Engineering topics

Joy, Marshall

Publications and source records attributed to Joy, Marshall.

47 records · Page 3

NASA NTRS1990

High energy, high resolution X-ray optics

The scientific goals of X-ray astronomy are considered to evaluate the relative advantages of using classical Wolter-1 optics or using a different approach. The portion of the X-ray band over 10 keV is unexploited in the present X-ray optics technology, and focussing in this portion of the band is crucial because nonfocussed experiments are background limited. The basic design of 'hard' X-ray optics is described theoretically emphasizing the very small angles of incidence in the grazing-incidence optics. Optimization of the signal-to-noise ratio is found to occur at a finite angular resolution. In real applications, the effective area reduced by the efficiency of the two reflections is 80 percent at energies up to 40 keV, and the quality of the reflecting surface can be monitored to minimize scattering. Focussing optics are found to offer improvements in signal-to-noise as well as more effective scientific return because microelectronic focal-plane technology is employed.

Weisskopf, Martin C.↗

NASA NTRS1989

The far-infrared structure of the luminous interacting galaxy Arp 299

The strongly interacting galaxies NGC 3690 and IC 694 (or Arp 299) exhibit extensive star formation, a large infrared luminosity, and possible nuclear activity. To determine the origin of the infrared luminosity in this system, high-resolution far-infrared profiles have been obtained in which two distinct sources can clearly be discerned; these observations reveal that 60 percent of the far-infrared luminosity comes from an unresolved source in the center of IC 694, with the remaining 40 percent originating in a compact source in NGC 3690. A new high-resolution 20-micron image of the Arp 299 system is compared with the far-infrared profiles, revealing that NGC 3690 is substantially hotter than IC 694 in the thermal infrared; the observed temperature gradient is opposite to that which is expected if the putative active nucleus in IC 694 generates a significant fraction of the total luminosity.

Joy, Marshall↗

NASA NTRS1988

Luminous extranuclear star formation in the interacting galaxy Arp 118 - NGC 1143/44

The interacting system Arp 118 (NGC 1143/44) has been observed at infrared and radio wavelengths. The interaction has produced a pair of distorted loops and several luminous radio and infrared sources in NGC 1144 which emit a total power of 2.5 x 10 to the 11th lunar masses, 80 percent of which is reradiated in the thermal infrared. Remarkably, the present observations reveal that much of the midinfrared emission originates in an extra-nuclear star-forming region. Arp 118 has many of the same characteristics as the well-studied interacting system Arp 299 (NGC 3690), including luminous extranuclear activity; the main difference between the two systems is that the nuclei of NGC 1143/44 are much less luminous at 10 microns than their counterparts in NGC 3690.

Joy, Marshall↗

NASA NTRS1988

Near-infrared line and continuum emission from the blue dwarf galaxy II Zw 40

A multicolor analysis of new near-infrared line and continuum measurements indicates that nebular recombination emission and photospheric radiation from young blue stars produce most of the near-infrared continuum emission in the central 6 arcsec of the dwarf galaxy II Zw 40. The derived nebular recombination level is in excellent agreement with independent observations of the radio free-free continuum. It is found that evolved stars, which dominate the near-infrared emission from normal galaxies, contribute no more than 25 percent of the total 2.2 micron flux in the central region of II Zw 40. It is concluded that the total mass of the evolved stellar population in the central 400 pc of the galaxy is less than about two hundred million solar. The total mass of recently formed stars is about two million solar, and the stellar mass ratio is exceptionally large. Thus, II Zw 40 is a quintessential starburst galaxy.

Joy, Marshall↗

NASA NTRS1988

The genesis of the ring galaxy Arp 144 (NGC 7828/29)

Multicolor near-infrared images have been obtained for the 'folded ring' galaxy Arp 144 (NGC 7828/29). About 10 to the 10th solar mass stellar nuclei associated with both NGC 7828 and NGC 7829 are found, indicating that this system is the result of an interaction between two similarly massive galaxies. The galaxy/intergalactic H I cloud collision model proposed by Freeman and de Vaucouleurs (1974) appears to be untenable, since it unequivocally predicts the existence of a single evolved stellar nucleus.

