arXiv subjects

M. I. Arifyanto

Publications and source records attributed to M. I. Arifyanto.

7 recordsLinked to original sources

arXiv2024

Comparing dark matter and MOND hyphotheses from the distribution function of A, F, early-G stars in the solar neighbourhood

Dark matter is hypothetical matter believed to address the missing mass problem in galaxies. However, alternative theories, such as Modified Newtonian Dynamics (MOND), have been notably successful in explaining the missing mass problem in various astrophysical systems. The vertical distribution function of stars in the solar neighbourhood serves as a proxy to constrain galactic dynamics in accordance to its contents. We employ both the vertical positional and velocity distribution of stars in cylindrical coordinates with a radius of 150 pc and a half-height of 200 pc from the galactic plane. Our tracers consist of main-sequence A, F, and early-G stars from the GAIA, RAVE, APOGEE, GALAH, and LAMOST catalogues. We attempt to solve the missing mass in the solar neighbourhood, interpreting it as either dark matter or MOND. Subsequently, we compare both hypotheses newtonian gravity with dark matter and MOND, using the Bayes factor (BF) to determine which one is more favoured by the data. We found that the inferred dark matter in the solar neighbourhood is in range of $\sim (0.01$-$0.07)$ M$_{\odot}$ pc$^{-3}$. We also determine that the MOND hypothesis's acceleration parameter $a_0$ is $(1.26 \pm 0.13) \times 10^{-10}$ m s$^{-2}$ for simple interpolating function. The average of bayes factor for all tracers between the two hypotheses is $\log \textrm{BF}\sim 0.1$, meaning no strong evidence in favour of either the dark matter or MOND hypotheses.

astro-ph.GA↗

arXiv2021

The Formation of Binary Star Clusters in the Milky Way and Large Magellanic Cloud

Recent observations of young embedded clumpy clusters and statistical identifications of binary star clusters have provided new insights into the formation process and subsequent dynamical evolution of star clusters. The early dynamical evolution of clumpy stellar structures provides the conditions for the origin of binary star clusters. Here, we carry out $N$-body simulations in order to investigate the formation of binary star clusters in the Milky Way and in the Large Magellanic Cloud (LMC). We find that binary star clusters can form from stellar aggregates with a variety of initial conditions. For a given initial virial ratio, a higher degree of initial substructure results in a higher fraction of binary star clusters. The number of binary star clusters decreases over time due to merging or dissolution of the binary system. Typically, $\sim 45\%$ of the aggregates evolve into binary/multiple clusters within $t=20$~Myr in the Milky Way environment, while merely $\sim30\%$ survives beyond $t=50$~Myr, with separations $\lesssim 50$~pc. On the other hand, in the LMC, $\sim 90\%$ of the binary/multiple clusters survive beyond $t=20$~Myr and the fraction decreases to $\sim 80\%$ at $t=50$~Myr, with separations $\lesssim 35~$pc. Multiple clusters are also rapidly formed for highly-substructured and expanding clusters. The additional components tend to detach and the remaining binary star cluster merges. The merging process can produce fast rotating star clusters with mostly flat rotation curves that speed up in the outskirts.

astro-ph.GA↗

arXiv2016

The dynamical fate of binary star clusters in the Galactic tidal field

Fragmentation and fission of giant molecular clouds occasionally results in a pair of gravitationally bound star clusters that orbit their mutual centre of mass for some time, under the influence of internal and external perturbations. We investigate the evolution of binary star clusters with different orbital configurations, with a particular focus on the Galactic tidal field. We carry out $N$-body simulations of evolving binary star clusters and compare our results with estimates from our semi-analytic model. The latter accounts for mass loss due to stellar evolution and two-body relaxation, and for evolution due to external tides. Using the semi-analytic model we predict the long-term evolution for a wide range of initial conditions. It accurately describes the global evolution of such systems, until the moment when a cluster merger is imminent. $N$-body simulations are used to test our semi-analytic model and also to study additional features of evolving binary clusters, such as the kinematics of stars, global cluster rotation, evaporation rates, and the cluster merger process. We find that the initial orientation of a binary star cluster with respect to the Galactic field, and also the initial orbital phase, are crucial for its fate. Depending on these properties, the binaries may experience orbital reversal, spiral-in, or vertical oscillation about the Galactic plane before they actually merge at $t\approx100$~Myr, and produce rotating star clusters with slightly higher evaporation rates. The merger process of a binary cluster induces an outburst that ejects $\sim10\%$ of the stellar members into the Galactic field.

