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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 91 records · Page 5
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NASA NTRS2004

Looking Closely at "Medusa": Star Forming Regions in NGC 4194

The "Medusa" (NGC 4194, Mrk 201) is a blue compact galaxy, with strong far infrared and radio emission. Ground-based observations exhibit a distorted image with a tidal tail and regions of strong star formation. A population of massive O and early B stars is evident from the IUE spectra HST survey of Seyfert and starburst galaxies notes NCG 4194 is an HII galaxy with lumpy HII regions and knots. The central starburst is apparently produced by a galaxy merger. As part of an investigation of star formation in interacting galaxies, we have obtained ultraviolet and visible images of the central regions of NGC 4194 with the Space Telescope Imaging Spectrograph on HST. Imaging was obtained in two ultraviolet (FUV-MAMA+F25QTZ, NUV-MAMA+F25CN182) and one visible (CCD+F28X50LP) band. Individual star forming knots (at HST resolution) have been identified. We present sized and luminosities for the individual knots, and the knot luminosity function. We compare our data to current starburst models to constrain stellar ages and populations. Knot characteristics as a function of location in the galaxy will also be discussed.

Weistrop, D.↗
NASA NTRS2010

Building on the Past - Looking to the Future: A Focus on Expanding Horizons - Part 2

The history of space endeavors stretches far from Robert Goddard s initial flights and will certainly extend far beyond the construction of the International Space Station. As society grows in knowledge of and familiarity with space, the focus of maintaining the safety of the crews and the habitability of the vehicles will be of the utmost importance to the National Aeronautics and Space Administration (NASA) community. Through the years, Payload Safety has developed not only as a Panel, but also as part of the NASA community, striving to enhance the efficiency and understanding of how business should be conducted as more International Partners become involved. The recent accomplishments of the first docking of the Japan Aerospace Exploration Agency (JAXA) HII Transfer Vehicle (HTV 1) and completion of the Japanese Experiment Module (JEM) or KIBO and the Russian MRM2 to the International Space Station (ISS) mark significant steps for the future of ISS. 2010 will mark the final flights of the Shuttle and the completion of ISS assembly. Future delivery of humans and hardware will rely on the Russian Progress and Soyuz, the Japanese HII Transfer Vehicle (HTV), the European Automated Transfer Vehicle (ATV) and US "Commercial Off-The-Shelf" (COTS) and Constellation vehicles. The International Partners (IPs) will have more capability in delivery as well as responsibility for review of hardware they deliver to assure safe operation. This is the second in a series of papers and presentations in what is hoped to be an annual update that illustrates challenges and lessons learned in the areas of communication (how hazard reports can be misunderstood), safety requirements (transitioning from Shuttle-centric to ISS-centric), and processes (review of hardware by RSC-E and Franchised ESA and JAXA PSRP) which have been vital in conducting the business of the Payload Safety Review Panel (PSRP). This year will focus on the items annotated above.

Guidry, Richard W.↗
NASA NTRS2013

Direct Measurement of Dust Attenuation in z approx. 1.5 Star-Forming Galaxies from 3D-HST: Implications for Dust Geometry and Star Formation Rates

The nature of dust in distant galaxies is not well understood, and until recently few direct dust measurements have been possible. We investigate dust in distant star-forming galaxies using near-infrared grism spectra of the 3D-HST survey combined with archival multi-wavelength photometry. These data allow us to make a direct comparison between dust towards star-forming regions (measured using Balmer decrements) and the integrated dust properties (derived by comparing spectral energy distributions [SEDs] with stellar population and dust models) for a statistically significant sample of distant galaxies. We select a sample of 163 galaxies between 1.36< or = z< or = 1.5 with H(alpha) SNR > or = 5 and measure Balmer decrements from stacked spectra. First, we stack spectra in bins of integrated stellar dust attenuation, and find that there is extra dust extinction towards star-forming regions (AV,HII is 1.81 times the integrated AV, star), though slightly lower than found for low-redshift starburst galaxies. Next, we stack spectra in bins of specific star formation rate (log sSFR), star formation rate (log SFR), and stellar mass (logM∗). We find that on average AV,HII increases with SFR and mass, but decreases with increasing sSFR. The amount of extra extinction also decreases with increasing sSFR and decreasing stellar mass. Our results are consistent with the two-phase dust model - in which galaxies contain both a diffuse and a stellar birth cloud dust component - as the extra extinction will increase once older stars outside the star-forming regions become more dominant. Finally, using our Balmer decrements we derive dust-corrected H(alpha) SFRs, and find evidence that SED fitting produces incorrect SFRs if very rapidly declining SFHs are included in the explored parameter space. Subject headings: dust, extinction- galaxies: evolution- galaxies: high-redshift

