Modeling of the Initial Mass Function Using the Metropolis−Hastings Algorithm
TL;DR: In this article, a stochastic model for the hierarchical fragmentation of a molecular cloud was developed, where the number of fragments, time between successive fragmentation steps, and mass of a fragment were considered as random variables, and fragment masses were generated using the Metropolis-Hastings algorithm.
Abstract: A stochastic model has been developed for the hierarchical fragmentation of a molecular cloud. Here, the number of fragments, time between successive fragmentation steps, and mass of a fragment are considered as random variables, and fragment masses are generated using the Metropolis-Hastings algorithm. The resulting mass spectra, computed at different projected distances and taking opacity into consideration, show a signature of mass segregation. The critical mass, mass spectrum, and mass segregation are consistent with the observations of young massive clusters in our Galaxy as well as in external galaxies.
Citations
More filters
TL;DR: In this paper, a stochastic model has been developed to study the hierarchical fragmentation process of young massive clusters in external galaxies considering close binary components along with individual ones, and the resulting mass spectra computed at different projected distances, show signature of mass segregation.
Abstract: A stochastic model has been developed to study the hierarchical fragmentation process of young massive clusters in external galaxies considering close binary components along with individual ones. Stellar masses for individual ones have been generated from truncated Pareto distribution and stellar masses for close binary components have been generated from a truncated Bi-variate Gumbel Exponential distribution. The above distribution is identified by fitting the observed bi-variate distribution of masses of eclipsing binary stars computed from the light curves catalogued in the package Binary Maker 3.0. The resulting mass spectra computed at different projected distances, show signature of mass segregation. Degree of mass segregation becomes reduced due to the inclusion of binary fraction. This might be due to the reduction of massive stars and inclusion of less massive stars rather than inclusion of single massive stars and the effect of line of sight length projected to an observer.
6 citations
21 Dec 2016
TL;DR: In this article, a stochastic model has been developed to study the hierarchical fragmentation procedure in Young Massive Clusters, where binary fragments along with individual stars have been primarily studied.
Abstract: To study the hierarchical fragmentation procedure in Young Massive Clusters, a stochastic model has been developed. Binary fragments along with individual stars are primarily studied in this work. Stellar masses for individual stars have been generated from the univariate truncated Pareto distribution and the stellar masses for binary stars have been generated from the truncated bi-variate Skew Normal Distribution using the Hamiltonian Monte Carlo method. The above distribution is used by observing the fitted bi-variate distribution of masses of all type of binary stars viz. visual binaries, spectroscopic binaries and eclipsing binaries. The resulting mass spectrum computed at different projected distances are observed under opacity limited fragmentation procedure and they display signature of mass segregation along the core to radius, whereas degree of segregation becomes reduced due to inclusion of all type of binary fragments in comparison to inclusion of eclipsing binaries only.
2 citations
TL;DR: In this article, an episodic model of star formation in giant and dwarf galaxies has been studied through a dynamical open system, where the system is subjected to dissipative processes e.g. outflow from the gaseous component caused by supernovae explosion and subsequent ram pressure stripping within the oscillation period.
Abstract:
The oscillatory model of star formation in giant and dwarf galaxies have been studied through a dynamical open system. In addition to various dynamical processes involving fractional masses of hot, warm, and cold gases, the system is subjected to dissipative processes e.g. outflow from the gaseous component caused by supernovae explosion and subsequent ram pressure stripping within the oscillation period. This is more realistic than a previous model which was considered conservative. The present episodic model has been found to be unimodal in general contrary to discrete episodes of star formation of decreasing amplitudes as found for closed systems. The duty cycles under various parametric conditions derived, vary in the range (2.0–40.0) × 107 yr for giant galaxies contrary to longer time, for example 9.0 × 107–1.0 × 109 yr for dwarf galaxies. This might be due to the low production rate of supernova in dwarf galaxies which reduces the evaporation rate of cold gas into hot gas making cold gas available for continuing the cycle for a longer time. The duty cycles have increased in both cases compared to the previous model by an order of one for giant galaxies and order of two for dwarf galaxies depending on the degree of dissipation. This might be due to the unimodal pattern of star formation which prevails for longer time in the late phase of galaxy evolution. Under very special parametric conditions limit cycles may occur i.e. star formation in discrete episodes, may occur involving one or more stable attractors especially in early-type dwarf and giant galaxies. Tendency of formation of multiple attractors are more likely in early-type giant spiral galaxies when the rate of dissipation is very slow.
