SEARCH · Search NASA

Results for “SDO”

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.

SourceResearch connectionFrom yearThrough year

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

At least 145 records · Page 8

All sources NASA NTRS DOE OSTI

NASA NTRS1976

An extrasolar extreme-ultraviolet object. II - The nature of HZ 43

A variety of data are presented concerning the spectrum, distance, temperature, and evolutionary state of the hot white dwarf HZ 43, the first extrasolar object to be detected in the EUV band. The data include spectrophotometry of the star and its red dwarf companion (HZ 43B), a trigonometric parallax for the star, its tangential velocity, and results of soft X-ray and EUV observations. The main conclusions are that: (1) the spectrum of HZ 43A is that of a hot DAwk star, (2) HZ 43B is a dM3.5e star, (3) the distance of the system is about 65 pc, (4) the tangential velocity is not atypical of white dwarfs, and (5) the stellar energy distribution of HZ 43A is well fitted by a black body with an effective temperature of approximately 110,000 K. Evolutionary implications of the existence of an object as hot as HZ 43A are briefly considered, and it is suggested that the progenitors of hot DA stars must include objects hotter than spectral type sdB, with logical possibilities being nuclei of planetary nebulae and sdO stars.

Margon, B.↗

NASA NTRS1980

The discovery of an O subdwarf in the globular cluster NGC 6712

Spectral data for C49 in the globular cluster NGC 6712 are examined with reference to evolutionary models for low-mass stars that are contracting into white dwarfs. The spectrum of this star is found to be almost identical to that of the first sdO star found in a globular cluster, star A in NGC 6397. Analysis of the spectral data using nonlocal thermodynamic equilibrium models gives surface parameters T not less than 50,000 K, log g = 5.5 plus or minus 0.5, and N(He)/N(H) approximately equal to 0.1. The results are consistent with the models considered.

Remillard, R. A.↗

NASA NTRS1986

An X-ray survey of hot white dwarf stars - Evidence for a m(He)/n(H) versus Teff correlation

Observations of 13 white dwarf and subdwarf stars using the Einstein Observatory High Resolution Image are reported. Included are stars of classes DA, DB, DAV, sDO, and sDB, with optically determined effective temperatures in the range 10,000-60,000 K. X-ray emission was detected from two of the 13: the very hot (55,000 K) DA1 star WD 2309 + 105 (= EG 233), with a count rate one-fifth that of HZ 43, and the relatively cool (26,000 K) DA3 star WD 1052 - 273 (=GD 125). The effective temperatures determined from ultraviolet and optical observations were used to place limits on the He content of the white dwarf photospheres, presuming that trace photospheric He is the missing opacity source which quenches the thermal X-rays in these stars. When presently obtained results were combined with those available from the literature evidence was found for a correlation between Teff and n(He)/n(H), in which HZ 43 is a conspicuous exception to the general trend. Both this correlation and the exceptional behavior of HZ 43 are qualitatively accounted for by a radiative acceleration model, in which the rate of upward movement of the He is a function of temperature and surface gravity

Petre, R.↗

NASA NTRS1986

Basic data on hydrogen-deficient stars

The current state of knowledge on the diistribution and motions of various types of hydrogen-deficient stars, and of their positions in the H-R diagram, is reviewed. It is concluded that the extreme helium stars (with the exception of the H-deficient binaries) and cool hydrogen-deficient stars belong to the population of the Galactic nuclear bulge, whereas the intermediate helium stars are young stars of Population I. The helium-rich sdO stars appear to be a local sample which is predominantly Population I.

