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At least 703 records · Page 39
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NASA NTRS1982

Variability of compact radio sources at a wavelength of 1 millimeter

Broad-band 1 mm continuum observations of 3C 273, 3C 279, BL Lac, 3C 84, OJ 287, and 3C 345 made between 1977 March and 1981 January are reported. With the possible exception of 3C 279, all of the objects exhibited evidence for variability in the 1 mm flux density on the time scale of a few months. Flux variations at wavelengths of 1 mm and 2 cm are well correlated for the 'blazars' (BL Lac objects and optically violent variable quasars) observed; emission outbursts occur simultaneously and have similar amplitude at the two wavelengths. In contrast, an outburst in the flux from the Seyfert galaxy 3C 84 was observed at a wavelength of 1 mm in early 1980 but has not appeared at 2 cm as of 1 yr later. The observed relationship between 'blazar' emission variability at 1 mm and 2 cm is inconsistent with the canonical expanding-source model of radio variability or any of its modifications. Instead, models in which the number of synchrotron-radiating electrons is time variable (due to particle injection or acceleration behind a relativistic shock) are required.

Ennis, D. J.↗
NASA NTRS2022

Compact Midwave Imaging System: Results from an Airborne Demonstration

The Compact Midwave Imaging System (CMIS) is a wide field of view, multi-angle, multi-spectral push frame imager that relies on the forward motion of the satellite to create a two-dimensional (2D) image swath. An airborne demonstration of CMIS was successfully completed in January-February 2021 on the NASA Langley Research Center Gulfstream III. The primary objective of the four-flight campaign was to demonstrate the capability of this unique instrument to perform stereo observations of clouds and other particulates (e.g. smoke) in the atmosphere. It is shown that the midwave infrared (MWIR) spectral bands of CMIS provide a unique 24/7 capability with high resolution for accurate stereo sensing.The instrument relies on new focal plane array (FPA) technology, which provides excellent sensitivity at much warmer detector temperatures than traditional technologies. This capability enabled a compact, low-cost design that can provide atmospheric motion vectors and cloud heights to support requirements for atmospheric winds in the 2017-2027 Earth Science Decadal Survey. Applications include day/night observations of the planetary boundary layer, severe weather, and wildfires. A comparison with current space-based earth science instruments demonstrates that the SWIR/MWIR multi-spectral capability of CMIS is competitive with larger, more expensive instrumentation. Imagery obtained over a controlled burn and operating nuclear power plant demonstrated the sensitivity of the instrument to temperature variations. The system relies on a mature stereoscopic imaging technique applied to the same scene from two independent platforms to unambiguously retrieve atmospheric motion vectors (AMVs) with accurate height assignment.This capability has been successfully applied to geostationary and low-earth orbit satellites to achieve excellent accuracy. When applied to a ground-point validation case, the accuracy for the CMIS aircraft observations was 20 m and 0.3 m/s for cloud heights and motion vectors, respectively. This result was confirmed by a detailed error analysis with analytical and covariance models. The results for CMIS cases with under flights of Aeolus, CALIPSO and Aqua provided a good validation of expected accuracies. The paper also showed the feasibility of accommodating CMIS on CubeSats to enable multiple instruments to be flown in a leader-follower mode.

stereo winds↗
NASA NTRS1990

0108 + 388 - A compact double source with surprising properties

49 cm, 6 cm, and 20 cm observations of the compact double ratio source 0108 + 388 are presented. Extended emission about 20 deg to the east of the core is detected which resembles a hot spot/lobe with a bridge of emission extending back to the core. This is the first detection of extended emission associated with such a source, and it is inconsistent with the suggestion that such sources are very young classical double radio sources. The inconsistency can be reconciled if the activity in this object is recurrent and the emission is the relic of a previous epoch of activity. Alternatively, the source may be a normal-aged radio galaxy in which most of the radio-emitting plasma is currently unable to escape the nuclear regions of the galaxy. The steep low-frequency spectrum of the core is probably related to the origin of the compact double and suggests that both components are very sharply confined on both their inner and outer edges.

