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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Intermediate Element Abundances In Galaxy Clusters

We present the average abundances of the intermediate elements obtained by performing a stacked analysis of all the galaxy clusters in the archive of the X-ray telescope AKA. We determine the abundances of Fe, Si, S, and Ni as a function of cluster temperature (mass) from 1 - 10 keV, and place strong upper limits on the abundances of Ca and Ar. In general, Si and Ni are overabundant with respect to Fe, while Ar and Ca are very underabundant. The discrepancy between the abundances of Si, S , Ar, and Ca indicate that the alpha-elements do not behave homogeneously as a single group. We show that the abundances of the most well-determined elements Fe, Si, and S in conjunction with recent theoretical supernovae yields do not give a consistent solution for the fraction of material produced by Type Ia and Type II supernovae at any temperature or mass. The general trend is for higher temperature clusters to have more of their metals produced in Type II supernovae than in Type Ias. The inconsistency of our results with abundances in the Milky Way indicate that spiral galaxies are not the dominant metal contributors to the intracluster medium (ICM). The pattern of elemental abundances requires an additional source of metals beyond standard SNIa and SNII enrichment. The properties of this new source are well matched to those of Type II supernovae with very massive, metal-poor progenitor stars. These results are consistent with a significant fraction of the ICM metals produced by an early generation of population III stars.

White, Nicholas E.↗
NASA NTRS1985

Improved optical spectrophotometry of supernova remnants in M33

Optical spectra of SNRs in M33 have been used to investigate abundance gradients and SNR evolution in this galaxy. Abundances of O, N, and S are derived from the spectra using new shock models by Dopita et al. (1984). The results for N and S show abundance gradients similar to those in NGC 300 and the Galaxy. The O abundances may be affected by possible contamination from H II regions and low-velocity shocks. Electron densities derived from the forbidden S II 6717 A/6731 A line ratio are used with a pressure equilibrium argument to estimate the initial explosion energy for each SNR. Evolutionary models for the remnants are investigated, and the distribution of the number of remnants with diameter is found to be consistent with free expansion of the SNRs to diameters of about 26 pc. The results may also be consistent with Sedov evolution if the ranges of initial supernova energies and surrounding interstellar medium densities are large enough.

Blair, W. P.↗
NASA NTRS1990

The interstellar medium in galaxies; Proceedings of the 2nd Teton Conference, Grand Teton National Park, WY, July 3-7, 1989

The present conference on the interstellar medium in galaxies discusses the cool phase of the interstellar medium, molecular clouds in spiral galaxies, interstellar dust in galaxies, and the diffuse interstellar medium. Attention is given to cooling flows and X-ray emission in early-type galaxies, the interstellar medium in active galaxies, abundances in extragalactic H II regions, and thermal phases of the interstellar medium in galaxies. Topics considered include large-scale interstellar gasdynamics in disk galaxies, gas during mergers, magnetic fields in galaxies, and large-scale star formation in the interstellar medium. Also discussed are gaseous halos and disks of galaxies at large redshift, the star-gas cycle in galaxies, measuring atomic hydrogen masses using the 21-cm line, and mass determinations from far-infrared and from CO observations.

Thronson, Harley A., Jr.↗
NASA NTRS1986

Abundances in dwarf irregular galaxies

The results of abundance studies of dwarf irregular galaxies and similar objects are reviewed with special attention to variations in the CNO element group. Observations of the forbidden N II and semiforbidden C III lines in the most metal-poor galaxy known, IZw 18, are presented for the first time and CNO abundances are derived via a photoionization model and discussed in the context of the abundances found in other metal-poor H II regions and galaxies.

Dufour, Reginald J.↗
NASA NTRS1994

UIT: Ultraviolet surface photometry of the spiral galaxy M74 (NGC 628)

