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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

HST ultraviolet spectropolarimetry of NGC 1068

We present multiaperture spectropolarimetric observations of the Seyfert 2 galaxy NGC 1068. The nuclear region of NGC 1068 was observed with three apertures (4.3 sec x 1.4 sec., 1.0 sec., and 0.3 sec.) by the Hubble Space Telescope (HST). These ultraviolet data allow us to study the scattered, nuclear light without the complication of polarization dilution caused by strong unpolarized starlight. In particular, we can determine the mechanism of the scattering and the size scale of the scattering region. Our data confirm the findings of Antonicci & Miller (1985) and Code et al. (1993). Shortward of 2700 A, the continuum polarization is constant, P is approximately 16%, at a position angle of 97 deg, indicating electron scattering as the mechanism for the polarization. In addition, the narrow-line emission is much less polarized than the continuum, and two broad lines, Mg II lambda lambda 2796, 2804 and C III lambda 1909, are seen in polarized flux Ly-alpha and C IV are not included in our spectral region). The total flux data also indicate that from approximately 2200 A to approximately 3000 A, the spectrum of NGC 1068 is strongly affected by blended Fe II emission. These polarimetry data are explained by the occulation/reflection model proposed by Antonucci & Miller (1985). According to this model, NGC 1068 harbors a Seyfert 1 nucleus which is obscured along the line of sight by an opaque torus. The symmetry axis of the torus is alinged with the radio axis. Radiation from the broad-line region and feature continuum source can escape along the poles of the torus where it is scattered to us. This scattered light receives a partial linear polarization, perpendicular to the symmetry axis of the torus. Our measurements of the relative fluxes and polarized fluxes in the three apertures indicated that the scattering region is spatially extended on a scale of approximatley 1 sec. Also, in the 0.3 sec aperture, and to a lesser extent in the 1.0 sec aperture, the polarization is is somewhat higher, and the position angle somewhat lower, than in largest aperture. Presumably, isolating the central part of the relecting region results in less geometrical cancellation of the polarization and an angle indicative of the location of the innermost scattering paricles.

Antonucci, Robert↗
DOE OSTI2021

The spectra of IceCube neutrino (SIN) candidate sources – II. Source characterization

ABSTRACT Eight years after the first detection of high-energy astrophysical neutrinos by IceCube, we are still almost clueless as regards to their origin, although the case for blazars being neutrino sources is getting stronger. After the first significant association at the $3\!-\!3.5\, \sigma$ level in time and space with IceCube neutrinos, i.e. the blazar TXS 0506+056 at z = 0.3365, some of us have in fact selected a unique sample of 47 blazars, out of which ∼16 could be associated with individual neutrino track events detected by IceCube. Building upon our recent spectroscopy work on these objects, here we characterize them to determine their real nature and check if they are different from the rest of the blazar population. For the first time we also present a systematic study of the frequency of masquerading BL Lacs, i.e. flat-spectrum radio quasars with their broad lines swamped by non-thermal jet emission, in a γ-ray- and IceCube-selected sample, finding a fraction >24 per cent and possibly as high as 80 per cent. In terms of their broad-band properties, our sources appear to be indistinguishable from the rest of the blazar population. We also discuss two theoretical scenarios for neutrino emission, one in which neutrinos are produced in interactions of protons with jet photons and one in which the target photons are from the broad-line region. Both scenarios can equally account for the neutrino–blazar correlation observed by some of us. Future observations with neutrino telescopes and X-ray satellites will test them out.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1977

Molecular clouds

An attempt is made to understand star formation in the context of the dense interstellar molecular gas from which stars are made. Attention is given to how molecular observations (e.g., UV spectroscopy and radio 21-cm and recombination line observations) provide data on the physical state of the dense interstellar gas; observations of H II regions, stellar associations, and dark nebulae are discussed. CO clouds are studied with reference to radial velocity, temperature, density, ionization, magnetic field.

