The Transition from Diffuse Molecular Gas to Molecular Cloud Material in Taurus

The short-lived 26Al radionuclide is thought to have been admixed into the initially 26Al-poor protosolar molecular cloud before or contemporaneously with its collapse. Bulk inner Solar System reservoirs record positively correlated variability in mass-independent 54Cr and 26Mg*, the decay product of 26Al. This correlation is interpreted as reflecting progressive thermal processing of in-falling 26Al-rich molecular cloud material in the inner Solar System. The thermally unprocessed molecular cloud matter reflecting the nucleosynthetic makeup of the molecular cloud before the last addition of stellar-derived 26Al has not been identified yet but may be preserved in planetesimals that accreted in the outer Solar System. We show that metal-rich carbonaceous chondrites and their components have a unique isotopic signature extending from an inner Solar System composition toward a 26Mg*-depleted and 54Cr-enriched component. This composition is consistent with that expected for thermally unprocessed primordial molecular cloud material before its pollution by stellar-derived 26Al. The 26Mg* and 54Cr compositions of bulk metal-rich chondrites require significant amounts (25–50%) of primordial molecular cloud matter in their precursor material. Given that such high fractions of primordial molecular cloud material are expected to survive only in the outer Solar System, we infer that, similarly to cometary bodies, metal-rich carbonaceous chondrites are samples of planetesimals that accreted beyond the orbits of the gas giants. The lack of evidence for this material in other chondrite groups requires isolation from the outer Solar System, possibly by the opening of disk gaps from the early formation of gas giants.

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Evidence for feedback and stellar-dynamically regulated bursty star cluster formation: the case of the Orion Nebula Cluster

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732151 ◽

2018 ◽

Vol 612 ◽

pp. A74 ◽

Cited By ~ 18

Author(s):

Pavel Kroupa ◽

Tereza Jeřábková ◽

František Dinnbier ◽

Giacomo Beccari ◽

Zhiqiang Yan

Keyword(s):

Molecular Cloud ◽

Massive Stars ◽

Cluster Formation ◽

Life Time ◽

Molecular Gas ◽

Orion Nebula ◽

Main Sequence Stars ◽

Sequence Of Events ◽

Proposed Model ◽

Magnitude Diagram

A scenario for the formation of multiple co-eval populations separated in age by about 1 Myr in very young clusters (VYCs, ages less than 10 Myr) and with masses in the range 600–20 000 M⊙ is outlined. It rests upon a converging inflow of molecular gas building up a first population of pre-main sequence stars. The associated just-formed O stars ionise the inflow and suppress star formation in the embedded cluster. However, they typically eject each other out of the embedded cluster within 106 yr, that is before the molecular cloud filament can be ionised entirely. The inflow of molecular gas can then resume forming a second population. This sequence of events can be repeated maximally over the life-time of the molecular cloud (about 10 Myr), but is not likely to be possible in VYCs with mass <300 M⊙, because such populations are not likely to contain an O star. Stellar populations heavier than about 2000 M⊙ are likely to have too many O stars for all of these to eject each other from the embedded cluster before they disperse their natal cloud. VYCs with masses in the range 600–2000 M⊙ are likely to have such multi-age populations, while VYCs with masses in the range 2000–20 000 M⊙ can also be composed solely of co-eval, mono-age populations. More massive VYCs are not likely to host sub-populations with age differences of about 1 Myr. This model is applied to the Orion Nebula Cluster (ONC), in which three well-separated pre-main sequences in the colour–magnitude diagram of the cluster have recently been discovered. The mass-inflow history is constrained using this model and the number of OB stars ejected from each population are estimated for verification using Gaia data. As a further consequence of the proposed model, the three runaway O star systems, AE Aur, μ Col and ι Ori, are considered as significant observational evidence for stellar-dynamical ejections of massive stars from the oldest population in the ONC. Evidence for stellar-dynamical ejections of massive stars in the currently forming population is also discussed.

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Molecular and ionized gas kinematics in the GC Radio Arc

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316012242 ◽

2016 ◽

Vol 11 (S322) ◽

pp. 133-136

Author(s):

N. Butterfield ◽

C.C. Lang ◽

E. A. C. Mills ◽

D. Ludovici ◽

J. Ott ◽

...

Keyword(s):

Star Formation ◽

Molecular Cloud ◽

Molecular Clouds ◽

Radio Continuum ◽

Molecular Gas ◽

The South ◽

Ionized Gas ◽

Molecular Emission ◽

Gas Kinematics

AbstractWe present NH3 and H64α+H63α VLA observations of the Radio Arc region, including the M0.20 – 0.033 and G0.10 – 0.08 molecular clouds. These observations suggest the two velocity components of M0.20 – 0.033 are physically connected in the south. Additional ATCA observations suggest this connection is due to an expanding shell in the molecular gas, with the centroid located near the Quintuplet cluster. The G0.10 – 0.08 molecular cloud has little radio continuum, strong molecular emission, and abundant CH3OH masers, similar to a nearby molecular cloud with no star formation: M0.25+0.01. These features detected in G0.10 – 0.08 suggest dense molecular gas with no signs of current star formation.

