arXiv subjects

Premana W. Premadi

Publications and source records attributed to Premana W. Premadi.

5 recordsLinked to original sources

arXiv2026

NGC 6134: a comprehensive study through photometric and kinematic analysis using Gaia DR3

Open clusters provide a unique laboratory for precisely constraining stellar age, distance, and metallicity, facilitating studies on exoplanet-host star correlations. Building on our previous membership study, we analyze photometric data to comprehensively characterize the open cluster NGC 6134 by determining its fundamental parameters, 3D spatial distribution, substructures, and mass segregation. Using the ASteCA code, we derive the cluster's parameters: $\mathrm{[Fe/H]} = 0.08 \pm 0.06$, $\log(t) = 9.14 \pm 0.01$, $d = 1064.43 \pm 15.19$ pc, and $A_\mathrm{v} = 1.03 \pm 0.05$ mag. Independent Bayesian inference of individual member distances yields a cluster distance of $1070.83 \pm 2.50$ pc, in excellent agreement with the ASteCA results. Spatial substructures are successfully mapped using Gaussian Mixture Models, revealing a three-component distribution corresponding to the cluster's core, tidal tail, and halo. Furthermore, Minimum Spanning Tree analysis indicates that the observed mass segregation is driven by dynamical evolution rather than primordial origins. Finally, our analysis of the cluster's Color--Magnitude Diagram identifies probable blue straggler stars and a main-sequence gap, which we conclude is strongly linked to the cluster's binary fraction.

astro-ph.GA↗

arXiv2023

Survey of Gravitationally lensed Objects in HSC Imaging (SuGOHI) $-$ X. Strong Lens Finding in The HSC-SSP using Convolutional Neural Networks

We apply a novel model based on convolutional neural networks (CNNs) to identify gravitationally-lensed galaxies in multi-band imaging of the Hyper Suprime Cam Subaru Strategic Program (HSC-SSP) Survey. The trained model is applied to a parent sample of 2 350 061 galaxies selected from the $\sim$ 800 deg$^2$ Wide area of the HSC-SSP Public Data Release 2. The galaxies in HSC Wide are selected based on stringent pre-selection criteria, such as multiband magnitudes, stellar mass, star formation rate, extendedness limit, photometric redshift range, etc. Initially, the CNNs provide a total of 20 241 cutouts with a score greater than 0.9, but this number is subsequently reduced to 1 522 cutouts by removing definite non-lenses for further inspection by human eyes. We discover 43 definite and 269 probable lenses, of which 97 are completely new. In addition, out of 880 potential lenses, we recovered 289 known systems in the literature. We identify 143 candidates from the known systems that had higher confidence in previous searches. Our model can also recover 285 candidate galaxy-scale lenses from the Survey of Gravitationally lensed Objects in HSC Imaging (SuGOHI), where a single foreground galaxy acts as the deflector. Even though group-scale and cluster-scale lens systems were not included in the training, a sample of 32 SuGOHI-c (i.e., group/cluster-scale systems) lens candidates was retrieved. Our discoveries will be useful for ongoing and planned spectroscopic surveys, such as the Subaru Prime Focus Spectrograph project, to measure lens and source redshifts in order to enable detailed lens modelling.

astro-ph.GA↗

arXiv2021

Properties of the Environment of Galaxies in Clusters of Galaxies CL 0024+1654 and RX J0152.7-1357

We report the results of combined analyses of X-ray and optical data of two galaxy clusters, CL 0024$+$1654 and RX J0152.7$-$1357 at redshift $z = 0.395$ and $z = 0.830$, respectively, which offer a holistic physical description of the two clusters. Our X-ray analysis yields temperature and density profile of the gas in the intra-cluster medium (ICM). Using optical photometric and spectroscopic data, complemented with mass distribution from gravitational lensing study, we investigate any possible correlation between the physical properties of the galaxy members, i.e., their color, morphology, and star formation rate (SFR) with their environments. We quantify the properties of the environment of each galaxy by galaxy number density, ICM temperature, and mass density. Although our result shows that the two clusters exhibit a weaker correlation compared to relaxed clusters, it still confirms the significant effect of the ICM on the SFRs in the galaxies. The closer relation between galaxy physical property and the condition of its immediate environment found in this work indicates the locality of galaxy evolution, even within a larger bound system such as cluster. Various physical mechanisms are suggested to explain the relation between the properties of galaxies and their environment.

astro-ph.GA↗

arXiv1998

Light Propagation in inhomogeneous Universes

astro-ph↗

arXiv1998

Light Propagation in inhomogeneous Universes

Using a multi-plane lensing method that we have developed, we follow the evolution of light beams as they propagate through inhomogeneous universes. We use a P3M code to simulate the formation and evolution of large-scale structure. The resolution of the simulations is increased to sub-Megaparsec scales by using a Monte Carlo method to locate galaxies inside the computational volume according to the underlying particle distribution. The galaxies are approximated by isothermal spheres, with each morphological type having its own distribution of masses and core radii. The morphological types are chosen in order to reproduce the observed morphology-density relation. This algorithm has an effective resolution of 9 orders of magnitudes in length, from the size of superclusters down to the core radii of the smallest galaxies. We consider cold dark matter models normalized to COBE, and perform a large parameter survey by varying the cosmological parameters Omega_0, lambda_0, H_0, and n (the tilt of the primordial power spectrum). The values of n are chosen by imposing particular values or sigma_8, the rms mass fluctuation at a scale of 8/h Mpc. We use the power spectrum given by Bunn & White. This is the largest parameter survey ever done is this field.

astro-ph↗