Baum, S. A.↗
NASA NTRS1973

Hand-held photomicroscope

A small, lightweight, compact, hand-held photomicroscope provides simultaneous viewing and photographing, with adjustable specimen illumination and exchangeable camera format. The novel photomicroscope comprises a main housing having a top plate, bottom plate, and side walls. The objective lens is mounted on the top plate in an inverted manner relative to the normal type of mounting. The specimen holder has an adjusting mechanism for adjustably moving the specimen vertically along an axis extending through the objective lens as well as transverse of the axis. The lens system serves to split the beam of light into two paths, one to the eyepiece and the other to a camera mounting. A light source is mounted on the top plate and directs light onto the specimen. A rheostat device is mounted on the top plate and coupled to the power supply for the light source so that the intensity of the light may be varied.

Zabower, H. R.↗
NASA NTRS1977

Conceptual design of closed Brayton cycle for coal-fired power generation

The objectives to be realized in developing a closed cycle gas turbine are (1) to exploit high temperature gas turbine technology while maintaining a working fluid which is free from combustion gas contamination, (2) to achieve compact turbo-equipment designs through pressurization of the working fluid, and (3) to obtain relatively simple cycle configurations. The technical/economic performance of a specific closed cycle gas turbine system was evaluated through the development of a conceptual plant and system design. This energy conversion system is designed for electric utility service and to utilize coal directly in an environmentally acceptable manner.

Shah, R. P.↗
NASA NTRS1985

An evaluation of fracture analysis methods

The results of an experimental and predictive round robin on the applications of fracture analysis methods are presented. The objective of the round robin was to verify whether fracture analysis methods currently in use can or cannot predict failure loads on complex structural components containing cracks. Fracture results from tests on a number of compact specimens were used to make the predictions. The accuracy of the prediction methods was evaluated in terms of the variation in the ratio of predicted to experimental failure loads, and the predictions methods are ranked in order of minimum standard error. A range of applicability of the different methods was also considered in assessing their usefulness. For 7075-T651 aluminum alloy, the best methods were: the effective K sub R curve; the critical crack-tip opening displacement (CTOD) criterion using a finite element analysis; and the K sub R curve with the Dugdale model. For the 2024-T351 aluminum alloy, the best methods included: the two-parameter fracture criterion (TPFC); the CTOD parameter using finite element analysis; the K-curve with the Dugdale model; the deformation plasticity failure assessment diagram (DPFAD); and the effective K sub R curve with a limit load condition. For 304 stainless steel, the best methods were the limit load analysis; the CTOD criterion using finite-element analysis TPFC and DPFAD. Some sample experimental results are given in an appendix.

Newman, J. C., Jr.↗
NASA NTRS1990

MS 0129.2 - 2237 - Interacting galaxies at z = 0.11

The X-ray source MS 0129.2 - 2237 is positionally coincident with an interacting system of galaxies. This paper presents the results of a spectroscopic and photometric investigation of the system, which show that a Seyfert 1.5, a Seyfert 2 nucleus or H II region, or a starburst galaxy, a normal galaxy plus possibly another galaxy where star-forming activity is taking place are strongly interacting. The redshift of the system is z = 0.11. The maximum projected diameter of the envelope common to the four spectroscopically distinct objects is about 98 kpc (H0 = 50 km/s M/pc and q0 = 0.5). The isolated environment in which the system lies suggests that these results present evidence of the final stage of the life of a compact group of galaxies where members are merging into an elliptical galaxy.

Maccagni, Dario↗
NASA NTRS1993

HST imaging of hydrogen-poor ejecta in Abell 30 and Abell 78 - Wind-blown cometary structures

HST Faint Object Camera images of hydrogen-poor gas in the planetary nebulae A30 and A78 have revealed remarkable 'cometary' structures in the O III 5007-A forbidden line. Most of these cometary structures, consisting of compact (0.15-0.5 arcsec) knots with radial tails several arcsec in length, are located in an equatorial plane in both nebulae. In addition, two bright, compact (0.3 arcsec) polar knots are present in A30, one of them forming a bow shock. Corresponding polar features in A78 are more diffuse. The central stars of both nebulae have energetic winds which are most likely responsible for the 'cometary' knot morphology. We interpret this morphology in terms of dense (several thousand electrons per cu cm) H-poor condensations whose outer expanding layers are swept outward by stellar winds. Photoionization modeling indicates that while dense knot cores are mostly heated by atomic photoionization, expanding tenuous gas is heated by photoelectrons ejected from abundant dust grains. Our models predict steep temperature gradients for which there is observational evidence and possible abrupt phase transitions in the expanding gas.

