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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Data inversion algorithm development for the hologen occultation experiment

The successful retrieval of atmospheric parameters from radiometric measurement requires not only the ability to do ideal radiometric calculations, but also a detailed understanding of instrument characteristics. Therefore a considerable amount of time was spent in instrument characterization in the form of test data analysis and mathematical formulation. Analyses of solar-to-reference interference (electrical cross-talk), detector nonuniformity, instrument balance error, electronic filter time-constants and noise character were conducted. A second area of effort was the development of techniques for the ideal radiometric calculations required for the Halogen Occultation Experiment (HALOE) data reduction. The computer code for these calculations must be extremely complex and fast. A scheme for meeting these requirements was defined and the algorithms needed form implementation are currently under development. A third area of work included consulting on the implementation of the Emissivity Growth Approximation (EGA) method of absorption calculation into a HALOE broadband radiometer channel retrieval algorithm.

Gordley, Larry L.↗
DOE OSTI2022

Massive star-forming galaxies have converted most of their halo gas into stars

In the local Universe, the efficiency for converting baryonic gas into stars is very low. In dark matter halos where galaxies form and evolve, the average efficiency varies with galaxy stellar mass and has a maximum of about 20% for Milky-Way-like galaxies. The low efficiency at higher mass is believed to be the result of some quenching processes, such as the feedback from active galactic nuclei. We perform an analysis of weak lensing and satellite kinematics for SDSS central galaxies. Our results reveal that the efficiency is much higher, more than 60%, for a large population of massive star-forming galaxies around 10 11 M ⊙ . This suggests that these galaxies acquired most of the gas in their halos and converted it into stars without being significantly affected by quenching processes. This population of galaxies is not reproduced in current galaxy formation models, indicating that our understanding of galaxy formation is incomplete. The implications of our results on circumgalactic media, star-formation quenching, and disk galaxy rotation curves are discussed. We also examine systematic uncertainties in halo-mass and stellar-mass measurements that might influence our results.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Possibilities and Limitations of Kinematically Identifying Stars from Accreted Ultra-faint Dwarf Galaxies

Abstract The Milky Way has accreted many ultra-faint dwarf galaxies (UFDs), and stars from these galaxies can be found throughout our Galaxy today. Studying these stars provides insight into galaxy formation and early chemical enrichment, but identifying them is difficult. Clustering stellar dynamics in 4D phase space ( E , L z , J r , J z ) is one method of identifying accreted structure that is currently being utilized in the search for accreted UFDs. We produce 32 simulated stellar halos using particle tagging with the Caterpillar simulation suite and thoroughly test the abilities of different clustering algorithms to recover tidally disrupted UFD remnants. We perform over 10,000 clustering runs, testing seven clustering algorithms, roughly twenty hyperparameter choices per algorithm, and six different types of data sets each with up to 32 simulated samples. Of the seven algorithms, HDBSCAN most consistently balances UFD recovery rates and cluster realness rates. We find that, even in highly idealized cases, the vast majority of clusters found by clustering algorithms do not correspond to real accreted UFD remnants and we can generally only recover 6% of UFDs remnants at best. These results focus exclusively on groups of stars from UFDs, which have weak dynamic signatures compared to the background of other stars. The recoverable UFD remnants are those that accreted recently, z accretion ≲ 0.5. Based on these results, we make recommendations to help guide the search for dynamically linked clusters of UFD stars in observational data. We find that real clusters generally have higher median energy and J r , providing a way to help identify real versus fake clusters. We also recommend incorporating chemical tagging as a way to improve clustering results.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1978

Space plasma laboratory - Experiment in simulated ionospheric plasma

Several experiments with simulated ionospheric plasma were performed in the Johnson Space Center's large (17 m diameter x 27 m height) vacuum chamber. Two of these, the RF discharge and the electron-beam plasma discharge, are described here. The RF experiment involved measurement of the loading on a 5 m dipole and a 5 m loop antenna caused by the presence of a plasma. The results indicate that when the RF frequency is near the electron gyro frequency a self-sustained plasma discharge is set up and the real part of the complex antenna impedance increases. The beam-plasma experiment was carried out to study a discharge produced by an electron beam with an energy of about 1 keV when the electron beam was injected parallel to the ambient magnetic field. As the beam current was raised to a critical level, a spontaneous transition occurred whereby a luminous halo was formed around the electron beam indicating a sustained discharge.

