40 research outputs found
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
Field blue straggler stars: Discovery of white dwarf companions to blue metal-poor stars using UVIT/AstroSat
Blue metal-poor (BMP) stars are the main-sequence stars that appear bluer and
more luminous than normal turn-off stars of metal-poor globular clusters. They
are believed to be either field blue straggler stars (FBSS) formed via
post-mass transfer mechanism or accreted from dwarf satellite galaxies of the
Milky Way. A significant fraction of BMP stars are discovered to be potential
binaries. We observed 27 BMP stars using UVIT/\textit{AstroSat} in two FUV
filters, F148W and F169M. We report the discovery of white dwarf (WD)
companions of 12 BMP stars for the first time. The WD companions have estimated
temperatures T 10500 18250 K, and masses 0.17 M
0.8 M. Based on [Fe/H] and space velocity, we group the 12 BMP/FBSS
stars as the thick disk (5) and halo (5), whereas two stars appear to be
in-between. All the 5 thick disk BMP/FBSS have extremely low-mass (M 0.2
M) WDs as companions, whereas the 5 halo BMP/FBSS have low (0.2
M M 0.4 M), normal (0.4 M M
0.6M), and high mass (M 0.6 M) WD companions. Our
analysis suggests that at least 44 of BMP stars are FBSS, and these
stars hold the key to understand the details of mass transfer, binary
properties, and chemical enrichment among the FBSS
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In Utero Gene Therapy (IUGT) Using GLOBE Lentiviral Vector Phenotypically Corrects the Heterozygous Humanised Mouse Model and Its Progress Can Be Monitored Using MRI Techniques
Funder: UK Thalassaemia SocietyAbstract: In utero gene therapy (IUGT) to the fetal hematopoietic compartment could be used to treat congenital blood disorders such as β-thalassemia. A humanised mouse model of β-thalassemia was used, in which heterozygous animals are anaemic with splenomegaly and extramedullary hematopoiesis. Intrahepatic in utero injections of a β globin-expressing lentiviral vector (GLOBE), were performed in fetuses at E13.5 of gestation. We analysed animals at 12 and 32 weeks of age, for vector copy number in bone marrow, peripheral blood liver and spleen and we performed integration site analysis. Compared to noninjected heterozygous animals IUGT normalised blood haemoglobin levels and spleen weight. Integration site analysis showed polyclonality. The left ventricular ejection fraction measured using magnetic resonance imaging (MRI) in treated heterozygous animals was similar to that of normal non-β-thalassemic mice but significantly higher than untreated heterozygous thalassemia mice suggesting that IUGT ameliorated poor cardiac function. GLOBE LV-mediated IUGT normalised the haematological and anatomical phenotype in a heterozygous humanised model of β-thalassemia
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Publisher Correction: In Utero Gene Therapy (IUGT) Using GLOBE Lentiviral Vector Phenotypically Corrects the Heterozygous Humanised Mouse Model and Its Progress Can Be Monitored Using MRI Techniques
An amendment to this paper has been published and can be accessed via a link at the top of the paper
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Publisher Correction: In Utero Gene Therapy (IUGT) Using GLOBE Lentiviral Vector Phenotypically Corrects the Heterozygous Humanised Mouse Model and Its Progress Can Be Monitored Using MRI Techniques.
An amendment to this paper has been published and can be accessed via a link at the top of the paper
UVIT Open Cluster Study. II. Detection of Extremely Low Mass White Dwarfs and Post?Mass Transfer Binaries in M67
A detailed study of the UV-bright stars in the old open star cluster M67 is presented based on the far-UV observations using the Ultra Violet Imaging Telescope (UVIT) on ASTROSAT. The UV and UV?optical color?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. The CMDs suggest the presence of excess UV flux in many members, which could be extrinsic or intrinsic to them. We construct multiwavelength spectral energy distributions (SEDs) using photometric data from the UVIT, Gaia DR2, Two Micron All Sky Survey, and Wide-Field Infrared Survey Explorer surveys, along with optical photometry. We fitted model SEDs to seven WDs and find that four of them have mass >0.5 M 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. Twelve sources with possible WD companions need further confirmation. Nine sources have X-ray and excess UV flux, possibly arising out of stellar activity. This study demonstrates that UV observations are key to detecting and characterizing the ELM WDs in nondegenerate 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
GRASG - a framework for "gridifying" and running applications on service-oriented grids
The convergence of grid computing technologies and Web services offers many opportunities to utilize resources distributed across the Internet and solves many issues of interoperability. As a result, enabling applications as Web services are required intensively. Hence, a framework for "gridifying" and running applications on service-oriented grids (GRASG) was built to offer developers a flexible and effective tool for "gridifying" applications and making use of distributed resources on grid environment without much effort from the developers. It allows users to quickly enable an application as a Web service and access this service in a simple fashion. Further, in order to make use of distributed resources, GRASG provides a metascheduling mechanism that is able to schedule jobs to grid resources using Web services protocol. These features reduce the time taken for application development and execution