Listing of Talk Abstracts

Stellar Ejecta: Steady, Eruptive and Explosive Mass Loss from Stars to Galaxies

Mike Barlow (UCL)

Mass loss events from stars enrich galaxies in heavy elements and dust. Steady mass loss from AGB stars has long been known to be an important contributor to the nitrogen, s-process element and dust enrichment of galaxies but do AGB stars dominate dust production? Core-collapse supernovae (CCSNe) from massive stars dominate the production of oxygen, while the question of whether massive stars or AGB stars dominate carbon production is still unresolved. The discovery of large quantities of dust in high redshift galaxies, emitting less than a billion years after the Big Bang, has forced a reassessment of the contribution of massive stars to the dust content of galaxies, whether via dusty Eta Carina-type eruptive events or by dust formation in supernova ejecta. In addition, the contributions from a recently recognised class of objects called `supernova imposters', which may originate from super-AGB stars or from massive star LBV events, are still to be pinned down. I will summarise recent work bearing on these questions, including observations from the Spitzer and Herschel space observatories.

Mass Return Through Supernova Remnants

William Blair (JHU/STScI)

While supernovae are one of the primary manufacturers of processed material in the universe, it is through supernova remnants and the interaction of shock waves with the surrounding regions of space that this material gets distributed back and mixed into the ISM. SNe and SNRs provide both material and energy for this process, and drive a wide range of physical phenomena, and on a broad range of physical scales. Detailed multiwavelength studies of individual young SNRs provide considerable insight to the topic of mass return, but the physical processes involved are complicated and not always easy to sort out. For example, are SNe/SNRs primarily creators or destroyers of dust? (If your answer is “yes,” then you agree with the experts.) How do the significant inhomogeneities seen in the elemental distributions of young SNRs get thoroughly mixed and distributed on larger spatial scales to create general ISM enrichment and observed trends such as galactic abundance gradients, as seen in many spiral galaxies? On even larger scales, the collective action of SNe and stellar winds in starbursts and star-forming regions are sufficient to energize and enrich the ISM of entire galaxies, and indeed feed the enrichment of the intergalactic medium through outflows such as seen so dramatically in M82. In this talk, I will provide an observational overview of many of these topics to set the stage for broader discussions of mixing and chemical enrichment.

Crystalline Silicate Dust in the Circumstellar Environment of Evolved Stars.

Joris Blommaert (Instituut voor Sterrenkunde, KU Leuven)

Crystalline silicates have been found around different types of evolved stars, including (post-) AGB stars and Planetary Nebulae. I will present Herschel-PACS spectroscopy covering the 69 micron forsterite dust feature of evolved stars. With the spectral resolution and sensitivity of PACS we can fit the profile of the forsterite feature which is very sensitive to temperature and the composition of olivine dust. By studying the forsterite feature in a wide range of evolved stars and from different populations (including Galactic Bulge and LMC) we want to determine the role of forsterite in the dust formation in circumstellar environments.

Matching the Luminosity Function of TP-AGB Stars from the SAGE Survey of the LMC with Population Synthesis Model Predictions

Gustavo Bruzual (CRyA)

We test the capability of stellar population synthesis models that incorporate a state-of-the-art description of the evolution of stars in the TP-AGB to reproduce the luminosity function of these stars derived from the SAGE survey of the LMC. We model the LMC stellar population by means of Montecarlo simulations which follow the star formation history of Harris & Zaritsky (2009). I will show that our models reproduce well the observed LF only when an adequate description of the reprocessing of the radiation of the central star in the dusty envelope of TP-AGB stars is taken into account (Gonzalez-Lopezlira et al., this conference).

Mass Return from Unresolved Stellar Populations

Stephane Charlot (Institut d'Astrophysique de Paris)

I will review mass return from unresolved stellar populations, with particular emphasis on how the bulk rates of mass loss from stellar populations are calculated, how the metallicity and dust mass return factors can be estimated from stellar population models, and the importance of stellar mass-loss processes for galaxy evolution models.

