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At least 73 records · Page 4
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NASA NTRS2003

Kinematics of the SgrB2(N-LMH) Molecular Core

Ethyl cyanide (CH3CH2CN) emission and absorption have been imaged with the Very Large Array (VLA) toward SgrB2(N-LMH) by means of the 5(sub 15)-4(sub 14) rotational transition at 43.5 GHz (lambda approx. 7 mm). The 1.5" x 1.4" VLA beam shows two principal sources of ethyl cyanide emission: an unresolved source approx. 5" north of the LMH that is kinematically consistent with simple expansion, contraction, or small-scale turbulence, and the resolved LMH core source itself that shows kinematics indicating an edge-on rotating disk that extends 23" (approx. 0.1 pc) in the approximate east-west direction. A search for the 7(sub 07)-6(sub 06) rotational transition of the amino acid glycine (NH2CH2COOH) at 43.7 GHz toward SgrB2(N-LMH) gave negative results.

Hollis, J. M.↗
NASA NTRS1978

Observed and theoretical profiles of the Si II lines at lambda 1814

Emission line spectra observed at the limb of the solar disc are presented for transitions of singly ionized silicon at lambdas 1816.93, 1817.45 and 1808.01. The profiles show self-reversals in the line cores. A non-LTE analysis for a simplified model of the silicon ion is presented, and calculated line profiles are compared with the observations. The study indicates that some modification of the Vernazza et al. (1973) model of the solar chromosphere in the transition region is needed to reconcile the calculated and observed profiles.

Finn, G. D.↗
NASA NTRS1982

The interstellar carbon abundance toward Delta Scorpii

Observations are presented of a semiforbidden transition of C II at lambda 2325 toward Delta Scorpii. This line is intrinsically so weak that saturation and blending problems are completely absent, allowing the C II column density to be determined unambiguously. Furthermore, since C II is the dominant ionization state of carbon in H I regions, the total carbon abundance follows directly. While the detection of weak, semiforbidden interstellar lines requires high resolution and high photometric accuracy, observations of these lines promise substantial improvements concerning the knowledge of gas-phase abundances and, consequently, of the composition and structure of grains. The reported results represent the first direct evidence from absorption measurements that carbon is depleted from the interstellar gas by amounts sufficient to provide a substantial fraction of the mass of interstellar grains.

Hobbs, L. M.↗
NASA NTRS1997

The NO Vibrational Fundamental Band: O2-Broadening Coefficients

Rovibrational spectra of the vibrational fundamental of nitric oxide at 1875 cm-1 have been recorded under O2-broadening conditions at 296 K and 0.0056 cm-1 resolution using the Solar Nemeth FTS at the Kitt Peak National Observatory. The use of a flow system, which maintains the NO2 at trace levels, has enabled the first measurement of these broadening coefficients. The broadening of the trace contaminant, N2O, allowed checks of the measured pressures. The least-squares analysis of the spectra includes the nuclear hyperfine structure in addition to (lambda) doubling. We observed differential broadening between the e and f (lambda) components of 2II 1/2 transitions as well as larger differences in broadening observed between 2II3/2 transitions.

Freedman, R. S.↗
NASA NTRS1996

Far-Infrared Spectroscopy of Planetary Nebulae with the KAO

We present new far-infrared line observations of the planetary nebulae (PNs) NGC 7027, NGC 7009, and NGC 6210 obtained with the Kuiper Airborne Observatory (KAO). The bulk of our data are for NGC 7027 and NGC 7009, including [Ne(V)] 24 micrometers, [O(IV)] 26 micrometers, [O(III)] (52, 88) micrometers, and [N(III)] 57 micrometers. Our data for [O(III)] (52, 88) and [N(III)] 57 in NGC 7027 represent the first measurements of these lines in this source. The large [O(III)] 52/88-micrometer flux ratio implies an electron density (cubic cm) of log N(sub e)[O(III)] = 4.19, the largest Ne ever inferred from these lines. We derive N(++)/O(++) = 0.394 +/- 0.062 for NGC 7027 and 0.179 +/- 0.043 for NGC 6210. We are able to infer the O(+3)/O(++) ionic ratio from our data. As gauged by this ionic ratio, NGC 7027 is substantially higher ionization than is NGC 7009 - consistent with our observation that the former produces copious [Ne(V)] emission while the latter does not. These data help characterize the stellar ionizing radiation field. From our [O(IV)] and [O(III)] fluxes, we are able to show that O(++) is by far the dominant oxygen ion in NGC 7009. As a result, the O/H abundance inferred using these data tends to corroborate the value found from UV/optical, collisionally excited lines. We determined accurate rest wavelengths for the [Ne(V)] 2s(2)2p(2)P(sub 1) to 2s(2)2p(2)3P(sub 0) (lambda(sub rest) = 24.316 +/- 0.008 micrometers) and [O(IV)] 2s(2)2p(2)P(sup 0, sub 3/2) to 2s(2)2p(2)P(sup 0, sub 1/2) (lambda(sub rest) = 25.887 +/- 0.007 micrometers) transitions from observations of one or both of the bright PNs NGC 7027 and NGC 7009. Our [O(IV)] value, to the best of our knowledge, is the most accurate direct determination of this lambda(sub rest). These new KAO data will be beneficial for comparison with ISO observations of these PNs.

