Evolution of very small particles in the southern part of Orion B observed by ISOCAM

Abergel, A.; Bernard, J.-P.; Boulanger, F.; Cesarsky, D.; Falgarone, É.; Jones, A. P.; Miville-Deschênes, M.-A.; Pérault, M.; Puget, J.‐L.; Huldtgren, M.; Kaas, A. A.; Nordh, L.; Olofsson, G.; André, P.; Bontemps, Sylvain; Casali, M.; Césarsky, C. J.; Copet, M. E.; Davies, Jonathan Ivor; Montmerle, T.; Persi, P.; Sibille, F.

doi:10.1051/0004-6361:20020324

Cited by 60 publications

(64 citation statements)

References 45 publications

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“…The detection, at both 8 and 21 µm, allows the rejection of peaks of infrared emission created by small grains at the interface of photo-dissociation regions and molecular clumps (e.g. Abergel et al 2002). The latter are actually externally heated sources whose peaks shift with wavelength and sometimes disappear at 21 µm.…”

Section: Coincidence With Mid-infrared Point Sourcesmentioning

confidence: 99%

The earliest phases of high-mass star formation: a 3 square degree millimeter continuum mapping of Cygnus X

Motte

Bontemps

Schilke

et al. 2007

A&A

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327

722

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Aims. Our current knowledge of high-mass star formation is mainly based on follow-up studies of bright sources found by IRAS, and is thus biased against its earliest phases, inconspicuous at infrared wavelengths. We therefore started searching, in an unbiased way and in the closest high-mass star-forming complexes, for the high-mass analogs of low-mass pre-stellar cores and class 0 protostars. Methods. We have made an extensive 1.2 mm continuum mosaicing study of the Cygnus X molecular cloud complex using the MAMBO cameras at the IRAM 30 m telescope. The ∼ 3 • 2 imaged areas cover all the high-column density (A V ≥ 15 mag) clouds of this nearby (∼ 1.7 kpc) cloud complex actively forming OB stars. We then compared our millimeter maps with mid-infrared images, and have made SiO(2-1) follow-up observations of the best candidate progenitors of high-mass stars. Results. Our complete study of Cygnus X with ∼ 0.09 pc resolution provides, for the first time, an unbiased census of massive young stellar objects. We discover 129 massive dense cores (FWHM size ∼ 0.1 pc, M 1.2 mm = 4 − 950 M ⊙ , volume-averaged density ∼ 10 5 cm −3 ), among which ∼ 42 are probable precursors of high-mass stars. A large fraction of the Cygnus X dense cores (2/3 of the sample) remain undetected by the MSX satellite, regardless of the mass range considered. Among the most massive (> 40 M ⊙ ) cores, infrared-quiet objects are driving powerful outflows traced by SiO emission. Our study qualifies 17 cores as good candidates for hosting massive infrared-quiet protostars, while up to 25 cores potentially host high-luminosity infrared protostars. We fail to discover in the high-mass analogs of pre-stellar dense cores (∼ 0.1 pc, > 10 4 cm −3 ) in Cygnus X, but find several massive starless clumps (∼ 0.8 pc, 7 × 10 3 cm −3 ) that might be gravitationally bound. Conclusions. Since our sample is derived from a single molecular complex and covers every embedded phase of high-mass star formation, it gives the first statistical estimates of their lifetime. In contrast to what is found for low-mass class 0 and class I phases, the infrared-quiet protostellar phase of high-mass stars may last as long as their better-known high-luminosity infrared phase. The statistical lifetimes of high-mass protostars and pre-stellar cores (∼ 3 × 10 4 yr and < 10 3 yr) in Cygnus X are one and two order(s) of magnitude smaller, respectively, than what is found in nearby, low-mass star-forming regions. We therefore propose that high-mass pre-stellar and protostellar cores are in a highly dynamic state, as expected in a molecular cloud where turbulent processes dominate.

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Section: Coincidence With Mid-infrared Point Sourcesmentioning

confidence: 99%

The earliest phases of high-mass star formation: a 3 square degree millimeter continuum mapping of Cygnus X

Motte

Bontemps

Schilke

et al. 2007

A&A

Self Cite

327

722

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“…A local increase in the photoelectric heating rate can have various causes. In particular, there is increasing observational evidence of evolution of the very small dust particles, including PAHs and very small grains (VSGs) in the illuminated parts of the cloud (Boulanger et al 1988(Boulanger et al , 1990Bernard et al 1993;Abergel et al 2002;Rapacioli et al 2005;Berné et al 2007;Compiègne et al 2008). Increasing the abundance of the smaller grains that dominate the photoelectric effect would lead to higher gas temperatures (e.g., Bakes & Tielens 1994;Weingartner & Draine 2001).…”

