L183 (L134N) Revisited

Pagani, L.; Lagache, G.; Bacmann, A.; Motte, F.; Cambrésy, L.; Fich, M.; Teyssier, D.; Miville-Deschênes, M.-A.; Pardo, J. R.; Apponi, A. J.; Stepnik, B.

doi:10.1051/0004-6361:20030903

Cited by 41 publications

(45 citation statements)

References 17 publications

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“…A few border maximum spatial structures reach low τ m < 10 values. The resulting temperature of the central density peak would be higher than the 7−9 K found by Pagani et al (2003Pagani et al ( , 2004. Thus, spatial structures below the dashed line at τ m < 10 are also not consistent with the observational data.…”

Section: Discussionmentioning

confidence: 68%

Direct evidence of dust growth in L183 from mid-infrared light scattering

Steinacker

Pagani

Bacmann

et al. 2010

A&A

Self Cite

144

182

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Context. Theoretical arguments suggest that dust grains should grow in the dense cold parts of molecular clouds. Evidence of larger grains has so far been gathered in near/mid infrared extinction and millimeter observations. Interpreting the data is, however, aggravated by the complex interplay of density and dust properties (as well as temperature for thermal emission). Aims. Direct evidence of larger particles can be derived from scattered mid-infrared (MIR) radiation from a molecular cloud observed in a spectral range where little or no emission from polycyclic aromatic hydrocarbons (PAHs) is expected. Methods. We present new Spitzer data of L183 in bands that are sensitive and insensitive to PAHs. The visual extinction A V map derived in a former paper was fitted by a series of 3D Gaussian distributions. For different dust models, we calculate the scattered MIR radiation images of structures that agree with the A V map and compare them to the Spitzer data. Results. The Spitzer data of L183 show emission in the 3.6 and 4.5 μm bands, while the 5.8 μm band shows slight absorption. The emission layer of stochastically heated particles should coincide with the layer of strongest scattering of optical interstellar radiation, which is seen as an outer surface on I band images different from the emission region seen in the Spitzer images. Moreover, PAH emission is expected to strongly increase from 4.5 to 5.8 μm, which is not seen. Hence, we interpret this emission to be MIR scattered light from grains located further inside the core, and call it "coreshine". Scattered light modeling when assuming interstellar medium dust grains without growth does not reproduce flux measurable by Spitzer. In contrast, models with grains growing with density yield images with a flux and pattern comparable to the Spitzer images in the bands 3.6, 4.5, and 8.0 μm. Conclusions. There is direct evidence of dust grain growth in the inner part of L183 from the scattered light MIR images seen by Spitzer.

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Section: Discussionmentioning

confidence: 68%

Direct evidence of dust growth in L183 from mid-infrared light scattering

Steinacker

Pagani

Bacmann

et al. 2010

A&A

Self Cite

144

182

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“…In this source, the estimated submm dust emissivity is higher than average (see Juvela et al 2015), but for such high opacities the column density derived from dust emission is still likely to be underestimated. Based partly on MIR absorption, the estimated maximum extinction exceeds A V = 100 mag, although only in an area with less than 1 in size (Pagani et al 2003(Pagani et al , 2015. At the resolution of 60 , the observed β values drop from β ∼ 2.0 in the surrounding regions down to β = 1.60 in the central core, the values being measured using 160-500 µm data at a resolution of 1 .…”

Section: Effects Of Temperature Variationsmentioning

confidence: 87%

Galactic cold cores

Juvela

Demyk

Doi

et al. 2015

A&A

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Context. The Galactic Cold Cores project has carried out Herschel photometric observations of 116 fields where the Planck survey has found signs of cold dust emission. The fields contain sources in different environments and different phases of star formation. Previous studies have revealed variations in their dust submillimetre opacity. Aims. The aim is to measure the value of dust opacity spectral index and to understand its variations spatially and with respect to other parameters, such as temperature, column density, and Galactic location. Methods. The dust opacity spectral index β and the dust colour temperature T are derived using Herschel and Planck data. The relation between β and T is examined for the whole sample and inside individual fields. Results. Based on IRAS and Planck data, the fields are characterised by a median colour temperature of 16.1 K and a median opacity spectral index of β = 1.84. The values are not correlated with Galactic longitude. We observe a clear T -β anti-correlation. In Herschel observations, constrained at lower resolution by Planck data, the variations follow the column density structure and β FIR can rise to ∼2.2 in individual clumps. The highest values are found in starless clumps. The Planck 217 GHz band shows a systematic excess that is not restricted to cold clumps and is thus consistent with a general flattening of the dust emission spectrum at millimetre wavelengths. When fitted separately below and above 700 µm, the median spectral index values are β FIR ∼ 1.91 and β(mm) ∼ 1.66. Conclusions. The spectral index changes as a function of column density and wavelength. The comparison of different data sets and the examination of possible error sources show that our results are robust. However, β variations are partly masked by temperature gradients and the changes in the intrinsic grain properties may be even greater.

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“…It is instructive to consider also the abundance variations from source to source. Converting column densities into relative abundances requires the molecular hydrogen column density, N H 2 , which we have determined (indirectly) from measurements of the dust emission, using bolometer maps available in the literature (Ward-Thompson et al 1999;Pagani et al 2003;Tafalla et al 2004;Bacmann et al 2000) and smoothing where necessary to a 20 beam. We assumed a dust temperature of 8 K and a 1.3 mm absorption coefficient of κ = 0.01 cm 2 g −1 (see HWFP08).…”

Section: Column Densities and Abundance Ratiosmentioning

confidence: 99%

Nitrogen chemistry and depletion in starless cores

Hily-Blant¹,

Walmsley

Forêts

et al. 2010

A&A

119

128

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Aims. We investigated the chemistry of nitrogen-containing species, principally isotopologues of CN, HCN, and HNC, in a sample of pre-protostellar cores. Methods. We used the IRAM 30 m telescope to measure the emission in rotational and hyperfine transitions of CN, HCN, 13 CN, H 13 CN, HN 13 C, and HC 15 N in L 1544, L 183, Oph D, L 1517B, L 310. The observations were made along axial cuts through the dust emission peak, at a number of regularly-spaced offset positions. The observations were reduced and analyzed to obtain the column densities, using the measurements of the less abundant isotopic variants in order to minimize the consequences of finite optical depths in the lines. The observations were compared with the predictions of a free-fall gravitational collapse model, which incorporates a non-equilibrium treatment of the relevant chemistry. Results. We found that CN, HCN, and HNC remain present in the gas phase at densities well above that at which CO depletes on to grains. The CN:HCN and the HNC:HCN abundance ratios are larger than unity in all the objects of our sample. Furthermore, there is no observational evidence for large variations of these ratios with increasing offset from the dust emission peak and hence with density. Whilst the differential freeze-out of CN and CO can be understood in terms of the current chemistry, the behaviour of the CN:HCN ratio is more difficult to explain. Models suggest that most nitrogen is not in the gas phase but may be locked in ices. Unambiguous conclusions require measurements of the rate coefficients of the key neutral-neutral reactions at low temperatures.

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L183 (L134N) Revisited

Cited by 41 publications

References 17 publications

Direct evidence of dust growth in L183 from mid-infrared light scattering

Direct evidence of dust growth in L183 from mid-infrared light scattering

Galactic cold cores

Nitrogen chemistry and depletion in starless cores

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