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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 127 records · Page 7
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NASA NTRS1986

Far-infrared investigation of the Taurus star-forming region using the IRAS database

The Infrared Astronomical Satellite (IRAS) has given us the first completely unbiased sky-survey in the far-infrared with wavebands centered at 12, 25, 60 and 100 microns. The Taurus-Auriga complex was selected as the first molecular cloud to be investigated in this study. The Taurus clouds were defined as lying between 04h and 05h in R.A. and +16 to +31 degrees in Dec., then the IRAS point-source catalogue was searched for sources with good or moderate quality fluxes in all three of the shortest IRAS bands. The sources which were selected in this way were then classified into subgroups according to their IRAS colors. Taurus is generally believed to be an area of low-mass star formation, having no luminous O-B associations within or near to the cloud complex. Once field stars, galaxies and planetary nebulae had been removed from the sample only the molecular cloud cores, T Tauri stars and a few emission-line A and B stars remained. The great majority of these objects are pre-main sequence in nature and, as stated by Chester (1985), main sequence stars without excess far-infrared emission would only be seen in Taurus if their spectral types were earlier than about A5 and then not 25 microns. By choosing our sample in this way we are naturally selecting the hotter and thus more evolved sources. To counteract this, the molecular cloud core-criterion was applied to soruces with good or moderate quality flux at 25, 60 and 100 microns, increasing the core sample by about one third. The candidate protostar B335 is only detected by IRAS at 60 and 100 microns while Taurus is heavily contaminated by cirrus at 100 microns. This means that detection at 25 microns is also required with those at 60 and 100 microns to avoid confusing a ridge of cirrus with a genuine protostar. The far-infrared luminosity function of these sources is then calculated and converted to the visual band by a standard method to compare with the field star luminosity function of Miller and Scalo. The eventual aim of this work is to obtain far-infrared luminosity functions for a number of molecular clouds which are known to be forming low-mass stars and to investigate how the slope is affected by changes in the density and turbulence of material.

Hughes, J. D.↗
NASA NTRS2004

The Case for Space-Borne Far-Infrared Line Surveys

The combination of sensitive direct detectors and a cooled aperture promises orders of magnitude improvement in the sensitivity and survey time for far-infrared and submillimeter spectroscopy compared to existing or planned capabilities. Continuing advances in direct detector technology enable spectroscopy that approaches the background limit available only from space at these wavelengths. Because the spectral confusion limit is significantly lower than the more familiar spatial confusion limit encountered in imaging applications, spectroscopy can be carried out to comparable depth with a significantly smaller aperture. We are developing a novel waveguide-coupled grating spectrometer that disperses radiation into a wide instantaneous bandwidth with moderate resolution (R ~ 1000) in a compact 2-dimensional format. A line survey instrument coupled to a modest cooled single aperture provides an attractive scientific application for spectroscopy with direct detectors. Using a suite of waveguide spectrometers, we can obtain complete coverage over the entire far-infrared and sub-millimeter. This concept requires no moving parts to modulate the optical signal. Such an instrument would be able to conduct a far-infrared line survey 10 6 times faster than planned capabilities, assuming existing detector technology. However, if historical improvements in bolometer sensitivity continue, so that photon-limited sensitivity is obtained, the integration time can be further reduced by 2 to 4 orders of magnitude, depending on wavelength. The line flux sensitivity would be comparable to ALMA, but at shorter wavelengths and with the continuous coverage needed to extract line fluxes for sources at unknown redshifts. For example, this capability would break the current spectroscopic bottleneck in the study of far-infrared galaxies, the recently discovered, rapidly evolving objects abundant at cosmological distances.

