Multicolor CCD photometry and stellar evolutionary analysis of NGC 1907, NGC 1912, NGC 2383, NGC 2384, and NGC 6709 using synthetic color-magnitude diagrams

We present the first CCD photometric observations of NGC 2383 and NGC 2384 in B, V, R, and I, NGC 1912, NGC 6709 in B, V, and I and NGC 1907 in B and V passbands, reaching down to a limiting magnitude of V ~ 20 mag for ~3300 stars put together. The results of the spectroscopic observations of 43 bright stars in the field of NGC 1912, NGC 2383, NGC 2384, and NGC 6709 are also presented. The color-magnitude diagrams (CMDs) of the clusters in V versus B-V, V versus V-R, and V versus V-I are presented. The distances and reddening to these clusters are determined using the cluster CMDs. The distances to the clusters NGC 1907, NGC 1912, NGC 2383, NGC 2384, and NGC 6709 are 1785 ± 260, 1820 ± 265, 3340 ± 490, 2925 ± 430, and 1190 ± 175 pc, respectively. Some gaps in the cluster main sequence have been identified. We have compared the observed color-magnitude diagrams of these four open clusters with the synthetic ones derived from one classical and two overshoot stellar evolutionary models. Overshoot models estimate older ages for clusters when compared to the classical models. The age of the clusters estimated using the isochrones of Bertelli et al. are 400, 250, 400, 20, and 315 Myr for the clusters NGC 1907, NGC 1912, NGC 2383, NGC 2384, and NGC 6709, respectively. A comparison of the synthetic color-magnitude diagrams with the observed ones indicates that the overshoot models should be preferred. The comparison of integrated luminosity functions do not clearly indicate as to which model is to be preferred. The values of the mass function slopes estimated for the clusters are x = 1.7 ± 0.15 for NGC 1912 (mass range: 1.7–3.9 M⊙) and NGC 6709 (1.7–3.4 M⊙), x = 1.3 ± 0.15 for NGC 2383 (1.7–3.1 M⊙), and x = 1.0 ± 0.15 for NGC 2384 (2.0–14.0). The present age estimates show that the closely located cluster pair NGC 1912 + NGC 1907 have similar ages, indicating that they may have born together, making them a good candidate to be a binary open cluster

Star Clusters in the Magellanic Clouds-1: Parameterisation and Classification of 1072 Clusters in the LMC

We have introduced a semi-automated quantitative method to estimate the age and reddening of 1072 star clusters in the Large Magellanic Cloud (LMC) using the Optical Gravitational Lensing Experiment (OGLE) III survey data. This study brings out 308 newly parameterised clusters. In a first of its kind, the LMC clusters are classified into groups based on richness/mass as very poor, poor, moderate and rich clusters, similar to the classification scheme of open clusters in the Galaxy. A major cluster formation episode is found to happen at 125 +- 25 Myr in the inner LMC. The bar region of the LMC appears prominently in the age range 60 - 250 Myr and is found to have a relatively higher concentration of poor and moderate clusters. The eastern and the western ends of the bar are found to form clusters initially, which later propagates to the central part. We demonstrate that there is a significant difference in the distribution of clusters as a function of mass, using a movie based on the propagation (in space and time) of cluster formation in various groups. The importance of including the low mass clusters in the cluster formation history is demonstrated. The catalog with parameters, classification, and cleaned and isochrone fitted CMDs of 1072 clusters, which are available as online material, can be further used to understand the hierarchical formation of clusters in selected regions of the LMC.Comment: 19 pages, 19figures, published in MNRAS on August 16, 2016 Supplementary material is available in the MNRAS websit

Evolution of INMARSAT systems and applications: The land mobile experience

Inmarsat has provided mobile satellite communication services for land mobile applications for well over a decade. Having started with the Inmarsat-A voice and telex system, Inmarsat is committed to the evolution of services towards a global personal, handheld satellite communicator. Over the years, users have benefitted from the evolution of technologies, increased user friendliness and portability of terminals and ever decreasing cost of operations. This paper describes the various present systems, their characteristics and applications, and outlines their contributions in the evolution towards the personal global communicator

UVIT Open Cluster Study. X. Rich Collection of Post Mass Transfer Systems in NGC 6791

