allowing us to identify spectral variability unique to the area of interest. This procedure also allows us to account for calibration problems in THEMIS-IR data, and for any atmospheric effects in both the THEMIS-IR and the TES data.

E Z Noe Dobrea↗
NASA NTRS2003

Analysis of Properties of the North Polar Layered Deposits: THEMIS Data in Context of MGS Data

One of the many questions of Martian exploration is to uncover the history of Mars, through analysis of the polar layered deposits (PLD). Martian polar ice caps hold most of the exposed water on the surface on Mars and yet their history and physical processed involved in their formation are unclear. We will attempt to contribute to our knowledge of the composition and stratigraphy of the polar deposits. In this work we present the latest imaging data acquired by the Mars Odyssey THermal EMission Imaging System (THEMIS) and place it into context of the Mars Global Surveyor (MGS) data. THEMIS provides capabilities for imaging in both thermal IR and visible color wavelengths. These observations are affected by atmospheric scattering and topography. The Mars Orbiter Laser Altimeter (MOLA) and Thermal Emission Spectrometer (TES) instruments on board of the MGS spacecraft can provide context information for THEMIS data. Of particular interest are Mars Orbiter Camera (MOC) images, which provide high resolution data. We are primarily interested in the seasonal evolution of ice cap temperatures during the first northern summer of THEMIS observations. Morphology, stratigraphy and composition of the layered deposits can be addressed by THEMIS VIS color images, along with MOC high resolution data and MOLA Digital Elevation Models (DEM). This work is intentionally descriptive. Based on the knowledge obtained by the orbiting spacecraft and described here, we will attempt to expose major directions for modeling and further understanding of of the physical processes involved in the formation of the polar layered terrain 2 Available data 2.1 THEMIS IR The THEMIS IR camera has 10 bands from 6 to 15 m. Due to to signal-to-noise restrictions the most useful band for polar observations is band 9 (12.57 m ). Band 10 (14.88 m ) data can be used for atmospheric calibration. An example of seasonal evolution observed by the THEMIS IR subsystem is shown in Figure 1. We have projected all IR images, covering a small area near 86N and 90E into a polar stereographic projection and then sampled time dimension in order to look at temperature evolution over the course of the summer. We are plotting averaged temperature data over two 1km2 regions of interest: layered material inside the trough and the surface of the residual ice cap. High resolution THEMIS IR data allows us to distinguish properties of bulk of layered terrain and ice. We were not able yet to distinguish properties of individual layers.

A B Ivanov↗
NASA NTRS2004

Upcoming and Future Missions in the Area of Infrared Astronomy: Spacecraft and Ground-based Observations

The IRIS instrument on the Voyager spacecrafts made major discoveries with regard to the giant planets, their moons and rings and paved the way for future infrared observations for planetary missions within our solar system. The CIRS instrument of Cassini with much greater spectral-spatial resolution and sensitivity than that provided by IRIS is now rapidly approaching the Saturnian system with orbit insertion on July 1, 2004, for which CIRS is expected to provide an order of magnitude advance beyond that provided by IRIS. The Mars program is also presently dominated by infrared observations in the near to mid-infrared spectral bands for missions such as Mars Global Surveyor and its TES instrument and Odyssey with its THEMIS instrument. In the case of Earth science we have such missions as TIMED, which makes infrared observations of the thermosphere using the SABER instrument. With the newly formed New Frontiers Program we have the opportunity for $650M missions such as Kuiper Belt-Pluto Explorer and Jupiter Polar Orbiter with Probes. Under the Flagship line, once per decade, we have the opportunity for $1B missions for which Europa is presently being considered; for this mission infrared measurements could look for hot spots within the maze of cracks and faults on Europa s surface. On Kuiper Belt- Pluto there is an imaging near-IR spectrometer called LEISA. Another mission on the horizon is Titan Orbiter Aerorover Mission (TOAM) for which there is planned a state-of-art version of CIRS called TIRS on the orbiter that will map out the atmospheric composition with unprecedented wavelength coverage and spectral-spatial resolution. This instrument will also provide temperature maps of the surface of Titan to look for hot spots where life may form. On the same mission there will be a descent imager on the Aerorover (i.e., balloon) similar to that provided by LEISA on the Pluto mission to provide compositional-topographical maps of Titan s surface. Other future mission will also be discussed. Improved thermal detectors could have important applications in solar physics, specifically in the detection of far-IR synchrotron emission from energetic electrons in solar flares. For infrared astronomy we have missions like SIRTF and JWST, which will cover the spectral range from near-IR to far-IR in the search and probing of both new and old planetary systems in our galaxy and the measurement of the most distant galaxies of our universe. SIRTF is scheduled to be launched in August 2003, while JWST will be launched next decade. Another mission is TPF, which will use interferometer techniques at infrared wavelengths to search for planetary systems beyond 2010. With regard to ground based telescopes we have, for example, the twin 10 meter Keck telescopes and the IRTF telescope at Mauna Kea. The Keck telescopes are presently using interferometer techniques. Over the next several decades there are plans for 50 meter to 200 meter telescopes providing near-IR to far-IR measurements with the eventual plan to combine all telescopes using interferometer techniques to provide unprecedented spectral-spatial resolution and sensitivity.

