<i>Spitzer</i>SAGE Survey of the Large Magellanic Cloud. II. Evolved Stars and Infrared Color-Magnitude Diagrams

Blum, Robert; Mould, Jeremy; Olsen, Knut; Frogel, J. A.; Werner, M. W.; Meixner, Margaret; Kemper, F.; Indebetouw, R.; Whitney, B. A.; Meade, M. R.; Babler, B.; Churchwell, E.; Gordon, K. D.; Engelbracht, C. W.; For, Bi-Qing; Misselt, K. A.; Vijh, U.; Leitherer, Claus; Volk, Kevin; Points, Sean; Reach, W. T.; Hora, J. L.; Bernard, J.-P.; Boulanger, F.; Bracker, S.; Cohen, Martin; Fukui, Y.; Gallagher, J.; Gorjian, Varoujan; Harris, Jason; Kelly, Douglas; Kawamura, Akiko; Latter, W. B.; Madden, S.; Mizuno, Akira; Mizuno, N.; Nota, A.; Oey, M. S.; Onishi, Toshikazu; Paladini, R.; Panagia, N.; Pérez‐González, Pablo G.; Shibai, Hiroshi; Sato, Shuji; Smith, Linda J.; Staveley‐Smith, L.; Tielens, A.M.; Ueta, Toshiya; Dyk, Schuyler D. Van; Zaritsky, Dennis

doi:10.1086/508227

Cited by 169 publications

(175 citation statements)

References 49 publications

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“…Vijh et al 2009;Boyer et al 2011) follow the scheme introduced by Blum et al (2006) to divide the found AGB objects into three distinct classes tagged "O-rich", "C-rich", and "Extreme". Recently, efforts were made to interpret the SEDs of these objects (defined by photometry compiled from various catalogues; cf.…”

Section: Extremely Reddened C Starsmentioning

confidence: 99%

Synthetic photometry for carbon-rich giants

Nowotny¹,

Aringer²,

Höfner

et al. 2013

A&A

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Late-type giant stars in the evolutionary stage of the asymptotic giant branch increasingly lose mass via comparatively slow but dense stellar winds. Not only do these evolved red giants contribute in this way to the enrichment of the surrounding interstellar medium, but the outflows also have a substantial influence on the spectro-photometric appearance of such objects. In the case of carbon-rich atmospheric chemistries, the developing cool circumstellar envelopes contain dust grains mainly composed of amorphous carbon. With increasing mass-loss rates, this leads to more and more pronounced circumstellar reddening. With the help of model calculations we aim at reproducing the observational photometric findings for a large sample of well-characterised galactic C-type Mira variables losing mass at different rates. We used dynamic model atmospheres, describing the outer layers of C-rich Miras, which are severly affected by dynamic effects. Based on the resulting structures and under the assumptions of chemical equilibrium as well as LTE, we computed synthetic spectra and synthetic broad-band photometry (Johnson-Cousins-Glass BVRIJHKL M). A set of five representative models with different stellar parameters describes a sequence from less to more evolved objects with steadily increasing mass-loss rates. This allowed us to study the significant influence of circumstellar dust on the spectral energy distributions and the (amplitudes of) lightcurves in different filters. We tested the photometric properties (mean NIR magnitudes, colours, and amplitudes) and other characteristics of the models (mass-loss rates, periods, and bolometric corrections) by comparing these with the corresponding observational data adopted from the literature. Using different kinds of diagrams we illustrate where the models are located in a supposed evolutionary sequence defined by observed C-type Mira samples. Based on comparisons of galactic targets with empirical relations derived for C stars in the Large Magellanic Cloud we discuss the relevance of metallicity and excess carbon (C-O) for the development of dust-driven winds. Having investigated the dynamic model atmospheres from different (mainly photometric) perspectives, we conclude that our modelling approach (meaning the combination of numerical method and a suitable choice of model parameters) is able to describe C-rich long-period variables over a wide range of mass-loss rates, i.e., from moderately pulsating objects without any dusty wind to highly dust-enshrouded Carbon Miras. Thus, we can trace the observed sequence of C-type Miras, which is mainly determined by the mass loss.

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Section: Extremely Reddened C Starsmentioning

confidence: 99%

Synthetic photometry for carbon-rich giants

Nowotny¹,

Aringer²,

Höfner

et al. 2013

A&A

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“…Only the subset of SAGE-Spec sources that had a full 5−37 μm spectrum are shown here. We refer the reader to Blum et al (2006) for a detailed description of the various stellar populations observed in these diagrams and to Paper IV for discussion on the locations of the oxygen-rich AGB candidates and models.…”

Section: Color-magnitude and Color-color Diagramsmentioning

confidence: 99%

“…4, is used in Blum et al (2006) and Paper I to select extreme AGB stars. It is somewhat similar to the K s vs. J − K s CMD.…”

Section: [36] Vs J − [36] Cmdmentioning

confidence: 99%

“…These properties allow in-depth studies of the entire LMC AGB population. One such study, the Spitzer Space Telescope (Werner et al 2004) Legacy program SAGE (Surveying the Agents of a Galaxy's Evolution; Meixner et al 2006), imaged a 7 × 7 • area centered on the LMC and found over 6 million point sources, including thousands of carbon-star candidates (Blum et al 2006;Srinivasan et al 2009). Follow-up spectroscopy from the Infrared Spectrometer (IRS, Houck et al 2004) on Spitzer was obtained as part of the SAGE-Spec program (Kemper et al 2010).…”

Section: Introductionmentioning

confidence: 99%

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The mass-loss return from evolved stars to the Large Magellanic Cloud

