We derive the fundamental parameters (temperature and luminosity) of 107 619 Hipparcos stars and place these stars on a true Hertzsprung–Russell diagram. This is achieved by comparing bt-settl model atmospheres to spectral energy distributions (SEDs) created from Hipparcos, Tycho, Sloan Digital Sky Survey, DENIS, Two Micron All Sky Survey, MSX, AKARI, IRAS and Wide-field Infrared Survey Explorer data. We also identify and quantify from these SEDs any infrared excesses attributable to circumstellar matter. We compare our results to known types of objects, focusing on the giant branch stars. Giant star dust production (as traced by infrared excess) is found to start in earnest around 680 L⊙.

Fundamental parameters and infrared excesses of Hipparcos stars

We investigate the infrared (IR) properties of cool, evolved stars in the Small Magellanic Cloud (SMC), including the red giant branch (RGB) stars and the dust-producing red supergiant (RSG) and asymptotic giant branch (AGB) stars using observations from the Spitzer Space Telescope Legacy program entitled Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity SMC, or SAGE-SMC. The survey includes, for the first time, full spatial coverage of the SMC bar, wing, and tail regions at IR wavelengths (3.6-160 μm). We identify evolved stars using a combination of near-IR and mid-IR photometry and point out a new feature in the mid-IR color-magnitude diagram that may be due to particularly dusty O-rich AGB stars. We find that the RSG and AGB stars each contribute 20% of the global SMC flux (extended + point-source) at 3.6 μm, which emphasizes the importance of both stellar types to the integrated flux of distant metal-poor galaxies. The equivalent SAGE survey of the higher-metallicity Large Magellanic Cloud (SAGE-LMC) allows us to explore the influence of metallicity on dust production. We find that the SMC RSG stars are less likely to produce a large amount of dust (as indicated by the [3.6] – [8] color). There is a higher fraction of carbon-rich stars in the SMC, and these stars appear to reach colors as red as their LMC counterparts, indicating that C-rich dust forms efficiently in both galaxies. A preliminary estimate of the dust production in AGB and RSG stars reveals that the extreme C-rich AGB stars dominate the dust input in both galaxies, and that the O-rich stars may play a larger role in the LMC than in the SMC.

Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud (SAGE-SMC). II. Cool Evolved Stars

We have updated our publicly available dust radiative transfer code (HOCHUNK3D) to include new emission processes and various three-dimensional (3D) geometries appropriate for forming stars. The 3D geometries include warps and spirals in disks, accretion hotspots on the central star, fractal clumping density enhancements, and misaligned inner disks. Additional axisymmetric (2D) features include gaps in disks and envelopes, "puffed-up inner rims" in disks, multiple bipolar cavity walls, and iteration of disk vertical structure assuming hydrostatic equilibrium (HSEQ). We include the option for simple power-law envelope geometry, which, combined with fractal clumping and bipolar cavities, can be used to model evolved stars as well as protostars. We include non-thermal emission from polycyclic aromatic hydrocarbons (PAHs) and very small grains, and external illumination from the interstellar radiation field. The grid structure was modified to allow multiple dust species in each cell; based on this, a simple prescription is implemented to model dust stratification. We describe these features in detail, and show example calculations of each. Some of the more interesting results include the following: (1) outflow cavities may be more clumpy than infalling envelopes. (2) PAH emission in high-mass stars may be a better indicator of evolutionary stage than the broadband spectral energy distribution slope; and related to this, (3) externally illuminated clumps and high-mass stars in optically thin clouds can masquerade as young stellar objects. (4) Our HSEQ models suggest that dust settling is likely ubiquitous in T Tauri disks, in agreement with previous observations.

/pdf/three-dimensional-radiation-transfer-in-young-stellar-2opbll7ala.pdf

Three-dimensional radiation transfer in young stellar objects

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 models of evolved stars and circumstellar dust shells composed of either silicate or carbonaceous dust. We fit GRAMS models to {approx}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 data set consists of thousands of evolved stars with individually determined evolutionary parameters such as luminosity and mass-loss rate. The GRAMS grid has a greater than 80% accuracy rate discriminating between oxygen- and carbon-rich chemistry. The global dust injection rate to the interstellar medium (ISM) of the LMC from RSGs and AGB stars is on the order of 2.1 Multiplication-Sign 10{sup -5} M{sub Sun} yr{sup -1}, equivalent to a total mass injection rate (including the gas) into the ISM of {approx}6 Multiplication-Sign 10{sup -3} M{sub Sun} yr{sup -1}. Carbon stars inject two and a half times as much dust into the ISM as do O-rich AGB stars, but the same amount ofmore » mass. We determine a bolometric correction factor for C-rich AGB stars in the K{sub s} band as a function of J - K{sub s} color, BC{sub K{sub s}}= -0.40(J-K{sub s}){sup 2} + 1.83(J-K{sub s}) + 1.29. We determine several IR color proxies for the dust mass-loss rate (M-dot{sub d}) from C-rich AGB stars, such as log M-dot{sub d} = (-18.90/((K{sub s}-[8.0])+3.37) - 5.93. We find that a larger fraction of AGB stars exhibiting the 'long-secondary period' phenomenon are more O-rich than stars dominated by radial pulsations, and AGB stars without detectable mass loss do not appear on either the first-overtone or fundamental-mode pulsation sequences.« less

The mass-loss return from evolved stars to the large magellanic cloud. vi. luminosities and mass-loss rates on population scales

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: vexp / ZL0:4. We compare
the sub-solar metallicity LMC OH/IR stars with carefully selected samples of
more metal-rich OH/IR stars, also at known distances, in the Galactic Centre and
Galactic Bulge. For 8 of the Bulge stars we derive pulsation periods for the first
time, using near-IR photometry from the VVV survey. We have modeled our LMC
OH/IR stars and developed an empirical method of deriving gas-to-dust ratios and
mass loss rates by scaling the models to the results from maser profiles. We have
done this also for samples in the Galactic Centre and Bulge and derived a new
mass loss prescription that includes luminosity, pulsation period, and gas-to-dust ratio
_M
= 1:06+3:5

/pdf/the-wind-speeds-dust-content-and-mass-loss-rates-of-evolved-y3rni5c1fk.pdf

The wind speeds, dust content, and mass-loss rates of evolved AGB and RSG stars at varying metallicity

We present the classification of 197 point sources observed with the Infrared Spectrograph in the SAGE-Spec Legacy programme on the Spitzer Space Telescope. We introduce a decision-tree method of object classification based on infrared spectral features, continuum and spectral energy distribution shape, bolometric luminosity, cluster membership and variability information, which is used to classify the SAGE-Spec sample of point sources. The decision tree has a broad application to mid-infrared spectroscopic surveys, where supporting photometry and variability information are available. We use these classifications to make deductions about the stellar populations of the Large Magellanic Cloud and the success of photometric classification methods. We find 90 asymptotic giant branch (AGB) stars, 29 young stellar objects, 23 post-AGB objects, 19 red supergiants, eight stellar photospheres, seven background galaxies, seven planetary nebulae, two H_(II) regions and 12 other objects, seven of which remain unclassified.

/pdf/the-sage-spec-spitzer-legacy-programme-the-life-cycle-of-26kte124hv.pdf

D. Paradis

Papers

The SAGE-Spec Spitzer Legacy programme: the life-cycle of dust and gas in the Large Magellanic Cloud - Point source classification I