Sittler, E. C., Jr.↗
NASA NTRS2004

The Far Infrared Lines of OH as Molecular Cloud Diagnostics

Future IR missions should give some priority to high resolution spectroscopic observations of the set of far-IR transitions of OH. There are 15 far-IR lines arising between the lowest eight rotational levels of OH, and ISO detected nine of them. Furthermore, ISO found the OH lines, sometimes in emission and sometimes in absorption, in a wide variety of galactic and extragalactic objects ranging from AGB stars to molecular clouds to active galactic nuclei and ultra-luminous IR galaxies. The ISO/LWS Fabry-Perot resolved the 119 m doublet line in a few of the strong sources. This set of OH lines provides a uniquely important diagnostic for many reasons: the lines span a wide wavelength range (28.9 m to 163.2 m); the transitions have fast radiative rates; the abundance of the species is relatively high; the IR continuum plays an important role as a pump; the contribution from shocks is relatively minor; and, not least, the powerful centimeter-wave radiation from OH allows comparison with radio and VLBI datasets. The problem is that the large number of sensitive free parameters, and the large optical depths of the strongest lines, make modeling the full set a difficult job. The SWAS montecarlo radiative transfer code has been used to analyze the ISO/LWS spectra of a number of objects with good success, including in both the lines and the FIR continuum; the DUSTY radiative transfer code was used to insure a self-consistent continuum. Other far IR lines including those from H2O, CO, and [OI] are also in the code. The OH lines all show features which future FIR spectrometers should be able to resolve, and which will enable further refinements in the details of each cloud's structure. Some examples are given, including the case of S140, for which independent SWAS data found evidence for bulk flows.

Smith, Howard A.↗
NASA NTRS2003

Ionizing radiation induces heritable disruption of epithelial cell interactions

Ionizing radiation (IR) is a known human breast carcinogen. Although the mutagenic capacity of IR is widely acknowledged as the basis for its action as a carcinogen, we and others have shown that IR can also induce growth factors and extracellular matrix remodeling. As a consequence, we have proposed that an additional factor contributing to IR carcinogenesis is the potential disruption of critical constraints that are imposed by normal cell interactions. To test this hypothesis, we asked whether IR affected the ability of nonmalignant human mammary epithelial cells (HMEC) to undergo tissue-specific morphogenesis in culture by using confocal microscopy and imaging bioinformatics. We found that irradiated single HMEC gave rise to colonies exhibiting decreased localization of E-cadherin, beta-catenin, and connexin-43, proteins necessary for the establishment of polarity and communication. Severely compromised acinar organization was manifested by the majority of irradiated HMEC progeny as quantified by image analysis. Disrupted cell-cell communication, aberrant cell-extracellular matrix interactions, and loss of tissue-specific architecture observed in the daughters of irradiated HMEC are characteristic of neoplastic progression. These data point to a heritable, nonmutational mechanism whereby IR compromises cell polarity and multicellular organization.