Konradi, A.↗
DOE OSTI2022

The dark side of galaxy stellar populations – II. The dependence of star-formation histories on halo mass and on the scatter of the main sequence

Nearby galaxies are the end result of their cosmological evolution, which is predicted to be influenced by the growth of their host dark matter haloes. This co-evolution potentially leaves signatures in present-day observed galaxy properties, which might be essential to further understand how the growth and properties of galaxies are connected to those of their host haloes. In this work, we study the evolutionary histories of nearby galaxies both in terms of their host haloes and the scatter of the star-forming main sequence by investigating their time-resolved stellar populations using absorption optical spectra drawn from the Sloan Digital Sky Survey. We find that galaxy star-formation histories depend on the masses of their host haloes, and hence they shape the evolution of the star-forming main sequence over cosmic time. Additionally, we also find that the scatter around the z = 0 star-forming main sequence is not (entirely) stochastic, as galaxies with currently different star-formation rates have experienced, on average, different star-formation histories. Furthermore, our findings suggest that dark matter haloes might play a key role in modulating the evolution of star formation in galaxies, and thus of the main sequence, and further demonstrate that galaxies at different evolutionary stages contribute to the observed scatter of this relation.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2001

HALOE Temperature Data Comparison with Rocket-Borne Falling Sphere Temperatures

Recent comparison of upper stratospheric and mesospheric temperatures measured with the HALOE instrument on UARS and the rocket-borne passive inflatable falling sphere launched from Wallops Island reveals a temperature bias of up to 10 K between about 66 and 72 km. Falling sphere measurements analyzed between 1991 and 1995 were used in the comparison, however, these measurements were processed with an earlier version of the reduction software that included temperature bias in the region of 70 km. The bias arose from a discontinuity in the falling sphere drag table. This discontinuity occurs when the sphere's fall velocity changes from the supersonic to the subsonic flow regime and has been called the MACH 1 problem. Improvement to the software employed and the availability of a new atmospheric model is now used to initiate reduction of the radar tracking data. It is possible new reduction of the existing data will reduce the bias currently observed. We plan to show changes, if any, in the size of the bias between HALOE and the falling sphere temperatures after reprocessing of the sphere measurements.

Schmidlin, F. J.↗
DOE OSTI2020

Chemical Analysis of the Ultrafaint Dwarf Galaxy Grus II. Signature of High-mass Stellar Nucleosynthesis

We present a detailed abundance analysis of the three brightest member stars at the top of the giant branch of the ultrafaint dwarf (UFD) galaxy Grus II. All stars exhibit a higher than expected [Mg/Ca] ratio compared to metal-poor stars in other UFD galaxies and in the Milky Way (MW) halo. Nucleosynthesis in high-mass ( 20 M ⊙) core-collapse supernovae has been shown to create this signature. The abundances of this small sample (three) stars suggests the chemical enrichment of Grus II could have occurred through substantial high-mass stellar evolution, and is consistent with the framework of a top-heavy initial mass function. However, with only three stars it cannot be ruled out that the abundance pattern is the result of a stochastic chemical enrichment at early times in the galaxy. The most metal-rich of the three stars also possesses a small enhancement in rapid neutron-capture (r-process) elements. The abundance pattern of the r-process elements in this star matches the scaled r-process pattern of the solar system and r-process enhanced stars in other dwarf galaxies and in the MW halo, hinting at a common origin for these elements across a range of environments. All current proposed astrophysical sites of r-process element production are associated with high-mass stars, thus the possible top-heavy initial mass function of Grus II would increase the likelihood of any of these events occurring. The time delay between the α and r-process element enrichment of the galaxy favors a neutron star merger as the origin of the r-process elements in Grus II.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1991

