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Benjamin Sargent

GRAMS Modeling of Oxygen-Rich Dust around Red Supergiant and AGB Stars in the Large Magellanic Cloud. Benjamin Sargent Collaborators: Sundar Srinivasan , Dave Riebel , Martha Boyer, Margaret Meixner March 28, 2012 Space Telescope Science Institute. Image: Gordon & SAGE team

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Benjamin Sargent

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  1. GRAMS Modeling of Oxygen-Rich Dust around Red Supergiant and AGB Stars in the Large Magellanic Cloud Benjamin Sargent Collaborators: SundarSrinivasan, Dave Riebel, Martha Boyer, Margaret Meixner March 28, 2012 Space Telescope Science Institute Image: Gordon & SAGE team (Meixner et al. 2006)

  2. Lifecycle of Matter: How much mass is lost from stars? AGB Stars: O-rich and C-rich dust produced RSG Stars: O-rich only

  3. Modeling Evolved Stars • Assume a spherical cow … • R-2 density drop-off from assumption of constant mass loss • Drawing not to scale! • Rout = 1000*Rmin assumption

  4. GRAMS: Grid of Red supergiant and AGB ModelS • GRAMS computed using 2Dust (Ueta & Meixner2003) radiative transfer modeling code • http://www.stsci.edu/science/2dust/grams_models.cgi • GRAMS  returns Mass Loss Rate, Luminosity, and Dust Chemistry

  5. Color-Color Diagram • O-rich models • C-rich models • O-rich AGBs • C-rich AGBs • Extreme AGBs • RSGs • O-rich (spec) • C-rich (spec) From Sargent et al 2011 X-axis (K-[3.6]) is stellar color, Y-axis ([3.6]-[24]) is overall IR color

  6. Comparison to Other Work • Generally, good agreement, except GRAMS MLRs disagree with G09 for low MLRs • GRAMS uses one dust type for all models; G09 used many dust types, but no dependence upon MLR, so dust type not behind factor x6 MLR discrepancy

  7. O-rich AGB Dust Properties • SEDs: U, B, V, I from MCPS (Zaritsky et al 1997); J, H, Ks from 2MASS (Skrutskie et al 2006), IRAC and MIPS-24 from SAGE • Right, SED of oxygen-rich (O-rich) AGB star; 2Dust (Ueta & Meixner 2003) model of O-rich AGB (Sargent et al 2010) • But …

  8. One Dust Type Doesn’t Fit All

  9. Isolating Dust Emission • SED is fit by GRAMS, star is subtracted • Measure centroid of features, continuum slope

  10. Spitzer-IRS Spectroscopic Studies of AGBs and RSGs • Average AGB 10μm feature centroid displaced to shorter λ‘s than RSGs’ (Sargent et al, in prep) • Similar discrepancy seen between Miras and non-Miras by Marengo et al (2001)

  11. RSG vs AGB Silicates • Star-subtracted continuum slope relatively independent of 10 μm silicate feature centroid

  12. RSG vs AGB Silicates, con’t • RSG shells have hotter dust, but if continuum slope were affecting centroid, hotter dust would mean shorter-wavelength centroids

  13. Conclusions • NASA ADAP grant NNX11AB06G • GRAMS model grid useful for determining mass loss from AGB and RSG stars • Difference between AGB and RSG average 10 μm feature centroid. Different avg dust optical properties? • Silicate feature peak wavelength difference not due to temperature effect on continuum • Thank you!

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