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Sanders, W. T.

Publications and source records attributed to Sanders, W. T..

At least 37 records · Page 2
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NASA NTRS1986

Cosmic X-ray physics

The analysis of the beryllium-filtered data from Flight 17.020 was completed. The data base provided by the Wisconsin diffuse X-ray sky survey is being analyzed by correlating the B and C band emission with individual velocity components of neutral hydrogen. Work on a solid state detector to be used in high resolution spectroscopy of diffuse or extend X-ray sources is continuing. A series of 21 cm observations was completed. A paper on the effects of process parameter variation on the reflectivity of sputter-deposited tungsten-carvon multilayers was published.

Mccammon, D.↗
NASA NTRS1985

Cosmic X-ray physics

A progress report of research activities carried out in the area of cosmic X-ray physics is presented. The Diffuse X-ray Spectrometer DXS which has been flown twice as a rocket payload is described. The observation times proved to be too small for meaningful X-ray data to be obtained. Data collection and reduction activities from the Ultra-Soft X-ray background (UXT) instrument are described. UXT consists of three mechanically-collimated X-ray gas proportional counters with window/filter combinations which allow measurements in three energy bands, Be (80-110 eV), B (90-187 eV), and O (e84-532 eV). The Be band measurements provide an important constraint on local absorption of X-rays from the hot component of the local interstellar medium. Work has also continued on the development of a calorimetric detector for high-resolution spectroscopy in the 0.1 keV - 8keV energy range.

Mccammon, D.↗
NASA NTRS1985

X-ray observations of Wolf-Rayet stars

X-ray observations have been made of a very luminous O8f star, four late WN stars, and eight O VI Wolf-Rayet stars. The X-ray pulse height distributions of the O8f star is analyzed to obtain information on source temperature, emission measure, and location relative to the stellar wind. Only upper limits are obtained for the X-rays from the Wolf-Rayet stars, but for the late WN stars the upper limits are well below the maximum Lx/Lbol detected in earlier surveys. For the O VI stars, the limits, used in conjunction with models for the production of the optical O VI lines, supply information about the excitation conditions in the winds.

Sanders, W. T.↗
NASA NTRS1984

Limits on diffuse X-ray emission from M101

Observed limits on diffuse X-ray emission from M101 require that the temperature of any coronal or matrix hot gas which is radiating an appreciable part (10 percent) of the average supernova power be less than 10(5.7)K. Furthermore, the fraction of the galactic plane occupied by hot bubbles similar to the one which apparently surrounds the sun is at most 25 percent in the region between 10 kpc and 20 kpc from the galactic center.

Mccammon, D.↗
NASA NTRS1984

Limits on soft X-ray flux from distant emission regions

The all-sky soft X-ray data of McCammon et al., and the new N sub H survey (Stark et al.) was used to place limits on the amount of the soft X-ray diffuse background that can originate beyond the neutral gas of the galactic disk. The X-ray data for two regions of the sky near the galactic poles are shown to be uncorrelated with 21 cm column densities. Most of the observed X-ray flux must therefore originate on the near side of the most distant neutral gas. The results from these regions are consistent with X-ray emission from a locally isotropic, unabsorbed source, but require large variations in the emission of the local region over large angular scales.

Burrows, D. N.↗
NASA NTRS1984

The Nature of the Soft X-ray Emitting Region in the Direction of the North Polar Spur

The spatial structure of the X-ray sky in the direction of the North Polar Spur was examined in two energy bands, the B band (0.10 to 0.18 keV) and the C band (0.15 to 0.28 keV). A model with two emitting regions, one local with unabsorbed emission, and the other more distant with emission partially absorbed by spatially varying amounts was investigated. Using the distribution of atomic hydrogen as a measure of absorbing material, this model was used to predict the flux in the direction of the North Polar Spur. The predicted flux was compared to the data obtained from several sounding rocket flights. The derived flux was found to correlate well with the observed data.

