Dust around evolved stars in the LMC

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Dust around evolved stars in the LMC
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Dust in the circumstellar envelope of an evolved
star
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Dust in the circumstellar envelope of an evolved
star
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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 (Z0.008).
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.
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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!
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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.
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Condensation sequence
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Density, temperature and pressure calculated from
van Loon et al. (1999).
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Luminous carbon star (C/Ogt1).
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.
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V778 Cyg is a galactic silicate carbon star.
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V778 Cyg is a galactic silicate carbon star.
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Galactic carbon stars
Strong emission.
Weaker emission
Absorption
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ISO
ISO
ISO
ISO
Spitzer
Continua ISO spectra are from Volk et al.
(2000). Continuum of IRAS 04496 is a 600 K black
body.
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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
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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.
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Overview 10 ?m feature in LMC stars