Dust Formation in Core-Collapse Supernovae

Geoffrey Clayton (Lousiana State University)

Our study of dust formation and evolution in CCSNe in the local universe has been motivated by the discovery, both surprising and exciting, that primordial galaxies contain large dust masses. The observed dust masses are up to 10 times that seen in the Milky Way, implying that dust was forming in large quantities less than 1 Gyr after the Big Bang. If CCSNe were responsible for all the dust seen in these early galaxies then 0.1-1 solar masses per SN would be required. However, the mechanisms for dust formation are quite complex. At the very earliest times, only dust from CCSNe will be available, while dust production from evolved AGB stars will not be significant for several hundred million years. The production of dust may be aided by grain growth through accretion in the interstellar medium using the SN and AGB dust as seeds. At present, detailed study of interstellar dust in primordial galaxies is not possible. Nor can SNe be observed in these galaxies at such great distances. However, a window into this problem can be opened by studying dust produced by CCSNe and their massive star progenitors in the local universe. Our program has significantly increased the sample of CCSNe for which dust masses have been measured. Our results so far show that small masses of dust (0.0001 - 0.01 solar masses) seem to be typical. These estimates are much smaller than the amount needed to account for the dust masses seen in primordial galaxies. However, recent Herschel observations of SN 1987A imply the presence of 0.4-0.7 solar masses of dust reopening the possibility of CCSNe as significant dust producers.

The Mass Loss Return from Nearby Evolved Stars as Deduced by Herschel

Leen Decin (Instituut voor Sterrenkunde, KULeuven)

Mass loss is the dominating factor in the post-main sequence evolution of most stars but many aspects of the mass loss mechanism(s) are still not understood. The Herschel Space Observatory offers the astronomers some unique instruments (HIFI, PACS and SPIRE) to study circumstellar environments around evolved stars. We present the latest results obtained in the framework of few guaranteed time and open time (key) programmes, including MESS, HIFISTARS, etc. The main focus of this talk will be on (i) the determination of the mass-loss history, (ii) the gaseous and dust chemical content of the surrounding envelope, and (iii) the complex interaction region between circumstellar and interstellar medium.

Massive Star Feedback of the 30 Doradus Region

Emile Doran (University of Sheffield)

The 30 Doradus region in the Large Magellanic Cloud offers the richest census of massive stars in the Local Group. The high mass-loss rates and ionising fluxes of the OB and Wolf-Rayet stars in 30 Doradus greatly influence the ISM, dispersing and enriching the gas. Its proximity enables spatially resolved photometry and spectroscopy of the brightest members, primarily from HST/WFC3 (de Marchi et al. 2011) and VLT/FLAMES (Evans et al. 2011). Estimates of the integrated mechanical and radiative feedback from O stars, B supergiants and Wolf-Rayet stars, located within 15 arcmin (225 pc) of R136a, have been made from a combination of calibrations and tailored analyses. We estimate the escape fraction of ionising photons from 30 Doradus and compare the results of our direct census of R136 with Starburst99 predictions.

The Evolution of Dust in the Local and Distant Universe

Eli Dwek (NASA/GSFC)

Interstellar dust is created in the quiescent winds of AGB stars and in the explosive ejecta of supernova remnants. The same SNe that form the dust also destroy dust: a fraction of the newly formed dust is destroyed when the reverse shock propagates back into the ejecta, and the pre-existing dust is destroyed by the supernova blast waves that expand into the general interstellar medium (ISM). Local observations of interstellar depletions, the extinction of starlight, and the infrared emission from the diffuse ISM suggest that most of the refractory elements must be depleted onto dust. This requires a delicate balancing act between the efficiencies of dust formation and destruction processes. These processes can be explored using a general chemical evolution code. The talk will present the results of calculations for the local solar neighborhood, as well as local and high-redshift galaxies.

Moderated Discussion: Mass Loss--Stars to Galaxies

John (Jay) Gallagher (University of Wisconsin-Madison)

Mass return from stars is a major branch of the evolutionary cycle of baryons as they collect within and are returned from galaxies. This meeting considers a range of stellar mass loss processes involving different classes of stars which we will discuss in this session. As a starting point we can consider basic distinctions between various classes of stellar outflows and how they might affect their host galaxies; e.g., energetic versus quiescent mass loss; chemically enriched winds; dust forming cases, ionized or molecular gas; etc. Equally important are the ages and locations of mass losing stars, as well as their mass loss rates since these serve to link the fate of ejected mass to properties of galactic environments. Our discussion therefore will attempt to take these factors into account to build an initial picture of the "astrophysical ecology" associated with stellar mass loss.

