Three-micron spectra of AGB stars and supergiants in nearby galaxies

Matsuura, M.; Zijlstra, A. A.; Loon, Jacco Th. van; Yamamura, I.; Markwick, A. J.; Whitelock, P. A.; Woods, Paul; Marshall, Jonathan R.; Feast, M. W.; Waters, L.B.F.M.

doi:10.1051/0004-6361:20042305

Cited by 69 publications

(136 citation statements)

References 56 publications

Supporting

Mentioning

121

Contrasting

Order By: Relevance

“…This may explain the remarkable strength of the molecular bands seen in the optical spectra of dust-enshrouded M-type AGB stars as well as in the optical and near-IR spectra of dustenshrouded carbon stars in the LMC (van Loon et al 1999a;Matsuura et al 2002Matsuura et al , 2005.…”

Section: The Hertzsprung-russell Diagram Of Dust-enshrouded Agb Starsmentioning

confidence: 92%

An empirical formula for the mass-loss rates of dust-enshrouded red supergiants and oxygen-rich Asymptotic Giant Branch stars

Loon¹,

Cioni

Zijlstra

et al. 2005

A&A

Self Cite

391

359

View full text Add to dashboard Cite

Abstract. We present an empirical determination of the mass-loss rate as a function of stellar luminosity and effective temperature, for oxygen-rich dust-enshrouded Asymptotic Giant Branch stars and red supergiants. To this aim we obtained optical spectra of a sample of dust-enshrouded red giants in the Large Magellanic Cloud, which we complemented with spectroscopic and infrared photometric data from the literature. Two of these turned out to be hot emission-line stars, of which one is a definite B[e] star. The mass-loss rates were measured through modelling of the spectral energy distributions. We thus obtain the massloss rate formula logṀ = −5.65 + 1.05 log(L/10 000 L ) − 6.3 log(T eff /3500 K), valid for dust-enshrouded red supergiants and oxygen-rich AGB stars. Despite the low metallicity of the LMC, both AGB stars and red supergiants are found at late spectral types. A comparison with galactic AGB stars and red supergiants shows excellent agreement between the mass-loss rate as predicted by our formula and that derived from the 60 µm flux density for dust-enshrouded objects, but not for optically bright objects. We discuss the possible implications of this for the mass-loss mechanism.

show abstract

Section: The Hertzsprung-russell Diagram Of Dust-enshrouded Agb Starsmentioning

confidence: 92%

An empirical formula for the mass-loss rates of dust-enshrouded red supergiants and oxygen-rich Asymptotic Giant Branch stars

Loon¹,

Cioni

Zijlstra

et al. 2005

A&A

Self Cite

391

359

View full text Add to dashboard Cite

show abstract

“…The model photosphere has a C/O ratio of 1.3. While this value is typical for Galactic Miras, the C/O ratio may be higher for Magellanic Cloud carbon stars (see, e.g., Matsuura et al 2005;Stanghellini et al 2005), which would change the optical depth due to increased molecular opacity. However, since we are limited by the small number of model photospheres available, we ignore these effects.…”

Section: Central Starmentioning

confidence: 94%

“…An accurate determination of the gas:dust ratio is still to be made for LMC carbon stars. Some observational and theoretical studies (e.g., Matsuura et al 2005;Wachter et al 2008) indicate that the carbon star gas:dust ratio may not be metallicity dependent. In fact, recent studies (Groenewegen et al 2007;Wachter et al 2008;Mattsson et al 2008) have found that the mass-loss rates of carbon stars may not be metallicity dependent.…”

Section: Dust Propertiesmentioning

confidence: 99%

“…The gas:dust ratio can be estimated from the mass fraction of SiC in the dust if we also know the fraction of the total Si mass that is in the dust. Assuming that the Si abundance scales with metallicity (The LMC silicon abundance is not well constrained; see the discussion in Matsuura et al 2005) we obtain Ψ in the range 200-570. However, we have assumed here that all of the Si goes into the dust.…”

