Search NASA⌕ Search

Engineering topics

Harwit, M.

Publications and source records attributed to Harwit, M..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

The Space Infrared Interferometric Telescope (SPIRIT): High-resolution Imaging and Spectroscopy in the Far-infrared

We report results of a recently-completed study of SPIRIT, a candidate NASA Origins Probe. SPIRIT is a spatial and spectral interferometer with an operating wavelength range 25 - 400 microns. SPIRIT will provide sub-arcsecond resolution images and spectra with resolution R = 3000 in a 1 arcmin field of view to accomplish three primary scientific objectives: (1) Learn how planetary systems form from protostellar disks, and how they acquire their chemical organization; (2) Characterize the family of extrasolar planetary systems by imaging the structure in debris disks to understand how and where planets form, and why some planets are ice giants and others are rocky; and (3) Learn how high-redshift galaxies formed and merged to form the present-day population of galaxies. Observations with SPIRIT will be complementary to those of the James Webb Space Telescope and the ground-based Atacama Large Millimeter Array. All three observatories could be operational contemporaneously. SPIRIT will pave the way to the 1 km maximum baseline interferometer known as the Submillimeter Probe of the Evolution of Cosmic Structure (SPECS). In addition to the SPIRIT mission concept, this talk will emphasize the importance of dense u-v plane coverage and describe some of the practical considerations associated with alternative interferometric baseline sampling schemes.

Leisawitz, D,↗
NASA NTRS2004

Probing the Invisible Universe: The Case for Far-IR/Submillimeter Interferometry

The question "How did we get here and what will the future bring?"captures the human imagination and the attention of the National Academy of Science's Astronomy and Astrophysics Survey Committee (AASC). Fulfillment of this fundamental goal requires astronomers to have sensitive, high angular and spectral resolution observations in the far-infrared/submillimeter (far- IR/sub-mm) spectral region. With half the luminosity of the universe and vital information about galaxy, star and planet formation, observations in this spectral region require capabilities similar to those currently available or planned at shorter wavelengths. In this paper we summarize the scientific motivation, some mission concepts and technology requirements for far-IR/sub-mm space interferometers that can be developed in the 2010-2020 timeframe.

Leisawitz, D.↗
NASA NTRS2003

Probing The Invisible Universe: The Case for Far-IR/Submillimeter Interferometry

The question "How did we get here and what will the future bring? captures the human imagination and the attention of the National Academy of Science s Astronomy and Astrophysics Survey Committee (AASC). Fulfillment of this fundamental goal requires astronomers to have sensitive, high angular and spectral resolution observations in the far-infrared submillimeter (far-IR-sub-mm) spectral region. With half the luminosity of the universe and vital information about galaxy, star and planet formation, observations in this spectral region require capabilities similar to those currently available or planned at shorter wavelengths. The scientific motivation, some mission concepts and technology requirements for far-IR-sub-mm space interferometers that can be developed in the 2010-2020 timeframe are summarized.

Leisawitz, D.↗
NASA NTRS1997

The Submillimeter Wave Astronomy Satellite: Science objectives and instrument description

The submillimeter wave astronomy satellite (SWAS) mission is dedicated to the investigation of star formation and interstellar chemistry. In order to perform the mission, SWAS will survey dense molecular clouds within the Milky Way Galaxy in either the ground state or a low-lying transition of five astrophysically-significant species: H2O, H2(18)O, O2, C I and (13)CO. The observation of these lines will: test theories that predict that these species are dominant coolants of molecular clouds during early stages of their collapse to form stars and planets, and supply information concerning the abundance of species central to the chemical models of dense interstellar gas. The SWAS will use two independent Schottky barrier diode mixers and a 53 x 68 sq cm, off-axis Cassegrain antenna.

Melnick, G. J.↗
NASA NTRS1989

Radio measurements in the fields of gamma-ray sources. III - The star formation region Rho-Ophiuchi

The star-forming region Rho-Ophiuchi, which has been detected as a COS-B gamma-ray source, 2CG 353+16, is observed in the radio continuum at wavelengths between 1.3 cm and 21 cm. Various known and new radio sources are identified. Time variability on scales of weeks to years for two sources can be assessed with high confidence levels. The H II region origin for Oph 1, Oph 6, Oph 9 and Oph 10 is ruled out. Five new radio sources are proposed as H II region candidates on the basis of their flat frequency spectrum.

