G. Pineau des Forets

French National Centre for Scientific Research, Lutetia Parisorum, Île-de-France, France

Are you G. Pineau des Forets?

Claim your profile

Publications (264)693.94 Total impact

  • W. Yvart · S. Cabrit · G. Pineau des Forets · J. Ferreira ·
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate whether the broad wings of H2O emission identified with Herschel towards low-mass Class 0 and Class 1 protostars may be consistent with an origin in a dusty MHD disk wind, and the constraints it would set on the underlying disk properties. We present synthetic H2O line profiles predictions for a typical MHD disk wind solution with various values of disk accretion rate, stellar mass, extension of the launching area, and view angle. We compare them in terms of line shapes and intensities with the HIFI profiles observed by the WISH Key Program. We find that a dusty MHD disk wind launched from 0.2--0.6 AU AU to 3--25 AU can reproduce to a remarkable degree the observed shapes and intensities of the broad H2O component, both in the fundamental 557 GHz line and in more excited lines. Such a model also readily reproduces the observed correlation of 557 GHz line luminosity with envelope density, if the infall rate at 1000 AU is 1--3 times the disk accretion rate in the wind ejection region. It is also compatible with the typical disk size and bolometric luminosity in the observed targets. However, the narrower line profiles in Class 1 sources suggest that MHD disk winds in these sources, if present, would have to be slower and/or less water rich than in Class 0 sources. In conclusion, MHD disk winds appear as a valid (though not unique) option to consider for the origin of the broad H2O component in low-mass protostars. ALMA appears ideally suited to further test this model by searching for resolved signatures of the warm and slow wide-angle molecular wind that would be predicted.
    Astronomy and Astrophysics 10/2015; DOI:10.1051/0004-6361/201525915 · 4.38 Impact Factor
  • Source
    P. Guillard · F. Boulanger · M. D. Lehnert · P. N. Appleton · G. Pineau des Forêts ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The build-up of galaxies is regulated by a complex interplay between gravitational collapse, galaxy merging and feedback related to AGN and star formation. The energy released by these processes has to dissipate for gas to cool, condense, and form stars. How gas cools is thus a key to understand galaxy formation. \textit{Spitzer Space Telescope} infrared spectroscopy revealed a population of galaxies with weak star formation and unusually powerful H$_2$ line emission. This is a signature of turbulent dissipation, sustained by large-scale mechanical energy injection. The cooling of the multiphase interstellar medium is associated with emission in the H$_2$ lines. These results have profound consequences on our understanding of regulation of star formation, feedback and energetics of galaxy formation in general. The fact that H$_2$ lines can be strongly enhanced in high-redshift turbulent galaxies will be of great importance for the \textit{James Webb Space Telescope} observations which will unveil the role that H$_2$ plays as a cooling agent in the era of galaxy assembly.
  • A. Gusdorf · R. Gusten · K. M. Menten · D. R. Flower · G. Pineau des Forets · C. Codella · T. Csengeri · al ·

    Astronomy and Astrophysics 09/2015; DOI:10.1051/0004-6361/201425325 · 4.38 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: OH is a key molecule in H2O chemistry, a valuable tool for probing physical conditions, and an important contributor to the cooling of shock regions. OH participates in the re-distribution of energy from the protostar towards the surrounding ISM. Our aim is to assess the origin of the OH emission from the Cepheus A massive star-forming region and to constrain the physical conditions prevailing in the emitting gas. We thus want to probe the processes at work during the formation of massive stars. We present spectrally resolved observations of OH towards the outflows of Cepheus A with the GREAT spectrometer onboard the SOFIA telescope. Three triplets were observed at 1834.7 GHz, 1837.8 GHz, and 2514.3 GHz (163.4, 163.1, and 119.2 microns), at angular resolutions of 16.3", 16.3", and 11.9", respectively. We present the CO (16-15) spectrum at the same position. We compared the integrated intensities in the redshifted wings to shock models. The two triplets near 163 microns are detected in emission with blending hyperfine structure unresolved. Their profiles and that of CO can be fitted by a combination of 2 or 3 Gaussians. The observed 119.2 microns triplet is seen in absorption, since its blending hyperfine structure is unresolved, but with three line-of-sight components and a blueshifted emission wing consistent with that of the other lines. The OH line wings are similar to those of CO, suggesting that they emanate from the same shocked structure. Under this common origin assumption, the observations fall within the model predictions and within the range of use of our model only if we consider that four shock structures are caught in our beam. Our comparisons suggest that the observations might be consistently fitted by a J-type model with nH > 1e5 cm-3, v > 20 km/s, and with a filling factor of ~1. Such a high density is generally found in shocks associated to high-mass protostars.
