The timescales on which astronomical dust grows remain poorly understood, with important consequences for our understanding of processes like circumstellar disk evolution and planet formation.A number of post-asymptotic giant branch stars are found to host optically thick, dust- and gas-rich circumstellar discs in Keplerian orbits. These discs exhibit evidence of dust evolution, similar to protoplanetary discs; however since post-AGB discs have substantially shorter lifetimes than protoplanetary discs they may provide new insights on the grain-growth process. We examine a sample of post-AGB stars with discs to determine the FIR and sub-mm spectral index by homogeneously fitting a sample of data from \textit{Herschel}, the SMA and the literature. We find that grain growth to at least hundreds of micrometres is ubiquitous in these systems, and that the distribution of spectral indices is more similar to that of protoplanetary discs than debris discs. No correlation is found with the mid-infrared colours of the discs, implying that grain growth occurs independently of the disc structure in post-AGB discs. We infer that grain growth to $\sim$mm sizes must occur on timescales $<<10^{5}$ yr, perhaps by orders of magnitude, as the lifetimes of these discs are expected to be $\lesssim10^{5}$~yr and all objects have converged to the same state. This growth timescale is short compared to the results of models for protoplanetary discs including fragmentation, and may provide new constraints on the physics of grain growth.
Spectroscopic studies have demonstrated that nearly all Galactic globular clusters (GCs) harbour multiple stellar populations with different chemical compositions. Moreover, colour-magnitude diagrams based exclusively on Strömgrem photometry have allowed us to identify and characterise multiple populations along the RGB of a large number of clusters. In this paper we show for the first time that Strömgren photometry is also very effcient at identifying multiple populations along the AGB, and demonstrate that the AGB of M3, M92, NGC362, NGC1851, and NGC6752 are not consistent with a single stel…
The initial conditions for the mass loss during the asymptotic giant branch (AGB) phase are set in their extended atmospheres, where, among others, convection and pulsation driven shocks determine the physical conditions. High resolution observations of AGB stars at (sub)millimetre wavelengths can now directly determine the morphology, activity, density, and temperature close to the stellar photosphere. We used the Atacama Large Millimeter/submillimeter Array (ALMA) high angular resolution observations to resolve the extended atmospheres of four of the nearest AGB stars: W Hya, Mira A, R Dor a…
We present a photometric and spectroscopic study of multiple populations along the asymptotic-giant branch (AGB) of the intermediate-metallicity globular clusters (GCs) NGC2808 and NGC6121 (M4). Chemical abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Fe, Co, Ni, Zn, Y, and Ce in AGB stars from high-resolution FLAMES+UVES@VLT spectra are reported for both clusters. Our spectroscopic results have been combined with multi-wavelength photometry from the HST UV survey of Galactic GCs and ground-based photometry, plus proper motions derived by combining stellar positions from ground-based image…
Post-AGB stars are the final stage of evolution of low-intermediate mass stars (M<8 Solar Masses). Those in binary systems have stable circumbinary discs. Using data from Herschel (PACS/SPIRE), we extend the SEDs of 50 galactic post-AGB binary systems to sub-millimetre wavelengths and use the slope of the SED as a diagnostic tool to probe the presence of large grains. Using a Monte Carlo radiative transfer code (MCMax), we create a large grid of models to quantify the observed spectral indices and use the presence of large grains in the disc as a proxy for evolution.
