Modeling Galactic Extinction With Dust and “Real” Polycyclic Aromatic Hydrocarbons

Mulas, G.; Zonca, Alberto; Casu, Silvia; Cecchi‐Pestellini, C.

doi:10.1088/0067-0049/207/1/7

Cited by 37 publications

(44 citation statements)

References 48 publications

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“…Present estimates are that 60%−70% of all C atoms stick onto dust particles (Sofia et al 2011;Cardelli 1996), whereas earlier values range between 30% and 40% (Sofia et al 2004). From extinction fitting, Mulas et al (2013) derive an average C abundance in grains of 145 ppm and estimate an uncertainty of about a factor of two. The abundance of O is uncertain within a factor of two.…”

Section: Element Abundancesmentioning

confidence: 65%

Dust in the diffuse interstellar medium

Siebenmorgen

Вощинников

Bagnulo

2014

A&A

112

123

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We present a model for the diffuse interstellar dust that explains the observed wavelength-dependence of extinction, emission, and the linear and circular polarisation of light. The model is set up with a small number of parameters. It consists of a mixture of amorphous carbon and silicate grains with sizes from the molecular domain of 0.5 up to about 500 nm. Dust grains with radii larger than 6 nm are spheroids. Spheroidal dust particles have a factor 1.5-3 greater absorption cross section in the far-infrared than spherical grains of the same volume do. Mass estimates derived from submillimetre observations that ignore this effect are overestimated by the same amount. In the presence of a magnetic field, spheroids may be partly aligned and polarise light. We find that polarisation spectra help to determine the upper particle radius of the otherwise rather unconstrained dust size distribution. Stochastically heated small grains of graphite, silicates, and polycyclic aromatic hydrocarbons (PAHs) are included. We tabulate parameters for PAH emission bands in various environments. They show a trend with the hardness of the radiation field that can be explained by the ionisation state or hydrogenation coverage of the molecules. For each dust component its relative weight is specified so that absolute element abundances are not direct input parameters. The model is compared to the average properties of the Milky Way, which seem to represent dust in the solar neighbourhood. It is then applied to specific sight lines towards four particular stars, with one of them located in the reflection nebula NGC 2023. For these sight lines, we present ultra-high signal-to-noise linear and circular spectro-polarimetric observations obtained with FORS at the VLT. Using prolate rather than oblate grains gives a better fit to observed spectra; the axial ratio of the spheroids is typically two and aligned silicates are the dominant contributors to the polarisation.

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Section: Element Abundancesmentioning

confidence: 65%

Dust in the diffuse interstellar medium

Siebenmorgen

Вощинников

Bagnulo

2014

A&A

112

123

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“…In any case, the extinction curve and DIBs are very likely to be extremely similar for all three stars of such a close system, unless circumstellar material makes a large contribution to them. Figure 9 shows the extinction curves reported by Fitzpatrick & Massa (2007) for HD 37020, HD 37022, and Herschel 36, together with their fits with the [CM] 2 dust model (Mulas et al 2013). Figure 10, for comparison, shows the extinction curve of HD 23180 (o Per), the closest proxy of HD 24398 (ζ Per) available in the sample of Fitzpatrick & Massa (2007), and the average galactic one.…”

Section: Discussionmentioning

confidence: 99%

Redshifted diffuse interstellar bands in the Orion OB1 association

Krełowski

Галазутдинов

Mulas

et al. 2015

Monthly Notices of the Royal Astronomical Society

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The wavelength displacement of the Diffuse Interstellar Bands at 4502, 5705, 5780, 6284, and 7224Å with respect to the well known, narrow atomic/molecular interstellar lines (of Caii and Nai) have been measured in the spectra of the 2 Orion Trapezium stars HD 37022 and HD 37020, using the HARPS-N spectrograph, fed with the 3.5 m Telescopio Nazionale Galileo, and the BOES spectrograph, fed with the 1.8m Korean telescope. The red-shift is ∼25 km/s for all these DIBs. We discuss the various possible origins of this very peculiar wavelength shift in the light of the particular physical conditions in the Orion Trapezium. The above mentioned shift is seemingly absent in the DIBs at 6196 and 6993Å.

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“…The variance-covariance matrix for the best-fitting parameters, measuring how tightly they are constrained by the fit, is obtained by synthetic statistics, by repeating the fit multiple times on data perturbed according to their errors. The details of this procedure, and the modifications in the MPFIT 1 Levenberg-Marquardt implementation to cope with underdetermination of some parameters, are described in Mulas et al (2013). The evolutionary model of carbon mantles is detailed in .…”

Section: Gordonmentioning

confidence: 99%

“…488 (0.012) 48 ( (8) 149 (60) 415 (80) 98 (60) 3.45 (0.04) -We adopt ε1 = 0.000001, ε2 = 0.01, ε3 = 0.0001 As described in Mulas et al (2013), the fit is severely underconstrained, mainly due to degeneracy in how many different PAH mixtures can add up to very nearly the same cumulative cross section. As a result, only some of the parameters are well determined by the fit, namely the ones defining the classical dust, and some collective properties of the PAH mixture.…”

Section: (23)mentioning

confidence: 99%

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Modeling Dust in the Magellanic Clouds

Zonca

Casu

Mulas

et al. 2015

ApJ

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We model the extinction profiles observed in the Small and Large Magellanic clouds with a synthetic population of dust grains consisting by core-mantle particles and a collection of free-flying polycyclic aromatic hydrocarbons. All different flavors of the extinction curves observed in the Magellanic Clouds can be described by the present model, that has been previously (successfully) applied to a large sample of diffuse and translucent lines of sight in the Milky Way. We find that in the Magellanic Clouds the extinction produced by classic grains is generally larger than absorption by polycyclic aromatic hydrocarbons. Within this model, the non-linear far-UV rise is accounted for by polycyclic aromatic hydrocarbons, whose presence in turn is always associated to a gap in the size distribution of classical particles. This hints either a physical connection between (e.g., a common cause for) polycyclic aromatic hydrocarbons and the absence of middle-sized dust particles, or the need for an additional component in the model, that can account for the non-linear far-UV rise without contributing to the UV bump at ∼217 nm, e.g., nanodiamonds.

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Modeling Galactic Extinction With Dust and “Real” Polycyclic Aromatic Hydrocarbons

Cited by 37 publications

References 48 publications

Dust in the diffuse interstellar medium

Dust in the diffuse interstellar medium

Redshifted diffuse interstellar bands in the Orion OB1 association

Modeling Dust in the Magellanic Clouds

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