  • D.R. Flower · G. Pineau des Forêts ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The planar MHD shock code mhd-vode has been developed in order to simulate both continuous (C) type shock waves and jump (J) type shock waves in the interstellar medium. The physical and chemical state of the gas in steady-state may also be computed and used as input to a shock wave model. The code is written principally in FORTRAN 90, although some routines remain in FORTRAN 77. The documented program and its input data are described and provided as supplementary material, and the results of exemplary test runs are presented. Our intention is to enable the interested user to run the code for any sensible parameter set and to comprehend the results. With applications to molecular outflow sources in mind, we have computed, and are making available as supplementary material, integrated atomic and molecular line intensities for grids of C- and J-type models; these computations are summarized in the Appendices.
    Astronomy and Astrophysics 06/2015; 578. DOI:10.1051/0004-6361/201525740 · 4.38 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have observed five sulphur-bearing molecules in foreground diffuse molecular clouds lying along the sight-lines to five bright continuum sources. We have used the GREAT instrument on SOFIA to observe the 1383 GHz $^2\Pi_{3/2} J=5/2-3/2$ transitions of SH towards the star-forming regions W31C, G29.96-0.02, G34.3+0.1, W49N and W51, detecting foreground absorption towards all five sources; and the EMIR receivers on the IRAM 30m telescope at Pico Veleta to detect the H$_2$S 1(10)-1(01), CS J=2-1 and SO 3(2)-2(1) transitions. In nine foreground absorption components detected towards these sources, the inferred column densities of the four detected molecules showed relatively constant ratios, with N(SH)/N(H$_2$S) in the range 1.1 - 3.0, N(CS)/N(H$_2$S) in the range 0.32 - 0.61, and N(SO)/N(H$_2$S) in the range 0.08 - 0.30. The observed SH/H$_2$ ratios - in the range (0.5-2.6) $\times 10^{-8}$ - indicate that SH (and other sulphur-bearing molecules) account for << 1% of the gas-phase sulphur nuclei. The observed abundances of sulphur-bearing molecules, however, greatly exceed those predicted by standard models of cold diffuse molecular clouds, providing further evidence for the enhancement of endothermic reaction rates by elevated temperatures or ion-neutral drift. We have considered the observed abundance ratios in the context of shock and turbulent dissipation region (TDR) models. Using the TDR model, we find that the turbulent energy available at large scale in the diffuse ISM is sufficient to explain the observed column densities of SH and CS. Standard shock and TDR models, however, fail to reproduce the column densities of H$_2$S and SO by a factor of about 10; more elaborate shock models - in which account is taken of the velocity drift, relative to H$_2$, of SH molecules produced by the dissociative recombination of H$_3$S$^+$ - reduce this discrepancy to a factor ~ 3.
    Astronomy and Astrophysics 02/2015; 577. DOI:10.1051/0004-6361/201425391 · 4.38 Impact Factor
  • Source
    Georgios Momferratos · Pierre Lesaffre · Edith Falgarone · Guillaume Pineau des Forêts ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The dissipation of kinetic and magnetic energy in the interstellar medium (ISM) can proceed through viscous, Ohmic or ambipolar diffusion (AD). It occurs at very small scales compared to the scales at which energy is presumed to be injected. This localized heating may impact the ISM evolution but also its chemistry, thus providing observable features. Here, we perform 3D spectral simulations of decaying magnetohydrodynamic turbulence including the effects of AD. We find that the AD heating power spectrum peaks at scales in the inertial range, due to a strong alignment of the magnetic and current vectors in the dissipative range. AD affects much greater scales than the AD scale predicted by dimensional analysis. We find that energy dissipation is highly concentrated on thin sheets. Its probability density function follows a lognormal law with a power-law tail which hints at intermittency, a property which we quantify by use of structure function exponents. Finally, we extract structures of high dissipation, defined as connected sets of points where the total dissipation is most intense and we measure the scaling exponents of their geometric and dynamical characteristics: the inclusion of AD favours small sizes in the dissipative range.