Thaddeus, P.↗
NASA NTRS1980

Stress-relieved solder joints

Mechanical stress on solder joints is reduced by procedure for soldering electronic components to circuit boards. Procedure was developed for radio-frequency (RF) strip-line circuits, for which dimensions must be carefully controlled to minimize parasitic capacitance and inductance. Procedure consists of loosening component from its mounting after each lead is soldered relieving induced stresses before next soldering step.

Zemenick, C. J.↗
NASA NTRS1980

CO observations of the galactic star-forming region W58

Observations of (C-12)O and (C-13)O have been made in the direction of the strong galactic radio source W58, which contains the compact H II regions K3-50 and ON-3. An extended molecular cloud with dimensions of 55 x 40 pc is associated with the northern part of the H II region complex. The density of the molecular cloud increases from west to east; the molecular cloud is bounded on the east by a larger H I cloud. Present star-formation activity is taking place at the position of maximum molecular density, at what appears to be the interface of the H I cloud and the H II region complex. The velocity structure of the CO cloud and the compact H II regions are in agreement with the blister model. Radio continuum and H I line observations show indications of a shell structure in the southwest of W58. Present star formation in W58 may be caused by this expanding shell.

Israel, F. P.↗
NASA NTRS1982

Goddard X-ray astronomy contributions to the IAU/COSPAR (1982)

The relation of X-ray flux to both the continuum flux in the optical and radio bands, and to the line emission properties of these objects were studied. The Einstein Observatory, because of increased sensitivity and improved angular resolution, increased substantially the number of known X-ray emitting active galactic nuclei. The Einstein imaging instruments detected morphology in AGN X-ray emission, in particular from jetlike structures in Cen-A, M87, and 3C273. The improved energy resolution and sensitivity of the spectrometers onboard the Observatory provide information on the geometry and ionization structure of the region responsible for the broad optical emission lines in a few AGN's. This information, combined with theoretical modeling and IUE and optical observations, allows the construction of a moderately detailed picture of the broad line region in these objects.

Holt, S. S.↗
NASA NTRS1983

MV-3 communication subsystem

The operational mobile VLBI data acquisition system (MV-3) requires that a voice link be established between the mobile data system and a fixed site. A communications subsystem was incorporated in the MV-3 design which consists of HF radio, VHF mobile radio telephone and conventional land line telephone. The HF antenna design was optimized for short and long range transmission using both inverted V and yagi antennas mounted on a self-supporting telescoping mast.

Parks, G. S.↗
NASA NTRS1983

Discovery of large radial velocities in the supernova remnant 3C 58

New spectroscopic observations of four filaments in 3C 58, three of which appear close to the remnant's radio center, are described. Observed line intensities and radial velocities are presented which indicate a high radial expansion velocity for the object and nearly zero radial velocities for filaments located along the remnant's edge. Large velocities are present nearer the remnant's center up to a maximum of about 900 km/s. These velocities strongly support the identification of 3C 58 as the remnant of the historical supernova seen in AD 1181. A crude estimate of the reddening of the object is made. The observed H-alpha/H-beta ratio of about six suggests only a modest amount of extinction. The object is unlikely to possess a mean expansion velocity of 10,000 km/s over 800 yr, and a previously estimated distance to the object of about 8 kpc is thus improbable.

Fesen, R. A.↗
NASA NTRS1984

Laboratory millimeter and submillimeter spectra of HNO and DNO

The identification of interstellar molecular species via the detection of one spectral line has recently become subject to close scrutiny. The radical HNO falls into the class of interstellar molecules identified in this manner. To corroborate this identification, observation of additional spectral lines is necessary. In this paper, laboratory millimeter and submillimeter wave spectra of both HNO and DNO are reported in the frequency region 150-500 GHz. Based on these spectral line measurements, models for HNO and DNO have been constructed to yield accurate frequencies for all rotational transitions of these species below 500 GHz involving J values smaller than 10. The spectral lines can be utilized by radio astronomers to confirm the identification of interstellar HNO and to search for interstellar DNO.

