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Harwit, Martin

Publications and source records attributed to Harwit, Martin.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Biosignatures and Planetary Properties to be Investigated by the TPF Mission

A major goal of Terrestrial Planet Finder (TPF) mission is to provide data to the biologists and atmospheric chemists who will be best able to evaluate the observations for evidence of life. This white paper reviews the benefits and challenges associated with remote spectroscopic observations of planets; it recommends wavelength ranges and spectral features; and it provides algorithms for detection of these features.

DesMarais, David J.↗
NASA NTRS2002

Extra-Solar Planetary Imager (ESPI) for Space Based Jovian Planetary Detection

We report on out Extra-Solar Planetary Imager (ESPI) study for a recent Midex (NASA Medium Class Explorer Mission) proposal. Proposed for ESPI was a 1.5 x 1.5 square meter Jacquinot apodized square aperture telescope. The combination of apodization and a square aperture telescope significantly reduces the diffracted light from a bright central source over much of the telescope focal plane. As a result, observations of very faint astronomical objects next to bright sources with angular separations as small as 0.32 arcseconds become possible. This permits a sensitive search for exo-planets in reflected light. The system is capable of detecting a Jupiter-like planet in a relatively long-period orbit around as many as 160 to 175 stars with a signal-to-noise ratio greater than 5 in observations lasting maximally 100 hours per star. We discuss the effects of wavefront error, mirror speckle, pointing error and signal-to-noise issues, as well as the scalability of our ESPI study with respect to NASA's Terrestrial Planet Finder mission.

Lyon, Rick G.↗
NASA NTRS2000

Implications of SWAS Observations for Interstellar Chemistry and Star Formation

A long standing prediction of steady state gas-phase chemical theory is that H2O and O2 are important reservoirs of elemental oxygen and major coolants of the interstellar medium. Analysis of SWAS observations has set sensitive upper limits on the abundance Of O2 and has provided H2O abundances toward a variety of star forming regions. Based on these results, we show that gaseous H2O and O2 are not dominant carriers of elemental oxygen in molecular clouds. Instead the available oxygen is presumably frozen on dust grains in the form of molecular ices, with a significant portion potentially remaining in atomic form, along with CO, in the gas phase. H2O and O2 are also not significant coolants for quiescent molecular gas. In the case of H2O, a number of known chemical processes can locally elevate its abundance in regions with enhanced temperatures, such as warm regions surrounding young stars or in hot shocked gas. Thus, water can be a locally important coolant. The new information provided by SWAS, when combined with recent results from the Infrared Space Observatory, also provide several hard observational constraints for theoretical models of the chemistry in molecular clouds and we discuss various models that satisfy these conditions.

Bergin, Edwin A.↗
NASA NTRS2000

An Analysis of Water Line Profiles in Star Formation Regions Observed by SWAS

We present spectral line profiles for the 557 GHz 1(sub 1,0) yields 1(sub 0,1) ground-state rotational transition of ortho-H2(16)O for 18 galactic star formation regions observed by SWAS. 2 Water is unambiguously detected in every source. The line profiles exhibit a wide variety of shapes, including single-peaked spectra and self-reversed profiles. We interpret these profiles using a Monte Carlo code to model the radiative transport. The observed variations in the line profiles can be explained by variations in the relative strengths of the bulk flow and small-scale turbulent motions within the clouds. Bulk flow (infall, outflow) must be present in some cloud cores, and in certain cases this bulk flow dominates the turbulent motions.

