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At least 721 records · Page 40

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NASA NTRS1977

Far-infrared observations of NGC 7027

Far-infrared observations of the planetary nebula NGC 7027 show that its total infrared flux is 2.4 by 10 to the -10th power W/sq m, approximately one-third of which is emitted in each of the intervals from 1 to 17, 17 to 30, and 30 to 300 microns. Sufficient energy to account for the corresponding infrared luminosity of 23,000 times the solar value at 1.77 kpc is available as diffuse nebular radiation or from moderate competition between dust and gas for Lyman continuum photons. Most of the infrared flux arises from a source comparable in size to the H II region. The flux at wavelengths greater than 17 microns can be attributed to grains with temperatures not exceeding 120 K and total mass such that the gas-to-dust ratio is close to the lower limit allowed by cosmic abundances.

Telesco, C. M.↗

NASA NTRS1977

High resolution infrared absorptivities for gaseous chlorine nitrate

High resolution infrared absorptivities of chlorine nitrate (ClONO2) are required in order to quantitatively evaluate, by examination of infrared spectra obtained recently from balloon-borne spectrometers, the possible occurrence of this compound in the stratosphere. In the present study, infrared absorptivities for four absorption bands of gaseous ClONO2 have been measured at 0.0625 per cm spectral resolution with a Fourier transform infrared (FT-IR) system. Spectra were obtained at two pressures (0.05 and 1.05 torr) of pure ClONO2 and with 125 torr of N2 added to a 0.50 torr sample. Absorptivities for a range of spectral resolutions (0.0625, 0.125, 0.25 and 0.50 per cm) have been calculated from the data.

Graham, R. A.↗

NASA NTRS1977

New infrared-CO source in M8

A far-infrared map of the M8 region at 69 microns with a 1-arcmin resolution shows an unresolved source 19 arcmin east of the main component. This source is a strong near-infrared emitter, with K = 4.8 and K - L = 2.6 mag. An intense peak in (C-12)O emission (brightness temperature about 36 K) coincides with the new infrared source. Comparison of millimeter-wave and infrared observations suggest that this source is an extremely young compact H II region. Evidence for a depletion of dust opacity inside the H II region is also found.

Wright, E. L.↗

NASA NTRS1977

Review of the absorption spectra of solid O2 and N2 as they relate to contamination of a cooled infrared telescope

During contamination studies for the liquid helium cooled shuttle infrared telescope facility, a literature search was conducted to determine the absorption spectra of the solid state of homonuclear molecules of O2 and N2, and ascertain what laboratory measurements of the solid have been made in the infrared. With the inclusion of one unpublished spectrum, the absorption spectrum of the solid oxygen molecule has been thoroughly studied from visible to millimeter wavelengths. Only two lines appear in the solid that do not also appear in the gas or liquid. A similar result is implied for the solid nitrogen molecule because it also is homonuclear. The observed infrared absorption lines result from lattice modes of the alpha phase of the solid, and disappear at the warmer temperatures of the beta, gamma, and liquid phases. They are not observed from polycrystalline forms of O2, while strong scattering is. Scattering, rather than absorption, is considered to be the principal natural contamination problem for cooled infrared telescopes in low earth orbit.

Smith, S. M.↗

NASA NTRS1978

A Multi-Band Far-Infrared Survey with a Balloon-Borne Telescope

Nine additional radiation sources, above a 3-sigma confidence level of 1300 Jy, were identified at 100 microns by far infrared photometry of the galactic plane using a 0.4 meter aperture, liquid helium cooled, multichannel far infrared balloon-borne telescope. The instrument is described, including its electronics, pointing and suspension systems, and ground support equipment. Testing procedures and flight staging are discussed along with the reduction and analysis of the data acquired. The history of infrared astronomy is reviewed. General infrared techniques and the concerns of balloon astronomers are explored.

Jacobson, M. R.↗

NASA NTRS1978

Far infrared polarization of the Kleinmann-Low Nebula in Orion

Elongated dust grains aligned by local magnetic fields are though to absorb background radiation and produce linear and circular polarization which exhibit strong wavelength dependence in the near infrared. The NASA Kuiper observatory 91 cm infrared telescope was used to observe polarization characteristics of the Kleinmann-Low nebula in four far infrared wavelength bands in order to detect emission from these same oriented grains at longer wavelengths, and determine whether this radiation shows a direction of polarization perpendicular to that seen in the near infrared. The polarization, if any, that characterized the radiation in the three longest wavelength filter positions (28-48 micron, 44-72 micron, and 70-115 micron) is small. The noisiest measurements were obtained in the 16-33 micron filter position. Possible explanations for the low polarization observed at long wavelengths are explored.

