Listing of Poster Abstracts

Dust-Driven Mass Loss in Cool Evolved Stars in The SMC: Are AGB Stars the Primary Dust Source at Low Metallicity?

Martha Boyer (STScI)

We estimate the total dust production of cool evolved stars in the Small Magellanic Cloud (SMC), using the 8-μm excess emission as a proxy for the mass-loss rate. We find that Asymptotic Giant Branch (AGB) and red supergiant (RSG) stars produce (8.6–9.5) x10^7 solar masses of dust per year, depending on the fraction of far-infrared sources that belong to the evolved star population (with 10%–50% uncertainty in individual dust-production rates). RSGs contribute the least (<4%), while carbon-rich AGB stars account for 87%–89% of the total dust input from cool evolved stars. We find that AGB stars contribute only 2.1% of the ISM dust. We also estimate the dust input from hot stars and supernovae (SNe), and find that if SNe produce 10^3 solar masses of dust each, then the total SN dust input and AGB input are roughly equivalent.

Dust in Bow Shocks: The Interaction Between Stellar Winds and the ISM

Nick Cox (Instituut voor Sterrenkunde, KU Leuven)

In this contribution we present recent results on a large set of Herschel/PACS observations of AGB stars and red supergiants, obtained as part of the MESS key program. This project focusses on spatially resolved bow shocks and detached shells associated with evolved stars. For over half the sample of almost 80 objects we detect evidence for wind-ISM interaction. Limiting the sample to nearby objects raises the 'detection-rate' to almost 80\%. We present several typical morphological classes that arise from wind-ISM interaction (e.g. fermata-, eye-, ring-, and irregular shapes). From theoretical predictions as well as hydrodynamical simulations we see that the shape and size of these interaction regions is set by a delicate balance of stellar (mass-loss, velocity) and interstellar (density, temperature) properties. Also, the formation of turbulent instabilities predicted by simulations are, for the first time, observed for some objects. In addition to the general survey results we will also highlight a few notable individual objects. It is becoming evident that for many evolved (intermediate-mass) stars their circumstellar material, known to significantly contribute to chemical enrichment of galaxies, is strongly affected by interactions with the surrounding interstellar medium.

Hunting for the Missing Massive Stars in the Galaxy

Nicolas Flagey (CalTech - JPL)

The MIPSGAL 24 microns Galactic Plane Survey has revealed more than 400 compact-extended objects. Less than 15% of these MIPSGAL bubbles (MBs) are known and identified as evolved stars. I will first present the catalog of these objects and their general properties, in terms of morphology, size, broadband fluxes, including results from the Herschel Galactic Plane Survey (HiGal). Then, I will detail some of the follow-up observations obtained to identify the origin of the mid- IR emission and the nature of the unknown objects. In particular, I will focus on: (1) Spitzer/IRS observations of 4 MBs that lead to the discovery of two planetary nebulae with very hot white dwarf, a Wolf- Rayet star and a Luminous Blue Variable candidate; (2) near-IR observations obtained with TripleSpec at Palomar of 13 MBs, that revealed at least 3 new massive stars: (3) recent Herschel/PACS-SED and SPIRE-FTS observations of a 35 additional MBs. I will summarize the results of these follow-up and others in terms of newly discovered massive stars thanks to IR surveys of our Galaxy.

Dust in Historical Galactic Type Ia Supernova Remnants With Herschel

Haley Gomez (Cardiff University)

The relative contributions of low/intermediate mass stars and supernovae to the interstellar dust budget in galaxies is still a controversial topic. Recently, significant amounts of cool dust have been discovered in the ejecta of core-collapse supernovae, but it is not clear whether all supernova remnants produce dust and how much of this survives the passage through the interstellar medium. In this poster, we present recent Herschel results of the dust emission in the Type Ia supernova ejecta of the Kepler and Tycho remnants which has interesting consequences for the "missing iron" problem in Type Ia ejecta.

IRSF/SIRIUS variable star survey in the Magellanic Clouds

Yoshifusa Ita (Astronomical Institute, Tohoku University)

We started the variable star survey in the Large and Small Magellanic Clouds in December 2000. Since then, we keep monitoring an area of 3 square degrees along the bar in the LMC, and also an area of 1 square degree in the central part of the SMC until the end of 2010. In the 10 years, we observed these areas about 80-90 and 100-110 times for LMC and SMC, respectively, with more than 3,000 days baseline. Our survey is the world's first and only one that provides near-infrared time-series data with such a long baseline.

