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NASA NTRS2011

Calibration of Star Formation Rates Across the Electromagnetic Spectrum

Measuring and mapping star-forming activity in galaxies is a key element for our understanding of their broad- band spectra, and their structure and evolution in our local, as well as the high-redshift Universe. The main tool we use for these measurements is the observed luminosity in various spectral lines and/or continuum bands. However, the available star-formation rate (SFR) indicators are often discrepant and subject to physical biases and calibration uncertainties. We are organizing a special session at the 2012 IAU General Assembly in Beijing, China (August 20-31, 2012) in order to bring together theoreticians and observers working in different contexts of star-formation to discuss the status of current SFR indicators, to identify open issues and to define a strategic framework for their resolution. The is an ideal time to synthesize information from the current golden era of space astrophysics and still have influence on the upcoming missions that will broaden our view of star-formation. We will be including high-energy constraints on SFR in the program and encourage participation from the high energy astrophysics community.

Cardiff, Ann H.↗

NASA NTRS2011

Connections Between Jet Formation and Multiwavelength Spectral Evolution in Black Hole Transients

Multiwavelength observations are the key to understand conditions of jet formation in Galactic black hole transient (GBHT) systems. By studying radio and optical-infrared evolution of such systems during outburst decays, the compact jet formation can be traced. Comparing this with X-ray spectral and timing evolution we can obtain physical and geometrical conditions for jet formation, and study the contribution of jets to X-ray emission. In this work, first X-ray evolution - jet relation for XTE J1752-223 will be discussed. This source had very good coverage in X-rays, optical, infrared and radio. A long exposure with INTEGRAL also allowed us to study gamma-ray behavior after the jet turns on. We will also show results from the analysis of data from GX 339-4 in the hard state with SUZAKU at low flux levels. The fits to iron line fluorescence emission show that the inner disk radius increases by a factor of greater than 27 with respect to radii in bright states. This result, along with other disk radius measurements in the hard state will be discussed within the context of conditions for launching and sustaining jets.

Kakemci, Emrah↗

NASA NTRS2003

Modified Polar-Format Software for Processing SAR Data

HMPF is a computer program that implements a modified polar-format algorithm for processing data from spaceborne synthetic-aperture radar (SAR) systems. Unlike prior polar-format processing algorithms, this algorithm is based on the assumption that the radar signal wavefronts are spherical rather than planar. The algorithm provides for resampling of SAR pulse data from slant range to radial distance from the center of a reference sphere that is nominally the local Earth surface. Then, invoking the projection-slice theorem, the resampled pulse data are Fourier-transformed over radial distance, arranged in the wavenumber domain according to the acquisition geometry, resampled to a Cartesian grid, and inverse-Fourier-transformed. The result of this process is the focused SAR image. HMPF, and perhaps other programs that implement variants of the algorithm, may give better accuracy than do prior algorithms for processing strip-map SAR data from high altitudes and may give better phase preservation relative to prior polar-format algorithms for processing spotlight-mode SAR data.

Chen, Curtis↗

NASA NTRS2012

Experimental Behavior of Sulfur Under Primitive Planetary Differentiation Processes, the Sulfide Formations in Enstatite Meteorites and Implications for Mercury.

Enstatite meteorites are the most reduced naturally-occuring materials of the solar system. The cubic monosulfide series with the general formula (Mg,Mn,Ca,Fe)S are common phases in these meteorite groups. The importance of such minerals, their formation, composition and textural relationships for understanding the genesis of enstatite chondrites (EC) and aubrites, has long been recognized (e.g. [1]). However, the mechanisms of formation of these sulfides is still not well constrained certainly because of possible multiple ways to produce them. We propose to simulate different models of formation in order to check their mineralogical, chemical and textural relevancies. The solubility of sulfur in silicate melts is of primary interest for planetary mantles, particularly for the Earth and Mercury. Indeed, these two planets could have formed, at least partly, from EC materials (e.g. [2, 3, 4]). The sulfur content in silicate melts depends on the melt composition but also on pressure (P), temperature (T) and oxygen fugacity fO2. Unfortunately, there is no model of general validity in a wide range of P-T-fO2-composition which describes precisely the evolution of sulfur content in silicate melts, even if the main trends are now known. The second goal of this study is to constrain the sulfur content in silicate melts under reducing conditions and different temperatures.