Herbig Ae/Be objects are pre-main sequence stars surrounded by gas- and dust-rich circumstellar discs. These objects are in the throes of star and planet formation, and their characterisation informs us of the processes and outcomes of planet formation processes around intermediate mass stars. Here we analyse the spectral energy distributions of disc host stars observed by the Herschel Open Time Key Programme `Gas in Protoplanetary Systems'. We present Herschel/PACS far-infrared imaging observations of 22 Herbig Ae/Bes and 5 debris discs, combined with ancillary photometry spanning ultraviolet…
We present a near-complete catalog of the metal-rich population of Thermally-Pulsing Asymptotic Giant Branch stars in the northwest quadrant of M31. This metal-rich sample complements the equally complete metal-poor Magellanic Cloud AGB catalogs produced by the SAGE program. Our catalog includes HST wide-band photometry from the Panchromatic Hubble Andromeda Treasury survey, HST medium-band photometry used to chemically classify a subset of the sample, and Spitzer mid- and far-IR photometry that we have used to isolate dust-producing AGB stars. We have detected 346,623 AGB stars; these include…
The heavy mass loss observed in evolved asymptotic giant branch (AGB) stars is usually attributed to a two-stage process: atmospheric levitation by pulsation-induced shock waves, followed by radiative acceleration of newly formed dust grains. The dust transfers momentum to the surrounding gas through collisions and thereby triggers a general outflow. Radiation-hydrodynamical models of M-type AGB stars suggest that these winds can be driven by photon scattering -- in contrast to absorption -- on Fe-free silicate grains of sizes 0.1--1\,$μ$m. In this paper we study photometric constraints for wi…
New UBV-photometry obtained in 2000-2008 is presented for the post-AGB star IRAS 22272+5435=V354 Lac. The star showed semi-regular light variations with varying amplitudes. The maximal amplitude did not exceed 0.5 in V-band. For 2000-2008, we have found a photometric period near 128 days. The analysis of long-term observations in 1990-2008 reveals variations with two close periods: 128 and 131 days, causing amplitude modulation. The V-(B-V) diagram shows a clear correlation: the star is generally bluer when brighter. From our UBV data, we derive E(B-V)=0.5 and conclude that the spectral type o…
We present a multiple stellar population (MSP) study of the globular cluster (GC) NGC~6752. We show that our new photometric CN index accurately traces the CN and the nitrogen abundances in cool giants, finding the discrete double red giant branch (RGB) and asymptotic giant branch (AGB) sequences with number ratios between the CN-weak and the CN-strong populations of \nrgb\ = 25:75 ($\pm$3; RGB) and 79:21 ($\pm$13; AGB). The discrepancy in these number ratios suggests that a significant fraction of the low-mass \cns\ stars failed to evolve into the AGB phase. However, unlike previous studies, …
We introduce new color indices $cn^\prime_{\rm JWL}$ (= $Ca_{\rm CTIO} - Ca_{\rm JWL}$) and $ch_{\rm JWL}$ [=$(JWL43 - b) - (b-y)$], accurate photometric measures of the CN band at $λ$3883 and the CH G band, respectively, in the study of the multiple populations (MPs) in globular clusters (GCs). Our photometric CN--CH relation for a large number of red-giant branch (RGB) in M5 shows that the evolutions of the CN and CH between the CN-w and CN-s populations are not continuous. Armed with our new color indices, we investigate the MPs of NGC 6723, finding the RGB populational number ratio of $n$(…
Context. The asymptotic giant branch (AGB) phase marks the end of the evolution for low- and intermediate-mass stars, which are fundamental contributors to the mass return to the interstellar medium and to the chemical evolution of galaxies. The detailed understanding of mass loss processes is hampered by the poor knowledge of the luminosities and distances of AGB stars. Aims. In a series of papers we are trying to establish criteria permitting a more quantitative determination of luminosities for the various types of AGB stars, using the infrared (IR) fluxes as a basis. An updated compilation…
Using our ingeniously designed new filter systems, we investigate the multiple stellar populations of the RGB and AGB in the GC M5. Our results are the following. (1) Our cn_jwl index accurately traces the nitrogen abundances in M5, while other color indices fail to do so. (2) We find bimodal CN distributions both in the RGB and the AGB sequences, with the number ratios between the CN-weak (CN-w) and the CN-strong (CN-s) of n(CN-w):n(CN-s) = 29:71(+/- 2) and 21:79(+/- 7), respectively. (3) We also find the bimodal photometric [N/Fe] distribution for M5 RGB stars. (4) Our cn_jwl-[O/Fe] and cn_j…
We aim to investigate mass loss and luminosity in a large sample of evolved stars in several Local Group galaxies with a variety of metalliticies and star-formation histories: the Small and Large Magellanic Cloud, and the Fornax, Carina, and Sculptor dwarf spheroidal galaxies. Dust radiative transfer models are presented for 225 carbon stars and 171 oxygen-rich evolved stars for which spectra from the Infrared Spectrograph on Spitzer are available. The spectra are complemented with available optical and infrared photometry to construct spectral energy distributions. A minimization procedure wa…
We present the results of our search for low- and intermediate mass evolved stars in the outer Galaxy using AllWISE catalogue photometry. We show that the [3.4]-[12] versus [4.6]-[22] colour-colour diagram is most suitable for separating C-rich/O-rich AGB and post- AGB star candidates. We are able to select 2,510 AGB and 24,821 post-AGB star candidates. However, the latter are severely mixed with the known young stellar objects in this diagram.
