scholarly journals Catching drifting pebbles

2018 ◽  
Vol 615 ◽  
pp. A178 ◽  
Author(s):  
Chris W Ormel ◽  
Beibei Liu
Keyword(s):  
Strong Coupling ◽  
Turbulent Diffusion ◽  
Stochastic Equation ◽  
Equation Of Motion ◽  
Parameter Study ◽  
Particle Inertia ◽  
Low Mass Stars ◽  
Outer Disk ◽  
Low Mass ◽  
Three Body

Turbulence plays a key role in the transport of pebble-sized particles. It also affects the ability of pebbles to be accreted by protoplanets because it stirs pebbles out of the disk midplane. In addition, turbulence suppresses pebble accretion once the relative velocities become too high for the settling mechanism to be viable. Following Paper I, we aim to quantify these effects by calculating the pebble accretion efficiency ε using three-body simulations. To model the effect of turbulence on the pebbles, we derive a stochastic equation of motion (SEOM) applicable to stratified disk configurations. In the strong coupling limit (ignoring particle inertia) the limiting form of this equation agrees with previous works. We conduct a parameter study and calculate ε in 3D, varying pebble and gas turbulence properties and accounting for the planet inclination. We find that strong turbulence suppresses pebble accretion through turbulent diffusion, agreeing closely with previous works. Another reduction of ε occurs when the turbulent rms motions are high and the settling mechanism fails. In terms of efficiency, the outer disk regions are more affected by turbulence than the inner regions. At the location of the H2O iceline, planets around low-mass stars achieve much higher efficiencies. Including the results from Paper I, we present a framework to obtain ε under general circumstances.

scholarly journals Dynamics of Galactic Nuclei Containing Massive Remnant Stars

1996 ◽  
Vol 174 ◽  
pp. 293-302
Author(s):  
H. M. Lee
Keyword(s):  
Stellar System ◽  
Dynamical Evolution ◽  
Galactic Nuclei ◽  
Low Mass Stars ◽  
Stellar Component ◽  
Long Time ◽  
Low Mass ◽  
Relaxation Time Scale ◽  
Three Body ◽  
Compact Cluster

We have examined the dynamical evolution of stellar system containing massive remnant stellar component. If individual mass of remnant stars is much heavier than that of normal stars which comprise most of the mass in the cluster, remnant stars quickly form a subsystem within the core of cluster of ordinary stars. The subsystem evolves on its own relaxation time scale which is very short. However, the post collapse expansion driven by the three-body binary heating becomes very slow because the expansion energy of the compact subcluster can be easily absorbed by surrounding cluster. The gravitational radiation can lead to the merger of binaries when binaries become very hard. A central seed black hole might form if repeated merger becomes very efficient. Otherwise, relatively stable two-component phase of central compact cluster of remnant stars surrounded by larger cluster of low mass stars would last for a long time.

scholarly journals Outbursts of young Sun-like stars may change how terrestrial planets form

2018 ◽  
Vol 14 (S345) ◽  
pp. 185-188
Author(s):  
P. Ábrahám ◽  
Á. Kóspál ◽  
L. Chen ◽  
A. Carmona
Keyword(s):  
Planetary System ◽  
Circumstellar Disk ◽  
The Sun ◽  
Low Mass Stars ◽  
Mid Infrared ◽  
Outer Disk ◽  
Amorphous Silicate ◽  
Low Mass ◽  
Silicate Feature ◽  
Infrared Monitoring

AbstractWhile the Sun is nowadays a quiet and well-balanced star, in its first few million years it might have been often out of temper, like those young low-mass stars which episodically undergo unpredictable outbursts. The prototype of one of the two classes of young erupting stars, EX Lupi, had its historically largest outburst in 2008. It brightened by a factor of 30 for six months, due to elevated accretion from the circumstellar disk on to the star. Our group observed the system during the outburst, and discovered the crystallisation of amorphous silicate grains in the inner disk by the heat of the outburst. Our mid-infrared monitoring of the freshly produced crystals revealed that their emission in the inner disk quickly dropped already within a year after the outburst. Here we report on new observations of the 10 µm silicate feature, obtained with the MIDI and VISIR instruments at Paranal Observatory, which demonstrate that within five years practically all forsterite disappeared from the inner disk. We attempt to model this process by an expanding wind that transports the crystals from the terrestrial zone to outer disk regions where comets are supposed to form. Since the eruptions of EX Lup are recurrent, we speculate that the early Sun also experienced similar brightenings, and the forming planetary system might have incorporated some of the mineralogical and chemical yields provided by the outbursts. EX Lup, as a proxy for the proto-Sun, may be a telltale object to understand the origin of molecules and minerals we routinely encounter on Earth.