Malavergne, V.↗

NASA NTRS2010

Genesis of Pre-Hurricane Felix (2007): Warm Core Formation, Precipitation Evolution, and Predictability - Part 2

This is the second of a two-part study examining the simulated formation of Atlantic Hurricane Felix (2007) in a cloud-representing framework. Here several open issues are addressed concerning the formation of the storm's warm core, the evolution and respective contribution of stratiform versus convective precipitation within the parent wave's pouch, and the sensitivity of the development pathway reported in Part I to different model physics options and initial conditions. All but one of the experiments include ice microphysics as represented by one of several parameterizations, and the partition of convective versus stratiform precipitation is accomplished using a standard numerical technique based on the high-resolution control experiment. The transition to a warm-core tropical cyclone from an initially cold-core, lower tropospheric wave disturbance is analyzed first. As part of this transformation process, it is shown that deep moist convection is sustained near the pouch center. Both convective and stratiform precipitation rates increase with time. While stratiform precipitation occupies a larger area even at the tropical storm stage, deep moist convection makes a comparable contribution to the total rain rate at the pregenesis stage, and a larger contribution than stratiform processes at the storm stage. The convergence profile averaged near the pouch center is found to become dominantly convective with increasing deep moist convective activity there. Low-level convergence forced by interior diabatic heating plays a key role in forming and intensifying the near-surface closed circulation, while the midlevel convergence associated with stratiform precipitation helps to increase the midlevel circulation and thereby contributes to the formation and upward extension of a tropospheric-deep cyclonic vortex. Sensitivity tests with different model physics options and initial conditions demonstrate a similar pregenesis evolution. These tests suggest that the genesis location of a tropical storm is largely controlled by the parent wave's critical layer, whereas the genesis time and intensity of the protovortex depend on the details of the mesoscale organization, which is less predictable. Some implications of the findings are discussed.

Wang, zhuo↗

NASA NTRS2012

A Preliminary Flight Investigation of Formation Flight for Drag Reduction on the C-17 Aircraft

Many theoretical and experimental studies have shown that aircraft flying in formation could experience significant reductions in fuel use compared to solo flight. To date, formation flight for aerodynamic benefit has not been thoroughly explored in flight for large transport-class vehicles. This paper summarizes flight data gathered during several two ship, C-17 formation flights at a single flight condition of 275 knots, at 25,000 ft MSL. Stabilized test points were flown with the trail aircraft at 1,000 and 3,000 ft aft of the lead aircraft at selected crosstrack and vertical offset locations within the estimated area of influence of the vortex generated by the lead aircraft. Flight data recorded at test points within the vortex from the lead aircraft are compared to data recorded at tare flight test points outside of the influence of the vortex. Since drag was not measured directly, reductions in fuel flow and thrust for level flight are used as a proxy for drag reduction. Estimated thrust and measured fuel flow reductions were documented at several trail test point locations within the area of influence of the leads vortex. The maximum average fuel flow reduction was approximately 7-8%, compared to the tare points flown before and after the test points. Although incomplete, the data suggests that regions with fuel flow and thrust reduction greater than 10% compared to the tare test points exist within the vortex area of influence.

