Gregory Clayton Sloan

An Infrared Census of DUST in Nearby Galaxies with Spitzer (DUSTiNGS). IV. Discovery of High-redshift AGB Analogs

The survey for DUST in Nearby Galaxies with Spitzer (DUSTiNGS) identified several candidate Asymptotic Giant Branch (AGB) stars in nearby dwarf galaxies and showed that dust can form even in very metal-poor systems (Z ∼0.008Z ). Here, we present a follow-up survey with WFC3/IR on the Hubble Space Telescope (HST), using filters that are capable of distinguishing carbon-rich (C-type) stars from oxygen-rich (M-type) stars: F127M, F139M, and F153M. We include six star-forming DUSTiNGS galaxies (NGC147, IC 10, Pegasus dIrr, SextansB, SextansA, and SagDIG), all more metal-poor than the Magellanic Clouds and spanning 1 dex in metallicity. We double the number of dusty AGB stars known in these galaxies and find that most are carbon rich. We also find 26 dusty Mtype stars, mostly in IC 10. Given the large dust excess and tight spatial distribution of these M-type stars, they are most likely on the upper end of the AGB mass range (stars undergoing Hot Bottom Burning). Theoretical models do not predict significant dust production in metal-poor M-type stars, but we see evidence for dust excess around M-type stars even in the most metal-poor galaxies in our sample (12 + log(O/H) = 7.26 − 7.50). The low metallicities and inferred high stellar masses (up to ∼10 M ) suggest that AGB stars can produce dust very early in the evolution of galaxies (∼30 Myr after they form), and may contribute significantly to the dust reservoirs seen in high-redshift galaxies.

An Infrared Study of the Circumstellar Material Associated with the Carbon Star R Sculptoris

The asymptotic giant branch (AGB) star R Sculptoris (R Scl) is one of the most extensively studied stars on the AGB. R Scl is a carbon star with a massive circumstellar shell (

Characterization and Calibration of the Infrared Spectrograph on the Spitzer Space Telescope

M_{shell}sim 7.3times10^{-3}~M_{odot}

Standard stars observed with the Infrared Spectrograph on the Spitzer Space Telescope

) which is thought to have been produced during a thermal pulse event

Spitzer Observations of eta Corvi: Evidence at ~1 Gyr for an LHB-Like Delivery of Organics and Water-Rich Material to the THZ of a Sun-Like Star

sim2200

Spitzer high-resolution MIR spectral atlas (Bernard-Salas+, 2009)

years ago. To study the thermal dust emission associated with its circumstellar material, observations were taken with the Faint Object InfraRed CAMera for the SOFIA Telescope (FORCAST) at 19.7, 25.2, 31.5, 34.8, and 37.1

Spectroscopic Study Of Individual Proto-planetary Disks Observed In The Small Magellanic Cloud

mu

An Infrared Spectroscopic Survey of the Small Magellanic Cloud

m. Maps of the infrared emission at these wavelengths were used to study the morphology and temperature structure of the spatially extended dust emission. Using the radiative transfer code DUSTY and fitting the spatial profile of the emission, we find that a geometrically thin dust shell cannot reproduce the observed spatially resolved emission. Instead, a second dust component in addition to the shell is needed to reproduce the observed emission. This component, which lies interior to the dust shell, traces the circumstellar envelope of R Scl. It is best fit by a density profile with

Characteristics Of Hydrocarbon Emission From Herbig Ae/be Stars

n propto r^{alpha}

MC AGB & red supergiants lum. and dM/dt (Groenewegen+, 2009)

where