C. Anu Radha

Bio: C. Anu Radha is an academic researcher from VIT University. The author has contributed to research in topics: Blue straggler & Open cluster. The author has an hindex of 4, co-authored 10 publications receiving 32 citations.

Ultraviolet stellar population of the old open cluster M67 (NGC 2682)

Abstract: We present the results of ultraviolet (UV) photometry of the old open cluster M67 obtained using Galaxy Evolution Explorer (GALEX) in far-ultraviolet (FUV) and near-ultraviolet (NUV) bands. UV detections of 18 blue straggler stars (BSSs), 3 white dwarfs (WDs), 4 yellow straggler stars, 2 sub-subgiants, and 25 X-ray sources are presented (along with an online catalog). We demonstrate the capability of UV colour magnitude diagrams (CMDs) along with the UV isochrones to identify potential stars which defy standard stellar evolution in this well studied cluster. We also detect a few main sequence turn-off and subgiant branch stars with excess flux in the FUV and/or NUV. UV continuum excess as well as Mg II $\it h$ +$\it k$ emission lines from the IUE archival spectra for 2 red giants are detected, suggestive of their chromospheric activity. We suggest that a large number of stars in this cluster are chromospherically active, whereas the bright BSS are unlikely to be active. We also estimate the fundamental parameters L/L$_{\odot}$, R/R$_{\odot}$ and T$_{eff}$ of the BSSs and 15 FUV bright stars by constructing the spectral energy distribution (SED) using multi-wavelength data. We identify three groups among the BSSs, based on their properties. The H-R diagram of BSSs with isochrones suggests that the BSSs in M67 are formed in the last 2.5 Gyr - 400 Myr, more or less continuously. We identify 7 potential MS+WD candidates based on large UV excess from a probable 11, based on SEDs.

Radiological health assessment due to gamma radiation levels of natural radioactivity of soil in vicinity of Nichahoma lignite belt, Kashmir Valley

Abstract: Abstract The measurements of activity concentrations in soil of the lignite belt and soil of the villages surrounding the lignite belt have been carried out in order to present the radiological health hazards due to gamma radiation levels of the soil to general public. A low- background Pb-shielded gamma spectroscopic counting assembly utilizing NaI(Tl) detector was employed for the measurements. The activity concentration of radionuclides have been determined and compared with the international and national recommended values. A correlation analysis was also performed in order to predict the contribution of the respective nuclides towards the measured dose rate and to the find the existence of these radioactive nuclides together in the study area.

Molecular dynamics simulation studies on influenza A virus H5N1 complexed with sialic acid and fluorinated sialic acid.

Abstract: HAHemagglutininMDMolecular DynamicsMM-PBSAMolecular Mechanics Poisson–Boltzmann Surface AreaNANeuraminidaseNAMDNanoscale Molecular Dynamic SimulationPMEMDParticle Mesh Ewald Molecular DynamicsRMSDR...

Evaluation of excess life time cancer risk due to natural radioactivity of the Lignite samples of the Nichahoma, lignite belt, North Kashmir, India

Abstract: Abstract Naturally occurring radionuclides of the 226Ra, 232Th, and 40K present in the lignite samples was measured by using a low-background Pb-shielded gamma spectroscopic counting assembly utilizing NaI(Tl) detector for the measurement and to evaluation the radiation hazard indices and excess life time cancer risk. The average values of specific activity concentrations in the investigated lignite samples was found to be 45.36 Bq kg−1 for 226Ra, 21.42 Bq kg−1 for 232Th, 40.51 Bq kg−1 for 40K and 79.11 Bq kg−1 for Raeq respectively. The average value excess life time cancer risk was found to be relatively higher than the world average. Moreover, the correlation analysis shows the strong dependence of excess lifetime cancer risk on measured dose and the radium equivalent activity.

Performance evaluation of gated volumetric modulated arc therapy

Abstract: Background : Aim of this study is to evaluate the accuracy of the gated volumetric modulated arc therapy (VMAT/RapidArc) using 2D planar dosimetry, DynaLog files and COMPASS 3D dosimetry system. Materials and Methods : Pre-treatment quality assurance of 10 gated VMAT plans was verified using 2D array and COMPASS 3D dosimetry system. Advantage of COMPASS over 2D planar is that it provides the clinical consequence of error in treatment delivery. Measurements were performed for non-gated and different phase ga.ng window level (80%, 50%, 30% & 20%) to know the impact of ga.ng in VMAT dose delivery. Results: In 2D planar dosimetry, gamma agreement index (GAI) for all measurements were more than 95%. DynaLog file analysis shows the average devia.ons be tween actual and expected posi.ons of monitor units, gantry and mul. -leaf collimator. The STDVs MU and gantry posi.on were less than 0.10 MU and 0.33° respec.vely. Root mean square (RMS) of the devia.ons of all leav es were less than 0.58 mm. The results from COMPASS show that 3D dose volume parameters for ten pa.ents measured for different phase ga.ng windo w level were within the tolerance level of ±5%. Average 3D gamma of PTV and OAR’s for different window level was less than 0.6. Conclusion: The results from this study show that gated VMAT delivery provided dose distribu.ons equivalent to non-gated delivery to within clinically acceptable limits and COMPASS along with Matrix

