Crystalline silicates in planetray nebulae with [WC] central stars

University of Groningen, Groningen, Groningen, Netherlands
Astronomy and Astrophysics (Impact Factor: 4.38). 03/1998; 331(3).
Source: arXiv


We present ISO-SWS spectroscopy of the cool dusty envelopes surrounding two
Planetary Nebulae with [WC] central stars, BD+30~3639 and He~2-113. The lambda
< 15micron region is dominated by a rising continuum with prominent emission
from C-rich dust (PAHs), while the long wavelength part shows narrow solid
state features from crystalline silicates. This demonstrates that the chemical
composition of both stars changed very recently (less than 1000 years ago). The
most likely explanation is a thermal pulse at the very end of the AGB or
shortly after the AGB. The H-rich nature of the C-rich dust suggests that the
change to C-rich chemistry did not remove all H. The present-day H-poor [WC]
nature of the central star may be due to extensive mass loss and mixing
following the late thermal pulse.

Download full-text


Available from: Jeroen Bouwman
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Abstract— Films condensed from vapors containing SiO, Fe, or Mg showed an amorphous structure. Infrared (IR) spectra and electron microscopic characterization have been carried out on these films. After the heat treatment of these films in air, IR peaks at approximately 18–23 μm appeared, in addition to peaks attributable to SiO2. These peaks can be attributed to metallic oxides such as FeO, Fe2O3, and MgO. It can be concluded that Fe- or Mg-bearing silicate minerals cannot be produced by the rapid cooling of SiO, Fe, or Mg vapors. Although IR spectra of FeO have been discussed in order to match some spectra obtained with the Infrared Space Observatory, the identification of FeO as the impurity would be very important because the IR spectra of FeO grains are very dependent on the shape and size of the grains. These impurities can also influence the IR spectral feature of SiO2.
    Full-text · Article · Oct 2000
  • [Show abstract] [Hide abstract]
    ABSTRACT: Carbon and silicate grains are the two main components of cosmic dust. There is increasing spectroscopic evidence that their composition varies according to the cosmic environment and the experienced processing. Irradiation from ultraviolet photons and cosmic rays, as well as chemical interactions with the interstellar gas play a crucial role for grain transformation. The study of 'laboratory analogues' represents a powerful tool to better understand the nature and evolution of cosmic materials. In particular, simulations of grain processing are fundamental to outline an evolutionary pathway for interstellar particles. In the present work, we discuss the ultraviolet and infrared spectral changes induced by thermal annealing, ultraviolet irradiation, ion irradiation and hydrogen atom bombardment in carbon and silicate analogue materials. The laboratory results give the opportunity to shed light on the long-standing problems of the attribution of ultraviolet and infrared interstellar spectral features.
    No preview · Article · Apr 2001 · Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy
  • [Show abstract] [Hide abstract]
    ABSTRACT: The 3.4 μm absorption band provides direct evidence for the presence of organic compounds in the diffuse interstellar medium. There is, however, a distinct absence of the band in the spectra of molecular cloud dust. The difference between diffuse and dense environments represents a strong constraint for any description of the formation and evolution of the band carrier material. Laboratory research under simulated interstellar medium conditions is of crucial interest for improving our understanding of the nature of this interstellar dust component. In fact, the composition of carbonaceous materials in the interstellar medium can vary in response to several evolutionary factors. Irradiation from UV photons and cosmic rays, as well as chemical interactions with the interstellar gas, can drive grain transformation. Here we discuss the results of experiments aimed at studying the interaction of nano-sized carbon grains with atomic hydrogen. H atoms induce the formation of CH bonds in carbon grains. After hydrogen exposure, the infrared spectrum of carbon grains is similar to that of the aliphatic component observed toward the Galactic center. The efficiency of the hydrogenation process and the amount of carbon which is necessary to reproduce the intensity of the interstellar feature are reported. Finally, implications for the formation and evolution of the organic materials responsible for the 3.4 μm band are discussed.
    No preview · Article · Sep 2002 · Advances in Space Research
Show more