Pahle, Joe↗

NASA NTRS2012

Compound-Specific Isotopic Analysis of Meteoritic Amino Acids as a Tool for Evaluating Potential Formation Pathways

Measurements of stable hydrogen, carbon, and nitrogen isotopic ratios (delta D, delta C-13, delta N-15) of organic compounds can reveal information about their origin and formation pathways. Several formation mechanisms and environments have been postulated for the amino acids detected in carbonaceous chondrites. As each proposed mechanism utilizes different precursor molecules, the isotopic signatures of the resulting amino acids may point towards the most likely of these proposed pathways. The technique of gas chromatography coupled with mass spectrometry and isotope ratio mass spectrometry provides compound-specific structural and isotopic information from a single splitless injection, enhancing the amount of information gained from small amounts of precious samples such as carbonaceous chondrites. We have applied this technique to measure the compound-specific C, N, and H isotopic ratios of amino acids from seven CM and CR carbonaceous chondrites. We are using these measurements to evaluate predictions of expected isotopic enrichments from potential formation pathways and environments, leading to a better understanding of the origin of these compounds.

Elsila, Jamie E.↗

NASA NTRS2012

Formation of South Pole-Aitken Basin as the Result of an Oblique Impact: Implications for Melt Volume and Source of Exposed Materials

The South Pole-Aitken Basin (SPA) is the largest, deepest, and oldest identified basin on the Moon and contains surfaces that are unique due to their age, composition, and depth of origin in the lunar crust [1-3] (Figure 1). SPA has been a target of interest as an area for robotic sample return in order to determine the age of the basin and the composition and origin of its interior [3-6]. As part of the investigation into the origin of SPA materials there have been several efforts to estimate the likely provenance of regolith material in central SPA [5, 6]. These model estimates suggest that, despite the formation of basins and craters following SPA, the regolith within SPA is dominated by locally derived material. An assumption inherent in these models has been that the locally derived material is primarily SPA impact-melt as opposed to local basement material (e.g. unmelted lower crust). However, the definitive identification of SPA derived impact melt on the basin floor, either by remote sensing [2, 7] or via photogeology [8] is extremely difficult due to the number of subsequent impacts and volcanic activity [3, 4]. In order to identify where SPA produced impact melt may be located, it is important to constrain both how much melt would have been produced in a basin forming impact and the likely source of such melted material. Models of crater and basin formation [9, 10] present clear rationale for estimating the possible volumes and sources of impact melt produced during SPA formation. However, if SPA formed as the result of an oblique impact [11, 12], the volume and depth of origin of melted material could be distinct from similar material in a vertical impact [13].

Petro, N. E.↗

NASA NTRS2012

An Initial Flight Investigation of Formation Flight for Drag Reduction on the C-17 Aircraft

Joe Pahle↗

NASA NTRS2012

Peak-Seeking Optimization of Spanwise Lift Distribution for Wings in Formation Flight

A method is presented for the optimization of the lift distribution across the wing of an aircraft in formation flight. The usual elliptical distribution is no longer optimal for the trailing wing in the formation due to the asymmetric nature of the encountered flow field. Control surfaces along the trailing edge of the wing can be configured to obtain a non-elliptical profile that is more optimal in terms of minimum drag. Due to the difficult-to-predict nature of formation flight aerodynamics, a Newton-Raphson peak-seeking controller is used to identify in real time the best aileron and flap deployment scheme for minimum total drag. Simulation results show that the peak-seeking controller correctly identifies an optimal trim configuration that provides additional drag savings above those achieved with conventional anti-symmetric aileron trim.

Hanson, Curtis E.↗

NASA NTRS2012

Peak-Seeking Optimization of Spanwise Lift Distribution for Wings in Formation Flight

A method is presented for the in-flight optimization of the lift distribution across the wing for minimum drag of an aircraft in formation flight. The usual elliptical distribution that is optimal for a given wing with a given span is no longer optimal for the trailing wing in a formation due to the asymmetric nature of the encountered flow field. Control surfaces along the trailing edge of the wing can be configured to obtain a non-elliptical profile that is more optimal in terms of minimum combined induced and profile drag. Due to the difficult-to-predict nature of formation flight aerodynamics, a Newton-Raphson peak-seeking controller is used to identify in real time the best aileron and flap deployment scheme for minimum total drag. Simulation results show that the peak-seeking controller correctly identifies an optimal trim configuration that provides additional drag savings above those achieved with conventional anti-symmetric aileron trim.

