scholarly journals The Dynamical Evolution of Young Clusters and Associations

1986 ◽  
Vol 7 ◽  
pp. 481-488 ◽  
Author(s):  
Robert D. Mathieu
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Initial Conditions ◽  
Dynamical Evolution ◽  
Short Review ◽  
Stellar Systems ◽  
Galactic Field ◽  
Dynamical State ◽  
Orbital Mixing ◽  
Formation Efficiency

A young cluster or association bears the imprint of the conditions at its birth for perhaps ten million years, after which the initial conditions are lost to either dilution in the galactic field or erasure by orbital mixing and stellar encounters. In its youngest years, however, the dynamical state of the system can provide valuable information concerning the structure and energetics of the parent gas, the star-formation efficiency and the star-formation process itself. This short review discusses recent theoretical and observational progress in the study of the very youngest of stellar systems.

scholarly journals The multiplicity of massive stars: a 2016 view

2016 ◽  
Vol 12 (S329) ◽  
pp. 110-117 ◽  
Author(s):  
Hugues Sana
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Massive Star ◽  
Main Sequence ◽  
Initial Conditions ◽  
Massive Stars ◽  
Massive Star Formation ◽  
Future Evolution

AbstractMassive stars like company. Here, we provide a brief overview of progresses made over the last 5 years by a number of medium and large surveys. These results provide new insights on the observed and intrinsic multiplicity properties of main sequence massive stars and on the initial conditions for their future evolution. They also bring new interesting constraints on the outcome of the massive star formation process.

scholarly journals The Herschel View of Star Formation

2012 ◽  
Vol 10 (H16) ◽  
pp. 31-48 ◽  
Author(s):  
Philippe André
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Initial Conditions ◽  
Filamentary Structure ◽  
Star Forming ◽  
Submillimeter Wavelengths ◽  
Global Rate ◽  
Prestellar Cores ◽  
Stellar Masses ◽  
Key Steps

AbstractRecent studies of the nearest star-forming clouds of the Galaxy at submillimeter wavelengths with the Herschel Space Observatory have provided us with unprecedented images of the initial conditions and early phases of the star formation process. The Herschel images reveal an intricate network of filamentary structure in every interstellar cloud. These filaments all exhibit remarkably similar widths - about a tenth of a parsec - but only the densest ones contain prestellar cores, the seeds of future stars. The Herschel results favor a scenario in which interstellar filaments and prestellar cores represent two key steps in the star formation process: first turbulence stirs up the gas, giving rise to a universal web-like structure in the interstellar medium, then gravity takes over and controls the further fragmentation of filaments into prestellar cores and ultimately protostars. This scenario provides new insight into the inefficiency of star formation, the origin of stellar masses, and the global rate of star formation in galaxies. Despite an apparent complexity, global star formation may be governed by relatively simple universal laws from filament to galactic scales.

scholarly journals FAR-ULTRAVIOLET SURVEYS OF GLOBULAR CLUSTERS: HUNTING FOR THE PRODUCTS OF STELLAR COLLISIONS AND NEAR MISSES

2004 ◽  
Vol 19 (27) ◽  
pp. 2013-2027 ◽  
Author(s):  
CHRISTIAN KNIGGE
Keyword(s):  
Binary Stars ◽  
Globular Clusters ◽  
Dynamical Evolution ◽  
Stellar Populations ◽  
Short Review ◽  
Stellar Systems ◽  
Near Misses ◽  
Close Encounters ◽  
Stellar Collisions ◽  
Far Ultraviolet

Globular clusters are gravitationally bound stellar systems containing on the order of 105 stars. Due to the high stellar densities in the cores of these clusters, close encounters and even physical collisions between stars are inevitable. These dynamical interactions can produce exotic types of single and binary stars that are extremely rare in the galactic field, but which may be important to the dynamical evolution of their host clusters. A common feature of these dynamically-formed stellar populations is that many of their members are relatively hot, and thus bright in the far-ultraviolet (FUV) waveband. In this short review, we describe how space-based FUV observations are being used to find and study these populations.

scholarly journals Angular momentum profiles of Class 0 protostellar envelopes

2020 ◽  
Vol 637 ◽  
pp. A92 ◽  
Author(s):  
M. Gaudel ◽  
A. J. Maury ◽  
A. Belloche ◽  
S. Maret ◽  
Ph. André ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Star Formation ◽  
Formation Process ◽  
Dynamic Range ◽  
Initial Conditions ◽  
Direct Consequence ◽  
High Dynamic Range ◽  
Momentum Conservation ◽  
Disk Formation ◽  
Rotational Motions

