Search NASA⌕ Search

SEARCH · Search NASA

Results for “Envelop Spectrum”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

The problem of V444 Cygni

High-resolution short-wavelength IUE spectra were used to characterize the eclipsing binary system V444 Cygni. Light curves derived from the data revealed a 'third light' in the system that could not be modeled solely in terms of the eclipse of one limb-darkened disk by another. The UV-visible light curve corresponded with one O component (10 solar masses) at an effective temperature (Teff) of 40,000 K and a WR star (9 solar masses) with a Teff of 30,000 K. The WR star is projected to have large, readily visible, magnetic field-supported plumes enveloping both stars. Light scattering by electrons in the plumes would cause the anomalies observed in the emission-line spectrum and continuum light from the objects.

Underhill, A. B.↗
NASA NTRS1988

The emergence of X-rays and gamma-rays from supernova 1987A

Attempts to arrive at a unified scenario for the optical, X-ray, and gamma-ray emission of SN 1987A are discussed. Theoretical spectra are in reasonable agreement with recent observations of hard X-rays by the Ginga and Mir satellites, but the early turn-on of X-rays suggests that the mantle and envelope may be 'leaky', perhaps as a result of Rayleigh-Taylor instabilities and clumping. The soft X-ray spectrum should be dominated by a 6.4 keV Fe K-alpha fluorescence line. The reported Ginga detection of 4-10 keV X-ray emission is also discussed.

Shull, J. Michael↗
NASA NTRS1994

Observations of 13.5 micron rotation-vibration lines of SiS in IRC +10216

We report the first observations of the 13.5 micron fundamental band of SiS in the spectrum of the heavily obscured carbon star IRC +10216. The lines are formed in the inner region of the circumstellar envelope where the gas is accerlerating and where the temperature ranges from 800-500 K. We have carried out a detailed model of the observed line profiles. Our observations are best fit by a gradient in the abundance of SiS. We derive an abundance relative to molecular hydrogen of x(SiS) = 4.3 x 10(exp -6) at a distance of twelve stellar radii from the central star rising to x(SiS) = 4.3 x 10(exp -5) at a few stellar radii from the surface of the star.

Boyle, R. J.↗
DOE OSTI2016

MO-FG-CAMPUS-TeP3-03: Calculation of Proton Pencil Beam Properties with Full Beamline Model in TOPAS

Purpose: Introducing Monte Carlo based dose calculation algorithms into proton therapy planning systems (TPS) leads to improved accuracy. However accurate modelling of the proton pencil beam impinging the patient is necessary. Current approaches rely on measurement-driven reconstruction of phase-space and spectrum properties, typically constrained to analytical model functions. In this study a detailed Monte Carlo model of the complete cyclotron-based delivery system was created with the aim of providing more representative beam properties at treatment position. Methods: A model of the Varian Probeam proton system from the cyclotron exit to isocenter was constructed in the TOPAS Monte Carlo framework. The beam evolution through apertures and magnetic elements was validated using Transport/Turtle calculations and additionally against measurements from the Probeam™ system at Scripps Proton Therapy Center (SPTC) in San Diego, CA. A voxelized water phantom at isocenter allowed for comparison of the dose-depth curve from the Probeam model with that of a corresponding Gaussian beam over the entire energy range (70–240 MeV). Measurements of relative beam fluence cross-profiles and depth-dose curves at and around isocenter were also compared to the MC results. Results: The simulated TOPAS beam envelope was found to agree with both the Transport/Turtle and measurements to within 5% for most of the beamline. The MC predicted energy spectrum at isocenter was found to deviate increasingly from Gaussian at energies below 160 MeV. The corresponding effects on the depth dose curve agreed well with measurements. Conclusion: Given the flexibility of TOPAS and available details of the delivery system, an accurate characterization of a proton pencil beam at isocenter is possible. Incorporation of the MC derived properties of the proton pencil beam can eliminate analytical approximations and ultimately increase treatment plan accuracy and quality. Both authors are employees of Varian Medical Systems.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1992

