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At least 1,693 records · Page 94
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

SEARCHING FOR EXTRATERRESTRIAL INTELLIGENCE SIGNALS IN ASTRONOMICAL SPECTRA, INCLUDING EXISTING DATA

The main purpose of this article is to make astronomers aware that Searches for Extraterrestrial Intelligence (SETIs) can be carried out by analyzing standard astronomical spectra, including those they have already taken. Simplicity is the outstanding advantage of a search in spectra. The spectra can be analyzed by simple eye inspection or a few lines of code that uses Fourier transform software. Theory, confirmed by published experiments, shows that periodic signals in spectra can be easily generated by sending light pulses separated by constant time intervals. While part of this article, like all articles on SETIs, is highly speculative the basic physics is sound. In particular, technology now available on Earth could be used to send signals having the required energy to be detected at a target located 1000 lt-yr away. Extraterrestrial Intelligence (ETI) could use these signals to make us aware of their existence. For an ETI, the technique would also have the advantage that the signals could be detected both in spectra and searches for intensity pulses like those currently carried out on Earth.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Photoelectron emission from metal surfaces induced by VUV-emission of filament driven hydrogen arc discharge plasma

Photoelectron emission measurements have been performed using a filament-driven multi-cusp arc discharge volume production H{sup −} ion source (LIISA). It has been found that photoelectron currents obtained with Al, Cu, Mo, Ta and stainless steel (SAE 304) are on the same order of magnitude. The photoelectron currents depend linearly on the discharge power. It is shown experimentally that photoelectron emission is significant only in the short wavelength range of hydrogen spectrum due to the energy dependence of the quantum efficiency. It is estimated from the measured data that the maximum photoelectron flux from plasma chamber walls is on the order of 1 A per kW of discharge power.

36 MATERIALS SCIENCE↗
DOE OSTI2012

A HIGH-RESOLUTION ATLAS OF URANIUM-NEON IN THE H BAND

We present a high-resolution (R Almost-Equal-To 50,000) atlas of a uranium-neon (U/Ne) hollow-cathode spectrum in the H band (1454-1638 nm) for the calibration of near-infrared spectrographs. We obtained this U/Ne spectrum simultaneously with a laser-frequency comb spectrum, which we used to provide a first-order calibration to the U/Ne spectrum. We then calibrated the U/Ne spectrum using the recently published uranium line list of Redman et al., which is derived from high-resolution Fourier transform spectrometer measurements. These two independent calibrations allowed us to easily identify emission lines in the hollow-cathode lamp that do not correspond to known (classified) lines of either uranium or neon, and to compare the achievable precision of each source. Our frequency comb precision was limited by modal noise and detector effects, while the U/Ne precision was limited primarily by the signal-to-noise ratio (S/N) of the observed emission lines and our ability to model blended lines. The standard deviation in the dispersion solution residuals from the S/N-limited U/Ne hollow-cathode lamp was 50% larger than the standard deviation of the dispersion solution residuals from the modal-noise-limited laser-frequency comb. We advocate the use of U/Ne lamps for precision calibration of near-infrared spectrographs, and this H-band atlas makes these lamps significantly easier to use for wavelength calibration.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Spectroscopy of a sample of unidentified gamma-ray Fermi sources

ABSTRACT The fourth-DR3 version (4FGL-DR3) of the Fermi-LAT catalogue of γ-ray sources contains ∼1000 objects at a galactic latitude |b| > 10° that are not identified with an optical counterpart. We performed a systematic study of these sources, focusing on 190 objects that have a unique X-ray counterpart in the available Swift/XRT observations. Optical counterparts were then selected, and optical spectra were found in the literature for 33 sources. We found that 21 could be classified as BL Lac objects. Among these, we were able to provide the redshift for eight of them, while for two others we established a lower limit to the redshift by detecting intervening absorption. The other 12 objects display optical spectra with prominent emission lines (0.036 < z < 1.65). These spectra are characterized by both broad and narrow emission lines, with the exception of three sources. One of these displays only broad emission lines, while the other two exclusively exhibit narrow lines. On the basis of the radio/optical flux ratio, all BL Lac objects in this study are radio-loud. Four sources out of the 12 with prominent emission lines can be classified as radio-loud, while at least five of the 12 sources with prominent lines are radio-quiet. This is somewhat unexpected, given the radio-loudness distribution of 4FGL-associated blazars.