Ultraviolet photometry, obtained from Ultraviolet Imaging Telescope (UIT) images at 1520 A (far-UV; magnitudes m(152)) and 2490 A (near-UV; magnitudes m(249)), of the spiral galaxy M74 (NGC 628) is compared with H-alpha, R, V, and B surface photometry and with models. M74's surface brightness profiles have a central peak with an exponential falloff; the exponential scale lengths of the profiles increase with decreasing wavelength for the broad-band images. The slope of the continuum-subtracted H-alpha profile is intermediate between those of far-UV and near-UV profiles, consistent with the related origins of H-alpha and UV emission in extreme Population I material. M74's color profiles all become bluer with increasing radius. The (m(152) - m(249)) color as measured by UIT averages near 0.0 (the color of an A0 star) over the central 20 sec radius and decreases from approximately -0.2 to approximately -0.4 from 20 sec to 200 sec. The spiral arms are the dominant component of the surface photometry colors; interarm regions are slightly redder. In the UV, M74's nuclear region resembles its disk/spiral arm material in colors and morphology, unlike galaxies such as M81. No UV 'bulge' is apparent. The m(152) - m(249) colors and models of M74's central region clearly demonstrate that there is no significant population of O or B stars present in the central 10 sec. M74's UV morphology and (m(152) - m(249)) color profiles are similar to those of M33, although M74 is approximately 0.5 mag redder. M81 has a smooth UV bulge which is much redder than the nuclear regions of M74 and M33. M74 is approximately 0.4 mag bluer than M81 in its outer disk, although M81 has bright UV sources only in spiral arms more than 5 kpc from its center. We investigate possible explanations for the color profiles of the galaxies and the differences among the galaxies: abundances; reddening due to internal dust; interplanetary magnetic field (IMF) variations, and the history of formation of the dominant generations of stars. Abundance and IMF variations do not produce large enough m(152) - m(249) or UV - V color differences. Comparing model UV/optical colors with those of M74 shows that M74's disk has undergone significant star formation over the past 500 Myr, and that either the star-formation history or the extinction varies systematically across M74's disk. Comparison of M74, M33, and M81 (UV - V) colors shows that M74 colors range from the bluest of M33's colors to the bluest of M81's. The failure of reddening models to cover the range of colors, and the known abundance range in such material, leads to the conclusion that star-formation history varies significantly as a function of radius in these galaxies, and that such variation is required to explain the range of colors observed in M74, M33, and M81.

Cornett, Robert H.↗
NASA NTRS1999

[Observations in the Outer Galaxy of Metal Abundances]

This project involved observations of far-infrared (FIR) fine-structure lines of [S III] (19,33 microns), [O III] (52,99 microns), and [N III] (57 microns) in the outer Galaxy (galactocentric radius R = 11-18 kpc), in order to study the variation of metal abundances with radius in the Galaxy. The metal abundance gradient is a fundamental input into models of galaxy evolution, and greatly constrains theories of galaxy evolution, stellar structure and evolution, and star formation. In addition, we observed the [C III (158 microns) and [O I] (63 microns) lines in these same regions to study molecular cloud structure in the low metallicity outer Galaxy. These observations were carried out over two weeks in August 1995 aboard the Kuiper Airborne Observatory, which was stationed at Hickam AFB at the time. Two Harvey Mudd students worked with me planning the observations and accompanied me on the flights. These students, and two other Harvey Mudd students, worked with me during the remaining time of the grant period analyzing these data and preparing them for publication These data have formed the basis for two journal articles in a professional astronomical journal. The first off these articles has been published (Rudolph et al. 1997, "Far-Infrared Abundance Measurements in the Outer Galaxy", The Astrophysical Journal, 489, 94-101). The second article is in preparation (Rudolph et al. 1999, "The Abundance Gradient in the Galaxy", in preparation for The Astrophysical Journal).

Source record↗
NASA NTRS1986

Cold atomic hydrogen in the inner galaxy

The VLA is used to measure 21 cm absorption in directions with the absolute value of b less than 1 deg., the absolute value of 1 less than 25 deg. to probe the cool atomic gas in the inner galaxy. Abundant H I absorption is detected; typical lines are deep and narrow, sometimes blending in velocity with adjacent features. Unlike 21 cm emission not all allowed velocities are covered: large portions of the l-v diagram are optically thin. Although not similar to H I emission, the absorption shows a striking correspondence with CO emission in the inner galaxy: essentially every strong feature detected in one survey is seen in the other. The provisional conclusion is that in the inner galaxy most cool atomic gas is associated with molecular cloud complexes. There are few or no cold atomic clouds devoid of molecules in the inner galaxy, although these are common in the outer galaxy.

