Engineering topics

Erickson, E. F.

Publications and source records attributed to Erickson, E. F..

At least 73 records · Page 4

NASA NTRS1978

The far-infrared spectrum of S140 IR

The spectrum of S140 IR from 65 to 345 kaysers (155-29 microns) has been measured with 9.4-kayser resolution. The emission in this spectral range is consistent with a 9-arcsec-diameter blackbody radiating at a temperature of 70 K. Attempts at finding a self-consistent radiative-transfer model of the source suggest that the near- and far-infrared observations cannot result from a spherically symmetric nebula with a continuous density distribution and a central exciting source. A number of compact near-infrared sources may be embedded in the cloud.

Tokunaga, A. T.↗

NASA NTRS1978

Far infrared spectrophotometry of Jupiter and Saturn

Infrared spectral measurements of Mars, Jupiter, and Saturn were obtained from 100 to 470 kaysers and, by taking Mars as a calibration source, brightness temperatures of Jupiter and Saturn were determined with approximately 5 kayser resolution. Internal luminosities were determined from the data and are reported to be approximately 8 times 10 to the minus tenth power of the sun's luminosity for Jupiter and approximately 3.6 times 10 to the minus tenth power of the sun's luminosity for Saturn. Comparison of data with spectra predicted by models suggests the need for an opacity source in addition to gaseous hydrogen and ammonia to help explain Jupiter's observed spectrum in the vicinity of 250 kaysers.

Erickson, E. F.↗

NASA NTRS1978

C3 and infrared spectrophotometry of Y Canum Venaticorum

The 1.2- to 5.6-micron spectrum of the carbon star Y CVn is presented and discussed. The observations were made from the Kuiper Airborne Observatory at an altitude of 12.5 km, thereby avoiding most of the absorption due to terrestrial water vapor. Comparison of Y CVn near 5 microns with laboratory spectra provides possible evidence for the presence of the linear triatomic molecule C3. For the first time in a carbon star the clearly formed band heads of the CN red system between 1.2 and 2.3 microns are observed. Corroborative evidence for the presence of the molecules HCN and C2H2 is presented, and the relative contributions of C3, HCN, and C2H2 to the 3.1-micron absorption band are discussed. Spectra of two other carbon stars, TX Psc and S Cep, are presented for comparison.

Goebel, J. H.↗

NASA NTRS1978

Engineering tests of the C-141 telescope

Data on image quality, chopper performance, and the closed-loop operation of the 91 cm telescope of the Kuiper Airborne Observatory which were obtained in September 1977 are presented.

Erickson, E. F.↗

NASA NTRS1978

Properties of the clouds of Venus, as inferred from airborne observations of its near-infrared reflectivity spectrum

The shape and absolute value of Venus' reflectivity spectrum is measured in the 1.2- to 4.0 micrometer spectral region with a circular variable filter wheel spectrometer having a spectral resolution of 1.5%. Comparing these spectra with synthetic spectra generated with a multiple-scattering computer code, a number of properties of the Venus clouds are inferred. Evidence is obtained indicating that the clouds are made of a water solution of sulfuric acid in their top unit optical depth, and that the clouds are made of this material down to an optical depth of at least 25. In addition, the acid concentration is 84 plus or minus 2% H2SO4 by weight in the top unit optical depth, the total optical depth of the clouds is 37.5 plus or minus 12.5, and the cross-sectional weighted mean particle radius lies between 0.5 and 1.4 micrometers in the top unit optical depth of the clouds. It is found that the average volume mixing ratio of H2SO4 and H2O contained in the cloud material both equal approximately 2 x 10 to the -6. Employing vapor pressure arguments, the acid concentration is shown to equal 84 plus or minus 6% at the cloud bottom and the water vapor mixing ratio beneath the clouds lies between 6 x 10 to the -4 and 10 to the -2.

Pollack, J. B.↗

NASA NTRS1978

Airborne infrared spectrophotometry of Mira variables

Airborne spectrophotometric observations of R Cas near minimum and maximum light, R Leo near minimum, and NML Tau near maximum are reported which were obtained over the wavelength range from 1.2 to 4 microns with 1.5% resolution. The spectral energy distributions of the three stars at the indicated times are presented, and it is shown that the H2O bands at 1.4, 1.9, and 2.7 microns are clearly evident in all the spectra, while the absorption bands of CO at about 1.6 and 2.3 microns are probably present although they are masked by the strong water vapor features. The results indicate that water vapor is the dominant opacity source in the atmospheres of Mira variables, that R Leo and NML Tau may be fitted well over the entire spectrum by respective single temperatures of 2250 and 1800 K, and that R Cas near both minimum and maximum cannot be adequately described by one temperature over the entire wavelength range investigated. The shapes and depths of the absorption bands are determined together with the apparent angular diameter of each star and the equivalent widths of the H2O + CO absorption bands. It is concluded that water vapor absorption is more strongly correlated with color temperature than with spectral type for R Cas and R Leo.

