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At least 55 records · Page 3
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NASA NTRS1974

Angular diameter of IRC+10011 at 2.2, 10, and 20 microns

The extent of the long-period variable infrared-emitting object IRC+10011 has been measured at 2.2, 10, and 20 microns, taking advantage of two lunar occultation this object has recently undergone. At 10 and 20 microns, the bulk of the radiation is found to come from an optically thick dust region about 0.1 sec in diameter. At 2.2 microns, the dominant source of radiation is the central Mira star, but the inner part of the dust shell is also visible.

Zappala, R. R.↗
NASA NTRS1975

CO observations of the expanding envelope of IRC plus 10216

High-sensitivity emission profiles were observed for the transition of C12O16 and C13O16 towards IRC + or - 10216. It appears that the spherically symmetric uniform mass-outflow model proposed by Morris is necessary to describe the line profiles. The outflow appears to be slightly accelerated, having a velocity of 15 km/sec at the edges of the CO cloud, compared with 12 km/sec for the more centrally confined molecules.

Kuiper, T. B. H.↗
NASA NTRS1976

CO observations of the expanding envelope of IRC + 10216

The paper reports high-sensitivity observations of (C-12)O and (C-13)O in the infrared source IRC + 10216, which were made with the NRAO 11-m telescope at frequencies of 115.2712 and 110.2014 GHz, respectively. The emission-line profiles are found to be in good qualitative agreement with model profiles predicted for a spherically symmetric and uniformly expanding envelope. Analysis of the profile shapes indicates that the (C-12)O line is optically thick, while the (C-13)O line is both optically thin and double-peaked. It is shown that the shape of the (C-12)O line is determined largely by the motion of the gas and that the expansion velocity at the edges of the CO cloud is 15 km/s, in contrast to 12 km/s for more centrally confined molecules. Based on the estimated (C-13)O content, the envelope mass is estimated to be 0.5 solar mass.

Kuiper, T. B. H.↗
NASA NTRS1976

Far-infrared observations of IRC + 10216

Broadband photometric observations of IRC + 10216 in five wavelength intervals from 50 to 1000 microns are reported. The observed radiation is interpreted as thermal emission from dust in the extended molecular cloud heated by the compact 2-20-micron source at the cloud core. The shape of the 50-1000-micron spectrum suggests that the emissivity of the dust particles varies approximately as the inverse wavelength over this spectral interval. The mass of dust inferred from the far-infrared emission is comparable with the mass of heavy molecules in the cloud.

Campbell, M. P.↗
NASA NTRS1977

Far infrared observations of IRC + 10216

Results are reported for measurements of IRC + 10216 at 100 microns made with the 91-cm telescope of NASA's Kuiper Airborne Infrared Observatory. The IR photometer employed consisted of a gallium-doped germanium photoconductive detector with a MOSFET preamplifier and load resistor. Signals obtained from the source at modulation frequencies of 30 and 100 Hz are plotted, and the 100-micron flux measurements are shown to be in agreement with previous bolometric measurements. It is noted that the sensitivity of the photoconductive detection system is comparable to that of the conventional bolometers that have been used in airborne IR observations.

Shivanandan, K.↗
NASA NTRS1977

Theoretical study of the butadiynyl and cyanoethynyl radicals - Support for the identification of C3N in IRC + 10216

Quantum-mechanical calculations, using the matrix Hartree-Fock model, have been performed for the butadiynyl and cyanoethynyl radicals. A rotation constant of 4753 MHz is calculated for C4H, while for C3N the value 4955 MHz is obtained. These may be compared with the rotation constant of 4947.5 MHz derived from the recently observed doublets in the millimeter-wave spectrum of IRC + 10216, suggesting the cyanoethynyl radical as the carrier species of these lines. The electric dipole moment and hyperfine coupling constants of both species are predicted.

