In an earlier paper, we determined the morphological types of galaxies in the Coma Cluster using ... more In an earlier paper, we determined the morphological types of galaxies in the Coma Cluster using data from the HST/ACS Coma Cluster treasury survey. We found that of the 132 members, 51 are non dwarfs and 81 are dwarfs. We define dwarfs to have a absolute luminosity M F814W ≥ -18.5 as in . In this paper, we determine the morphological types of these dwarf galaxies and make a detailed study of their properties. Using GALFIT, we determine the structural properties of our sample and with spectroscopic redshifts, we determined memberships and distances to identify dwarfs. A visual examination of the residual images reveals that our sample of 78 dwarf galaxies comprises of: dwarf lenticular (dS0) 22%, dwarf Elliptical (dE) 69%, dwarf spirals (dSp) 4%, dwarf ring (dring) 1%, dwarf barred spirals (dSBp) 3% and dwarf irregular (dIrr) 1% galaxies. We find that the bulge-disk decomposition (Sérsic + exponential) fits are good only for the dS0 galaxies. The remainder of the sample gives good fits only for single Sérsic fits. The Colour Magnitude Relation (CMR) shows that the dEs are redder and fainter than the rest of the sample (except one dIrr galaxy). The Kormendy relation reveals that dE galaxies have lower surface brightness than the rest of the sample. Our research leads us to the conclusion that dwarf galaxies appear to have a different formation and evolution process than non-dwarf galaxies.
In this paper, we apply the machine learning clustering algorithm Density Based Spatial Clusterin... more In this paper, we apply the machine learning clustering algorithm Density Based Spatial Clustering of Applications with Noise (DBSCAN) to study the membership of stars in twelve open clusters (
Exploring the collinear Lagrangian points of exoplanet systems with P–R drag and oblateness
Journal of astrophysics and astronomy, Feb 8, 2024
Using GMM in open cluster membership: An insight
Astronomy and computing, 2024
Effect of gas percentage during minor mergers on the star formation in galaxies
Proceedings of the International Astronomical Union
We study the effect of minor mergers on star formation using simulations. We use GADGET4 code whi... more We study the effect of minor mergers on star formation using simulations. We use GADGET4 code which has both collisionless and hydrodynamical particles. Our goal is to establish a relation between gas percentage present in the galaxies and the star formation in the merged galaxy. We use 1:10 minor mergers and we run the isolated simulations with varying gas percentages in the primary galaxy. We observe that the gas particles convert into stars due to the impact of the minor merger. As the gas percentage increases in the primary disk of the galaxy, more number of stars are formed. We also observed that newly formed star particles settle down in the disk of the primary galaxy and increase the thickness of the disk. We also observe that the thickness of the stellar disk containing the old stars also increases due to the impact of the merger.
The Serpens Molecular Cloud is one of the most active sites of ongoing star formation at a distan... more The Serpens Molecular Cloud is one of the most active sites of ongoing star formation at a distance of about 300 pc, and hence is very well-suited for studies of young low-mass stars and sub-stellar objects. In this paper, for the Serpens star forming region, we find potential members of the Young Stellar Objects population from the Gaia DR3 data and study their kinematics and distribution. We compile a catalog of 656 YSOs from available catalogs ranging from X-ray to the infrared. We use this as a reference set and cross-match it to find 87 Gaia DR3 member stars to produce a control sample with revised parameters. We queried the DR3 catalog with these parameters and found 1196 stars. We then applied three different density-based machine learning algorithms (DBSCAN, OPTICS and HDBSCAN) to this sample and found potential YSOs. The three clustering algorithms identified a common set of 822 YSO members from Gaia DR3 in this region. We also classified these objects using 2MASS and WISE data to study their distribution and the progress of star formation in Serpens.