    Monthly Notices of the Royal Astronomical Society 02/2015; 443(1). DOI:10.1093/mnras/stu853 · 5.11 Impact Factor
  • Source
    F. Daniel · A. Faure · P. J. Dagdigian · M. -L. Dubernet · F. lique · G. Pineau des Forets ·
    [Show abstract] [Hide abstract]
    ABSTRACT: We present quantum dynamical calculations that describe the rotational excitation of H$_2$O due to collisions with H atoms. We used a recent, high accuracy potential energy surface, and solved the collisional dynamics with the close-coupling formalism, for total energies up to 12 000 cm$^{-1}$. From these calculations, we obtained collisional rate coefficients for the first 45 energy levels of both ortho- and para-H$_2$O and for temperatures in the range T = 5-1500 K. These rate coefficients are subsequently compared to the values previously published for the H$_2$O / He and H$_2$O / H$_2$ collisional systems. It is shown that no simple relation exists between the three systems and that specific calculations are thus mandatory.
    Monthly Notices of the Royal Astronomical Society 01/2015; 446:2312. DOI:10.1093/mnras/stu2287 · 5.11 Impact Factor
  • Source
    P. Guillard · F. Boulanger · M. D. Lehnert · G. Pineau des Forets · F. Combes · E. Falgarone · J. Bernard-Salas ·
    [Show abstract] [Hide abstract]
    ABSTRACT: We detect bright [CII]158$\mu$m line emission from the radio galaxy 3C 326N at z=0.09, which shows weak star formation ($SFR<0.07$M$_{\odot}$~yr$^{-1}$) despite having strong H$_2$ line emission and $2\times 10^9$M$_{\odot}$ of molecular gas. The [CII] line is twice as strong as the 0-0S(1) 17$\mu$m H$_2$ line, and both lines are much in excess what is expected from UV heating. We combine infrared Spitzer and Herschel data with gas and dust modeling to infer the gas physical conditions. The [CII] line traces 30 to 50% of the molecular gas mass, which is warm (70<T<100K) and at moderate densities $700<n_{H}<3000$cm$^{-3}$. The [CII] line is broad with a blue-shifted wing, and likely to be shaped by a combination of rotation, outflowing gas, and turbulence. It matches the near-infrared H$_2$ and the Na D optical absorption lines. If the wing is interpreted as an outflow, the mass loss rate would be larger than 20M$_{\odot}$/yr, and the depletion timescale shorter than the orbital timescale ($10^8$yr). These outflow rates may be over-estimated because the stochastic injection of turbulence on galactic scales can contribute to the skewness of the line profile and mimic outflowing gas. We argue that the dissipation of turbulence is the main heating process of this gas. Cosmic rays can also contribute to the heating but they require an average gas density larger than the observational constraints. We show that strong turbulent support maintains a high gas vertical scale height (0.3-4kpc) in the disk and can inhibit the formation of gravitationally-bound structures at all scales, offering a natural explanation for the weakness of star formation in 3C 326N. To conclude, the bright [CII] line indicates that strong AGN jet-driven turbulence may play a key role in enhancing the amount of molecular gas (positive feedback) but yet can prevent star formation on galactic scales (negative feedback).