Wilson, S.↗
NASA NTRS1977

A high-resolution infrared spectrum of IRC +10216

The IR-emitting core and shell of IRC +10216 are investigated using a high-resolution spectrum covering the wavelength interval between 3 and 5 microns. Line identifications made or confirmed include those due to (C-12)(O-16), (C-13)(O-16), (C-12)(O-17), and (C-12)(O-18). A mean heliocentric velocity of about -32 km/s is obtained from the 42 least blended (C-12)O and (C-13)O lines, and the following isotopic abundance ratios are derived by comparing equivalent widths of the observed lines: C-12/C-13, C-12/C-14, O-16/O-17, and O-17/O-18. The structure of the expanding gas shell is examined, an explanation is offered for the lack of P Cygni profiles in the spectrum, and an unsuccessful search for other molecules is briefly discussed. It is concluded that a low C-12/C-13 ratio is not necessarily a signature of a carbon star.

Barnes, T. G.↗
NASA NTRS1978

NH3 in IRC plus 10216

Ammonia was detected in the circumstellar envelope of IRC +10216 by means of three infrared absorption lines in the nu sup 2 band around 950/cm. The lines are fully resolved at a resolution of 0.22 km/sec and indicate that most of the circumstellar gas is accelerated to expansion velocities around 14 km/sec within a few stellar radii. The NH3 profiles indicate a rotational temperature between 400 and 700 K, and H2 density between 10 to the 8th power/cu cm and 10 to the 10th power/cu cm, and NH3 column density of 10 to the 17th power/sq cm. The H2 density indicates that the mass of the circumstellar envelope within a 1 arcsec radius is approximately 0.1 solar masses.

Betz, A. L.↗
NASA NTRS1979

The brightness distribution of IRC +10216 at 11 microns

The brightness distribution of IRC +10216 at a wavelength of 11 microns was measured in detail using a spatial interferometer. This brightness distribution appears to have azimuthal symmetry; an upper limit of 1.1 may be set to the ellipticity at 11 microns if the object has a major axis oriented either along or perpendicular to the major axis of the optical image. The radial distribution shows both compact and extended emission. The extended component, which is due to thermal emission from circumstellar dust, contributes 91% of the total flux and has a 1/e diameter of 0.90 minutes. The tapered shape of this component is consistent with a l/r squared dust density dependence. The compact component is unresolved (less than 0.2 minutes in diameter) and represents emission from the central star seen through the circumstellar envelope.

Sutton, E. C.↗
NASA NTRS1979

NH3 in IRC +10216

Ammonia has been detected in the circumstellar envelope of IRC +10216 by means of three infrared absorption lines in the nu-2 band around 950 kaysers. The profiles are well resolved at a resolution of 0.22 km/s and show that most of the circumstellar gas is accelerated to expansion velocities around 14 km/s within a few stellar radii. The observed ammonia requires a rotational temperature between 400 and 700 K, an H2 density between 100 million and 10 billion per cu cm, and an NH3 column density of 10 to the 17th per sq cm. The H2 density indicates that the mass of the circumstellar envelope within a 1 arcsec radius is about 0.1 solar mass.

Betz, A. L.↗
NASA NTRS1979

The brightness distribution of IRC +10216 at 11 microns

The brightness distribution of IRC +10216 at a wavelength of 11 microns has been measured in detail by using spatial interferometer. This brightness distribution appears to have azimuthal symmetry; an upper limit of 1.1 may be set to the ellipticity at 11 microns if the object has a major axis oriented either along or perpendicular to the major axis of the optical image. The radial distribution shows both compact and extended emission. The extended component, which is due to thermal emission from circumstellar dust, contributes 91% of the total flux and has a 1/e diameter of 0.90 arcsec. The tapered shape of this component is consistent with a dust density dependence on the inverse square of radial distance. The compact component is unresolved (less than 0.2 arcsec in diameter) and represents emission from the central star seen through the circumstellar envelope.

Sutton, E. C.↗
NASA NTRS1979

Near-infrared observations of a new molecular feature in IRC + 10216

This letter presents a spectrum of IRC + 10216 in the 3000-4400-kayser region at 9-kayser resolution. A molecular feature at 3400-3600 kaysers has been detected which is attributed to an unspecified N-H bonded molecule; the feature appears to be variable in phase with the infrared light curve. Evidence is given for temperature variations of the emitting dust shell in phase with the infrared light curve. The results suggest that the variability of the molecular feature is due to reversible dissociation of the responsible molecule, which could occur at the higher temperatures accompanying the maxima of the light curve.