Dickey, J. M.↗
NASA NTRS2009

The Energetic Trans-Iron Cosmic-ray Experiment (ENTICE)

The ENTICE experiment is one of two instruments that comprise the "Orbiting Astrophysical Spectrometer in Space (OASIS)", which is presently undergoing a NASA "Astrophysics Strategic Mission Concept Study". ENTICE is designed to make high precision measurements of the abundances of individual elements from neon through the actinides and, in addition, will search for possible superheavy nuclei in the galactic cosmic rays. The ENTICE instrument utilizes silicon detectors, aerogel and acrylic Cherenkov counters, and a scintillating optical fiber hodoscope to measure the charge and energy of these ultra-heavy nuclei for energies greater than 0.5 GeV/nucleon. It is a large instrument consisting of four modules with a total effective geometrical factor of approx.20 sq m sr. Measurements made in space for a period of three years with ENTICE will enable us to determine if cosmic rays include a component of recently synthesized transuranic elements (Pu-94 and Cm-96), to measure the age of that component, and to test the model of the OB association origin of galactic cosmic rays. Additionally, these observations will enable us to study how diffusive shock acceleration of cosmic rays operates differently on interstellar grains and gas. Keywords: cosmic rays Galaxy:abundances

Binns, W. R.↗
NASA NTRS2004

On the Measurement of Elemental Abundance Ratios in Inner Galaxy H II Regions

Although abundance gradients in the Milky Way Galaxy certainly exist, details remain uncertain, particularly in the inner Galaxy, where stars and H II regions in the Galactic plane are obscured optically. In this paper we revisit two previously studied, inner Galaxy H II regions: G333.6-0.2 and W43. We observed three new positions in G333.6-0.2 with the Kuiper Airborne Observatory and reobserved the central position with the Infrared Space Observatory's Long Wavelength Spectrometer in far-infrared lines of S++, N++, N+, and O++. We also added the N+ lines at 122 and 205 microns to the suite of lines measured in W43 by Simpson et al.. The measured electron densities range from approx. 40 to over 4000 per cu cm in a single HII region, indicating that abundance analyses must consider density variations, since the critical densities of the observed lines range from 40 to 9000 per cu cm. We propose a method to handle density variations and make new estimates of the S/H and N/H abundance ratios. We find that our sulfur abundance estimates for G333.6-0.2 and W43 agree with the S/H abundance ratios expected for the gradient previously reported by Simpson et al., with the S/H values revised to be smaller owing to changes in collisional excitation cross sections. The estimated N/H, S/H, and N/S ratios are the most reliable because of their small corrections for unseen ionization states (< or approx. 10%). The estimated N/S ratios for the two sources are smaller than what would be calculated from the N/H and S/H ratios in our previous paper. If all low excitation H II regions had similar changes to their N/S ratios as a result of adding measurements of N+ to previous measurements of N++, there would be no or only a very small gradient in N/S. This is interesting because nitrogen is considered to be a secondary element and sulfur is a primary element in galactic chemical evolution calculations. We compute models of the two H II regions to estimate corrections for the other unseen ionization states. We find, with large uncertainties, that oxygen does not, have a high abundance, with the result that the N/O ratio is as high (approx. 0.35) as previously reported. The reasons for the uncertainty in the ionization corrections for oxygen are both the non-uniqueness of the H II region models and the sensitivity of these models to different input atomic data and stellar atmosphere models. We discuss these predictions and conclude that only a few of the latest models adequately reproduce H II region observations, including the well-known, relatively-large observed Ne++/O++ ratios in low- and moderate-excitation H II regions.

Simpson, Janet P.↗
NASA NTRS1984

Variation of Oxygen and Nitrogen Abundances in the Galaxy

Results from a program of far-infrared observations of oxygen and nitrogen in Galactic planetary nebulae and H II regions are presented and discussed. Results indicate that the N/O abundance increases inward towards the galactic center, with a steep rise at the outer edge of the 5 kpc ring of active star-formation. The N/O abundances in the inner galaxy are about 2 to 3 times higher than in H II regions in the solar neighborhood and outer galaxy.