Stellar photometry with the Hubble Space Telescope Wide-field/Planetary camera - A progress report

The prospects for the use of the Wide-Field/Planetary Camera (WFPC) for stellar photometry are described. The large halos of the point-spread function (PSF) resulting from spherical aberration and from spatial, temporal, and color variations of the PSF are the main limitations to accurate photometry. Degradations caused by crowding are exacerbated by the halos of the PSF. An attempt is made to quantify these effects and determine the current accuracy of stellar photometry with the WFPC. In realistic cases, the brighter stars in crowded fields have 0.09 mag errors; fainter stars have larger errors depending on the degree of crowding. It is shown that measuring Cepheids in Virgo Cluster galaxies is not currently possible without inordinate increases in exposure times.

Holtzman, Jon A.↗
NASA NTRS2017

Efficient NRHO to DRO transfers in cislunar space

There has been recently a growing interest in cislunar missions, in particular for supporting human deep space exploration. Understanding the dynamical envi-ronment between various cislunar orbits is therefore useful. The current study is focused on finding efficient transfer trajectory options between a Near-Rectilinear Halo Orbit (NRHO) and a Distant Retrograde Orbit (DRO) in the Earth-Moon system. A general methodology is introduced to design these trans-fers in a systematic way, including the use of solar perturbations and lunar fly-bys. Representative solutions are presented and compared in terms of delta-v and flight time, including a transfer requiring 56 m/s only.

Lantoine, Gregory↗
DOE OSTI2026

Beam halo formation with different cathode distributions

Beam halo refers to the low-density distribution of particles extending beyond the beam core, and its generation and mitigation are important topics in particle accelerator design. Effective mitigation of beam halo is essential for the cooler design based on Energy Recovery Linac (ERL), which must deliver an electron beam with average beam current of 100 mA and a charge 1 nC per bunch. In the ERL injector and booster linacs, space charge effects are stronger due to relatively low beam energy (6 MeV). Additionally, the longer bunch length of approximately 100 ps in this regime vs the RF period of 5.08 ns makes the formation of beam halos more likely. Therefore, effective collimation of beam halo is critical to maintaining the required beam parameters. To design an effective collimation scheme, several halo distributions were generated at the cathode and used to study halo formation within the injector-merger. This paper presents different halo distributions and halo formation, providing insights on halo collimation strategy.

Accelerator Physics↗
DOE OSTI2020

Dark matter cores and cusps in spiral galaxies and their explanations

We compare proposed solutions to the core vs cusp issue of spiral galaxies, which has also been framed as a diversity problem, and demonstrate that the cuspiness of dark matter halos is correlated with the stellar surface brightness. We compare the rotation curve fits to the SPARC sample from a self-interacting dark matter (SIDM) model, which self-consistently includes the impact of baryons on the halo profile, and hydrodynamical N-body simulations with cold dark matter (CDM). The SIDM model predicts a strong correlation between the core size and the stellar surface density, and it provides the best global fit to the data. The CDM simulations without strong baryonic feedback effects fail to explain the large dark matter cores seen in low surface brightness galaxies. On the other hand, with strong feedback, CDM simulations do not produce galaxy analogs with high stellar and dark matter densities, and therefore they have trouble in explaining the rotation curves of high surface brightness galaxies. This implies that current feedback implementations need to be modified. We also explicitly show how the concentration-mass and stellar-to-halo mass relations together lead to a radial acceleration relation (RAR) in an averaged sense, and reiterate the point that the RAR does not capture the diversity of galaxy rotation curves in the inner regions. These results make a strong case for SIDM as the explanation for the cores and cusps of field galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Velocity Independent Constraints on Spin-Dependent DM-Nucleon Interactions from IceCube and PICO