Context. Understanding the initial properties of star forming material and how they affect the star formation process is a key question. The infalling gas must redistribute most of its initial angular momentum inherited from prestellar cores before reaching the central stellar embryo. Disk formation has been naturally considered as a possible solution to this “angular momentum problem”. However, how the initial angular momentum of protostellar cores is distributed and evolves during the main accretion phase and the beginning of disk formation has largely remained unconstrained up to now. Aims. In the framework of the IRAM CALYPSO survey, we obtained observations of the dense gas kinematics that we used to quantify the amount and distribution of specific angular momentum at all scales in collapsing-rotating Class 0 protostellar envelopes. Methods. We used the high dynamic range C18O (2−1) and N2H+ (1−0) datasets to produce centroid velocity maps and probe the rotational motions in the sample of 12 envelopes from scales ~50 to ~5000 au. Results. We identify differential rotation motions at scales ≲1600 au in 11 out of the 12 protostellar envelopes of our sample by measuring the velocity gradient along the equatorial axis, which we fit with a power-law model v ∝ rα. This suggests that coherent motions dominate the kinematics in the inner protostellar envelopes. The radial distributions of specific angular momentum in the CALYPSO sample suggest the following two distinct regimes within protostellar envelopes: the specific angular momentum decreases as j ∝ r1.6±0.2 down to ~1600 au and then tends to become relatively constant around ~6 × 10−4 km s−1 pc down to ~50 au. Conclusions. The values of specific angular momentum measured in the inner Class 0 envelopes suggest that material directly involved in the star formation process (<1600 au) has a specific angular momentum on the same order of magnitude as what is inferred in small T-Tauri disks. Thus, disk formation appears to be a direct consequence of angular momentum conservation during the collapse. Our analysis reveals a dispersion of the directions of velocity gradients at envelope scales >1600 au, suggesting that these gradients may not be directly related to rotational motions of the envelopes. We conclude that the specific angular momentum observed at these scales could find its origin in other mechanisms, such as core-forming motions (infall, turbulence), or trace an imprint of the initial conditions for the formation of protostellar cores.

scholarly journals A Gaia view of the two OB associations Cygnus OB2 and Carina OB1: the signature of their formation process

2019 ◽  
Vol 490 (1) ◽  
pp. 440-454 ◽  
Author(s):  
Beomdu Lim ◽  
Yaël Nazé ◽  
Eric Gosset ◽  
Gregor Rauw
Keyword(s):  
Formation Process ◽  
Proper Motion ◽  
Dynamical Evolution ◽  
Structural Features ◽  
Stellar Systems ◽  
Star Forming ◽  
Kinematic Study ◽  
Ob Associations ◽  
Size Relation ◽  
Kinematic Properties

ABSTRACT OB associations are the prime star-forming sites in galaxies. However, the detailed formation process of such stellar systems still remains a mystery. In this context, identifying the presence of substructures may help in tracing the footprints of their formation process. Here, we present a kinematic study of the two massive OB associations Cygnus OB2 and Carina OB1 using the precise astrometry from the Gaia Data Release 2 and radial velocities. From the parallaxes of stars, these OB associations are confirmed to be genuine stellar systems. Both Cygnus OB2 and Carina OB1 are composed of a few dense clusters and a halo which have different kinematic properties: the clusters occupy regions of 5–8 parsecs in diameter and display small dispersions in proper motion, while the haloes spread over tens of parsecs with two to three times larger dispersions in proper motion. This is reminiscent of the so-called line width–size relation of molecular clouds related to turbulence. Considering that the kinematics and structural features were inherited from those of their natal clouds would then imply that the formation of OB associations may result from structure formation driven by supersonic turbulence, rather than from the dynamical evolution of individual embedded clusters.

scholarly journals The Short-Period Binary Frequency Among Low-Mass Pre-Main Sequence Stars

1992 ◽  
Vol 135 ◽  
pp. 30-40
Author(s):  
Robert D. Mathieu
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Main Sequence ◽  
Early Period ◽  
Dynamical Evolution ◽  
Orbital Evolution ◽  
Semi Major Axis ◽  
Single Star ◽  
Binary Formation ◽  
Short Period