The Rapid Dust Evolution in Galaxies in Recent Cosmic History

Haley Gomez (Cardiff University)

Recently, it's become possible to investigate the origin and evolution of dust in thousands of galaxies using data from the H-ATLAS. The most massive H-ATLAS galaxies show a large increase in the dust content five billion years ago compared to the present epoch. These observations are difficult to explain using standard dust models, one possibility could be contributions from a non-stellar source of dust in galaxies e.g. grain growth in the interstellar medium; this would imply that less than 10% of dust in the interstellar medium would be provided by stars. I will discuss other possible explanations for this evolution in the dust mass in recent cosmic history.

Introducing Mass-Loss Self-Consistently in Population Synthesis Models

Rosa A. Gonzalez-Lopezlira (UNAM, AIfA )

I will talk about how we have introduced spectra of mass-losing TP-AGB stars in the latest Bruzual-Charlot models. Based on the stellar masses, luminosities, metallicities, temperatures, C/O ratios and mass loss rates, at each evolutionary stage and for each stellar type we calculate pulsation period, wind expansion velocity, dust composition, gas-to-dust mass ratio and opacity. It is important to highlight that both dust composition and gas-to-dust ratio vary in time for each type of star. Given the opacity and the dust composition, we then calculate the reprocessing of the radiation of the central star in the dusty envelope. Since the connections between stellar properties, mass loss, and envelope properties are treated in a consistent way, we can calculate the emission of stars with higher and lower mass loss rates than those in the tracks, in order to explore the impact of varying mass loss rates on the integrated properties of stellar populations.

Models of Dynamic Atmospheres and Winds of Cool Giants

Susanne Höfner (Uppsala University)

Models of dynamic atmospheres and winds of cool giants have improved significantly in recent years, as shown by detailed comparisons with observations of individual stars. Theoretical predictions of mass loss rates and dust yields, covering large regions of stellar parameter space, are, however, still few and far between. In this talk I will give an overview of current wind models for cool giants, discussing their strong sides and shortcomings, as well as the resulting implications for stellar evolution models.

Regulation of Galactic Evolution by Long-Term Stellar Mass-Loss: N-Body Simulations

Bruno Jungwiert (Astronomical Institute ASCR - Prague)

Mass-loss from low- and intermediate-mass stars substantially regulates star formation and transfer of angular momentum in galaxies, thus critically affecting their structure, dynamics and gas depletion time-scales. I will describe various implementations of time-dependent stellar-mass into N-body models of galaxy evolution. Based on these, I will present new estimates of gas inflow rate into the central hundred parsecs of spiral and lenticular galaxies due to combined effects of bar-induced transport and gas return from stellar populations of disks, bulges and central star clusters. The effects of stellar mass-loss on strength, pattern speed and destruction/renewal of bars, as well as on star formation rate and abundance gradients in galactic disks, will also be discussed.

The Mineralogy of the Dust Returned to the Interstellar Medium of the Magellanic Clouds

Ciska Kemper (ASIAA)

Within the context of the hugely successful SAGE-LMC and SAGE-SMC surveys, Spitzer photometry observations of the Large and Small Magellanic Clouds have revealed millions of infrared point sources in each galaxy. The brightest infrared sources are generally dust producing and mass-losing evolved stars, and several tens of thousands of such stars have been classified. From the infrared photometry, it is relatively straight-forward to derive dust mass loss rates, however to study in detail the composition of the dust produced, infrared spectroscopy has proved invaluable. SAGE-Spec is the spectroscopic follow-up to the SAGE-LMC survey, and it has obtained Spitzer-IRS 5-40 micron spectroscopy of about 200 sources in the LMC. Combined with archival data from other programs, observations at a total of ~1000 pointings have been obtained in the LMC, while ~250 IRS pointings were observed in the SMC. Of these, a few hundred pointings represent dust producing and mass-losing evolved stars, covering a range in colors, luminosities, and thus mass-loss rates. Red Supergiants and O-rich and C-rich AGB stars are the main dust producers and are well represented in the spectroscopic sample. The infrared spectroscopy covers resonances of common astrophysical minerals, such as silicates, oxides and silicon carbide, and can thus be used to pin down the composition of the dust produced. In this talk I will review what we know about the mineralogy of dust producing evolved stars, and discuss their relative importance in the total dust budget.

