Engineering topics

Loewenstein, R. F.

Publications and source records attributed to Loewenstein, R. F..

At least 19 records

NASA NTRS1992

Dust and gas contributions to the energy output of SN 1987A on day 1153

SN 1987A spectra at 16-30 microns taken on days 1152 and 1154 after core collapse are presented. The observations are used to derive the mass of radiating Fe II in the ejecta, the mass and temperature of the dust that gives rise to the continuum emission, and the bolometric luminosity of the SN. The observed luminosity requires that the Co-57/Co-56 mass production rate be enhanced by a factor of (4.5 +/- 1.6) compared to its solar value, if 0.0001 solar mass of Ti-44 were produced in the ejecta.

Dwek, E.↗

NASA NTRS1990

Observations of 40-70 micron bands of ice in IRAS 09371 + 1212 and other stars

IRAS 09371 + 1212 is still an absolutely unique object. This M giant star, with circumstellar CO and a spectacular bipolar nebula, displays unique IRAS FIR colors which had been attributed to strong emission in the 40-70-micron bands of ice, as subsequently supported by the observation of a strong 3.1-micron absorption band. The results of the KAO observations have confirmed its unusual nature: the far-infrared bands of ice are by far the strongest known. Its dust temperature, 50 K or less, is by far the lowest known for a late-type circumstellar envelope.

Omont, A.↗

NASA NTRS1989

Far-infrared spectrophotometry of SN 1987A - Days 265 and 267

The paper presents 16-66-micron spectra of SN 1987A taken on days 266 and 268 after core collapse. The spectrum consists of a nearly flat continuum, strong emission lines of hydrogen, and fine-structure lines of Fe II, Fe III, Co II, S I, and possibly Fe I, Ni II, and S III. From the relative strength of three lines which arise from transitions within the ground and excited states of Fe II, the temperature and a lower limit on the density of the line-emitting region are derived. From the line strengths, the abundances of Fe and S I, the end products of explosive nucleosynthesis in the supernova are estimated. An upper limit is also set to the amount of Co II remaining in the mantle. The low measured mass of Fe suggests that the ejecta are clumpy. The flat continuum is most likely free-free emission from the expanding supernova ejecta. About 35 percent of this emission arises from the ionized metals in the mantle; the rest arises from ionized hydrogen. At the time of these observations, there is no evidence for any emission from dust that may have formed in the supernova ejecta or from preexisting dust in the surrounding medium.

Moseley, S. H.↗

NASA NTRS1989

Far-infrared observations of thermal dust emission from supernova 1987A

Observations of SN1987A in the spectral range 18-35 microns taken on November 16 and 23, 1988, 632 and 639 days after core collapse, are reported. A strong and rather flat continuum underlies weak fine-structure lines from heavy elements and declines slowly between 24 and 30 microns. The spectral shape indicates thermal emission from an almost featureless dust component, probably graphite, with silicates contributing less than 20 percent of the emitting dust mass. Some of the emission may be an 'echo' of supernova light reflected from a preexisting dust cloud, but a better explanation which can account for the entirety of emission from infrared to gamma wavelengths, is that dust is being formed in the supernova ejecta. This also accounts more naturally for the inferred dust composition.

Moseley, S. H.↗

NASA NTRS1988

Airborne 20-65 micron spectrophotometry of Comet Halley

Observations of Comet Halley with a grating spectrometer on board the Kuiper Airborne Observatory on four nights in Dec. 1985 to Apr. 1986 are reported. Low resolution 20 to 65 micrometer spectra of the nucleus with a 40 arcsec FWHM beam was obtained on 17 Dec. 1985, and on 15 and 17 Apr. 1986. On 20 Dec. 1985, only a 20 to 35 micrometer spectrum was obtained. Most of the data have been discussed in a paper where the continuum was dealt with. In that paper, models were fit to the continuum that showed that more micron sized particles of grain similar to amorphous carbon were needed to fit the spectrum than were allowed by the Vega SP-2 mass distribution, or that a fraction of the grains had to be made out of a material whose absorption efficiency fell steeper than lambda sup -1 for lambda greater than 20 micrometers. Spectra was also presented taken at several points on the coma on 15 Apr. which showed that the overall shape to the spectrum is the same in the coma. Tabulated values of the data and calibration curves are available. The spectral features are discussed.

Glaccum, William↗

NASA NTRS1987

Dust reradiation from M43

Far-IR and molecular observations of M43 and its neutral environment are presented. Dust particles mixed with plasma, atoms, and molecules of the observed region are found to produce the measured far-IR emissions. M43 and its neutral environment have a simple morphology, consisting primarily of a relatively dust-free H II region and its centrally located exciting star lying next to the dense concentration of neutral material known as the Orion Ridge. The exciting star, NU Ori, is an important source of excitation of the dust associated with M43. Dust mixed with gas lying along or outside the near circular boundary of M43 is important for the energy balance of the M43 region. The amount of far-IR reradiation observed from the central 1 arcmin of M43 is equivalent to only about one percent of the NU Ori luminosity. a fraction implying a small value for the normalized absorption optical depth. This may partly explain why extinction by dust appears to have little effect on the excitation of the M43 plasma.