scholarly journals Pillars, Jets and Dynamical Features

2010 ◽  
Vol 6 (S270) ◽  
pp. 319-322
Author(s):  
Matthias Gritschneder ◽  
Andreas Burkert ◽  
Thorsten Naab ◽  
Stefanie Walch
Keyword(s):  
Molecular Clouds ◽  
Hii Regions ◽  
Parameter Study ◽  
Low Mass Stars ◽  
Physical Conditions ◽  
Gravitational Forces ◽  
Irregular Structures ◽  
Low Mass ◽  
Dynamical Features ◽  
The Impact

AbstractWe present high resolution simulations on the impact of ionizing radiation on turbulent molecular clouds. The combination of hydrodynamics, gravitational forces and ionization in the tree-SPH code iVINE naturally leads to the formation of elongated filaments and clumps, which are in excellent agreement with the pillars observed around HII regions. Including gravity the formation of a second generation of low-mass stars with surrounding protostellar disks is triggered at the tips of the pillars, as also observed. A parameter study allows us to determine the physical conditions under which irregular structures form and whether they resemble large pillars or a system of small, isolated globules.

scholarly journals Stellar-mass black holes in star clusters: implications for gravitational-wave radiation

2009 ◽  
Vol 5 (S266) ◽  
pp. 213-218
Author(s):  
Sambaran Banerjee ◽  
Holger Baumgardt ◽  
Pavel Kroupa
Keyword(s):  
Black Holes ◽  
Star Clusters ◽  
Stellar Mass ◽  
Wave Radiation ◽  
Initial Population ◽  
Low Mass Stars ◽  
Low Mass ◽  
Three Body ◽  
Massive Clusters ◽  
Hubble Time

AbstractWe study the dynamics of stellar-mass black holes (BHs) in star clusters, with particular attention to the formation of BH–BH binaries, which are interesting as sources of gravitational waves (GWs). We examine the properties of these BH–BH binaries through direct N-body simulations of Plummer clusters of N ≤ 105 low-mass stars with an initial population of stellar-mass BHs, using the nbody6 code. We find that the stellar-mass BHs segregate rapidly into the cluster core and form a dense subcluster of BHs in which BH–BH binaries form through three-body encounters. While most BH binaries are ejected from the cluster by recoils due to superelastic encounters with the single BHs, we find that for clusters with N ≳ 5 × 104, typically a few of them harden sufficiently so that they can merge via GW emission within the cluster. Also, for each of such clusters there are a few escaping BH binaries that merge within a Hubble time, with most merger times being within a few Gyr. These results imply that the intermediate-age massive clusters constitute the most important class of star cluster candidates that can produce dynamical BH–BH mergers at the present epoch. The BH–BH merger rates obtained from our computations imply a significant detection rate (~30 yr−1) for the proposed Advanced LIGO GW detector.

scholarly journals The equation of motion phonon method and its application in the neutron rich oxygen region

2018 ◽  
Vol 194 ◽  
pp. 01003
Author(s):  
G. De Gregorio ◽  
F. Knapp ◽  
N. Lo Iudice ◽  
P. Veselý
Keyword(s):  
Experimental Data ◽  
Strong Coupling ◽  
Satisfactory Agreement ◽  
Cross Section ◽  
Level Density ◽  
Equation Of Motion ◽  
Low Energy ◽  
Nuclear Systems ◽  
Three Body ◽  
Chiral Potential

An equation of motion phonon method, developed for even-even nuclear systems and extended to odd nuclei, is applied to 22O and to its odd neighbors 23O and 23F. A calculation using the chiral potential NNLOopt is carried out in a space encompassing up to two phonons. The computed dipole cross section in 22O and the spectra of 22O and 23O are in a satisfactory agreement with the experimental data. However, the calculation describes poorly the spectrum of 23F. This discrepancy originates from the strong coupling between the odd proton and the 22O phonons of neutron nature. This coupling pushes down in energy several states enhancing the level density at low energy. We suggest that a viable route for the solution of this problem could be the inclusion of the three-body interaction using the new chiral potential NNLOsat.