Coded 16-CPFSK for downlink applications

A bandwidth-efficient constant-envelope Proof-of-Concept (POC) modem is described. The modem was developed on an Advanced Modulation Techniques Development contract for the NASA/Lewis Research Center. The POC modem employs 16-ary Continuous Phase Frequency Shift Keying (16-CPFSK) modulation. The 16 frequencies are spaced every 1/16th baud rate which produces a compact spectrum allowing 2 bits/sec/Hz operation. The modem is designed for 200 mb/s Time Division Multiple Access (TDMA) application with 100 MHz adjacent channel spacing. Overall rate 3.4 convolutional coding is incorporated. The demodulator differs significantly from typical quadrature phase detector approaches in that phase is coherently measured by processing the baseband output of a frequency discriminator. Baud rate phase samples for the baseband processor are subsequently decoded to yield the original data stream. The method of encoding onto the 16-ary symbol-ending phase nodes, together with convolutional coding gain, results in near Quadrature Phase Shift Keying (QPSK) theoretical performance. The modulated signal is of constant envelope; thus the power amplifier can be saturated for peak performance. The spectrum is inherently bandlimited and requires no RF filter for sidelobe containment. Two novel theoretical techniques are used in this 16-CPFSK modem: (1) coherent phase measurements are obtained by processing an FM discriminator baseband output; and (2) modulation is accomplished via a closed-loop-linearized voltage controlled oscillator (VCO).

Davis, Robert↗
DOE OSTI2022

PCP consensus protein/peptide alphavirus antigens stimulate broad spectrum neutralizing antibodies

Vaccines based on proteins and peptides may be safer and if calculated based on many sequences, more broad-spectrum than those designed based on single strains. Physicochemical Property Consensus (PCP con ) alphavirus (AV) antigens from the B-domain of the E2 envelope protein were designed, synthesized recombinantly and shown to be immunogenic (i.e. sera after inoculation detected the antigen in dotspots and ELISA). Antibodies in sera after inoculation with B-region antigens based on individual AV species (eastern or Venezuelan equine encephalitis (EEEV con , VEEV con ), or chikungunya (CHIKV con ) bound only their cognate protein, while those designed against multiple species (Mosaik con and EVC con ) recognized all three serotype specific antigens. The VEEV con and EEEV con sera only showed antiviral activity against their related strains (in plaque reduction neutralization assays (PRNT 50/80 ). Peptides designed to surface exposed areas of the E2-A-domain of CHIKV con were added to CHIKV con inocula to provide anti-CHIKV antibodies. EVC con , based on three different alphavirus species, combined with E2-A-domain peptides from AllAV con , a PCPcon of 24 diverse AV, generated broad spectrum, antiviral antibodies against VEEV, EEEV and CHIKV, AV with less than 35% amino acid identity to each other (>65% diversity). This is a promising start to a molecularly defined vaccine against all AV. A further study with these antigens can illuminate what areas are most important for a robust immune response, resistant to mutations in rapidly evolving viruses. The validated computational methods can also be used to design broad spectrum antigens against many other pathogen families.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1992

The orbital parameters and the IUE spectrum of the single-lined spectroscopic binary HD 698

IUE observations of the spectroscopic binary HD 698 show that its continuous spectrum corresponds to that of a B5 III-II object and that, even in the ultraviolet, the object is single-lined. The spectrum displays several sets of lines, all in absorption, where features can be distinguished that partake of the orbital motion of the B5 component, lines that suggest the existence of nonthermal sources of energy, and lines that form at the boundary of the circumstellar envelope, part of them being of purely interstellar origin. The circumbinary envelope appears to expand and then starts decelerating before the layer is reached where the resonance doublet of Si IV originates. The 'discrete absorptions' that are characteristics of the spectra of early-type stars are present in the spectrum. New values of the orbital period and of the rest of the orbital parameters are determined on the basis of all the available ground-based data.