NGC 6791 is one of the richest old open clusters in the Milky Way. Its position above the Galactic plane and the number density makes it an interesting middle ground between Galactic open and globular clusters. We aim to detect the UV bright population of NGC 6791 using \textit{AstroSat}/UVIT images in near-UV and far-UV filters and characterise the known post mass transfer systems such as blue straggler stars (BSSs). We identified 20 members with large UV flux (out of 91 cluster members among 1180 detections), suggestive of binarity, interactions or stellar activity using multi-wavelength spectral energy distribution analysis. We characterised 62 isolated cluster members, including five hot subdwarfs (sdA/sdB). Additionally, we detected ten sdA/sdB/extremely low mass white dwarf (ELM) type candidates hidden alongside other cluster members. Additionally, we report the discovery of four candidate blue lurkers, which are main sequence stars with mass accretion history. We report that this cluster has a variety of stellar (pre-)remnants, such as sdBs, sdAs, and ELM white dwarfs, that are by-products of binary evolution. The above are likely to be post mass transfer binaries found throughout the evolutionary phases from the main sequence to the post horizontal branch. Therefore, this dynamically old open cluster is unique, making it an ideal testbed for dynamical studies.Comment: 8 pages, 2 figures, catalogue available in CDS, accepted in A&

Investigating Determinants of Project Portfolio Management Adoption

Recently, there has been an emphasis on managing projects strategically within the organization using project portfolio management (PPM). However, the extent of adoption of this innovation and the enabling factors are not well understood in academics and practice. This research-inprogress investigates a model of PPM adoption using data being collected from project managers. The model identifies a total of nine variables capturing various environmental, PPM, and organizational factors that could potentially impact the adoption decision of PPM. The survey is hosted on the Project Management Institute’s (PMI) website in order to collect data from PMI members worldwide. The data will be analyzed using logistic regression to identify the factors that have a significant impact on PPM adoption. This research is part of a larger multi-method research of PPM adoption and infusion and the results of this research will help practitioners and researchers better understand factors that impact PPM adoption decisions

Globular cluster systems in giant elliptical galaxies : a probe for the galaxy formation and evolution

Most of the globular clusters in the universe reside in gaint elliptical galaxies. The number of GCs present in them is about a few thousands. Due to their large distances (≥ 10 Mpc), it is impossible to observe their individual members. However, their integrated light observations can be obtained and used to understand them. The observables of the globular cluster systems (GCS) such as luminosity and mass distributions, specific frequencies, metallicity distributions and kinematics can be related to the competing hypotheses for galaxy formation : in situ, mergers, or accretions. Comprehensive recent discussions can be seen in Ashman & Zepf (1998) and Harris (1999a)

Star Clusters in the Magellanic Clouds - II. Age-Dating, Classification and Spatio-Temporal Distribution of the SMC Clusters

Aim: We aim to estimate the age and reddening parameters of already identified star clusters within the Small Magellanic Cloud (SMC) in a consistent way using available photometric data, classify them based on their mass and strength, and study their spatio- temporal distribution. Methods: We have used a semi-automated quantitative method, developed in the first paper of this series (Paper I), to estimate the cluster parameters using the V and I band photometric data from the Optical Gravitational Lensing Experiment (OGLE) III survey. Results: We estimated parameters of 179 star clusters (17 newly parameterised) and classified them into 4 groups. We present an online catalog of parameters, and cleaned and isochrone-fitted Color Magnitude Diagrams of 179 clusters. We compiled age information of 468 clusters by combining previous studies with our catalog, to study their spatio-temporal distribution. Most of the clusters located in the southern part of the SMC are in the age range 600 Myr-1.25 Gyr, whereas, the clusters younger than 100 Myr are mostly found in the northern SMC, with the central SMC showing continuous cluster formation. The peak of the cluster age distribution is identified at 130 Myr, very similar to the Large Magellanic Cloud (LMC) in Paper I. Conclusion: We suggest that the burst of cluster formation at 130 Myr is due to the most recent LMC-SMC interaction. 90% of the studied sample is found to have mass <1700 M_sun, suggesting that the SMC is dominated by low mass clusters. There is a tentative evidence for compact clusters in the LMC when compared to those in the Galaxy and the SMC. A progressive shifting of cluster location from the South to North of the SMC is identified in last 600 Myr. The details of spatio-temporal distribution of clusters presented in two videos in this study can be used as a tool to constrain details of the recent LMC-SMC interactions.Comment: The paper is accepted for publication in A&A journa