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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Images of star-forming regions. II - The circumstellar environment of L1551 IRS 5

The circumstellar environment of L 1551 IRS 5 is investigated based on high-resolution 8000 A (i) and 9000 A (z) broadband CCD images. A small conical reflection nebula extending from a bright semistellar knot located near the cusp of the nebula is noted. It is suggested that the point-like structure at lambda of less than about 3.7 microns may represent a bright knot of dust-scattered light located on the inner surface of a flattened circumstellar disk surrounding the radio source. Evidence is found of sharp changes in the position angle of the jet emanating from IRS 5, possibly resulting from precession of the jet nozzle provided by a dense inner disk which has dynamically decoupled from the much larger flattened molecular structure.

Campbell, Bel↗
NASA NTRS1988

Vertical profiles of heating derived from IR-based precipitation estimates during FGGE SOP-1

This paper examines a technique for retrieving from geostationary IR data the vertical profiles of heating and cooling due to moist diabatic processes. First, GOES IR imagery is used to estimate precipitation fields which are independent of fields inferred from residuals in heat budget analysis based on the FGGE level III-b data. Vertical distributions of the associated heating are then obtained using thermodynamic data from the level III-b analysis, one-dimensional cloud models, and the satellite-estimated precipitation. The technique was applied to infer heating in the South Pacific convergence zone during a portion of FGEE SOP-1, and the results were compared with heat-budget calculations made using the ECMWF analyses.

Robertson, Franklin R.↗
NASA NTRS1988

Near-infrared imaging of Lynds 1551 IRS 5

High-spatial-resolution 1.6-micron (H) and 2.2-micron (K) images of the well-known young stellar object (YSO) L1551 IRS 5 reveal an extended, conically-shaped reflection nebula. The comparison of the images at the two wavelengths shows a shift in the position of the flux maximum, demonstrating that the H band maximum is not identical with the illuminating star. Morphological differences between the H band and K band images as well as a color map indicate that extinction effects in the reflection nebula are important. The results support a model that posits that, at H and K, the star in IRS 5 is surrounded by an optically thick disk and illuminates the inner wall of the nozzle created by the anisotropic mass outflow from the embedded young star.

Hodapp, Klaus-Werner↗
NASA NTRS1989

Nonlinear optical processes for the mid-IR region

The 2 - 5 micron (mid-IR) region is of interest for a number of applications. Efficient up-conversion and down-conversion techniques are being developed to obtain optical sources at mid-IR wavelengths. These techniques are reviewed and recent results using AgGaSe2 are reported. Gain in AgGaSe2 as high as 13 has been observed with a pump wavelength of 1.73 microns and a signal wavelength of 3.39 microns. Optical parametric oscillation in the 2.9 - 6.8 micron region has also been demonstrated.

Schepler, K. L.↗
NASA NTRS1990

IR detectors based on n-i-p-i superlattices

The principles of operation of n-i-p-i photodetectors are discussed. Special consideration is given to issues that are relevant to the performance of IR detectors such as noise, dark current, and surface effects. In addition, a novel IR detector that promises to provide information about the spectral distribution of the infrared radiation emitted from an object and, consequently, about its temperature, independent of the distance between detector and object is discussed. This detector makes use of the possibility to modulate the internal electric fields of an n-i-p-i superlattice with an applied voltage. By this technique the spectral responsivity of the detector may be controlled electrically and some information about the shape of the emission spectrum may be obtained.

Ruden, P. Paul↗
NASA NTRS1989

The relationship between IR, optical, and UV extinction

An analysis is presented for the variability of absolute IR, optical, and UV extinction, A(sub lambda), derived through the ratio of total-to-selective extinction, R, for 31 lines of sight for which reliable UV extinction parameters were derived. These data sample a wide range of environments and are characterized by 2.5 is less than or equal to R is less than or equal to 6.0. It was found that there is a strong linear dependence between extinction expressed as A(sub lambda)/A(sub V) and 1/R for 1.25 micron is less than or equal to lambda is less than or equal to 0.12 micron. Differences in the general shape of extinction curves are largely due to variations in shape of optical/near-UV extinction corresponding to changes in R, with A(sub lambda)/A(sub V) decreasing for increasing R. From a least-squares fit of the observed R-dependence as a function of wavelength for 0.8/micron is less than or greater than 1/lambda is less than or equal to 8.3/micron, an analytic expression was generated from which IR, optical, and UV extinction curves of the form A(sub lambda)/A(sub V) can be reproduced with reasonable accuracy from a knowledge of R. It was also found that the absolute bump strength normalized to A(sub V) shows a general decrease with increasing R, suggesting that some fraction of bump grains may be selectively incorporated into coagulated grains. Finally, it was found that absolute extinction normalized by suitably chosen color indices results in a minimization of the R-dependence of portions of the UV curve, allowing A(sub lambda) to be estimated for these wavelengths independent of R.