Sahade, Jorge↗
NASA NTRS2003

High-Velocity Absorption Features in FUSE Spectra of Eta Carinae

Numerous broad (200 to 1000 km/sec) features in the FUSE spectrum (905-1187 A) of eta Carinae are identified as absorption by a forest of high-velocity narrow lines formed in the expanding circumstellar envelope. These features were previously thought to be P-Cygni lines arising in the wind of the central star. The features span a heliocentric velocity range of -140 to -580 km/sec and are seen prominently in low-ionization ground-state transitions (e.g. N I 1134-35, Fe II 1145-42, 1133, 1127- 22, P II 1153, C I 1158) in addition to C III] 1176 A. The high-velocity components of the FUSE transitions have depths about 50% below the continuum. The identifications are consistent with the complex velocity structures seen in ground- and excited-state transitions of Mg I, Mg 11, Fe II, V II, etc observed in STIS/E230H spectra. The origin of other broad features of similar width and depth in the FUSE spectrum, but without low-velocity ISM absorption, are unidentified. However, they are suspected of being absorption of singly-ionized iron-peak elements (e.g. Fe II, V II, Cr II) out of excited levels 1,000 to 20,000 cmE-l above the ground state. The high-velocity features seen in Fe II 1145 are also present in Fe II 1608 (STIS/E140M), but are highly saturated in the latter. Since these transitions have nearly identical log (flambda) (1.998 vs. 2.080), the differences in the profiles are attributable to the different aperture sizes used (30 x 30 arcsec for FUSE, 0.2 x 0.2 arcsec for STIS/E140M). The high-velocity gas appears to be very patchy or has a small covering factor near the central star. Eta Carinae has been observed several times by FUSE over the past three years. The FUSE flux levels and spectral features in eta Car are essentially unchanged over the 2000 March to June 2002 period, establishing a baseline far-UV spectrum in advance of the predicted spectroscopic minimum in 2003.

Sonneborn, G.↗
DOE OSTI2016

Evidence from Sofia imaging of polycyclic aromatic hydrocarbon formation along a recent outflow in NGC 7027

We report spatially resolved (FWHM ∼ 3.″8–4.″6) mid-IR imaging observations of the planetary nebula (PN) NGC 7027 taken with the 2.5 m telescope on board the Stratospheric Observatory for Infrared Astronomy (SOFIA). Images of NGC 7027 were acquired at 6.3, 6.6, 11.1, 19.7, 24.2, 33.6, and 37.1 μm using the Faint Object Infrared Camera for the SOFIA Telescope (FORCAST). The observations reveal emission from polycyclic aromatic hydrocarbons (PAHs) and warm dust (T{sub D}∼90 K) from the illuminated inner edge of the molecular envelope surrounding the ionized gas and central star. The DustEM code was used to fit the spectral energy distribution of fluxes obtained by FORCAST and the archival infrared spectrum of NGC 7027 acquired by the Short Wavelength Spectrometer (SWS) on the Infrared Space Observatory (ISO). Best-fit dust models provide a total dust mass of 5.8{sub −2.6}{sup +2.3}×10{sup −3} M{sub ⊙}, where carbonaceous large (a = 1.5 μm) and very small (a∼12 A-ring ) grains, and PAHs (3.1 A-ring <a<12 A-ring ) compose 96.5, 2.2, and 1.3% of the dust by mass, respectively. The 37 μm optical depth map shows minima in the dust column density at regions in the envelope that are coincident with a previously identified collimated outflow from the central star. The optical depth minima are also spatially coincident with enhancements in the 6.2 μm PAH feature, which is derived from the 6.3 and 6.6 μm maps. We interpret the spatial anti-correlation of the dust optical depth and PAH 6.2 μm feature strength and their alignment with the outflow from the central star as evidence of dust processing and rapid PAH formation via grain–grain collisions in the post-shock environment of the dense (n{sub H}∼10{sup 5} cm{sup −3}) photo-dissociation region and molecular envelope.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1977

High-resolution rocket spectra of the 1920-A and 1720-A features in the spectrum of Zeta Tauri

High-resolution ultraviolet spectrograms of the B-shell star Zeta Tau reveal two features characteristic of B supergiants, one at 1720 A and the other at 1920 A. The presence of these features in the spectrum of this object shows that they are indicative of an extended atmosphere - either the tenuous atmosphere of a supergiant or the envelope surrounding a rapidly rotating main-sequence star - and are therefore not purely luminosity criteria. The high spectral resolution allows an identification of the contributors to these features. The dominant contributor to the 1920-A feature is Fe III, while the primary contributor to the 1720-A feature is Al II.

