New insights into the dust properties of the Taurus molecular cloud TMC-2 and its surroundings

Burgo, C. del; Laureijs, R. J.

doi:10.1111/j.1365-2966.2005.09044.x

Cited by 21 publications

(17 citation statements)

References 27 publications

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“…Variations in dust's optical properties are visible even on a scale of the galactic anticentre hemisphere, anywhere where A V > ∼ 1 mag (Cambresy et al 2005). Del Burgo & Laureijs (2005) used observations of the Taurus molecular cloud TMC-2 between 60 µm and 200 µm to separate the emission into cold and warm components. They found that far-IR emissivity of the cold component is a few times larger than that of the diffuse interstellar medium, and that the change in the properties of the big dust particles takes place at intermediate densities of n(H 2 ) ≈ 10 3 cm −3 .…”

Section: Introductionmentioning

confidence: 99%

ISO far-infrared observations of the high-latitude cloud L1642

Lehtinen¹,

Juvela²,

Mattila³

et al. 2007

A&A

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Aims. Our aim is to compare the infrared properties of big, "classical" dust grains with visual extinction in the cloud L1642. In particular, we study the differences in grain emissivity between diffuse and dense regions in the cloud. Methods. The far-infrared properties of dust are based on large-scale 100 µm and 200 µm maps. Extinction through the cloud was derived by using the star count method in the B-and I-bands, and colour excess method in the J, H, and K s bands. Radiative transfer calculations were used to study the effects of increasing absorption cross-section on the far-infrared emission and dust temperature. Results. Dust emissivity, measured by the ratio of far-infrared optical depth to visual extinction, τ(far-IR)/A V , increases with decreasing dust temperature in L1642. There is about a two-fold increase in emissivity over the dust temperature range of 19 K−14 K. Radiative transfer calculations show that, in order to explain the observed decrease of dust temperature towards the centre of L1642, an increase of absorption cross-section of dust at far-IR is necessary. This temperature decrease cannot be explained solely by the attenuation of interstellar radiation field. Increased absorption cross-section also manifests itself as an increased emissivity. We find that, due to temperature effects, the apparent value of optical depth τ app (far-IR), derived from 100 µm and 200 µm intensities, is always lower than the true optical depth.

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Section: Introductionmentioning

confidence: 99%

ISO far-infrared observations of the high-latitude cloud L1642

Lehtinen¹,

Juvela²,

Mattila³

et al. 2007

A&A

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“…The diffuse ISM component has a typical temperature of about 17.5 K (Boulanger et al 1996) while the colder condensation component has a typical temperature of about 12.5 K (del Burgo & Laureijs 2005). Observations with ISO, Spitzer, SPM/PRONAOS and IRAS of different regions in the interstellar medium indicate increased dust emissivities in colder regions (Bernard et al 1999;del Burgo et al 2003;Stepnik et al 2003;del Burgo & Laureijs 2005;Kiss et al 2006;Ridderstad et al 2006;Lehtinen et al 2007;Bot et al 2009;Paradis et al 2009). This increase in emissivity observed at wavelengths ≥200 μm is often explained by a change in the properties of the cold dust.…”

Section: Introductionmentioning

confidence: 99%

Aggregate dust connections and emissivity enhancements

Koehler

Guillet

Jones

2011

A&A

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Context. Observations of cold condensed clouds in the interstellar medium show an enhancement in the dust emissivity at long wavelengths. Model calculations with the discrete-dipole approximation (DDA) can explain this enhancement with the coagulation of dust particles into aggregates. Aims. We study the nature of grain-grain contacts and their effects on the aggregate optical properties. Methods. We use DDA and the T-matrix method (TMM) to calculate the absorption properties of aggregate dust grains and analyse where and why the enhancement in the emissivity occurs. Results. We find that the absorption coefficient changes with material composition and with the contact area between monomers. A larger contact area, with DDA, compared to a zero-point contact with TMM, results in an enhancement of the absorption coefficient for wavelengths where the considered material has a large value n (the real part of the refractive index). Conclusions. DDA seems to be the most realistic way of taking into account "real" inter-particle contact effects in aggregate particles.

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“…Lagache et al 1998;Bernard et al 1999;Stepnik et al 2003;del Burgo et al 2003;Planck Collaboration 2011b). Additionally, an increase in the dust opacity by a factor between 2 and 4 is observed in these denser regions at long wavelengths, which is inferred from the low dust temperature, and not always by comparison to the gas or A V (Bernard et al 1999;Hotzel et al 2001;Cambrésy et al 2001;Stepnik et al 2003;Bianchi et al 2003;del Burgo et al 2003;del Burgo & Laureijs 2005;Kiss et al 2006;Lehtinen et al 2007;Ridderstad et al 2006;Bot et al 2009;Paradis et al 2009;Planck Collaboration 2011b). Moreover, the abundance of the very small grains (VSGs, 1−15 nm in radius), that are stochastically heated and responsible for the 60 μm emission, decreases by ∼80-100% in the transition from diffuse to dense molecular clouds (Laureijs et al 1991;Abergel et al 1994Abergel et al , 1996Lagache et al 1998;Stepnik et al 2003;Kramer et al 2003).…”

Section: Introductionmentioning

confidence: 99%

Dust coagulation processes as constrained by far-infrared observations

Koehler

Stepnik

Jones

et al. 2012

A&A

111

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Aims. We develop a simple model of coagulated dust particles of two sizes (3.5 and 60 nm radius) to understand the nature and the effects of coagulation, which could explain the evolution of the far-infrared (FIR) dust opacity observed in the transition between the diffuse and the dense interstellar medium (ISM) (n H > 10 3 cm −3 ). Methods. Using the discrete-dipole approximation (DDA) method, we have calculated the absorption coefficient, directly proportional to the opacity, of coagulated grains with varying numbers of sub-grains and of different grain composition. Results. We show that, in the transition from diffuse to dense clouds, an increase in the FIR opacity by a factor of about 2.7 is possible and a decrease in the grain temperature by up to 3−4 K can be explained by the presence of coagulated aggregates composed of four big grains and 4000 very small grains (40% of the volume of the BGs). The coagulation of very small grains into the aggregates leads to a decrease in the 60 μm emission. Conclusions. This model can explain the observed increase in opacity at long wavelengths, the decrease in temperature from the diffuse ISM to denser regions with the coagulation of grains into aggregates and the absence of the 60 μm emission with the coagulation of very small grains onto the surface of the big grains.

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New insights into the dust properties of the Taurus molecular cloud TMC-2 and its surroundings

Cited by 21 publications

References 27 publications

ISO far-infrared observations of the high-latitude cloud L1642

ISO far-infrared observations of the high-latitude cloud L1642

Aggregate dust connections and emissivity enhancements

Dust coagulation processes as constrained by far-infrared observations

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