Dinerstein, H. L.↗
NASA NTRS1994

H II regions and the abundance properties of spiral galaxies

We investigate the relationships between the characteristic oxygen abundance, the radial abundance gradient, and the macroscopic properties of spiral galaxies by examining the properties of individual H II regions within those galaxies. Our observations of the line flux ratio (O II) lambda lambda 3726, 3729 + (O III) lambda lambda 4959, 5007)/H beta for 159 H II regions in 14 spiral galaxies are combined with published data to provide a sample of 39 disk galaxies for which (O II) + (O III)/H beta has been measured for at least five H II regions. We find that the characteristic gas-phase abundances and luminosities of spiral galaxies are strongly correlated. This relationship maps almost directly onto the luminosity-metallicity relationship of irregular galaxies and is also quite similar to that found for elliptical and dwarf spheroidal galaxies. Within our sample of spirals, a strong correlation between characteristic abundance and Hubble type also exists. The correlation between luminosity and Hubble type complicates the issue, but we discuss several interpretations of the correlations. The relationship between circular velocity and characteristic abundance is also discussed. We find that the slopes of the radial abundance gradients, when expressed in units of dex/isophotal radius, do not significantly correlate with either luminosity or Hubble type. However, the hypothesis that both early and very late type spirals have shallower gradients than intermediate spirals is consistent with the data. We find suggestive evidence that the presence of a bar induces a flatter gradient and also briefly discuss whether abundance gradients are exponential, as is usually assumed. We investigate the properties of individual H II regions in a subset of 42 regions for which we have spectra that cover almost the entire spectral range from 3500 to 9800 A. We use those data to estimate the densitites and ionizing spectra within the H II regions. We confirm that the ionizing spectrum hardens with increasing radius and decreasing abundance. We find no correlation between the ionization parameter and either radius or abundance, but this may be due to significant scatter introduced by the simple conversion of line ratios to ionization parameter.

Zaritsky, Dennis↗
NASA NTRS1995

A determination of the thick disk chemical abundance distribution: Implications for galaxy evolution

We present a determination of the thick disk iron abundance distribution obtained from an in situ sample of F/G stars. These stars are faint, 15 less than or approximately = V less than or approximately = 18, selected on the basis of color, being a subset of the larger survey of Gilmore and Wyse designed to determine the properties of the stellar populations several kiloparsecs from the Sun. The fields studied in the present paper probe the iron abundance distribution of the stellar populations of the galaxy at 500-3000 pc above the plane, at the solar Galactocentric distance. The derived chemical abundance distributions are consistent with no metallicity gradients in the thick disk over this range of vertical distance, and with an iron abundance distribution for the thick disk that has a peak at -0.7 dex. The lack of a vertical gradient argues against slow, dissipational settling as a mechanism for the formation of the thick disk. The photometric and metallicity data support a turn-off of the thick disk that is comparable in age to the metal-rich globular clusters, or greater than or approximately = 12 Gyr, and are consistent with a spread to older ages.

Gilmore, Gerard↗
NASA NTRS1993

High chemical abundances in stripped Virgo spiral galaxies

Based on a comparison of the oxygen abundances in H 2 regions in field and Virgo cluster late type spiral galaxies, Shields, Skillman, & Kennicutt (1991) suggested that the highly stripped spiral galaxies in the Virgo cluster have systematically higher abundances than comparable field galaxies. In April 1991 and May 1992 we used the blue channel spectrograph on the MMT to obtain new observations of 30 H 2 regions in Virgo spiral galaxies. These spectra cover the wavelength range from (O II) lambda 3727 to (S II) lambda 6731. We now have observed at least 4 H II regions in 9 spiral galaxies in the Virgo cluster. Combining (O II) and (O III) line strengths, we calculate the H II region oxygen abundances based on the empirical calibration of Edmunds & Pagel (1984). These observations show: (1) The stripped, low luminosity Virgo spirals (N4689, N4571) truly have abundances characteristic of much more luminous field spirals; (2) Virgo spirals which show no evidence of stripping (N4651, N4713) have abundances comparable to field galaxies; and (3) Evidence for transition galaxies (e.g., N4254, N4321), with marginally stripped disks and marginal abundance enhancements. The new observations presented here confirm the validity of the oxygen over-abundances in the stripped Virgo spirals. Shields et al. (1991) discussed two different mechanisms for producing the higher abundances in the disks of stripped galaxies in Virgo. The first is the supression of infall of near-primordial material, the second is the suppression of radial inflow of metal-poor gas. Distinguishing between the two cases will require more observations of the Virgo cluster spirals and a better understanding of which parameters determine the variation of abundance with radius in field spirals (cf., Garnett & Shields 1987).