Sastry, K. V. L. N.↗
NASA NTRS1984

The QUASAT mission: An overview

The QUASAT VLBI mission to provide images of the total intensity and polarized emission of compact radio sources in continuum and line with a combination of angular resolution and quality unattainable from Earth is summarized. The astrophysical goals encompass the study of active nuclei at scales appropriate to the outer reaches of accretion disks and the optical broad and narrow line regions; the study of galactic continuum sources in stars and in the galactic center; and spectroscopic studies of galactic and extragalactic molecular masers to determine their role in the life cycle of stars, and their use as direct distance indicators.

Schilizzi, R. T.↗
NASA NTRS1984

Brackett-alpha line profiles of young stellar objects

Profiles of the Br-alpha line of H I at a velocity resolution of 45 km/s are presented for the compact imbedded infrared objects BN, S106/IRS 3, GLS 490, GL 961, GL 989, Mon. R2/IRS 2, and for the visible objects LkH-alpha 101, T Tau, and R Mon. A proportionality obtained between Br-alpha luminosity and bolometric luminosity is shown to extend over three orders of magnitude, supporting the idea that the physical conditions and gas motions in the circumstellar envelopes of stellar objects are closely related over a wide range of luminosities. The Br-alpha line strengths are compared to radio continuum flux densities in the context of stellar wind models. Momentum deposition rates deduced from Br-alpha or radio continuum fluxes are consistent with those available in the radiation fields, which appear capable of driving the ionized gas outflows in the vicinity of the core sources. The results of a comparison of the H-alpha and Br-alpha profiles for T Tau are discussed.

Persson, S. E.↗
NASA NTRS1986

Detection of OH from Comet Halley in the far-infrared

The 2 Pi 3/2 (J = 5/2 yields 3/2 + yields - parity) transition of OH was detected in comet Halley at 119.44 microns. The upper limit to the line intensity of the - yields + parity transition is 119.23 microns. The ratio of these lines is consistent with radiative pumping of the rotational levels through absorption of near ultraviolet solar photons which excite the low lying vibrational levels of OH. The far-infrared lines probe the inner regions of the coma where OH is produced through photodissociation of a parent molecule (presumably H2O). Hence, these lines complement the 18 cm radio measurements which are sensitive to the outer regions of the comet coma. The OH production rate is highly model dependent but is of the order 2 to 4 times 10 to the 29th power molecules/sec.

Stacey, Gordon J.↗
NASA NTRS1993

Models of the Cartwheel ring galaxy: Spokes and starbursts

Recent observations of this famous ring galaxy, including optical and near-infrared CCD surface photometry, and VLA radio continuum and 21 cm line mapping (Higdon 1992b, in prep.), have inspired a renewed modeling effort. Toomre's (1978, in The Large-scale Structure of the Universe, eds. Longair and Einasto) series of restricted three-body simulations demonstrated how the multiple rings could be produced in a nearly head-on galaxy collision. New models with a halo-dominated potential based on the 21 cm rotation curve are able to reproduce such details as the spacing between rings, ring widths, offset of the nucleus, and several kinematical features, thus providing strong support for the collisional theory. The new observations have shown there are little or no old stars in Cartwheel; it may consist almost entirely of gas and stars produced as a result of compression in the ring wave. To model this process Smooth Particle Hydrodynamics (SPH) simulations of the Cartwheel disk have been performed. Fixed gravitational potentials were used to represent the Cartwheel and a roughly 30 percent mass collision partner. The interaction dynamics was treated as in the usual restricted three-body approximation, and the effects of local self-gravity between disk particles were calculated. We are particularly interested in testing the theory that enhanced star formation in waves is the result of gravitational instability in the compressed region (see e.g. Kennicutt 1989, ApJ 344, 685). The gas surface density in a number of simulations was initialized to a value slightly below the threshold for local gravitational instability throughout most of the disk. The first ring wave produces relatively modest compressions (a factor of order a few), triggering instability in a narrow range of wavelengths. Self-gravity in the disk is calculated over a comparable range of scales. Simulations were run with isothermal, adiabatic, and adiabatic with radiative cooling characterized by a relatively short timescale. The isothermal approximation is good except in the vicinity of the strong second (inner) ring, and several snapshots from one case are shown in the figure below. Flocculent spiral segments are present before the collision, and these are compressed into dense knots in the ring wave. These knots are likely to be sites of vigorous star formation. In the strong rarefaction behind the outer ring most of the knots are radially stretched and sheared, giving rise to spoke-like features. A few dense knots are evidently very tightly bound, because they retain their coherence and are stretched relatively little through the rarefaction. This is in accord with evidence for continuing star formation in some spokes (Marcum, Appleton and Higdon 1992). The number and spacing of spokes is a direct function of the scale of the gravitational instability in the disk. Thus, the gravitational instability theory, together with the hypothesis that massive stars are only formed in dense knots of gas, can account for most of the distinct morphology of the Cartwheel.