Bock, J. J.↗
NASA NTRS1977

A high-resolution far-infrared survey of the W31 region

A 1-m balloon-borne telescope was used to conduct a far-infrared survey of the W31 region at an effective wavelength of 69 microns with a resolution of 1 arcmin. Within this region seven far-infrared sources were observed. Five of these sources were associated with thermal radio emission. For each of these sources the infrared luminosity is much greater than the Ly-alpha luminosity, a situation requiring either dust absorption of Lyman-continuum photons or a large nonionizing stellar luminosity. Two faint infrared sources had no radio counterparts. Far-infrared radiation was not detected from two known radio sources and from one midinfrared source in this region.

Wright, E. L.↗
NASA NTRS1987

Far-infrared continuum emission from the nucleus, starburst, and extended spiral arms of NGC 1068

Far-infrared slit scans across NGC 1068 are used to better define the contribution of the active nucleus, starburst disk, and extended spiral arms in the luminous output of this bright Seyfert 2 galaxy. The decomposition of the emission from the bright, inner 3 kpc of this galaxy suggests that at 50 microns, about half the emission is from star formation in a starburst disk and half from the compact, centrally heated circumnuclear cloud. The 100-micron profile of the starburst disk is asymmetric with respect to the nucleus. This appears to be the result of an extraordinary star-forming complex about a kiloparsec away from the center. With the application of maximum entropy deconvolution to the scans, evidence is found for 100-micron emission from the extended spiral arms of the galaxy. The far-infrared emission from the starburst region is distinguished from that of the extended spiral arms. In terms of both total luminosity and surface brightness, the extended spiral arms of NGC 1068 are at the bright end of the range of far-infrared emission from quiescent, noninteracting spirals.

Lester, D. F.↗
NASA NTRS1991

The far-infrared morphology of the double-ringed galaxy NGC 4736 (M94) - A ring surrounding an extended nucleus

High spatial resolution 100-micron observations of the central region of the double-ringed spiral galaxy NGC 4736 (M94) were obtained using the Kuiper Airborne Observatory. The data show a strong central peak with secondary peaks at the radius of the inner ring (50 arcsec = 1.6 kpc). The nuclear emission is extended at 100 microns, with a radius of 15 arcsec (500 pc). The far-infrared morphology is similar to that of the molecular gas, while the H I distribution shows a pronounced central depression. Since most of the hydrogen gas in the inner regions of NGC 4736 is in molecular form, it is concluded that the far-infrared emission from NGC 4736 arises mainly from dust associated with molecular gas. The H-alpha distribution differs dramatically from the far-infrared and molecular gas distributions. The ring dominates the H-alpha emission, while the total 100-micron ring emission is only slightly larger than that of the nucleus, yielding an L(FIR)/L(H-alpha) for the nucleus about 100 times that of the ring. The bolometric luminosity of the stars in the inner 1 kpc of NGC 4736 is sufficient to power the far-infrared from this region, which suggests that a significant fraction of the far-infrared emission in the nuclear region of NGC 4736 is powered by non-OB stars rather than by star formation.

Smith, Beverly J.↗
NASA NTRS1994

A rocket-borne observation of the far-infrared sky at high Galactic latitude

We have measured the surface brightness of the far-infrared sky at lambda = 134, 154, and 186 micrometers at high Galactic latitude using a liquid-He-cooled, rocket-borne telescope. The telescope scanned over a 5 deg x 20 deg region which includes infrared cirrus, high-latitude molecular clouds, the starburst galaxy M82, and the H I Hole in Ursa Major, a region with uniquely low H I column density. The measured brightness at 134, 154, and 186 micrometers is well correlated with the 100 micrometers brightness measured by IRAS and, in regions excluding molecular clouds, with H I column density. The spectrum of the component correlated with H I is well fitted by a gray-body spectrum with a temperature of 16.4 (+2.3/-1.8) K, assuming an emissivity proportional to lambda(exp -2). Assuming a constant far-infrared dust emissivity per hydrogen nucleus, the ratio of the H2 column density to the velocity-integrated CO intensity in the high-latitude molecular cloud is NH2/W(sub co) = (1.6 +/- 0.3) x 10(exp 20)/sq cm/(K km/s). The residual brightness after subtracting the emission correlated with H I column density is lambda I(sub lambda)(154 micrometers) = (1.4 +/- 0.6) x 10(exp -12) W/sq cm/sr, yielding an upper limit to the far-infrared extragalactic background radiation of lambda I(sub lambda)(154 micrometers) is less than 2.6 x 10(exp -12) W/sq cm/sr.