The Initial-Final Mass Relation

Jason Kalirai (STScI)

Over 98% of all stars will end their lives as white dwarfs. The progenitors of these stars lost mass to their surroundings during the late stages of stellar evolution. This is a quiescent process involving winds and thermal pulses on the red giant and asymptotic giant branche. Meauring this mass loss is fundamental to both establish the yield that is returned to the interstellar medium and also to establish tests for stellar evolution theory. Yet, this mass loss from stars to galaxies is very difficult to measure through the study of the giant stars themselves. I will present a new study of stellar mass loss for low mass stars through the stellar initial-final mass relation. By spectroscopically measuring the masses of white dwarfs that are forming in different stellar environments (e.g., over a range of ages), new insights on the stellar yield have recently been established for all stars over a broad range of initial masses, M = 1 - 7 Msun. This work suggests that the relation between initial and final mass is, Mfinal = (0.109 +/- 0.007)*Minitial + (0.428 +/- 0.025) Msun, which directly provides the total integrated mass loss in any population with low mass stars.

The Herschel Planetary Nebula Survey (HerPlaNS)

Djazia Ladjal (University of Denver)

HerPlaNS is a Herschel Open Time program that exploits the unprecedented spatial resolving power in the far infrared of the Herschel Space Observatory to investigate a sample of 11 planetary nebulae (PNe). The aim of the program is to study the chemistry, the energetics and the physical evolution of the nebula by tracing the cold dust component by means of imaging data with PACS and SPIRE and tracing the gas component by means of spectroscopy observations with PACS and SPIRE at different locations in the nebula. Combining both imaging and spectroscopy data will teach us about the interplay between the gas and dust as well as the interaction between the stellar material and the interstellar medium. HerPlaNS offers a novel view of Planetary Nebulae by it spatial spectral and imaging data. In this talk, l will introduce the HerPlaNS program and discuss some of our preliminary results and what they teach us about the final evolution of dust and gas for low and intermediate mass stars.

The Potential of JWST to Measure the Mass-Loss Return from Stars to Galaxies

Margaret Meixner (STScI)

The JWST telescope will have the sensitivity and spectral resolving power to analyze the mass-loss return from stars to galaxies in the Local Volume of galaxies. For example, color magnitude diagrams from photometric imaging with NIRCam and MIRI can be used to identify dusty evolved stars which can then be compared to precomputed models such as GRAMS to derive dust mass loss returns. Spectroscopy of sources with MIRI or NIRSpec can help identify the dust species with type of star and environment. Time monitoring of recent supernova explosions can be traced to look for the signatures of dust production. Measurements of planetary nebulae in nearby galaxies can support studies of dust production vs. metal abundance in stars.

The GRAMS Grid: Determination of the LMC Dust Budget with Population Scale Radiative Transfer Modeling

David Riebel (Johns Hopkins University)

In order to understand the evolved star contribution to the luminosity and dust-mass return to galaxies, we present results from the first application of the Grid of Red Supergiant and Asymptotic Giant Branch ModelS (GRAMS) model grid to the entire evolved stellar population of the Large Magellanic Cloud (LMC). GRAMS is a pre-computed grid of 80,843 radiative transfer (RT) models of evolved stars and circumstellar dust shells composed of either silicate or carbonaceous dust. We have fit GRAMS models to 30,000 Asymptotic Giant Branch (AGB) and Red Supergiant (RSG) stars in the LMC, using 12 bands of photometry from the optical to the mid-infrared. Our modeling results have allowed us to accurately determine the dust injection rate from evolved stars in the LMC through direct summation. I will also discuss the current progress of the SAGE-Var program, to be published late this year.

Thirty Years of SN 1980K: Evidence for Light Echoes

Ben Sugerman (Goucher College)

We report optical and mid-infrared photometry of SN 1980K between 2004 and 2009, which show slow monotonic fading consistent with previous spectroscopic and photometric observations made 8 to 17 years after outburst. The slow rate-of-change over two decades suggests that this evolution may result from scattered and thermal light echoes off of extended circumstellar material. We find that unresolved echoes from a circumstellar shell ~14 lt-yr from the progenitor, and containing about 0.02$ solar masses of carbon-rich dust, can explain the broadband spectral and temporal evolution. The size, mass and dust composition are in good agreement with the contact discontinuity observed in scattered echoes around SN 1987A.

Parametrized Study of Mass Loss

Lee Anne Willson (Iowa State University)

We have used the streamlined, parameter-based Bowen code to study the effects of physical processes and model parameters on mass loss rates and atmospheric structure for AGB stars. We also have developed a process for taking the most reliable elements of models and combining these with the most reliable results from observations to produce a prescription for AGB mass loss. This process uses observations to choose models that fit the observed deathline, the location where dlogM/dt = dlogL/dt along an evolutionary track. It then uses models to examine the dependence of the mass loss rates on stellar and model parameters, with particular emphasis on the slope dlogMdot/dlogL taken along an evolutionary track R(L, M, composition, mixing length). To explore all 7 stellar and model parameters for a range of L for each initial M and composition we have produced a grid of ~100,000 models. For all cases, dlogMdot/dlogL at the deathline is large – median values around 12 – meaning the duration of the mass loss phase is short and the modulation of mass loss rates by shell flashing will be large. This also means that for the purposes of population studies the main data required is the location of the deathline, the quantity that is also best amenable to observational constraints.