Binary Effects in Mass Flow Variations in AGB Envelopes

Hyosun Kim (ASIAA)

Recent observations of strikingly well-defined spirals around asymptotic giant branch (AGB) stars point to the importance of the presence of binary companions to explain the properties of the evolved giant envelopes. In a binary system, the structure of the mass lost by an AGB star is altered (1) by modifying the distribution of the wind velocity due to the reflex motion of the AGB star and (2) by gathering a fraction of the wind material into the gravitational potential of the companion so as to create a gravitational density wake. We examine, and compare, these two effects associated with a binary companion using high-resolution three-dimensional hydrodynamical simulations. Our study on the details of density and velocity distribution of the modulated AGB wind in a simple hydrodynamic model reveals the importance of hydrodynamic effects, which were not found in previous analytic and ballistic calculations. It is found that the reflex motion of the AGB star determines the overall shape of the outflowing envelope in which the gravitational influence of the companion star is spatially restricted. Attention is focused on the morphological and kinematic properties of the circumstellar pattern as potential probes for the binary properties. In particular, we present the envelope shapes as a function of viewing inclination angle. In addition to a spiral pattern providing evidence of binary, we also emphasize the arc pattern representing the same structure viewed at different inclination angles. In particular, the arc pattern becomes spherically symmetric when the orbital motion of the AGB star is significantly slower than its wind speed. Furthermore, in comparable-mass binary systems, the gravitational wake of the companion forms clumpy shapes on the rather broader arc pattern caused by the reflex motion of the mass-losing star.

Mass Loss in Evolutionary Models of Low- and Intermediate-Mass Stars

Dr.  Paola Marigo (University of Padova, Dept. of Physics and Astronomy)

Mass loss by stellar winds significantly affects the post main-sequence evolution of low- and intermediate-mass stars (0.9 <= M/Msun <= 6-8), as they climb along their Hayashi lines in the HR diagram. In this presentation I review the main formalisms for the mass-loss rates of current use in stellar evolutionary models, both for the RGB and AGB phases. The expected dependencies on basic stellar parameters (mass, luminosity, effective temperature, chemical composition), and the critical uncertainties of the underlying theories of stellar winds, are discussed in terms of their impact on the evolutionary properties of these stars, i.e. lifetimes, initial-final mass relation, nucleosynthesis and chemical yields.

Mass Loss from Massive Stars: What We Know and What We (I) Don't

Philip Massey (Lowell Observatory)

The chemical enrichment of galaxies depends upon the mass loss of stars, their numbers, and the composition of the returned material. In this talk I'll briefly cover our knowledge of the mass loss rates from O and B stars, Luminous Blue Variables, Wolf-Rayet stars, and red supergiants. I will emphasize the main uncertainties in our understanding of stellar winds, at least from the point of view of an observer.

Supernovae & Gamma-Ray Bursts

Maryam Modjaz (New York University)

I will review the main types of the growing zoo of cataclysmic cosmic explosions, namely the different flavors of Supernovae and GRBs, as well as the most recent estimates of their respective explosions rates and of the SN-GRB connection. Furthermore, I will present and critically assess observational estimates of ejecta masses and, to lesser extent, ejecta composition for the various subtypes. Finally I will outline the promise of current and future transient surveys for understanding the diverse deaths of stars, specifically as a function of environment.

Lots of Dust from Massive Galactic WR Stars!

Anthony Moffat (Université de Montréal)

While no WN stars are known to make dust, many WC stars, with 40% C in their winds, are prolific producers of amorphous-carbon dust. This occurs continuously or episodically via compression due to wind-wind collisions in binary WC+OB systems or, more frequently, from cooler, late-type WC8-9 stars, many (all?) of which may also be binary. Up to 10^{-6} Mo/a in pure carbon dust can be produced in a single object. Current on-going NIR line- and continuum-imaging surveys are revealing hundreds of new Galactic WR stars (with thousands more waiting to be discovered), including an increasingly recognized population of WC8-9 stars towards the Galactic centre. If the Galaxy contains 100-1000 WC8-9 stars, these along with other WC+OB systems could yield a total of 10^{-4} – 10^{-3} Mo/a in Galactic dust, similar to other more conventional dust producers such as AGB, RG, novae and SNe at 10^{-3}, and PNe and protostars at 10^{-4} Mo/a. In the early Universe, massive WC stars could have been the first sources of heavy elements even before SNe, providing the first building blocks for the formation of planets.

