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Erickson, E. F.

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

At least 37 records · Page 2
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NASA NTRS1990

Shocked forbidden O I 63 micron line emission from the supernova remnant IC 443

Observations of the fine-structure emission from the forbidden O I 63 micron line in the SNR IC 443 are presented. It is shown that the emission correlates well with the distribution of line emission from shock-excited molecular hydrogen, which leads to the conclusion that the line is shock-excited. X-ray heating as well as UV-heating from a photodissociation region is ruled out as a possible excitation mechanism for the emission. It is shown that the forbidden O I 63 micron line is an important contributor to the total emission in the IRAS 60 micron band, estimated as approximately 40-75 percent of the total band flux. An attempt to shock model the line emission from IC 443 is made; however, to match the observational evidence, it has to be assumed that the shock is J-type, and that the oxygen chemistry is suppressed so that oxygen remains in atomic form and does not get converted into H2O. However, no theoretical rationale for these assumptions can be provided.

Burton, Michael G.↗
NASA NTRS1989

SOFIA: Stratospheric Observatory for Infrared Astronomy

SOFIA will be a three meter class telescope operating in a Boeing 747, offering astronomers routine access to infrared wavelengths unavailable from the ground, and with the means to observe transient astronomical events from anywhere in the world. The concept is based on 15 years of experience with NASA's Kuiper Airborne Observatory (KAO), which SOFIA will replace in the mid 1990's. SOFIA's wavelength range covers nearly four decades of the electromagnetic spectrum: from the visible, throughout the infrared and submillimeter, to the microwave region. Relative to the KAO, SOFIA will be roughly ten times more sensitive for compact sources, enabling observations of fainter objects and measurements at higher spectral resolution. Also, it will have three times the angular resolving power for wavelengths greater than 30 microns, permitting more detailed imaging at far infrared wavelengths.

Erickson, E. F.↗
NASA NTRS1988

Determination of N/O from far-infrared line observations of Galactic H II regions

Measurements of the 52- and 88-micron forbidden O III line ratios and the 57-micron forbidden N III line ratio for six H II regions have been obtained with the NASA Kuiper Airborne Observatory. The derived N/O ratio for most Galactic regions (of about 0.2-0.3) is greater than that obtained by optical studies, and it exceeds the solar value. Although enhancement of N/O at a galactocentric distance of about 6 kpc may be possible, no evidence is found for an overall linear gradient in N/O with galactocentric distance, suggesting that N-14 is predominantly produced by primary rather than secondary nucleosynthesis.

Rubin, R. H.↗
NASA NTRS1987

Far-infrared spectroscopy of star formation regions in M82

Emission lines of (O III) at 52 microns and 88 microns and of (N III) at 57 microns in the nucleus of the galaxy M82 have been observed from the Kuiper Airborne Observatory with the facility's cooled grating spectrometer. The (N III) line has not been previously detected in any extragalactic source. The fluxes in the lines indicate approx. 4 x 10 to the 7th power M of ionized gas and a large population of massive stars (equivalent to 5 x 10 to the 5th power 08.5 stars), sufficient to power the infrared luminosity of the nucleus. We use the 52 to 88 micron line intensity ratio to find an average electron density of 210 + or - 75 in the nucleus; this is 10 to 100 times lower than values typically observed in individual compact H II regions in our Galaxy. The relative line strengths of the (O III) and (N III) lines imply an N(++)/O(++) ratio of 0.45 + or - 0.1, significantly lower than is measured by the same method in individual H II regions at similar galactocentric distances (equal to or less than 400 pc) in our Galaxy. This lower N(++)/O(++) ratio may be due to a lower N/O ratio, higher stellar temperatures, or both, in M82. At spectral resolutions of approx. 90 km/s, all three line profiles are similarly asymmetric. They can be well fitted by two Gaussian distributions with widths of approx. 150 km/s and central velocities of approx. 110 and approx. 295 km/s, bracketing the systemic velocity of the nucleus of approx. 210 km/s. Within uncertainties, both the N(++)/O(++) ratio and the electron density are the same for both Gaussian components; this indicates no major large-scale gradient in either quantity within the nucleus.

