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 in the circumstellar envelope of an evolved

star

Dust in the circumstellar envelope of an evolved

star

Why use the LMC?

2) Gas chemistry and density are set by (circum-)stellar parameters and metallicity.

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).

3) Gas chemistry and density determine dustmineralogy.

4) The LMC thus allows for a study of dust mineralogy as function of chemistry, density and metallicity.

Tool

Lower sensitivity than Spitzer, but:1) Higher spectral resolution.2) Covers some wavelength ranges not covered by Spitzer.

37 Infrared Space Observatory (ISO) spectra: CAM (4-17 m), PHT-S (2.5-11.6 m), and SWS (2-45 m).

Data modeled by Van Loon et al. (1999), but with emphasis on mass loss rates and luminosities, NOT detailed mineralogy!

First results

A dusty disk around the Red Super Giant star WOH G064 (=IRAS 04553-6825).

Correlation between the 10 m feature peak position and mass loss rate of M-stars.

SiC dust instead of silicate dust around the luminous carbon star IRAS 04496-6958.

Condensation sequence

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

IRAS 04496-6958

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.

Luminous carbon star (C/O>1).

Spitzer data leads to new interpretation: NO silicate dust is present. Instead we see carbon rich SiC dust.

Silicateemission

V778 Cyg is a galactic silicate carbon star.

SiCabsorption

V778 Cyg is a galactic silicate carbon star.

Strongemission.

Weaker emission

Absorption

Galactic carbon stars

Spitze

r

ISO

ISO

ISO

ISO

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

Conclusions

A dusty disk around the Red Super Giant star WOH G064 (=IRAS 04553-6825).

Correlation between the 10 m feature peak position and mass loss rate of M-stars.

SiC dust instead of silicate dust around the LMC carbon star IRAS 04496-6958

Aim of our study

1) the dust formation process around these stars.

Investigate the mineralogy of dust around evolved stars in the LMC toconstrain:

2) the enrichment of the interstellar medium with new dust.

3) the nature of the dust that goes into new planetary systems.

Overview 10 m feature in LMC stars