Infrared observations of young star clusters provide vital clues to the star formation process an... more Infrared observations of young star clusters provide vital clues to the star formation process and evolution of stars. This brief report on my thesis gives a brief description of the observations and analysis of the young star clusters NGC 1960, NGC 2453 and NGC 2384 observed in the near infrared bands at the Mt Abu Infrared Observatory, Gurushikhar in February 2000. Estimates of distance and age for these clusters for the first time using JHK data have been obtained. The colour-magnitude diagrams of these clusters have been extended to the fainter end as far as possible. The observed data was compared to that obtained by 2MASS. A more detailed paper will be published elsewhere.
Search for Low-Mass Objects in the Globular Cluster M4. I. Detection of Variable Stars
The Astronomical Journal, 2016
With every new discovery of an extra-solar planet, the absence of planets in globular clusters (G... more With every new discovery of an extra-solar planet, the absence of planets in globular clusters (GCs) becomes more and more conspicuous. Null detection of transiting hot Jupiters in globular clusters 47 Tuc, omega Cen and NGC6397 presents an important puzzle, raising questions about the role played by cluster metallicity and environment on formation and survival of planetary systems in densely populated stellar clusters. GCs were postulated to have many free-floating planets, for which the microlensing (ML) is an established tool for detection. Dense environment, well-constrained distances and kinematics of lenses and sources, and photometry of thousands of stars simultaneously make GCs the ideal targets to search for the microlensing. We present first results of a multi-site, 69-nights long campaign to search for ML signatures of low-mass objects in the globular cluster M4, which was chosen due to its proximity, location and an actual existence of a planet. M4 was observed in R and I bands by two telescopes, 1-m T40 and 18-inch C18, of WISE Observatory, Tel Aviv, Israel, from April to July 2011. Observations on 1-m telescope were carried out in service mode, gathering 6 to 18 20-sec exposures a night for a total of 69 nights. C18 observations were done for about 4 hrs a night for 7 nights in May 2011. We employ the semi-automated pipeline to calibrate and reduce the images to the light curves that our group is developing for this purpose which includes the differential photometry package DIAPL, written by Wozniak and modified by W. Pych. Several different diagnostics are employed for search of variability/transients. While no high-significance ML event was found in this observational run, we have detected more than twenty new variables and variable candidates in M4 field, which we present here.
The astrophysical parameters of the open star cluster Mayer 3 have been estimated using the Newto... more The astrophysical parameters of the open star cluster Mayer 3 have been estimated using the Newtonian focus (f/4.84) of the 1.88 m Telescope of Kottamia Observatory in Egypt. The VRI observations have been carried out down to a limiting magnitude of V∼ 20 mag. To emphasize the main astrophysical parameters, Near-Infra Red, Two Micron All Sky Survey (2MASS-JHK) database has been used. Analyzing the color-magnitude diagrams and radial density distribution of Mayer 3, the cluster's age, reddening, distance from the Sun, the limited border, core and tidal radii are evaluated. The photometrical membership, the Galactocentric coordinates from the Galactic center and Galactic plane are estimated. Luminosity-mass functions, and the total mass of the cluster are established. Finally, the relaxation time estimation conclude that Mayer 3 is not dynamically relaxed yet.
We shall present with examples how analysis of astronomy data can be used for an educational purp... more We shall present with examples how analysis of astronomy data can be used for an educational purpose to train students in methods of data analysis, statistics, programming skills and research problems. Special reference will be made to our IAU-OAD project `Astronomy from Archival Data' where we are in the process of building a repository of instructional videos and reading material for undergraduate and postgraduate students. Virtual Observatory tools will also be discussed and applied. As this is an ongoing project, by the time of the conference we will have the projects and work done by students included in our presentation. The material produced can be freely used by the community.