    Astronomy and Astrophysics 10/2014; 574. DOI:10.1051/0004-6361/201423612 · 4.38 Impact Factor
  • Source
    P. Gratier · J. Pety · P. Boissé · S. Cabrit · P. Lesaffre · M. Gerin · G. Pineau des Forets ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Context. Some runaway stars are known to display IR arc-like structures around them, resulting from their interaction with surrounding interstellar material. The properties of these features as well as the processes involved in their formation are still poorly understood. Aims.We aim to understand the physical mechanisms that shape the dust arc observed near the runaway O-star AE Aur (HD 34078). Methods.We obtained and analyzed a high spatial resolution (4.4'') map of the 12CO(1-0) emission that is centered on HD 34078, and that combines data from both the IRAM interferometer and 30 m single-dish antenna. Results: One third of the 30 m flux mainly originates from two small (no larger than 5'' × 10'' or 0.013 × 0.026 pc), and bright (1 and 3 K peak temperatures) CO globulettes. The line of sight toward HD 34078 intersects the outer part of one of the globulettes, which accounts for both the properties of diffuse UV light observed in the field and the numerous molecular absorption lines detected in HD 34078's spectra, including those from highly excited H2. Their modeled distance from the star(0.2 pc) is compatible with the fact that they lie on the 3D paraboloid, which fits the arc detected in the 24 μm Spitzer image. Four other compact CO globulettes are detected in the mapped area, all lying close to the rim of this paraboloid. These globulettes have a high density and linewidth, and are strongly pressure-confined or transient. Conclusions: The presence of molecular globulettes at such a close distance from an O star is unexpected, and probably related to the high proper motion of HD 34078. Indeed, the good spatial correlation between the CO globulettes and the IR arc suggests that they result from the interaction of the radiation and wind emitted by HD 34078 with the ambient gas. However, the details of this interaction remain unclear. A wind mass-loss rate significantly larger than the value inferred from UV lines is favored by the large IR arc size, but does not easily explain the low velocity of the CO globulettes. The effect of radiation pressure on dust grains also meets several issues in explaining the observations. Further observational and theoretical work is needed to fully elucidate the processes shaping the gas and dust in bow shocks around runaway O stars. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).PdeB map in FITS format is only available at the CDS via anonymous ftp to ftp://cdsarc.u-strasbg.fr ( or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/570/A71
    Astronomy and Astrophysics 10/2014; 570:71G. DOI:10.1051/0004-6361/201423466 · 4.38 Impact Factor
  • Source
    Benjamin Godard · Edith Falgarone · Guillaume Pineau Des Forêts ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Context. Tens of light hydrides and small molecules have now been detected over several hundreds sight lines sampling the diffuse interstellar medium (ISM) in both the Solar neighbourhood and the inner Galactic disk. They provide unprecedented statistics on the first steps of chemistry in the diffuse gas. Aims. These new data confirm the limitations of the traditional chemical pathways driven by the UV photons and the cosmic rays (CR) and the need for additional energy sources, such as turbulent dissipation, to open highly endoenergetic formation routes. The goal of the present paper is to further investigate the link between specific species and the properties of the turbulent cascade in particular its space-time intermittency. Methods. We have analysed ten different atomic and molecular species in the framework of the updated model of turbulent dissipation regions (TDR). We study the influence on the abundances of these species of parameters specific to chemistry (density, UV field, and CR ionisation rate) and those linked to turbulence (the average turbulent dissipation rate, the dissipation timescale, and the ion neutral velocity drift in the regions of dissipation). Results. The most sensitive tracers of turbulent dissipation are the abundances of CH+ and SH+, and the column densities of the J = 3, 4, 5 rotational levels of H2 . The abundances of CO, HCO+, and the intensity of the 158 $\mu$m [CII] emission line are significantly enhanced by turbulent dissipation. The vast diversity of chemical pathways allows the independent determinations of free parameters never estimated before: an upper limit to the average turbulent dissipation rate, $\overline{\varepsilon}$ < 10$^{-23}$ erg cm$^{-3}$ s$^{-1}$ for $n_H$=20 cm$^{-3}$, from the CH+ abundance; an upper limit to the ion-neutral velocity drift, $u_{in}$ < 3.5 km s$^{-1}$, from the SH+ to CH+ abundance ratio; and a range of dissipation timescales, 100 < $\tau_V$ < 1000 yr, from the CO to HCO+ abundance ratio. For the first time, we reproduce the large abundances of CO observed on diffuse lines of sight, and we show that CO may be abundant even in regions with UV-shieldings as low as $5 \times 10^{-3}$ mag. The best range of parameters also reproduces the abundance ratios of OH, C2H, and H2O to HCO+ and are consistent with the known properties of the turbulent cascade in the Galactic diffuse ISM. Conclusions. Our results disclose an unexpected link between the dissipation of turbulence and the emergence of molecular richness in the diffuse ISM. Some species, such as CH+ or SH+, turn out to be unique tracers of the energy trail in the ISM. In spite of some degeneracy, the properties of the turbulent cascade, down to dissipation, can be captured through specific molecular abundances.