Section: Dust Propertiesmentioning

confidence: 99%

See 1 more Smart Citation

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

Srinivasan

Sargent

Matsuura

et al. 2010

A&A

Self Cite

View full text Add to dashboard Cite

We present a radiative transfer model for the circumstellar dust shell around a Large Magellanic Cloud (LMC) long-period variable (LPV) previously studied as part of the Optical Gravitational Lensing Experiment (OGLE) survey of the LMC. OGLE LMC LPV 28579 (SAGE J051306.40-690946.3) is a carbon-rich asymptotic giant branch (AGB) star for which we have Spitzer broadband photometry and spectra from the SAGE and SAGE-Spec programs along with broadband UBVIJHK s photometry. By modeling this source, we obtain a baseline set of dust properties to be used in the construction of a grid of models for carbon stars. We reproduce the spectral energy distribution of the source using a mixture of amorphous carbon and silicon carbide with 15% SiC by mass. The grain sizes are distributed according to the KMH model, with γ = 3.5, a min = 0.01 μm and a 0 = 1.0 μm. The best-fit model produces an optical depth of 0.28 for the dust shell at the peak of the SiC feature (11.3 μm), with an inner radius of about 1430 R or 4.4 times the stellar radius. The temperature at this inner radius is 1310 K. Assuming an expansion velocity of 10 km s −1 , we obtain a dust mass-loss rate of 2.5 × 10 −9 M yr −1 . We calculate a 15% variation in this mass-loss rate by testing the sensitivity of the fit to variation in the input parameters. We also present a simple model for the molecular gas in the extended atmosphere that could give rise to the 13.7 μm feature seen in the spectrum. We find that a combination of CO and C 2 H 2 gas at an excitation temperature of about 1000 K and column densities of 3 × 10 21 cm −2 and 10 19 cm −2 respectively are able to reproduce the observations. Given that the excitation temperature is close to the temperature of the dust at the inner radius, most of the molecular contribution probably arises from this region. The luminosity corresponding to the first epoch of SAGE observations is 6580 L . For an effective temperature of about 3000 K, this implies a stellar mass of 1.5−2 M and an age of 1−2.5 Gyr for OGLE LMC LPV 28579. We calculate a gas mass-loss rate of 5.0 × 10 −7 M yr −1 assuming a gas:dust ratio of 200. This number is comparable to the gas mass-loss rates estimated from the period, color and 8 μm flux of the source.

show abstract

“…Matsuura et al 2005;Dijkstra et al 2005). Nevertheless, Speck et al (2000) found differences in the dust composition of RSG and AGB stars, the former often exhibiting Ca-Al-rich silicates instead of magnesium silicates.…”

Section: Introductionmentioning

confidence: 97%

The dust condensation sequence in red supergiant stars

Verhoelst

Zypen²,

Hony

et al. 2009

A&A

130

146

View full text Add to dashboard Cite

Context. Red supergiant (RSG) stars exhibit significant mass loss by means of a slow, dense wind. They are often considered to be the more massive counterparts of Asymptotic Giant Branch (AGB) stars. While AGB mass loss is related to their strong pulsations, the RSG are often only weakly variable. This raises the question of whether their wind-driving mechanism and the dust composition of the wind are the same. Aims. We study the conditions at the base of the wind by determining the dust composition of a sample of RSG. The dust composition is assumed to be sensitive to the density, temperature, and acceleration at the base of the wind. We compare the derived dust composition with the composition measured in AGB star winds. Methods. We compile a sample of 27 RSG infrared spectra (ISO-SWS) and supplement these with photometric measurements to derive the full spectral energy distribution (SED). These data are modelled using a dust radiative-transfer code, taking into account the optical properties of the relevant candidate materials to search for correlations between mass-loss rate, density at the inner edge of the dust shell, and stellar parameters. Results. We find strong correlations between the dust composition, mass-loss rate, and the stellar luminosity, roughly in agreement with the theoretical dust condensation sequence. We identify the need for a continuous (near-)IR dust opacity and tentatively propose amorphous carbon, and we note significant differences with AGB star winds in terms of the presence of PAHs, absence of "the" 13 μm band, and a lack of strong water bands. Conclusions. Dust condensation in RSG is found to experience a freeze-out process that is similar to that in AGB stars. Together with the positive effect of the stellar luminosity on the mass-loss rate, this suggests that radiation pressure on dust grains is an important ingredient in the driving mechanism. Still, differences with AGB stars are manifold and thus the winds of RSG should be studied individually in further detail.

show abstract

Three-micron spectra of AGB stars and supergiants in nearby galaxies

Cited by 69 publications

References 56 publications

An empirical formula for the mass-loss rates of dust-enshrouded red supergiants and oxygen-rich Asymptotic Giant Branch stars

An empirical formula for the mass-loss rates of dust-enshrouded red supergiants and oxygen-rich Asymptotic Giant Branch stars

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

The dust condensation sequence in red supergiant stars

Contact Info

Product

Resources

About