Schlickeiser, R.↗
NASA NTRS1987

The most luminous far-infrared extragalactic sources

Extremely luminous far-infrared sources are difficult to explain as active sites of star formation, because their ratios of optical-to-infrared luminosities are extremely low. It is shown that brief intervals during which interacting galaxies collide can account for extremely high (more than 10 to the 11th) solar luminosities. The small fraction of the population that exhibits extreme luminosity also roughly equals the fraction of spiral galaxies expected to be observed undergoing collisions at any given time. A number of potential tests that would distinguish the model from others is proposed.

Harwit, M.↗
NASA NTRS1986

Far-infrared spectral studies from the G. P. Kuiper Airborne Observatory

The grant to carry out far-infrared spectral studies of astronomical sources from the G. P. Kuiper Airborne Observatory was first funded in October 1978 and officially ended on October 31, 1986. During these eight years, A variety of previously undetected spectral lines was discovered, and these were used to determine the physical and chemical conditions prevailing in regions of active star formation. They served to clarify the nature of the ionized hydrogen regions often adjacent to star-forming clouds, the characteristics of shocks which may signify the onset of star formation, and the nature of coolants that channel away energy thus enabling a cloud to collapse to form new stars.

Harwit, M.↗
NASA NTRS1986

Is IRAS cirrus cloud emission largely fine-structure radiation?

The contribution of line emission to the diffuse 'cirrus' radiation components observed by IRAS at 60 and 100 microns, respectively, is evaluated. The cirrus radiation was observed straddling the galactic plane to latitudes of + or - 80 degrees. Comparison of the observed brightness from cirrus clouds with forbidden line emission of O I and O III at 63 and 88 microns showed that the flux levels observed by IRAS are of the same order as the fine-structure line emission predicted by Stacey et al. (1985). It is argued that the fine-structure line emission from neutral gas at 63 microns as well as the line emission from diffuse ionized clouds at 88 microns, are significant components in most clouds, in some clouds they are the prime source of cirrus radiation.

Harwit, M.↗
NASA NTRS1986

The great observatories for space astrophysics

Motivated by the ancient urge to observe, measure, compute, and understand the nature of the Universe, the available advanced technology is used to place entire observatories into space for investigations across the spectrum. Stellar evolution, development and nature of the Universe, planetary exploration, technology, NASA's role, and careers in asronomy are displayed.

Harwit, M.↗
NASA NTRS1985

Observations of far-infrared transitions between excited states of OH

In observations of the Kleinmann-Low Nebula were detected of Orion 84.42 and 84.60 micron transitions between the P-2 sub 3/2 and Pi-2 sub 3/2 (J = 5/2) levels of OH with respective fluxes of 1.0 + or - 0.3 to the minus 17th power and 1.4 + or - 0.4 x 10 to the minus 17th power W cm/sq. When compared to 119 micron flux levels of OH and 153 micron flux levels of these radicals by Viscuso, these results suggest appreciable self-absorption of OH line radiation within the Nebula. It is probable that the CO emission due to the J = 31 yields 30 rotational transition at 84.411 micron makes a substantial contribution to the observed 84.42 micron flux, and that it also is at least partially absorbed at the 84.42 micron OH transition frequency. The 88.55 and 88.78 micron (J = 9/2 to 7/2) transitions of CH also were sought, but yielded only to upper limits of 3 x 10 to the minus 18th power W /sq cm each. A search of W3-IRS5 yields upper limits to the 84.42 micron OH and 87.19 micron CO (J = 30 to 29) transitions of 2 x 10 minus 18th power W cm/2.