Smith, J.↗

NASA NTRS1986

Airborne spectrophotometry of P/Halley from 20 to 65 microns

Simultaneous 20 to 65 microns spectrometry and 100 microns photometry of P/Halley obtained on board the Kuiper Airborne Observatory (KAO) in 1985 Dec. and 1986 April are discussed. Spectra with resolution 30 to 50 were obtained with the NASA/Goddard 24 channel grating spectrometer. Measurements were made on the nucleus as well as 5 points along and perpendicular to the Sun-tail direction. The observations reveal the absence of any strong spectral features. The color temperature of the dust varies over time scales as short as 2 days, but is higher than that expected for a rapidly rotating blackbody at the same distance from the Sun. The color temperature does not vary within 1 arcmin of the nucleus, but the coma is brighter on the sunward side than on the antisunward side.

Glaccum, W.↗

NASA NTRS1985

Far infrared and submillimeter brightness temperatures of the giant planets

The brightness temperatures of Jupiter, Saturn, Uranus, and Neptune in the range 35 to 1000 micron. The effective temperatures derived from the measurements, supplemented by shorter wavelength Voyager data for Jupiter and Saturn, are 126.8 + or - 4.5 K, 93.4 + or - 3.3 K, 58.3 + or - 2.0 K, and 60.3 + or - 2.0 K, respectively. The implications of the measurements for bolometric output and for atmospheric structure and composition are discussed. The temperature spectrum of Jupiter shows a strong peak at approx. 350 microns followed by a deep valley at approx. 450 to 500 microns. Spectra derived from model atmospheres qualitatively reproduced these features but do not fit the data closely.

Hildebrand, R. H.↗

NASA NTRS1985

Far-infrared and submillimeter brightness temperatures of the giant planets

The brightness temperatures of Jupiter, Saturn, Uranus, and Neptune were measured in the 35-1000 micron range with the 3-m NASA Infrared Telescope Facility (at wavelengths greater than 350 microns) and with the Kuiper Airborne Observatory (at wavelengths less than 350 microns). The data indicate the presence in Jupiter's spectrum of excess radiation (compared to theoretical models) at 300-400 microns. In addition, slightly less flux was observed from Saturn at 200 microns than predicted by atmospheric models, which suggests the possible presence of an unmodeled absorber. The submillimeter fluxes from Uranus and Neptune appear to be most consistent with low mixing ratios (less than 1 percent) of CH4 in their deep atmospheres.

Hildebrand, R. H.↗

NASA NTRS1985

Active star formation in NGC 2264

The region of NGC 2264 near the cone nebula is the site of active star formation in a rotating ring seen nearly edge on as a two lobed source. Allen's infrared source (IRS 1) surrounds a B3V star still embedded in the southern lobe of the cloud. The northern lobe, IRS 2, also probably contains young stars.

Schwartz, P. R.↗

NASA NTRS1984

Far Infrared and Submillimeter Observations of the Giant Planets

Far infrared measurements of the effective temperatures of Jupiter, Saturn, Uranus and Neptune were made. The measurements presented here cover the range from 35-1000 micrometers in relatively narrow bands. The observations at lambda 350 micrometers were made at the 3m NASA Infrared Telescope Facility (IRTF) of the Mauna Kea Observatory; those at lambda 350 micrometer were made on the Kuiper Airborne Observatory (KAO). All observations of Saturn were made when the ring inclination to Earth was 1.7 deg assuring an unambiguous measurement of the flux from the disk itself. Mars was used as the calibration reference. The results represent a consistent set of calibration standards. In these measurements, it is assumed that sub b(lambda = 350 micrometers) = T sub (lambda 350 micrometers). Measurements have been made of roughly 50% of the total flux emitted by Jupiter, 65% by Saturn, and 92% by Uranus and Neptune. These measurements therefore permit a considerable reduction in the uncertainties associated with the bolometric thermal outputs of the planets. The effective temperatures (T sub e) and the ratios of emitted to absorbed solar radiation were calculated.

Loewenstein, R. F.↗

NASA NTRS1984

The Orion Molecular Cloud at Far-infrared Wavelengths

A new, 34 in resolution far-infrared continuum map of Orion Molecular Cloud 1 and its environs, including M43 is presented. The source is dominated by a single, bright peak at the position of the embedded infrared cluster, with the 60 micro m flux density falling off steeply in all directions away from it. A total luminosity for IRc2 of 20,000 L(solar) is estimated, although this may be a lower limit, depending upon the transfer of radiation in the vicinity of the object. Several condensations appear in this map, which, along with radio molecular observations, support the view that significant fragmentation has taken place within the cloud.