Non-NASA Center↗
NASA NTRS2002

Remote sensing of planetary properties and biosignatures on extrasolar terrestrial planets

The major goals of NASA's Terrestrial Planet Finder (TPF) and the European Space Agency's Darwin missions are to detect terrestrial-sized extrasolar planets directly and to seek spectroscopic evidence of habitable conditions and life. Here we recommend wavelength ranges and spectral features for these missions. We assess known spectroscopic molecular band features of Earth, Venus, and Mars in the context of putative extrasolar analogs. The preferred wavelength ranges are 7-25 microns in the mid-IR and 0.5 to approximately 1.1 microns in the visible to near-IR. Detection of O2 or its photolytic product O3 merits highest priority. Liquid H2O is not a bioindicator, but it is considered essential to life. Substantial CO2 indicates an atmosphere and oxidation state typical of a terrestrial planet. Abundant CH4 might require a biological source, yet abundant CH4 also can arise from a crust and upper mantle more reduced than that of Earth. The range of characteristics of extrasolar rocky planets might far exceed that of the Solar System. Planetary size and mass are very important indicators of habitability and can be estimated in the mid-IR and potentially also in the visible to near-IR. Additional spectroscopic features merit study, for example, features created by other biosignature compounds in the atmosphere or on the surface and features due to Rayleigh scattering. In summary, we find that both the mid-IR and the visible to near-IR wavelength ranges offer valuable information regarding biosignatures and planetary properties; therefore both merit serious scientific consideration for TPF and Darwin.

Planets↗
NASA NTRS2006

Comet Mineralogy as Inferred from Infrared Spectra of Comets

For most comets, infrared (IR) spectroscopy (remote sensing) is the method through which we diagnose the mineralogy and size distribution of dust in their comae. The shape and contrast of the IR spectral features depend on the particle size: optically active minerals (absorbing of visible and near-IR solar photons) and submicron solid grains or highly porous (> 90% vacuum) grains primarily contribute to the shapes of the observed resonances. Comet mineralogies typically are determined by fitting thermal emission models of ensembles of discrete mineral grains to observed IR spectral energy distributions. The absorptivities (Q-abs) and scattering efficiencies (Q-scat) of the discrete mineral grains are computed using Mie scattering, Maxwell-Garnet mixing, Discrete Dipole Approximation, and Multi-Layered Sphere codes. These techniques when applied to crystalline minerals, specifically olivine (Mg_x, Fe_1-x)2 Si04, x>0.9, require the use of ellipsoidal shaped particles with elongated axial ratios or hollow spheres to produce the shapes of the resonances observed both from comet comae and laboratory samples. The wavelength positions of the distinct resonances from submicron-radii crystalline silicates, as well as their thermal equilibrium temperatures, constrain the crystalline olivine to have a relatively high Mg-content (x>0.9, or Fo>90). Only resonances computed for submicron Mg-rich crystalline olivine and crystalline orthopyroxene match the observed IR spectral features. However, this has led to the interpretation that micron-radii and larger crystals are absent from comet comae. Furthermore, the mass fraction of silicate crystals is dependent upon whether just the submicron portion of the size distribution is being compared or the submicron crystals compare to the aggregates of porous amorphous silicates that are computationally tractable as porous spheres. We will discuss the Deep Impact results as examples of these challenges to interpreting mid-IR spectra of short-period comets.

Wooden, Diane H.↗
NASA NTRS2010

GASPS Photometry of the Tucana-Horologium Association

The GASPS Open Time Key Programme on Herschel represents a new opportunity to sensitively probe protoplanetary and debris disks at far-IR wavelengths. We present preliminary PACS 70 and 160 micron photometry of eighteen stars in the 30 Myr-old Tucana-Horologium association. Of these eighteen, eight were detected in the 70 micron band. Four of these eight were also detected in the 160 micron band. We constructed SEDs for these systems using optical data from Hipparcos (B and V), near-IR data from 2MASS (J, H, and K), mid-IR data from IRAS and Spitzer MIPS (12 and 24 microns, respectively), and the new far-IR data from PACS. For the stars showing IR excess emission, we fit simple single-temperature blackbody curves to the IR excess in order to determine the rough dust abundances and temperatures. Dust observations at these wavelengths will also be important for comparison with upcoming Herschel PACS spectra that will search for gas in the disks. Our goal is to determine or limit the ever-allusive gas-to-dust ratio for these disk systems.