Aims: We explore the wealth of high quality photometric data provided by data release 2 of the Gaia mission for long period variables (LPVs) in the Large Magellanic Cloud. Our goal is to identify stars of various types and masses along the Asymptotic Giant Branch. Methods: For this endeavour, we developed a new multi-band approach combining Wesenheit functions W_{RP,BP-RP} and W_{K_s,J-K_s} in the Gaia BP, RP and 2MASS J, K_s spectral ranges, respectively, and use a new diagram (W_{RP,BP-RP}-W_{K_s,J-K_s}) versus K_s to distinguish between different kinds of stars in our sample of LPVs. We use…
The carbon-to-oxygen (C/O) ratio of asymptotic giant branch (AGB) stars constitutes an important index of evolutionary and environment/metallicity factor. We develop a method for mass C/O classification of AGBs in photometric surveys without using periods. For this purpose we rely on the slopes in the tracks of individual stars in the colour-magnitude diagram. We demonstrate that our method enables the separation of C-rich and O-rich AGB stars with little confusion. For the Magellanic Clouds we demonstrate that this method works for several photometric surveys and filter combinations. As we re…
We selected a sample of post-AGB candidates in the Magellanic Clouds on the basis of their near- and mid-infrared colour characteristics. Fifteen of the most optically bright post-AGB candidates were observed with the South African Large Telescope in order to determine their stellar parameters and thus to validate or discriminate their nature as post-AGB objects in the Magellanic Clouds. The spectral types of absorption-line objects were estimated according to the MK classification, and effective temperatures were obtained by means of stellar atmosphere modelling. Emission-line objects were cl…
(abridged) Variability is a key property of stars on the asymptotic giant branch (AGB). Their pulsation period is related to the luminosity and mass-loss rate (MLR) of the star. Long-period variables (LPVs) and Mira variables are the most prominent of all types of variability of evolved stars. However, the reddest, most obscured AGB stars are too faint in the optical and have eluded large variability surveys. Our goal is to obtain a sample of LPVs with large MLRs by analysing WISE W1 and W2 light curves (LCs) for about 2000 sources, photometrically selected to include known C-stars with the 11…
Post-AGB stars are exquisite probes of AGB nucleosynthesis. However, the previous lack of accurate distances jeopardised comparison with theoretical AGB models. The $Gaia$ Early Data Release 3 ($Gaia$ EDR3) has now allowed for a breakthrough in this research landscape. In this study, we focus on a sample of single Galactic post-AGBs for which chemical abundance studies were completed. We combined photometry with geometric distances to carry out a spectral energy distribution (SED) analysis and derive accurate luminosities. We subsequently determined their positions on the HR-diagram and compar…
The evolution and lifetimes of thermally pulsating asymptotic giant branch (TP-AGB) stars suffer from significant uncertainties. In this work, we analyze the numbers and luminosity functions of TP-AGB stars in six quiescent, low metallicity ([Fe/H] $\lesssim -0.86$) galaxies taken from the ANGST sample, using HST photometry in both optical and near-infrared filters. The galaxies contain over 1000 TP-AGB stars (at least 60 per field). We compare the observed TP-AGB luminosity functions and relative numbers of TP-AGB and RGB stars, to models generated from different suites of TP-AGB evolutionary…
Stellar winds observed in asymptotic giant branch (AGB) stars are usually attributed to a combination of stellar pulsations and radiation pressure on dust. Shock waves triggered by pulsations propagate through the atmosphere, compressing the gas and lifting it to cooler regions, which create favourable conditions for grain growth. If sufficient radiative acceleration is exerted on the newly formed grains through absorption or scattering of stellar photons, an outflow can be triggered. Strong candidates for wind-driving dust species in M-type AGB stars are magnesium silicates (Mg$_2$SiO$_4$ and…