Strecker, D. W.↗

NASA NTRS1977

Observation of preplanetary disks around MWC 349 and LKH-alpha 101

Infrared spectra of three highly reddened emission-line objects (MWC 349, MWC 297, and LKH-alpha 101) have been obtained from both aircraft and ground-based observatories. These spectra show bright emission lines which are consistent with recombination in an H II region. Additional optical data for MWC 349 yield a model which consists of a central O6.5 star with circumstellar disk seen face-on, a surrounding H II region, and circumstellar dust. The parameters of the disk are discussed in terms of the viscous dissipation model of Lynden-Bell and Pringle (1974). The observations are in excellent agreement with the predictions of the model and represent the first substantial case for a newly formed star with a preplanetary disk.

Thompson, R. I.↗

NASA NTRS1977

The far-infrared spectrum of the core of Sagittarius B2

A Michelson interferometer aboard NASA's Kuiper Airborne Observatory has been used to measure the spectrum of Sgr B2 from 40 to 200 kaysers with 5-kayser resolution in a 1.4-arcmin beam. The measured spectrum is smooth and featureless with a broad maximum at about 85 kaysers. The data can be fitted analytically with a model corresponding to thermal emission by a uniform sla of dust filling the beam, with an average temperature of approximately 32 K, an optical depth at 100 microns of about 1.6, and a spectral index of the dust emissivity about 1.5. The absence of features implies either that the source is optically thick or that the emission spectrum of the individual grains is smooth in the passband. The possible physical significance of this model is discussed.

Erickson, E. F.↗

NASA NTRS1977

The brightness temperatures of Saturn and its rings at 39 microns

The relative rings-to-disk brightness (specific intensity) of Saturn at 39 microns was resolved using a 224-cm telescope, and the total flux of Saturn relative to Jupiter in the same bandpass was measured from the NASA Learjet Observatory. These two measurements, which were made with Saturn's rings near maximum inclination, determine the disk and average ring (A and B) brightness in terms of an absolute flux calibration of Jupiter in the same bandpass. While present uncertainties in Jupiter's absolute calibration make it impossible to compare existing measurements unambiguously, it is nevertheless possible to conclude the following: (1) observations between 20 and 40 microns are all compatible (within 2 sigmas) with a disk brightness temperature of 94 K and do not agree with the radiative equilibrium models of Trafton (1967); (2) the rings at large tilt contribute a flux component comparable to that of the planet itself for wavelengths not exceeding about 40 microns; and (3) there is a decrease of approximately 22% in the relative ring:disk brightness between effective wavelengths of 33.5 and 39 microns.

Nolt, I. G.↗

NASA NTRS1977

Spectrum of the Kleinmann-Low nebula from 29 to 125 micrometers

The infrared spectrum of the Kleinmann-Low nebula in M42 has been measured from 80 to 350 kaysers (approximately 29 to 125 microns) with a Michelson interferometer aboard the NASA Kuiper Airborne Observatory. The frequency spectrum peaks at about 185 kaysers. A simple model of the emission implies that the temperature is in the range 70-95 K and that the optical depth is at least 0.2 at the peak frequency. A possible absorption is seen at about 176 kaysers. Thermal emission by dust at a temperature of 71 K, with the absorption cross section proportional to frequency, provides a good fit to the data. Other thermal-emission models can also fit the spectrum. The data are compared with previous broad-band measurements. Upper limits are placed on expected line emission from the surrounding H II region at the position of the nebula.

Erickson, E. F.↗

NASA NTRS1977

An infrared foreoptics adaptor for the Learjet Telescope

A foreoptics adapter has been built for the Learjet telescope which permits simultaneous viewing of the visible star field in the image plane and acquisition of astronomical data at infrared wavelengths (less than 1 micrometer). The device uses an adjustable dichroic beamsplitter to transmit visible wavelengths to an eyepiece (or television camera), and to reflect infrared wavelengths to a port where an infrared detector system can be mounted. The instrument is intended as a multiple user facility for the Learjet telescope. This report describes the adapter and its use.

Erickson, E. F.↗

NASA NTRS1977

Analytical calculation of the areas of Saturn's disk and rings

The area of the visible disk, the area of the ansae (visible rings not overlapping the disk), and the area of overlap (visible rings overlapping the disk) were analytically determined to account for the thermal emission from the rings. These parameters were available in the ephemeris.