Heap, S. R.↗
NASA NTRS1992

Protonated acetylene - An important circumstellar and interstellar ion

In a circumstellar envelope, a substantial amount of acetylene is transported in a wind to the outer envelope, where it can be photoionized by interstellar radiation and then converted into C2H3(+) by a low-temperature reaction with H2. New chemical modeling calculations indicate that sufficient C2H3(+) may be produced in the outer envelope of IRC + 10216 to be observable. Similar considerations suggest that C2H3(+) should also be detectable in interstellar clouds, provided its rotational spectrum has been measured accurately in the laboratory.

Glassgold, A. E.↗
NASA NTRS1987

The dust coma of comet P/Halley - Measurements on the Vega-1 and Vega-2 spacecraft

Measurements obtained with the Dust Counter and Mass Analyzer instruments on the Vega 1 and 2 spacecraft are used to study properties of the coma of comet P/Halley. Well-defined envelope boundaries for the inverse square dependence of flux with distance from the nucleus are found, and regions of enhanced fluxes above these R exp -2 baselines inside these boundaries are identified as dust jets. The mass spectrum of the giant flux enhancement noted near the closest approach of Vega 1 is shown to be similar to the preencounter spectra. The data suggest the emission from the nucleus of large conglomerates of small particles which disintegrate as they travel outward, explaining the 10 to the -13th g particles observed beyond the envelope boundaries.

Simpson, J. A.↗
NASA NTRS1986

The asymmetric profile of the H76 alpha line emission from MWC349

MWC349 is an emission-line star found by Merrill, Humason and Burwell (1932). Braes, Habing and Schoenmaker (1972) discovered that it is a strong radio source. The radio emission originates in a massive ionized wind that is expanding with a velocity of about 50 km s(-1). Its continuum spectrum fits well a nu(0.6) power law from the cm wavelengths to the far-IR. Radio recombination line emission from the envelope of MWC349 was first detected by Altenhoff, Strittmatter and Wendker (1981). We have obtained good signal-to-noise ratio, Very Large Array observations of the H76 alpha radio recombination line from the ionized wind of MWC349. Our data reveal that the profile is markedly asymmetric, with a steep rise on the blue side. This asymmetry could be due to non-LTE effects in the formation and transfer of the line or to intrinsic asymmetries in the envelope. Our analysis suggests that most probably the peculiar profile is caused by a non-LTE enhancement of the line emission from the side of the envelope nearer to the observer. This asymmetry has the opposite sense than that observed in optical and IR recombination lines, where a different effect (absorption of the stellar continuum by the gas in the wind between the star and the observer) is known to be dominant, leading to the classic P Cygni profile. We propose that the profiles of the radio recombination lines from ionized stellar winds will have this characteristic shape, while optical and IR recombination lines are characterized by P Cygni-like profiles. Unfortunately, at present the detection of radio recombination lines from ionized stellar winds is only feasible for MWC349 and a few other objects.

Rodriquez, L. F.↗
NASA NTRS1982

Subluminous Wolf-Rayet stars - Observations

Even though the loss of the outer, H-rich envelope may be a necessary condition for forming WR stars, it is clearly not a sufficient one. This is because the majority of planetary nuclei do not have a WR-type spectrum. The question why some central stars are WR stars while others are, say, O stars is addressed here. The question is approached by ascertaining how the properties of WR-type central stars differ from those of O-type stars. The study therefore begins with the classification and calibration of WR spectra. It is found that whereas the WR phenomenon may occur in stars of any mass, it is limited to stars that have been stripped (or mixed) down to their cores. The fact of prior envelope loss, however, is not sufficient to predict which stars will develop WR characteristics. Instead, a comprehensive description of envelope loss, including a detailed accounting of interior conditions and processes at the core envelope interface, will be required to explain the onset of WR characteristics.