Rubin, Robert H.↗
NASA NTRS1985

Astronomical identification of the C3H radical

The C3H radical has been identified in the millimeter-wave spectra of IRC +10216 and TMC-1. In IRC +10216, four rotational transitions have been observed, three in the lower fine-structure ladder (2Pi1/2) and one in the upper (2Pi3/2), each a resolved or partially resolved lambda-doublet. In TMC-1, both lambda components of the lowest lying 3/2-1/2 transition of the 2Pi1/2 ladder have been observed, each with well-resolved hfs. In IRC +10216, the excitation of C3H is similar to that of SiCC: the rotational temperature Trot within the 2Pi1/2 ladder is low (8.5 K), because of rapid radiative decay, while Trot across the ladders is high (about 52 K), because interconnecting far-IR radiative transitions are only weakly permitted. The column density of C3H in IRC +10216 averaged over the estimated source diameter of 84 arcsec is 2.8 x 10 to the 13th/sq cm, an order of magnitude less than that of C2H and C4H.

Thaddeus, P.↗
NASA NTRS1980

Hybrid atmospheres and winds in supergiant stars

Ultraviolet spectra showing evidence for hybrid chromospheres and winds are found in the supergiant Alpha Aqr (G2 Ib) and Beta Aqr (G0 Ib). Characteristics of both solar-type transition regions and the cool chromospheric regions typical of later supergiants such as Lambda Vel (K5 Ib) are present. This suggests a gradual transition between activity and winds analogous to solar conditions and the cool, massive winds of luminous late-type stars.

Hartmann, L.↗
NASA NTRS1987

A study of the infrared emission from the O I (3d 3D0) and (4s 5S0) states produced by electron impact excitation of O2

The absolute emission cross section values for the O I(3p 3P-3d 3D0, lambda = 11,287 A) and the (3p 5P-4s 5S0, lambda = 11,299 A) multiplets excited by electron impact on O2 have been measured. These infrared oxygen emission features appear prominently in auroral spectra and were observed in electron bombardment of O2. The former cross section has a value of 3.05 x 10 to the -19th + or - 15 percent at 100 eV, while the latter's value is 4.14 x 10 to the -19th sq cm + or - 15 percent. The quintet emission at lambda = 11,299 A is the only deexcitation channel for the 4s 5S0 state and thus represents the total excitation cross section for that state. However, the lambda = 11,287 A branch from the O I (3d 3D0) state only constitutes about 25 percent of the total 3d 3D0 cross section, with the major branch from this state being the transition to the ground state observed at lambda = 1027 A. The branching ratio is in good agreement with the theoretical calculation of Padhan and Saraph (1977).

Erdman, P. W.↗
NASA NTRS1974

A search for microwave emission from CH in Comet Kohoutek /1973f/

A search was conducted for the three 9-cm transitions of the ground state Lambda-doublet of CH in comet Kohoutek, using the CSIRO 64-m radio telescope and the Onsala Space Observatory's 25.6-m telescope. No lines were detected during the observing periods, and upper limits are given for the corresponding antenna temperatures.

Rydbeck, O. E. H.↗
NASA NTRS1995

A reanalysis of the SWP-HI IUE observations of Capella

We have reanalyzed the numerous high-resolution, far-ultraviolet observations of Capella made by the International Ultraviolet Explorer (IUE) in its 16 yr lifetime. Our purpose was to search for long-term profile variations in Capella's ultraviolet emission lines and to complement the analysis of Goddard High Resolution Spectrograph (GHRS) observations of Capella, discussed in a companion paper (Linsky et al. 1995). We implemented a state-of-the-art photometric correction and spectral extraction procedure to improve S/N and control potential sources for systematic errors. Nevertheless, we were unable to find compelling evidence for any significant long-term profile variations. Previous work has shown that the G8 primary star is only a minor contributor to the high-excitation transition region lines but is a significant contributor to the low-excitation chromospheric lines. We have found exceptions to this rule, however. We find that the G8 star is responsible for a significant portion of Capella's N V lambda lambda 1239, 1243 emission, but is not a large contributor to the S I lambda 1296, Cl I lambda 1352, and O lambda 1356 lines. We suggest possible explanations for these behaviors. We also find evidence that the He II lambda 1640 emission from the G1 star is from the transition region, while the He II lambda 1640 emission from the G8 star is chromospheric, consistent with the findings of Linsky et al. (1994). The C II lambda 1336 line shows a weak central reversal. It is blueshifted by about 9 km/s with respect to the centroid of the emission from the G1 star. While the central reversal of the C II line is blueshifted by about 9 km/s with respect to the centroid of the emission from the G1 star. While the central reversal of the C II line is blueshifted, the central reversal of the Si III lambda 1207 line discussed by Linsky et al. (1994) is not.