    Astronomy and Astrophysics 08/2014; 570. DOI:10.1051/0004-6361/201423526 · 4.38 Impact Factor
  • D. R. Flower · G. Pineau des Forets ·
    [Show abstract] [Hide abstract]
    ABSTRACT: We have computed C- and J-type models of shock waves in molecular outflow sources. In addition to the (optically thin) emission line spectrum of molecular hydrogen, the spectra of CO, OH, SiO, H2O and NH3 were computed by means of the large velocity gradient approximation. We find that the intensities of the OH lines are particularly sensitive to the character (C- or J-type) of the shock wave. The results of these computations were used to guide the interpretation of the spectrum of the outflow source NGC 1333 IRAS 4B, recently observed by Herschel/PACS and the Spitzer satellites. We find that the best overall fit to the spectrum of this object is provided by quasi-time-dependent (CJ-type) models, which have both C- and J-type characteristics; the dynamical age of the emitting region is found to be of the order of 102 yr. The principal limitation to the robustness of the predictions of the current model relate to the possible effects of dust on the dynamical and thermal profiles of the gas. Specifically, the shattering and vaporization of grains, which can enhance the total grain cross-section, have not been taken into account. Furthermore, there remain significant uncertainties relating to the rate of reformation of H2 molecules, on dust grains, at the high gas kinetic temperatures at which this process occurs in the shock wave.
    Monthly Notices of the Royal Astronomical Society 12/2013; 436(3):2143-2150. DOI:10.1093/mnras/stt1720 · 5.11 Impact Factor
  • Source
    Romane Le Gal · Pierre Hily-Blant · Alexandre Faure · Guillaume Pineau des Forêts · Claire Rist · Sébastien Maret ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The aim of the present work is to perform a comprehensive analysis of the interstellar chemistry of nitrogen, focussing on the gas-phase formation of the smallest polyatomic species and in particular nitrogen hydrides. We present a new chemical network in which the kinetic rates of critical reactions have been updated based on recent experimental and theoretical studies, including nuclear spin branching ratios. Our network thus treats the different spin symmetries of the nitrogen hydrides self-consistently together with the ortho and para forms of molecular hydrogen. This new network is used to model the time evolution of the chemical abundances in dark cloud conditions. The steady-state results are analysed, with special emphasis on the influence of the overall amounts of carbon, oxygen, and sulphur. Our calculations are also compared with Herschel/HIFI observations of NH, NH$_2$, and NH$_3$ detected towards the external envelope of the protostar IRAS 16293-2422. The observed abundances and abundance ratios are reproduced for a C/O gas-phase elemental abundance ratio of $\sim0.8$, provided that the sulphur abundance is depleted by a factor larger than 2. The ortho-to-para ratio of H$_2$ in these models is $\sim10^{-3}$. Our models also provide predictions for the ortho-to-para ratios of NH$_2$ and NH$_3$ of $\sim2.3$ and $\sim0.7$ respectively. We conclude that the abundances of nitrogen hydrides in dark cloud conditions are consistent with the gas-phase synthesis predicted with our new chemical network.
    Astronomy and Astrophysics 11/2013; 562. DOI:10.1051/0004-6361/201322386 · 4.38 Impact Factor
  • P. Guillard · N. Nesvadba · P. Ogle · M. Lehnert · F. Boulanger · P. Appleton · G. Pineau des Forêts ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Observations by the Spitzer Space Telescope have revealed a population of radio galaxies with enhanced infrared molecular hydrogen (H_2) line cooling, above that expected by star formation heating alone. We present Herschel observations of these galaxies, which show unusually powerful [C II]λ 158μm line emission of very broad line-width. The C^+/PAH and C^+/FIR flux ratios are found to be extremely large, in most cases greatly in excess of that expected by photoelectric heating of the gas, and comparable in power to the mid-infrared H_2 lines. In contrast, [O I] emission is found to be quite weak. We show that the [C II] line emission mostly traces the molecular gas, and that a very large fraction of this gas is diffuse and warm. We also briefly discuss the possible heating sources of the gas (turbulent heating and/or cosmic rays). These results have profound consequences on our interpretation of FIR cooling lines at high-redshifts and on our understanding of dissipation of energy, feedback and energetics of galaxy formation in general. The fact that C^+ and H_2 can be strongly enhanced in shocks and turbulent systems in general will be of great importance for ALMA (and perhaps SPICA) observations which will extend Herschel observations to much higher redshifts, where the proportion of turbulently-heated molecular gas may be more important.