Cardelli, Jason A.↗
NASA NTRS1990

Study of mid IR fiber transmission and mode patterns under laser induced stimulated Brillouin scattering

Mid IR fiber transmission and exit radiation mode patterns at various incident CO2 laser power levels appear to be effective diagnostic tools for monitoring laser induced stimulated Brillouin scattering in various mid IR fibers. Such processes are deemed to be essential mechanisms for fiber-optic amplifiers and switches as potential replacements of current repeaters and bistable devices.

Yu, C.↗
NASA NTRS1991

Testing models of low-mass star formation - High-resolution far-infrared observations of L1551 IRS 5

A 50 and 100 micron wavelength study of L151 IRS 5 has yielded data consistent with the Adams et al. (1987) theoretical model prediction. It has proven possible to constrain a range of possible density gradients through source-emission modeling on the basis of the spherically-symmetric radiative transfer program of Egan et al. (1988) and a comparison of the observed scans at 50 and 100 microns. Attention is given to the effects of varying the dust grain properties of the spherical energy distribution of the source; the amount of mid-IR emission is highly sensitive to dust opacity and, because of poorly understood dust properties, is not a sensitive test for the presence of disks.

Butner, Harold M.↗
NASA NTRS1990

Influence of temperature gradients on the measurement accuracy of IR imaging systems

Implementing a new experimental aerodynamic technique, a long electrically heated wire was placed across flows with general velocity distributions (wakes, jets). By measuring the temperature distribution along the wire with an IR camera, the flow behavior was identified. Furthermore, it is suggested that by using Nusselt number correlations, the velocity distributions can be deduced. Comparing the results with predictions based on heat transfer correlations, it was found that the IR camera cannot accurately track high gradient temperature fields. A correction procedure is outlined to account for the errors found in the measured results.

Gartenberg, Ehud↗
NASA NTRS1991

Fine structure of the late Eocene Ir anomaly in marine sediments

The Late Eocene Ir abundance profile in deep sea cores from Ocean Drilling Program Leg 113 Hole 689B on the Maude Rise off of Antarctica was studied with 410 samples continuously in 10 cm increments and measured with the Iridium Coincidence (ICS). The ICS was subsequently modified to measure 13 other elements simultaneously with the Ir. The abundance profiles of these elements were then determined in the Late Eocene Massignano section in central Italy with 250 samples (encompassing roughly 2 million years of accumulation) which were collected about every 5 cm in about 2 cm increments. These studies augmented a previous one (which included many elements) of deep sea cores from Deep Sea Drilling Project Site 592 on the Lord Howe Rise in the Tasman Sea between Australia and New Zealand. In the latter study, 50 samples (encompassing roughly 0.7 million years of accumulation) were collected continuously in 10 cm increments. The results from these studies are discussed.

Asaro, F.↗
NASA NTRS1992

The molecular hydrogen emission around L1551 IRS 5 - Shock-heated molecular gas at the base of the molecular outflow

Spatially resolved observations of the v = 1-0 S(1) molecular hydrogen emission toward L1551 IRS 5 using the grating spectrometer at KPNO are presented. The S(1) emission consists of a ridge component extending toward west along the optical jet from its peak on IRS 5 and a diffuse component which traces the innermost region of the cavity enclosed by the molecular outflow. The ridge component represents shock-heated molecular gas at the root of the optical jet. The diffuse component is too bright to be of scattered origin; it most likely arises from shock-heated gas within the cavity and could represent an acceleration process of the molecular outflow.

Yamashita, Takuya↗
NASA NTRS1993

Near-IR imaging of moderate redshift galaxy clusters

We have obtained near-IR imaging of 3 moderate-z clusters on the 1.3 m at KPNO with SQIID, a new camera offering wide-field (5.5 arcmin) simultaneous JHK band imaging. Our photometry on a sample of approximately 100 likely member galaxies in one of the clusters, Abell 370 at z = 0.37, shows that we can obtain magnitudes good to 20 percent down to K = 18, considerably below the estimated K* = 16.5 at this redshift. These data indicate that there are no systematic problems in obtaining photometry at faint levels with SQIID. With the development of larger arrays, the field is open to progress. The resulting J, H, and K data for three clusters are combined with previously obtained multiband optical photometry. We present an investigation of the spectral properties and evolution of the dominant cold stellar populations by comparing optical-to-IR colors and color-magnitude diagrams to predictions from population synthesis models and galaxy spectral evolution codes.

Stanford, S. A.↗
NASA NTRS1993

Distant radio galaxies in the near IR

We are carrying out a program of near IR imaging and spectroscopy of radio galaxies with redshifts of 1.5 and greater. One of its principal goals is to constrain the ages and star formation histories of massive galaxies at early epochs. The radio galaxies are drawn from the survey of 1Jy class sources by McCarthy et al (1989) and McCarthy (1990). The sample contains 18 radio galaxies with redshifts greater than 2 and an additional 10 objects with 1.5 less than z less than 2.0. The redshifts were obtained from long slit spectra with the CTIO 4 m. While the galaxies are quite faint (r approximately = 21-24.5) all have Lyman alpha emission with rest frame equivalent widths of 100 - 1000 A. Multicolor photometry in the g,r,i and J,H,K bands has been obtained with the 2.5-m Du Pont Telescope on Las Campanas and with the Hale 5 m telescope at Palomar. We have recently obtained near IR spectra, using the 4 m telescopes at KPNO and CTIO, of a few objects with the goal of determining the Lyman alpha/H-alpha ratio and hence the reddening.

