GRAMS Modeling of Oxygen-Rich Dust around Red

Supergiant and AGB Stars in the Large Magellanic Cloud

Benjamin SargentCollaborators: Sundar Srinivasan, Dave Riebel, Martha Boyer, Margaret Meixner

March 28, 2012

Space Telescope Science Institute

Image: Gordon & SAGE team (Meixner et al. 2006)

Lifecycle of Matter: How much mass is lost from stars?

AGB Stars: O-rich and C-rich dust produced RSG Stars: O-rich only

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

GRAMS: Grid of Red supergiant and AGB ModelS

• GRAMS computed using 2Dust (Ueta & Meixner 2003) radiative transfer modeling code

• http://www.stsci.edu/science/2dust/grams_models.cgi• GRAMS returns Mass Loss Rate, Luminosity, and

Dust Chemistry

O-rich C-rich

Teff (K) 2100-4700 2600-4000

Lum (Lsun) 103 - 106 103 – 105.5

τ10 (O-rich)τ11 (C-rich)

10-4 - 26 10-3 - 4

Rmin (Rstar) 3 - 15 1.5 - 12

Color-Color Diagram• O-rich models• C-rich models• O-rich AGBs• C-rich AGBs• Extreme AGBs• RSGs• O-rich (spec)• C-rich (spec)

X-axis (K-[3.6]) is stellar color, Y-axis ([3.6]-[24]) is overall IR color

From Sargent et al 2011

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

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 …

One Dust Type Doesn’t Fit All

Isolating Dust Emission

• SED is fit by GRAMS, star is subtracted• Measure centroid of features, continuum slope

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)

RSG vs AGB Silicates

• Star-subtracted continuum slope relatively independent of 10 μm silicate feature centroid

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

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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