Roberge, Donaldson J.↗
NASA NTRS2010

Recent Advances in Laboratory Infrared Spectroscopy of Polycyclic Aromatic Hydrocarbons: PAHs in the Far Infrared

Over 25 years of observations and laboratory work have shown that the mid-IR spectra of a majority of astronomical sources are dominated by emission features near 3.3, 6.2, 7.7, and 11.2 microns, which originate in free polycyclic aromatic hydrocarbon (PAH) molecules. PAHs dominate the mid-IR emission from many galactic and extragalactic objects. As such, this material tracks a wide variety of astronomical processes, making this spectrum a powerful probe of the cosmos Apart from bands in the mid-IR, PAHs have bands spanning the Far-IR (FIR) and emission from these FIR features should be present in astronomical sources showing the Mid-IR PAH bands. However, with one exception, the FIR spectral characteristics are known only for a few neutral small PAHs trapped in salt pellets or oils at room temperature, data which is not relevant to astrophysics. Furthermore, since most emitting PAHs responsible for the mid-IR astronomical features are ionized, the absence of any experimental or theoretical PAH ion FIR spectra will make it impossible to correctly interpret the FIR data from these objects. In view of the upcoming Herschel space telescope mission and SOFIA's FIR airborne instrumentation, which will pioneer the FIR region, it is now urgent to obtain PAH FIR spectra. This talk will present an overview recent advances in the laboratory spectroscopy of PAHs, Highlighting the FIR spectroscopy along with some quantum calculations.

Mattioda, Andrew L.↗
NASA NTRS2011

A Spitzer Survey for Dust in Type IIn Supernovae

Recent observations suggest that Type IIn supernovae (SNe IIn) may exhibit late-time (>100 days) infrared (IR) emission from warm dust more than other types of core-collapse SNe. Mid-IR observations, which span the peak of the thermal spectral energy distribution, provide useful constraints on the properties of the dust and, ultimately, the circumstellar environment, explosion mechanism, and progenitor system. Due to the low Type IIn rate (<10% of all core-collapse SNe), few IR observations exist for this subclass. The handful of isolated studies, however, show late-time IR emission from warm dust that, in some cases, extends for five or six years post-discovery. vVhile previous Spitzer/IRAC surveys have searched for dust in SNe, none have targeted the Type IIn subclass. This article presents results from a warm Spitzer/IRAC survey of the positions of all 68 known SNe IIn within a distance of 250 Mpc between 1999 and 2008 that have remained unobserved by Spitzer more than 100 days post-discovery. The detection of late-time emission from ten targets (approx. 15 %) nearly doubles the database of existing mid-IR observations of SNe IIn. Although optical spectra show evidence for new dust formation in some cases, the data show that in most cases the likely origin of the mid-IR emission is pre-existing dust, which is continuously heated by optical emission generated by ongoing circumstellar interaction between the forward shock and circumstellar medium. Furthermore, an emerging trend suggests these SNe "turn off" at " approx. 1000-2000 days post-discovery once the forward shock overruns the dust shell. The mass-loss rates associated with these dust shells are consistent with luminous blue variable (LBV) progenitors having similar mass-loss histories.

