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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 541 records · Page 30
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NASA NTRS1990

Deep narrow band imagery of the diffuse ISM in M33

Very deep narrow band images were obtained for several fields in the local group spiral galaxy M33 using a wide field reimaging Charge Coupled Device (CCD) camera on the 1.5 m telescope at Palomar Observatory. The reimaging system uses a 306 mm collimator and a 58 mm camera lens to put a 16 minute by 16 minute field onto a Texas Instruments 800 x 800 pixel CCD at a resolution of 1.2 arcseconds pixel (-1). The overall system is f/1.65. Images were obtained in the light of H alpha (S II) lambda lambda 6717, 6731, (O III) lambda 5007, and line-free continuum bands 100A wide, centered at 6450A and 5100A. Assuming a distance of 600 kpc to M33 (Humphreys 1980, Ap. J., 241, 587), this corresponds to a linear scale of 3.5 pc pixel (-1), and a field size of 2.8 kpc x 2.8 kpc. Researchers discuss the H alpha imagery of a field centered approx. equal to 8 minutes NE of the nucleus, including the supergiant HII region complex NGC 604. Two 2000 second H alpha images and two 300 second red continuum images were obtained of two slightly offset fields. The fields were offset to allow for discrimination between real emission and possible artifacts in the images. All images were resampled to align them with one of the H alpha frames. The continuum images were normalized to the line images using the results of aperture photometry on a grid of stars in the field, then the rescaled continuum data were directly subtracted from the line data.

Hester, J. Jeff↗
NASA NTRS1989

The spatial distribution of infrared radiation from visible reflection nebulae

The emission at IRAS 12 and 25 micron bands of reflection nebulae is far in excess of that expected from the longer wavelength equilibrium thermal emission. The excess emission in the IRAS 12 micron band is a general phenomenon, seen in various components of interstellar medium such as IR cirrus clouds, H II regions, atomic and molecular clouds, and also normal spiral galaxies. This excess emission has been attributed to UV excited fluorescence in polycyclic aromatic hydrocarbon (PAH) molecules or to the effect of temperature fluctuations in very small grains. Results are presented of studies of IRAS data on reflection nebulae selected from the van den Bergh reflection nebulae sample. Detailed scans of flux ratio and color temperature across the nebulae were obtained in order to study the spatial distribution of IR emission. A model was used to predict the spatial distribution of IR emission from dust grains illuminated by a B type star. The model was also used to explore the excitation of the IRAS 12 micron band emission as a function of stellar temperature. The model predictions are in good agreement with the analysis of reflection nebulae, illuminated by stars with stellar temperature ranging from 21,000 down to 3,000 K.

Luan, Ling↗
NASA NTRS1989

Grains in galactic haloes

Researchers considered the effect of extensive forces on dust grains subjected to the light and matter distribution of a spiral galaxy (Greenberg et al. (1987), Ferrini et al. (1987), Barsella et al (1988). Researchers showed that the combined force on a small particle located above the plane of a galactic disk may be either attractive or repulsive depending on a variety of parameters. They found, for example, that graphite grains from 20 nm to 250 nm radius are expelled from a typical galaxy, while silicates and other forms of dielectrics, after initial expulsion, may settle in potential minimum within the halo. They discuss only the statistical behavior of the forces for 17 galaxies whose luminosity and matter distribution in the disk, bulge and halo components are reasonably well known. The preliminary results of the study of the motion of a dust grain for NGC 3198 are given.

Ferrara, Andrea↗
NASA NTRS1991

HST imaging of the inner 3 arcseconds of NGC 1068 in the light of forbidden O III 5007 A

The Planetary Camera aboard HST has been used to obtain a high spatial resolution forbidden O III 5007 A image of the nucleus of the barred spiral galaxy NGC 1068. This image shows more detail than any previously published images and resolves the NLR into several distinct clouds arranged in an apparently conical geometry. The individual emission-line regions appear to be resolved with sizes of 0.1-0.2 arcsec. There is a strong apparent correspondence between the 1.3 cm radio structure and several of the forbidden O III 5007 A clouds, although there are also bright emission-line clouds for which there are no radio counterparts. In particular, the radio 'triple' of Ulvestad et al. (1987) appears to correspond directly to the forbidden O III 5007 A clouds A-D. It is concluded that the distribution of the clouds is consistent with ionization core models. The hidden nucleus is located somewhere in the southern radio component and may be coincident with the H2O megamaser.