Ulgiati, Alberto (ORCID:0009000736025276)↗
DOE OSTI2015

Experimental evidence of hot carriers solar cell operation in multi-quantum wells heterostructures

We investigated a semiconductor heterostructure based on InGaAsP multi quantum wells (QWs) using optical characterizations and demonstrate its potential to work as a hot carrier cell absorber. By analyzing photoluminescence spectra, the quasi Fermi level splitting Δμ and the carrier temperature are quantitatively measured as a function of the excitation power. Moreover, both thermodynamics values are measured at the QWs and the barrier emission energy. High values of Δμ are found for both transition, and high carrier temperature values in the QWs. Remarkably, the quasi Fermi level splitting measured at the barrier energy exceeds the absorption threshold of the QWs. This indicates a working condition beyond the classical Shockley-Queisser limit.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

ON THE VARIATIONS OF FUNDAMENTAL CONSTANTS AND ACTIVE GALACTIC NUCLEUS FEEDBACK IN THE QUASI-STELLAR OBJECT HOST GALAXY RXJ0911.4+0551 at z = 2.79

We report on sensitive observations of the CO(J = 7{yields}6) and C I({sup 3}P{sub 2} {yields} {sup 3}P{sub 1}) transitions in the z = 2.79 QSO host galaxy RXJ0911.4+0551 using the IRAM Plateau de Bure interferometer. Our extremely high signal-to-noise spectra combined with the narrow CO line width of this source (FWHM = 120 km s{sup -1}) allows us to estimate sensitive limits on the spacetime variations of the fundamental constants using two emission lines. Our observations show that the C I and CO line shapes are in good agreement with each other but that the C I line profile is of the order of 10% narrower, presumably due to the lower opacity in the latter line. Both lines show faint wings with velocities up to {+-}250 km s{sup -1}, indicative of a molecular outflow. As such, the data provide direct evidence for negative feedback in the molecular gas phase at high redshift. Our observations allow us to determine the observed frequencies of both transitions with so far unmatched accuracy at high redshift. The redshift difference between the CO and C I lines is sensitive to variations of {Delta}F/F with F = {alpha}{sup 2}/{mu} where {alpha} is the fine structure constant and {mu} is the electron-to-proton mass ratio. We find {Delta}F/F (6.9 {+-} 3.7) Multiplication-Sign 10{sup -6} at a look-back time of 11.3 Gyr, which, within the uncertainties, is consistent with no variations of the fundamental constants.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1987

Evidence for large-scale winds from starburst galaxies. II - An optical investigation of powerful far-infrared galaxies

The results of long-split spectroscopy of 20 powerful (about 10 to the 12th solar luminosities) far-infrared galaxies (FIRGs) are discussed, and deep narrowband images of the prototypical tepid FIRGs Arp 220 and NGC 6240 are presented. The results show that, as a class, the emission-line spectra of tepid FIRGs are most similar to LINERs, but about half are intermediate between LINERs and low-excitation H II regions. Huge (10,000-100,000-pc) and morphologically spectacular emission-line nebulae resembling the M82 filament system are associated with both NGC 6240 and Arp 220. It is proposed that the model of Chevalier and Clegg (1985) and McCarthy et al. (1987) for M82 be generalized to encompass powerful FIRGs as a class.

