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Mclaren, R. A.

Publications and source records attributed to Mclaren, R. A..

13 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

High spatial resolution 10 micron imaging of IRC + 10216

Precise high-resolution 10-micron images of the carbon star IRC + 10216 have been obtained with a scanned linear array. The low noise and high dynamic range of these images permit deconvolution of the telescope point-spread function, revealing the radial brightness distribution of the circumstellar dust shell: approximate reflection symmetry is found in west-east scans, with a distinct division into two components of diameter about 0.40 and 2.2 arcsec. It is shown that this morphology is consistent with published interferometric data that had cast doubt upon an earlier, idealized two-component model. The observed brightness distribution implies that the circumstellar dust density may deviate substantially from the 1/r squared radial dependence expected for spherically symmetric outflow with constant velocity and constant rate of mass loss.

Bloemhof, E. E.↗
NASA NTRS1980

Infrared observations of circumstellar ammonia in OH/IR supergiants

Ammonia has been detected in the circumstellar envelopes of VY Canis Majoris, VX Sagittarii, and IRC +10420 by means of several absorption lines in the nu-2 vibration-rotation band near 950 kaysers. The line profiles are well resolved (0.2 km/sec resolution) and show the gas being accelerated to terminal expansion velocities near 30 km/sec. The observations reveal a method for determining the position of the central star on VLBI maps of OH maser emission to an accuracy of approximately 0.2 arcsec. A firm lower limit of 2 x 10 to the 15th/sq cm is obtained for the NH3 column density in VY Canis Majoris.

Mclaren, R. A.↗
NASA NTRS1980

Infrared heterodyne spectroscopy of circumstellar molecules

Ammonia has been detected in the circumstellar envelopes of IRC+10216, VY CMa, VX Sgr, and IRC+10420. A number of absorption lines of (N-14)H3 in the nu sub 2 vibration-rotation band around 28 THz (950 per cm) have been observed at a velocity resolution of 0.2 km/s. Typical linewidths are 1 to 4 km/s, and the details of the line profiles provide additional insights on the process of mass loss in these stars.

Betz, A. L.↗
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 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 NTRS1978

Laser heterodyne spectroscopy

High-resolution heterodyne spectroscopic studies of the atmosphere of Venus are surveyed with attention to Doppler shifts in the 10-micron CO2 lines. While the C-12(O-16)2 emission lines formed in the mesosphere near 115 km indicate that the winds are distinctly subsolar to antisolar, C-13(O-16)2 absorption lines for the stratosphere at about 75 km confirm that the pattern is a strong retrograde rotation with an average equatorial velocity of 90 plus or minus 7 m/sec. It is concluded that the winds change from retrograde to subsolar-to-antipolar between 80 and 115 km.

Betz, A. L.↗
NASA NTRS1977

Infrared heterodyne spectroscopy of CO2 in the atmosphere of Mars

An infrared heterodyne spectrometer with a resolving power of 6 million has been used to obtain detailed profiles of the 10-micron absorption lines of CO2 in the atmosphere of Mars. An analysis of the results with an empirical model-atmosphere calculation indicates a nearly pure CO2 atmosphere with an average surface pressure of 5.2 + or - 0.5 mbar in the observed regions, a subsolar surface temperature near 275 K, an atmospheric temperature of 235 to 240 K above the subsolar point, and a lapse rate of 2 K/km.

Betz, A. L.↗
NASA NTRS1976

Heterodyne detection of CO2 emission lines and wind velocities in the atmosphere of Venus

Strong 10-micron line emission from (C-12)(O-16)2 in the upper atmosphere of Venus has been detected by heterodyne techniques. Observations of the absolute Doppler shift of the emission features indicated mean zonal wind velocities less than 10 m/s in the upper atmosphere near the equator. No evidence was found for the 100-m/s wind velocity implied by the apparent four-day rotation period of ultraviolet cloud features.

Betz, A. L.↗
NASA NTRS1976

Nonthermal 10 micron CO2 emission lines in the atmospheres of Mars and Venus

Mechanisms are examined for excitation of strong 10-micron CO2 emission lines seen on Mars and Venus. Line absorption of near-infrared solar flux directly by CO2 or H2O with collisional transfer of energy to CO2 are proposed as likely excitation mechanisms. Altitudes for peak 10-micron emission are estimated to be near 80 km for Mars and 120 km for Venus.

Johnson, M. A.↗
NASA NTRS1975

Heterodyne detection of CO2 emission lines and wind velocities in the atmosphere of Venus

Strong 10 micrometer line emission from (C-12)(O-16)2 in the upper atmosphere of Venus was detected by heterodyne techniques. Observations of the absolute Doppler shift of the emission features indicate mean zonal wind velocities less than 10 m/sec in the upper atmosphere near the equator. No evidence was found of the 100 m/sec wind velocity implied by the apparent 4-day rotation period of ultraviolet cloud features.

Betz, A. L.↗
NASA NTRS1975

Heterodyne detection of CO2 emission lines and wind velocities in the atmosphere of Venus

Strong 10 micrometer line emission from (c-12)(o-16)2 in the upper atmosphere of Venus was detected by heterodyne techniques. Observations of the absolute Doppler shift of the emission features indicate mean zonal wind velocities less than 10 m/sec in the upper atmosphere near the equator. No evidence was found of the 100 m/sec wind velocity implied by the apparent 4-day rotation period of ultraviolet cloud features.

Betz, A. L.↗