George William Hawkins

Discovery of an extended nebula around AFGL 2343 (HD 179821) at 10 microns

We present images at 8.5, 10.5, and 12.5 {mu}m which reveal that AFGL 2343 (HD 179821) is surrounded by a dusty nebula 4{double_prime}{minus}5{double_prime} in diameter at 10.5 and 12.5 {mu}m. This G5 Ia supergiant has long been suspected of having a detached dusty envelope because of its optical brightness and large IR excess. The nebula is ringlike and slightly elongated, with bright patches or clumps to the northeast. An 8.5 {mu}m image is dominated by the photosphere of the central star, which also appears to a lesser extent in the 10.5 and 12.5 {mu}m images. A full radiative transfer model of the nebula correctly predicts the observed inner (1{close_quote}{close_quote}.1) and outer (1{close_quote}{close_quote}.9) radii of the shell and the spectral energy distribution of the shell. With the aid of this model, we find that AFGL 2343 is almost certainly an extremely massive star at a distance of about 6 kpc, which has recently undergone an enormous mass-loss event, during which {dot {ital M}}=10{sup {minus}2} {ital M}{sub {circle_dot}} yr{sup {minus}1}, while the current mass-loss rate is less than 2{times}10{sup {minus}6} {ital M}{sub {circle_dot}} yr{sup {minus}1}. {copyright} {ital 1995 The American Astronomical Society.}

Mid-IR (8-13 μm) images of the 21 μm, carbon rich proto-planetary nebulae

We present 9.7 and 11.8 μm narrow band (Δλ/λ=10%) images of three carbon (C-) rich proto-planetary nebulae with an unusual 21 μm feature: IRAS 07134+ 1005, IRAS 22272+5435, and IRAS 04296+3429. The images were taken at UKIRT using the Berkeley/IGPP/LEA mid-IR camera. All three objects have a bipolar shape adding to the existing evidence that C-rich PPNe are by nature bipolar. Furthermore, we find the same bipolar morphology in a previous study of the C-rich, young planetary nebula, IRAS 21282+5050. We believe these four objects form an evolutionary sequence which links the C-rich asymptotic giant branch (AGB) stars with the C-rich planetary nebulae (PNe). From this evolutionary sequence, we conclude that bipolarity in C-rich PNe begins on the AGB and that the dynamical ages of these PPNe are in fair agreement with theoretical ages for a 0.6 M⊙ hydrogen burning core star.

Mid-IR (8–13μm) Images of the 21 µm, Carbon rich Proto-Planetary Nebulae

We present 9.7 and 11.8 µm narrow band (Δλ/λ = 10%) images of three carbon (C-) rich proto-planetary nebulae with an unusual 21 µm feature: IRAS 07134+ 1005, IRAS 22272+5435, and IRAS 04296+3429. The images were taken at UKIRT using the Berkeley/IGPP/LEA mid-IR camera. All three objects have a bipolar shape adding to the existing evidence that C-rich PPNe are by nature bipolar. Furthermore, we find the same bipolar morphology in a previous study of the C-rich, young planetary nebula, IRAS 21282+5050. We believe these four objects form an evolutionary sequence which links the C-rich asymptotic giant branch (AGB) stars with the C-rich planetary nebulae (PNe). From this evolutionary sequence, we conclude that bipolarity in C-rich PNe begins on the AGB and that the dynamical ages of these PPNe are in fair agreement with theoretical ages for a 0.6 M⊙ hydrogen burning core star.

10 µ m Images of AGB Stars & Supergiants

We present mid-IR and far-IR images of a variety of AGB stars and red supergiants. The mid-IR images were all taken with the Berkeley/Livermore mid-IR array camera, which employs a 10 x 64 pixel Hughes photoconductor. All the images reported here were taken using a 10% bandpass CVF, at various wavelengths in the 10µm atmospheric window. These were supplemented by IRAS images, some constructed from survey scans, others made as Additional Observations during the pointed phase of the IRAS mission. We have so far observed 11 such sources with our mid-IR camera, and report here that only two of them (R Aql and V Hya) appear to be unresolved.