Thronson, H. A., Jr.↗

NASA NTRS1984

Dust Reradiation from NGC 6946

Far infrared measurements of dust reradiation for the spiral galaxy NGC 6946 are presented. The measurements consist of maps and an energy distribution, all made with a resolution of 49 sec. Effective wavelengths are 120 and 170 microns for the maps and 60, 120, and 170 microns for the energy distribution. Much of the reradiating dust has a temperature of 20 K. The amount of starlight reradiated at far infrared wavelengths is approx. 6 x 10 to the 10th power L(solar) or about half the total amount of starlight produced by the nucleus and disk of NGC 6946. A bright nuclear peak centered on a 5' wide disk describes the reradiation morphology at 170 microns. The disk contributes approx. 90% of the total reradiation; the 49 sec diameter region centered on the nucleus gives the small remainder. The morphology of reradiated starlight is compared to the familiar starlight morphology observed at optical wavelengths.

Smith, J.↗

NASA NTRS1984

On the nature of the material surrounding Vega

Observations of Vega at 193 microns indicate that the far-infrared emission from the circumstellar material discovered by IRAS (Aumann et al. 1984) may decline more rapidly than a Planck spectrum at wavelengths greater than 100 microns. This suggests that the emitting particles may be smaller than the millimeter-sized objects proposed by Aumann et al. (1984). Small grains would be driven from the stellar system by radiation pressure, or their orbits would decay as a result of Poynting -Robertson drag. In order to maintain a state of dynamic equilibrium, a continuous supply of new particles would be required. It is hypothesized that the small grains are ejected by sublimation of volatile material from larger comet-like bodies in a partially coalesced preplanetary disk. A reservoir containing less than a few hundred earth masses could sustain the source over the lifetime of the star.

Harper, D. A.↗

NASA NTRS1984

Far-infrared selected star formation regions

Detailed far-IR observations and complementary submillimeter, 5 GHz continuum and C(O-18) observations of a sample of eight far-IR selected luminous regions of star formation are presented. The observations show that the sources of luminosity coincide with density peaks in the molecular clouds and that the exciting stars lie deep within these condensations. The far-IR sources have diversely shaped 40-180 micron spectra even though their 60-100 micron color temperatures are similar. The radio and far-IR results together show that the exciting stars are in clusters containing either zero-age main-sequence and pre-main-sequence stars or consisting entirely of pre-main-sequence objects. C(O-18) and submillimeter observations imply gas densities approximately 100,000-high enough to make T(dust) approximately T(gas).

Harper, D. A.↗

NASA NTRS1984

Far-IR selected star formation regions

Detailed far-IR observations and complemenary submillimeter, 5 GHz continuum and c(18)0 observations of a sample of far-IR selected luminous regions of star formation. The clouds and that the exciting stars lie deep within these condensations. The far-IR sources have diversely shaped 40 micron to 180 micron spectra even through their 60 micron to 100 micron color temperatures are similar. The radio and far-IR results together show that the exciting stars are in clusters containing either zero-age main sequence and pre-main sequence stars or consisting entirely of premain sequence objects. C(18)0 and submillimeter observations imply gas densities approximately .00005 - high enough to make t(sub dust) approximately t(sub gas).

Jaffe, D. T.↗

NASA NTRS1984

NGC 2024: Far-infrared and radio molecular observations

Far infrared continuum and millimeter wave molecular observations are presented for the infrared and radio source NGC 2024. The measurements are obtained at relatively high angular resolution, enabling a description of the source energetics and mass distribution in greater detail than previously reported. The object appears to be dominated by a dense ridge of material, extended in the north/south direction and centered on the dark lane that is seen in visual photographs. Maps of the source using the high density molecules CS and HCN confirm this picture and allow a description of the core structure and molecular abundances. The radio molecular and infrared observations support the idea that an important exciting star in NGC 2024 has yet to be identified and is centered on the dense ridge about 1' south of the bright mid infrared source IRS 2. The data presented here allows a presentation of a model for the source.

Thronson, H. A., Jr.↗

NASA NTRS1984

The energetics and mass structure of regions of star formation: S201

Theoretical predictions about dust and gas in star forming regions are tested by observing a 4 arcmin region surrounding the radio continuum source in 5201. The object was mapped in two far infrared wavelengths and found to show significant extended emission. Under the assumption that the molecular gas is heated solely via thermal coupling with the dust, the volume density was mapped in 5201. The ratios of infrared optical depth to CO column density were calculated for a number of positions in the source. Near the center of the cloud the values are found to be in good agreement with other determinations for regions with lower column density. In addition, the observations suggest significant molecular destruction in the outer parts of the object. Current models of gas heating were used to calculate a strong limit for the radius of the far infrared emitting grains, equal to or less than 0.15 micron. Grains of about this size are required by the observation of high temperature (T equal to or greater than 20 K) gas in many sources.

Thronson, H. A., Jr.↗