Crystalline silicates in planetray nebulae with [WC] central stars

Astronomy and Astrophysics (Impact Factor: 4.48). 01/1998;
Source: arXiv

ABSTRACT 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.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Abstract— The laboratory analyses of cosmic dust analogues—that in the context of this paper include interstellar, circumstellar as well as cometary dust—have a critical role in the study of circumstellar and cometary dust. The morphological, structural and chemical characterization of these analogues are critical for comparisons of their infrared and ultraviolet spectra with those obtained by astronomical observations, as well as for modeling purposes. Besides, the results from these laboratory studies are important to the success of space missions to comets when testing and calibrating the payload instruments. The interpretations of returned scientific data would benefit from the comparison with data recorded by the instruments in a laboratory setting for different classes of previously characterized analogues. We produced various types of condensed samples: (1) Mg,Fe-silicates, (olivine, pyroxene), (2) carbon-rich dust, and (3) mixed carbon-silicate dust. The samples were prepared using different techniques, viz. (1) laser bombardment of solid targets in an Ar and O2 atmosphere, (2) arc discharge in an Ar and H2 atmosphere, and (3) grinding powders of natural minerals. We simulated various post-condensation processes, such as thermal annealing, ultraviolet irradiation, ion bombardment and exposure to atomic hydrogen. These processes produced compound samples of a wide range of physico-chemical properties. To identify their textures, morphologies, grain compositions and crystallographic properties we used electron microscopy and far-ultraviolet to far-infrared (millimeter range) spectroscopy.
    01/2010; 37(11):1623 - 1635. DOI:10.1111/j.1945-5100.2002.tb00816.x
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Abstract— We investigated thermoluminescence of silicates that are of interest in the interstellar and circumstellar medium after irradiation by -rays and fast neutrons. The silicates are forsterite, orthoenstatite, olivine, quartz, and crystalline silicon. The irradiated enstatite shows weak and broad peaks at 545 and 760 nm. In contrast, irradiated bulk and powder samples of forsterite show strong and broad peaks at 640–660 nm. Although thermoluminescence of bulk forsterite is very similar to the extended red emission (ERE) of the Red Rectangle nebula, irradiated powdered forsterite did not reveal any sharp emission features over the broad band. Further, we investigated the possibility of thermoluminescence of crystalline silicon and found that luminescence scarcely appears. It is emphasized that the prominent carrier of ERE is forsterite and fused quartz.
    01/2010; 37(11):1591 - 1598. DOI:10.1111/j.1945-5100.2002.tb00813.x
  • 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.
    10/2000; 35(6):1269 - 1273. DOI:10.1111/j.1945-5100.2000.tb01515.x

Full-text (2 Sources)

Available from
May 28, 2014