Department of Physics
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Item VizieR Online Data Catalog: Positions, plx, & phot. from Gaia for Berkeley 39 (Chand+, 2024)(2025-09) Vaidya, KausharIn order to characterize the BSS and YSS populations, we use multiwavelength data, ranging from UV to infrared (IR). UV data: The fluxes of sources in UV wavelengths are obtained from the Ultraviolet and Optical Telescope (Swift/UVOT) and Galaxy Evolution Explorer (GALEX). The Swift spacecraft is equipped with UVOT, a 30cm telescope sensitive in the optical/UV band in the wavelength range of 170-650nm. We utilize near-UV (NUV) data (Siegel+2019, J/AJ/158/35) from UVOT in this work. Berkeley 39 was observed by Swift/UVOT in three UV filters, UVW2 (180-260nm), UVM2 (200-280nm), and UVW1 (220-400nm), in 2011. In addition to the Swift/UVOT data, we also use data from GALEX, a 50cm aperture space-based telescope which observed Berkeley 39 in its NUV band (1770-2730Å). Optical data: Gaia data (DR3; Gaia Collab.+2022, I/355) provides proper motions, parallaxes, and three-band photometry (G, GBP, GRP) for over a billion sources observed between 25 July 2014 and 28 May 2017. The wavelength of filter G is centered at 673nm, GBP at 532nm, and GRP at 797nm. The Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) is a ground-based telescope which observed from 2010 to 2015 for its first data release (Chambers+2019, II/349). It utilizes five filters, g, r, i, z, and y, with effective wavelengths 481, 617, 752, 866, and 962nm respectively.Item Vizier online data catalog: tidal tails in the open cluster ngc 752(VizieR, 2021) Vaidya, KausharAgarwal et al. (2021MNRAS.502.2582A) using Gaia DR2 (2018A&A...616A...1G, Cat. I/345) data with their novel machine learning membership determination algorithm found hints of tidal tails in NGC 752. Also, Hu et al. (2021ApJ...912....5H, Cat. J/ApJ/912/5) also identify the elongated morphology of the peripheral regions of NGC 752 from the Gaia DR2 data using the members identified by Cantat-Gaudin et al. (2018A&A...618A..93C, Cat. J/A+A/618/A93). As the first step, we do a membership selection in NGC 752 from the Gaia EDR3 (2021A&A...649A...1G, Cat. I/350) data set is carried out in a region of radius 5 degrees around its centre. This sample is termed All sources. We use ML-MOC (Agarwal et al. 2021MNRAS.502.2582A) to identify cluster members using the proper motion and parallax information. It identifies cluster members in the PM-ω parameter space, independent of the spatial density of the cluster, thereby allowing for the identification of faint extended spatial structures such as tidal tailsItem Blue Straggler Stars: setting up a dynamical clock for open clusters(The PoPuPS, 2024) Vaidya, KausharBlue straggler stars are late bloomers that are bluer and brighter than the main sequence turnoff stars on a color-magnitude diagram of a cluster. Being a massive population compared to their other cluster siblings, their sedimentation level has been used to probe the dynamical evolution of globular clusters. In a series of studies, we explored the dynamical evolution of old open clusters, for the first time, making use of this same trait of the BSS that they settle quicker in the cluster core than any other cluster population. In these works, we have compared the theoretical estimation of dynamical ages, Nrelax, with the observed signatures of blue straggler stars segregation either by placing open clusters in Family I/II/III classification of dynamical ages defined in globular clusters or by estimating the area enclosed between the cumulative radial distributions of BSS and another reference population in 23 open clusters.Item Uocs xiv: study of the open cluster ngc 2627 using uvit/astrosat(IOP, 2024-07) Vaidya, KausharWe study the intermediate-age open cluster NGC 2627, located at a distance of ∼2 kpc, using UVIT/AstroSat and other archival data. Using a machine learning-based algorithm, ML-MOC, on the Gaia DR3 data, we identify 422 cluster members, including four blue straggler stars (BSSs), one yellow straggler star (YSS), one blue lurker (BL), one red clump (RC) star, and two binary candidates with detection in both UVIT/F148W and UVIT/F169M filters. We characterise them using multiwavelength spectral energy distributions (SEDs). Out of the above nine sources, one BSS, the BL, and one binary candidate have a source nearby; hence, we did not fit their SEDs. Of the remaining six sources, we successfully fit two with single-component SEDs and four with binary-component SEDs. The binary-component SED-based parameters indicate that the hot companions of BSSs, the YSS, the RC star, and the binary candidate are extremely low-mass white dwarfs, confirming that at least four out of nine stars (44%) are formed via the mass transfer channel. We fit King's profile function to the high-probability (p > 0.8) cluster members and estimate the cluster core radius (rC) to be 3.84' and the tidal radius (rt) to be 36.85'. We find that the equal-mass binaries are most concentrated towards the cluster center, followed by the single massive stars, and single low-mass stars. The BSS population of the cluster is also found to be located within a radius r ∼ 10 × rC from the cluster center, suggesting the dynamical evolution of the cluster.Item Dynamical evolution of four old galactic open clusters traced by their constituent stars with gaia DR3(IOP, 2024-10) Vaidya, KausharWe investigate the evolutionary stages of four open clusters—Berkeley 39, Collinder 261, NGC 6819, and NGC 7789—of ages ranging