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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

A search for chromospheric emission in A-type stars using the Goddard High-Resolution Spectrograph

We have used the Goddard High-Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST) to search for chromospheric emission in the ultraviolet C II 1335 A lines of eight A-type stars. The B-V colors of these stars range from 0.12 to 0.22. We have detected emission in the spectrum of the A7 V star Altair, but in no other star. We present tentative evidence that the emission from Altair is blueshifted by approximately 60 km per sec or more with respect to the photospheric spectrum of this star. We interpret this as expansion and suggest that the base of the A star winds that we have proposed in earlier work may lie within the chromosphere. Together with International Ultraviolet Explorer (IUE) spectra, our observations indicate that in ordinary main-sequence stars the onset of convection zones capable of supporting detectable chromospheres occurs in the close vicinity of B-V = 0.22.

Simon, Theodore↗
NASA NTRS1995

Data processing of solar EUV instruments on the METEOR satellite

The Multiple Experiment Transporter into Earth Orbit and Return-Solar EUV Experiment (METEOR-SEE) project will take daily extreme ultraviolet (EUV) irradiance spectra starting in the summer of 1995. The METEOR-SEE package consists of an EUV grating spectrograph (EGS) and a cluster of 5 soft x-ray photometers (XP's). Both these instruments have flown previously on NASA sounding rockets. Because of the scope of the project, new data processing algorithms had to be developed for the SEE instruments onboard the METEOR satellite. An overview of the data flow describes how satellite data are collected and processed. Detailed descriptions of specific routines will show what data processing entails.

Brown, Hipook↗
NASA NTRS1995

Secular variation of activity in comets 2P/Encke and 9P/Tempel 1

We compare production rates of H20 derived from International Ultraviolet Explorer (IUE) spectra from multiple apparitions of 2 comets, 2P/Encke and 9P/Tempel 1, whose orbits are in near-resonance with that of the Earth. Since model-induced errors are primarily a function of observing geometry, the close geometrical matches afforded by the resonance condition results in the cancellation of such errors when taking ratios of production rates. Giving careful attention to the variation of model parameters with solar activity, we find marginal evidence of change in 2P/Encke: a 1-sigma pre-perihelion decrease averaging 4%/revolution over 4 apparitions from 1980-1994, and a 1-sigma post-perihelion increase of 16%/revolution for 2 successive apparitions in 1984 and 1987. We find for 9P/Tempel 1, however, a 7-sigma decrease of 29%/revolution over 3 apparitions from 1983-1994, even after correcting for a tracking problem which made the fluxes systematically low. We speculate on a possible association of the character of long-term brightness variations with physical properties of the nucleus, and discuss implications for future research.

Haken, Michael↗
NASA NTRS1998

Lanthanide Complexes as a Test for Evidence of Life

The objective of this research is to advance the understanding of the interaction of lanthanide metals with biological organic molecules and to develop a technique to detect these compounds in the solid state and in situ in Mars and other planetary bodies. The detection of these complexes should provide evidence of life past or present. In addition, detection of the metals alone will provide important information about the geological history of a planetary body. Lanthanides were chosen as our focus of interest because they form very stable complexes with organic molecules in solution and they produce intense luminescence in the ultraviolet and visible spectra. The rare earth complexes available are mostly synthetic for diverse applications in medicine. There is not much work done on the complexes that form in nature. Lanthanides have many applications and they are mined aR over the world, however, since the interest has been only in the elements, the analytical techniques employed destroy any organic ligands that may be present. In order to determine if and which lanthanide complexes form in nature and their concentration, soil samples have been collected from areas rich in soluble lanthanide compounds like phosphates and also rich in vegetation. The soil samples will be analyzed and the lanthanide complexes if present will be isolated and characterized. A spectrometer to detect the lanthanide complexes in situ and in the solid state will be designed. In this workshop, the research approach and its implications will be discussed.

Benavides, Jeannette↗
NASA NTRS2001

Multiwavelength Modeling of Nove Atmospheres

LMC 1988 #1 was a slow, CO type, dust forming classical nova. It was the first extragalactic nova to be observed with the IUE satellite. We have successfully fitted observed ultraviolet and optical spectra of LMC 1988 #1 taken within the first two months of its outburst (when the atmosphere was still optically thick) with synthetic spectra computed using PHOENIX nova model atmospheres. The synthetic spectra reproduce most of the features seen in the spectra and provide V band magnitudes consistent with the observed light curve. The fits are improved by increasing the CNO abundances to 10 times the solar values. The bolometric luminosity of LMC 1988 #1 was approximately constant at 2 x 10(exp 38) ergs per second at a distance of 47.3 kpc for the first 2 months of the outburst until the formation of the dust shell.