Gull, G. E.↗

NASA NTRS1978

Strong far-infrared emission from a compact source in sharpless 140

High-spatial-resolution observations of S140 are presented at wavelengths from 35 to 175 microns. A single strong far-infrared source has been found coincident with a compact near-infrared and H2O maser source and the center of a molecular cloud. The far-infrared spectrum suggests either significant absorption in the 20-micron region or a two-temperature dust structure. The infrared luminosity of approximately 20,000 suns is comparable to that of a late O or early B star, although no radio continuum flux has been seen from this object. The source is quite likely a dust-embedded protostar.

Harvey, P. M.↗

NASA NTRS1978

The infrared emission of the Galactic center

Ground-based and airborne infrared observations of the Galactic center near Sgr A are presented. The principal results include: (1) A map at 56 microns (28-arcsec beam FWHM) which shows a ridge of emission in which are immersed two peaks, one at the infrared cluster and another 1 arcmin to the southwest. Early-type stars may produce much of the luminosity seen as thermally reradiated far-infrared flux. (2) A map of the infrared cluster at 34 microns (8.5-arcsec beam) which indicates that the distribution at this wavelength is similar to that at 21 microns, with most of the compact sources which emit at wavelengths shorter than 20 microns emitting relatively weakly at 34 microns. (3) A map at 10 microns which combines observations obtained with 1.5-, 2.3-, 3-, 5.5-, and 20-arcsec beams and shows for the first time the extended 10-micron structure, including the southwestern component, in relation to the cluster of compact sources. Most of the compact 10-micron sources have the structure and spectra to be expected if a luminous object is embedded in a tenuous dust cloud.

Rieke, G. H.↗

NASA NTRS1978

Far-infrared observations of H II regions in M33

Three H II regions in M33, namely, IC 133, NGC 595, and NGC 604, have been observed at far-infrared wavelengths. Only NGC 604, the strongest radio source of the three, was detected. The far-infrared radiation appears to be thermal emission from dust. The amount of dust known to be present in NGC 604 from comparison of optical and radio data is sufficient to account for the observed far-infrared emission. The total power radiated in the far-infrared is comparable to the total luminosity of the exciting stars of the H II region.

Gatley, I.↗

NASA NTRS1979

Far infrared maps of the ridge between OMC-1 and OMC-2

Dust continuum emission from a 6 ft x 20 ft region surrounding OMC-1 and OMC-2 were mapped at 55 and 125 microns with 4 ft resolution. The dominant features of the maps are a strong peak at OMC-1 and a ridge of lower surface brightness between OMC-1 and OMC-2. Along the ridge the infrared flux densities and the color temperature decreases smoothly from OMC-1 to OMC-2. OMC-1 is heated primarily by several optical and infrared stars situated within or just at the boundary of the cloud. At the region of minimum column density between OMC-1 and OMC-2 the nearby B0.5 V star NU Ori may contribute significantly to the dust heating. Near OMC-2 dust column densities are large enough so that, in addition to the OMC-2 infrared cluster, the nonlocal infrared sources associated with OMC-1 and NU Ori can contribute to the heating.

Keene, J.↗

NASA NTRS1978

Instrumentation for infrared astronomy

During the last 10 years, infrared astronomy, based on observations in the wavelength range from 2 to 1000 micrometers, has become a major field of observational astrophysics. This development is mainly related to two major technical advances. Extremely sensitive detectors have been developed and become available for astronomical applications. Motivated by the first development, major groups have expended much effort in building and operating telescopes above most or all of the earth's atmosphere in order to circumvent its opacity and emission throughout the range. Attention is given to advances in the area of infrared detectors, platforms for infrared astronomy, focal plane instruments, high spatial resolution instrumentation, and infrared polarization measurements.

Soifer, B. T.↗

NASA NTRS1978

The MOM tunneling diode - Theoretical estimate of its performance at microwave and infrared frequencies

A theoretical analysis of the metal-oxide-metal (MOM) antenna/diode as a detector of microwave and infrared radiation is presented with the experimental verification conducted in the far infrared. It is shown that the detectivity at room temperature can be as high as 10 to the 10th per W Hz exp 1/2 at frequencies of 10 to the 14th Hz in the infrared. As a result, design guidelines are obtained for the lithographic fabrication of thin-film MOM structures that are to operate in the 10-micron region of the infrared spectrum.

Sanchez, A.↗

NASA NTRS1978

Effect of tropospheric aerosols upon atmospheric infrared cooling rates

The effect of tropospheric aerosols on atmospheric infrared cooling rates is investigated by the use of recent models of infrared gaseous absorption. A radiative model of the atmosphere that incorporates dust as an absorber and scatterer of infrared radiation is constructed by employing the exponential kernel approximation to the radiative transfer equation. Scattering effects are represented in terms of a single scattering albedo and an asymmetry factor. The model is applied to estimate the effect of an aerosol layer made of spherical quartz particles on the infrared cooling rate. Calculations performed for a reference wavelength of 0.55 microns show an increased greenhouse effect, where the net upward flux at the surface is reduced by 10% owing to the strongly enhanced downward emission. There is a substantial increase in the cooling rate near the surface, but the mean cooling rate throughout the lower troposphere was only 10%.