Morrison, J. P.↗
NASA NTRS1984

Ultrasoft X-ray Background Observations of the Local Interstellar Medium

Preliminary results from a May 8, 1984 sounding rocket survey of the soft X-ray background are presented. The X-ray detectors are sensitive to X-rays in three soft X-ray bandpasses: 80 to 110 eV, 90 to 188 eV, and 284 to 532 eV (at 20% of peak response). The lowest energy X-rays in this range have a mean free path of order 10 to the 19th power/sq cm and provide information about the local interstellar medium. The count rate in the 80 to 110 eV energy band (the Be band) tracks the 90 to 188 (eV band (the B band) very well, indicating that the same approx. 1 million degree gas that is responsible for the B band emission may be responsible for the bulk of the Be band X-rays as well.

Sanders, W. T.↗
NASA NTRS1984

Limits on soft X-ray flux from distant emission regions

The all-sky soft X-ray data of McCammon et al. and the new N sub H survey (Stark et al. was used to place limits on the amount of the soft X-ray diffuse background that can originate beyond the neutral gas of the galactic disk. The X-ray data for two regions of the sky near the galactic poles are shown to be uncorrelated with 21 cm column densities. Most of the observed x-ray flux must therefore originate on the near side of the most distant neutral gas. The results from these regions are consistent with X-ray emission from a locally isotropic, unabsorbed source, but require large variations in the emission of the local region over large angular scales.

Burrows, D. N.↗
NASA NTRS1984

Limits on diffuse X-ray emission from M101

Observed limits on diffuse X-ray emission from M101 require that the temperature of any coronal or matrix hot gas which is radiating an appreciable part ( 10%) of the average supernova power be less than 10(5.7)K. Furthermore, the fraction of the galactic plane occupied by hot buttles similar to the one which apparently surrounds the Sun is at most 25% in the region between 10 kpc and 20 kpc from the galactic center.

Mccammon, D.↗
NASA NTRS1983

The soft X-ray diffuse background

Maps of the diffuse X-ray background intensity covering essentially the entire sky with approximately 7 deg spatial resolution are presented for seven energy bands. The data were obtained on a series of ten sounding rocket flights conducted over a seven-year period. The different nature of the spatial distributions in different bands implies at least three distinct origins for the diffuse X-rays, none of which is well-understood. At energies of approximately 2000 eV, an isotropic and presumably extragalactic 500 and 1000 eV, an origin which is at least partially galactic seems called for. At energies 284 eV, the observed intensity is anticorrelated with neutral hydrogen column density, but we find it unlikely that this anticorrelation is simply due to absorption of an extragalactic or halo source. Previously announced in STAR as N83-20892

Mccammon, D.↗
NASA NTRS1983

Possible contributions of supernova remnants to the soft X-ray diffuse background (0.1 - 1 keV)

Almost all of the B band (0. 10-0.19 keV) and C band (0.15-0.28 keV) X-rays probably originate in a hot region surrounding the sun, which Cox and Anderson modeled as a supernova remnant. This same region may account for a significant fraction of the M band (0.5-1 keV) X-rays if the nonequilibrium models of Cox and Anderson are applicable. A population of distant SNR similar to the local region, with center-to-center spacing of about 300 pc, could provide enough galactic M band emission to fill in the dip in the count rate in the galactic plane that would otherwise be present due to absorption of both the extra galactic power law flux and any large-scale-height stellar (or galactic halo) emission.

Sanders, W. T.↗
NASA NTRS1982

Possible contributions of supernova remnants to the soft X-ray diffuse background (0.1 - 1keV)

Almost all of the B band (0.10-0.19 keV) and C band (0.15-0.28 keV) X-rays probably originate in a hot region surrounding the Sun, which Cox and Anderson modeled as a supernova remnant. This same region may account for a significant fraction of the M band (0.5-1 keV) X-rays if the nonequilibrium models of Cox and Anderson are applicable. A population of distant SNR similar to the local region, with center-to-center spacing of about 300 pc, could provide enough galactic M band emission to fill in the dip in the count rate in the galactic plane that would otherwise be present due to absorption of both the extra galactic power law flux and any large-scale-height stellar (or galactic halo) emission.