scholarly journals Ages of Galactic and Extragalactic Star Clusters of Various Abundances

1983 ◽  
Vol 6 ◽  
pp. 109-117 ◽  
Author(s):  
R.D. Cannon
Keyword(s):  
Star Clusters ◽  
Magellanic Clouds ◽  
Open Clusters ◽  
Simultaneous Solution ◽  
Low Mass Stars ◽  
Cluster Systems ◽  
Distant Cluster ◽  
Low Mass

In this review I shall concentrate mainly on globular star clusters in our Galaxy since these are the objects for which most work has been done recently, both observationally and theoretically. However, I shall also discuss briefly the oldest open clusters and clusters in the Magellanic Clouds. Little can be said about more distant cluster systems, since the only observations available are of integrated colours or spectra and these seem to be rather unreliable indicators of age. It is perhaps worth pointing out that the title may be slightly misleading; the problem is not so much to determine the ages of clusters of known abundances, as to obtain the best simultaneous solution for both age and composition, since some of the most important abundances (notably helium and oxygen) are virtually unobservable in little-evolved low mass stars.

scholarly journals Exploring Flaring Behaviour on Low Mass Stars, Solar-type Stars and the Sun

2019 ◽  
Vol 15 (S354) ◽  
pp. 384-391
Author(s):  
L. Doyle ◽  
G. Ramsay ◽  
J. G. Doyle ◽  
P. F. Wyper ◽  
E. Scullion ◽  
...  
Keyword(s):  
High Energy ◽  
The Sun ◽  
Low Mass Stars ◽  
Highly Active ◽  
Rotation Phase ◽  
Solar Type ◽  
Low Mass ◽  
Insight Into ◽  
Reconnection Model ◽  
High Cadence

AbstractWe report on our project to study the activity in both the Sun and low mass stars. Utilising high cadence, Hα observations of a filament eruption made using the CRISP spectropolarimeter mounted on the Swedish Solar Telescope has allowed us to determine 3D velocity maps of the event. To gain insight into the physical mechanism which drives the event we have qualitatively compared our observation to a 3D MHD reconnection model. Solar-type and low mass stars can be highly active producing flares with energies exceeding erg. Using K2 and TESS data we find no correlation between the number of flares and the rotation phase which is surprising. Our solar flare model can be used to aid our understanding of the origin of flares in other stars. By scaling up our solar model to replicate observed stellar flare energies, we investigate the conditions needed for such high energy flares.

scholarly journals The effect of photoionizing feedback on the shaping of hierarchically-forming stellar clusters

2020 ◽  
Vol 499 (1) ◽  
pp. 668-680
Author(s):  
Alejandro González-Samaniego ◽  
Enrique Vazquez-Semadeni
Keyword(s):  
Star Formation ◽  
Early Stage ◽  
Stellar Clusters ◽  
Low Mass Stars ◽  
Transfer Scheme ◽  
Star Forming ◽  
Secondary Star ◽  
Low Mass ◽  
Hydrodynamical Simulations ◽  
Formation Efficiency

ABSTRACT We use two hydrodynamical simulations (with and without photoionizing feedback) of the self-consistent evolution of molecular clouds (MCs) undergoing global hierarchical collapse (GHC), to study the effect of the feedback on the structural and kinematic properties of the gas and the stellar clusters formed in the clouds. During this early stage, the evolution of the two simulations is very similar (implying that the feedback from low-mass stars does not affect the cloud-scale evolution significantly) and the star-forming region accretes faster than it can convert gas into stars, causing the instantaneous measured star formation efficiency (SFE) to remain low even in the absence of significant feedback. Afterwards, the ionizing feedback first destroys the filamentary supply to star-forming hubs and ultimately removes the gas from it, thus first reducing the star formation (SF) and finally halting it. The ionizing feedback also affects the initial kinematics and spatial distribution of the forming stars because the gas being dispersed continues to form stars, which inherit its motion. In the non-feedback simulation, the groups remain highly compact and do not mix, while in the run with feedback, the gas dispersal causes each group to expand, and the cluster expansion thus consists of the combined expansion of the groups. Most secondary star-forming sites around the main hub are also present in the non-feedback run, implying a primordial rather than triggered nature. We do find one example of a peripheral star-forming site that appears only in the feedback run, thus having a triggered origin. However, this appears to be the exception rather than the rule, although this may be an artefact of our simplified radiative transfer scheme.

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