Duffy, P. B.↗
NASA NTRS1986

The ionization structure of the Orion Nebula - Infrared line observations and models

Observations of the forbidden O III 52 and 88 microns lines and the forbidden N III 57 microns line have been made at six positions and the forbidden Ne III 36 microns line at four positions in the Orion Nebula to probe its ionization structure. The wavelength of the forbidden Ne III line was measured to be 36.009-36.017 microns. Electron densities and abundance ratios of N(++)/O(++) have been calculated and compared to other radio and optical observations. Detailed one-component and two-component (bar plus halo) spherical models were calculated for exciting stars with effective temperatures of 37,000-40,000 K and log g = 4.0 and 4.5. Both the new IR observations and the visible line measurements of oxygen and nitrogen require Teff of no more than 37,000 K. However, the doubly ionized neon requires a model with Teff of at least 39,000 K, which is more consistent with that inferred from the radio flux or spectral type. These differences in Teff are not due to effects of dust on the stellar radiation field but are probably due to inaccuracies in the assumed stellar spectrum. Neon and nitrogen are approximately solar, but oxygen is half-solar in abundance. From the IR O(++) lines, it is concluded that the ionization bar results from an increase in column depth rather than from a local density enhancement.

Simpson, J. P.↗
NASA NTRS1986

The ionization structure of the Orion nebula: Infrared line observations and models

Observations of the (O III) 52 and 88 micron lines and the (N III) 57 micron line have been made at 6 positions and the (Ne III) 36 micron line at 4 positions in the Orion Nebula to probe its ionization structure. The measurements, made with a -40" diameter beam, were spaced every 45" in a line south from and including the Trapezium. The wavelength of the (Ne III) line was measured to be 36.013 + or - 0.004 micron. Electron densities and abundance ratios of N(++)/O(++) have been calculated and compared to other radio and optical observations. Detailed one component and two component (bar plus halo) spherical models were calculated for exciting stars with effective temperatures of 37 to 40,000K and log g = 4.0 and 4.5. Both the new infrared observations and the visible line measurements of oxygen and nitrogen require T sub eff approx less than 37,000K. However, the double ionized neon requires a model with T sub eff more than or equal to 39,000K, which is more consistent with that inferred from the radio flux or spectral type. These differences in T sub eff are not due to effects of dust on the stellar radiation field, but are probably due to inaccuracies in the assumed stellar spectrum. The observed N(++)/O(++) ratio is almost twice the N(+)/O(+) ratio. The best fit models give N/H = 8.4 x 10 to the -5 power, O/H = 4.0 x 10 to the -4 power, and Ne/H = 1.3 x 10 to the -4 power. Thus neon and nitrogen are approximately solar, but oxygen is half solar in abundance. From the infrared O(++) lines it is concluded that the ionization bar results from an increase in column depth rather than from a local density enhancement.

Simpson, J. P.↗
NASA NTRS1986

Far infrared spectroscopy of star formation regions in M82

Emission lines of (O III) at 52 microns and 88 microns and of (N III) at 57 microns in the nucleus of the galaxy M82 have been observed from the Kuiper Airborne Observatory with the facility's cooled grating spectrometer. The (N III) line has not been previously detected in any extragalactic source. The fluxes in the lines indicate approx 4 x 10 to the 7th power M of ionized gas and a large population of massive stars (equivalent to 5 x 10 to the 5th power 08.5 stars), sufficient to power the infrared luminosity of the nucleus. We use the 52 to 88 micron line intensity ratio to find an average electron density of 210 + or 75 in the nucleus; this is 10 to 100 times lower than values typically observed in individual compact HII regions in our Galaxy. The relative line strengths of the (O III) and (N III) lines imply an N(++)/O(++) ratio of 0.45 + or - 0.1, significantly lower than is measured by the same method in individual HII regions at similar galactocentric distances (equal to or less than 400 pc) in our Galaxy. This lower N(++)/O(++) ratio may be due to a lower N/O ratio, higher stellar temperatures, or both, in M82. At spectral resolutions of approx. 90 km/s, all three line profiles are similarly asymmetric. They can be well fitted by two Gaussian distributions with widths of approx. 150 km/s and central velocities of approx. 110 and approx. 295 km/s, bracketing the systemic velocity of the nucleus of approx. 210 km/s. Within uncertainties, both the N(++)/O(++) ratio and the electron density are the same for both Gaussian components; this indicates no major large-scale gradient in either quantity within the nucleus.

Duffy, P. B.↗
NASA NTRS1986

Detection of (Si II) (34.8 micron) emission in Orion-KL - A measurement of the silicon abundance in dense interstellar gas

The first detection of the ground state fine structure transition of Si+ at a rest wavelength determined to be 34.815 + or - 0.004 micron are reported. These observations were obtained with the facility spectrometer on NASA's Kuiper Airborne Observatory. A 6' NW-SE strip scan across the Orion-KL region shows Si II emission from both the extended photodissociation region surrounding theta 1 Ori C and from the shocked gas NW of BN-KL. The inferred gas-phase silicon elemental abundance relative to hydrogen in the dense 10 to the 5/cc primarily neutral photodissociation region is approximately 2.6 x 10 the -6, a factor of 0.075 times the solar value and 3.4 times greater than the abundance in the moderate density aprox. 10 to the 3/cc cloud toward Zeta Oph The silicon abundance in the shocked gas is approximately solar, indicating that any pre-existing grains have been destroyed in the shock wave or that the preshock gas carries a near solar abundance of gas phase silicon. The shock-excited Si II (34.8 micron) emission may arise from shocked wind material in the outflow around IRc2, with wind velocities approx. 100 km/s.

