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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Observations of the SiC2 radical toward IRC + 10216 at 1.27 centimeters

The first centimeter-wave transition of the recently identified SiC2 radical has been observed in the envelope of the evolved carbon star IRC + 10216. The excellent agreement between the measured astronomical rest frequency and the predicted frequency, and the measured line intensity support the SiC2 identification. The high-resolution line profile and mapping data are used to estimate the size of the IRC + 10216 SiC2 envelope and the abundance of SiC2 relative to H2.

Snyder, L. E.↗
NASA NTRS1986

Molecular ions in the circumstellar envelope of IRC + 10216

Assuming a steady and spherically symmetric mass loss, the spatial distribution of the ionization in a C-rich circumstellar envelope (CSE) is calculated, and it is shown that molecular ions dominate the ionization and chemistry of a large part of the CSE. Cosmic ray ionization of molecular hydrogen yields H3(+), and the photoionization of acetylene and neutral carbon yields C2H2(+) and C(+). In the system, the primary ions generate a series of heavier molecular ions by reactions with neutral molecules before being destroyed by dissociative recombination. The most promising candidate for mm-wavelength detection is found to be HCO(+), and IRC + 10216 antenna temperatures are calculated for different telescope sizes. Photoproduced C2H2(+), the most abundant intermediate distance CSE ion, may be responsible for the synthesis of various heavy hydrocarbon molecules at levels observed in IRC + 10216.

Glassgold, A. E.↗
NASA NTRS1986

The spatial structure of IRC + 10216 and NGC 7027 in the far-infrared

Spatial scans of IRC + 10216 and NGC 7027 were made at 50 and 100 microns using a diffraction-limited slit. Maximum entropy deconvolution techniques were applied to the data and, in effect, the structure of these sources was probed down to a scale far smaller than previously achieved at these wavelengths. IRC + 10216 was unresolved on a spatial scale of several arcsecs and a low upper limit to either the dust-gas ratio or the bulk emissivity of the grains was implied for the large molecular envelope surrounding the star. NGC 7027 was easily resolved in the scans, with far-infrared emission distribution corresponding closely with the distribution of ionized gas and shorter wavelength infrared emission.

Lester, D. F.↗
NASA NTRS1991

CN and HCN in the infrared spectrum of IRC + 10216

The abundance of HCN in the inner circumstellar shell of IRC + 10216 has been remeasured using the 12-micron nu2 band. The 12-micron lines are less saturated than HCN 3-micron lines previously detected in the spectrum of IRC + 10216. The observed 12-micron HCN line is formed in the circumstellar shell from about 4 to 12 R sub * in accord with a photospheric origin for HCN. The derived HCN abundance in the 4 to 12 R sub* region is 4 x 10 exp-5 and the column density is 7 x 10 exp 18/sq cm. The 5-micron CN vibration-rotation fundamental band was detected for the first time in an astronomical source. Using four CN lines, the CN column density was determined to be 2.6 x 10 exp 15/sq cm and the rotational temperature to be 8 +/-2 K. The peal radial abundance is 1 x 10 exp -5. The values for the temperature and abundance are in good agreement with microwave results and with the formation of CN from the photolysis of HCN.

Wiedemann, G. R.↗
NASA NTRS1993

The formation of cyanopolyyne molecules in IRC + 10216

Molecule formation in the outer envelope of the carbon-rich star IRC + 10216 is investigated, with special emphasis on the chemistry of the cyanopolyynes HC(i)N (i = 3, 5, 7). Basic elements of the photochemical model of Glassgold et al. (1986) are revised. A dust model suitable to IRC + 10216 is used for which the extinction properties in the far-UV are those of 500 A amorphous carbon particles. A new chemical route to the formation of large cyanopolyynes is proposed, based on reactions of the radicals C3N and C5N with acetylene, and shown to be efficient. Our results agree qualitatively with observations of the spatial distributions of HCN, CN, HC3N, and C3N, but the calculated column densities of the higher-order cyanopolyynes appear to be too small. The amount of the allenic radical HC2N produced by molecular ion reactions with atomic N agrees with recent observations.

Cherchneff, Isabelle↗
NASA NTRS1993

IRC +10420 - A cool hypergiant near the top of the H-R diagram

New observations were obtained for the OH/IR star IRC +10420, including optical/infrared imaging, spectroscopy, polarimetry, and photometry. The observations, which indicate a very rich and complex circumstellar environment for the star. A model for IRC +10420 star is proposed, in which a true core-burning supergiant is surrounded by a rotating equatorial disk of gas and dust that is viewed from about midway above the plate.

