The Project “spice”

Rouan, D.; Epchtein, N.; Muizon, M. de; Lacombe, F.; Puget, P.; Tiphéne, D.; Boulanger, F.; Desert, X.; Guyot, G.; D’Hendecourt, L.; Lamarre, J.-M.; Léger, Alain; Pajot, F.; Puget, J.; Caux, E.; Giard, M.; Serra, G.; Césarsky, C. J.; Vigroux, L.; Omont, A.

doi:10.1007/978-94-011-0946-8_9

Cited by 31 publications

(47 citation statements)

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“…Salama 1999 and references therein). Indeed, as shown by Rouan et al (1992) and quantitatively studied in Mulas (1998) and Malloci et al (2003), infrared emission is supposed to be the dominant mechanism driving the rotation of an isolated PAH in the ISM, hence suggesting a direct link between DIB spectral profiles and IR emission bands.…”

Section: Introductionmentioning

confidence: 77%

Testing the “strong” PAHs hypothesis

Mulas

Malloci

Benvenuti

2003

A&A

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Abstract. In Paper I (Malloci et al. 2003) we proved the profile invariance of the first permitted electronic transition of the typical Polycyclic Aromatic Hydrocarbon cation C 32 H 14 + as a first necessary check for the "strong" PAHs hypothesis. In this paper we derive a quantitative relation between the intensities of the former band, which ought to be observable in absorption in the visible range, and those of the far-IR bands, which are predicted by the PAH model to be simultaneously present in emission. Contrary to the mid-IR bands, collectively known as "Unidentified Infrared Bands" (UIBs), which do not discriminate specific molecules, the far IR, skeletal bands can be expected to be a fingerprint of each single species. This fact provides a number of independent constraints which must be simultaneously fulfilled for a successful PAH identification. Our approach thus offers a powerful criterion for the identification of specific PAHs, both in the presently available ISO data and in those of the forthcoming SIRTF and Herschel missions. As an interesting by-product, we quantitatively evaluate the impact of isotopic substitutions ( 13 C→ 12 C and D →H) on the resulting infrared emission bands.

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Section: Introductionmentioning

confidence: 77%

Testing the “strong” PAHs hypothesis

Mulas

Malloci

Benvenuti

2003

A&A

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“…Ejection of H or H 2 from the edges of PAHs may yield a significant rotational excitation if it occurs asymmetrically, thus generating a systematic torque by the rocket effect (Rouan et al 1992). We note below E ej the kinetic energy of the ejected fragment.…”

Section: Appendix A: Mid-ir Absorption Cross-sectionmentioning

confidence: 99%

“…As in Rouan et al (1992), we assume an efficient intramolecular vibration to rotation energy transfer (IVRET). We take n(J) to be the same for all vibrational levels, equal to a Maxwell distribution n(J) = n 0 J 2 exp(−J 2 /J 2 0 ), where n 0 is a normalization factor.…”

Section: Angular Momentum Distributionmentioning

confidence: 99%

The long-wavelength emission of interstellar PAHs: characterizing the spinning dust contribution