Ashby, Matthew L. N.↗
NASA NTRS1999

Infrared Space Observatory Observations of Far-Infrared Rotational Emission Lines of Water Vapor Toward the Supergiant Star VY Canis Majoris

We report the detection of numerous far-infrared emission lines of water vapor toward the supergiant star VY Canis Majoris. A 29.5-45 micron grating scan of VY CMa, obtained using the Short-Wavelength Spectrometer (SWS) of the Infrared Space Observatory at a spectral resolving power lambda/delat.lambda of approximately 2000, reveals at least 41 spectral features due to water vapor that together radiate a total luminosity of approximately 25 solar luminosity . In addition to pure rotational transitions within the ground vibrational state, these features include rotational transitions within the (010) excited vibrational state. The spectrum also shows the (sup 2)product(sub 1/2) (J = 5/2) left arrow (sup 2)product(sub 3/2) (J = 3/2) OH feature near 34.6 micron in absorption. Additional SWS observations of VY CMa were carried out in the instrument's Fabry-Perot mode for three water transitions: the 7(sub 25)-6(sub 16) line at 29.8367 micron, the 4(sub 41)-3(sub 12) line at 31.7721 micron, and the 4(sub 32)-3(sub 03) line at 40.6909 micron. The higher spectral resolving power lambda/delta.lambda of approximately 30,000 thereby obtained permits the line profiles to be resolved spectrally for the first time and reveals the "P Cygni" profiles that are characteristic of emission from an outflowing envelope.

Neufeld, David A.↗
NASA NTRS1998

Infrared Space Observatory Observations of Molecular Hydrogen in HH 54: Measurement of a Nonequilibrium Ratio of Ortho- to Para-H2

We have detected the S(1), S(2), S(3), S(4), and S(5) pure rotational lines of molecular hydrogen toward the outflow source HH 54 using the Short Wavelength Spectrometer on board the Infrared Space Observatory. The observed H2 line ratios indicate the presence of warm molecular gas with an H2 density of at least 10(sup 5) /cc and a temperature approximately 650 K in which the ratio of ortho- to para-H2 is only 1.2 -+ 0.4, significantly smaller than the equilibrium ratio of 3 expected in gas at that temperature. These observations imply that the measured ratio of ortho- to para-H2 is the legacy of an earlier stage in the thermal history of the gas when the gas had reached equilibrium at a temperature approximately 90 K. Based upon the expected timescale for equilibration, we argue that the nonequilibrium ratio of ortho- to para-H2 observed in HH 54 serves as a chronometer that places a conservative upper limit of approximately 5000 yr on the period for which the emitting gas has been warm. The S(2)/,S(l) and S(3)/S(1) H2 line ratios measured toward HH 54 are consistent with recent theoretical models of Timmermann for the conversion of para- to ortho-H2 behind slow, C-type shocks, but only if the preshock ratio of ortho- to para-H2 was approximately < 0.2.

Neufeld, David A.↗
NASA NTRS1998

Infrared Space Observatory Observations of Molecular Hydrogen in HH 54: Measurement of a Nonequilibrium Ratio of Ortho- to Para-H2

We have detected the S(1), S(2), S(3), S(4), and S(5) pure rotational lines of molecular hydrogen toward the outflow source HH 54 using the Short Wavelength Spectrometer on board the Infrared Space Observatory. The observed H2 line ratios indicate the presence of warm molecular gas with an H2 density of at least 10(exp 5) cm(exp -3) and a temperature approximately 650 K in which the ratio of ortho- to para-H2 is only 1.2 +/- 0.4, significantly smaller than the equilibrium ratio of 3 expected in gas at that temperature. These observations imply that the measured ratio of ortho- to para-H2 is the legacy of an earlier stage in the thermal history of the gas when the gas had reached equilibrium at a temperature approximately less than 90 K. Based upon the expected timescale for equilibration, we argue that the nonequilibrium ratio of ortho- to para-H2 observed in HH 54 serves as a chronometer that places a conservative upper limit of approximately 5000 yr on the period for which the emitting gas has been warm. The S(2)/S(1) and S(3)/S(1) H2 line ratios measured toward HH 54 are consistent with recent theoretical models of Timmermann for the conversion of para- to ortho-H2 behind slow, C-type shocks, but only if the preshock ratio of ortho- to para-H2 was approximately less than 0.2.