Borkowski, Kazimierz J.↗
NASA NTRS2007

First X-ray Observations of the Young Pulsar J1357-6429

The first short Chandra and XMM-Newton observations of the young and energetic pulsar J1357-6429 provided strong indications of a tail-like pulsar-wind nebula associated with this object, as well as strong pulsations of its X-ray flux with a pulsed fraction above 40% and a thermal component dominating at lower photon energies (below 2 keV). The elongated nebular is very compact in size. about 1" x 1.5" and might be interpreted as a pulsar jet. The thermal radiation is most plausibly emitted from the entire neutron star surface of an effective temperature about 1 MK covered with a magnetized hydrogen atmosphere At higher energies the pulsar's emission is of a nonthermal (magnetospheric) origin, with a power-law spectrum of a photon index Gamma approx. equals 1.1. This makes the X-ray properties of PSR J1357-6429 very similar to those of the youngest pulsars J1119-6127 and Vela with a detected thermal radiation.

Zavlin, Vyacheslav E.↗
NASA NTRS2008

X-ray Timing Measurements

We present new, extended X-ray timing measurements of the ultra-compact binary candidates V407 Vul and RX J0806.3+1527 (J0806), as well as a summary of the first high resolution X-ray spectra of 50806 obtained with the Chandra/LETG. The temporal baseline for both objects is approximately 12 years, and our measurements confirm the secular spin-up in their X-ray periods. The spin-up rate in 50806 is remarkably uniform at 3.55x10(exp -16)Hz/s, with a measurement precision of 0.2%. We place a limit (90% confidence) on 1 d dot nu < 4x10(exp -26)Hz/sq s. Interestingly, for V407 Vul we find the first evidence that the spin-up rate is slowing, with d dot\nu = -2.8 pm 1x10(exp -26)Hz/sq s. This provides the first indication that torques in addition to gravitational radiation are present in V407 Vul. Further monitoring could constrain the nature of the torque, as either accretion induced or due to unipolar induction. We also obtained the first high resolution X-ray spectrum of J0806 with an 80 ksec Chandra/LETG observation. We find evidence for emission features in the 25-50 AA range, with the strongest feature centered at 27 AA. The spectrum appears largely devoid of common lines of oxygen, nitrogen and neon, and we suggest the 27 AA feature may be associated with heavier species, such as magnesium, silicon or sulphur. Deeper observations will be needed to fully exploit the strong diagnostic potential of high resolution spectroscopy for these objects.

Strohmayer, T.↗
NASA NTRS2011

A Dual Source Ion Trap Mass Spectrometer for the Mars Organic Molecule Analyzer of ExoMars 2018

We present details on the objectives, requirements, design and operational approach of the core mass spectrometer of the Mars Organic Molecule Analyzer (MOMA) investigation on the 2018 ExoMars mission. The MOMA mass spectrometer enables the investigation to fulfill its objective of analyzing the chemical composition of organic compounds in solid samples obtained from the near surface of Mars. Two methods of ionization are realized, associated with different modes of MOMA operation, in a single compact ion trap mass spectrometer. The stringent mass and power constraints of the mission have led to features such as low voltage and low frequency RF operation [1] and pulse counting detection.

Brickerhoff, William B.↗
NASA NTRS2016

On the Nature of the Enigmatic Object IRAS 19312+1950: A Rare Phase of Massive Star Formation?