The Properties of Gas in and Around Dwarf Galaxies and Its Role in Regulating Star Formation

Jill Naiman (University of California, Santa Cruz)

In this contribution, I'll discuss the ability of dwarf galaxies to accumulate ISM gas and trigger star formation before and after they are accreted into the MW halo. By including self gravity, mass and energy input from stellar winds, realistic cooling and a star formation prescription in three dimensional hydrodynamical simulations, we build a self consistent model for gas retention in  these systems as they are incorporated into the Milky Way as either inhabitants of a group of galaxies or cold filaments or in isolation. Ample evidence would be presented in this talk that the stellar makeup of dwarf galaxies in the MW halo is largely determined by their pre-merger environment.

AGB Dust Production at Different Metallicities

Ambra Nanni (SISSA)

In parallel with a new upcoming release of the Padova-Trieste stellar tracks covering the evolution from the pre-main sequence up to the end of the Asymptotic Giant Branch (AGB) phase, we present new calculations of the dust yields ejected by low- and intermediate-mass stars (0.9 Msun <= M <= 6 Msun) during the Thermally Pulsating AGB (TP-AGB) phase. In M-stars (with C/O < 1) we follow the evolution of corundum, silicates (olivine, pyroxene and quartz), periclase and iron, whereas for C-stars (with C/O > 1) we consider amorphous carbon, silicon carbide and iron dust. The dynamical wind model and the growth of dust grains are followed assuming the Ferrarotti & Gail (2006) scheme, but different for a few important modifications mostly related to the treatment of the dust opacities. We discuss the dependence of (a) the dust mineralogy along the AGB phase and (b) the integrated dust yields as a function of the initial mass (hence age) and metallicity of the AGB mass-losing stars. Several choices of the initial metallicity have been adopted, Z=0.001, 0.004, 0.006, 0.008, 0.015, 0.017, for both scaled-solar and alpha-enhanced chemical mixtures. A few important relations, such as those linking i) the mass-loss rates vs the terminal wind velocities and ii) the mass-loss rates vs the pulsation periods, are compared to observations of AGB stars in the Galaxy and Magellanic Clouds.

"Properties of Mass Loss From Supernova Progenitors Determined From Radio Observations"

Nino Panagia (STScI)

Studies of radio supernovae (RSNe), the earliest stages of supernova remnant (SNR) formation, over the past 30 years include more than two dozen detected objects and about 200 upper limits. These studies have lead to accurate estimates of the density and the structure of the circumstellar material. By inference, for each SN we have determined the corresponding mass loss rate and the evolution of the pre-supernova stellar wind, so as to ascertain the nature of the exploding stars and reveal the last stages of stellar evolution before explosion.

Supernovae Dust and Metal Enrichment Observed in Young Supernova Remnants

Jeonghee Rho (SETI Institute/NASA Ames Research Center)

