Sean C. Casey

IRC +10420 - A cool hypergiant near the top of the H-R diagram

New data are reported for the OH/IR star IRC+10420, including optical/infrared imaging, spectroscopy, polarimetry, and photometry. We conclude the following: 1. The optical spectrum is that of a very luminous F supergiant (F Ia+) with a very strong O I blend at 7774 A. Hα is strongly in emission and shows a double-peaked profile similar to the emission seen in stars with rotating equatorial disks. 2. The optical image taken through polarizing filters is elongated, and shows that the star must be intrinsically polarized at a position angle near 90°. The 8.7 μm image is also elongated, but at a position angle near 150°

Emission from dust in visual reflection nebulae at infrared and submillimeter wavelengths

Far-IR and submillimeter images of five bright visual reflection nebulae, IC 446, NGC2247, NGC 2245, NGC 7023, and CED 201 are presented and used with composite IR spectra to derive parameters such as the fraction of nebulae emission attributed to molecule-sized grains, the range of nebulae grain albedos, gas densities, and gas cloud geometries. The results show that 30-45 percent of the nebulae emission lies at wavelengths of less than 30 microns. The variation in IR luminosity may be related to variations in nebulae gas density and less than optimal gas cloud geometries rather than to anomalous grain albedos. Relative extinction efficincies of roughly 1000-5000 are inferred for stellar photospheres with effective wavelengths of roughly 0.25-0.5 micron. The resultant mass-extinction coefficient is roughly 10-50 sq cm/g. 79 refs.

HAWC: a far-infrared camera for SOFIA

When SOFIA enters operation, it will be the largest far- infrared telescope available, so it will have the best intrinsic angular resolution. HAWC (High-resolution Airborne Wideband Camera) is a far-infrared camera designed to cover the 40 - 300 micron spectral range at the highest possible angular resolution. Its purpose is to provide a sensitive, versatile, and reliable facility-imaging capability for SOFIAs user community during its first operational use.

Submillimeter continuum emission from galaxies - Star formation and the interstellar medium in the local group dwarf IC 10

Far-infrared (95 and 160 micron) maps and visual broad-band and line images of the nearby, luminous irregular galaxy IC 10 are discussed. Observations of the dust emission make it possible to constrain the total mass of gas and the rate of star formation derived for the galaxy. The total star-formation rate is estimated to be about 0.15 solar mass/yr, and the e-folding time for exhaustion of the interstellar gas due to the star formation is only a few billion years. To determine the source of the cool dust in emission at approximately 100-250 microns from many galaxies, 60, 100, and 160 micron photometry, obtained previously, is compared; and CO, H I, and dust emission is correlated. Based on the correlation between the various cool components of the interstellar medium, it is concluded that the likely location of the dust that dominates the emission at about 160, and possibly 100, microns is within both the diffuse atomic gas and in surface layers of molecular clouds. 57 refs.

Star formation and the interstellar medium in two peculiar, nonspiral galaxies - NGC 1569 and NGC 3593

This paper discusses far-IR and optical observations aimed at investigating the far-IR energy distribution of two peculiar galaxies without spiral arms which are actively forming stars: NGC 1569, a Magellanic irregular galaxy, and NGC 3593, a dusty S0/a galaxy. The data are used to determine the characteristic temperatures of the dust and to infer dust and molecular gas masses which are combined with other data to explore the characteristics of the interstellar media. Visual-wavelength continuum and H-alpha images are presented and used to estimate current and past star formation rates and the efficiency of stellar creation. 81 refs.

The interacting galaxy pair NGC 4485 and NGC 4490 - star formation and the interstellar medium

The 100- and 160-micron continuum emission from cool dust in the interacting gas-rich pair of galaxies, NGC 4490 and NGC 4485, was mapped. Visual continuum and H-alpha images of the pair were obtained. The state of the interstellar medium and the rate and efficiency of star formation are investigated. 49 refs.