Haas, M. R.↗
NASA NTRS1986

Observations of the J = 10 manifold of the pure rotational band of phosphine on Saturn

Saturn was observed in the vicinity of the J = 10 manifold of the pure rotational band of phosphine on 1984 July 10 and 12 from NASA's Kuiper Airborne Observatory with the facility far-infrared cooled grating spectrometer. On each night observations of the full disk plus rings were made at 4 to 6 discrete wavelengths which selectively sampled the manifold and the adjacent continuum. The previously reported detection of this manifold is confirmed. After subtraction of the flux due to the rings, the data are compared with disk-averaged models of Saturn. It is found that PH3 must be strongly depleted above the thermal inversion (approx. 70 mbar). The best fitting models consistent with other observational constaints indicate that PH3 is significantly depleted at even deeper atmospheric levels ( or = 500 mbar), implying an eddy diffusion coefficient for Saturn of 10 to the 4 cm sq/sec.

Haas, M. R.↗
NASA NTRS1985

The 1983 June 15 occultation by Neptune. I - Limits on a possible ring system

Observations on 15 June 1983 of an occultation of a star by Neptune from Mauna Kea, Mount Stromlo, Siding Spring, and the Kuiper Airborne Observatory show no evidence for equatorial rings between 25,300 and 200,000 km (R/N/ = 25,269 km). Within most of this region, the upper limit on the optical depth along the line of sight, for rings broader than 6 km , is 0.04, which corresponds to a normal optical depth of 0.016. These results rule out a Neptunian ring system similar to that of Saturn or Uranus, but not a system of low optical depth similar to the Jovian rings. The data show no features that appear likely to have been caused by material in the equatorial plane of Neptune near the Roche limit.

Elliot, J. L.↗
NASA NTRS1985

Observations of the J = 10 manifold of the pure rotational band of phosphine on Saturn

Saturn was observed in the vicinity of the J = 10 manifold of the pure rotational band of phosphine on 1984 July 10 and 12 from NASA's Kuiper Airborne Observatory with the facility far-infrared cooled grating spectrometer. On each night observations of the full disk plus rings were made at 4 to 6 discrete wavelengths which selectively sampled the manifold and the adjacent continuum. The previously reported detection of this manifold is confirmed. After subtraction of the flux due to the rings, the data are compared with disk-averaged models of Saturn. It is found that PH3 must be strongly depleted above the thermal inversion (approx. 70 mbar). The best fitting models consistent with other observational constraints indicate that PH3 is significantly depleted at even deeper atmospheric levels (or = 500 mbar), implying an eddy diffusion coefficient for Saturn of 10 to the 4 cm sq/sec.

Haas, M. R.↗
NASA NTRS1985

Detection of [SiLL] (34.8 micron) emission in Orion-KL: A measurement of the silicon abundance in dense interstellar gas

The first detection of the ground state fine structure transition of Si+ at a rest wavelength determined to be 34.815 + or - 0.004 micron are reported. These observations were obtained with the facility spectrometer on NASA's Kuiper Airborne Observatory. A 6' NW-SE strip scan across the Orion-KL region shows SiII emission from both the extended photodissociation region surrounding theta 1 Ori C and from the shocked gas NW of BN-KL. The inferred gas-phase silicon elemental abundance relative to hydrogen in the dense 10 to the 5/cc primarily neutral photodissociation region is approximately 2.6 x to the -6, a factor of 0.075 times the solar value and 3.4 times greater than the abundance in the moderate density approx. 10 to the 3/cc cloud toward zeta Oph. The silicon abundance in the shocked gas is approximately solar, indicating that any pre-existing grains have been destroyed in the shock wave or that the preshock gas carries a near solar abundance of gas phase silicon. The shock-excited SiII (34.8 micron) emission may arise from shocked wind material in the outflow around IRc2, with wind velocities approx. 100 km/s.