Direct↗
NASA NTRS1971

Colin Gum and the discovery of the Gum nebula

The research of Colin Gum in the field of astronomy is reviewed. It includes a radio survey at 200 MHz, a photographic survey for HII regions in the Southern Milky Way from longitude 220 deg to 20 deg, and a catalogue of 85 physically separate regions. He suggested that certain faint nebulosities were part of a large, nearby H II region excited by gamma Velorum and zeta Puppis. He was also concerned with 21-cm studies.

Kerr, F. J.↗
NASA NTRS1973

Cas A X-ray spectrum: Evidence for iron line emission

A sensitive measurement by rocket borne detectors of the X-ray flux from Cas A has revealed a steep continuum and a broad spectral feature in the region where line radiation from iron nuclei would be expected. The flux in this feature is .0122 plus or minus .0017 photons/sq cm/s: the total energy flux from 2 to 10 KeV is 1.02 x 10 to the minus 9th power ergs/sq cm/s. The presence of broad iron lines is consistent with a model in which approximately 13 MeV/nucleon iron nuclei charge exchange with surrounding interstellar oxygen and other heavy atoms. The model suggests that a substantial fraction of the energy from the outburst has gone into low energy cosmic rays which produce the observed HII region surrounding the remnant.

Serlemitsos, P. J.↗
NASA NTRS1972

Balloon observations of galactic and extragalactic objects at 100 microns.

Recent far-infrared balloon-borne instruments have yielded observations of a number of bright sources at 100 microns. Many of these coincide with HII regions where molecular line emision has been detected. There is some indication of 100 micron emission which does not coincide with radio measurements.

Hoffmann, W. F.↗
NASA NTRS1973

Interstellar grains.

Questions of interstellar extinction are discussed together with the spatial distribution of dust, the scattering of light by grains, diffuse interstellar absorption lines, and questions of interstellar polarization. Theoretical extinction curves are considered, giving attention to ice grains, graphite grains, polycyclic hydrocarbons, silicate grains, core-mantle grains, mixtures of grains, and the total amount of dust. Aspects of grain temperature and grain potential are examined along with processes on grain surfaces, the scattering of X rays by interstellar grains, the origin and destruction of grains, and the dust in the HII regions.

Aannestad, P. A.↗
NASA NTRS1978

The annihilation of galactic positrons

The probabilities of various channels of galactic positron annihilation were evaluated and the spectrum of the resulting radiation was calculated. The narrow width (FWHM less than 3.2 keV) of the 0.511 MeV line observed from the galactic center implies that a large fraction of positrons should annihilate in a medium of temperature less than 100,000 K and ionization fraction greater than 0.05. HII regions at the galactic center could be possible sites of annihilation.

Bussard, R.↗
NASA NTRS1977

A 102-cm balloon-borne telescope for far-infrared astronomy

The Center for Astrophysics-University of Arizona balloon-borne, inertially-guided, 102 cm telescope was designed to perform photometry and high resolution mapping of far-infrared (40-250 micron) celestial sources. To date the telescope has now been flown and successfully recovered a total of ten times. Six of the flights have produced useful astronomical data, resulting in more than 40 hours of observations of numerous objects, such as HII regions, dark clouds, molecular clouds, galaxies, the galactic center, planets, and an asteroid. Maps with a resolution of 1 arcmin FWHM have been achieved with absolute position accuracies of plus or minus 10 arcsec. The rms noise equivalent flux density of the system is approximately 70 Jy/(Hz) to the 1/2. From the launch site in Texas, sources as far south as - 50 degrees declination have been observed.

