Simulation of old open clusters for UVIT on ASTROSAT

Ultra Violet Imaging Telescope (UVIT) is one of the payloads on the first Indian multi wavelength satellite ASTROSAT expected to be launched by Indian Space Research Organisation (ISRO) in the year 2015. We have performed simulations of UV studies of old open clusters for the UVIT. The colour magnitude diagrams (CMDs) and spatial appearances have been created using 10 filters of FUV channel (130 - 180 nm) and NUV channel (200 - 300nm) available for observations on the UVIT, for three old open clusters M67, NGC 188 and NGC 6791. The CMDs are simulated for different filter combinations, and they are used to identify the loci of various evolutionary sequences, white dwarfs, blue stragglers, red giants, sub giants, turn off stars and the main sequence of the clusters. The present work helps in identifying the potential area of study in the case of three old open clusters, by considering the availability of filters and the detection limits of the instrument. We also recommend filter combinations, which can be used to detect and study the above mentioned evolutionary stages. The simulations and the results presented here are essential for the optimal use of the UVIT for studies of old open clusters.Comment: Accepted for publication in RAA; 25 pages, 19 figures, 1 tabl

On the determination of age and mass functions of stars in young open star clusters from the analysis of their luminosity functions

Based on the CCD observations of remote young open clusters NGC 2383, NGC 2384, NGC 4103, NGC 4755, NGC 7510 and Hogg 15, we constructed their observed luminosity functions (LFs). The observed LFs are corrected for field star contamination determined with the help of galactic star count model. In the case of Hogg 15 and NGC 2383 we also considered the additional contamination from neighbouring clusters NGC 4609 and NGC 2384 respectively. These corrections provided the realistic pattern of cluster LF in the vicinity of the MS turn on point and at fainter magnitudes, revealed the so called H-feature arising due to transition of the Pre-MS phase to MS, which is dependent on the cluster age. The theoretical LFs were constructed representing a cluster population model with continuous star formation for a short time scale and a power law Initial Mass Function (IMF) and these were fitted to the observed LF. As a result we are able to determine for each cluster a set of parameters, describing cluster population (the age, duration of star formation, IMF slope and percentage of field star contamination). It was found that in spite of the non-monotonic behaviour of observed LFs, cluster IMFs can be described as the power law functions with slopes similar to Salpeter's value. The present MS turn on cluster ages are several times lower than those derived from the fitting of theoretical isochrones to the turn off region of the upper Main Sequences.Comment: 17 pages, 5 figures, To appear in MNRA

Optical/IR studies of Be stars in NGC 6834 with emphasis on two specific stars

We present optical and infrared photometric and spectroscopic studies of two Be stars in the 70--80-Myr-old open cluster NGC 6834. NGC 6834(1) has been reported as a binary from speckle interferometric studies whereas NGC 6834(2) may possibly be a gamma Cas-like variable. Infrared photometry and spectroscopy from the United Kingdom Infrared Telescope (UKIRT), and optical data from various facilities are combined with archival data to understand the nature of these candidates. High signal-to-noise near-IR spectra obtained from UKIRT have enabled us to study the optical depth effects in the hydrogen emission lines of these stars. We have explored the spectral classification scheme based on the intensity of emission lines in the $H$ and $K$ bands and contrasted it with the conventional classification based on the intensity of hydrogen and helium absorption lines. This work also presents hitherto unavailable UBV CCD photometry of NGC 6834, from which the evolutionary state of the Be stars is identified.Comment: Published in Research in Astronomy and Astrophysics, RAA 14 (2014) 1173-1192, 20 pages, 10 figure

Real Time Clock based Energy Efficient Automatic Dual Axis Solar Tracking System

Energy derived from the sun is one of the most promising options. Solar energy is one of the alternate natural energy resources. In this proposed system, real time clock (RTC) based embedded solar tracking system is used to track the solar. The built system is, the design of dual axis and open loop tracking system. In this two axis tracking system, one axis is equipped with automation unit. Another one axis is adjusted manually by once in a month. Time based algorithm is successfully performed to various months in order to track the sun. In this tracking system, the azimuth angle is controlled by real time clock. Zenith angles were controlled manually by monthly once. An entire asymmetric solar dish concentrator is covered by 1 x 1 inch glass mirrors. The solar dish concentrator has reached maximum solar concentration with the help of this continuous RTC tracking method. The proposed system experiment was conducted in the month of March, April and May 2017. The maximum temperature of 415 oC was recorded at the time of experiment.This paper describes the design, implementation and performance of a real time clock (RTC) based dual axis solar tracking system and asymmetric solar dish concentrator. Numerous algorithm and functional program methodologies are implemented in order to optimizing the energy efficiency of the RTC based simple electromechanical dual axis solar energy tracking system. In this presented work, a RTC (Real Time Clock) based dual axis solar tracking system and solar dish concentrator is designed, implemented and tested based on current time and photodiode sensor based daily tracking method. In daily morning, the photo diode sensor in solar tracking system is used to align the solar concentrator for the initial position. The developed solar tracking system can follow the sun at various days, months and seasons. So, the solar tracking system needs a RTC (Real Time Clock) in order to leading the solar tracking system in finding sun’s position for the daily, monthly and seasonal movement. So, the combination of both RTC and sensor based tracking system gives the designed solar tracking system as an efficient one. Time based algorithm is successfully performed to various months in order to track the sun. An entire asymmetric solar dish concentrator is covered by 1 x 1 inch glass mirrors. The solar dish concentrator has reached maximum solar concentration with the help of this continuous RTC tracking method. The experiment was conducted in the month of March, April and May 2017. The maximum temperature of 415oC was recorded at the time of experiment. It is found that thermal power gain of RTC based dual axis solar tracking system is 75% compared to the fixed solar concentrator system

Genome sequence of a novel alloherpesvirus isolated from glass catfish (Kryptopterus bicirrhis)

The 149,343-bp genome of silurid herpesvirus 1, which was isolated in Thailand from glass catfish, was sequenced. The genome was most closely related to that of ictalurid herpesvirus 2, which infects black bullhead catfish. To our knowledge, this was the first silurid catfish alloherpesvirus genome to be sequenced

Tau aggregation and progressive neuronal degeneration in the absence of changes in spine density and morphology after targeted expression of Alzheimer's disease-relevant tau constructs in organotypic hippocampal slices

Alzheimer's disease (AD) is characterized by progressive loss of neurons in selected brain regions, extracellular accumulations of amyloid beta, and intracellular fibrils containing hyperphosphorylated tau. Tau mutations in familial tauopathies confirmed a central role of tau pathology; however, the role of tau alteration and the sequence of tau-dependent neurodegeneration in AD remain elusive. Using Sindbis virus-mediated expression of AD-relevant tau constructs in hippocampal slices, we show that disease-like tau modifications affect tau phosphorylation at selected sites, induce Alz50/MC1-reactive pathological tau conformation, cause accumulation of insoluble tau, and induce region-specific neurodegeneration. Live imaging demonstrates that tau-dependent degeneration is associated with the development of a "ballooned" phenotype, a distinct feature of cell death. Spine density and morphology is not altered as judged from algorithm-based evaluation of dendritic spines, suggesting that synaptic integrity is remarkably stable against tau-dependent degeneration. The data provide evidence that tau-induced cell death involves apoptotic as well as nonapoptotic mechanisms. Furthermore, they demonstrate that targeted expression of tau in hippocampal slices provides a novel model to analyze tau modification and spatiotemporal dynamics of tau-dependent neurodegeneration in an authentic CNS environment