Evans, I. N.↗
NASA NTRS1992

Annual progress report

The emission components of spiral galaxies between 12 microns and 90 cm are identified. Additionally, an attempt to understand the relationships between them was made. The specific goal was to gain some understanding on the nature of the radio-infrared correlation. The results are summarized.

Duric, Nebojsa↗
NASA NTRS1991

Radio properties of extragalactic IRAS sources

The present study identifies extragalactic sources from the IRAS Faint Source Catalog by position coincidence with radio sources stronger than 25 mJy and lying north of +5 deg on the Green Bank 4.85 GHz sky maps. Published VLA maps, new 4.86 GHz VLA maps made with 15-arcsec resolution, and accurate optical positions are used to confirm 122 of these candidate identifications. Normal and starburst spiral galaxies were found to comprise about 97 percent of the FIR flux-limited sample. Radio-loud 'monsters' with q less than 2.25 dominate the radio emission from about 2 percent of the FIR source sample, and radio-quiet monsters are responsible for the FIR emission from less than about 1 percent of the FIR sample. All of the radio-identified sources are optically identified, mostly with relatively bright nearby galaxies. No evidence was found for any new populations of high-redshift FIR sources, nonthermal sources with steep FIR/optical spectra, or dust-shrouded sources visible only at FIR and radio wavelengths.

Condon, J. J.↗
NASA NTRS1992

Detection of Ca II absorption in the QSO 0958 + 559 due to a Heiles shell in NGC 3079

Optical observations of the QSO 0958 + 559 and the nearby, edge-on spiral galaxy NGC 3079 are presented. Spectra of the QSO show Ca II absorption lines due to extended gas in NGC 3079; the Na absorption lines due to NGC 3079 are not detected. An unrelated higher redshift absorption system at 1.1327 is also present in the QSO spectrum. The QSO sightline shines directly through a Heiles shell. The coincidence in position coupled with the agreement between the Ca II absorption and shell emission velocities demonstrates that the QSO absorption system is due to gas in this shell. This system is discussed in comparison with the six other low-redshift QSO-galaxy pair absorption systems, and the influence of Heiles shells on the interpretation of higher redshift QSO absorption systems is addressed.

Womble, Donna S.↗
NASA NTRS1992

Galactic disks, infall, and the global value of Omega

Stringent limits on the current rate of infall of satellite systems onto spiral galaxies are set on the basis of the thinness and coldness of Galactic disks. For infalling satellites on isotropically oriented circular orbits, it is shown that, due to scattering, the thermal energy gain of the disk exceeds the satellite energy loss from dynamical friction by a factor of 1.6, with 25 percent deposited in z motion and 75 percent in planar motions. It is found that no more than 4 percent of the Galactic mass inside the solar radius can have accreted within the last 5 billion years, or else its scale and its Toomre Q-parameter would exceed observed values. In standard cold-dark-matter-dominated models for the growth of structure with Omega sub tot of 1, the mass accreted in dark matter lumps rises faster than t exp 2/3 and would exceed 28 percent in the last 5 Gyr. It is proposed that heating from satellite infall accounts for a substantial fraction of the increase of velocity dispersion and scale height with age that is observed in the Galaxy.

Toth, G.↗
NASA NTRS1992

Observations of the 2.2-micron emission from the halo of NGC 4244 at large galactocentric distances

Observations of 2.2-micron emission from the halo of the edge-on spiral galaxy NGC 4244 are reported. These observations were made at larger radii from the center of the galaxy and with a smaller beam than reported in previous studies. The emission detected is consistent with the de Vaucouleurs r exp 1/4 law, and the mass-to-light ratio given by the present measurements at 2.2 microns is in good agreement with previous results. The present data reveal no evidence for a massive halo of cool objects.

Bergstrom, J. W.↗
NASA NTRS1992

Detection of WC9 stars in NGC 1365

We report the discovery of a broad emission feature at 5696 A in a giant extragalactic H II region in the barred spiral galaxy NGC 1365, identified with a C III emission line seen in some Wolf-Rayet stars. The absence of comparable C IV emission in 5808 A implies the observed feature is from stars of WC9 subtype. This constitutes the first unequivocal detection of WC9 stars in a giant H II region and the first example of these stars outside our Galaxy. Their presence in the high-abundance environment of NGC 1365 supports the notion that late WC-type progenitors form only in "metal-rich" circumstances.