Matthews, S.↗

NASA NTRS1976

An investigation of the optimization of parameters affecting the implementation of fourier transform spectroscopy at 20-500 micron from the C-141 airborne infrared observatory

A program for 20-500 micron spectroscopy from the NASA flying C141 infrared observatory is being carried out with a Michelson interferometer. The parameters affecting the performance of the instrument are studied and an optimal configuration for high performance on the C-141 aircraft is recommended. As each parameter is discussed the relative merits of the two modes of mirror motion (rapid scan or step and integrate) are presented.

Thompson, R. I.↗

NASA NTRS1976

WINDOW: A computer program for planning astronomical observations

A FORTRAN computer program called WINDOW was written to simplify the planning of astronomical observations of a number of objects in a limited time. The program lists the azimuths at 15 minute intervals of up to 20 objects while they are in a given range of elevation angles - the window - and gives the elevation angle of each object at its time of transit. This work was motivated by the need to use observing time efficiently on flights of NASA-Ames' Lear Jet and C-141 observatories; WINDOW permits the investigator to prepare preliminary flight plans. However, the program is suited to planning ground-based observations as well. The program and a sample flight plan are described.

Erickson, E. F.↗

NASA NTRS1975

Water vapor absorption spectra of the upper atmosphere /45-185 per cm/

The far IR nighttime absorption spectrum of the earth's atmosphere above 14 km is determined from observations of the bright moon. The spectra were obtained using a Michelson interferometer attached to a 30-cm telescope aboard a high-altitude jet aircraft. Comparison with a single-layer model atmosphere implies a vertical column of 3.4 plus or minus 0.4 microns of precipitable water on 30 August 1971 and 2.4 plus or minus 0.3 microns of precipitable water on 6 January 1972.-

Augason, G. C.↗

NASA NTRS1975

A determination of the composition of the Venus clouds from aircraft observations in the near infrared

Summary of the evidence showing that the first optical depth of the Venus cloud layer is composed of a water solution of sulfuric acid, including earlier aircraft observations of Venus' reflectivity in the region from 1 to 4 microns obtained at a phase angle of 120 deg. Analyses of these aircraft results indicated that of all the proposed cloud candidates only a sulfuric acid solution with a concentration of 75% or more H2SO4 by weight was consistent with the observed 3-micron cloud feature. Aircraft observations of Venus are presented which were obtained in the same spectral region at a phase angle of 40 deg and in the region from 3 to 6 microns at a phase angle of 136 deg. Comparing the two sets of observations in the region from 1 to 4 microns, a striking phase effect is found: the reflectivity is much lower in the 3-micron region and there is a much more marked decline between 1.3 and 2.5 microns for the data obtained at the smaller phase angle. The observations made at the 40-deg phase angle are consistent with the theoretical behavior of a sulfuric acid cloud and imply that the sulfuric acid is present to at least many tens of optical depth below the cloud tops. Arguments concerning the concentration of the solution are reviewed, and it is concluded that the best current estimate is about 85% H2SO4 by weight.

Pollack, J. B.↗

NASA NTRS1975

Evaluation of image quality in a Cassegrain-type telescope with an oscillating secondary mirror

A ray-trace analysis is described of aberrations and extreme rays of a Cassegrain-type telescope with a tilted secondary mirror. The work was motivated by the need to understand the factors limiting image quality and to assist in the design of secondary mirrors for three telescopes with oscillating secondary mirrors (OSM) used at Ames Research Center for high altitude infrared astronomy. The telescopes are a 31-cm-diameter Dall-Kirkham (elliptical primary, spherical secondary) flown aboard a Lear jet, a 71-cm balloon-borne Dall-Kirkham flown on the AIROscope gondola, and a 91-cm true Cassegrain (parabolic primary, hyperbolic secondary) flown aboard a C-141 jet transport. The optics for these telescopes were not designed specifically for OSM operation, but all have OSM's and all must be used with various detector configurations; therefore, a facility that evaluates the performance of a telescope for a given configuration is useful. The analytical expressions are summarized and results for the above systems are discussed. Details of the calculation and a discussion of the computer program are given in the appendices.

Erickson, E. F.↗

NASA NTRS1974

Lear jet telescope system

The telescope system was designed as a multi-user facility for observations of celestial objects at infrared wavelengths, where ground-based observations are difficult or impossible due to the effects of telluric atmospheric absorption. The telescope is mounted in a Lear jet model 24B which typically permits 70 min. of observing per flight at altitudes in excess of 45,000 ft (13 km). Telescope system installation is discussed, along with appropriate setup and adjustment procedures. Operation of the guidance system is also explained, and checklists are provided which pertain to the recommended safe operating and in-flight trouble-shooting procedures for the equipment.

Erickson, E. F.↗