Fazio, G. G.↗
NASA NTRS1979

An infrared study of the NGC 7538 region

Infrared observations of the NGC 7538 region at wavelengths from 1 micron to 1 mm are presented and analyzed with the aim of understanding both the large-scale structure of this region of current star formation and the properties of the individual compact objects within it. At far-infrared wavelengths (25-130 microns), emission is seen from the visible H II region, from the vicinity of the previously known maser sources and dust-embedded compact HII regions, and from a new region called NGC 7538(E). Coincident with NGC 7538(E) are a point-like 1-25 micron infrared source, NGC 7538-IRS9, which probably provides the power for the far-infrared emission, and an extended source of 2.2 micron emission which appears to be an infrared reflection nebula. The compact H II regions, the maser sources and IRS9 are located within a dense molecular cloud at the edge of the optical H II region. This cloud, which has a mass of approximately 9000 solar masses, is detected in emission at 1 mm. The NGC 7538 region appears to contain examples of different stages in the formation of massive stars; it is suggested that the center of star formation is moving systematically to the southeast in this region.

Werner, M. W.↗
NASA NTRS1982

Radio and X-ray structure of Centaurus A

Recent studies of the nearby radio galaxy Centaurus A with the Very Large Array and the Einstein X-Ray Observatory reveal complex radio and X-ray structures. A prominent one-sided jet comprised of resolved knots located 0.2-6 kpc from the nucleus is seen in both radio and X-rays. The X-ray emission is probably synchrotron, requiring in situ reacceleration up to about ten million. Inverse Compton emission is not a likely explanation though a thermal model in which the nucleus ejects dense 100,000 solar mass clouds cannot be excluded. An elongated X-ray region is also found near the 'middle' radio lobe and optical HII regions about 30 kpc NE of the nucleus. Conditions around the active nucleus, the absence of X-rays from the inner radio lobes, and X-ray evidence for a hot interstellar medium are briefly discussed

Feigelson, E. D.↗
NASA NTRS1982

Observations of the 145.5 micron (OI) emission line in the Orion nebula

A first set of observations of the (OI) 3P to 3P1 (145.5 micron) transition was obtained. The line was observed both in a beam centered on the Trapezium, and in a 7 times wider beam encompassing most of the Orion Nebula. A wide beam map of the region was constructed which shows that most of the emission is confined to the central regions of the nebula. These observations may be compared with reported measurement of the 3P1 to 3P2 (63.2 micron) transition in Orion and are consistent with optically thin emission in the 145.5 micron line and self-adsorbed 63.2 micron emission lines. Mechanisms are discussed for the excitation of neutral oxygen. It is included that much of the observed emission originates in the thin, radio-recombination-line-emitting CII/HI envelope bordering on the HII region.

Stacey, G. J.↗
NASA NTRS1983

Detection of sulphur in the galactic center

A strong detection at the (SIII) 18.71 micron line is reported for the Galactic Center region, Sgr A West. A line flux of 1.7 + or - 0.2x10 to the -17th power W cm(-2) is found for a 20-arc second beam-size measurement centered on IRS 1. A preliminary analysis indicates that the SIII abundance relative to hydrogen is consistent with the cosmic abundance of sulfur, 1.6x10 to the -5th power, if a filling factor of unity within the known clumps is assumed. However, the sulfur abundance in the Galactic Center may be as much as a factor of 3 overabundant if a filling factor of 0.03 is adopted, a value found to hold for some galactic HII regions.