Viscuso, P. J.↗
NASA NTRS1985

Submillimeter observations of OH and CH in M42

The 2Pi(1/2) J = 3/2 to 1/2 transitions of OH at 163.12 and 163.40 microns have been detected, and upper limits have been obtained for the 2Pi(3/2) J = 3/2 to 1/2 transitions of CH at 149.09 and 149.39 microns, in observations of the Kleinmann-Low nebula of Orion. The results indicate emission from a gas cloud at a temperature of roughly 1000 K, having thickness of roughly 5 x 10 to the 14th cm with density about 7 million/cu cm and OH abundance of roughly 12 x 10 to the -6th. The OH column density is about 4 x 10 to the 16th/cu cm in the emitting regions. Optical depth effects play a major role in determining the relative strengths of the observed lines.

Viscuso, P. J.↗
NASA NTRS1985

Observation of far-infrared transitions between excited states of OH

Spectra of the Kleinmann-Low nebula in Orion detected the 84.42 and 84.60 micron transitions between the 2Pi(3/2) J = 7/2 and 2Pi(3/2) J = 5/2 levels of OH with respective fluxes of 1 x 10 to the -17th and 1.4 x 10 to the -17th W/sq cm. When compared to the 119 micron flux levels of OH discussed by Watson (1982) and the 163 micron flux levels of OH by Viscuso et al. (1985), these results suggest appreciable self-absorption of OH line radiation within the nebula. The CO emission due to the J = 31 to 30 rotational transition at 84.411 microns makes a substantial contribution to the observed 84.22 micron flux, and is probably at least partially absorbed at the 84.42 micron OH transition frequency.

Viscuso, P. J.↗
NASA NTRS1985

Submillimeter observations of OH and CH in M42

The (sup 2) pi sub 1/2 (J = 3/2 to 1/2) transitions of OH at 163.12 and 163.40 micro m have been detected and upper limits have been obtained for the (sup 2) pi sub 3/2 (J = 3/2 to 1/2) transitions of CH at 149.09 and 149.39 micro m, in observations of the Kleinmann-Low Nebula of Orion. All four flux levels lie between 1 and 1.2 x 10 to the 17th power/sq.cm. The OH lines are bright when compared to the lower, (sup 2) pi sub 3/2 (J = 5/2 to 3/2) fluxes reported and imply that the 119 micro m emission observed is partially self-absorbed. The combined results provide strong constraints. Taken together with existing data on molecular hydrogen and CO and recent data on other OH transition, they suggest OH emission from post-shock regions at temperatures T approx 1000 k, densities approx. 7 x 10 to the 6th powr/cu cm N sub OH approx 80/cu cm optically thick for the (sup 2) pi sub 3/2 (J = 5/2 to 3/2), 119 micro m but only partially self-absorbing in the (J = 7/2 to 3/2), 84 micro m transitions over a Doppler velocity bandwidth of 30 km/sec. The OH column density is N sub OH approx 4 x 10 to the 16th powr/sq cm. in the emitting regions which occupy a fraction of approx 0.1 of a 1' x 1' field of view centered on the Becklin-Neugebauer source. The CO (J = 31 to 30), 84 micro m transition appears to lie sufficiently close to one of the 84 micro m OH line components to be partially absorbed as well, through a Bowen-type mechanism.

Viscuso, P. J.↗
NASA NTRS1984

Submillimeter astronomy and the problem of star formation

Sources that have traditionally been called 'protostars,' because they were strong emitters of infrared radiation embedded in dust clouds, are now recognized to be 'newly formed' stars instead. Recent developments in submillimeter astronomy should permit a redoubling of efforts to find bodies that are the actual predecessors of newly formed stars. This renewed search for true protostars will be aided by advances that have occurred in submillimeter spectroscopy; these will permit an analysis of the physical conditions and chemical constitution of cooler protostellar clouds, and may provide insight into circumstances favoring protostellar collapse.

Harwit, M.↗
NASA NTRS1984

The significance of far-infrared spectra of the interstellar medium

This paper deals with the analysis of interstellar clouds through infrared and submillimeter observations. The determination of temperature, density, state of ionization and abundance of different chemical constituents is discussed for clouds exhibiting a range of optical depths. There is a preferred choice of spectral features useful for examining different types of gaseous complexes. The prospects for improving the understanding of chemical reaction schemes in interstellar clouds are outlined. Prime advances may be expected in improved data on the abundance of atoms; diatomic hydrides; other small, hydrogen-containing molecules; and their ions.

Harwit, M.↗