Engineering topics
Publications and source records attributed to Erickson, Edwin F..
Measurements of far-infrared lines and continuum from G0.095 + 0.012 and the E2 thermal 'arched' radio filament near the Galactic center are well explained by numerous embedded stars with T(eff) about 35,000 K. The structure of the filament and the apparent absence of hotter stars are qualitatively difficult to reconcile with this idea.
Measurements of far-infrared lines and continuum from GO.095 + 0.012 and the E2 thermal 'arched' radio filament near the Galactic center are well explained by numerous embedded stars with T(sub eff) approximately 35,000 K. The structure of the filament and the apparent absence of hotter stars are qualitatively difficult to reconcile with this idea.
Properties of two compact H II regions, K3-50 A and G45.13 + 0.14 A, were investigated by measuring FIR fluxes from forbidden O III 51.8 and 88.4 micron lines, forbidden N III 57.3 micron line, forbidden S III 33.5 micron line, and forbidden Ne III 36.0 micron line of these regions, using a cooled grating spectrometer on NASA's Kuiper Airborne Observatory. For both H II regions, the ratio of the two FIR O(2+) lines indicates an electron density of about 1000/cu cm, which for K3-50 A is a factor of 10 to 100 lower than the density determined from optical line observations of the lower excitation species S(+) and N(+) and than the peak rms density deduced from radio continuum measurements by Turner and Matthews (1984). Detailed spherically symmetric models of the two sources were constructed using all available measurements.
The far-infrared lines of (O III) 51.8 and 88.4 microns, (N III) 57.3 microns, (S III) 33.5 microns, and (Ne III) 36.0 microns have been measured in the compact H II regions G45.13+0.14 A and K3-50 A. These measurements were made with the facility cooled grating spectrometer on flights of NASA's Kuiper Airborne Observatory. For both sources, the ratio of the two O(++) lines indicates an electron density N(sub e) approx. 10(exp 3)cm(sup -3). For K3-50 A, this is a factor of 10 to a hundred times lower than the density determined from near-infrared and optical line observations of lower excitation species and from radio measurements of the peak continuum emission. A comparison with other far-infrared measurements for both sources shows that the lower excitation, higher critical density S(++) lines originate from higher density material than do the O(++) lines. Detailed, spherically symmetric models for both sources are presented. These models require clumping, different abundances than the Orion Nebula, and an enhancement in the standard Kurucz stellar atmospheres at energies E greater than 41 eV to obtain reasonable agreement with the measurements. The average nitrogen-to-oxygen abundance ratio for these two H II regions is N/O approx. 0.2, in agreement with other far-infrared studies at Galactic radii greater than or equal to 6 kpc.
The forbidden F II profiles at 18 and 26 micron from SN 1987A have been measured with a resolution of about 400 km/s. The central portion of each profile is well-fitted by a Gaussian with a FWHM of 2900 and 2500 km/s, respectively. The centroid velocity is redshifted relative to the LSR by 450 + or - 200 km/s at 18 microns and by 680 + or - 200 km/s at 26 microns. The integrated line fluxes alone imply a maximum expansion velocity of about 2000 km/s and a minimum expansion velocity much less than the maximum. A significant fraction of the iron has mixed with the overlying hydrogen regions. There is a high-velocity emission feature at about +3500 km/s relative to the main emission peak which contains about 3 percent of the total iron mass and has T about 2600 K. The measured 26 micron line flux corresponds to a total singly ionized iron mass of 0.026 solar. The line fluxes and profiles are inconsistent with a physically thin shell of gas and show that there is a wide range of expansion velocities for the iron.