Drilling, J. S.↗

NASA NTRS1988

High-resolution spectroscopy of central stars of planetary nebulae - LSS 1362

High resolution spectra of the hot sdO star LSS 1362, a central star of a planetary nebula, are analyzed by means of model atmosphere techniques. Improved NLTE model atmospheres based on the newly developed 'accelerated lambda iteration' method are used. The very high effective temperature (100000 K) derived previously from the UV energy distribution is confirmed. The surface gravity (log g = 5.3) and a normal helium abundance are derived. A mass of 0.65 solar mass and a luminosity of 10 exp 3.9 solar luminosities result from a comparison with evolutionary tracks. The distance is 1.1 kpc and the nebula has a diameter of about 0.25 pc to 0.5 pc. Weak photospheric emission lines of He II, CIV, Nv, and O v are detected. These lines are slightly blue-shifted with respect to the absorption line spectrum which is regarded as evidence for an atmospheric velocity field. It is conjectured that the observed broadening of the metal lines (25 km/s) may be caused by the velocity field rather than by rotation.

Heber, U.↗

NASA NTRS1991

Absolute far-ultraviolet spectrophotometry of hot subluminous stars from Voyager

Observations, obtained with the Voyager ultraviolet spectrometers, are presented of absolute fluxes for two well-known hot subluminous stars: BD + 28 deg 4211, an sdO, and G191 - B2B, a hot DA white dwarf. Complete absolute energy distributions for these two stars, from the Lyman limit at 912 A to 1 micron, are given. For BD + 28 deg 4211, a single power law closely represents the entire observed energy distribution. For G191 - B2B, a pure hydrogen model atmosphere provides an excellent match to the entire absolute energy distribution. Voyager absolute fluxes are discussed in relation to those reported from various sounding rocket experiments, including a recent rocket observation of BD + 28 deg 4211.

Holberg, J. B.↗

NASA NTRS1991

Far ultraviolet spectrophotometry of BD +28 4211

The results are reported of a November 1989 rocket flight which recorded a flux-calibrated spectrum of BD +28 4211 from 912 to 1150 A with 1A resolution. BD +28 4211, an SdO-type star, is commonly used as an ultraviolet calibration source in the IUE wavelength band. The present work extends the useful range of this standard shortward of Lyman-alpha. Since previous experiments show marked disparity, this study can be useful in determining a standard in the 912 to 1216 A band.

Cook, Timothy A.↗

NASA NTRS1993

The spectrum of the central star of the planetary nebula in M22

New optical observations of the central star of the planetary nebula IRAS 18333-2357 in the globular cluster M22 show lines of H I, He II, C IV, N IV, and N V. The spectrum closely resembles the sdO star KS 292, which has surface abundances enhanced by products of hydrogen shell burning and helium burning, and an effective temperature of 75,000 K. The lines of C in IRAS 18333-2357 seem somewhat stronger than in KS 292, and the lines of N are considerably stronger. The presence of substantial hydrogen is surprising in view of the hydrogen-poor nature of the nebular ejecta. If IRAS 18333-2357 is as hot as its analog, its luminosity is about 14,000 lunar luminosity. This value is higher than that theoretically expected for single-star evolution of M22 cluster stars.

Harrington, J. P.↗

NASA NTRS1994

Analysis of helium-rich subdwarf O stars. 1: NLTE models, methods, and fits for 21 Palomar Green survey sdOs

Atmospheric parameters for 21 helium-rich hot subdwarf O stars from the Palomar Green survey are found from fits of non-local thermodynamic equilibrium (NLTE) models to optical spectra. About 250 new NLTE models in the parameter range T(sub eff) from 35,000 to 65,000 K, log (g) from 4.0 to 6.5, and epsilon(He) from 50% He to 99% He have been calculated. A fit for each object is presented. Estimated distances and luminosities are calculated, assuming a mass of 0.5 solar masses. Large distances above the Galactic plane are found, and this implies that the majority of the sdO stars belong to a different stellar population than the sdB, planetary nebulae and white dwarf stars. Possibilities may include the halo and a 'thick disk.' Kinematical data from the literature are also discussed in view of the found distances. Five of the stars have been observed, modeled, and analyzed by Dreizler et al., and significant differences exist between their results and ours for these stars. The reason for these differences is not yet known, but the problem does not alter the conclusions about population membership that we present.

