1,721,091 research outputs found
The structural properties of multiple populations in globular clusters: The instructive case of NGC 3201
Full text linkAll multiple population (MP) formation models in globular clusters (GCs) predict that second population (SP) stars form more centrally concentrated than the first population (FP). As dynamical evolution proceeds, spatial differences are progressively erased and only dynamically young clusters are expected to retain a partial memory of the initial structural differences. In recent years, this picture has been supported by observations of the MP radial distributions of both Galactic and extragalactic GCs. However, more recent observations have suggested that in some systems, FPs might actually form more centrally segregated, with NGC 3201 being one significant example of such a possibility. Here, we present a detailed morphological and kinematic characterization of the MPs in NGC 3201, based on a combination of photometric and astrometric data. We show that the distribution of the SP is clearly bimodal. Specifically, the SP is significantly more centrally concentrated than the FP within similar to 1.3 cluster's half-mass radius. Beyond this point, the SP fraction increases again, likely due to asymmetries in the spatial distributions of the two populations. The central concentration of the SP observed in the central regions implies that it formed more centrally concentrated than the FP, even more so than what is observed in the present-day. This interpretation is supported by the key information provided by the MP kinematic properties. Indeed, we find that the FP is isotropic across all the sampled cluster extension, while the velocity distribution of the SP becomes radially anisotropic in the cluster's outer regions, as expected for the dynamical evolution of SP stars formed more centrally concentrated than the FP. The combination of spatial and kinematic observations provide key insights into the dynamical properties of this cluster and lend further support to scenarios in which the SP forms more centrally concentrated than the FP
Stability of dense stellar clusters against relativistic collapse
No full textStability of dense stellar clusters against relativistic collapse is investigated by approximate methods, similar to the static criteria of stellar stability. The equilibrium models with Maxwellian distribution function with cutoff, studied by Zel'dovich & Podurets (ZP) (1965), have been considered. Three new methods for stability investigation are considered. They give only approximate results about the stability, because adiabatic perturbations of the collisionless Maxwellian model lead to complicated non-Maxwellian distribution, which cannot be written analytically. However, these results are more precise than those of ZP, obtained from consideration of the sequence of Maxwellian models with different temperature. The coincidence of the temperatures in the critical point, T = 0.223 mc^2 leads us to believe that these methods, although approximate, provide rather relatively good precision not worse than 0.001
Stability of the dense stellar clusters - II
No full textStability of dense stellar clusters to relativistic collapse is investigated by an approximate method, similar to static criteria of stellar stability. The equilibrium models with Maxwellian distribution function with cutoff, studied by Zel'dovich and Podurets (ZP), have been considered
The role of rotation on the formation of second generation stars in globular clusters
Full text linkBy means of 3D hydrodynamic simulations, we explore the effects of rotation in the formation of second-generation (SG) stars in globular clusters (GC). Our simulations follow the SG formation in a first-generation (FG) internally rotating GC; SG stars form out of FG asymptotic giant branch (AGB) ejecta and external pristine gas accreted by the system. We have explored two different initial rotational velocity profiles for the FG cluster and two different inclinations of the rotational axis with respect to the direction of motion of the external infalling gas, whose density has also been varied. For a low (10-24 g cm-3) external gas density, a disc of SG helium-enhanced stars is formed. The SG is characterized by distinct chemo-dynamical phase space patterns: it shows a more rapid rotation than the FG with the helium-enhanced SG subsystem rotating more rapidly than the moderate helium-enhanced one. In models with high external gas density (), the inner SG disc is disrupted by the early arrival of external gas and only a small fraction of highly enhanced helium stars preserves the rotation acquired at birth. Variations in the inclination angle between the rotation axis and the direction of the infalling gas and the velocity profile can slightly alter the extent of the stellar disc and the rotational amplitude. The results of our simulations illustrate the complex link between dynamical and chemical properties of multiple populations and provide new elements for the interpretation of observational studies and future investigations of the dynamics of multiple-population GCs
LINEAR-STABILITY OF SPHERICAL COLLISIONLESS STELLAR-SYSTEMS
No full textThe linear stability analysis is presented here in a self-contained form, and several general issues, related to the symmetry properties of the relevant equations and to the boundary conditions are formulated. A numerical code for the study of the linear stability of collisionless spherical stellar systems with no radial truncation is constructed and applied to survey a family of astrophysically interesting anisotropic equilibrium models. The code is flexible, in that it can accept any reasonable initial distribution function f=f(E, J(2)) and is not restricted to a specific mass model. We have focused on the l=2 modes and on the so-called radial orbit instability. Marginal stability has been identified, corresponding to a value of 2K(r)/K-T = 1.58 for the ratio of the total radial to tangential kinetic energy, somewhat on the low side with respect to a generally accepted stability criterion. As the ratio 2K(r)/K-T increases, the number of unstable modes and the value of their growth rates are found to increase considerably, so that for negative-temperature models we have found up to six modes, with a growth rate much higher than the inverse half-mass crossing time and matching the timescales available in the innermost regions of the galaxy. For these negative-temperature models the density perturbations are very concentrated and indicate that the system would evolve rapidly through sizable poloidal motions which are bound to redistribute both the orbits and the mass in the central parts of the galaxy. The results shown are briefly compared with those derived from N-body simulations
Stability of dense stellar clusters against relativistic collapse. II Maxwellian distribution functions with different cutoff parameters
Full text linkWe investigate the stability of dense stellar clusters against relativistic collapse by approximate
methods described in the previous paper in this series. These methods, together with the analysis of the
fractional binding energy of the system, have been applied to sequences of equilibrium models, with
cutoff in the distribution function, which generalize those studied by Zeldovich & Podurets. We show
the existence of extreme configurations, which are stable all the way up to infinite values of the central
redshift
Stability of the dense stellar clusters to relativistic collapse. Maxwellian distribution functions with different cutoff parameters
No full textThe role of Type Ia supernova feedback on the second generation formation in globular clusters
No full textVery little is known about the physical processes which determined the end of star formation in globular clusters (GC). By means of 3D hydrodynamic simulations, we study for the first time how the formation and the chemical properties of second generation (SG) stars in a massive proto-GC are affected by SNe Ia explosions belonging to the first stellar generation, one likely cause for the quenching of star formation in these systems. In our model, the formation of SG stars starts ∼ 40 Myr after the cluster birth and is due to the retention of the fresh ejecta of first generation asymptotic giant branch stars plus accretion of cold, pristine gas. At the same time, SNe Ia start exploding, carving hot and tenuous bubbles in the interstellar medium. I have focused on SNe Ia effects on the iron and helium abundances and studied the role of various parameters in regulating the efficiency of SN Ia feedback. According to our results, SN explosions are able to halt star formation only if the pristine gas is tenuous (with density ∼ 1cm-3), whereas they have little effects if the pristine gas density is ∼ 10 cm-3. Finally, we show that gas from SNe Ia may produce an iron spread as found in Type II GCs, an anomalous sub-category of GCs
Globular clusters in the Fornax cluster: A report from the FDS survey
Full text linkThe Fornax Deep Survey (FDS) is a multi-band imaging survey of the Fornax cluster of galaxies, executed with the ESO VLT Survey Telescope (VST). The survey is designed to reach unprecedented surface brightness and point-source magnitude depth over one virial radius of the cluster. The scientific objectives of the survey are numerous: the study of the galaxy luminosity function, derivation of galaxy scaling relations, determination of the properties of compact stellar systems, an accurate determination of distances and 3-D geometry of the Fornax cluster, analysis of diffuse stellar light and galaxy interactions, etc
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