Herter, T.↗
NASA NTRS1984

Detection of shocked atomic gas in the Kleinmann-Low nebula

The 63 micrometer (3)p(1)-(3)P(2) fine structure line emission of neutral atomic oxygen at the center of the Orion nebula with a resolution of 30" is presented. There are three main emission peaks. One is associated with the region of strongest thermal radio continuum radiation close to the Trapezium cluster, and probably arises at the interface between the HII region and the dense Orion molecular cloud. The other two line emission peaks, associated with the Kleinmann Low nebula, are similar in both distribution and velocity to those of the 2 micrometer S(1) line of molecular hydrogen and of the high velocity wings of rotational CO emission. The OI emission from the KL nebula can be produced in the shocked gas associated with the mass outflows in this region and is an important coolant of the shocked gas.

Werner, M.↗
NASA NTRS1984

Abundances in galactic H2 regions, 3: G25.4-0.2, G45.5+0.06, M8, S159 and DR22

Measurements of the ARII (6.99 microns), ArIII (8.99 microns), NeII (12.81 microns), SIII (18.71 microns), and SIV (10.51 microns) lines are presented for five compact HII regions along with continuum spectroscopy. From these data and radio data, lower limits to the elemental abundances of Ar, S, and Ne were deduced. The complex G25.4-0.2 is only 5.5 kpc from the galactic center, and is considerably overabundant in all these elements. Complex G45.5+0.06 is at seven kpc from the galactic center, and appears to be approximately consistent with solar abundance. The complex S159 in the Perseus Arm, at 12 kpc from the galactic center, has solar abundance, while M8 in the solar neighborhood may be somewhat overabundant in Ar and Ne. Complex DR 22, at 10 kpc from the galactic center in the Cygnus Arm, is overabundant in Ar. A summary of results from a series of papers on abundances is given.

Pipher, J. L.↗
NASA NTRS1984

Infrared mapping of galaxian centers: Star forming regions with kiloparsec scale sizes

A 1 to 20 micron mapping of the centers of galaxies encompassing the regions that extend out to several kiloparsecs from the nuclei is reviewed. Power emerging at or = 5 microns is a direct measure of the number of young stars present. This conclusion is strongly supported by the large-scale association of the infrared-emitting regions with visual continuum and line emission indicative of young stars, and by the similarity of the energy distributions to those of Galactic HII region/molecular cloud complexes. Much of the young-star activity is completely hidden from view. At shorter wavelengths, a variety of processes, including bremsstrahlung, are evident.

Telesco, C. M.↗
NASA NTRS1984

Probe of the Nearby Interstellar Medium by the Vacant Line of Sight to Beta Cma

The line of sight to Beta CM a was probed by Copernicus observations. This particular line of sight is remarkable for the low mean densities. The density was found to be bar N sub H approximately .002/cu cm. Two separate regions were distinguished: (1) A local nearby HI region extends over a few parsecs from the Sun with a density of the order of 0.1/cu cm and a temperature of 11000 to 12500 K; (2) An HII region lies somewhere beyond the HI region and is spread over about 60pc. Its total hydrogen mean density is of the same order as the HI region, i.e., of approximately 0.1 cu cm and it contains only elements in low ionization state. All the ata are coherent with the picture of a cloud in ionization equilibrium at T approximately 23000 deg K.

Gry, C.↗
NASA NTRS1984

The galactic gamma-ray distribution: Implications for galactic structure and the radial cosmic ray gradient

The radial distribution of gamma ray emissivity in the Galaxy was derived from flux longitude profiles, using both the final SAS-2 results and the recently corrected COS-B results and analyzing the northern and southern galactic regions separately. The recent CO surveys of the Southern Hemisphere, were used in conjunction with the Northern Hemisphere data, to derive the radial distribution of cosmic rays on both sides of the galactic plane. In addition to the 5 kpc ring, there is evidence from the radial asymmetry for spiral features which are consistent with those derived from the distribution of bright HII regions. Positive evidence was also found for a strong increase in the cosmic ray flux in the inner Galaxy, particularly in the 5 kpc region in both halves of the plane.

Harding, A. K.↗