astro-ph.GA↗

arXiv2015

New Non-Parametric Approach to Determine Proper Motion of Star Clusters

The bulk motion of star clusters can be determined after careful membership analysis using parametric or non-parametric approaches. This study aims to implement non-parametric membership analysis based on Binned Kernel Density Estimator which accounts measurements errors (simply called BKDE-e) and to determine the average proper motion of each cluster. This method is applied to 178 selected star clusters with angular diameter less than 20 arc minutes. Proper motion data from UCAC4 are used for membership determination. Non-parametric analysis using BKDE-e successfully determined the average proper motion of 129 clusters, with good accuracy. Compared to COCD and NCOVOCC, there are 79 clusters with less than $3σ$ difference. Moreover, we are able to analyse distribution of the member stars in vector point diagram which is not always normal distribution.

astro-ph.GA↗

arXiv2015

The Implementation of Binned Kernel Density Estimation to Determine Open Clusters' Proper Motions: Validation of the Method

Stellar membership determination of an open cluster is an important process to do before further analysis. Basically, there are two classes of membership determination method: parametric and non-parametric. In this study, an alternative of non-parametric method based on Binned Kernel Density Estimation that accounts measurements errors (simply called BKDE-e) is proposed. This method is applied upon proper motions data to determine cluster's membership kinematically and estimate the average proper motions of the cluster. Monte Carlo simulations show that the average proper motions determination using this proposed method is statistically more accurate than ordinary Kernel Density Estimator (KDE). By including measurement errors in the calculation, the mode location from the resulting density estimate is less sensitive to non-physical or stochastic fluctuation as compared to ordinary KDE that excludes measurement errors. For the typical mean measurement error of 7 mas/yr, BKDE-e suppresses the potential of miscalculation by a factor of two compared to KDE. With median accuracy of about 93%, BKDE-e method has comparable accuracy with respect to parametric method (modified Sanders algorithm). Application to real data from The Fourth USNO CCD Astrograph Catalog (UCAC4), especially to NGC 2682 is also performed. The mode of member stars distribution on Vector Point Diagram is located at $μ_α\cosδ=-9.94\pm0.85$ mas/yr and $μ_δ=-4.92\pm0.88$ mas/yr. Although the BKDE-e performance does not overtake parametric approach, it serves a new view of doing membership analysis, expandable to astrometric and photometric data or even in binary cluster search.

astro-ph.GA↗

arXiv2005

Fine structure in the phase space distribution of nearby subdwarfs

We analysed the fine structure of the phase space distribution function of nearby subdwarfs using data extracted from various catalogues. Applying a new search strategy based on Dekker's theory of galactic orbits, we found four overdensely populated regions in phase space. Three of them were correlated with previously known star streams: the Hyades-Pleiades and Hercules streams in the thin disk of the Milky Way and the Arcturus stream in the thick disk. In addition we find evidence for another stream in the thick disk, which resembles closely the Arcturus stream and probably has the same extragalactic origin.

astro-ph↗

arXiv2005

Kinematics of Nearby Subdwarf Stars

We present an analysis of the space motions of 742 subdwarf stars based on the sample of Carney et al. (1994, CLLA). Hipparcos parallaxes, TYC2+HIP proper motions and Tycho2 proper motions were combined with radial velocities and metallicities from CLLA. The kinematical behavior is discussed in particular in relation to their metallicities. The majority of these sample stars have metal abundances of [Fe/H] >-1 and represent the thick disk population. The halo component, with [Fe/H] <-1.6, is characterized by a low mean rotation velocity and a radially elongated velocity ellipsoid. In the intermediate metallicity range (-1.6 < [Fe/H] <-1), we find a significant number of subdwarfs with disklike kinematics. We interpret this population of stars as a metal-weak thick disk population.

astro-ph↗