D. A. Garcia-Hernandez — Page 7

arXiv2004

The Mid-IR Emission Structure of IRAS 16594-4656

We report TIMMI2 diffraction-limited mid-IR images of the multipolar PPN IRAS 16594-4656. By using the Lucy-Richardson deconvolution algorithm we recover a two-peaked morphology in the innermost region at 8.6 and 11.5 microns. We interpret the observed mid-IR structure as the detection of the two limb-brightened peaks indicating the presence of a dusty toroidal structure in IRAS 16594-4656. We find that the supposed biconical openings of the dust torus are in good agreement with one of the bipolar outflows identified in the HST optical images.

astro-ph↗

arXiv2002

Near-IR spectroscopy of planetary nebulae precursors

We present near-IR spectroscopy of a sample of 30 IRAS sources recently identified as late AGB stars, post-AGB stars or early PNe. The spectra obtained are centered at various wavelengths covering the molecular hydrogen v=1-0 S(1) and v=2-1 S(1) emission lines, the recombination lines of hydrogen Br-gamma, Pf-gamma and Br-alpha, and the CO[v=2-0] first overtone bandhead at 2.294 microns. As a result of these observations we have increased from 4 to 13 the total number of proto-PNe detected in molecular hydrogen. When the molecular hydrogen is fluorescence-excited the detection rate is found to be directly correlated with the evolutionary stage of the central star, rather than with the nebular morphology. In contrast, shocked-excited molecular hydrogen is detected only in strongly bipolar proto-PNe, sometimes even at an early stage in the post-AGB phase. The strong correlation of shocked-excited molecular hydrogen emission with bipolarity found confirms the result previously reported by Kastner et al. (1996) in evolved PNe. However, our results show that this correlation does not exist in the case of fluorescence-excited molecular hydrogen.

astro-ph↗