Whether supernovae (SNe) are major dust creators in the Universe has been a long-standing debate. Recent Spitzer and Herschel observations of the young supernova remnants (SNRs) of Cas A and SN1987A detected a significant amount of dust. We serendipitously identified a dust feature at 21 micron from a Crab-like SNR, G54.1+0.3 with the Spitzer IRS. The 21-micron dust feature is remarkably similar to that of Cas A. The dust coincides with the ejecta emission, suggesting that dust has been formed in ejecta. We also present detection of cold dust from G54.1+0.3 using SHARCII (at 350 micron), LABOCA (at 870 micron), and archival Herschel images. We present spectral fitting of SED using continuous distributions of ellipsoidal (CDE) grain models and find that silica (SiO2) is mainly responsible for the 21-micron feature. We will show an estimate the dust mass using the SED from 5 to 870 micron. We also present another three young supernova remnants which show infrared emission as produced by ejecta and dust. The ejecta are identified with broad ionic lines using ISO/LWS spectra, and we combined ISO and Herschel photometer data to derive the dust mass associated the ejecta. The element of carbon has been known to be underabundant in Cas A compared with the expected values in nucleosysntheses models. We present detections of Carbon Monoxide (CO) molecules, the fundamental band using AKARI spectra and the first overtone using near-infrared narrow-band imaging with Palomar 200 inch telescope. AKARI IRC spectra unambiguously reveal the broad characteristic CO ro-vibrational band profile at 4.6 micron, implying on-going chemical processes of molecules, dust, and ejecta. A dozen of CO spectra were extracted, all of which show CO including at the position of unshocked ejecta at the center. It indicates that CO molecules form in the ejecta at an early phase. A simple CO emission model in LTE were applied to the spectra to obtain first-order estimates of the excitation temperatures and CO masses. CO are warm (2000 K) and show very high densities. Our observations suggest that significant amounts of carbon have been locked up in CO and less carbon is available to return to the ISM. This raises the fundamental question of the amount of carbon returning to the ISM from supernovae. We will discuss its implication in molecule formation and gas enrichment of supernovae, the origin of dust in the early Universe and the dust cycle in the ISM. Finally, we will present possible SOFIA observations to study the mass loss return from stars to galaxies.

The Panchromatic Hubble Andromeda Treasury: Bright UV Stars in the Bulge of M31

Philip Rosenfield (University of Washington)

As part of the Panchromatic Hubble Andromeda Treasury multi-cycle program, we observed a 12” × 6.5” area of the bulge of M31 with the WFC3/UVIS filters F275W and F336W. From these data we have assembled a sample of ~8000 UV-bright, old stars, vastly larger than previously available. We use updated Padova stellar evolutionary tracks to classify these hot stars into three classes, including Post-AGB stars (P-AGB), Post-Early AGB (PE-AGB) stars and AGB-manqué stars. P-AGB stars are the end result of the asymptotic giant brach (AGB) phase and are expected in a wide range of stellar populations, whereas PE-AGB and AGB-manqué stars are the result of insufficient envelope masses to allow a full AGB phase, and are expected to be particularly prominent at high helium or alpha abundances when the mass loss on the red giant branch is high. Our data support previous claims that most UV-bright sources in the bulge are likely hot (extreme) horizontal branch stars (EHB) and their progeny. We construct the first radial profiles of these stellar populations, and show that they are highly centrally concentrated, even more so than the integrated UV or optical light. However, we find that this UV-bright population does not dominate the total UV luminosity at any radius, as we are detecting the progeny of the EHB stars that are the likely source of the UV excess (UVX) found in several elliptical and bulges of large spiral galaxies. We calculate that only a few percent of MS stars in the central bulge can have gone through the HP-HB phase and that this percentage decreases strongly with distance from the center. We also find that the surface density of hot UV-bright stars has the same radial variation as that of low-mass X-ray binaries. I will discuss our findings, as well as age, metallicity, and abundance variations as possible explanations for the observed radial variation in the UV-bright population.

GRAMS Modeling of Oxygen-Rich Dust Around Red Supergiant and AGB Stars in the Large Magellanic Cloud

Benjamin Sargent (Space Telescope Science Institute)

My colleagues and I are studying mass loss from evolved stars. Such stars lose their own mass in their dying stages, and in their expelled winds they form stardust. To model mass loss from these evolved stars, my colleagues and I have constructed GRAMS: the Grid of Red supergiant and Asymptotic giant branch star ModelS. These GRAMS radiative transfer models are fit to optical through mid-infrared photometry of red supergiant (RSG) stars and asymptotic giant branch (AGB) stars. In these studies, we fit GRAMS models to the photometry and spectroscopy of LMC evolved star candidates identified from the SAGE-LMC (PI: M. Meixner) Spitzer Space Telescope Legacy survey. I will discuss the construction and validation of the Oxygen-rich (O-rich) models in GRAMS. I will also discuss how Spitzer Infrared Spectrograph (IRS) spectral studies of the dust produced by RSG and O-rich AGB stars in the LMC constrain the GRAMS O-rich models, especially with regard to the properties of the dust grains in these stars' circumstellar shells. These spectral studies make use of data obtained by the SAGE-Spec (PI: F. Kemper) Spitzer Legacy program and other Spitzer programs.