Joy, Marshall↗

NASA NTRS1988

Far-infrared observations of a luminous dust-shrouded source in the nucleus of NGC 4945

High-resolution far-infrared observations of the galaxy NGC 4945 have been obtained from the Kuiper Airborne Observatory. Using new observational techniques and nonlinear deconvolution routines, it is found that virtually all of the far-infrared luminosity originates from a nuclear source no larger than 12 arcsec x 9 arcsec (225 pc x 170 pc) in extent. This size constraint, coupled with the far-infrared dust temperature, indicates that the source is deeply embedded in dust: the lower limit for the 100 micron optical depth is 0.35, which is by far the largest yet measured in an external galaxy. Published optical spectra of NGC 4945 reveal a heavily obscured nonthermal source which exhibits broad line profiles typical of a Seyfert 2 active nucleus; it is concluded that the far-infrared emission is probably due to thermal radiation from dust grains surrounding the nonthermal nuclear source. A compact cluster of massive young stars may also contribute to the infrared luminosity, but the evidence for such star-forming activity is weak.

Brock, David↗

NASA NTRS1988

The origin of the infrared luminosity in Centaurus A

The origin of the infrared luminosity in Centaurus A is studied using new tracking and data acquisition techniques which yield diffraction-limited profiles at both 50 and 100 microns. Ninety percent of the 100 micron flux is found to originate in a source which extends 5 kpc along the optical dust lane that bisects the galaxy; the remaining 10 percent comes from an unresolved source coincident with the active radio nucleus. The extended 100 micron emission profile is fully consistent with a uniform disk of thermally radiating particles; when combined with results of previous studies at shorter wavelengths, these measurements indicate that nearly all of the infrared luminosity is produced by thermally emitting grains which are heated by massive young stars distributed throughout the optically thick dust lane.

Joy, Marshall↗

NASA NTRS1987

Infrared emission from young stars in the nucleus of M82

New observational and analytical techniques were used to obtain high-resolution NIR and FIR profiles of the luminous peculiar galaxy M82. The strongest NIR emission is found to be coincident with the dynamical center of the galaxy; a secondary NIR source, a factor of two fainter than the nucleus, is located 10 deg to the southewest. Simultaneous 40-micron and 100-micron profiles of M82 reveal an asymmetric distribution, with peak FIR emission diplaced about 5 arcsec to the west of center, and a plateau of emission extending about 5 arcsec to the east. The best positional determination indicates that the peak FIR emission from M82 is coincident with a cluster of young stars located to the southwest of the galactic nucleus at a projected distance of 10 arcsec (150 pc).

Joy, Marshall↗

NASA NTRS1987

Far-infrared detection of a circumstellar dust torus around Sharpless 106

High angular resolution scans at 42 and 95 microns have been obtained of the far-infrared source associated with S106. Using maximum entropy deconvolution techniques it is found that the far-IR-emitting dust appears to be distributed in a toroidal shape around the central star.This result is similar to the morphology implied to millimeter line and continuum mapping on a variety of size scales.

Harvey, Paul M.↗

NASA NTRS1987

A near-infrared study of the luminous merging galaxies NGC 2623 and ARP 148

As part of an investigation of the physical mechanisms which produce large infrared luminosities in interacting systems, multicolor near-infrared maps were obtained of the long tailed galaxy NGC 2623 and the ring galaxy Arp 148. The near-infrared broadband spectrum was decomposed to obtain the contribution of four processes: emission from evolved stars, nebular continuum emission, thermal reradiation, and extinction. This multicolor analysis, along with 2 micrometer maps and 10 micrometer measurements, is used to determine the structure of these interacting galaxies and to delineate regions of star formation.

Joy, Marshall↗

NASA NTRS1987

A near-infrared study of the luminous merging galaxies NGC 2623 and Arp 148

A broad-band spectral decomposition method has been developed to determine the contributions of evolved stars, H II regions, warm dust, and obscuration to the near-infrared continuum in interacting systems. The multicolor decomposition is applied to near-infrared measurements of the long-tailed galaxy NGC 2623 and the ring system Arp 148 to determine the galactic structure and to delineate regions of galactic activity. The infrared analysis confirms that these galaxies are coalescing; since a single nucleus is observed in the infrared, the merger must be complete. Arp 148 is found to be the product of a close collision of two galaxies, and the multicolor analysis implies that this system is in an early stage of coalescence. A substantial fraction of the nuclear regions of Arp 148 and NGC 2623 may be attributed to the presence of young stars.

Joy, Marshall↗