Section: Local Heating Via the Photoelectric Effectmentioning

confidence: 99%

Excitation of H₂in photodissociation regions as seen bySpitzer

Habart

Abergel

Boulanger

et al. 2011

A&A

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Aims. We present spectroscopic observations obtained with the infrared Spitzer Space Telescope, which provide insight into the H 2 physics and gas energetics in photodissociation regions (PDRs) of low to moderate far-ultraviolet (FUV) fields and densities. Methods. We analyze data on six well known Galactic PDRs (L1721, California, N7023E, Horsehead, rho Oph, N2023N), sampling a poorly explored range of excitation conditions (χ ∼ 5−10 3 ), relevant to the bulk of molecular clouds in galaxies. Spitzer observations of H 2 rotational lines are complemented with H 2 data, including ro-vibrational line measurements, obtained with ground-based telescopes and ISO, to constrain the relative contributions of ultraviolet pumping and collisions to the H 2 excitation. The data analysis is supported by model calculations with the Meudon PDR code. Results. The observed column densities of rotationally excited H 2 are observed to be much higher than PDR model predictions. In the lowest excitation PDRs, the discrepancy between the model and the data is about one order of magnitude for rotational levels J ≥ 3. We discuss whether an enhancement in the H 2 formation rate or a local increase in photoelectric heating, as proposed for brighter PDRs in former ISO studies, may improve the data-model comparison. We find that an enhancement in the H 2 formation rates reduces the discrepancy, but the models still fall short of the data. Conclusions. This large disagreement suggests that our understanding of the formation and excitation of H 2 and/or of PDRs energetics is still incomplete. We discuss several explanations, which could be further tested using the Herschel Space Telescope.

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“…And observations have identified small-scale (∼ 0.01−1 pc) fluctuations in the local dust-to-gas ratio of large grains in a number of nearby molecular clouds (Thoraval et al 1997(Thoraval et al , 1999Abergel et al 2002;Flagey et al 2009;Boogert et al 2013). Across different regions in the ISM, variations in extinction curves and emission/absorption features similarly suggest there may be large fluctuations in the relative abundance of large grains (Miville-Deschênes et al 2002;Gordon et al 2003;Dobashi et al 2008;Paradis et al 2009).…”

Section: Introductionmentioning

confidence: 99%

The dynamics of charged dust in magnetized molecular clouds

Lee

Hopkins

Squire

2017

Monthly Notices of the Royal Astronomical Society

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We study the dynamics of large, charged dust grains in turbulent giant molecular clouds (GMCs). Massive dust grains behave as aerodynamic particles in primarily neutral dense gas, and thus are able to produce dramatic small-scale fluctuations in the dust-to-gas ratio. Hopkins & Lee (2016) directly simulated the dynamics of neutral dust grains in super-sonic MHD turbulence, typical of GMCs, and showed that the dust-to-gas fluctuations can exceed factor ∼ 1000 on small scales, with important implications for star formation, stellar abundances, and dust behavior and growth. However, even in primarily neutral gas in GMCs, dust grains are negatively charged and Lorentz forces are non-negligible. Therefore, we extend our previous study by including the effects of Lorentz forces on charged grains (in addition to drag). For small charged grains (sizes 0.1 µm), Lorentz forces suppress dust-to-gas ratio fluctuations, while for large grains (sizes 1 µm), Lorentz forces have essentially no effect, trends that are well explained with a simple theory of dust magnetization. In some special intermediate cases, Lorentz forces can enhance dust-gas segregation. Regardless, for the physically expected scaling of dust charge with grain size, we find the most important effects depend on grain size (via the drag equation) with Lorentz forces/charge as a second-order correction. We show that the dynamics we consider are determined by three dimensionless numbers in the limit of weak background magnetic fields: the turbulent Mach number, a dust drag parameter (proportional to grain size) and a dust Lorentz parameter (proportional to grain charge); these allow us to generalize our simulations to a wide range of conditions.

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Evolution of very small particles in the southern part of Orion B observed by ISOCAM

Cited by 60 publications

References 45 publications

The earliest phases of high-mass star formation: a 3 square degree millimeter continuum mapping of Cygnus X

The earliest phases of high-mass star formation: a 3 square degree millimeter continuum mapping of Cygnus X

Excitation of H₂in photodissociation regions as seen bySpitzer

The dynamics of charged dust in magnetized molecular clouds

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Evolution of very small particles in the southern part of Orion B observed by ISOCAM

Cited by 60 publications

References 45 publications

The earliest phases of high-mass star formation: a 3 square degree millimeter continuum mapping of Cygnus X

The earliest phases of high-mass star formation: a 3 square degree millimeter continuum mapping of Cygnus X

Excitation of H2in photodissociation regions as seen bySpitzer

The dynamics of charged dust in magnetized molecular clouds

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Product

Resources

About

Excitation of H₂in photodissociation regions as seen bySpitzer