Hanson, Curtis E.↗

NASA NTRS2013

ALMA Observations of the Galactic Center: SiO Outflows and High Mass Star Formation Near Sgr A

Using ALMA observations of the Galactic center with a spatial resolution of 2.61" x 0.97 ", we detected 11 SiO (5-4) clumps of molecular gas in the within 0.6pc (15") of Sgr A*, interior of the 2-pc circumnuclear molecular ring. Three SiO (5-4) clumps closest to Sgr A* show the largest central velocities of approximately 150 kilometers per second and broadest asymmetric linewidths with total linewidths FWZI approximately 110-147 kilometers per second. Other clumps are distributed mainly to the NE of the ionized minispiral with narrow linewidths of FWHM approximately 11-27 kilometers per second. Using CARMA data, LVG modeling of the broad velocity clumps, the SiO (5-4) and (2-1) line ratios constrain the column density N(SiO) approximately 10(exp 14) per square centimeter, and the H2 gas density n(sub H2) = (3-9) x 10(exp 5) per cubic centimeter for an assumed kinetic temperature 100-200K. The SiO (5-4) clumps with broad and narrow linewidths are interpreted as highly embedded protostellar outflows, signifying an early stage of massive star formation near Sgr A* in the last 104 years. Additional support for the presence of YSO outflows is that the luminosities and velocity widths lie in the range detected from protostellar outflows in star forming regions in the Galaxy. Furthermore, SED modeling of stellar sources along the N arm show two YSO candidates near SiO clumps supporting in-situ star formation near Sgr A*. We discuss the nature of star formation where the gravitational potential of the black hole dominates. In particular, we suggest that external radiative pressure exerted on self-shielded molecular clouds enhance the gas density, before the gas cloud become gravitationally unstable near Sgr A*.

Yusef-Zadeh, F.↗

NASA NTRS2013

Olivine Weathering aud Sulfate Formation Under Cryogenic Conditions

High resolution photography and spectroscopy of the martian surface (MOC, HiRISE) from orbit has revolutionized our view of Mars with one of the most important discoveries being wide‐spread layered sedimentary deposits associated with sulfate minerals across the low to mid latitude regions of Mars. The mechanism for sulfate formation on Mars has been frequently attributed to playa‐like evaporative environments under prolonged warm conditions. An alternate view of the ancient martian climate contends that prolonged warm temperatures were never present and that the atmosphere and climate has been similar to modern conditions throughout most of its history. This view has had a difficult time explaining the sedimentary history of Mars and in particular the presence of sulfate minerals which seemingly need more water. We suggest here that mixtures of atmospheric aerosols, ice, and dust have the potential for creating small films of cryo‐concentrated acidic solutions that may represent an important unexamined environment for understanding weathering processes on Mars. This study seeks to test whether sulfate formation may be possible at temperatures well below 0degC in water limited environments removing the need for prolonged warm periods to form sulfates on early Mars. To test this idea we performed laboratory experiments to simulate weathering of mafic minerals under Mars‐like conditions. The weathering rates measured in this study suggest that fine grained olivine on Mars would weather into sulfate minerals in short time periods if they are exposed to H2SO4 aerosols at temperatures at or above ‐40degC. In this system, the strength of the acidic solution is maximized through eutectic freezing in an environment where the silicate minerals are extremely fine grained and have high surface areas. This provides an ideal environment despite the very low temperatures. On Mars the presence of large deposits of mixed ice and dust is undisputed. The presence of substantial sulfur‐rich volcanism, and sulfur‐rich surface deposits also makes it very likely that sulfate aerosols have also been an important component of the martian atmosphere. Thus mixtures of ice, dust, and sulfate aerosols are likely to have been common on the martian surface. Given the fact that it is not difficult to achieve surface temperatures above ‐40degC on Mars throughout its history, it seems likely that sulfate formation on Mars is controlled by the availability of sulfate aerosols and not by the martian climate. The current polar regions of Mars and Earth provide interesting analogs. Large regions of sulfaterich material have been detected on and around the modern north polar region of Mars. The prevalence of ice‐dust mixtures in this region and the existence of sulfates within the ice cap itself are strong evidence for the origin of the sulfates from inside the ice deposits. In addition sulfates have been found in ice deposits in Greenland and Mount Fuji on Earth that have been attributed to forming within the ice deposit. These sulfates can form either through interaction with dust particles in the atmosphere or through weathering inside the ice itself.