Kawada, M.↗
NASA NTRS1995

Modeling the light-travel-time effect on the far-infrared size of IRC +10216

Models of the far-infrared emission from the large circumstellar dust envelope surrounding the carbon star IRC +10216 are used to assess the importance of the light-travel-time effect (LTTE) on the observed size of the source. The central star is a long-period variable with an average period of 644 +/- 17 days and a peak-to-peak amplitude of two magnituds, so a large light-travel-time effect is seen at 1 min radius. An attempt is made to use the LTTE to reconcile the discrepancy between the observations of Fazio et al. and Lester et al. regarding the far-infrared source size. This discrepancy is reviewed in light of recent, high-spatial-resolution observations at 11 microns by Danchi et al. We conclude that IRC +10216 has been resolved on the arcminute scale by Fazio et al. Convolution of the model intensity profile at 61 microns with the 60 sec x 90 sec Gaussian beam of Fazio et al. yields an observed source size full width at half maximum (FWHM) that ranges from approximately 67 sec to 75 sec depending on the phase of the star and the assumed distance to the source. Using a simple r(exp -2) dust distribution and the 106 deg phase of the Fazio et al. observations, the LTTE model reaches a peak size of 74.3 sec at a distance of 300 pc. This agrees favorably with the 78 sec x 6 sec size measured by Fazio et al. Finally, a method is outlined for using the LTTE as a distance indicator to IRC +10216 and other stars with extended mass outflows.

Wright, Edward L.↗
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.↗
NASA NTRS1991

Far-Infrared Lines from G45.13 + 0.14 and K 3-50 A: Density Fluctuations in Compact H 2 Regions

The far-infrared lines of (O III) 51.8 and 88.4 microns, (N III) 57.3 microns, (S III) 33.5 microns, and (Ne III) 36.0 microns have been measured in the compact H II regions G45.13+0.14 A and K3-50 A. These measurements were made with the facility cooled grating spectrometer on flights of NASA's Kuiper Airborne Observatory. For both sources, the ratio of the two O(++) lines indicates an electron density N(sub e) approx. 10(exp 3)cm(sup -3). For K3-50 A, this is a factor of 10 to a hundred times lower than the density determined from near-infrared and optical line observations of lower excitation species and from radio measurements of the peak continuum emission. A comparison with other far-infrared measurements for both sources shows that the lower excitation, higher critical density S(++) lines originate from higher density material than do the O(++) lines. Detailed, spherically symmetric models for both sources are presented. These models require clumping, different abundances than the Orion Nebula, and an enhancement in the standard Kurucz stellar atmospheres at energies E greater than 41 eV to obtain reasonable agreement with the measurements. The average nitrogen-to-oxygen abundance ratio for these two H II regions is N/O approx. 0.2, in agreement with other far-infrared studies at Galactic radii greater than or equal to 6 kpc.

Colgan, Sean W. J.↗
NASA NTRS1974

High pressure far infrared spectroscopy of ionic solids

A high-pressure far-infrared cell operating at up to truly hydrostatic pressures of 8 kbar is described and used to determine the anharmonic self-energies associated with the transverse optic modes of ionic solids in which q approximately equals zero. The cell allows far-infrared studies in the spectral range below 120 reciprocal cm. The transverse optic modes were investigated to determine their mode Gruneisen constants and the pressure dependence of their inverse lifetimes in RbI, CsI, and TlCl.