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Relative Alignment between the Magnetic Field and Molecular Gas Structure in the Vela C Giant Molecular Cloud Using Low- and High-density Tracers

The Astrophysical Journal ◽

10.3847/1538-4357/ab1eb0 ◽

2019 ◽

Vol 878 (2) ◽

pp. 110 ◽

Cited By ~ 14

Author(s):

Laura M. Fissel ◽

Peter A. R. Ade ◽

Francesco E. Angilè ◽

Peter Ashton ◽

Steven J. Benton ◽

...

Keyword(s):

Magnetic Field ◽

Molecular Cloud ◽

High Density ◽

Molecular Gas ◽

Giant Molecular Cloud ◽

The Magnetic Field

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A VLBI Study of H2O Maser Spots Associated with a Molecular Outflow ρ Oph-East

International Astronomical Union Colloquium ◽

10.1017/s0252921100019126 ◽

1994 ◽

Vol 140 ◽

pp. 60-61

Author(s):

Takahiro Iwata ◽

Hiroshi Takaba ◽

Kin-Ya Matsumoto ◽

Seiji Kameno ◽

Noriyuki Kawaguchi

Keyword(s):

Molecular Cloud ◽

Observational Evidence ◽

Molecular Gas ◽

Mass Star ◽

Dynamical Interaction ◽

Star Forming ◽

Star Forming Regions ◽

Molecular Outflow ◽

Low Mass ◽

A Site

A molecular outflow is one of the most conspicuous active phenomena associated with protostars, and the kinetic energy of its outflowing mass is as large as that of random motions of ambient molecular cloud, which suggests that outflow has dynamically influence on ambient molecular gas. Possible observational evidence which suggests the existence of dynamical interaction between molecular outflow and ambient molecular cloud has been detected in several star forming regions (Fukui et al. 1986; Iwata et al. 1988). Recent detections of H2O maser emission associated with low-mass protostars (e.g. Comoretto et al. 1990) also suggest that there still exist active phenomena in the low-mass star forming regions.Molecular outflow ρ Oph-East, discovered toward a low-mass protostar IRAS 16293-2422 (Fukui et al. 1986), has been known as a site of dynamical interaction between molecular outflowing gas and ambient molecular cloud by CO and NH3 observation (Mizuno et al. 1990). Existence of several strong H2O maser spots (Wilking & Claussen 1987; Wotten 1989; Terebey et al. 1992) also suggests that active phenomena are occurring in this region. In this paper, we report our result of H2O maser observation for molecular outflow ρ Oph-East with milli-arcsecond resolution by VLBI.

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Histogram of oriented gradients: a technique for the study of molecular cloud formation

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834300 ◽

2019 ◽

Vol 622 ◽

pp. A166 ◽

Cited By ~ 13

Author(s):

J. D. Soler ◽

H. Beuther ◽

M. Rugel ◽

Y. Wang ◽

P. C. Clark ◽

...

Keyword(s):

Spectral Line ◽

Spatial Correlation ◽

Molecular Cloud ◽

Galactic Plane ◽

Cloud Formation ◽

Molecular Gas ◽

Histogram Of Oriented Gradients ◽

Spatial Correlations ◽

Mhd Turbulence ◽

Physical Conditions

We introduce the histogram of oriented gradients (HOG), a tool developed for machine vision that we propose as a new metric for the systematic characterization of spectral line observations of atomic and molecular gas and the study of molecular cloud formation models. In essence, the HOG technique takes as input extended spectral-line observations from two tracers and provides an estimate of their spatial correlation across velocity channels. We characterized HOG using synthetic observations of HI and 13CO (J = 1 → 0) emission from numerical simulations of magnetohydrodynamic (MHD) turbulence leading to the formation of molecular gas after the collision of two atomic clouds. We found a significant spatial correlation between the two tracers in velocity channels where vHI ≈ v13CO, almost independent of the orientation of the collision with respect to the line of sight. Subsequently, we used HOG to investigate the spatial correlation of the HI, from The HI/OH/recombination line survey of the inner Milky Way (THOR), and the 13CO (J = 1 → 0) emission from the Galactic Ring Survey (GRS), toward the portion of the Galactic plane 33°.75 ≤l ≤ 35°.25 and |b| ≤ 1°.25. We found a significant spatial correlation between the two tracers in extended portions of the studied region. Although some of the regions with high spatial correlation are associated with HI self-absorption (HISA) features, suggesting that it is produced by the cold atomic gas, the correlation is not exclusive to this kind of region. The HOG results derived for the observational data indicate significant differences between individual regions: some show spatial correlation in channels around vHI ≈ v13CO while others present spatial correlations in velocity channels separated by a few kilometers per second. We associate these velocity offsets to the effect of feedback and to the presence of physical conditions that are not included in the atomic-cloud-collision simulations, such as more general magnetic field configurations, shear, and global gas infall.