Huschildt, P. H.↗
NASA NTRS2001

Ultraviolet Signatures of Stars and Gas in Starburst Galaxies

We extracted about 500 short wavelength prime (SWP) (high-dispersion) International Ultraviolet Explorer (IUE) spectra of B0 to B8 stars of all luminosity classes for the purpose of creating a stellar library. Several hundred scientifically useful high-dispersion B-star spectra are in the IUE Archive. The data were taken either with the purpose of performing stellar-wind studies or investigations of interstellar absorption lines. Due to the nature of these projects, the S/N of the data is the maximum achievable with the IUE satellite. Rountree and Sonneborn and Walborn, Parker, and Nichols extracted a subset of B spectral classification standards from the IUE Archive to construct atlases of IUE high-dispersion spectra. Their work served as our guideline for the data extraction.

Leitherer, Claus↗
NASA NTRS2002

Jupiter Systems Data Analysis Program Galileo Multi-Spectral Analysis of the Galilean Satellites

Progress was made on this project at the University of Colorado, particularly concerning analysis of data of the galilean moons Io and Europa. The goal of the Io portion of this study is to incorporate Near Infrared Mapping Spectrometer (NIMS) measured sulfur dioxide (SO2) frost amounts into models used with Ultraviolet spectrometer (UVS) spectra, in order to better constrain SO2 gas amounts determined by the UVS. The overall goal of this portion of the study is to better understand the thickness and distribution of Io's SO2 atmosphere. The goal of the analysis of the Europa data is to better understand the source of the UV absorption feature centered near 280 rim which has been noted in disk-integrated spectra primarily on the trailing hemisphere. The NIMS data indicate asymmetric water ice bands on Europa, particularly over the trailing hemisphere, and especially concentrated in the visibly dark regions associated with chaotic terrain and lines. The UPS data, the first-ever disk-resolved UV spectra of Europa, shown that the UV absorber is likely concentrated in regions where the NIMS data show asymmetric water ice bands. The material that produces both spectral features is likely the same, and we use data from both wavelength regions to better understand this material, and whether it is endogenically or exogenically produced. This work is still in progress at JPL.

Hendrix, Amanda↗
NASA NTRS2007

Improving IUE High Dispersion Extraction

We present a different method to extract high dispersion International Ultraviolet Explorer (IUE) spectra from the New Spectral Image Processing System (NEWSIPS) geometrically and photometrically corrected (SI HI) images of the echellogram. The new algorithm corrects many of the deficiencies that exist in the NEWSIPS high dispersion (SIHI) spectra . Specifically, it does a much better job of accounting for the overlap of the higher echelle orders, it eliminates a significant time dependency in the extracted spectra (which can be traced to the background model used in the NEWSIPS extractions), and it can extract spectra from echellogram images that are more highly distorted than the NEWSIPS extraction routines can handle. Together, these improvements yield a set of IUE high dispersion spectra whose scientific integrity is sign ificantly better than the NEWSIPS products. This work has been supported by NASA ADP grants.

Lawton, Patricia J.↗
NASA NTRS2012

Role of Massive Stars in the Evolution of Primitive Galaxies

An important factor controlling galaxy evolution is feedback from massive stars. It is believed that the nature and intensity of stellar feedback changes as a function of galaxy mass and metallicity. At low mass and metallicity, feedback from massive stars is mainly in the form of photoionizing radiation. At higher mass and metallicity, it is in stellar winds. IZw 18 is a local blue, compact dwarf galaxy that meets the requirements for a primitive galaxy: low halo mass greater than 10(exp 9)Msun, strong photoionizing radiation, no galactic outflow, and very low metallicity,log(O/H)+12=7.2. We will describe the properties of massive stars and their role in the evolution of IZw 18, based on analysis of ultraviolet images and spectra obtained with HST.

Heap, Sara↗
NASA NTRS2014

On Helium-Dominated Stellar Evolution: The Mysterious Role of the O(He)-Type Stars