Harshvardhan, MR.↗

NASA NTRS1979

Far-infrared observations of optical emission-line stars - Evidence for extensive cool dust clouds

Far-infrared observations (40-160 microns) of eight optical emission-line stars are presented. Six of these stars, LkH-alpha 198, T Tau, LkH-alpha 101, V380 Ori, R Mon, and MWC 1080, show substantially more far-infrared emission than would be expected on the basis of a blackbody extrapolation of their 10-20-micron fluxes. Additionally, in three cases, the far-infrared emission is shown to be spatially extended (greater than 40 arcsec). A simple model of the thermal emission from cool circumstellar dust (30-70 K) shows that these stars are surrounded by material left over from the star formation process; this result confirms the extreme youth of these stars. MWC 349 was detected at a level consistent with the expected free-free flux from its surrounding H II region, and RY Tau was not detected in the far-infrared; there is little circumstellar dust with temperatures of 20-100 K in these objects.

Harvey, P. M.↗

NASA NTRS1979

Design alternatives for the Shuttle Infrared Telescope Facility

The paper discusses the Shuttle Infrared Telescope Facility (SIRTF), a versatile astronomical telescope that can accomodate photometric, spectroscopic, and polarimetric measurements. It is expected to be 100 to 1000 times more sensitive than any existing infrared telescope; detailed designs of cooled IR telescopes were made for the Infrared Astronomical Satellite and the Small Helium Cooled Infrared Telescope for Spacelab 2. Rocket tests verified the capability of using superfluid helium as a cryogen in zero gravity. Constraints on funds for Shuttle payloads require an evolutionary approach to the development of the full potential of SIRTF, necessitating consideration of design alternatives involving the optical configuration, the cryogen, the mechanical structure, and size of SIRTF.

Witteborn, F. C.↗

NASA NTRS1979

Spacelab 2 infrared telescope cryogenic system

The paper discusses the development of a cryogenic helium system to provide cooling to a scanning infrared telescope for the Spacelab 2 mission. The infrared optical/detector system and related electronics are being developed by the Smithsonian Astrophysical Observatory and the University of Arizona. A superfluid helium dewar and porous plug phase separator permit gas cooling of the infrared focal plane assembly to about 2.5 K, and of the two telescope sections to 8 K and 60 K. The design of the cryogenic system,including a commandable vacuum cover, and the prelaunch liquid helium servicing and maintenance approach were discussed. It is concluded that the system will satisfy the Infrared Telescope requirements, and the superfluid helium system shall be capable of satisfying cryogenic helium cooled requirements for the next several years.

Urban, E. W.↗

NASA NTRS1980

Solar panel thermal cycling testing by solar simulation and infrared radiation methods

For the solar panels of the European Space Agency (ESA) satellites OTS/MAROTS and ECS/MARECS the thermal cycling tests were performed by using solar simulation methods. The performance data of two different solar simulators used and the thermal test results are described. The solar simulation thermal cycling tests for the ECS/MARECS solar panels were carried out with the aid of a rotatable multipanel test rig by which simultaneous testing of three solar panels was possible. As an alternative thermal test method, the capability of an infrared radiation method was studied and infrared simulation tests for the ultralight panel and the INTELSAT 5 solar panels were performed. The setup and the characteristics of the infrared radiation unit using a quartz lamp array of approx. 15 sq and LN2-cooled shutter and the thermal test results are presented. The irradiation uniformity, the solar panel temperature distribution, temperature changing rates for both test methods are compared. Results indicate the infrared simulation is an effective solar panel thermal testing method.

Nuss, H. E.↗

NASA NTRS1981

Far-infrared properties of dust in the reflection nebula NGC 7023

Thermal emission from dust in the reflection nebula NGC 7023 has been observed at wavelengths between 40 and 400 microns. The observed far-infrared emission comes from a region approximately 4 arcmin in diameter and shows spatial structure which correlates well with the distribution of reflected visible radiation. Temperature and optical depth maps indicate that the dust which emits the far-infrared radiation is heated by UV and visual radiation from the central star (HD 200775) and that the dust density increases steeply northwest of the star. The far-infrared data are not consistent with either the spherical or uniform slab geometries used in earlier analyses of optical observations. Comparisons of the far-infrared measurements with optical and UV measurements give a value between 2000 and 5000 for the ratio of extinction efficiency in the UV to that at 125 microns. This value is compared with the results of other observational studies and with theoretical grain models.

Whitcomb, S. E.↗