How Stars Die: Infrared Spectroscopy of Dusty Carbon Stars in the Local Group

Greg Sloan (Cornell University)

During the cryogenic phase of the Spitzer Space Telescope mission, the Infrared Spectrograph observed over 200 carbon stars in the Local Group, covering environments with a range of metallicities. These studies have revealed that the strength of SiC dust emission and acetylene absorption both depend on metallicity, but the most surprising result is the lack of a dependency of the overall dust opacity on metallicity. Exploring the budget of free carbon in these systems reveals another surprise: One would expect more dust at lower metallicities, not less. The lack of a dependence of dust quantity on metallicity suggests that it is the quantity of dust that triggers the final mass-loss episodes in a star's lifetime. This presentation explains the reasoning leading to this suggestion and discusses the consequences for how stars enrich their environment with freshly fused elements.

Carbonaceous Dust in the GRAMS Grid

Sundar Srinivasan (Institut d'Astrophysique de Paris (IAP))

Asymptotic giant branch (AGB) as well as red supergiant (RSG) stars recycle large amounts of nuclear processed material into the interstellar medium in the form of dust and gas. To aid in deriving the total dust return from these evolved stars to a galaxy, we constructed the Grid of RSG and AGB ModelS (GRAMS), which includes >12000 radiative transfer models for carbon stars. The models span a large range of photosphere and dust shell parameters, including effective temperature, surface gravity, dust shell inner radius and optical depth. The grid has already been used to determine the total AGB/RSG dust injection rate to the Large Magellanic Cloud (LMC), showing the significant (and perhaps dominant) contribution to the dust return from carbon stars. The present version of the grid is computed for a fixed set of dust properties -- a 9:1 mixture (by mass) of amorphous carbon and silicon carbide. Our group is currently using spectra for Large Magellanic Cloud (LMC) carbon stars from the SAGE-Spec program (PI: Kemper) to derive the most appropriate dust mixture to use, by varying the grain mass ratio and including other dust species. We show that the model-derived dust mass-loss rates (MLR) are very sensitive to the opacities provided as input. For instance, the dust MLR varies by a factor of 2--4 depending on the choice of amorphous carbon optical constants, several sets of which are available in the literature. We address this issue by comparing the results of modeling for various opacities. This study is an important first step towards incorporating an improved description of carbon dust into the GRAMS grid and quantifying the uncertainties inherent in the choice of dust composition, which will in turn help us fine-tune the global dust injection from carbon stars.

Mass Loss from the Structured Winds of Hot, Massive Stars

Jon Sundqvist (University of Delaware)

Hot, massive stars possess strong stellar winds driven by line scattering of the star's intense continuum radiation field. But while initial models assumed a stationary and smooth wind, it is nowadays observationally as well as theoretically well-established that these winds are indeed highly structured. This talk discusses consequences of the small-scale structures associated with the strong instability inherent to the line-driving of hot star winds. We demonstrate the importance of a proper treatment of such wind clumping to accurately interpret wind diagnostics and obtain reliable estimates of mass-loss rates. Particularly, while some first attempts to account for clumping suggested drastic reductions (of an order of magnitude, or even more) of previously accepted mass-loss rates for O-stars, this talk shows how by using new, improved descriptions of clumpy winds, we can alleviate these big discrepancies among observed values, values predicted by the line-driven wind theory, and values included in current models of massive star evolution.

Ejecta Around Evolved Massive Stars Observed with Herschel

Chloi Vamvatira-Nakou (University of Liege)

In the context of 'Mass-loss of Evolved StarS' Herschel guaranteed time key programme, we have obtained imaging and spectroscopic observations of nebulae associated with Luminous Blue Variable and Wolf-Rayet stars using PACS, one of the three instruments onboard the Herschel Space Observatory. The detailed study of these nebulae, which radiate strongly in the IR due to the heating of dust, is crucial for understanding the massive stars evolution. These observations allow us to study the dust and the gas in the nebulae and understand the mass-loss history of their central star. A description of these observations and results of the data analysis of the LBV nebula WRAY 15-751 are presented. A second fainter and more extended shell was detected around the star. Modeling of the dust nebula was performed and dust masses were derived. Our spectroscopic observations allowed us to derive the N/O abundance, the characteristics of the HII region and of the photo-dissociation region of the nebula, providing a better estimate of the total mass returned to the interstellar medium.