Adopting the Standard Halo Model (SHM) of an isotropic Maxwellian velocity distribution for dark matter (DM) particles in the Galaxy, the most stringent current constraints on their spin-dependent scattering cross-section with nucleons come from the IceCube neutrino observatory and the PICO-60 $\hbox {C}_3\hbox {F}_8$ superheated bubble chamber experiments. The former is sensitive to high energy neutrinos from the self-annihilation of DM particles captured in the Sun, while the latter looks for nuclear recoil events from DM scattering off nucleons. Although slower DM particles are more likely to be captured by the Sun, the faster ones are more likely to be detected by PICO. Recent N-body simulations suggest significant deviations from the SHM for the smooth halo component of the DM, while observations hint at a dominant fraction of the local DM being in substructures. We use the method of Ferrer et al. (JCAP 1509: 052, 2015) to exploit the complementarity between the two approaches and derive conservative constraints on DM-nucleon scattering. Our results constrain $\sigma _{\mathrm{SD}} \lesssim 3 \times 10^{-39} \mathrm {cm}^2$ ($6 \times 10^{-38} \mathrm {cm}^2$) at $\gtrsim 90\%$ C.L. for a DM particle of mass 1 TeV annihilating into $\tau ^+ \tau ^-$ ($b\bar{b}$) with a local density of $\rho _{\mathrm{DM}} = 0.3~\mathrm {GeV/cm}^3$. The constraints scale inversely with $\rho _{\mathrm{DM}}$ and are independent of the DM velocity distribution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Velocity-dependent annihilation radiation from dark matter subhalos in cosmological simulations

Here, we use the suite of Milky Way-like galaxies in the Auriga simulations to determine the contribution to annihilation radiation from dark matter subhalos in three velocity-dependent dark matter annihilation models: Sommerfeld, p-wave, and d-wave models. We compare these to the corresponding distribution in the velocity-independent s-wave annihilation model. For both the hydrodynamical and dark-matter-only simulations, only in the case of the Sommerfeld-enhanced annihilation does the total annihilation flux from subhalos exceed the total annihilation flux from the smooth halo component within the virial radius of the halo. Progressing from Sommerfeld to the s, p, and d-wave models, the contribution from the smooth component of the halo becomes more dominant, implying that for the p-wave and d-wave models the smooth component is by far the dominant contribution to the radiation. Comparing to the Galactic center excess observed by Fermi-LAT, for all simulated halos the emission is dominated by the smooth halo contribution. However, it is possible that for Sommerfeld models, extrapolation down to mass scales below the current resolution limit of the simulation would imply a non-negligible contribution to the gamma-ray emission from the Galactic Center region.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2016

Summary of 2016 Light Microscopy Module (LMM) Physical Science Experiments on ISS. Update of LMM Science Experiments and Facility Capabilities

This presentation will feature a series of short, entertaining, and informative videos that describe the current status and science support for the Light Microscopy Module (LMM) facility on the International Space Station. These interviews will focus on current experiments and provide an overview of future capabilities. The recently completed experiments include nano-particle haloing, 3-D self-assembly with Janus particles and a model system for nano-particle drug delivery. The videos will share perspectives from the scientists, engineers, and managers working with the NASA Light Microscopy program.

Sicker, Ronald J.↗
DOE OSTI2020

The Universe at z > 10: predictions for JWST from the universemachine DR1

The James Webb Space Telescope (JWST) is expected to observe galaxies at z > 10 that are presently inaccessible. Here, we use a self-consistent empirical model, the universemachine, to generate mock galaxy catalogues and light-cones over the redshift range z = 0-15. These data include realistic galaxy properties (stellar masses, star formation rates, and UV luminosities), galaxy–halo relationships, and galaxy–galaxy clustering. Mock observables are also provided for different model parameters spanning observational uncertainties at z < 10. We predict that Cycle 1 JWST surveys will very likely detect galaxies with M* > 10 7 M⊙ and/or M 1500 < -17 out to at least z ~ 13.5. Number density uncertainties at z > 12 expand dramatically, so efforts to detect z > 12 galaxies will provide the most valuable constraints on galaxy formation models. Additionally, the faint-end slopes of the stellar mass/luminosity functions at a given mass/luminosity threshold steepen as redshift increases. This is because observable galaxies are hosted by haloes in the exponentially falling regime of the halo mass function at high redshifts. Hence, these faint-end slopes are robustly predicted to become shallower below current observable limits (M* < 10 7 M⊙ or M 1500 > -17). For reionization models, extrapolating luminosity functions with a constant faint-end slope from M 1500 = -17 down to M 1500 = -12 gives the most reasonable upper limit for the total UV luminosity and cosmic star formation rate up to z ~ 12. We compare to three other empirical models and one semi-analytic model, showing that the range of predicted observables from our approach encompasses predictions from other techniques. Public catalogues and light-cones for common fields are available online.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRSDate not supplied

