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Vineeth Valsan

Publications and source records attributed to Vineeth Valsan.

6 recordsLinked to original sources

Investigating the properties of nearby young moving groups using GaiaDR3

Moving groups, which are gravitationally unbound collections of stars spread over large portions of the sky, pose challenges to their identification. Analyzing the three-dimensional spatial motion of stars is one method to identify their members. Despite several studies in the past, a reliable and conclusive catalog of moving group stars is currently lacking. Our objective is to present a most recent and updated catalog of nearby young moving group (NYMG) candidates in the solar neighborhood and investigate their properties using updated science data from the Gaia Data Release 3 (DR3). We searched for candidates of twelve NYMGs within a distance of 150 pc using Gaia DR3. To determine the membership, we employed the Bayesian algorithm BANYAN-Sigma. We compiled a total list of 3,153 NYMG candidates, of which 1,651 were new candidates. We also assessed the credibility of the literature defined 'Good-box' criterion with the latest comprehensive catalog of NYMGs from our study. We homogeneously estimated the ages of the NYMG candidates using Gaia DR3 photometry data. The analysis revealed that our NYMG candidates display a large scatter on the CMDs resulting in a large range of estimated ages from isochrones. Additionally, we conducted an infrared (IR) excess analysis to identify disk candidates among our final sample. Our spectral energy distribution (SED) analysis found 51 stars with IR excess. We present a largely inclusive list of all the NYMG candidates within 150 pc of Solar neighbourhood using Gaia DR3. The wide range of ages obtained from isochrone fitting underscores the need for more robust age analysis techniques to accurately determine the ages of NYMG members. The presence of IR excess in the 51 stars confirms the existence of disks indicating that they could be potential candidates for exoplanet detections.

astro-ph.SR

Spectroscopic study of late-type emission-line stars using the data from LAMOST DR6

Low-mass emission-line stars belong to various evolutionary stages, from pre-main-sequence young stars to evolved stars. In this work, we present a catalog of late-type (F0 to M9) emission-line stars from the LAMOST Data Release 6. Using the scipy package, we created a Python code that finds the emission peak at H-alpha in all late-type stellar spectra. A dataset of 38,152 late-type emission-line stars was obtained after a rigorous examination of the photometric quality flags and the signal-to-noise ratio of the spectra. Adopting well-known photometric and spectroscopic methods, we classified our sample into 438 infrared excess sources, 4,669 post-main-sequence candidates, 9,718 Fe/Ge/Ke sources, and 23,264 dMe sources. From a cross-match with known databases, we found that 29,222 sources, comprising 65 IR excess sources, 7,899 Fe/Ge/Ke stars, 17,533 dMe stars, and 3,725 PtMS candidates, are new detections. We measured the equivalent width of the major emission lines observed in the spectra of our sample of emission-line stars. Furthermore, the trend observed in the line strengths of major emission lines over the entire late-type spectral range is analyzed. We further classified the sample into 4 groups based on the presence of Hydrogen and Calcium emission lines. This work presents a large dataset of late-type emission-line stars, which can be used to study active phenomena in late-type stars.

astro-ph.SR

Simulation of a Laue lens with bent Ge(111) crystals

In the context of Laue project for focusing hard X-/ soft gamma-rays, an entire Laue lens, using bent Ge(111) crystal tiles, with 40 meters curvature radius, is simulated with a focal length of 20 meters. The focusing energy band is between 80 keV and 600 keV. The distortion of the output image of the lens on the focal plane due to the effect of crystal tile misalignment as well as the radial distortion arising from the curvature of the crystal is discussed in detail. Expected detection efficiency and instrument background is also estimated. Finally the sensitivity of the Laue lens is calculated. A quantitative analysis of the results of these simulation is also presented.

physics.ins-det

Results of the simulations of the petal/lens as part of the LAUE project

In the context of the LAUE project for focusing hard X-/gamma rays, a petal of the complete lens is being assembled at the LARIX facility in the Department of Physics and Earth Science of the University of Ferrara. The lens petal structure is composed of bent Germanium and Gallium Arsenide crystals in transmission geometry. We present the expectations derived from a mathematical model of the lens petal. The extension of the model for the complete LAUE project in the 90 -- 600 keV energy range will be discussed as well. A quantitative analysis of the results of these simulations is also presented.

astro-ph.IM

Bent crystal selection and assembling for the LAUE project

For the first time, with the Laue project, bent crystals are being used for focusing photons in the 80-300 keV energy range. The advantage is their high reflectivity and better Point Spread Function with respect to the mosaic flat crystals. Simulations have already shown their excellent focusing capability which makes them the best candidates for a Laue lens whose sensitivity is also driven by the size of the focused spot. Selected crystals are Germanium (perfect, (111)) and Gallium Arsenide (mosaic, (220)) with 40 m curvature radius to get a spherical lens with 20 m long focal length. A lens petal is being built. We report the measurement technique by which we are able to estimate the exact curvature of each tile within a few percent of uncertainty and their diffraction efficiency. We also discuss some results.

astro-ph.IM

Expected performance of a Laue lens based on bent crystals

In the context of the LAUE project devoted to build a long focal length focusing optics for soft gamma-ray astronomy (70/100 keV to $>$600 keV), we present results of simulation of a Laue lens, based on bent crystals in different assembling configurations (quasi-mosaic and reflection-like geometries). The main aim is to significantly overcome the sensitivity limits of the current generation of gamma-ray telescopes and improve the imaging capability.

astro-ph.IM