Intermediate Mass Evolved Star Winds - An Observer's Perspective

Jacco van Loon (Keele University)

Intermediate mass stars span lifetimes from less than a dynamical crossing time of a galaxy to exceeding the age of the Universe, and their mass loss has therefore contributed to galaxy evolution from the epoch of galaxy assembly to the present day. In this review I discuss the measurement of stellar mass loss from intermediate mass stars: how does the mass loss vary in time and with stellar mass, metallicity, and other parameters? What is the observed effect of mass loss from intermediate mass stars on the galaxy they inhabit? How certain are these measurements and conclusions, and how could we improve both?

Circumstellar Envelopes: AGB Mass-Loss Signatures

Eva Villaver (Universidad Autonoma de Madrid)

We have investigated the imprint of low-and intermediate-mass stellar winds in the Interstellar Medium (ISM). We show the structures expected to form according to standard mass-loss parameterizations, what is the information that can be recovered, and how the sizes of the envelopes are strongly linked to the assumed timescales of heavy mass-loss rates. Moreover, stars are expected to move according to the kinematical galactic component to which they belong. We show how the stellar motion influences the structure, dynamics, and the history of mass-loss that can be inferred from the ejected envelope.

The Resolved Enrichment Histories of Early Type Galaxies

Jakob Walcher (Leibniz Insitute fo Astrophysics)

Early-type galaxies are known to be enhanced in alpha-elements, in accordance with their old ages and therefore short formation timescales. We will present results obtained by spectral fitting of high S/N spectra of such early type galaxies with the improved "differential stellar population models" of Walcher etal., 2009. Through extensive simulation we show that we can recover the enrichment history of the stellar populations per galaxy. We find a tight correlation between the age of the stellar population and the alpha-enhancement, much tighter than the correlation between velocity dispersion and enhancement. Based on the chemical signature we separate the galaxies in our sample according to the origin of the younger stellar populations in two groups: 1) those dominated by an extended in-situ star formation and 2) those dominated by minor mergers.

Circumstellar Dust in the Remnant of Kepler's Type Ia Supernova

Brian Williams (NASA Goddard Space Flight Center)

Kepler's supernova remnant, the remains of the supernova of 1604, is known to be the result of a Type Ia supernova, and shows IR, optical, and X-ray evidence for an encounter between the blast wave and a dense circumstellar medium (CSM), the only remnant of a Type Ia supernova to do so. As such, it provides a unique opportunity to study the pre-supernova outflow from the progenitor system via the interaction with a fast shock wave, as well as dust grain formation and destruction processes. Although Kepler is the result of a Type Ia, the characteristics of the progenitor system remain a mystery. It is unknown, for instance, whether the dense CSM was generated by a companion star to the supernova or by the pre-supernova star itself. We present low-resolution 7.5-38 $mu$m IR spectra of the remnant, obtained with the {it Spitzer Space Telescope}. Spectra of regions where the blast wave is encountering the CSM show strong features at 10 and 18 $mu$m. These spectral features are most consistent with various silicate particles, likely formed in the stellar outflow from the progenitor system during the AGB stage of evolution. While it is possible that some features may arise from freshly formed ejecta dust, morphological evidence suggests that it is more likely that they originate from dust in the CSM. The hottest dust in the remnant originates in the regions of dense, radiatively shocked clumps of gas, identified in optical images. Models of collisionally heated dust show that such shocks are capable of heating grains to temperatures of $> 150$ K. The significant quantities of silicate dust are consistent with an O-rich AGB star in the progenitor system, but the lack of crystalline silicate features in the spectrum limits the mass-loss rate of the star to 10$^{-5}$ solar masses per year.

The Chemical Impact of Stellar Mass Loss

Rosemary Wyse (Johns Hopkins University)

I will discuss recent results concerning the elemental abundances of stars in the Milky Way Galaxy and in satellite dwarf galaxies, and what can thus be inferred about the stellar Initial Mass Function and mixing processes in the interstellar medium. I will also briefly discuss gas retention/outflow in dwarf galaxies.