Context. About a quarter of all post-asymptotic giant branch (AGB) stars are hydrogen-deficient. Stellar evolutionary models explain the carbon-dominated H-deficient stars by a (very) late thermal pulse scenario where the hydrogen-rich envelope is mixed with the helium-rich intershell layer. Depending on the particular time at which the final flash occurs, the entire hydrogen envelope may be burned. In contrast, helium-dominated post-AGB stars and their evolution are not yet understood. Aims. A small group of very hot, helium-dominated stars is formed by O(He)-type stars. A precise analysis of their photospheric abundances will establish constraints to their evolution. Methods. We performed a detailed spectral analysis of ultraviolet and optical spectra of four O(He) stars by means of state-of-the-art non-LTE model-atmosphere techniques. Results. We determined effective temperatures, surface gravities, and the abundances of H, He, C, N, O, F, Ne, Si, P, S, Ar, and Fe. By deriving upper limits for the mass-loss rates of the O(He) stars, we found that they do not exhibit enhanced mass-loss. The comparison with evolutionary models shows that the status of the O(He) stars remains uncertain. Their abundances match predictions of a double helium white dwarf (WD) merger scenario, suggesting that they might be the progeny of the compact and of the luminous helium-rich sdO-type stars. The existence of planetary nebulae that do not show helium enrichment around every other O(He) star precludes a merger origin for these stars. These stars must have formed in a different way, for instance via enhanced mass-loss during their post-AGB evolution or a merger within a common-envelope (CE) of a CO-WD and a red giant or AGB star. Conclusions. A helium-dominated stellar evolutionary sequence exists that may be fed by different types of mergers or CE scenarios. It appears likely that all these pass through the O(He) phase just before they become WDs.

evolution↗
NASA NTRS2023

Recurrent 3he-Rich Solar Energetic Particle Injections Observed By Solar Orbiter at ∼0.5 Au

We report Solar Orbiter observations of six recurrent solar energetic particle injections in 2022 March 3−6 at ∼0.5 au. All but one were associated with jets emanating from a plage near a large sunspot in active region 12 957. We saw large jets in injections with high 3He and Fe enrichments and minor jets in injections with no or lower enrichments. Furthermore, the event with the highest enrichment showed a more compact configuration of the underlying photospheric magnetic field. The higher fluences as well as harder spectra were seen in the event with a simultaneous jet and wider eruption. However, in this case, the energy buildup time in the source might be required to produce such spectra. Extreme-ultraviolet images from Solar Orbiter revealed a number of intersecting loops at the base of jets not seen from 1 au that might be a precondition for the recurrent events.

Sun: particle emission↗
NASA NTRS2024

Large Interferometer For Exoplanets (LIFE) XIII. The value of Combining Thermal Emission and Reflected Light for the Characterization of Earth Twins

Context. Following the recommendations to NASA (in the Astro2020 Decadal survey) and ESA (through the Voyage2050 process), the search for life on exoplanets will be a priority in the next decades. Two concepts for direct imaging space missions are being developed for this purpose: the Habitable Worlds Observatory (HWO) and the Large Interferometer for Exoplanets (LIFE). These two concepts operate in different spectral regimes: HWO is focused on reflected light spectra in the ultraviolet, visible, and near-infrared (UV/VIS/NIR), while LIFE will operate in the mid-infrared (MIR) to capture the thermal emission of temperate exoplanets. Aims. In this study, we aim to assess the potential of HWO and LIFE to characterize a cloud-free Earth twin orbiting a Sun-like star at a distance of 10 pc, both as separate missions and in synergy with each other. We aim to quantify the increase in information that can be gathered by joint atmospheric retrievals on a habitable planet. Methods. We performed Bayesian retrievals on simulated data obtained by an HWO-like mission and a LIFE-like one separately, then jointly. We considered the baseline spectral resolutions currently assumed for these concepts and used two increasingly complex noise simulations, obtained using state-of-the-art noise simulators. Results. An HWO-like concept would allow one to strongly constrain H 2 O, O 2 , and O 3 in the atmosphere of a cloud-free Earth twin, while the atmospheric temperature profile is not well constrained (with an average uncertainty ≈100 K). LIFE-like observations would strongly constrain CO 2 , H 2 O, and O 3 and provide stronger constraints on the thermal atmospheric structure and surface temperature (down to ≈10 K uncertainty). For all the investigated scenarios, both missions would provide an upper limit on CH 4 . A joint retrieval on HWO and LIFE data would accurately define the atmospheric thermal profile and planetary parameters. It would decisively constrain CO 2 , H 2 O, O 2 , and O 3 and find weak constraints on CO and CH 4 . The significance of the detection is in all cases greater than or equal to the single-instrument retrievals. Conclusions. Both missions provide specific information that is relevant for the characterization of a terrestrial habitable exoplanet, but the scientific yield can be maximized by considering synergistic studies of UV/VIS/NIR+MIR observations. The use of HWO and LIFE together will provide stronger constraints on biosignatures and life indicators, with the potential to be transformative for the search for life in the Universe.

E Alei↗
NASA NTRS1984

The discontinuity near 1600 A in the spectra of DA white dwarfs

Ultraviolet spectroscopic observations of two relatively cool DA white dwarfs, L481 - 60 (= WD 1544 - 37) and BPM 1266 ( = WD 2105 - 82), with the International Ultraviolet Explorer (IUE) satellite show a strong drop in their spectral energy distributions below 1600 A. Published model atmospheres and thier visual spectra suggest that these two stars have effective temperatures in the vicinity of 9,000-10,000 K, and it is proposed that the 1600 A feature could be due to the 342(1S) 3s2(1S) photoionization edge of Mg I.