Mccarthy, P. J.↗
NASA NTRS1993

Ly alpha and IR galaxy companions of high redshift damped Ly alpha QSO absorbers

We have used a Near-Infrared Camera and Multi-Object Spectrometer (NICMOS3) HgCdTe 256x256 array detector with the Infrared (IR) camera on the 2.3m telescope at Steward Observatory to image several Quasi-Stellar Object (QSO) fields. The limiting magnitude is K'(2.1 microns) = 21.0 - 21.5 mag per square arcsec for a 3 sigma detection in 3 hours of in-field chopping observations. Each QSO line-of-sight samples several known absorbers with Mg2(lambda)2796-2803 A and/or C4(lambda)1548-1551 A absorption doublets. The equivalent width distributions of the low and high ionization absorption lines of the absorber sample are identical to those of the parent population of all absorbers. This selection process, used already for a spectroscopic survey of Mg2 absorption lines in C4-selected absorption systems at high z, gives a methodical approach to observing, reduces the observer biases, and makes a more efficient use of telescope time. This selection guarantees that imaging of the sample of QSO fields will provide complete sampling of the whole population of high z QSO absorbers. Follow-up optical and IR spectroscopy of these objects is scheduled for redshift measurement and confirmation of the absorbing galaxies and the cluster members.

Caulet, Adeline↗
NASA NTRS1992

Remote sensing of water vapor in the near IR from EOS/MODIS

Consideration is given to the selection of spectral channels in the near-infrared IR which are to be employed for the derivation of total column water vapor using the MODIS instrument on the NASA's Earth Observing System. Data obtained show that the three near-IR water vapor channels on the MODIS instrument enable remote sensing of the total column water vapor with an absolute accuracy of +/- 13 percent. An absolute accuracy of +/-7 percent can be obtained if additional MODIS channels are used to decrease the effect of uncertainty in the spectral reflectance of the surface, subpixel clouds, haze, and temperature profile on the derived water vapor.

Kaufman, Yoram J.↗
NASA NTRS1992

Ramgarh Crater, Rajasthan, India - Study of multispectral images obtained by Indian remote sensing satellite (IRS-IA)

Ramgarh Crater, Rajasthan, India is a potential impact crater that has not been studied so far. The proximity of Ramgarh Crater to the Deccan flood basalt terrain makes it important to examine the spatial and temporal relationship of this crater to Deccan Volcanism because recent studies propose a strong link between impact cratering and major flood basalt eruptions. A detailed multidisciplinary study is necessary to evaluate the structure and lithology of Ramgarh Crater and its temporal relationship to the emplacement of Deccan eruptions in India. Application of the IRS-IA data to study the lithologic/surface characteristics of Ramgarh Crater (attempted for the first time) indicates the potential application of remote sensing data in these studies. The IRS-IA data are of good quality and resolution. Our preliminary assessment has shown that these data are helpful in generating lithology soil vegetation profiles of Ramgarh Crater region. These 'profile maps' would be useful for targeting the specific areas in the region for a closer look and ground truth verification during the field work and sample collection in the region.

Murali, A. V.↗
NASA NTRS1993

Infrared images of Monoceros R2 IRS 3 - Evidence for a circumstellar disk

Diffraction-limited IR images of the protostellar system Mon R2 IRS 3 reveal a bright conical nebula which extends about 0.5 arcsec south from the southern component of the previously known star pair. The bright nebula is probably dust scattering the starlight which emerges along the polar axis of a large (greater than 500 AU) circumstellar disk. We estimate a lower limit to the disk mass of 3 X 10 exp -2 solar masses. A faint, previously unknown pointlike source lies 0.37 arcsec east of the northern star.

Koresko, C. D.↗
NASA NTRS1994

Near-IR diode laser absorption for measurement of tropospheric HO2

The possibility of using tunable lead salt diode lasers in the infrared for measurement of tropospheric HO2 has been frequently considered. Although the sensitivity of diode laser absorption has been improved through the use of high frequency detection techniques, nature has been unkind in that the HO2 absorption cross sections are weak. Even using the most optimistic assumptions about attainable path length and detectable absorbance, measurement of tropospheric HO2 by diode laser absorption in the mid-IR appears marginal. A possible alternative method for measuring HO2 is by absorption at near-infrared wavelengths. Several absorption bands of HO2 occur in the wavelength region between 1.2 and 1.6 micron due to electronic transitions and overtones of the fundamental vibrational modes. InGaAsP diode lasers operate in this wavelength region and can be used for high resolution spectroscopy in a manner analogous to the lead salt lasers. A diode laser system in the near-IR offers some advantages.

Stanton, Alan C.↗