UVIT Open Cluster Study. II. Detection of Extremely Low Mass White Dwarfs and Post–Mass Transfer Binaries in M67

Abstract: A detailed study of the ultraviolet (UV) bright stars in the old open star cluster, M67 is presented based on the far-UV observations using the {\it Ultra Violet Imaging Telescope} ({\it UVIT}) on {\it ASTROSAT}. The UV and UV-optical colour-magnitude diagrams (CMDs) along with overlaid isochrones are presented for the member stars, which include blue straggler stars (BSSs), triple systems, white dwarfs (WDs) and spectroscopic binaries (SB). The CMDs suggest the presence of excess UV flux in many members, which could be extrinsic or intrinsic to them. We construct multi-wavelength spectral energy distribution (SED) using photometric data from the {\it UVIT, Gaia} DR2, 2MASS and WISE surveys along with optical photometry. We fitted model SEDs to 7 WDs and find 4 of them have mass $>$ 0.5 \(M_\odot\) and cooling age of less than 200 Myr, thus demanding BSS progenitors. SED fits to 23 stars detect extremely low mass (ELM) WD companions to WOCS2007, WOCS6006 and WOCS2002, and a low mass WD to WOCS3001, which suggest these to be post mass transfer (MT) systems. 12 sources with possible WD companion need further confirmation. 9 sources have X-ray and excess UV flux, possibly arising out of stellar activity. This study demonstrates that UV observations are key to detect and characterise the ELM WDs in non-degenerate systems, which are ideal test beds to explore the formation pathways of these peculiar WDs. The increasing detection of post-MT systems among BSSs and main-sequence stars suggests a strong MT pathway and stellar interactions in M67.

On the Origin of Sub-Subgiant Stars II: Binary Mass Transfer, Envelope Stripping, and Magnetic Activity

Abstract: Sub-subgiant stars (SSGs) lie to the red of the main-sequence and fainter than the red giant branch in cluster color-magnitude diagrams (CMDs), a region not easily populated by standard stellar evolution pathways. While there has been speculation on what mechanisms may create these unusual stars, no well-developed theory exists to explain their origins. Here we discuss three hypotheses of SSG formation: (1) mass transfer in a binary system, (2) stripping of a subgiant's envelope, perhaps during a dynamical encounter, and (3) reduced luminosity due to magnetic fields that lower convective efficiency and produce large star spots. Using the stellar evolution code MESA, we develop evolutionary tracks for each of these hypotheses, and compare the expected stellar and orbital properties of these models with six known SSGs in the two open clusters M67 and NGC 6791. All three of these mechanisms can create stars or binary systems in the SSG CMD domain. We also calculate the frequency with which each of these mechanisms may create SSG systems, and find that the magnetic field hypothesis is expected to create SSGs with the highest frequency in open clusters. Mass transfer and envelope stripping have lower expected formation frequencies, but may nevertheless create occasional SSGs in open clusters. They may also be important mechanisms to create SSGs in higher mass globular clusters.

Ultraviolet stellar population of the old open cluster M67 (NGC 2682)

Abstract: We present the results of ultraviolet (UV) photometry of the old open cluster M67 obtained using Galaxy Evolution Explorer (GALEX) in far-ultraviolet (FUV) and near-ultraviolet (NUV) bands. UV detections of 18 blue straggler stars (BSSs), 3 white dwarfs (WDs), 4 yellow straggler stars, 2 sub-subgiants, and 25 X-ray sources are presented (along with an online catalog). We demonstrate the capability of UV colour magnitude diagrams (CMDs) along with the UV isochrones to identify potential stars which defy standard stellar evolution in this well studied cluster. We also detect a few main sequence turn-off and subgiant branch stars with excess flux in the FUV and/or NUV. UV continuum excess as well as Mg II $\it h$ +$\it k$ emission lines from the IUE archival spectra for 2 red giants are detected, suggestive of their chromospheric activity. We suggest that a large number of stars in this cluster are chromospherically active, whereas the bright BSS are unlikely to be active. We also estimate the fundamental parameters L/L$_{\odot}$, R/R$_{\odot}$ and T$_{eff}$ of the BSSs and 15 FUV bright stars by constructing the spectral energy distribution (SED) using multi-wavelength data. We identify three groups among the BSSs, based on their properties. The H-R diagram of BSSs with isochrones suggests that the BSSs in M67 are formed in the last 2.5 Gyr - 400 Myr, more or less continuously. We identify 7 potential MS+WD candidates based on large UV excess from a probable 11, based on SEDs.