Ysard¹,

Verstraete²

2010

A&A

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Context. The emission of cold dust grains at long wavelengths will soon be observed by the Planck and Herschel satellites and will provide new constraints on the nature of interstellar dust. In particular, the microwave galactic anomalous foreground detected between 10 to 90 GHz, proposed as coming from small spinning grains (PAHs), should help to define these species better. Moreover, understanding the fluctuations of the anomalous foreground quantitatively over the sky is crucial for CMB studies. Aims. We focus on the long-wavelength emission of interstellar PAHs in their vibrational and rotational transitions. We present here the first model that coherently describes the PAH emission from the near-IR to microwave range. Methods. We take quantum effects into account to describe the rotation of PAHs and compare our results to current models of spinning dust to assess the validity of the classical treatment used. Between absorptions of stellar photons, we followed the rovibrational radiative cascade of PAHs. We used the exact-statistical method of Draine & Li to derive the distribution of PAH internal energy and followed a quantum approach for the rotational excitation induced by vibrational (IR) transitions. We also examined the influence of the vibrational relaxation scheme and of the low-energy cross-section on the PAH emission. We study the emissivity of spinning PAHs in a variety of physical conditions (radiation field intensity and gas density), search for specific signatures in this emission that can be looked for observationally, and discuss how the anomalous foreground may constrain the PAH size distribution. Results. Simultaneously predicting the vibrational and rotational emission of PAHs, our model can explain the observed emission of the Perseus molecular cloud from the IR to the microwave range with plausible PAH properties. We show that for λ ≥ 3 mm the PAH vibrational emission no longer scales with the radiation field intensity (G 0 ), unlike the mid-IR part of the spectrum (which scales with G 0 ). This emission represents less than 10% of the total dust emission at 100 GHz. Similarly, we find the broadband emissivity of spinning PAHs per carbon atom to be rather constant for G 0 ≤ 100 and for proton densities n H < 100 cm −3 . In the diffuse ISM, photon exchange and gas-grain interactions play comparable roles in exciting the rotation of PAHs, and the emissivity of spinning PAHs is dominated by the contribution of small species (bearing less than 100 C atoms). We show that the classical description of rotation used in previous works is a good approximation and that unknowns in the vibrational relaxation scheme and low-energy cross-section affect the PAH rotational emissivity around 30 GHz by less than 15%. Conclusions. The contrasted behaviour of the PAH vibrational and rotational emissivities with G 0 provides a clear prediction that can be tested against observations of anomalous and dust mid-IR emissions: this is the subject of a companion paper. Comparison of these emissions complem...

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“…Ballester et al 1990;Rouan et al 1992;Lazarian 1994;Wolff et al 1997). Depending on the polarisation (i.e.…”

Section: Introductionmentioning

confidence: 99%

Linear and circular spectropolarimetry of diffuse interstellar bands

Cox

Ehrenfreund

Foing

et al. 2011

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Context. The identification of the carriers of diffuse interstellar bands (DIBs) remains one of the long-standing mysteries in astronomy. The detection of a polarisation signal in a DIB profile can be used to distinguish between a dust or gas-phase carrier. The polarisation profile can give additional information on the grain or molecular properties of the absorber. Aims. To measure the polarisation efficiency of the carriers of the diffuse interstellar bands. Methods. In order to detect and measure the linear and circular polarisation of the DIBs we observed reddened lines of sight showing continuum polarisation. For this study we selected two stars HD 197770 and HD 194279. We used high-resolution (R ∼ 64 000) spectropolarimetry in the wavelength range from 3700 to 10 480 Å with the ESPaDOnS échelle spectrograph mounted at the CFHT. Results. High S/N and high resolution Stokes V (circular), Q and U (linear) spectra were obtained. We constrained upper limits by a factor of 10 for previously observed DIBs. Furthermore, we analysed ∼30 additional DIBs for which no spectropolarimetry data has been obtained before. This included the 9577 Å DIB and the 8621 Å DIB. The former is attributed to the C + 60 fullerene, which could become aligned in a magnetic field. The latter shows a tight correlation with the amount of dust in the line-of-sight and therefore most likely may show a polarisation signal related the aligned grains. Conclusions. The lack of polarisation in 45 DIB profiles suggests that none of the absorption lines is induced by a grain-type carrier. The strict upper limits, less than ∼0.01%, derived for the observed lines-of-sight imply that if DIBs are due to gas-phase molecules these carriers have polarisation efficiencies which are at least 6 times, and up to 300 times, smaller than those predicted for grainrelated carriers.

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The Project “spice”

Cited by 31 publications

References 0 publications

Testing the “strong” PAHs hypothesis

Testing the “strong” PAHs hypothesis

The long-wavelength emission of interstellar PAHs: characterizing the spinning dust contribution

Linear and circular spectropolarimetry of diffuse interstellar bands

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