Heckman, Timothy M.↗
DOE OSTI2013

ON THE MECHANISM OF HARD X-RAY EMISSION FROM MAGNETARS

Persistent activity of magnetars is associated with electric discharge that continually injects relativistic particles into the magnetosphere. Large active magnetic loops around magnetars must be filled with outflowing particles that interact with radiation via resonant scattering and spawn electron-positron pairs. The outflow energy is processed into copious e {sup {+-}} until the plasma enters outer parts of the loop where the magnetic field is reduced below 10{sup 13} G. In the outer zone, photons scattered by the outflow do not convert to e {sup {+-}} pairs and the outflow radiates its energy away. The escaping radiation forms a distinct hard X-ray peak in the magnetar spectrum. It has the following features: (1) its luminosity L = 10{sup 35}-10{sup 36} erg s{sup -1} can easily exceed the thermal luminosity from the magnetar surface, (2) its spectrum extends from 10 keV to the MeV band with a hard spectral slope, which depends on the object inclination to the line of sight, (3) the anisotropic hard X-ray emission exhibits strong pulsations as the magnetar spins, (4) the emission spectrum typically peaks around 1 MeV, but the peak position significantly oscillates with the spin period, (5) the emission is dominated by the extraordinary polarization mode at photon energies below {approx}1 MeV, and (6) the decelerated pairs accumulate and annihilate at the top of the magnetic loop, and emit the 511 keV line with luminosity L {sub ann} {approx} 0.1 L. Features (1)-(3) agree with available data; (4)-(6) can be tested by future observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

DISSECTION OF H{alpha} EMITTERS : LOW-z ANALOGS OF z > 4 STAR-FORMING GALAXIES

Strong H{alpha} emitters (HAEs) dominate the z {approx} 4 Lyman-break galaxy (LBG) population. We have identified local analogs of these HAEs using the Sloan Digital Sky Survey. At z < 0.4, only 0.04% of the galaxies are classified as HAEs with H{alpha} equivalent widths ({approx}> 500 A) comparable to that of z {approx} 4 HAEs. Local HAEs have lower stellar mass and lower ultraviolet (UV) luminosity than z {approx} 4 HAEs, yet the H{alpha}-to-UV luminosity ratio, as well as their specific star formation rate, is consistent with that of z {approx} 4 HAEs, indicating that they are scaled-down versions of high-z star-forming galaxies. Compared to the previously studied local analogs of LBGs selected using rest-frame UV properties, local HAEs show similar UV luminosity surface density, weaker D{sub n} (4000) break, lower metallicity, and lower stellar mass. This implies that the local HAEs are less evolved galaxies than the traditional Lyman break analogs. In the stacked spectrum, local HAEs show a significant He II {lambda}4686 emission line suggesting a population of hot, massive stars similar to that seen in some Wolf-Rayet galaxies. Low [N II]/[O III] line flux ratios imply that local HAEs are inconsistent with being systems that host bright active galactic nuclei. Instead, it is highly likely that local HAEs are galaxies with an elevated ionization parameter, either due to a high electron density or large escape fraction of hydrogen ionizing photons as in the case of Wolf-Rayet galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

MAGNETIC NANOPARTICLES IN THE INTERSTELLAR MEDIUM: EMISSION SPECTRUM AND POLARIZATION

The presence of ferromagnetic or ferrimagnetic nanoparticles in the interstellar medium would give rise to magnetic dipole radiation at microwave and submillimeter frequencies. Such grains may account for the strong millimeter-wavelength emission observed from a number of low-metallicity galaxies, including the Small Magellanic Cloud. We calculate the absorption and scattering cross sections for such grains, with particular attention to metallic Fe, magnetite Fe{sub 3}O{sub 4}, and maghemite {gamma}-Fe{sub 2}O{sub 3}, all potentially present in the interstellar medium. The rate of Davis-Greenstein alignment by magnetic dissipation is also estimated. We determine the temperature of free-flying magnetic grains heated by starlight and calculate the polarization of the magnetic dipole emission from both free-fliers and inclusions. For inclusions, the magnetic dipole emission is expected to be polarized orthogonally relative to the normal electric dipole radiation. Magnetic dipole radiation will contribute significantly to the 20-40 GHz anomalous microwave emission only if a large fraction of the Fe is in metallic Fe iron nanoparticles with extreme elongations. Finally, we present self-consistent dielectric functions for metallic Fe, magnetite Fe{sub 3}O{sub 4}, and maghemite {gamma}-Fe{sub 2}O{sub 3}, enabling calculation of absorption and scattering cross sections from microwave to X-ray wavelengths.