We present 43 GHz VLA spectra for 51 AGB sources with the goal of verifying an infrared (IR) color cut intended to separate Carbon-rich (C) and Oxygen-rich (O) AGB sources throughout the Galaxy. The color cut is a simple line in the $[K_s]-[A]$ versus $[A]-[E]$ color-color diagram based on 2MASS and MSX photometry, and was originally derived from SiO detection rates in the Bulge Asymmetries and Dynamical Evolution (BAaDE) sample. The division is fully supported by the spectra presented here, which show that SiO maser detections lie on the O-rich side, and SiO nondetections and a single HC$_3$N…
Asymptotic giant branch (AGB) stars are significant contributors to the chemical enrichment of the interstellar medium (ISM) of galaxies. It is therefore essential to constrain the AGB contribution to the dust budget in galaxies. Recent estimates of the total dust injection rate to the Large and Small Magellanic Clouds (LMC and SMC; Riebel et al. 2012, Boyer et al. 2012, Srinivasan et al. in prep) have used data from the Spitzer Space Telescope SAGE (Surveying the Agents of Galaxy Evolution; Meixner et al. 2006) and SAGE-SMC (Gordon et al. 2011) surveys. When sorted by dust chemistry, the data…
Mapping the Inner Milky Way with Infrared-Derived Distances to AGB Stars
University of New Mexico（新墨西哥大学）；Inter-University Centre for Astronomy and Astrophysics (IUCAA)（大学间天文学与天体物理学中心）；National Radio Astronomy Observatory（国家射电天文台）
Debris disks, the tenuous rocky and icy remnants of planet formation, are believed to be evidence for planetary systems around other stars. The JCMT/SCUBA-2 debris disk legacy survey 'SCUBA-2 Observations of Nearby Stars' (SONS) observed 100 nearby stars, amongst them HD~76582, for evidence of such material. Here we present imaging observations by JCMT/SCUBA-2 and \textit{Herschel}/PACS at sub-millimetre and far-infrared wavelengths, respectively. We simultaneously model the ensemble of photometric and imaging data, spanning optical to sub-millimetre wavelengths, in a self-consistent manner. A…
Certain types of large amplitude AGB variable are proving to be powerful distance indicators that will rival Cepheids in the JWST era of high precision infrared photometry. These are predominantly found in old populations and have low mass progenitors. At the other end of the AGB mass-scale, large amplitude variables, particularly those undergoing hot bottom burning, are the most luminous representatives of their population. These stars are less than one Gyr old, are often losing mass copiously and are vital to our understanding of the integrated light of distant galaxies as well as to chemica…
A number of empirical correlations that allows us to calculate the effective temperature and surface gravity for a set evolved post-AGB and RV Tauri stars are determined using as calibrators the intrinsic colours of 2MASS (Two Micron All Sky Survey) photometry. We have analyzed a total sample of 36 stars where 25 are post-AGB stars and 11 are RV Tauri stars, respectively. A group of 11 stars with parallaxes measures were used as calibrators of the absolute magnitude. The result for T$_{\rm eff}$ and log g from intrinsic colours (J-H)$_{0}$ and (H-K$_{s}$)$_{0}$ at the near-infrared pass bands …
The visually brightest stars in globular clusters (GCs) are the ones evolving off the asymptotic giant branch (AGB) and passing through spectral types F and A--the "yellow" post-AGB (yPAGB) stars. yPAGB stars are potentially excellent "Population II" standard candles for measuring extragalactic distances. A recent survey of the Galactic GC system, using uBVI photometry to identify stars of low surface gravities with large Balmer discontinuities, discovered a candidate luminous yPAGB star in the GC M19 (NGC 6273), designated ZNG 4. The same survey also identified a bright, hotter candidate blue…