IRAS19312+1950 is a peculiar object that has eluded firm characterization since its discovery, with combined maser properties similar to an evolved star and a young stellar object (YSO). To help determine its true nature, we obtained infrared spectra of IRAS19312+1950 in the range 5-550 microns using the Herschel and Spitzer space observatories. The Herschel PACS maps exhibit a compact, slightly asymmetric continuum source at 170 microns, indicative of a large, dusty circumstellar envelope. The far-IR CO emission line spectrum reveals two gas temperature components: approx. = 0.22 Stellar Mass of material at 280+/-18 K, and ≈1.6 Me of material at 157+/-3 K. The OI 63 micron line is detected on-source but no significant emission from atomic ions was found. The HIFI observations display shocked, high-velocity gas with outflow speeds up to 90 km/s along the line of sight. From Spitzer spectroscopy, we identify ice absorption bands due to H2O at 5.8 microns and CO2 at 15 microns. The spectral energy distribution is consistent with a massive, luminous (approx. 2 × 10(exp 4) Stellar Luminosity) central source surrounded by a dense, warm circumstellar disk and envelope of total mass approx. 500-700 Stellar Mass with large bipolar outflow cavities. The combination of distinctive far-IR spectral features suggest that IRAS19312+1950 should be classified as an accreting, high-mass YSO rather than an evolved star. In light of this reclassification, IRAS19312+1950 becomes only the fifth high-mass protostar known to exhibit SiO maser activity, and demonstrates that 18 cm OH maser line ratios may not be reliable observational discriminators between evolved stars and YSOs.

ISM: molecules aEuro" masers aEuro" stars↗
NASA NTRS2021

VLTI-MATISSE Chromatic Aperture-Synthesis Imaging of η Carinae’s Stellar Wind Across the Brα Line: Periastron Passage Observations in February 2020

Context: Eta Carinae is a highly eccentric, massive binary system (semimajor axis∼15.5 au) with powerful stellar winds and a phase-dependent wind-wind collision (WWC) zone. The primary star, ηCar A, is a luminous blue variable (LBV); the secondary, η Car B, is a Wolf-Rayet or O star with a faster but less dense wind. Aperture-synthesis imaging allows us to study the mass loss from the enigmatic LBV η Car. Understanding LBVs is a crucial step toward improving our knowledge about massive stars and their evolution. Aims: Our aim is to study the intensity distribution and kinematics of η Car’s WWC zone. Methods: Using the VLTI-MATISSE mid-infrared interferometry instrument, we perform Brα imaging of η Car’s distorted wind. Results: We present the first VLTI-MATISSE aperture-synthesis images of η Car A’s stellar wind in several spectral channels distributed across the Brα 4.052 μm line (spectral resolving power R∼960). Our observations were performed close to periastron passage in February 2020 (orbital phase∼14.0022). The reconstructed iso-velocity images show the dependence of the primary stellar wind on wavelength or line-of-sight (LOS) velocity with a spatial resolution of 6 mas (∼14 au). The radius of the faintest outer wind regions is∼26 mas (∼60 au). At several negative LOS velocities, the primary stellar wind is less extended to the northwest than in other directions. This asymmetry is most likely caused by the WWC. Therefore, we see both the velocity field of the undisturbed primary wind and the WWC cavity. In continuum spectral channels, the primary star wind is more compact than in line channels. A fit of the observed continuum visibilities with the visibilities of a stellar wind CMFGEN model (CMFGEN is an atmosphere code developed to model the spectra of a variety of objects) provides a full width at half maximum fit diameter of the primary stellar wind of 2.84±0.06 mas (6.54±0.14 au). We compare the derived intensity distributions with the CMFGEN stellar wind model and hydrodynamic WWC models.

G Weigelt↗
NASA NTRS1980

The continuous spectrum of Markarian 421 during periods of X-ray satellite observations

New UBVRI photometry of Mrk 421 obtained during periods of X-ray satellite observations are presented. An X-ray light curve for 1977 November from the HEAO A-1 experiment is also given. The decomposition of the UBVR fluxes into a compact nonthermal component and an extended galactic component shows that there are coordinated variations in the optical nonthermal and X-ray emission. The data are consistent with the hypothesis that the mini-BL Lac object is emitting by the synchrontron-self-Compton process. The host galaxy of this composite source has properties like those of a giant elliptical.

Mufson, S. L.↗
NASA NTRS1990

Cometary compact H II regions are stellar-wind bow shocks

Comet-shaped H II regions, like G34.3 + 0.2, are easily explained as bow shocks created by wind-blowing massive stars moving supersonically through molecular clouds. The required velocities of the stars through dense clumps are less than about 10 km/s, comparable to the velocity dispersion of stars in OB associations. An analytic model of bow shocks matches the gross characteristics seen in the radio continuum and the velocity structure inferred from hydrogen recombination and molecular line observations. The champagne flow model cannot account for these structures. VLBI observations of masers associated with the shells of cometary compact H II regions should reveal tailward proper motions predominantly parallel to the shell, rather than perpendicular. It is predicted that over a decade baseline, high signal-to-noise VLA observations of this class of objects will show headward pattern motion in the direction of the symmetry axis, but not expansion. Finally, shock-generated and coronal infrared lines are also predicted.

