Obscured AGB stars in the Magellanic Clouds

Loup, C.; Zijlstra, A. A.; Waters, L.B.F.M.; Groenewegen, M. A. T.

doi:10.1051/aas:1997377

Cited by 56 publications

(75 citation statements)

References 21 publications

(46 reference statements)

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“…We complement our sample with objects from van Loon et al (1998) and Trams et al (1999) A further 34 IRAS-detected objects with spectral subclassification are available from Loup et al (1997;their …”

Section: Additional Samplesmentioning

confidence: 99%

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

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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.

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Section: Additional Samplesmentioning

confidence: 99%

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

383

359

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“…The targets were selected from IRAS sources (Loup et al 1997;Groenewegen & Blommaert 1998), sources observed with ISO (Groenewegen et al 2000;Cioni et al 2003), and Spitzer IRS targets (Kraemer et al 2005Sloan et al 2006;Lagadec et al 2007;Sloan et al 2008). These include six stars in the intermediate-age populous star cluster NGC 419, of which the four bluest and least dusty stars would probably not have been selected had they not been part of the cluster sample of Spitzer targets.…”

Section: Target Selectionmentioning

confidence: 99%

Molecules and dust production in the Magellanic Clouds

Loon¹,

Cohen

Oliveira³

et al. 2008

A&A

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146

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We present ESO/VLT spectra in the 2.9−4.1 μm range for a large sample of infrared stars in the Small Magellanic Cloud (SMC), mainly carbon stars, massive oxygen-rich Asymptotic Giant Branch (AGB) stars, and red supergiants. Strong emission from Polycyclic Aromatic Hyrdrocarbons (PAHs) is detected in the spectrum of the post-AGB object MSX SMC 29. Water ice is detected in at least one Young Stellar Object, IRAS 01042−7215, for the first time in the SMC. The strength and shapes of the molecular bands detected in the evolved stars are compared with similar data for stars in the Large Magellanic Cloud (LMC). Absorption from acetylene in carbon stars is found to be equally strong in the SMC as in the LMC, but the LMC stars show stronger dust emission in their infrared colours and veiling of the molecular bands. This suggests that a critical link exists in the formation of dust from the molecular atmosphere in carbon stars which scales with the initial metallicity. Nucleation seeds based on a secondary element such as titanium or silicon provide a plausible explanation. In oxygen-rich stars, both the nucleation seeds and molecular condensates depend on secondary elements (in particular titanium, silicon, and/or aluminium), which explains the observed lower molecular abundances and lower dust content in the SMC stars. Emission from silicon monoxide seen in some oxygen-rich AGB stars and red supergiants in the SMC suggests that these metal-poor stars are able to drive strong pulsation shocks through their molecular layers. Data for pulsating dusty AGB stars and supergiants in the LMC are used to show that pulsation is likely the critical factor in driving mass loss, as long as dust forms, rather than the stellar luminosity. Finally, we suggest that the reduced dust production and consequently slower winds of metal-poor AGB stars and red supergiants are more likely to result in chemical inhomogeneities and small-scale structure in the interstellar medium.

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“…Searches for LPV's seem to be reasonably complete for optical Miras, but were not sensitive enough to extract semi-regular and irregular variables. For TP-AGB stars with high massloss rates, only the brightest and most luminous ones could have been detected by IRAS (Loup et al 1997), missing obscured AGB stars with luminosities lower than about 10 4 £0. Finally, AGB stars with intermediate mass-loss rates, well known and numerous in our Galaxy, would have been completely missed both by optical/I-band and IRAS searches.…”

Section: Brief History Of Previous Surveysmentioning

confidence: 99%