We present millimetre (SMA) and sub-millimetre (SCUBA-2) continuum observations of the peculiar star KIC 8462852 which displayed several deep and aperiodic dips in brightness during the Kepler mission. Our observations are approximately confusion-limited at 850 $μ$m and are the deepest millimetre and sub-millimetre photometry of the star that has yet been carried out. No significant emission is detected towards KIC 8462852. We determine upper limits for dust between a few 10$^{-6}$ M$_{\oplus}$ and 10$^{-3}$ M$_{\oplus}$ for regions identified as the most likely to host occluding dust clumps a…
By using self-consistent dynamic model atmospheres which simulate pulsation-enhanced dust-driven winds of AGB stars we studied in detail the influence of (i) pulsations of the stellar interiors, and (ii) the development of dusty stellar winds on the spectral appearance of long period variables with carbon-rich atmospheric chemistry. While the pulsations lead to large-amplitude photometric variability, the dusty envelopes cause pronounced circumstellar reddening. Based on one selected dynamical model which is representative of C-type Mira variables with intermediate mass loss rates, we calculat…
The UK Infrared Telescope M33 monitoring project. VI. Feedback from dusty stellar winds across the galactic disc
School of Astronomy, Institute for Research in Fundamental Sciences (IPM)（基础科学研究所）；Lennard-Jones Laboratories, Keele University（基尔大学）；Department of Physics, Sharif University of Technology（谢里夫理工大学）；School of Physics, Birjand University（比尔詹德大学）
We present the results of our survey of 1612 MHz circumstellar OH maser emission from asymptotic giant branch (AGB) stars and red supergiants (RSGs) in the Large Magellanic Cloud. We have discovered four new circumstellar maser sources in the LMC, and increased the number of reliable wind speeds from IR stars in the LMC from 5 to 13. Using our new wind speeds, as well as those from Galactic sources, we have derived an updated relation for dust driven winds: $v_{exp} \propto Z L^{0.4}$. We compare the sub-solar metallicity LMC OH/IR stars with carefully selected samples of more metal-rich OH/IR…
By tracing the distribution of cool dust in the extended envelopes of post-AGB stars and (proto)-planetary nebulae ((P)PNe) we aim to recover, or constrain, the mass loss history experienced by these stars in their recent past. The Far-Infrared Surveyor (FIS) instrument on board the AKARI satellite was used to obtain far-infrared maps for a selected sample of post-AGB stars and (P)PNe. We derived flux densities (aperture photometry) for 13 post-AGB stars and (P)PNe at four far-infrared wavelengths (60, 90, 140, and 160 um). Radial (azimuthally averaged) profiles are used to investigate the pre…
Stellar population synthesis (SPS) models are a key ingredient of many galaxy evolution studies. Unfortunately, the models are still poorly calibrated for certain stellar evolution stages. Of particular concern is the treatment of the thermally-pulsing asymptotic giant branch (TP-AGB) phase, as different implementations lead to systematic differences in derived galaxy properties. Post-starburst galaxies are a promising calibration sample, as TP-AGB stars are thought to be most prominently visible during this phase. Here, we use post-starburst galaxies in the NEWFIRM medium-band survey to asses…
It is commonly believed that winds of cool giants in their late evolutionary stages are driven by radiative pressure on dust grains, but the actual grain species responsible for driving winds of M-type AGB stars are still a matter of debate (see Höfner, this volume). The optical properties of the dust particles responsible for initiating the outflow affect the stellar spectra in two ways: (i) indirectly, through their influence on the dynamical structure of the atmosphere/envelope and the resulting molecular features, and (ii) directly, by changes of the spectral energy distribution due to abs…
We present low spectral resolution molecular interferometric observations at 1.2 mm obtained with the Combined Array for Research in Millimetre-wave Astronomy (CARMA) towards the C-rich AGB star IRC+10216. We have mapped the emission of several lines of SiS, H13CN, SiO, and SiC2 in the ground and first excited vibrational states with a high angular resolution of 0.25 arcsec. These observations have allowed us to partially resolve the emission of the envelope at distances from the star <50 stellar radii (R*), where the stellar wind is mainly accelerated. The structure of the molecular emission …