Skillman, E. D.↗
NASA NTRS1995

Far-infrared lines from H II regions: Abundance variations in the galaxy

Far-infrared lines of (N III) (57 microns), (O III) (52, 88 microns), (Ne III) (36 microns), and (S III) (19, 33 microns) have been measured in the H II regions G1.13 - 0.11, W31B, G23.95 + 0.15, G25.38 - 0.18, G29.96 - 0.02, W43, W51e, S156, S158, NGC 3576, NGC 3603, and G298.22-0.34. These observations were made with the facility Cryogenic Grating Spectrometer on the Kuiper Airborne Observatory to examine variations in abundances throughout the Galaxy. Previously published observations of G0.095 + 0.012, G333.60 - 0.21, G45.13 + 0.14A, K3-50, and M17 are also discussed. The giant H II region 30 Doradus in the Large Magellanic Cloud (LMC) was observed for comparison. Fluxes for (Ne II) (12.8 microns), (S IV) (10.5 microns), and the radio free-free continuum were collected from the literature for those sources. Electron densities were estimated from FIR line-pair ratios, and ionic abundances were estimated from the FIR line and radio fluxes. The excitation was estimated from the O(2+)/S(2+) ratio. Corrections for unseen ionization stages were calculated with the use of constnat-density H II region models. The validity and range of applicability of such semiempirical ionization correction schemes are discussed. The abundances with respect to hydrogen exhibit gradients with R(sub G) comparable to those previously measured for our Galaxy and for other galaxies. The overall gradients are d (log N/H)/dR = -0.10 +/- 0.02 dex/kpc, d(log Ne/H)/dR = -0.08 +/- 0.02 dex/kpc and d(log S/H)/dR = 0.07 +/- 0.02 dex/kpc. Compared to the Orion Nebula, the intermediate R(sub G) H II regions with 6 is less than R(sub G) is less than 11 kpc have similar or lower S/H and N/O ratios. The N/O ratios in the inner Galaxy are more than twice those observed in the Orion Nebula and intermediate R(sub G) H II regions. In fact, all the abundance ratios are as well or better fitted by a step fit with two levels than by a linear gradient. As has been noted in previous studies, the N/O ratio estimated from infrared observations of the doubly ionized N and O lines in H II regions is larger than the ratio estimated from optical observations of the singly ionized N and O lines. The Ne(2+)/O(2+) ratio is observed to be essentially constant over a wide range of excitation. This contradicts predictions of model H II regions calculated with the use of Local Thermodynamic Equilibrium (LTE) model stellar atmospheres. We conclude that these stellar atmospheres significantly underestimate the actual emergent fluxes for energies greater than 41 eV.

Simpson, Janet P.↗
NASA NTRS2000

The Heavy Element Abundance in Groups of Galaxies

Over the past few years we have analyzed a sample of clusters observed by the Advanced Spacecraft for Cosmology Astrophysics (ASCA) X-ray satellite. We performed spatially resolved X-ray spectroscopy of a sample of 18 relaxed clusters of galaxies with gas temperatures below 4 keV. The spectral analysis was done using ASCA/SIS (Solid state Imaging Spectrometer) data combined with imaging data from ROSAT/PSPC (German acronym for X-ray satellite/Position Sensitive Proportional Counter) and Einstein/IPC (Imaging Proportional Counter) observations. We derived temperature profiles using single-temperature fits for all of the clusters in the sample, and also corrected for the presence of cold gas in the center of so-called 'cooling flow' clusters. For all of the clusters in the sample we derived Si and Fe abundance profiles. For a few of the clusters we also were able to derive Ne and S abundance profiles. We compared the elemental abundances derived at similar overdensities in all of the clusters in the sample. We also compared element mass-to-light ratios for the entire sample. We concluded that the preferential accretion of low entropy, low abundance gas into the potentials of groups and cold clusters can explain most of the observed trends in metallicity. In addition, we discussed the importance of preheating of the intracluster medium by Type II supernovae on the cluster scaling relations.

David, Laurence↗
NASA NTRS1989

Star formation rates and abundance gradients in disk galaxies

Analytic models for the evolution of disk galaxies are presented, placing special emphasis on the radial properties. These models are straightforward extensions of the original Schmidt (1959, 1963) models, with a dependence of star formation rate on gas density. The models provide successful descriptions of several measures of galactic disk evolution, including solar neighborhood chemical evolution, the presence and amplitude of metallicity and color gradients in disk galaxies, and the global rates of star formation in disk galaxies, and aid in the understanding of the apparent connection between young and old stellar populations in spiral galaxies.

Wyse, Rosemary F. G.↗