  • P. Boissé · S. R. Federman · G. Pineau des Forets · A. M. Ritchey ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Context. Spatial structure in molecular material has a strong impact on its physical and chemical evolution and is still poorly known, especially on very small scales. Aims: To better characterize the small-scale structure in diffuse molecular gas and in particular to investigate the CH+ production mechanism, we study the spatial distribution of CH+, CH, and CN towards the bright star ζ Per on scales in the range 1-20 AU. Methods: We use ζ Per's proper motion and the implied drift of the line of sight through the foreground gas at a rate of about 2 AU yr-1 to probe absorption line variations between adjacent lines of sight. The good S/N, high or intermediate resolution spectra of ζ Per, obtained in the interval 2003-2011, allow us to search for low column-density and line width variations for CH+, CH, and CN. Results: CH and CN lines appear remarkably stable in time, implying an upper limit δN/N ≤ 6% for CH and CN (3σ limit). The weak CH+λ4232 line shows a possible increase of 11% during the interval 2004-2007, which appears to be correlated with a comparable increase in the CH+ velocity dispersion over the same period. Conclusions: The excellent stability of CH and CN lines implies that these species are distributed uniformly to good accuracy within the cloud. The small size implied for the regions associated with the CH+ excess is consistent with scenarios in which this species is produced in very small (a few AU) localized active regions, possibly weakly magnetized shocks or turbulent vortices. Based on observations made at McDonald Observatory (USA) and Observatoire de Haute-Provence (France).
    Astronomy and Astrophysics 11/2013; 559:131-. DOI:10.1051/0004-6361/201322562 · 4.38 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present the first Herschel spectroscopic detections of the [OI]63 and [CII]158 micron fine-structure transitions, and a single para-H2O line from the 35 x 15 kpc^2 shocked intergalactic filament in Stephan's Quintet. The filament is believed to have been formed when a high-speed intruder to the group collided with clumpy intergroup gas. Observations with the PACS spectrometer provide evidence for broad (> 1000 km s^-1) luminous [CII] line profiles, as well as fainter [OI]63micron emission. SPIRE FTS observations reveal water emission from the p-H2O (111-000) transition at several positions in the filament, but no other molecular lines. The H2O line is narrow, and may be associated with denser intermediate-velocity gas experiencing the strongest shock-heating. The [CII]/PAH{tot) and [CII]/FIR ratios are too large to be explained by normal photo-electric heating in PDRs. HII region excitation or X-ray/Cosmic Ray heating can also be ruled out. The observations lead to the conclusion that a large fraction the molecular gas is diffuse and warm. We propose that the [CII], [OI] and warm H2 line emission is powered by a turbulent cascade in which kinetic energy from the galaxy collision with the IGM is dissipated to small scales and low-velocities, via shocks and turbulent eddies. Low-velocity magnetic shocks can help explain both the [CII]/[OI] ratio, and the relatively high [CII]/H2 ratios observed. The discovery that [CII] emission can be enhanced, in large-scale turbulent regions in collisional environments has implications for the interpretation of [CII] emission in high-z galaxies.
