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Dust around evolved stars in the LMC

University of Missouri-Columbia & University of Virginia. C. Dijkstra, A. K. Speck, R.B. Reid, C. Markwick-Kemper. Dust around evolved stars in the LMC. Dust in the circumstellar envelope of an evolved star. Dust in the circumstellar envelope of an evolved star. Why use the LMC?.

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Dust around evolved stars in the LMC

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  1. University of Missouri-Columbia & University of Virginia C. Dijkstra, A. K. Speck, R.B. Reid, C. Markwick-Kemper Dust around evolved stars in the LMC

  2. Dust in the circumstellar envelope of an evolved star

  3. Dust in the circumstellar envelope of an evolved star

  4. Why use the LMC? 1) All stars in the LMC are at same distance (50 kpc). This allows for well constrained (circum-)stellar parameters when modeling spectra. Also, the metallicity of the LMC is known (Z=0.008). 2) Gas chemistry and density are set by (circum-)stellar parameters and metallicity. 3) Gas chemistry and density determine dust mineralogy. 4) The LMC thus allows for a study of dust mineralogy as function of chemistry, density and metallicity.

  5. Tool 37 Infrared Space Observatory (ISO) spectra: CAM (4-17 m), PHT-S (2.5-11.6 m), and SWS (2-45 m). Lower sensitivity than Spitzer, but: 1) Higher spectral resolution. 2) Covers some wavelength ranges not covered by Spitzer. Data modeled by Van Loon et al. (1999), but with emphasis on mass loss rates and luminosities, NOT detailed mineralogy!

  6. First results Correlation between the 10 m feature peak position and mass loss rate of M-stars. A dusty disk around the Red Super Giant star WOH G064 (=IRAS 04553-6825). SiC dust instead of silicate dust around the luminous carbon star IRAS 04496-6958.

  7. Condensation sequence

  8. Density, temperature and pressure calculated from van Loon et al. (1999).

  9. IRAS 04496-6958 Luminous carbon star (C/O>1). Based on ISO spectroscopy, Trams et al. (1999) suggest presence of oxygen-rich silicate dust, making this the first known extra-galactic silicate carbon star. Spitzer data leads to new interpretation: NO silicate dust is present. Instead we see carbon rich SiC dust.

  10. Silicate emission V778 Cyg is a galactic silicate carbon star.

  11. SiC absorption V778 Cyg is a galactic silicate carbon star.

  12. Galactic carbon stars Strong emission. Weaker emission Absorption

  13. ISO ISO ISO ISO Spitzer Continua ISO spectra are from Volk et al. (2000). Continuum of IRAS 04496 is a 600 K black body.

  14. Conclusions Correlation between the 10 m feature peak position and mass loss rate of M-stars. A dusty disk around the Red Super Giant star WOH G064 (=IRAS 04553-6825). SiC dust instead of silicate dust around the LMC carbon star IRAS 04496-6958

  15. Aim of our study Investigate the mineralogy of dust around evolved stars in the LMC to constrain: 1) the dust formation process around these stars. 2) the enrichment of the interstellar medium with new dust. 3) the nature of the dust that goes into new planetary systems.

  16. Overview 10 m feature in LMC stars

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