Wood, Brian E.↗
NASA NTRS1990

Technical challenges involved in supporting the Lambda Point Experiment

The Lambda Point Experiment (LPE) is one of the instruments included in the U.S. Microgravity Payload Mission 1 planned for one of the Space Shuttle flights in 1992. The objective of the experiment is to measure the heat capacity of liquid helium within a narrow interval around the transition between superfluid and normal helium (the lambda point) with an unprecedented temperature resolution of about 10 to the -10th. Multiple technical challenges are presented in the areas of structural support, safety analysis, and modal frequency tests. This paper describes the technical challenges of JPL's multidisciplinary involvement in support of these experiments in microgravity.

Petrac, D.↗
NASA NTRS2004

Transient Three-Dimensional Analysis of Side Load in Liquid Rocket Engine Nozzles

Three-dimensional numerical investigations on the nozzle start-up side load physics were performed. The objective of this study is to identify the three-dimensional side load physics and to compute the associated aerodynamic side load using an anchored computational methodology. The computational methodology is based on an unstructured-grid, and pressure-based computational fluid dynamics formulation, and a simulated inlet condition based on a system calculation. Finite-rate chemistry was used throughout the study so that combustion effect is always included, and the effect of wall cooling on side load physics is studied. The side load physics captured include the afterburning wave, transition from free- shock to restricted-shock separation, and lip Lambda shock oscillation. With the adiabatic nozzle, free-shock separation reappears after the transition from free-shock separation to restricted-shock separation, and the subsequent flow pattern of the simultaneous free-shock and restricted-shock separations creates a very asymmetric Mach disk flow. With the cooled nozzle, the more symmetric restricted-shock separation persisted throughout the start-up transient after the transition, leading to an overall lower side load than that of the adiabatic nozzle. The tepee structures corresponding to the maximum side load were addressed.

Wang, Ten-See↗
NASA NTRS1990

VLA searches for formaldehyde and cyanoacetylene emission from comet P/Brorsen-Metcalf (1989o)

In Sep. 1989, Very Large Array (VLA) searches were conducted for both formaldehyde (H2CO) and cyanoacetylene (HC3N) emission from Comet P/Brorsen-Metcalf (1989o). In early July, this comet was outgassing strongly at a brighter than average preperihelion rate, and the hope was that it would continue to do so through perihelion. By observing the 1 sub 11 to 1 sub 10 transition of H2CO at 4,829.659 MHz (6 cm lambda) during the phase of maximum outgassing, it was expected that spectra would be collected with a high signal to noise ratio which would show the temporal behavior of formaldehyde relative to other molecules. During this same observation period, a search was also made for the J-1-0, F-2-1 rotational transition of cyanoacetylene at 9098.3321 MHz (3.3 cm lambda).

Snyder, Lewis E.↗
NASA NTRS2009

Exoplanetary Spin-Orbit Alignment: Results from the Ensemble of Rossiter-McLaughlin Measurements

One possible diagnostic of planet formation, orbital migration, and tidal evolution is the angle between a planet's orbital axis and the spin axis of its parent star. In general, Psi cannot be measured, but for transiting planets one can measure the angle lambda between the sky projections of the two axes via the Rossiter-McLaughlin effect. In this paper we showed how to combine measurements of lambda in different systems to derive statistical constraints on Psi, using a Bayesian analysis. The results provided evidence for two distinct modes of planet migration.

Fabrycky, Daniel C.↗
NASA NTRS1987

The lambda point experiment in microgravity

An experiment for performing high-resolution measurements of the heat capacity singularity at the lambda point of helium in microgravity conditions is described. By obtaining such measurements in space, it is expected that the intrinsic distortion of the transition would be reduced by at least two orders of magnitude, allowing the theory of cooperative phase transitions to be more effectively tested. Technology developments for the lambda point experiment include a new high-resolution thermometer, an advanced thermal control system, and a reusable flight-qualified superfluid helium dewar.