The pre-main sequence (PMS) binary frequency is a fundamental datum in the study of binary formation. It reflects on numerous basic issues, such as:• The formation process. Binary stars are the primary branch of the star-formation process, and thus their frequency is an essential challenge to star-formation theories. (Indeed, the infrequency of single-star formation is likely as significant as the binary frequency.)• The epoch of binary formation. Assessing whether the binary population exists in total by the pre-main sequence phase sets an upper limit on the binary formation timescale.• Early period evolution. The frequency distribution as a function of period of PMS binaries, when compared to the distribution at the zero-age main sequence, can shed light on early orbital evolution.• The interaction of binaries with disks. The formation and consequent dynamical evolution of a binary with semi-major axis less than typical disk radii must substantially modify disk structures and accretion flows. Thus the binary frequency might differ between PMS stars with and without associated disks.

scholarly journals The Dynamical Evolution of Young Open Clusters

1985 ◽  
Vol 113 ◽  
pp. 463-465
Author(s):  
Michael Margulis ◽  
Charles J. Lada ◽  
David Dearborn
Keyword(s):  
Potential Function ◽  
Molecular Clouds ◽  
Initial Conditions ◽  
Stellar System ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Open Clusters ◽  
Stellar Systems ◽  
Spherically Symmetric ◽  
Star Forming

Using numerical N-body calculations we have simulated the dynamical evolution of young clusters as they emerge from molecular clouds. Starting with initially virialized systems of stars and gas we follow the evolution of these systems from the time immediately after the stars have formed in a cloud until a time long after all the residual star-forming gas has been dispersed. In the models stellar systems were composed of 50, and in some cases 100, stars and these stars were represented as point masses. The stellar mass function followed a power law with an index of −2.5 and ranged over two decades in mass (Scalo 1978). Gas in the models was represented as an extra term in the gravitational potential function governing stellar motions, and was set to follow a density distribution corresponding to a spherically symmetric Plummer potential function (Plummer 1911). Starting with these initial conditions, stellar motions were then integrated and evolution of each stellar system was followed as gas was dispersed from the vicinity of the stars as a function of time.

scholarly journals Radiation pressure limits on the star formation efficiency and surface density of compact stellar systems

2018 ◽  
Vol 481 (4) ◽  
pp. 4895-4906 ◽  
Author(s):  
Roland M Crocker ◽  
Mark R Krumholz ◽  
Todd A Thompson ◽  
Holger Baumgardt ◽  
Dougal Mackey
Keyword(s):  
Star Formation ◽  
Radiation Pressure ◽  
Surface Density ◽  
Stellar Systems ◽  
Formation Efficiency

scholarly journals Dynamical evolution of population III stellar systems and the resulting binary statistics

2020 ◽  
Vol 501 (1) ◽  
pp. 643-663
Author(s):  
Boyuan Liu ◽  
Georges Meynet ◽  
Volker Bromm
Keyword(s):  
Initial Conditions ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Initial Mass Function ◽  
Close Binary ◽  
Close Binaries ◽  
Small Scale ◽  
Stellar Systems ◽  
X Ray ◽  
Population Iii

ABSTRACT We use N-body simulations to study the dynamical evolution of population III (Pop III) stellar systems and the resulting binary statistics. We design a physically motivated framework for the initial conditions of Pop III star clusters, based on small-scale hydrodynamic simulations and the scale-free nature of disc evolution during Pop III star formation. Our novel approach enables us to explore the dependence of binary statistics on initial conditions and arrive at more robust predictions for the signals of Pop III X-ray binaries (XRBs) and binary black hole (BBH) mergers, compared to simple extrapolations of Pop III protostar systems. We find that binary properties are highly sensitive to the initial cluster size and distribution of binary separation, while the effect of initial mass function is relatively minor. Our simulations predict less close binaries, and thus, significantly lower efficiencies (by a factor of ∼10–104) for the formation and accretion of Pop III XRBs, than found in previous studies, implying that the contribution of Pop III XRBs to the cosmic X-ray background is negligible and their feedback effects are unimportant. We estimate the efficiency of Pop III BBH mergers as $\sim 10^{-5}\!-\!10^{-4}\ \rm M_{\odot }^{-1}$, for which three-body hardening by surrounding stars in dense star clusters or close binary interactions is required to facilitate in-spirals of BBHs. All simulation data, including catalogues of Pop III binaries and multiple systems, are publicly available.

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