36 MATERIALS SCIENCE↗
NASA NTRS1991

Mojave remote sensing field experiment

The Mojave Remote Sensing Field Experiment (MFE), conducted in June 1988, involved acquisition of Thermal Infrared Multispectral Scanner (TIMS); C, L, and P-band polarimetric radar (AIRSAR) data; and simultaneous field observations at the Pisgah and Cima volcanic fields, and Lavic and Silver Lake Playas, Mojave Desert, California. A LANDSAT Thematic Mapper (TM) scene is also included in the MFE archive. TM-based reflectance and TIMS-based emissivity surface spectra were extracted for selected surfaces. Radiative transfer procedures were used to model the atmosphere and surface simultaneously, with the constraint that the spectra must be consistent with field-based spectral observations. AIRSAR data were calibrated to backscatter cross sections using corner reflectors deployed at target sites. Analyses of MFE data focus on extraction of reflectance, emissivity, and cross section for lava flows of various ages and degradation states. Results have relevance for the evolution of volcanic plains on Venus and Mars.

Arvidson, Raymond E.↗
DOE OSTI2013

LOW-IONIZATION OUTFLOWS IN HIGH EDDINGTON RATIO QUASARS

The broad Mg II {lambda}2800 doublet has been frequently studied in connection with its potentially important role as a virial estimator of black hole mass in high-redshift quasars. An important task, therefore, is the identification of any line components that are likely related to broadening by non-virial motions. High signal-to-noise median composite spectra (binned in the {sup f}our-dimensional eigenvector 1'' context of Sulentic et al.) were constructed for the brightest 680 Sloan Digital Sky Survey Data Release 7 quasars in the 0.4 {<=} z {<=} 0.75 range where both Mg II {lambda}2800 and H{beta} are recorded in the same spectra. Composite spectra representing 90% of the quasars confirm previous findings that FWHM(Mg II {lambda}2800) is about 20% narrower than FWHM(H{beta}). The situation is clearly different for the most extreme (Population A) sources, which are the highest Eddington radiators in the sample. In the median spectra of these sources, FWHM Mg II {lambda}2800 is equal to or greater than FWHM(H{beta}) and shows a significant blueshift relative to H{beta}. We interpret the Mg II {lambda}2800 blueshift as the signature of a radiation-driven wind or outflow in the highest accreting quasars. In this interpretation, the Mg II {lambda}2800 line width-affected by blueshifted emission-is unsuitable for virial mass estimation in Almost-Equal-To 10% of quasars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

WATER AND METHANOL MASER ACTIVITIES IN THE NGC 2024 FIR 6 REGION

The NGC 2024 FIR 6 region was observed in the water maser line at 22 GHz and the methanol class I maser lines at 44, 95, and 133 GHz. The water maser spectra displayed several velocity components and month-scale time variabilities. Most of the velocity components may be associated with FIR 6n, while one component was associated with FIR 4. A typical lifetime of the water maser velocity components is about eight months. The components showed velocity fluctuations with a typical drift rate of about 0.01 km s{sup -1} day{sup -1}. The methanol class I masers were detected toward FIR 6. The methanol emission is confined within a narrow range around the systemic velocity of the FIR 6 cloud core. The methanol masers suggest the existence of shocks driven by either the expanding H II region of FIR 6c or the outflow of FIR 6n.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

RADIO-SELECTED BINARY ACTIVE GALACTIC NUCLEI FROM THE VERY LARGE ARRAY STRIPE 82 SURVEY

Galaxy mergers play an important role in the growth of galaxies and their supermassive black holes. Simulations suggest that tidal interactions could enhance black hole accretion, which can be tested by the fraction of binary active galactic nuclei (AGNs) among galaxy mergers. However, determining the fraction requires a statistical sample of binaries. We have identified kiloparsec-scale binary AGNs directly from high-resolution radio imaging. Inside the 92 deg{sup 2} covered by the high-resolution Very Large Array survey of the Sloan Digital Sky Survey (SDSS) Stripe 82 field, we identified 22 grade A and 30 grade B candidates of binary radio AGNs with angular separations less than 5'' (10 kpc at z = 0.1). Eight of the candidates have optical spectra for both components from the SDSS spectroscopic surveys and our Keck program. Two grade B candidates are projected pairs, but the remaining six candidates are all compelling cases of binary AGNs based on either emission line ratios or the excess in radio power compared to the Hα-traced star formation rate. Only two of the six binaries were previously discovered by an optical spectroscopic search. Based on these results, we estimate that ∼60% of our binary candidates would be confirmed once we obtain complete spectroscopic information. We conclude that wide-area high-resolution radio surveys offer an efficient method to identify large samples of binary AGNs. These radio-selected binary AGNs complement binaries identified at other wavelengths and are useful for understanding the triggering mechanisms of black hole accretion.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1985