Lowndes, R. P.↗
NASA NTRS1982

The far-infrared spectrum of the OH radical

It is thought likely that the study of spectral lines in the far-infrared might provide at least as much information about the physics and chemistry of the interstellar environment as radioastronomy. However, by comparison with the microwave region, the far-infrared is largely unexplored. There is a pressing need for good laboratory data to aid searches and assignments of spectra from the interstellar clouds and nebulae. Brown et al. (1981) have conducted a study of the laser magnetic resonance (LMR) spectrum of the OH radical in its ground state at far-infrared wavelengths. The present investigation is concerned with the computation of the frequencies of individual hyperfine transitions involving all rotational levels up to J = 4 1/2. The results of the calculation are presented in a table. The results are summarized in a diagram which shows the low-lying energy levels of OH. The frequencies of transitions between levels studied directly in the LMR spectrum are quite reliable.

Brown, J. M.↗
NASA NTRS1985

Far-infrared observations of young clusters embedded in the R Coronae Australis and Rho Ophiuchi dark clouds

Multicolor far-infrared maps in two nearby dark clouds, R Coronae Australis and Rho Ophiuchi, have been made in order to investigate the individual contribution of low-mass stars to the energetics and dynamics of the surrounding gas and dust. Emission from cool dust associated with five low-mass stars has been detected in CrA and four in Rho Oph; their far-infrared luminosities range from 2 solar luminosities to 40 solar luminosities. When an estimate of the bolometric luminosity was possible, it was found that typically more than 50 percent of the star's energy was radiated longward of 20 microns. Meaningful limits to the far-infrared luminosities of an additional 11 association members in CrA and two in Rho Oph were also obtained. The dust optical depth surrounding the star R CrA appears to be asymmetric and may control the dynamics of the surrounding molecular gas. The implications of these results for the cloud energetics and star formation efficiency in these two clouds are discussed.

Wilking, B. A.↗
NASA NTRS1990

Far-infrared emission from dusty ellipticals

The incidence of dust lanes in elliptical galaxies has been estimated at approx. 40 percent by Sadler and Gerhard (1985), although the observed fraction is lower because of inclination effects. A similar percentage of ellipticals has been detected by the Infrared Astronomy Satellite (IRAS) at 100 microns (Knapp et al. 1989); these have far-infrared colors expected for emission from cool dust (S sub 60 micron/S sub 100 micron approx. 1/3). For the far-infrared detected galaxies, neither L sub 100 microns/L sub B nor L sub 60 microns/L sub 100 microns are very dependent on dust content, suggesting that the source of the infrared luminosity is the same in both cases; and hence that dust is responsible even when not detected optically. Despite this indication, L sub 100 microns does not prove to be a good indicator of the quantity of cool interstellar matter in elliptical galaxies, as measured by the mass of neutral hydrogen. There even exist several examples of ellipticals with dust, strong 100 micron flux density and sensitive limits on HI mass (Walsh et al. in preparation). Chief reasons for the lack of correlation include the existence of other important sources of far-IR power in ellipticals, such as nonthermal continuum emission extending from longer wavelengths in flat spectrum radio sources (Golombek, Miley and Neugebauer 1988); and the fact that far-infrared luminosity per unit dust mass is extremely sensitive to the temperature of the ambient radiation field, which is not accurately known. In addition to having their appearance distorted by dust, several ellipticals also show such features as shells, box-shaped isophotes or inner disks. These may be signatures of past mergers, which could also add to the ISM content of the system.

Walsh, Duncan↗
NASA NTRS2004

Design of a Far-Infrared Spectrometer for Atmospheric Thermal Emission Measurements

Global measurements of far infrared emission from the upper troposphere are required to test models of cloud radiative forcing, water vapor continuum emission, and cooling rates. Spectra with adequate resolution can also be used for retrieving atmospheric temperature and humidity profiles, and yet there are few spectrally resolved measurements of outgoing longwave flux at wavelengths longer than 16 m. It has been difficult to make measurements in the far infrared due to the need for liquid-helium cooled detectors and large optics to achieve adequate sensitivity and bandwidth. We review design considerations for infrared Fourier transform spectrometers, including the dependence of system performance on basic system parameters, and discuss the prospects for achieving useful sensitivity from a satellite platform with a lightweight spectrometer using uncooled detectors.