Phillips, Andrew C.↗
NASA NTRS1993

Heavy element abundances and massive star formation

The determination of the stellar initial mass function (IMF) remains a great challenge in astronomy. In the solar neighborhood, the IMF is reasonable well determined for stellar masses from about 0.1 to 60 solar mass. However, outside the solar neighborhood, the IMF is poorly known. Among those frequently discussed arguments favoring a different IMF outside the solar neighborhood are the estimated time to consume the remaining gas in spiral galaxies, and the high rate of forming massive stars in starburst galaxies. An interesting question then is whether there may be an independent way of testing possible variations in the IMF. Indeed, the heavy elements in the interstellar medium are mostly synthesized in massive stars, so increasing, or decreasing, the fraction of massive stars naturally leads to a variation in the heavy element yield, and thus, the metallicity. The observed abundance should severely constrain any deviations of the IMF from the locally determined IMF. We focus on element oxygen, which is the most abundant heavy element in the interstellar medium. Oxygen is ejected only by massive stars that can become Type 1 supernovae, and the oxygen abundance is, therefore, a sensitive function of the fraction of massive stars in the IMF. Adopting oxygen enables us to avoid uncertainties in Type 1 supernovae. We use the nucleosynthesis results to calculate the oxygen yield for given IMF. We then calculate the oxygen abundance in the interstellar medium assuming instantaneous recycling of oxygen.

Wang, Boqi↗
NASA NTRS1993

The formation of low-ionization emission in the halo of NGC 891

Imaging and Spectroscopic study first revealed the presence of a diffuse ionized medium (DIM), having unusual excitation, pervading the lower halo of the edge-on spiral galaxy NGC 891. Emission from this DIM is strongest northeast of the nucleus, at radii between 2 and 8 kpc (hereafter region 1). The (N2)(lambda)6583/H(alpha) and (S2)(lambda) (lambda)6716,6731/H(alpha) ratios increase dramatically with z in region 1, from 0.6 and 0.5 respectively at z is approximately equal to 500 pc to 1.1 and 1.0 at z is approximately equal to 1 kpc, while nondetections of (O1)(lambda)6300 and (O3)(lambda)5007 emission yield upper limits of (O1)(lambda)6300/H(alpha) less than or equal to 0.05 and (O3)(lambda)5007/H(alpha) less than or equal to 0.15 for z less than 1 kpc. Previous photoionization models, using the radiation field from disk O and B stars, have been successful in reproducing the elevated (N2)(lambda)6583/H(alpha) and (S2)(lambda)(lambda)6716.6731/H(alpha) ratios observed. However, these radiation bounded models also produce significant (O3)(lambda)5007 emission, in conflict with the observed upper limit. Here, we report the results of new, matter bounded models for the photoionization of the DIM in region 1 of NGC 891.

Sokolowski, James↗
NASA NTRS1993

The effects of flaring in H1 on the observed velocity field of spirals

This work is part of a larger project in which we want to determine the shapes of dark halos around spiral galaxies. Rotation curves 'probe' the halos in the radial direction. The derived halo mass distributions are badly constrained. The local halo densities fully determine the width of the gas distribution once the gaseous velocity dispersion is known. There where the dark halo dominates, the Full Width at Half Maximum (FWHM) of the gas layer is proportional to (rho(sub halo))(exp -0.5). Therefore, measuring the width of the gas layer probes the halo density directly. In a dark halo dominated potential, the FWHM of the gas layer increases linearly with radius. This increase of the thickness of the gas layer is known as 'flaring'. Flaring has been found inside the stellar disk. Beyond the edge of the stellar disk, the analysis is hampered by the onset of the warp. Since the galaxy we are studying, NGC 4244, has no significant warp we hope to extend Rupen's analysis into the halo dominated regime. The usual method to derive a rotation curve from an observed 2-dimensional velocity field is to assume that the hydrogen is distributed in infinitely thin rings. For a flaring disk, any line of sight samples many different parts of the galaxy, all having different densities and projected velocities. In order to fully exploit the information contained in the gas distribution, we have to understand the effects of flaring on the observables (the spectrum for each point of the galaxy). We have investigated the effects of a flaring disk on the observed velocity field. It is obvious that the largest (kinematical) effects are to be expected for low density dark halos at large inclinations. For low mass galaxies we expect that the flaring of the H1 layer will have a major effect on the observed kinematics. For galaxy with intermediate V(sub max,halo) seen at intermediate inclinations, one overestimates Vsin(i) typically by a few percent. For more massive galaxies, any effects arising from the flaring H1 layer are minuscule unless the inclination is not too far from 90 deg.