2 citations
TL;DR: In this article, a stochastic model of fragmentation of molecular clouds has been developed for studying the resulting Initial Mass Function (IMF) where the number of fragments, interoccurrence time of fragmentation, masses and velocities of the fragments are random variables.
References
More filters
TL;DR: In this article, the spectral evolution of stellar populations at ages between 100,000 yr and 20 Gyr at a resolution of 3 A across the whole wavelength range from 3200 to 9500 A for a wide range of metallicities.
Abstract: We present a new model for computing the spectral evolution of stellar populations at ages between 100,000 yr and 20 Gyr at a resolution of 3 A across the whole wavelength range from 3200 to 9500 A for a wide range of metallicities. These predictions are based on a newly available library of observed stellar spectra. We also compute the spectral evolution across a larger wavelength range, from 91 A to 160 micron, at lower resolution. The model incorporates recent progress in stellar evolution theory and an observationally motivated prescription for thermally-pulsing stars on the asymptotic giant branch. The latter is supported by observations of surface brightness fluctuations in nearby stellar populations. We show that this model reproduces well the observed optical and near-infrared colour-magnitude diagrams of Galactic star clusters of various ages and metallicities. Stochastic fluctuations in the numbers of stars in different evolutionary phases can account for the full range of observed integrated colours of star clusters in the Magellanic Clouds. The model reproduces in detail typical galaxy spectra from the Early Data Release (EDR) of the Sloan Digital Sky Survey (SDSS). We exemplify how this type of spectral fit can constrain physical parameters such as the star formation history, metallicity and dust content of galaxies. Our model is the first to enable accurate studies of absorption-line strengths in galaxies containing stars over the full range of ages. Using the highest-quality spectra of the SDSS EDR, we show that this model can reproduce simultaneously the observed strengths of those Lick indices that do not depend strongly on element abundance ratios [abridged].
10,384 citations
TL;DR: In this paper, the evolutionary significance of the observed luminosity function for main-sequence stars in the solar neighborhood is discussed and it is shown that stars move off the main sequence after burning about 10 per cent of their hydrogen mass and that stars have been created at a uniform rate in a solar neighborhood for the last five billion years.
Abstract: The evolutionary significance of the observed luminosity function for main-sequence stars in the solar neighborhood is discussed. The hypothesis is made that stars move off the main sequence after burning about 10 per cent of their hydrogen mass and that stars have been created at a uniform rate in the solar neighborhood for the last five billion years. Using this hypothesis and the observed luminosity function, the rate of star creation as a function of stellar mass is calculated. The total number and mass of stars which have moved off the main sequence is found to be comparable with the total number of white dwarfs and with the total mass of all fainter main-sequence stars, respectively.
8,607 citations
Book•
01 Jan 1999TL;DR: This new edition contains five completely new chapters covering new developments and has sold 4300 copies worldwide of the first edition (1999).
Abstract: We have sold 4300 copies worldwide of the first edition (1999). This new edition contains five completely new chapters covering new developments.
6,884 citations
TL;DR: In this paper, the authors quantify the complex interdependence of stellar binarity, the stellar mass-luminosity relation, the mass function, the colour-magnitude relation and the Galactic disc structure, all of which must be understood when analysing star-count data and stellar luminosity functions.
Abstract: We quantify the complex interdependence of stellar binarity, the stellar mass-luminosity relation, the mass function, the colour-magnitude relation and Galactic disc structure, all of which must be understood when analysing star-count data and stellar luminosity functions. We derive a mass-M V relation and a model for the change of stellar luminosity with changes in chemical abundance and age. Combination of this with detailed modelling of all astrophysical and observational contributions to the Malmquist scatter allows us to model star-count data without approximating Malmquist corrections. We show for the first time that a single mass function and normalization explain the stellar distribution towards both Galactic poles, as well as the distribution of stars within a distance of 5.2 pc of the Sun
1,710 citations