Sanders, W. T.↗
NASA NTRS1982

On the origin of the 1 keV diffuse X-ray background

Soft X-ray sky survey data for high galactic latitudes are used to constrain simple geometric models for the source of the diffuse X-ray background at 1 keV. The intensity maps show two extended and enhanced features, in Eridanus and in the direction of the galactic center, with a relatively uniform sky away from these features and an observed degree of isotropy consistent with a model in which the 0.5-1.2 keV background consists of an isotropic extragalactic component and a thick disk galactic component. A temperature of 2-3 million K and an emission pressure of 0.004 per cm to the 6th pc are derived for the galactic component from an assumed spectrum of 11E to the -1.4 power photons/sq cm s sr keV. While consistent with the data, a local, isotropically distributed source model is shown to pose physical difficulties.

Nousek, J. A.↗
NASA NTRS1982

X-rays from Wolf-Rayet stars observed by the Einstein Observatory

Preliminary results of three X-ray surveys are presented. Out of a sample of 20 stars, X-rays were detected from four Wolf-Rayet stars and two O8f(+) stars. The detected stars have about the same mean value as O stars for the X-ray to total luminosity ratio, L(x)/L = 10 to the -7th, but exhibit a much larger variation about the mean. The spectral energy distributions are also found to be like that of O stars in that they do not exhibit large attenuation of X-rays softer than 1 keV. This indicates that for both the O stars and WR stars much of the X-ray emission is coming from hot wisps or shocks in the outer regions of the winds and not from a thin source at the base of the wind. The general spectral shape and flux level place severe restrictions on models that attribute the lack of hydrogen emission lines to extremely high temperatures of the gas in the wind.

Sanders, W. T.↗
NASA NTRS1982

The soft X-ray diffuse background

Maps of the diffuse X-ray background intensity covering essentially the entire sky with approx. 7 deg spatial resolution are presented for seven energy bands. The data were obtained on a series of ten sounding rocket flights conducted over a seven-year period. The different nature of the spatial distributions in different bands implies at least three distinct origins for the diffuse X-rays, none of which is well-understood. At energies or approx. 2000 eV, an isotropic and presumably extraglalactic 500 and 1000 eV, an origin which is at least partially galactic seems called for. At energies 284 eV, the observed intensity is anticorrelated with neutral hydrogen column density, but we find it unlikely that this anticorrelation is simply due to absorption of an extragalactic or halo source.

Mccammon, D.↗
NASA NTRS1981

X-ray emission from Of stars and OB supergiants

The result of a survey of X-ray emission from luminous early-type stars is reported in which observations were made using the imaging proportional counter on the Einstein Observatory. The survey suggests that all Of stars and OB supergiants earlier than B1 I are X-ray sources with luminosities not less than 10 to the 32nd ergs/s and that some later B supergiants have X-ray luminosities not less than 10 to the 31st ergs/s. The X-ray luminosities are roughly 10 to the -7.2nd of the bolometric luminosities for supergiants earlier than B1 and perhaps a factor of 3 less for later B supergiants. Spectral analysis of the X-rays in conjunction with information on anomalous ionization in the wind from four of the strongest sources implies that the data are not consistent with a model in which the X-rays originate in a thin slab coronal zone at the base of the wind. Constraints on the source of X-rays from B supergiants are derived by combining the X-ray flux information with that on ultraviolet line anomalies.

Cassinelli, J. P.↗
NASA NTRS1981

X-ray detection of the symbiotic star AG Draconis

The detection of the yellow symbiotic star AG Draconis is reported. The star was detected by an imaging proportional counter at a count rate of 0.27 counts/s. The object is an intense source of very soft X-rays, and the X-ray luminosity is estimated to be equal to approximately 10 to the 32nd ergs/s, with a temperature of less than 2,000,000 K. If an interstellar column density of 3 x 10 to the 20th/sq cm is assumed, the emission measure is deduced to be greater than 3 x 10 to the 55th/ cu cm from the X-ray data, and less than 3 x 10 to the 59th/cu cm from the optical data. The observation is discussed in the context of various models of the symbiotic stars.

Anderson, C. M.↗