Johnson, David G.↗
NASA NTRS1974

Far-infrared emission from H II regions. II - Multicolor photometry of selected sources and 2.2 min resolution maps of M42 and NGC 2024

Medium- and broad-bandwidth photometric measurements have been made of seven compact H II regions at wavelengths between 30 and 650 microns. The results are consistent with the hypothesis that the far-infrared flux is continuum radiation from dust grains. Color temperatures range from 33 to 85 K. For most of the sources, the infrared flux is low enough so that the dust could conceivably be mixed with the ionized gas. In at least one case, however, the far-infrared spectrum and luminosity of the source cannot be reconciled with reasonable grain models unless the far-infrared flux comes from a shell surrounding the H II region. M42 (Orion) and NGC 2024 (Orion B) have been mapped at 90 microns with a resolution (half-power beam diameter) of 2.2 min. Although the peak far-infrared brightness in M42 occurs at the position of the Kleinmann-Low infrared nebula, most of the flux originates in a more extended (about 6 x 8 min) source. The energy for the diffuse component could be supplied by the stars in the Trapezium cluster. However, the single early-type star visible in NGC 2024 is not luminous enough to account for either the infrared flux or the observed free-free flux.

Harper, D. A.↗
NASA NTRS2021

Far-infrared Imager and Polarimeter for the Origins Space Telescope

The far-infrared imager and polarimeter (FIP) for the Origins Space Telescope (Origins) is a basic far-infrared imager and polarimeter. The camera will deliver continuum images and polarization measurements at 50 and 250μm. Currently available detector technologies provide sufficient sensitivity for background limited observations from space, at least on a single pixel basis. FIP incorporates large next-generation superconducting detector arrays and our technology development plan will push the pixel numbers for the arrays to the required size of 8000. Two superconducting detector technologies are currently candidates for the instrument: transition edge sensors or microwave kinetic inductance devices. Using these detectors and taking advantage of the cryogenic telescope that is provided by Origins, FIP will achieve mapping speeds of up to eight orders of magnitude faster than what has been achieved by existing observatories. The science drivers for FIP include observations of solar system objects, dust properties, and magnetic field studies of the nearby interstellar medium, and large scale galaxy surveys to better constrain the star formation history of the universe to address one of the main themes of Origins: “How does the Universe work?” In addition to the science, the FIP instrument plays a critical functional role in aligning the mirrors during on orbit observatory commissioning.

Astronomy↗
NASA NTRS1994

Far-infrared emission from the bulges of early-type spirals: KAO observations of NGC 4736 (M94) and NGC 3627 (M66)

We present new high spatial resolution Kuiper Airborne Observatory (KAO) 50 and 100 micrometers measurements of the ringed Sab galaxy NGC 4736 and the Sb galaxy NGC 3627. We detect strong far-infrared emission (approximately 10(exp 9) solar luminosity) from the bulge areas of these galaxies, regions where there is little observed star formation. This far-infrared radiation is extended over the bulge with spatial distributions similar to that of the old stellar population. The ratio of far-infrared to H-alpha luminosity for these central sources is significantly larger than for the star-forming regions in these galaxies. This ratio is higher than can be accounted for by dust heating due to a population of young stars with a mass distribution similar to the Salpeter initial mass function assuming current estimates of extinction, unless the upper mass limit is unusually low (approximately B1 stars). On the other hand, the bolometric luminosity of the observed bulge stars is sufficient to account for the far-infrared radiation. Thus, older stars are likely to be important in heating dust in these bulges. The dust in the centers of these galaxies is quite warm, approximately 40 K (lambda(exp -1) emissivity), however, the interstellar radiation fields derived from the optical luminosities are consistent with these temperatures without invoking hidden central star formation or a dusty active galactic nucleus.

Smith, Beverly J.↗