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Abundance variations of tracers and their effects on our determination of molecular cloud structure

Symposium - International Astronomical Union ◽

10.1017/s0074180900198882 ◽

1991 ◽

Vol 147 ◽

pp. 177-181

Author(s):

Paul F. Goldsmith

Keyword(s):

Molecular Cloud ◽

Molecular Clouds ◽

Column Density ◽

Critical Issue ◽

Structure Stability ◽

Molecular Gas ◽

Cloud Structure ◽

Molecular Tracer ◽

Short Presentation

Our understanding of the molecular phase of the interstellar medium is critically dependent on use of various lines from different molecular species to trace this dense material. As our knowledge of molecular clouds becomes more refined, and we pursue in detail issues of molecular cloud structure, stability, and how star formation depends on and affects the molecular gas, it is appropriate to examine the basis by which we determine the morphology of clouds, their density, and other key parameters. This is obviously a major undertaking, well beyond the scope of the short presentation at this conference, so I will concentrate on one very basic, but critical issue, which is that of abundance variations of tracers of density and molecular column density which are widely used to delineate the denser portions of all types of molecular clouds. In this summary, I will first highlight some of the apparent indications of significant variations of abundance within individual clouds, as a way of indicating some potential dangers and the importance of the molecular tracer selected. I will also briefly suggest how such variations may be themselves important diagnostics of cloud structure and evolution.

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Building protoplanetary disks from the molecular cloud: redefining the disk timeline

Astronomy and Astrophysics ◽

10.1051/0004-6361/201730677 ◽

2019 ◽

Vol 624 ◽

pp. A93 ◽

Cited By ~ 2

Author(s):

K. Baillié ◽

J. Marques ◽

L. Piau

Keyword(s):

Molecular Cloud ◽

Protoplanetary Disk ◽

Giant Planets ◽

Type I ◽

Initial State ◽

Disk Formation ◽

Heat Transition ◽

Cloud Material ◽

Selection Of ◽

Collapse Phase

Context. Planetary formation models are necessary to understand the characteristics of the planets that are the most likely to survive. Their dynamics, their composition and even the probability of their survival depend on the environment in which they form. We therefore investigate the most favorable locations for planetary embryos to accumulate in the protoplanetary disk: the planet traps. Aims. We study the formation of the protoplanetary disk by the collapse of a primordial molecular cloud, and how its evolution leads to the selection of specific types of planets. Methods. We use a hydrodynamical code that accounts for the dynamics, thermodynamics, geometry and composition of the disk to numerically model its evolution as it is fed by the infalling cloud material. As the mass accretion rate of the disk onto the star determines its growth, we can calculate the stellar characteristics by interpolating its radius, luminosity and temperature over the stellar mass from pre-calculated stellar evolution models. The density and midplane temperature of the disk then allow us to model the interactions between the disk and potential planets and determine their migration. Results. At the end of the collapse phase, when the disk reaches its maximum mass, it pursues its viscous spreading, similarly to the evolution from a minimum mass solar nebula (MMSN). In addition, we establish a timeline equivalence between the MMSN and a “collapse-formed disk” that would be older by about 2 Myr. Conclusions. We can save various types of planets from a fatal type-I inward migration: in particular, planetary embryos can avoid falling on the star by becoming trapped at the heat transition barriers and at most sublimation lines (except the silicates one). One of the novelties concerns the possible trapping of putative giant planets around a few astronomical units from the star around the end of the infall. Moreover, trapped planets may still follow the traps outward during the collapse phase and inward after it. Finally, this protoplanetary disk formation model shows the early possibilities of trapping planetary embryos at disk stages that are anterior by a few million years to the initial state of the MMSN approximation.

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Erratum: Molecular cloud formation as seen in synthetic H i and molecular gas observations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stv2913 ◽

2016 ◽

Vol 456 (3) ◽

pp. 3212-3212

Author(s):

Jonathan S. Heiner ◽

Enrique Vázquez-Semadeni ◽

Javier Ballesteros-Paredes

Keyword(s):

Molecular Cloud ◽

Cloud Formation ◽

Molecular Gas

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Ices in star forming regions

Symposium - International Astronomical Union ◽

10.1017/s0074180900009232 ◽

1997 ◽

Vol 178 ◽

pp. 45-60 ◽

Cited By ~ 11

Author(s):

A.G.G.M. Tielens ◽

D.C.B. Whittet

Keyword(s):

Ir Spectra ◽

Gas Phase ◽

Molecular Cloud ◽

Oxidation Reactions ◽

Star Forming ◽

Star Forming Regions ◽

Interstellar Ice ◽

Simple Molecules ◽

Absorption Features ◽

Cloud Material

IR spectra of sources associated with molecular cloud material show a variety of absorption features attributed to simple molecules, such as H2O, CO, CH3OH, CO2, CH4, and OCS in icy grain mantles. These identifications are reviewed. These molecules are formed through accretion and reaction of gas phase species on grain surfaces. The high abundance of CH3OH and CO2 point towards the importance of hydrogenation and oxidation reactions in this process. Observations also show that thermal outgassing is of great importance for the composition of interstellar ice mantles. Both these processes are discussed in some detail.

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