Thejll, P.↗

NASA NTRS1994

The Successive H2O Binding Energies for Fe(H2O)n(+)

The binding energy, computed using density functional theory (DFT), are in good agreement with experiment. The bonding is electrostatic (charge-dipole) in origin for all systems. The structures are therefore determined mostly by metal-ligand and ligand-ligand repulsion. The computed structure for FeH2O(+) is C(2v) where sp hybridization is important in reducing the Fe-H2O repulsion. Fe(H2O)2(+) has D2d symmetry where sdo hybridization is the primary factor leading to the linear O-Fe-O geometry. The bonding in Fe(H2O)3(+) and Fe(H2O)4(+) are very complex because ligand-ligand and metal-ligand repulsion, both for the in-plane and out-of-plane water lone-pair orbitals, are important.

Ricca, Alessandra↗

NASA NTRS2001

The Origin of Hot Subluminous Horizontal-Branch Stars in (omega) Centauri and NGC 2808

Hot subluminous stars lying up to 0.7 mag below the extreme horizontal branch (EHB) are found in the ultraviolet (UV) color magnitude diagrams of both (omega) Cen and NGC 2808. In order to explore the evolutionary status of these subluminous stars, we have evolved a set of low-mass stars continuously from the main sequence through the helium-core flash to the HB (horizontal branch) for a wide range in the mass loss along the red-giant branch (RGB). Stars with the largest mass loss evolve off the RGB to high effective temperatures before igniting helium in their cores. Our results indicate that the subluminous EHB stars, as well as the gap within the EHB of NGC 2808, can be explained if these stars undergo a late helium-core flash while descending the white-dwarf cooling curve. Under these conditions the convection zone produced by the helium flash will penetrate into the stellar envelope, thereby mixing most, if not all, of the envelope hydrogen into the hot helium-burning interior, where it is rapidly consumed. This phenomenon is analogous to the 'born-again' scenario for producing hydrogen-deficient stars following a very late helium-shell flash. This 'flash mixing' of the stellar envelope greatly enhances the envelope helium and carbon abundances and, as a result, leads to a discontinuous jump in the HB effective temperature. We argue that the EHB gap in NGC 2808 is associated with this theoretically predicted dichotomy in the HB morphology. Using new helium- and carbon-rich stellar atmospheres, we show that these changes in the envelope abundances of the flash-mixed stars will suppress the UV flux by the amount needed to explain the hot subluminous EHB stars in (omega) Cen and NGC 2808. Moreover, we demonstrate that models without flash mixing lie, at most, only approximately 0.1 mag below the EHB, and hence fail to explain the observations. Flash mixing may also provide a new evolutionary channel for producing the high gravity, helium-rich sdO and sdB stars.

Sweigart, Allen V.↗

NASA NTRS2002

Progress Towards the Solar Dynamics Observatory

The Solar Dynamics Observatory, or SDO, is scheduled to be the first mission to launch in 2007 under the new Living With a Star (LWS) program. It builds on the success of SOHO and other recent solar missions, but will observe the Sun at greater resolution and faster time cadence with a set of remote sensing instruments generating data in excess of 100 megabytes per second. The Science Definition Team produced a report consisting of a series of science objectives and a baseline instrument complement. Instrument proposals were due in April 2002, with selection to occur in the late summer of 2002. The spacecraft is being built at NASA Goddard Spacecraft Center by a team of engineers which are currently undergoing the formulation process. The presentation will discuss the current status of the science investigation selection and the spacecraft formulation.

Thompson, B. J.↗

NASA NTRS2005

Seismic Study of the Solar Interior: Inferences from SOI/MDI Observations During Solar Activity

Work on the structure, asphericity and dynamics of the solar interior from p-mode frequencies and frequency splittings was carried out primarily in collaboration with Dr. Eff-Darwich (University of La Laguna, Tenerife). This ongoing collaboration produced new results for the inversion of the internal solar rotation rate and further development in inversion methodologies. It also resulted in inferences on the solar stratification. Substantial progress towards the characterization of high-degree p-modes has been achieved. In collaboration with Drs. Rabello-Soares and Schou (Stanford University), we have gained a clear conceptual understanding of the various elements that affect the leakage matrix of the SOI/MDI instrument. This work has precise implications on the properties and the characterization of the HMI instrument being developed for the SDO mission.