    The Astrophysical Journal 09/2013; 777(1). DOI:10.1088/0004-637X/777/1/66 · 5.99 Impact Factor
  • Source
    Pierre Hily-Blant · G. Pineau des Forets · Alexandre Faure · Romane Le Gal · Marco Padovani ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Understanding the origin of the composition of solar system cosmomaterials is a central question, not only in the cosmochemistry and astrochemistry fields, and requires various approaches to be combined. Measurements of isotopic ratios in cometary materials provide strong constraints on the content of the protosolar nebula. Their relation with the composition of the parental dark clouds is, however, still very elusive. In this paper, we bring new constraints based on the isotopic composition of nitrogen in dark clouds, with the aim of understanding the chemical processes that are responsible for the observed isotopic ratios. We have observed and detected the fundamental rotational transition of C$^{15}$N towards two starless dark clouds, L1544 and L1498. We were able to derive the column density ratio of C$^{15}$N over $^{13}$CN towards the same clouds, and obtain the CN/C$^{15}$N isotopic ratios, which were found to be $500\pm75$ for both L1544 and L1498. These values are therefore marginally consistent with the protosolar value of 441. Moreover, this ratio is larger than the isotopic ratio of nitrogen measured in HCN. In addition, we present model calculations of the chemical fractionation of nitrogen in dark clouds, which make it possible to understand how CN can be deprived of $^{15}$N and HCN can simultaneously be enriched in heavy nitrogen. The non-fractionation of N2H+, however, remains an open issue and we propose some chemical way of alleviating the discrepancy between model predictions and the observed ratios.
    Astronomy and Astrophysics 08/2013; 557. DOI:10.1051/0004-6361/201321364 · 4.38 Impact Factor
  • Source
    Pierre Hily-Blant · G. Pineau Des Forêts · Alexandre Faure · Romane Le Gal · Marco Padovani ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Accepted for publication in A&A ; http://dx.doi.org/10.1051/0004-6361/201321364
  • A. Faure · P. Hily-Blant · R. Le Gal · C. Rist · G. Pineau des Forêts ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The ortho-para chemistry of ammonia in the cold interstellar medium is investigated using a gas-phase chemical network. Branching ratios for the primary reaction chain involved in the formation and destruction of ortho- and para-NH3 were derived using angular momentum rules based on the conservation of the nuclear spin. We show that the "anomalous" ortho-to-para ratio of ammonia (~0.7) observed in various interstellar regions is in fact consistent with nuclear spin selection rules in a para-enriched H2 gas. This ratio is found to be independent of temperature in the range 5-30 K. We also predict an ortho-to-para ratio of ~2.3 for NH2. We conclude that a low ortho-to-para ratio of H2 naturally drives the ortho-to-para ratios of nitrogen hydrides below the statistical values.
    The Astrophysical Journal Letters 05/2013; 770(1):L2. DOI:10.1088/2041-8205/770/1/L2 · 5.34 Impact Factor
  • D. R. Flower · G. Pineau Des Forets ·
    [Show abstract] [Hide abstract]
    ABSTRACT: We have developed further the technique of time-dependent modelling of magnetohydrodynamic shock waves, with a view to interpreting the molecular line emission from outflow sources. The extensively observed source L1157 B1 was chosen as an exemplar of the application of this technique. (8 data files).

Publication Stats

3k Citations
693.94 Total Impact Points


  • 2004-2015
    • French National Centre for Scientific Research
      • Institut d'astrophysique spatiale (IAS)
      Lutetia Parisorum, Île-de-France, France
  • 2000-2015
    • Université Paris-Sud 11
      • Institut d'Astrophysique Spatiale
      Orsay, Île-de-France, France
  • 1995-2015
    • Ecole Normale Supérieure de Paris
      • Laboratoire de Radioastronomie
      Lutetia Parisorum, Île-de-France, France
  • 2000-2013
    • Institut d'Astrophysique Spatiale
      Lutetia Parisorum, Île-de-France, France
  • 2006
    • Institute for Advanced Study
      Princeton Junction, New Jersey, United States
  • 2005
    • Institut de Radioastronomie Millimétrique
      Grenoble, Rhône-Alpes, France
  • 1975-2005
    • Observatoire de Paris
      Lutetia Parisorum, Île-de-France, France
  • 2001
    • Université de Rennes 2
      Roazhon, Brittany, France
  • 1997
    • University of Bristol
      • School of Chemistry
      Bristol, England, United Kingdom
  • 1983-1997
    • Durham University
      • Department of Physics
      Durham, England, United Kingdom
  • 1994
    • Max Planck Institute for Radio Astronomy
      Bonn, North Rhine-Westphalia, Germany
  • 1987-1992
    • Institute of Geophysics, China Earthquake Administration
      Peping, Beijing, China
  • 1991
    • Duke University
      • Department of Physics
      Durham, North Carolina, United States
  • 1988
    • Harvard-Smithsonian Center for Astrophysics
      Cambridge, Massachusetts, United States