We present approx. 400 km/s resolution profiles of the 17.94 and 25.99 micron [Fe II] transitions from SN 1987A at t approx. 400 days after core collapse. These observations used the facility cooled grating spectrometer aboard NASA's Kuiper Airborne Observatory. The two profiles are similar and have FWHM line widths of approx. 2700 km/s. The higher signal-to-noise 18 micron profile is somewhat asymmetric, falling off more steeply on the redshifted side than on the blue. Gaussian fits to the profiles yield an average centroid velocity of 280 +/- 140 km/s relative to the Large Magellanic Cloud. The wings of the profiles extend to velocities is approx. greater than 3000 km/s. This shows that a significant fraction of the iron has been mixed outward into the hydrogen-rich envelope, which has a minimum expansion velocity of 2100-2400 km/s. Both profiles also contain an unresolved 3-5 sigma emission feature on the redshifted wing at nu(LSR) approx. + 3900 km/s. We interpret this feature as emission from a high-velocity clump of material containing approx. 3% of the total iron mass. The total line flux of the 26 micron ground-state transition yields an optically thin, singly ionized iron mass of 0.026 solar mass, relatively independent of the assumed temperature. This is significantly less than the 0.06 Me of Fe+ determined from the decline of the optical light curve and the ionization of measured nickel lines, implying that the iron transitions still have appreciable optical depth. However, because of the small change in the 26 micron line flux from our measurement at 250 days, and the similarity of our profiles to the 1.26 micron [Fe II] profile, most of the emission is believed to originate from optically thin material with a temperature of 4406 +/- 400 K. A comparison of the data with spherically symmetric models indicates a power-law density exponent of -3.2 +/- 1.1 and a minimum expansion velocity of 650 +/- 650 km/s for this optically thin component. The [Fe II] line fluxes and profiles also imply that the remainder of the material has high optical depth and is distributed in clumps throughout the ejecta, rather than being concentrated at low velocities in the center of a smooth density distribution.
Researchers investigated the physical conditions in the infrared bright galaxies NGC 6946, IC 342, and Arp 299 through measurements of far-infrared emission lines from Si II, O I, C II, and O III using the facility Cooled Grating Spectrometer on the Kuiper Airborne Observatory. These data are interpreted using our theoretical models for photodissociation regions and H II regions. For the central 45 inches of these galaxies, researchers determined that the dominant excitation mechanism for the far infrared radiation (FIR) lines is far ultraviolet radiation (FUR) radiation from young stars, and the authors derived the total mass, density, and temperature of the warm atomic gas and the typical sizes, number densities, and filling factors for the interstellar clouds.
SOFIA, a proposed 3-meter class telescope in a Boeing 747 aircraft, would have the ability to make astronomical observations over a wavelength range from 0.3 microns to 1.6mm. Relative to the KAO (Kuiper Airborne Observatory) the larger telescope on SOFIA would provide a factor of 10 improvement in sensitivity for compact sources and a factor of 3 improvement in (diffraction-limited) angular resolution at wavelengths beyond 30 microns. In addition, SOFIA will retain the major features of the KAO which have made the airborne astronomy program so successful. Among these are continuous in-flight access to focal plane instruments while flying at or above 41,000 ft altitude; pointing stability of 0.2 arcseconds; and mobility and scheduling flexibility to accommodate targets of opportunity such as comets, eclipses, occultations, and novae.
The first observation of the 26-micron line from singly ionized iron in SN 1987A is reported. The total flux is 4.5 + or - 0.9 x 20 to the -18th W/sq cm. The line width (FWHM) is 4000 + or - 600 km/s. The minimum iron mass is found to be about 0.02 solar, indicating that the emission originates in the heavy element mantle and not in the hydrogen-rich envelope. Since this mass is less than estimates based on near-infrared measurements or the optical light curve, the emission is probably optically thick. In this case, the flux measurement together with the observed line width suggest a temperature of 3500 + or - 1500 K for the mantle. The broad line width suggests that mixing of the ejected iron with lighter elements in overlying layers has occurred.
The paper presents observations of the 63 micron forbidden O I line from Herbig-Haro objects and their exciting stars. Forbidden O I 63 micron emission is detected toward the HH-exciting stars T Tau, DG Tau, L1551 IRS 5, and toward the HH objects HH 7-11, HH 42A, and HH 43 which are displaced from their exciting stars. The forbidden O I emission is associated with these flows on the basis of its spatial coincidence and its negative radial velocities. If the exciting stars drive bipolar flows in which the 63 micron emission follows that at 6300 A, the absence of redshifted 63 micron lines from the three exciting stars might indicate that the disks hypothesized to overlie the receding lobes of these flows are still optically thick in the far-infrared.