ALBERT

Description: We have detected forbidden O I 63 micron and forbidden Si II 35 micron emission from the oxygen-rich, M2 lab supergiant, Alpha Orionis (Betelgeuse). The forbidden O I line flux is 2.4 +/- 0.2 x 10 exp -18 W/sq cm, and the forbidden Si II line flux is 0.9 +/- 0.4 x 10 exp -18 W/sq cm. These fluxes are consistent with the thermal model of Rodgers and Glassgold (1991), which indicates that the emission arises in dense, warm gas in Alpha Ori's inner envelope and implies that nearly all of the available O and Si is in atomic form. This is the first reported detection of FIR, fine-structure emission from the inner or transition region of a circumstellar envelope, where molecules and dust are expected to form.

Description: We describe a semiempirical methodology-based on measurements of far-infrared (FIR) lines-that yields information on electron densities in regions where various ionic species exist, effective temperatures (T(sub eff)) for stars ionizing H II regions, and gas-phase heavy element abundances. Although this capability has long been available via optical data, the special features of FIR lines-relative insensitivity to extinction and electron temperature variations-extend the analysis ability. Several line ratios serve as diagnostics of electron density, N(sub e), probing different ionization conditions and different density regimes. The more N(sub e)-diagnostic observations made, the more reliable will be the deciphering of the actual variation in density throughout a nebula. A method to estimate T(sub eff) from the FIR (N III)/(N II) line ratio requires that the nebula be ionization bounded and that substantially all of the flux from the revevant lines be observed. However, to estimate T(sub eff) by a second method that uses the ratio of FIR (S III)/(O III) lines, an ionization-bounded nebula is a sufficient, but not necessary, condition. These restrictions are unnecessary for estimating densities and heavy element abundances. We show that a fairly general determination of metallicity, via the S/H ratio, may be made for H II regions with observations of just two lines-(S III) 19 micron and a hydrogen recombination line (or appropriate substitute). These techniques are applied to recent FIR data for the G333.6-0.2 H II region, including application to the recently measured (N II) 122 and 205 micron lines.

Description: Forbidden Si II and Si I line emission from Orion's BN-KL was measured using a cryogenic grating spectrometer aboard NASA's Kuiper Airborne Observatory. It is believed that the bulk of the forbidden Si II emission in Orion originates in photodissociated gas at the interface between the H II region and its parent molecular cloud. There is, however, a twofold enhancement in forbidden Si II emission near IRc2, which is attributed to fast dissociative J-shock where the wind from IRc2 impact slower moving material. Model fits suggest a silicon gas-phase depletion near ITc2 of 0.3-1.0 relative to solar. The spatial distribution of the forbidden Si II emission has a centralized peak.

Description: 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.

Description: 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.

Description: We demonstrate that when there are gas density variations within a nebula, various line ratios used to determine electron density (Ne) can give different results. When there are non-constant density conditions, it is shown that by using one (average) Ne, significant, systematic biases may occur in the derived chemical abundance ratios. The abundance ratio of a heavy element (when a collisionally excited line is used) to ionized hydrogen may be subject to a large underestimate in the presence of density fluctuations. The more Ne-diagnostic observations made, the more reliable will be the deciphering of the actual Ne variation throughout a nebula.

Description: We discuss measurements of the far-infrared (FIR) fine structure lines from (S III) (33 microns), (Si II) (35 microns), (O III) (51, 88 microns), (OI) (63 microns), (C II) (158 microns), and the adjacent continua in a strip crossing two of the thermal radio filaments in the Galactic Center 'Arch'. The near spatial coincidence of the line and continuum emission maxima with the radio filaments demonstrates that any excitation mechanism must account for both the line and continuum emission. The peak FIR luminosity and (O III) emission pose difficulties for collisional excitation models; photoionization of molecular cloud edges by a random distribution of stars is the most plausible mechanism proposed.

Description: We have detected (O I) 63 micron and (Si II) 35 micron emission from the oxygen-rich, M supergiants alpha Orionis (Betelgeuse), alpha Scorpii (Antares), and alpha Herculis (Rasalgethi). The measured fluxes indicate that the emission originates in dense, warm gas in the inner envelope or transition region where molecules and dust are expected to form and the acceleration of the wind occurs. Mass-loss rates are derived, evidence for time variability is presented, and results for other evolved stars are included.

Description: We report the first observations of H15 alpha (169.4114 microns) and H10 alpha (52.5349 microns) in MWC 349 from the KAO. We obtain a 3 sigma upper limit of 2 x 10(exp -19) W/sq cm for H15 alpha and a flux of 3.6 +/- 1.3 x 10(exp -19) W/sq for H10 alpha. These fluxes are consistent with an appreciable excess due to laser amplification down to quantum numbers n approx. equals 10.

Description: We summarize some of our KAO observations of far-infrared ionic fine-structure lines from Galactic H II regions, and discuss their interpretation.