Niles, Paul B.↗

NASA NTRS2013

Carbonate Mineral Formation on Mars: Clues from Stable Isotope Variation Seen in Cryogenic Laboratory Studies of Carbonate Salts

The geologic history of water on the planet Mars is intimately connected to the formation of carbonate minerals through atmospheric CO2 and its control of the climate history of Mars. Carbonate mineral formation under modern martian atmospheric conditions could be a critical factor in controlling the martian climate in a means similar to the rock weathering cycle on Earth. The combination of evidence for liquid water on the martian surface and cold surface conditions suggest fluid freezing could be very common on the surface of Mars. Cryogenic calcite forms readily when a rise in pH occurs as a result of carbon dioxide degassing quickly from freezing Ca-bicarbonate-rich water solutions. This is a process that has been observed in some terrestrial settings such as arctic permafrost cave deposits, lakebeds of the Dry Valleys of Antarctica, and in aufeis (river icings) from rivers of N.E. Alaska. We report here the results of a series of laboratory experiments that were conducted to simulate potential cryogenic carbonate formation on the planet Mars. These results indicate that carbonates grown under martian conditions (controlled atmospheric pressure and temperature) show enrichments from starting bicarbonate fluids in both carbon and oxygen isotopes beyond equilibrium values with average delta13C(DIC-CARB) values of ~20.5%0 which exceed the expected equilibrium fractionation factor of [10(sup 3) ln alpha = ~13%0] at 0 degC. Oxygen isotopes showed a smaller enrichment with delta18O(H2O-CARB) values of ~35.5%0, slightly exceeding the equilibrium fractionation factor of [10(sup 3) ln alpha = ~34%0 ] at 0degC. Large kinetic carbon isotope effects during carbonate precipitation could substantially affect the carbon isotope evolution of CO2 on Mars allowing for more efficient removal of 13C from the Noachian atmosphere enriched by atmospheric loss. This mechanism would be consistent with the observations of large carbon isotope variations in martian materials despite the relative paucity of carbonate minerals in the martian crust.

Socki, Richard↗

NASA NTRS2013

The Radial Distribution of Star Formation in Galaxies at z~1 From The 3D-HST Survey

The assembly of galaxies can be described by the distribution of their star formation as a function of cosmic time.Thanks to the WFC3 grism on the Hubble Space Telescope (HST) it is now possible to measure this beyond thelocal Universe. Here we present the spatial distribution of H emission for a sample of 54 strongly star-forming-galaxies at z~1 in the 3D-HST Treasury survey. By stacking the Halpha emission, we find that star formation occurredin approximately exponential distributions at z~1, with a median Sersic index of n=1.0 plus or minus 0.2. The stacks areelongated with median axis ratios of b/a 0.58 plus or minus 0.09 in Halpha consistent with (possibly thick) disks at randomorientation angles. Keck spectra obtained for a subset of eight of the galaxies show clear evidence for rotation, withinclination corrected velocities of 90-330 km per second. The most straightforward interpretation of our results is that starformation in strongly star-forming galaxies at z~1 generally occurred in disks. The disks appear to be scaled-upversions of nearby spiral galaxies: they have EW(Halpha)~100 Angstroms out to the solar orbit and they have star formation surface densities above the threshold for driving galactic scale winds.