Wegner, G.↗
NASA NTRS1983

Observations of emission in bright, low redshift quasars

Ultraviolet, infrared, and optical spectra were combined to obtain a data set sample as broad as possible in the range of hydrogen lines in individual quasars. From the measured Lyman fluxes, coupled with Balmer and Paschen line fluxes measured in these same objects, an effort was made to establish observational constraints that would guide models of the broad emission line regions of quasars. It was found that IUE spectra were generally of sufficiently high quality to derive line profiles of the ultraviolet lines Lyman alpha and CIV 1550 A, which were compared to the Balmer line profiles. The objects observed and the line fluxes are tabulated. Plots of line profiles are included.

Source record↗
NASA NTRS2000

Thermal Emission Spectra of Phobos, Vesta, Ceres, and Pallas: A Comparison

Ultraviolet, visual, and near-infrared spectra of Phobos, obtained by Mariner 9 and Viking Orbiters, were interpreted to suggest a compositional similarity with carbonaceous chrondrites. Such a composition would be inconsistent with the moon's origin in the proto-Mars region, as Mars is composed chiefly of differentiated silicates. This interpretation was used to suggest that the moons originated in the main-asteroid belt, with subsequent capture and orbital evolution into their current locations. Interpretations of more recent visual and near-infrared spectra, obtained by Phobos-2 and Mars Pathfinder, have demonstrated that the Phobos spectrum is more similar to spectra of other classes of asteroids and lunar soils. If lunar mare soil is the correct analogy, then such a composition suggests a formation of Phobos from materials similar to that on Mars, i.e. basalts, and would not require a dynamically difficult capture and orbital evolution. During the science phasing orbits of the Mars Global Surveyor mission Thermal Emission Spectrometer (TES) observations of Phobos were acquired at each of four encounters. The spectral variability observed for localized surface regions on Phobos has been previously reported and is greatest near the northern wall of Stickney crater. Interpretation of the thermal infrared spectra of airless bodies, based upon most existing laboratory measurements, is complicated by the absence of interstitial gases on the celestial objects that would act to minimize potential thermal gradients in the upper layers of the surface. As an aid to interpretation of the TES Phobos spectra are compared to telescopic and airborne thermal infrared spectra of asteroids from several classes, including Ceres (G), Pallas (B), and Vesta (V). The asteroid spectra provide a direct analogy to the physical situation encountered at the surface of Phobos, albeit different thermal gradients may exist for each surface. This work is supported by NASA RTOP's 344-30-30-01 and 344-34-21-08.

Roush, Ted↗
NASA NTRS1986

X-ray spectra of BL Lacertae objects

An analysis of previous X-ray spectral measurements of BL Lac objects indicates that the ultraviolet-through-X-ray spectra have a two-component, concave-up power law structure and that the soft X-ray spectrum is an extrapolation of the ultraviolet power law. The X-ray intensities of these objects were found to be highly variable. Though no significant amount of cold, low ionization gas is found to be present in these objects, evidence is presented of intrinsic excess absorption that may be due to hot highly ionized gas.

Urry, C. Megan↗
NASA NTRS1980

The boundary line in the H-R diagram for stellar chromospheres and the theory of convection

Ultraviolet emission-line spectra of A, F, and early G stars have been observed with the International Ultraviolet Explorer. For supergiants, classical chromospheric and transition-layer emission is seen only on the red side of the Cepheid instability strip. For luminosity classes III-V, chromospheric emission can be detected for spectral types F2 and later. For none of the A stars was normal chromospheric emission detected, regardless of their rotational velocities or peculiarities (i.e., Am or Ap).

Boehm-Vitense, E.↗
NASA NTRS1994

A far-ultraviolet atlas of symbiotic stars observed with IUE. 1. The SWP range

This atlas contains sample spectra from the far-ultraviolet observations of 32 symbiotic stars obtained with the International Ultraviolet Explorer (IUE) satellite. In all, 394 low-resolution spectra from the short-wavelength primary (SWP) camera covering the range 1200-2000 A have been extracted from the IUE archive, calibrated, and measured. Absolute line fluxes and wavelengths for the prominent emission lines have been tabulated. Tables of both the general properties of these symbiotics and of features specific to the spectrum of each are included. The spectra shown are representative of the different classes of symbiotic stars that are currently in the IUE archive. These include known eclipsing systems and those that have been observed in outburst (as well as quiescence).

Meier, S. R.↗