Optimizing Consumable Gas Tank Usage while Maintaining Emergency Reserves Between Two Pressure Control Systems on Gateway

Two of NASA’s Lunar Space Station (Gateway) modules, the Habitation and Logistics Outpost (HALO) and International Habitat (IHAB) contain a pressure control system (PCS) that is used to supply Nitrogen (N2) and Oxygen (O2) to maintain a habitable environment within Gateway, with only one of the PCS active at any given time. To protect the crew during a contingency that is affecting pressure control and therefore gas consumables, Gateway is required to have sufficient amount of reserve consumable gas across the entire habitable Gateway stack of modules until the gas can be replenished by crew changing out a gas tank. This will occur in a non-contingency setting either on the current mission or on the next mission. To access the stack reserve Gateway features a Nitrogen Oxygen Transfer System (NOTS) between HALO and IHAB that allows each module’s PCS to access the gas tanks in the other module. The PCS designs are different between the two modules and lack interchangeable tanks so which module has active PCS must be accounted for in logistics planning. This paper describes the logistics resupply planning analysis used to determine the most efficient use of the tanks within each PCS, and a method for switching which module is active for PCS while maintaining the stack reserve that preserves enough gas to cover contingency cases.

Rachel Anne Sturtz↗
NASA NTRS2020

Phase Control and Eclipse Avoidance in Near Rectilinear Halo Orbits

The baseline trajectory proposed for the Gateway is a southern Earth-Moon L2 Near Rectilinear Halo Orbit (NRHO). Designed to avoid eclipses, the NRHO exhibits a resonance with the lunar synodic period. The current investigation details the eclipse behavior in the baseline NRHO. Then, phase control is added to the orbit maintenance algorithm to regulate perilune passage time and maintain the eclipse-free characteristics of the Gateway reference orbit. A targeting strategy is designed to periodically target back to the long-horizon virtual reference if the orbit diverges over time in the presence of additional perturbations.

Davis, Diane C.↗
DOE OSTI2021

Core Mass Estimates in Strong Lensing Galaxy Clusters: A Comparison between Masses Obtained from Detailed Lens Models, Single-halo Lens Models, and Einstein Radii

The core mass of galaxy clusters is both an important anchor of the radial mass distribution profile and probe of structure formation. With thousands of strong lensing galaxy clusters being discovered by current and upcoming surveys, timely, efficient, and accurate core mass estimates are needed. Here, we assess the results of two efficient methods to estimate the core mass of strong lensing clusters: the mass enclosed by the Einstein radius (M(<θ E ) where θ E is approximated from arc positions; Remolina González et al. 2020), and single-halo lens model (M SHM ; Remolina González et al. 2021), against measurements from publicly available detailed lens models (M DLM ) of the same clusters. We use data from the Sloan Giant Arc Survey, the Reionization Lensing Cluster Survey, the Hubble Frontier Fields, and the Cluster Lensing and Supernova Survey with Hubble. We find a scatter of 18.2% (8.2%) with a bias of -7.1% (1.0%) between M corr (<θ arcs ) (M SHM ) and M DLM . Last, we compare the statistical uncertainties measured in this work to those from simulations. This work demonstrates the successful application of these methods to observational data. As the effort to efficiently model the mass distribution of strong lensing galaxy clusters continues, we need fast, reliable methods to advance the field.

79 ASTRONOMY AND ASTROPHYSICS↗