We have conducted a highly sensitive census of the evolved-star population in the metal-poor dwarf galaxy Leo P and detected four asymptotic giant branch (AGB) star candidates. Leo P is one of the best examples of a nearby analog of high-redshift galaxies because of its primitive metal content (2% of the solar value), proximity, and isolated nature, ensuring a less complicated history. Using medium-band optical photometry from the Hubble Space Telescope (HST), we have classified the AGB candidates by their chemical type. We have identified one oxygen-rich source which appears to be dusty in bo…
(abridged) Stable circumbinary discs around evolved post-Asymptotic Giant branch (post-AGB) binary systems show many similarities with protoplanetary discs around young stellar objects. These discs can provide constraints on both binary evolution and the formation of macrostructures within circumstellar discs. Here we focus on one post-AGB binary system: IRAS08544-4431. We aim to refine the physical model of IRAS08544-4431 with a radiative transfer treatment and continue the near-infrared and mid-infrared interferometric analysis covering the H-, K-, L-, and N-bands. We aim to capture the prev…
Periodic activity on the (sub)mm surface of the AGB star Mira A
Chalmers University of Technology（查尔姆斯理工大学）；Observatorio Astronómico Nacional (OAN-IGN)（国家天文台）；European Southern Observatory (ESO)（欧洲南方天文台）；Uppsala University（乌普萨拉大学）
We have carried out a search for optically visible post-AGB candidates in the Small Magellanic Cloud (SMC). We used mid-IR observations from the Spitzer Space Telescope to select optically visible candidates with a mid-IR excess. We obtained low-resolution optical spectra for 801 candidates. After removing contaminants and poor quality spectra, the final sample comprised of 63 post-AGB/RGB candidates of A - F spectral type. Using the spectra, we estimated the stellar parameters: effective temperature, surface gravity and [Fe/H]. We also estimated the reddening and deduced the luminosity using …
We combine variability information from the MAssive Compact Halo Objects (MACHO) survey of the Large Magellanic Cloud (LMC) with infrared photometry from the Spitzer Space Telescope Surveying the Agents of a Galaxy's Evolution (SAGE) survey to create a dataset of ~30 000 variable red sources. We photometrically classify these sources as being on the first ascent of the Red Giant Branch (RGB), or as being in one of three stages along the Asymptotic Giant Branch (AGB): oxygen-rich, carbon-rich, or highly reddened with indeterminate chemistry ("extreme" AGB candidates). We present linear period-l…
JWST NIRCam and MIRI Reveal the Dust-Producing AGB Population of NGC 6822
Institute for Astronomy, University of Edinburgh（爱丁堡大学天体物理研究所）；UK Astronomy Technology Centre, Royal Observatory（英国天文技术中心，皇家天文台）；IPAC, California Institute of Technology（加州理工学院IPAC）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；Department of Physics & Engineering Physics, Morgan State University（摩根州立大学物理与工程物理系）；Department of Physics, Maynooth University（梅努斯大学物理系）；Space Telescope Science Institute（太空望远镜科学研究所）；NASA Goddard Space Flight Center（美国国家航空航天局戈达德太空飞行中心）；SETI Institute（搜寻地外文明研究所）；Centre for Astrophysics Research, Department of Physics, Astronomy and Mathematics, College Lane Campus, University of Hertfordshire（赫特福德大学College Lane校区物理、天文与数学系天体物理研究中心）
We present the third and final part of a census of Asymptotic Giant Branch (AGB) stars in Local Group dwarf irregular galaxies. Papers I and II presented the results for WLM and IC 1613. Included here are Phoenix, LGS 3, DDO 210, Leo A, Pegasus dIrr, and Sextans A. Spitzer photometry at 3.6, 4.5, 5.8, and 8 are presented, along with a more thorough treatment of background galaxy contamination than was presented in papers I and II. We find that at least a small population of completely optically obscured AGB stars exists in each galaxy, regardless of the galaxy's metallicity, but that higher-me…