Struck-Marcell, Curtis↗
NASA NTRS1993

The 'Taffy' galaxies UGC 12914/5

The interacting spiral galaxy pair UGC 12914/5 was mapped with the 'VLA' for a 1.49 GHz atlas of the IRAS Bright Galaxy Sample. Half of the flux from UGC 12914/5 arises from the gap between UGC 12914 and UGC 12915, across which the radio contours are drawn like filaments of taffy. The bright radio continuum connecting UGC 12914 with UGC 12915 is a synchrotron source which therefore probably contains both cosmic rays and magnetic fields. It is suggested that the filaments were stripped from UGC 12914 and UGC 12915 as their stellar disks interpenetrated during a recent encounter; this implies that the radio bridge is a relic whose properties contain information about direct collisions of galaxies with gaseous disks. New maps have been made of the radio continuum and H I line emission from UGC 12914/5 in order to verify the stripping hypothesis.

Condon, J. J.↗
NASA NTRS1992

Cosmic rays and shock waves in active galaxies

Studies of nonthermal radio emission in the inner regions of active galaxies reveal clear morphological evidence for shock waves. It is argued that the shocks are driven by collimated outflow of plasma from the AGN. I describe a model in which the synchrotron radio emission arises from ambient relativistic electrons and magnetic fields which have been compressed in a radiative shock wave. No active particle acceleration at the shock front is required in this picture. The prospects for diagnosing active acceleration from radio continuum and optical emission line observations are briefly discussed.

Wilson, Andrew S.↗
NASA NTRS2000

Detection of X-ray Emission From Galaxies Inside The Bootes Void

We report the x-ray properties of Bootes void galaxies detected by the ROSAT All-Sky Survey (RASS). By searching the fields of 26 radio and 27 emission-line-selected void galaxies, we have detected 9 x-ray emitting void galaxies at >2.7-sigma confidence level. Five of these 9 galaxies are in the IP,AS subsample. We expect 2 detections at the redshift of the Bootes void based on previous positional cross-correlation studies of the RASS and IRAS Point Source Catalogue sources. Three of the x-ray emitting galaxies are AGNs (IRAS~14288+5255, Mrk~845, and IRAS 15195+5050), and the remaining 6 are all likely emission line galaxies (PC~1357+4641, CG~547, CG~922, IRAS~14SOO+4804, CG~637, and IRAS~15092+3940). The far infrared flux levels of the AGN sources implies most of the observed x-ray emissivity is from starburst activity. We have carried out timing and spectral analysis for the narrow-line Seyfert 1 galaxy Mrk~845. Poor statistics prevents detailed analysis of the remaining sources. only two galaxies in our sample, BHI 1514+3819 and FSS 1515+3823, were observed during ROSAT pointed observations resulting in a nondetection at the 1-sigma level.

Kim, Chulhee↗