Neufeld, David A.↗
NASA NTRS1997

Review of the workshop

During the workshop, the importance of an interplay between observations, laboratory simulations, theoretical modeling, and instrument characterization was highlighted. The laboratory and theoretical fits to astronomical spectra are underlined. The importance of calibrations and of the observations performed by the Infrared Space Observatory (ISO) for the understanding of stars are stressed.

Harwit, Martin↗
NASA NTRS1994

Infrared astronomy from the Moon

The purpose of this paper is to exhibit the advantages and limitations to infrared astronomical observations form the moon. The most obvious apparent advantage is the lack of a lunar atmosphere; radiation arriving from the universe is neither extinguished nor refracted as it approaches the lunar surface. However, the Earth's atmosphere's protection against cosmic rays is also lost, and infrared detectors are highly sensitive to irradiation by energetic particles. A second apparent advantage is the relative ease with which beams from an array of telescopes can be interferometrically combined; again the vacuum environment with constant refractive index of unity throughout, permits combination without phase delay across the entire spectral range. But thermal radiation from optical components and stray radiation from the lunar environment, just outside the light path, tend to lessen that advantage, except in narrow-spectral-band spatial interferometry, in which only the radiation in individual spectral lines is mapped, and broad-band thermal emission can be effectively filtered out. On the Moon's night side, and in polar craters on the Moon, radiative cooling should permit the attainment of high sensitivity with large telescopes. Just as the proposed Edison spacecraft primary mirror is expected to reach temperatures around 40 K, so also large lunar primary mirrors might be expected to reach temperatures in that range, making the zodiacal glow the main source of noise at wavelengths shortward of 25 micrometers. The slow rota tion of the Moon, and the lack of vibrations from natural sources such as winds, should provide advantages in guiding on specific astronomical sources. To learn as much as possible about the difficulties of remote observations in a hostile environment, Antarctic observatories should be used as test beds for the rigors of lunar observations. The strenuous requirements for successful astronomical observations from the South Pole are similar to those expected to be encountered in observations conducted from the Moon.

Harwit, Martin↗
NASA NTRS1992

Cosmic curvature and condensation

It is shown that the universe may consist of a patchwork of domains with different Riemann curvature constants k = 0, +/-1. Features of a phase transition in which flat space breaks up in a transition 2k0 - k(-) + k(+) with initial scale factors R(-) = R(+) are postulated and explored. It is shown that such a transition is energetically permitted, has the equivalent of a Curie temperature, and can lead in a natural way to the formation of voids and galaxies. It is predicted that, if the ambient universe on average is well fitted by a purely k(-) space, with only occasional domains of k(+) containing galaxies, a density parameter of (A(z sub c + 1)) super -1 should be expected, where z sub c represents the redshift of the earliest objects to have condensed, and A takes on values ranging from about 5 to 3. Present observations of quasars would suggest a density of about 0.03 or 0.05, respectively, but it could be lower if earlier condensation took place.

Harwit, Martin↗
NASA NTRS1990

The submillimeter wave astronomy satellite

The Submillimeter Wave Astronomy Satellite (SWAS) selected for flight as part of the Small Explorer Program is described. SWAS consists of a 55 by 71 cm near optical quality off axis primary mirror, two heteorodyne radiometers with Schottky barrier diode mixers, and a single broadband (1.4 GHz) Acousto Optical Spectrometer (AOS). SWAS primary objective is to conduct a high spectral resolution survey of galactic molecular clouds in low lying transitions of water, molecular oxygen, atomic carbon and isotopic carbon monoxide. These species are crucial in gaining a better understanding of the chemistry and cooling of dense molecular clouds.

Melnick, Gary J.↗
NASA NTRS1989

What is the evidence on antigalaxies?