Srinivasan

Sargent

Meixner

2011

A&A

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110

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Context. Outflows from asymptotic giant branch (AGB) and red supergiant (RSG) stars inject dust into the interstellar medium. The total rate of dust return provides an important constraint to galactic chemical evolution models. However, this requires detailed radiative transfer (RT) modeling of individual stars, which becomes impractical for large data sets. An alternative approach is to select the best-fit spectral energy distribution (SED) from a grid of dust shell models, allowing for a faster determination of the luminosities and mass-loss rates for entire samples. Aims. We have developed the Grid of RSG and AGB ModelS (GRAMS) to measure the mass-loss return from evolved stars. The models span the range of stellar, dust shell and grain properties relevant to evolved stars. The GRAMS model database will be made available to the scientific community. In this paper we present the carbon-rich AGB model grid and compare our results with photometry and spectra of Large Magellanic Cloud (LMC) carbon stars from the SAGE (Surveying the Agents of Galaxy Evolution) and SAGE-Spec programs. Methods. We generate models for spherically symmetric dust shells using the 2Dust code, with hydrostatic models for the central stars. The model photospheres have effective temperatures between 2600 and 4000 K and luminosities from ∼2000 L to ∼40 000 L . Assuming a constant expansion velocity, we explore five values of the inner radius R in of the dust shell (1.5, 3, 4.5, 7 and 12 R star ). We fix the outer radius at 1000 R in . Based on the results from our previous study, we use amorphous carbon dust mixed with 10% silicon carbide by mass. The grain size distribution follows a power-law and an exponential falloff at large sizes. The models span twenty-six values of 11.3 μm optical depth, ranging from 0.001 to 4. For each model, 2Dust calculates the output SED from 0.2 to 200 μm. Results. Over 12 000 models have dust temperatures below 1800 K. For these, we derive synthetic photometry in optical, nearinfrared and mid-infrared filters for comparison with available data. We find good agreement with magnitudes and colors observed for LMC carbon-rich and extreme AGB star candidates from the SAGE survey, as well as spectroscopically confirmed carbon stars from the SAGE-Spec study. Our models reproduce the IRAC colors of most of the extreme AGB star candidates, consistent with the expectation that a majority of these enshrouded stars have carbon-rich dust. Finally, we fit the SEDs of some well-studied carbon stars and compare the resulting luminosities and mass-loss rates with those from previous studies.

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“…There is also a significant population of background galaxies, uniformly distributed over the SAGE-LMC footprint (Whitney et al 2008;Kozłowski & Kochanek 2009). The SAGE-Spec program (Kemper et al 2010) is a Spitzer spectroscopic follow-up survey designed to verify the initial SAGE-LMC classifications (Meixner et al 2006;Blum et al 2006;Whitney et al 2008) and investigate the nature of sources that could not be identified based on their photometry. Here we report on a point-source, in the SAGE-LMC catalogue 1 identified as SAGE1CJ053634.78-722658.5, (hereafter referred to as SAGE1CJ053634) at moderate redshift (z = 0.14) as derived from the observed wavelength of the polycyclic aromatic hydrocarbon (PAH) features, which is entirely dominated in its IR spectral energy distribution (SED) by warm dust (silicate) emission, rather than emission from star formation which is the case in nearly all other galaxies yet observed.…”

Section: Introductionmentioning

confidence: 99%

TheSpitzerdiscovery of a galaxy with infrared emission solely due to AGN activity

Hony

Kemper

Woods

et al. 2011

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Aims. We present an analysis of a galaxy (SAGE1CJ053634.78-722658.5) at a redshift of 0.14 of which the infrared (IR) emission is entirely dominated by emission associated with the active galactic nucleus. Methods. We present the 5−37 μm Spitzer/IRS spectrum and broad wavelength spectral energy distribution (SED) of SAGE1CJ053634.78-722658.5, an IR point-source detected by Spitzer/SAGE. The source was observed in the SAGE-Spec program and was included to determine the nature of sources with deviant IR colours. The spectrum shows a redshifted (z = 0.14 ± 0.005) silicate emission feature with an exceptionally high feature-to-continuum ratio and weak polycyclic aromatic hydrocarbon (PAH) emission bands. We compare the source with models of emission from dusty tori around AGNs. We present a diagnostic diagram that will help to identify similar sources based on Spitzer/MIPS and Herschel/PACS photometry. Results. The SED of SAGE1CJ053634.78-722658.5 is peculiar because it lacks far-IR emission due to cold dust and a clear stellar counterpart. We find that the SED and the IR spectrum can be understood as emission originating from the inner ∼10 pc around an accreting black hole. There is no need to invoke emission from the host galaxy, either from the stars or from the interstellar medium, although a possible early-type host galaxy cannot be excluded based on the SED analysis. The hot dust around the accretion disk gives rise to a continuum, which peaks at 4 μm, whereas the strong silicate features may arise from optically thin emission of dusty clouds within ∼10 pc around the black hole. The weak PAH emission does not appear to be linked to star formation, as star formation templates strongly over-predict the measured far-IR flux levels. Conclusions. The SED of SAGE1CJ053634.78-722658.5 is rare in the local universe but may be more common in the more distant universe. The conspicuous absence of host-galaxy IR emission places limits on the far-IR emission arising from the dusty torus alone.

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SpitzerSAGE Survey of the Large Magellanic Cloud. II. Evolved Stars and Infrared Color-Magnitude Diagrams

Cited by 169 publications

References 49 publications

Synthetic photometry for carbon-rich giants

Synthetic photometry for carbon-rich giants

The mass-loss return from evolved stars to the Large Magellanic Cloud

TheSpitzerdiscovery of a galaxy with infrared emission solely due to AGN activity

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