Olling, Rob↗
NASA NTRS1992

The near-ultraviolet spectrum of Markarian 205

We report measurements of the absorption and of the emission lines between 1600 and 3200 A in the spectrum of the nearby AGN Markarian 205 (z = 0.071), which lies at a projected distance of 3 kpc (H0 = 100 km/s) from the nucleus of the nearby barred spiral galaxy, NGC 4319 (z = 0.0047). The results were obtained using high-resolution (R = 1300) observations with the Faint Object Spectrograph of the HST. A total of 15 absorption lines, 13 of which are produced by Galactic gas, and four AGN emission lines are detected. Two of the absorption lines, the Mg II resonant doublet, are produced by gas in the intervening galaxy NGC 4319. This is the first detection of absorption due to intervening gas in this famous quasar-galaxy pair.

Bahcall, John N.↗
NASA NTRS1993

The first detection of a collapsed core globular cluster in M31

We report on the observations of a globular cluster (designated G105 = Bo 343) in the nearby spiral galaxy M31, using the Hubble Space Telescope (HST). Image deconvolutions using three different methods indicate that this cluster has a density profile with the morphology characteristic of stellar systems which have undergone core collapse, i.e., a power-law density cusp near the center. This is the first such detection in a galaxy as distant as M31. This discovery may lead to extensive future statistical studies of the globular cluster system of M31, and thus a better understanding of its evolution.

Bendinelli, O.↗
NASA NTRS1993

The progenitor of supernova 1993J - A stripped supergiant in a binary system?

Supernova 1993J in the spiral galaxy M81 is the brightest supernova since SN1987A and, like the latter, appears to be another 'peculiar' type II supernova. The available photometry of the supernova region before the explosion requires the presence of at least two supergiants (one of early spectral type and the other of late type), but the actual progenitor has yet to be identified. We show that the explosion of a late-type supergiant can explain the initial sharp peak in the supernova light curve, provided that the star had lost almost all of its hydrogen-rich envelope before the explosion. In our model, the secondary brightening of the supernova, about 10 days later, is then a consequence of the radioactive decay of Ni-56 (and subsequently Co-56) produced in the explosion. The progenitor could have lost its hydrogen-rich envelope either in a strong stellar wind or, as seems more likely, through mass transfer to a companion star. In the latter case, the companion should reappear after the supernova photosphere has receded, the system having become a binary composed of a neutron star with a massive stellar companion.

Podsiaklowski, PH.↗
NASA NTRS1993

Interaction of NGC 2276 with the NGC 2300 group - Fabry-Perot observations of the H-alpha velocity field

We report kinematic observations of H-alpha emission from the spiral galaxy NGC 2276 obtained with a Fabry-Perot Camera. The 'bow shock' appearance and enhanced star formation in NGC 2276 have been attributed by Mulchaey et al. (1993) to a ram-pressure interaction with the dense IGM detected in ROSAT observations of the NGC 2300 group of galaxies. Along the 'bow shock' limb of the galaxy, we observe strong H-alpha emission and significant kinematic perturbations located immediately interior to an abrupt decrease in the scale length of the optical disk. Although ram-pressure forces may be important in the evolution of the outer gaseous disk, the peculiar kinematics and the truncation in the stellar disk are difficult to explain in a ram-pressure model; a more likely cause is tidal interaction, probably with the elliptical galaxy NGC 2300.

Gruendl, Robert A.↗
NASA NTRS1990

Ultraviolet observations of NGC 4395, the least luminous and nearest known Seyfert 1 nucleus

The purpose of the grant was to obtain and analyze International Ultraviolet Explorer (IUE) spectra of the spiral galaxy NGC 4395, which contains the nearest and least luminous known Seyfert nucleus. The ultraviolet (UV) spectra was to be used to test the intriguing hypothesis that the 'activity' could be explained by purely stellar phenomena, and to further explore the unprecedented properties of this nucleus. To test the feasibility of the project (the nucleus of NGC 4395 is very faint), one IUE shift was allocated, with the possibility of three additional shifts later on. Ultraviolet observations were attempted with IUE on 4 June 1989. Unfortunately, it was found that the only available guide star could no longer be detected sufficiently well with the FES, whose present sensitivity is lower than it was at the beginning of the IUE mission. Thus, it is no longer possible to observe NGC 4395 with IUE. Given these circumstances, as well as the faintness of the nucleus of NGC 4395, a Cycle 2 HST proposal for observations of this object was submitted.

Filippenko, Alexei V.↗