from 1.6 to 6 Gyr. These clusters have previously been classified into dynamically young and intermediate age groups based on the segregation level of BSS with respect to red-giant-branch stars and main-sequence stars, respectively. We identify members of these four clusters using the ML-MOC algorithm on Gaia DR3 data. To examine the relative segregation of cluster members of different evolutionary stages, we utilize cumulative radial distributions, proper motion distributions, and spatial distributions in galactocentric coordinates. Our analysis shows that Berkeley 39 and NGC 6819 exhibit moderate signs of population-wise segregation from evolved to less-evolved members. NGC 7789 shows signs of mass segregation only in the cumulative radial distributions. On the other hand, Collinder 261 exhibits high segregation of BSS in the cumulative radial distribution, while other populations show the same level of segregation.Item Characterization of Blue and Yellow Straggler Stars of Berkeley 39(IOP, 2024) Vaidya, KausharWe characterize blue straggler stars (BSSs) and yellow straggler stars (YSSs) of the open cluster (OC) Berkeley 39 using multiwavelength observations including the Swift/Ultraviolet and Optical Telescope (UVOT). Our analysis also makes use of ultraviolet (UV) data from Galaxy Evolution Explorer, optical data from Gaia DR3 and Panoramic Survey Telescope and Rapid Response System, and infrared data from Two Micron All Sky Survey, Spitzer/IRAC, and Wide-field Infrared Survey Explorer. Berkeley 39 is a ∼6 Gyr old Galactic OC located at a distance of ∼4200 pc. We identify 729 sources as cluster members utilizing a machine-learning algorithm, ML-MOC, on Gaia DR3 data. Of these, 17 sources are classified as BSS candidates and four as YSS candidates. We construct multiwavelength spectral energy distributions (SEDs) of 16 BSS and two YSS candidates, within the Swift/UVOT field, to analyze their properties. Out of these, eight BSS candidates and both the YSS candidates are successfully fitted with single-component SEDs. Five BSS candidates show marginal excess in the near-UV (NUV; fractional residual <0.3 in all but one UVOT filter), whereas three BSS candidates show moderate to significant excess in the NUV (fractional residual >0.3 in at least two UVOT filters). We present the properties of the BSS and YSS candidates, estimated based on the SED fits.Item Contact Binary Variables as X-ray Sources(ARXIV, 2005-08) Vaidya, KausharWe present cross-identification of archived X-ray point sources with W UMa variable stars found in the All-Sky Automated Survey (ASAS). In a surveyed sky area of 300 square degrees of ASAS, 36 W UMa stars have been found associated with X-ray emission. We compute the distances of these W UMa systems and hence their X-ray luminosities. Our data support the "supersaturation" phenomenon seen in these fast rotators, namely that the faster a W UMa star rotates, the weaker its X-ray luminosity.Item Photometry with NICMOS-3 Array Detector from Mt. Abu IR Observatory(Automated Data Analysis in Astronomy, 2002) Vaidya, KausharPhotometry with NICMOS-3 Array Detector from Mt. Abu IR Observatory - NASA/ADS Now on home page ads icon ads Enable full ADS view NASA/ADS Photometry with NICMOS-3 Array Detector from Mt. Abu IR Observatory Baliyan, KS ; Sanchawala, K. ; Ganesh, S. ; Joshi, UC ; Shah, CR Abstract Publication: Automated Data Analysis in Astronomy Pub Date: 2002 Bibcode: 2002adaa.conf..235B No Sources Found © The SAO/NASA Astrophysics Data System adshelp[at]cfa.harvard.edu The ADS is operated by the Smithsonian Astrophysical Observatory under NASA Cooperative Agreement NNX16AC86AItem GRB 050502a : r band observation at Lulin observatory(GRB Coordinates Network, 2005) Vaidya, KausharRB 050502a : r band observation at Lulin observatory. - NASA/ADS Now on home page ads icon ads Enable full ADS view NASA/ADS GRB 050502a : r band observation at Lulin observatory. Sanchawala, K. ; Wu, WL ; Huang, KY ; Ip, WH ; Qiu, Y. ; Zhou, W. ; Lou, YQ ; Urata, Y. Abstract Publication: GRB Coordinates Network Pub Date: 2005 Bibcode: 2005GCN..3335....1S full text sources Publisher | data products SIMBAD (1) © The SAO/NASA Astrophysics Data System adshelp[at]cfa.harvard.edu The ADS is operated by the Smithsonian Astrophysical Observatory under NASA Cooperative Agreement NNX16AC86A NASA logo Smithsonian logo Resources About ADS ADS Help What's New Careers@ADS Social @adsabs ADS Blog Project Switch to full ADS Is ADS down? (or is it just me...) Smithsonian Institution Smithsonian Privacy Notice Smithsonian Terms of Use Smithsonian Astrophysical Observatory NASAItem X-Ray Young Stars in the Carina Nebula(Protostars and Planets V Posters, 2005) Vaidya, KausharX-Ray Young Stars in the Carina Nebula - NASA/ADS Now on home page ads icon ads Enable full ADS view NASA/ADS X-Ray Young Stars in the Carina Nebula Sanchawala, K. ; Chen, W. -P. ; Lee, H. -T. ; Nakajima, Y. ; Tamura, M. ; Sato, S. ; Chu, Y. -H. Abstract Publication: Protostars and Planets V Posters Pub Date: 2005 Bibcode: 2005prpl.conf.8242S No Sources Found data products Chandra (1) © The SAO/NASA Astrophysics Data System adshelp[at]cfa.harvard.edu The ADS is operated by the Smithsonian Astrophysical Observatory under NASA Cooperative Agreement NNX16AC86A NASA logo Smithsonian logo Resources About ADS ADS Help What's New Careers@ADS Social @adsabs ADS Blog Project Switch to full ADS Is ADS down? (or is it just me...) Smithsonian Institution Smithsonian Privacy Notice Smithsonian Terms of Use Smithsonian Astrophysical Observatory NASA