Heap, S. R.↗
NASA NTRS1972

Surface composition of magnetic neutron stars.

The relative abundances of seven constituent nuclei, He4, C12, O16, Ne20, Mg24, Si28, and Fe56, are calculated as a function of time for neutron star atmospheres within which exist magnetic fields of the order of 10 to the 13th G. The opacity, equation of state of the electrons, and cooling rate of the magnetic star are discussed, and it is shown to be a reasonable approximation to assume an atmosphere to be isothermal. The effects of particle diffusion are included in the nuclear reaction network. Computations are performed both for a constant mass atmosphere and for an atmosphere in which mass is being ejected. It is found that the final abundances are model-independent, as long as the initial model contains predominantly He4. The relative abundances are compared to the cosmic ray spectrum. For both the constant-mass and mass-loss atmospheres, nucleosynthesis proceeds virtually completely to Fe56. However the outermost layers of the envelope, in which no mass is being ejected, are composed almost entirely of He4 with trace amounts of Fe56. After the loss of about 10 to the 21st g, only Fe56 is ejected from atmospheres expelling mass.

Rosen, L. C.↗
DOE OSTI2021

Detection of an Atmosphere on a Rocky Exoplanet

We report the detection of an atmosphere on a rocky exoplanet, GJ 1132 b, which is similar to Earth in terms of size and density. The atmospheric transmission spectrum was detected using Hubble WFC3 measurements and shows spectral signatures of aerosol scattering, HCN, and CH{sub 4} in a low mean molecular weight atmosphere. We model the atmospheric loss process and conclude that GJ 1132 b likely lost the original H/He envelope, suggesting that the atmosphere that we detect has been reestablished. We explore the possibility of H{sub 2} mantle degassing, previously identified as a possibility for this planet by theoretical studies, and find that outgassing from ultra-reduced magma could produce the observed atmosphere. In this way we use the observed exoplanet transmission spectrum to gain insights into magma composition for a terrestrial planet. The detection of an atmosphere on this rocky planet raises the possibility that the numerous powerfully irradiated super-Earth planets, believed to be the evaporated cores of sub-Neptunes, may, under favorable circumstances, host detectable atmospheres.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1975

Supernova 1972e in NGC 5253

Absolute energy distributions of the Type I supernova 1972e in NGC 5253 extending to about 700 days after maximum light have been obtained. A physical model of the expanding envelope, based on the identification of the feature at 6550 A with H-alpha is proposed. It consists of a differentially expanding atmosphere, with electron density ranging from 10 billion near maximum light to about 10 million 340 days later, illuminated by a photosphere with temperature in the range from 10,000 K to 7000 K. Under these conditions, the identifications of Ca II 8600-A, H, and K lines, the Na D lines, and the Mg I b lines forming P Cygni lines are quite plausible. More than 200 days after maximum, the spectrum is dominated by four features between 4200 and 5500 A. Three of these four features match the blended emissions from over 100 Fe II forbidden lines. If this identification is correct, the envelope requires about 0.01 solar mass of iron, which corresponds to an Fe/H ratio about 20 times higher than the cosmic abundance. Possible identifications of the fourth feature with the Mg I 4571-A line or permitted lines of Fe II are also discussed.

Kirshner, R. P.↗
NASA NTRS1981

The 1979-1980 eclipse of Zeta Aurigae. I - The circumstellar envelope

A model of the K-star wind far from the K star, and its interaction with the B star, has been derived from a study of Mg(+) and C(+++) resonance lines in the spectrum of Zeta Aurigae during 1979 and 1980. A mass loss rate from the K star of 2 x 10 to the -8th solar masses/year is suggested by the data; the rate of accretion of the K supergiant's material by the B star then being such that the matter accreted over a period of ten years is of the order of the total mass of the photosphere of the B star.

Chapman, R. D.↗