Recent observations show collisions or mergers among galaxies to be far more frequent than formerly anticipated. IRAS data have shown the most luminous FIR sources to involve such mergers. The luminosity of some of those mergers could be fueled by annihilation of matter and antimatter, and it is possible that this mechanism provides a way in which the existence of antigalaxies in the universe could become evident. If galaxy-antigalaxy collisions were prevalent among IRAS mergers, the 100-MeV gamma-ray flux from the most luminous merging galaxies would be roughly twice as high as the observed IR flux. Current data on a few of the brightest sources disqualify these as colliding galaxy-antigalaxy pairs. A systematic absence of gamma radiation from all ultraluminous IRAS sources would imply that antigalaxies must be rare or else located at extreme redshifts. In any case, galaxy-antigalaxy collisions cannot constitute a substantial fraction of all IRAS mergers, because their combined gamma flux would exceed the observed gamma-ray background.

Harwit, Martin↗
NASA NTRS1988

Extremely luminous far-infrared colliding galaxies - Computation of colliding-galaxy luminosity function

A computational model used to determine the luminosity function for gaseous galaxies in collision is described. It is based on the assumption of high-velocity encounters of two thin, gas-rich disks having identical radii and thickness, able to approach each other from arbitrary directions, with arbitrary orientations and with arbitrary degree of overlap. The distribution of expected luminosities generated in the dissipation of translational energy is then found to closely fit the observed distribution of luminosities of extremely luminous IRAS galaxies. Bursts of star formation resulting from such collisions would not have the correct luminosity function.

Harwit, Martin↗
NASA NTRS1988

The promise of astrophysical observation conducted from space

The roles of instrumentation and the Space Station in addressing the most important questions in astrophysics are considered. The growth in the power of astronomical instruments over the past several decades is reviewed. Progress that can be made in the coming decades in understanding the origin of the universe, in learning more about quasars, black holes, and the fundamental laws of physics, and in possibly detecting other planetary systems and extraterrestrial life is considered.

Harwit, Martin↗
NASA NTRS1987

Regularly pulsed neutrinos from supernova SN1987A?

Some consequences of the 8.9 millisecond periodicity observed in neutrino events from SN1987A with the Kamiokonde and IMB experiments are discussed. Interpreting the apparent period as a rotation of a compact object would imply that the neutrino emission is anisotropic and that the neutrino mass, averaged over all observed flavors, is less than 0.2 eV/c-squared. It is also noted that P = 8.9 ms is a reasonable period for very young pulsars.

Harwit, Martin↗
NASA NTRS1987

Extremely Luminous Far-infrared Sources (ELFS)

The Infrared Astronomical Satellite (IRAS) survey uncovered a class of Extremely Luminous Far Infrared Sources (ELFS), exhibiting luminosities up to and occasionally exceeding 10 to the 12th power L sub 0. Arguments are presented to show that sources with luminosities L equal to or greater than 3 x 10 to the 10th power L sub 0 may represent gas rich galaxies in collision. The more conventional explanation of these sources as sites of extremely active star formation fails to explain the observed low optical luminosities of ELFS as well as their high infrared excess. In contrast, a collisional model heats gas to a temperature of approx. 10 to the 6th power K where cooling takes place in the extreme ultraviolet. The UV is absorbed by dust and converted into far infrared radiation (FIR) without generation of appreciable optical luminosity. Gas recombination as it cools generates a Lyman alpha photon only once for every two extreme ultraviolet approx. 50eV photons emitted by the 10 to the 6th power gas. That accounts for the high infrared excess. Finally, the model also is able to explain the observed luminosity distribution of ELFS as well as many other traits.

Harwit, Martin↗
NASA NTRS1987

Hinge spectrometer - A grating Fabry-Perot instrument for far-infrared/submillimeter spectroscopy in space

A compact submillimeter spectrometer can be constructed through the use of a combination of grating and Fabry-Perot techniques. The instrument has only one moving part, a grating that pivots about an accurately placed hinge. The entire optical train is cooled to liquid helium temperature for low-background low-noise operation and is designed for use in astronomical observations from aircraft, balloons, or space vehicles. Resolving power R about 20,000 at about 150 microns is demonstrated.

Harwit, Martin↗