Homogeneous samples of photometric data, coupled with uniform methods of data analysis are essent... more Homogeneous samples of photometric data, coupled with uniform methods of data analysis are essential to make statistical inferences based on the fundamental parameters of clusters. These studies can contribute to understanding the galactic disk, formation and evolution of clusters, molecular cloud fragmentation, star formation and evolution. In this work, we study a sample of young clusters viz. King 16, NGC 1931, NGC 637 and NGC 189 using photometric data from the Two Micron All Sky Survey (2MASS) (Skrutskie et al. 2006). The 2MASS covers 99.99 % of the sky in the near-infrared J (1.25 µm), H (1.65 µm) and Ks (2.16 µm) bands (henceforth Ks shall be refered to as K). Hence the 2MASS database has the advantages of being homogeneous, all sky (enabling the study of the outer regions of clusters where the low mass stars dominate) and covering near infrared wavelengths where young clusters can be well observed in their dusty environments. Dutra and Bica (2001) discovered 42 objects at in...
Proceedings of the International Astronomical Union
We shall describe the various activities done by us in Covid Times including outreach and educati... more We shall describe the various activities done by us in Covid Times including outreach and educational workshops in Physics and Astronomy. We shall discuss the caveats in virtual teaching of Astronomy and the lessons learnt in the process.
Near infrared photometry of the young open cluster NGC 1960
Abstract. We present the preliminary results of observations of NGC 1960 which was observed from ... more Abstract. We present the preliminary results of observations of NGC 1960 which was observed from the Mt Abu Infrared Observatory, using the NICMOS3 infrared array mounted on the 1.2 m Cassegrain focus telescope. The observations were made in February 2000. The data ...
The Galaxy Population of the Core of Coma Cluster
Monthly Notices of the Royal Astronomical Society
In this paper we present the structural properties and morphology of galaxies in the central regi... more In this paper we present the structural properties and morphology of galaxies in the central region of the Coma Cluster brighter than 19.5m in the F814W band. from the HST/ACS Coma Cluster Treasury Survey. Using mainly spectroscopic redshifts, we find 132 members from our sample of 219 galaxies. In our sample of 132 members, we find 51 non-dwarfs and 81 dwarfs and amongst our 32 non-members, we find 4 dwarfs and 28 non dwarfs. We do not have redshifts for the remaining 55 galaxies. We present bulge-disc decomposition of the sample using GALFIT and obtain parameters for our sample. Using visual inspection of residuals, we do a a morphological classification of the galaxies. We studied the relation of morphological types with Bulge to Total Light Ratio (B/T), color magnitude relation (CMR), Sérsic index (n), Kormendy relation and cross-correlations between these parameters for the bulges and galaxies. This work helps us understand important relations between various parameters like B/...
The System of Open Star Clusters Revisited
Dynamical evolution of a young stellar aggregate in the presence of a massive shell of gas using N-body simulations
We study secondary star formation in an expanding shell about a stellar agregate using n-body sim... more We study secondary star formation in an expanding shell about a stellar agregate using n-body simulations. We use the (Ahmad-Cohen) Aarseth code for the n-body simulations to study the dynamical effects of interactions of an older generation of stars with a randomly forming second generation of stars in a aggregate. The observational effects of these interactions will be described in
Effect of the gas percentage on the thickness of the galactic discs during minor mergers using hydrodynamical simulations
Proceedings of the International Astronomical Union
We study the minor mergers of galaxies using simulations. For this we use GADGET2 code. We presen... more We study the minor mergers of galaxies using simulations. For this we use GADGET2 code. We present results of simulations of minor mergers of disc galaxies of mass ratio 1:10. These simulations consist of collisionless as well as hydrodynamical runs including a gaseous component in the galactic disc of primary galaxy. Our goal is to establish the characteristics of discs obtained after the merger.We observe that the primary galaxy discs are not destroyed after the merger. We take different initial conditions for the primary galaxy varying the gas percentage in disc from 0–40 percentage and study the thickness of the disc after the merger. We generally observe that the thickness of the disc increases after the merger for any gas percentage. We also observe that as the gas percentage increases in the disc of initial primary galaxy, the increase in the thickness keeps decreasing.
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Papers by Priya Hasan