Fox, Ori D.↗
NASA NTRS2011

A Spitzer Survey for Dust in Type IIn Supernovae

Recent observations suggest that Type IIn supernovae (SNe IIn) may exhibit late-time (greater than 100 days) infrared (IR) emission from warm dust more than other types of core-collapse SNe. Mid-IR observations, which span the peak of the thermal spectral energy distribution, provide useful constraints on the properties of the dust and, ultimately, the circumstellar environment, explosion mechanism, and progenitor system. Due to the low SN IIn rate (less than 10% of all core-collapse SNe), few IR observations exist for this subclass. The handful of isolated studies, however, show late-time IR emission from warm dust that, in some cases, extends for five or six years post-discovery. While previous Spitzer/IRAC surveys have searched for dust in SNe, none have targeted the Type IIn subclass. This article presents results from a warm Spitzer/IRAC survey of the positions of all 68 known SNe IIn within a distance of 250 Mpc between 1999 and 2008 that have remained unobserved by Spitzer more than 100 days postdiscovery. The detection of late-time emission from ten targets (approximately 15%) nearly doubles the database of existing mid-IR observations of SNe IIn. Although optical spectra show evidence for new dust formation in some cases, the data show that in most cases the likely origin of the mid-IR emission is pre-existing dust, which is continuously heated by optical emission generated by ongoing circumstellar interaction between the forward shock and circumstellar medium. Furthermore, an emerging trend suggests that these SNe decline at approximately 1000-2000 days post-discovery once the forward shock overruns the dust shell. The mass-loss rates associated with these dust shells are consistent with luminous blue variable (LBV) progenitors.

Fox, Ori D.↗
NASA NTRS2011

System Re-set: High LET Radiation or Transient Musculoskeletal Disuse Cause Lasting Changes in Oxidative Defense Pathways Within Bone

Six months post-IR, there were no notable changes in skeletal expression of 84 principal genes in the p53 signaling pathway due to low dose IR (0.5Gy), HU, or both. In contrast, numerous genes relevant to oxidative stress were regulated by the treatments, typically in a direction indicative of increased oxidative stress and impaired defense. IR and HU independently reduced (between 0.46 to 0.88 fold) expression levels of Noxa1, Gpx3, Prdx2, Prdx3, and Zmynd17. Surprisingly, transient HU alone (sham-irradiated) decreased expression of several redox-related genes (Gpx1,Gstk1, Prdx1, Txnrd2), which were not affected significantly by IR alone. Irradiation increased (1.13 fold) expression of a gene responsible for production of superoxides by neutrophils (NCF2). Of interest, only combined treatment with HU and IR led to increased expression levels of Ercc2, (1.19 fold), a DNA excision repair enzyme. Differences in gene expression levels may reflect a change in gene expression on a per cell basis, a shift in the repertoire of specific cell types within the tissue, or both. Serum nitrite/nitrate levels were elevated to comparable levels (1.6-fold) due to IR, HU or both, indicative of elevated systemic nitrosyl stress. CONCLUSIONS The magnitude of changes in skeletal expression of oxidative stress-related genes six months after irradiation and/or transient unloading tended to be relatively modest (0.46-1.15 fold), whereas the p53 pathway was not affected. The finding that many different oxidative stress-related genes differed from controls at this late time point implicates a generalized impairment of oxidative defense within skeletal tissue, which coincides with both profound radiation damage to osteoprogenitors/stem cells in bone marrow and impaired remodeling of mineralized tissue.

Kumar, Akhilesh↗
NASA NTRS2012

Measurement of Two-Phase Flow and Heat Transfer Parameters using Infrared Thermometry

A novel technique to measure heat transfer and liquid film thickness distributions over relatively large areas for two-phase flow and heat transfer phenomena using infrared (IR)thermometry is described. IR thermometry is an established technology that can be used to measure temperatures when optical access to the surface is available in the wavelengths of interest. In this work, a midwave IR camera (3.6-5.1 microns) is used to determine the temperature distribution within a multilayer consisting of a silicon substrate coated with a thin insulator. Since silicon is largely transparent to IR radiation, the temperature of the inner and outer walls of the multilayer can be measured by coating selected areas with a thin, IR opaque film. If the fluid used is also partially transparent to IR, the flow can be visualized and the liquid film thickness can be measured. The theoretical basis for the technique is given along with a description of the test apparatus and data reduction procedure. The technique is demonstrated by determining the heat transfer coefficient distributions produced by droplet evaporation and flow boiling heat transfer.

Kim, Tae-Hoon↗