12CO and 13CO lines, as well as a mm-wave continuum, have been observed for a sample of 22 OH/IR stars in directions within 2 degrees of the Galactic Centre. Photometry data have been gathered from the literature to construct SEDs and to determine pulsational variability. Radiative transfer models have been used to interpret the data. All stars in the sample were detected in at least one CO line, and 8 objects were detected in 324 GHz continuum. Based on luminosity criteria, the sample is divided into 17 objects that most likely lie within the inner Galactic Bulge, and 5 objects that are most …
We present photoelectric and spectral observations of a hot candidate proto-planetary nebula - early B-type supergiant with emission lines in spectrum - IRAS 19336-0400. The light and color curves display fast irregular brightness variations with maximum amplitudes dV=0.30 mag, dB=0.35 mag, dU=0.40 mag and color-brightness correlations. By the variability characteristics IRAS 19336-0400 appears similar to other hot proto-planetary nebulae. Based on low-resolution spectra in the range lambda 4000-7500 A we have derived absolute intensities of the emission lines H_alpha, H_beta, H_gamma, [SII], …
Context: Post-Asymptotic Giant Branch (AGB) binaries are surrounded by stable dusty and gaseous disks similar to the ones around young stellar objects. Whereas significant effort is spent on modeling observations of disks around young stellar objects, the disks around post-AGB binaries receive significantly less attention, even though they pose significant constraints on theories of disk physics and binary evolution. Aims: We want to examine the structure of and phenomena at play in circumbinary disks around post-AGB stars. We continue the analysis of our near-infrared interferometric image of…
(Abridged) Dust radiative transfer models are presented for 101 carbon stars and 86 oxygen-rich evolved stars in the Magellanic Clouds for which 5-35 \mum\ {\it Spitzer} IRS spectra are available. The spectra are complemented with available optical and infrared photometry to construct the spectral energy distribution. A minimisation procedure is used to fit luminosity, mass-loss rate and dust temperature at the inner radius. Different effective temperatures and dust content are also considered. Periods from the literature and from new OGLE-III data are compiled and derived. The O-rich stars ar…
The total dust return rate from AGB and RSG star outflows is 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. Another 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. 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 …
In order to determine the composition of the dust in the circumstellar envelopes of oxygen-rich asymptotic giant branch (AGB) stars we have computed a grid of modust radiative-transfer models for a range of dust compositions, mass-loss rates, dust shell inner radii and stellar parameters. We compare the resulting colours with the observed oxygen-rich AGB stars from the SAGE-Spec Large Magellanic Cloud (LMC) sample, finding good overall agreement for stars with a mid-infrared excess. We use these models to fit a sample of 37 O-rich AGB stars in the LMC with optically thin circumstellar envelope…
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 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 published dataset consists of thousands of evolved…
(abridged)Variability is a key property of stars on the asymptotic giant branch (AGB). Their pulsation period is related to the luminosity and mass-loss rate of the star. The long-period variables (LPVs) and Mira variables are the most prominent of all types of variability of evolved stars. The reddest, most obscured AGB stars are too faint in the optical and have eluded large variability surveys. Selection criteria are derived based on colour-colour and colour-magnitude diagrams from the combination of VISTA Magellanic Cloud (VMC) survey, Spitzer IRAC and AllWISE data. After eliminating LPVs …