Van Buren, Dave↗
NASA NTRS1991

Development and mechanical properties of structural materials from lunar simulant

Development of versatile engineering materials from locally available materials in space is an important step toward establishment of outposts such as on the moon and Mars. Here development of the technologies for manufacture of structural and construction materials on the moon, utilizing local lunar soil (regolith), without the use of water, is an important element for habitats and explorations in space. It is also vital that the mechanical behavior such as strength and flexural properties, fracture toughness, ductility, and deformation characteristics are defined toward establishment of the ranges of engineering applications of the materials developed. The objectives include two areas: (1) thermal liquefaction of lunar simulant (at about 1100 C) with different additives (fibers, powders, etc.); and (2) development and use of a traxial test device in which lunar simulants are first compacted under cycles of loading, and then tested with different vacuums and initial confining or insitu stress. The second area was described in previous progress reports and publications; since the presently available device allows vacuum levels up to only 10(exp -4) torr, it is recommended that a vacuum pump that can allow higher levels of vacuum is acquired.

Desai, Chandra S.↗
NASA NTRS2003

Discovery of an Obscured Supernova in Arp 299

The galaxy merger Arp 299, at a distance of 40 Mpc, is one of the most extensively studied interacting starburst galaxies known. It has been the site of 4 known supernovae (SNe) since 1990. Arp 299 contains a number of strong radio and infrared condensations, with the strongest starburst occurring in 'Source A,' in the nuclear region of the eastern galaxy. Source A has an inferred supernova rate of 0.5-0.7/yr, and its star formation peaked 6-8 Myr ago. Our recent observations identify a new radio-loud SN in Source A, which occurred sometime between April 2002 and February 2003. We imaged Arp 299 at milliarcsecond resolution at two epochs, in April 2002 and February 2003, using the Very Long Baseline Array and (at the first epoch) the Green Bank Telescope. In 2002, four compact radio sources were found in Source A at 2.3 GHz, with flux densities ranging from 0.3 to 1.7 mJy. In 2003, 8.4 GEz images revealed a new 3 mJy source, as well as the four objects detected a year earlier. The new radio SN is more than 1000 times more powerful than the galactic supernova remnant Cassiopeia A and is located located only 12 milliarcseconds (2.5 pc projected) from the strongest source seen in 2002. Milliarcsecond radio imaging is the only technique that could have detected this supernova, since it is embedded within an 80 mJy VLA source and buried in gas and dust (Av 15-25 mag). We suggest that both the new supernova and its nearest neighbor are occurring within a super star cluster, perhaps a newly formed globular cluster akin to those seen in a number of nearby galaxies and particularly galaxy mergers. If so, we are observing this cluster just as its massive stars have begun to explode into a very dense surrounding medium. The likelihood that most supernovae in such a medium will be radio-loud implies that future VLBI imaging over a number of years could lead to a direct measurement of the supernova rate in the Source A starburst, placing powerful constraints on models of present-day star formation processes.

Neff, Susan↗
NASA NTRS2011

A Summary on Progress in Materials Development for Advanced Lithium-ion Cells for NASA's Exploration Missions

Vehicles and stand-alone power systems that enable the next generation of human missions to the moon will require energy storage systems that are safer, lighter, and more compact than current state-of-the-art (SOA) aerospace quality lithium-ion (Li-ion) batteries. NASA is developing advanced Li-ion cells to enable or enhance future human missions to Near Earth Objects, such as asteroids, planets, moons, libration points, and orbiting structures. Advanced, high-performing materials are required to provide component-level performance that can offer the required gains at the integrated cell level. Although there is still a significant amount of work yet to be done, the present state of development activities has resulted in the synthesis of promising materials that approach the ultimate performance goals. This paper on interim progress of the development efforts will present performance of materials and cell components and will elaborate on the challenges of the development activities and proposed strategies to overcome technical issues.

Reid, Concha M.↗