Lipa, J. A.↗
NASA NTRS2015

Primary Dendrite Arm Spacings in Al-7Si Alloy Directionally Solidified on the International Space Station

Samples from directionally solidified Al- 7 wt. % Si have been analyzed for primary dendrite arm spacing (lambda) and radial macrosegregation. The alloy was directionally solidified (DS) aboard the ISS to determine the effect of mitigating convection on lambda and macrosegregation. Samples from terrestrial DS-experiments thermal histories are discussed for comparison. In some experiments, lambda was measured in microstructures that developed during the transition from one speed to another. To represent DS in the presence of no convection, the Hunt-Lu model was used to represent diffusion controlled growth under steady-state conditions. By sectioning cross-sections throughout the entire length of a solidified sample, lambda was measured and calculated using the model. During steady-state, there was reasonable agreement between the measured and calculated lambda's in the space-grown samples. In terrestrial samples, the differences between measured and calculated lambda's indicated that the dendritic growth was influenced by convection.

Angart, Samuel↗
NASA NTRS1986

Vertical motions in the quiescent prominences observed in the He I Lambda10830Angstrom line

The observations contain two-dimensional spectral scans of a total of 17 different prominences on the solar disk from the period 3 to 9 May 1981, using the main spectrograph of the solar vacuum telescope at Sacramento Peak. The following conclusions may be drawn from the data: (1) Blue shifts are much more common than red shifts. In many cases more than 90 per cent of the projected prominence area is associated with blue shifts. (2) The darkest prominence regions show the largest blue shift (v less than 3 km s-1). (3) Red shifts are most commonly seen at prominence edges. (4) The general pattern of prominence velocity persists for several hours. On the scale of about 10 arcsec and less, changes are detectable in the course of 2 to 5 minutes. The observed predominance of the blue shifts is largely in agreement with earlier results from H alpha (cf. Martres et al. 1981). It cannot, however, be concluded definitely that the observed shift really represents a net flow of matter. The situation could possibly be analogous to that of the solar transition region where lines such as C IV lambda 1548 angstroms seem to indicate a net inflow, which can hardly be true, at velocities greater than 4 km s(-1) in the quiet Sun (Athay et al. 1983; Gurman and Athay 1983). If the typical structure element of the prominence is sub-resolution, i.e., 2 to 3 arcsec or worse, as in the present case, an apparent net shift could result if the ascending and the decending elements have different temperature and/or pressure. Different lines could then indicate different flow velocities and even opposite directions.

Engvold, Oddbjorn↗
NASA NTRS1993

Infrared coronal emission lines and the possibility of their maser emission in Seyfert nuclei

Energetic emitting regions have traditionally been studied via x-ray, UV and optical emission lines of highly ionized intermediate mass elements. Such lines are often referred to as 'coronal lines' since the ions, when produced by collisional ionization, reach maximum abundance at electron temperatures of approx. 10(exp 5) - 10(exp 6) K typical of the sun's upper atmosphere. However, optical and UV coronal lines are also observed in a wide variety of Galactic and extragalactic sources including the Galactic interstellar medium, nova shells, supernova remnants, galaxies and QSOs. Infrared coronal lines are providing a new window for observation of energetic emitting regions in heavily dust obscured sources such as infrared bright merging galaxies and Seyfert nuclei and new opportunities for model constraints on physical conditions in these sources. Unlike their UV and optical counterparts, infrared coronal lines can be primary coolants of collisionally ionized plasmas with 10(exp 4) less than T(sub e)(K) less than 10(exp 6) which produce little or no optical or shorter wavelength coronal line emission. In addition, they provide a means to probe heavily dust obscured emitting regions which are often inaccessible to optical or UV line studies. In this poster, we provide results from new model calculations to support upcoming Infrared Space Observatory (ISO) and current ground-based observing programs involving infrared coronal emission lines in AGN. We present a complete list of infrared (lambda greater than 1 micron) lines due to transitions within the ground configurations 2s(2)2p(k) and 3s(2)3p(k) (k = 1 to 5) or the first excited configurations 2s2p and 3s3p of highly ionized (x greater than or equal to 100 eV) astrophysically abundant (n(X)/n(H) greater than or equal to 10(exp -6)) elements. Included are approximately 74 lines in ions of O, Ne, Na, Mg, Al, Si, S, Ar, Ca, Fe, and Ni spanning a wavelength range of approximately 1 - 280 microns. We present new results from detailed balance calculations, new critical densities for collisional de-excitation, intrinsic photon rates, branching ratios, and excitation temperatures for the majority of the compiled transitions. The temperature and density parameter space for dominant cooling via infrared coronal lines is presented, and the relationship of infrared to optical coronal lines is discussed.

Greenhouse, Matthew A.↗