Krassner, J.↗
NASA NTRS1980

An optical emission-line phase of the extreme carbon star IRC +30219

Optical spectroscopic monitoring of the extreme carbon star IRC +30219 has revealed striking changes between 1977 and 1980. The stellar photosphere was barely visible in early 1979. There was an emission line spectrum consisting of H, forbidden O I, forbidden O II, forbidden N I, forbidden N II, forbidden S II, and He I. It is likely that these lines arose in a shocked region where recent stellar mass loss encountered the extensive circumstellar envelope. By late 1979, this emission-line spectrum had vanished, and the photosphere had reappeared. The weakening of the photospheric features in early 1979 was caused by increased attenuation of starlight and overlying thermal emission, both due to recently condensed hot dust grains.

Cohen, M.↗
NASA NTRS1981

Ethylene in IRC +10216

Ethylene has been detected in the circumstellar gas surrounding the supergiant star IRC +10216. Two lines of the nu sub 7 vibration-rotation band near 28 THz (949/cm) have been seen in absorption at an expansion velocity of 14 km/sec relative to the central star. The line intensities indicate a rotational temperature of T greater than 400 K and a radial C2H4 column density of 10 to the 16th to 10 to the 17th per sq cm.

Betz, A. L.↗
NASA NTRS1982

Observations of the 30 micron feature in IRC + 10216

Infrared observations from 30 to 37 microns of IRC+10216 extend the wavelength coverage of the 30-micron feature found in four carbon stars and two planetary nebulae by Forrest, Houck, and McCarthy (1981). The present data confirm the existence of this newly observed feature and determine its shape beyond 30 microns. The determination of the long-wavelength end of the spectral excess depends critically on the assumed underlying continuum. A combined spectrum of the excess is presented and shows the feature to extend to at least 37 microns.

Herter, T.↗
NASA NTRS1984

Silane in IRC +10216

Silane has been detected in the gas surrounding IRC +10216. Thirteen absorption lines in the nu-4 band around 917/cm were observed at 0.2 km/s resolution. A lower limit to the radial column density is 2 x 10 to the 15th/sq cm, and the relative strengths of the transitions indicate an average rotational temperature of 173 K.

Goldhaber, D. M.↗
NASA NTRS1985

Far-infrared spectrum of IRC + 10216

Far-infrared observations of IRC + 10216 in the wavelength range 20-160 microns are presented. The observations were performed simultaneously in four bands with effective wavelengths of 21, 42, 73, and 135 microns, respectively. The scan profile across the source at 21 microns is found to be wider than that for a point source. Interpreting the far-infrared spectrum on the basis of a model in which circumstellar grains are heated by a central source, the radial density dependence is r exp -2, and the emissivity dependence is lambda exp -n, it is found that n = 1-1.2. Time variations of a smaller magnitude at longer wavelengths as compared to the variation at near-infrared wavelengths can also be understood on the basis of this model. Using the mass-loss rate derived from CO observations, the mass absorption coefficient of the grains at 100 microns is found to be not less than 40/sq cm g.

Rengarajan, T. N.↗
NASA NTRS1985

The spectra of Orion A and IRC + 10216 between 72.2 and 91.1 GHz

Spectral scans of Orion A and the envelope of IRC + 10216, obtained with resolution 1 MHz over the complete range from 72.2 to 91.1 GHz using the radome-enclosed 20-m mm-wave telescope at Onsala Space Observatory during 1979-1982, are presented graphically (as main-beam brightness temperature in 500-MHz bands), providing the data basis is for the discussion of Johansson et al. (1984). Observing parameters include main-beam efficiency 0.58, aperture efficiency 0.44, FHPBW 47 arcsec, and total-system noise temperature 300-500 K.

Johansson, L. E. B.↗