Haas, M. R.↗
NASA NTRS1985

Observations of far-infrared transitions between excited states of OH

In observations of the Kleinmann-Low Nebula were detected of Orion 84.42 and 84.60 micron transitions between the P-2 sub 3/2 and Pi-2 sub 3/2 (J = 5/2) levels of OH with respective fluxes of 1.0 + or - 0.3 to the minus 17th power and 1.4 + or - 0.4 x 10 to the minus 17th power W cm/sq. When compared to 119 micron flux levels of OH and 153 micron flux levels of these radicals by Viscuso, these results suggest appreciable self-absorption of OH line radiation within the Nebula. It is probable that the CO emission due to the J = 31 yields 30 rotational transition at 84.411 micron makes a substantial contribution to the observed 84.42 micron flux, and that it also is at least partially absorbed at the 84.42 micron OH transition frequency. The 88.55 and 88.78 micron (J = 9/2 to 7/2) transitions of CH also were sought, but yielded only to upper limits of 3 x 10 to the minus 18th power W /sq cm each. A search of W3-IRS5 yields upper limits to the 84.42 micron OH and 87.19 micron CO (J = 30 to 29) transitions of 2 x 10 minus 18th power W cm/2.

Viscuso, P. J.↗
NASA NTRS1985

Observation of far-infrared transitions between excited states of OH

Spectra of the Kleinmann-Low nebula in Orion detected the 84.42 and 84.60 micron transitions between the 2Pi(3/2) J = 7/2 and 2Pi(3/2) J = 5/2 levels of OH with respective fluxes of 1 x 10 to the -17th and 1.4 x 10 to the -17th W/sq cm. When compared to the 119 micron flux levels of OH discussed by Watson (1982) and the 163 micron flux levels of OH by Viscuso et al. (1985), these results suggest appreciable self-absorption of OH line radiation within the nebula. The CO emission due to the J = 31 to 30 rotational transition at 84.411 microns makes a substantial contribution to the observed 84.22 micron flux, and is probably at least partially absorbed at the 84.42 micron OH transition frequency.

Viscuso, P. J.↗
NASA NTRS1985

An FIR cooled grating spectrometer for the Kuiper Airborne Observatory

The design and performance of a liquid-He-cooled spectrometer being developed for the Kuiper Airborne Observatory (KAO) to study FIR lines originating in the interstellar medium are discussed. Currently, the spectrometer contains six Ge:Ga photoconductor detectors mounted in integrating cavities and cooled to about 3 K; the collimator focal plane has space for 39 such detectors. The instrument achieves a maximum resolving power of 6000 by means of a 45-cm long echelle grating and is optically capable of operating in the spectral range 25-300 microns. A laboratory spectrum of water vapor, an atmospheric water absorption feature measured from the KAO with Mars as a source, and the forbidden O(2+) emission from W51-IRS1 are shown.

Erickson, E. F.↗
NASA NTRS1985

All-aluminum optical system for a large cryogenically cooled far infrared echelle spectrometer

In the past few years, NASA's Kuiper Airborne Observatory (KAO) has made it possible to conduct pioneering observations of far infrared lines from astronomical sources. Such observations, in the case of wavelengths in the approximate range from 20 to 350 microns, cannot be performed from ground-based sites, because of telluric water absorption effects. Lines in the considered range provide information about the interstellar gas in molecular, neutral atomic, and ionized form of occurrence. The present paper provides a description of the development of the cryogenic optical system of a spectrometer designed to exploit the potential of the KAO for observing the far infrared lines. Attention is given to design goals and considerations, details of optical design, the fabrication of the optical system, the cryostat, and performance.

Erickson, E. F.↗
NASA NTRS1984

Detection of the J-10 Manifold of the Pure Rotational Band of Phosphine on Saturn

The detection of the J = 10 manifold of the pure rotational band of PH3 on Saturn is reported. The observations were made from the far-infrared cooled grating spectrometer. The wavelengths and observed brightness temperatures for the full disk plus rings are 89 + or - 3 K at 97.04 micrometer, 77 + or - 3 K at 102.72 micrometer, 77 + or - 3 K at 102.94 micrometer, and 83 + or - 3 K at 105.12 micrometers. The points of 97.04 and 105.12 micrometers establish the continuum level and the two points near 103 micrometers measure the depth of the PH3 manifold. After the flux due to the rings is subtracted, the depth of the feature is 16 + or - 6 K relative to the nearby 102 K continuum. These results are compared to theoretical models which parameterize the PH3 mixing ratio as x = x sub zero (P/P sub zero)(alpha) for P P sub zero and as x = x sub zero for P or = P, where P is the total pressure and alpha = H/h is the ratio of the dynamical scale height (H) and the scale height for decreasing the PH3 mixing ratio (h). The parameters x sub zero, P sub zero, and h were varied, as well as the H/He mixing ratio and the pressure-temperature profile. The data are well fitted using pressure-temperature profiles. The preferred values of h, P sub zero, and x sub zero imply that there is little or no PH3 above the thermal inversion and that the mixing ratio below the inversion is consistent with PH3 being 1 to 4 times overabundant relative to the solar P/H ratio.

Haas, M. R.↗