Korzennik, Sylvain G.↗

NASA NTRS2004

Performance of AEA 80 Ah Battery under GEO Profiles

This viewgraph presentation is divided into the following sections: 1) AEA Geosynchronous Earth Orbit (GEO) Life Testing; 2) AEA/Goddard Space Flight Center (GSFC) 20 Ah Battery; 3) AEA/GSFC 80 Ah Battery; 4) Solar Dynamic Observatory (SDO) Life Test; 5) Test Results; 6) Correlation; 7) Conclusions.

Russel, N.↗

NASA NTRS2006

Electrical Power System Architectures for In-House NASA/GSFC Missions

This power point presentation reviews the electrical power system (EPS) architecture used for a few NASA GSFC's missions both current and planned. Included in the presentation are reviews of electric power systems for the Space Technology 5 (ST5) mission, the Solar Dynamics Observatory (SDO) Mission, and the Lunar Reconnaissance Orbiter (LRO). There is a slide that compares the three missions' electrical supply systems.

Yun, Diane D.↗

NASA NTRS2006

The Virtual Solar Observatory and the Heliophysics Meta-Virtual Observatory

The Virtual Solar Observatory (VSO) has survived its infancy and provides metadata search and data identification for measurements from 45 instrument data sets held at 12 online archives, as well as flare and coronal mass ejection (CME) event lists. Like any toddler, the VSO is good at getting into anything and everything, and is now extending its grasp to more data sets, new missions, and new access methods using its application programming interface (API). We discuss and demonstrate recent changes, including developments for STEREO and SDO, and an IDL-callable interface for the VSO API. We urge the heliophysics community to help civilize this obstreperous youngster by providing input on ways to make the VSO even more useful for system science research in its role as part of the growing cluster of Heliophysics Virtual Observatories.

Gurman, J. B.↗

NASA NTRS2008

Development of Time-Distance Helioseismology Data Analysis Pipeline for SDO/HMI

The Helioseismic and Magnetic Imager of SDO will provide uninterrupted 4k x 4k-pixel Doppler-shift images of the Sun with approximately 40 sec cadence. These data will have a unique potential for advancing local helioseismic diagnostics of the Sun's interior structure and dynamics. They will help to understand the basic mechanisms of solar activity and develop predictive capabilities for NASA's Living with a Star program. Because of the tremendous amount of data the HMI team is developing a data analysis pipeline, which will provide maps of subsurface flows and sound-speed distributions inferred form the Doppler data by the time-distance technique. We discuss the development plan, methods, and algorithms, and present the status of the pipeline, testing results and examples of the data products.

DuVall, T. L., Jr.↗

NASA NTRS2008

The Flare Irradiance Spectral Model (FISM) and its Contributions to Space Weather Research, the Flare Energy Budget, and Instrument Design

The Flare Irradiance Spectral Model (FISM) is an empirical model of the solar irradiance spectrum from 0.1 to 190 nm at 1 nm spectral resolution and on a 1-minute time cadence. The goal of FISM is to provide accurate solar spectral irradiances over the vacuum ultraviolet (VUV: 0-200 nm) range as input for ionospheric and thermospheric models. The seminar will begin with a brief overview of the FISM model, and also how the Solar Dynamics Observatory (SDO) EUV Variability Experiment (EVE) will contribute to improving FISM. Some current studies will then be presented that use FISM estimations of the solar VUV irradiance to quantify the contributions of the increased irradiance from flares to Earth's increased thermospheric and ionospheric densites. Initial results will also be presented from a study looking at the electron density increases in the Martian atmosphere during a solar flare. Results will also be shown quantifying the VUV contributions to the total flare energy budget for both the impulsive and gradual phases of solar flares. Lastly, an example of how FISM can be used to simplify the design of future solar VUV irradiance instruments will be discussed, using the future NOAA GOES-R Extreme Ultraviolet and X-Ray Sensors (EXIS) space weather instrument.

Chamberlin, Phillip↗