Radial↗

NASA NTRS2014

Martian Cryogenic Carbonate Formation: Stable Isotope Variations Observed in Laboratory Studies

The history of water on Mars is tied to the formation of carbonates through atmospheric CO2 and its control of the climate history of the planet. Carbonate mineral formation under modern martian atmospheric conditions could be a critical factor in controlling the martian climate in a means similar to the rock weathering cycle on Earth. The combination of evidence for liquid water on the martian surface and cold surface conditions suggest fluid freezing could be very common on the surface of Mars. Cryogenic calcite forms easily from freezing solutions when carbon dioxide degasses quickly from Ca-bicarbonate-rich water, a process that has been observed in some terrestrial settings such as arctic permafrost cave deposits, lake beds of the Dry Valleys of Antarctica, and in aufeis (river icings) from rivers of N.E. Alaska. A series of laboratory experiments were conducted that simulated cryogenic carbonate formation on Mars in order to understand their isotopic systematics. The results indicate that carbonates grown under martian conditions show variable enrichments from starting bicarbonate fluids in both carbon and oxygen isotopes beyond equilibrium values.

Socki, Richard A.↗

NASA NTRS2013

Aqua-planet simulations of the formation of the South Atlantic convergence zone

The impact of Amazon Basin convection and cold fronts on the formation and maintenance of the South Atlantic convergence zone (SACZ) is studied using aqua-planet simulations with a general circulation model. In the model, a circular patch of warm sea-surface temperature (SST) is used to mimic the effect of the Amazon Basin on South American monsoon convection. The aqua-planet simulations were designed to study the effect of the strength and latitude of Amazon Basin convection on the formation of the SACZ. The simulations indicate that the strength of the SACZ increases as the Amazon convection intensifies and is moved away from the equator. Of the two controls studied here, the latitude of the Amazon convection exerts the strongest effect on the strength of the SACZ. An analysis of the synoptic-scale variability in the simulations shows the importance of frontal systems in the formation of the aqua-planet SACZ. Composite time series of frontal systems that occurred in the simulations show that a robust SACZ occurs when fronts penetrate into the subtropics and become stationary there as they cross eastward of the longitude of the Amazon Basin. Moisture convergence associated with these frontal systems produces rainfall not along the model SACZ region and along a large portion of the northern model Amazon Basin. Simulations in which the warm SST patch was too weak or too close to the equator did not produce frontal systems that extended into the tropics and became stationary, and did not form a SACZ. In the model, the SACZ forms as Amazon Basin convection strengthens and migrates far enough southward to allow frontal systems to penetrate into the tropics and stall over South America. This result is in agreement with observations that the SACZ tends to form after the onset of the monsoon season in the Amazon Basin.

South American Monsoon↗

NASA NTRS2013

The Photochemistry of Pyrimidine in Pure H2O Ice Subjected to Different Radiation Environments and the Formation of Uracil

Nucleobases are N-heterocycles which are the informational subunits of DNA and RNA. They include pyrimidine bases (uracil, cytosine, and thymine) and purine bases (adenine and guanine). Nucleobases have been detected in several meteorites, although no Nheterocycles have been observed in space to data. Laboratory experiments showed that the ultraviolet (UV) irradiation of pyrimidine in pure H2O ice at low temperature (<=20 K) leads to the formation of pyrimidine derivatives including the nucleobase uracil and its precursor 4(3H)-pyrimidone. These results were confirmed by quantum chemical calculations. When pyrimidine is mixed with combinations of H2O, NH3, CH3OH, and CH4 ices under similar conditions, uracil and cytosine are formed. In the present work we study the formation of 4(3H)-pyrimidone and uracil from the irradiation of pyrimidine in H2O ice with high-energy UV photons (Lyman , He I, and He II lines) provided by a synchrotron source. The photo-destruction of pyrimidine in these H2O ices as well as the formation yields for 4(3H)-pyrimidone and uracil are compared with our previous results in order to study the photo-stability of pyrimidine and the production efficiency of uracil as a function of the photon energy.

Radiation↗