Line identifications, line strengths, and continuum flux measurements in the ultraviolet spectrum of Arcturus

The ultraviolet spectrum of Arcturus has been observed at high resolution with the IUE satellite. Line identifications, mean absolute 'continuum' flux measurements, integrated absolute emission-line fluxes, and measurements of selected absorption line strengths are presented for the 2250-2930 A region. In the 1150-2000 A region, identifications are given primarily on the basis of low-resolution spectra. Chromospheric emission lines have been identified with low-excitation species including H I, C I, C II, O I, Mg I, Mg II, Al II, Si I, Si II, S I, and Fe II; there is no evidence for lines of C IV, N V, or other species requiring high temperatures. A search for molecular absorption features in the 2500-2930 A interval has led to several tentative identifications, but only OH could be established as definitely present. Iron lines strongly dominate the identifications in the 2250-2930 A region, Fe II accounting for about 86 percent of the emission features and Fe I for 43 percent of the identified absorption features.

Carpenter, K. G.↗
DOE OSTI2013

INTERACTING COSMIC RAYS WITH MOLECULAR CLOUDS: A BREMSSTRAHLUNG ORIGIN OF DIFFUSE HIGH-ENERGY EMISSION FROM THE INNER 2 Degree-Sign Multiplication-Sign 1 Degree-Sign OF THE GALACTIC CENTER

The high-energy activity in the inner few degrees of the Galactic center is traced by diffuse radio, X-ray, and {gamma}-ray emission. The physical relationship between different components of diffuse gas emitting at multiple wavelengths is a focus of this work. We first present radio continuum observations using the Green Bank Telescope and model the nonthermal spectrum in terms of a broken power-law distribution of {approx}GeV electrons emitting synchrotron radiation. We show that the emission detected by Fermi is primarily due to nonthermal bremsstrahlung produced by the population of synchrotron emitting electrons in the GeV energy range interacting with neutral gas. The extrapolation of the electron population measured from radio data to low and high energies can also explain the origin of Fe I 6.4 keV line and diffuse TeV emission, as observed with Suzaku, XMM-Newton, Chandra, and the H.E.S.S. observatories. The inferred physical quantities from modeling multiwavelength emission in the context of bremsstrahlung emission from the inner {approx}300 Multiplication-Sign 120 pc of the Galactic center are constrained to have the cosmic-ray ionization rate {approx}1-10 Multiplication-Sign 10{sup -15} s{sup -1}, molecular gas heating rate elevating the gas temperature to 75-200 K, fractional ionization of molecular gas 10{sup -6}-10{sup -5}, large-scale magnetic field 10-20 {mu}G, the density of diffuse and dense molecular gas {approx}100 and {approx}10{sup 3} cm{sup -3} over 300 pc and 50 pc path lengths, and the variability of Fe I K{alpha} 6.4 keV line emission on yearly timescales. Important implications of our study are that GeV electrons emitting in radio can explain the GeV {gamma}-rays detected by Fermi and that the cosmic-ray irradiation model, like the model of the X-ray irradiation triggered by past activity of Sgr A*, can also explain the origin of the variable 6.4 keV emission from Galactic center molecular clouds.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Final Report: Spectral Analysis of L-shell Data in the Extreme Ultraviolet from Tokamak Plasmas

We performed detailed analyses of extreme ultraviolet spectra taken by Lawrence Livermore National Laboratory on the National Spherical Torus Experiment at Princeton Plasma Physics Laboratory and on the Alcator CKmod tokamak at the M.I.T. Plasma Science and Fusion Center. We focused on the emission of iron, carbon, and other elements in several spectral band pass regions covered by the Atmospheric Imaging Assembly on the Solar Dynamics Observatory. We documented emission lines of carbon not found in currently used solar databases and demonstrated that this emission was due to charge exchange.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