Jones, Terry J.↗
NASA NTRS1994

The particle-size distribution in the dust ejected from IRC +10216

We propose that in the outer envelope (more than 15 sec from the star) around IRC +10216 the grains are amorphous carbon spheres of radius a with a size distribution of the form n(a) approximately equals d(exp -3.5) exp (-a/a(sub 0)) and a(sub 0) approximately equals 0.10 micrometers. Small grains (a much less than a(sub 0)) are required to explain the shielding of circumstellar molecules against destruction by interstellar ultraviolet radiation. Larger grains (a much greater than a(sub 0)) are required to explain the observed circumstellar polarization at the K band. In this model approximately 0.1% of the mass in the ejected dust is contained in particles that are larger than 1 micrometer in diameter. If the size distribution of the ejected SiC particles is similar to the size distribution that we derive for the amorphous carbon grains, then at least some of the micron-sized SiC inclusions in meteorites thought to originate from mass-losing carbon stars may have been produced in the outflows from stars such as IRC +10216.

Jura, M.↗
NASA NTRS1995

Detection of MgCn in IRC + 10216: A new metal-bearing free radical

A new metal-containing molecule, MgCN, has been detected toward the late-type star IRC + 10216, using the NRAO 12 m and IRAM 30 m telescopes. The N = 11 approaches 10, 10 approaches 9, and 9 approaches 8 transtions of this species which has a (sup 2)Sigma(sup +) ground state, have been observed in the outer envelope of this object at 3 mm. For the N = 11 approaches 10 transitions, the two spin-rotation components are clearly resolved and conclusively identify this new radical. These measurements imply a column of density for MgCN of N(sub tot) approximately 10(exp 12)/sq cm in the outer shell, which corresponds to a fractional abundance of f approximately 7x10(exp -10). This molecule, the metastable isomer of MgNC, is the third metal-bearing species thus far identified in the outer shell of IRC + 10216, and its detection implies a ratio of MgNC/MgCN approximately 22/1. MgCN may be formed through a reaction scheme involving magnesium and HNC or CN, both prominent outer shell molecules, or through synthesis on grains.

Ziurys, L. M.↗
NASA NTRS1995

Physical structure of the IRC+10216 wind: Molecular sidereoarcheology

We present KAO observations of the CO J=9-8 and 12-11 lines in the C-star IRC+10216; these are the highest rotational transitions so far observed in any AGB star. A model is developed for the CO emission by IRC+10216 in all the observed CO rotational transitions.

Skinner, C. J.↗
DOE OSTI2020

Materials Data on IrC by Materials Project

IrC is Zincblende, Sphalerite structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Ir4+ is bonded to four equivalent C4- atoms to form corner-sharing IrC4 tetrahedra. All Ir–C bond lengths are 2.01 Å. C4- is bonded to four equivalent Ir4+ atoms to form corner-sharing CIr4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on IrC by Materials Project

IrC is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ir4+ is bonded to six equivalent C4- atoms to form a mixture of corner and edge-sharing IrC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ir–C bond lengths are 2.20 Å. C4- is bonded to six equivalent Ir4+ atoms to form a mixture of corner and edge-sharing CIr6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on IrC by Materials Project

IrC is Tungsten Carbide structured and crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Ir4+ is bonded to six equivalent C4- atoms to form a mixture of distorted face, edge, and corner-sharing IrC6 pentagonal pyramids. All Ir–C bond lengths are 2.21 Å. C4- is bonded to six equivalent Ir4+ atoms to form a mixture of distorted face, edge, and corner-sharing CIr6 pentagonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on IrC by Materials Project

IrC is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Ir4+ is bonded in a body-centered cubic geometry to eight equivalent C4- atoms. All Ir–C bond lengths are 2.36 Å. C4- is bonded in a body-centered cubic geometry to eight equivalent Ir4+ atoms.

36 MATERIALS SCIENCE↗
NASA NTRS1969

The unusual infrared object IRC plus 10216

Unusual IR object IRC plus 10216 interpreted as galactic source surrounded by optically thick dust shells, noting resemblance to black body energy distribution

Becklin, E. E.↗
NASA NTRS1972

Infrared diameter of IRC + 10216 determined from lunar occultations.

Lunar occultations of IRC + 10216 have been used to determine the size of the regions emitting 2.2-, 3.5-, 4.8-, and 10-micron radiation. The results are interpreted as the first direct measurement of the physical size of a dust shell surrounding a late-type star.

Toombs, R. I.↗
NASA NTRS1974

Detection of O-17 in IRC+10216

Lines of the fundamental vibration-rotation band of C-12 O-17 have been observed near 4.7 micron in IRC+10216. Lines of C-12 O-18 were not detected, indicating a lower limit of 5 for the abundance ratio O-17/O-18. A lower limit of 200 and a probable value of 400 is obtained for the ratio O-16/O-17. The presence of C-12 O-17 is also indicated in alpha Her and alpha Sco.

Rank, D. M.↗
NASA NTRS1974

Infrared observations of anonymous IRC sources

Infrared (0.9 to 18 microns) observations of 232 anonymous 2-micron Sky survey (IRC) sources are reported. Most of the objects appear to be late-type stars with little or no long-wave excess. About ten percent exhibit large excesses. Thirty-one of the brightest 11-micron sources have been remeasured to determine variability. These brighter objects appear to fall into two groups; one group resembles NML Tauri, while the other is like NML Cygni.

Strecker, D. W.↗