• R. K. S. Yadav

      Articles written in Journal of Astrophysics and Astronomy

    • Multicolour CCD Photometric Study of Galactic Star Clusters SAI 63 and SAI 75

      R. K. S. Yadav S. I. Leonova R. Sagar E. V. Glushkova

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      We present 𝑈𝐵𝑉𝐼 CCD photometric observations obtained in the field of open clusters SAI 63 and SAI 75. CCD optical data obtained for the first time for these clusters are used to derive the fundamental parameters of the clusters. Stellar surface density profile indicates that radii of SAI 63 and SAI 75 are ∼ 3'.5 and 2'.5 respectively. The reddenings 𝐸(𝐵 - 𝑉) are 0.44 ± 0.05 and 0.34 ± 0.05 mag for SAI 63 and SAI 75 respectively while the corresponding distances are 2.2 ± 0.2 and 3.5 ± 0.3 kpc. An age of 450 ± 50 Myr for SAI 63 and 90 ± 10 Myr for SAI 75 is determined using the theoretical isochrones of Z = 0.019. Our analysis shows that reddening law is normal towards SAI 75.

    • A search for variable stars in the four open star clusters

      ALOK DURGAPAL GEETA RANGWAL D. BISHT HARMEEN KAUR R. K. S. YADAV J. C. PANDEY

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      We present a CCD photometric survey for the search of variable stars in four open clusters namely Berkeley 69, King 5, King 7 and Berkeley 20. The time series observations were carried out for 1 and/or 2 nights for each of the clusters in the year 1998, which have led to identify nineteen variable stars in theseclusters. Out of these 19 variable stars, five stars show $\delta$ Scuti-like variability and two stars show W UMa type variability. In other stars, we could not find the periods, and hence the type of variability due to the lack of sufficient data. The periods of $\delta$ Scuti type stars are found to be in the range of 0.13–0.21 days, whereas the two stars in the cluster Berkeley 20, which showed W UMa type variability have orbital periods of 0.396 and 0.418 days, respectively. Using the Gaia data, the basic parameters of the clusters Berkeley 69, King 7 and King 5 are also revised. The age and reddening are estimated to be $0.79\pm 0.09$ Gyr and $0.68 \pm 0.03$ mag for Berkeley 69, $0.79\pm 0.09$ Gyr and $1.22 \pm 0.03$ mag for the cluster King 7 and $1.59\pm 0.19$ Gyr and $0.63\pm 0.02$ mag for the cluster King 5, respectively. The signature of mass segregation is found in the clusters King 7 and King 5.

    • Study of dynamical status of the globular cluster NGC 1851 using ultraviolet imaging telescope

      GAURAV SINGH R. K. S. YADAV SNEHALATA SAHU ANNAPURNI SUBRAMANIAM

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      We present the study of dynamical status of the globular cluster NGC 1851. A combination of multi-wavelength space and ground-based data sets are used for the present analysis. In order to select the genuine cluster members, we used the astro-photometric data available from HST and GAIA-DR2 catalogs. The BSS radial distribution of the cluster is plotted from the center of the cluster to the outskirts. The radial distribution of BSS shows a central peak, followed by a dip at the intermediate radii ($r_{\rm min}\sim 90''$) and a rising trend in the outskirts. We also estimated $A^+_{rh}$ parameter as $0.391 \pm 0.006$ to validate the findings of the radial distribution study. On the basis of the minima in the BSS radial distribution and the value of $A^+_{rh}$ parameter, we conclude that NGC 1851 belongs to Family II classification and is an intermediate dynamical statecluster.

    • Photometric calibrations and characterization of the 4K$\times$4K CCD imager, the first-light axial port instrument for the 3.6m DOT

      AMIT KUMAR S. B. PANDEY AVINASH SINGH R. K. S. YADAV B. K. REDDY N. NANJAPPA S. YADAV R. SRINIVASAN

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      In the present work, recent characterization results of the 4K$\times$4K CCD imager (a first light instrument of the 3.6m devasthal optical telescope; DOT) and photometric calibrations are discussed along with measurements of the extinction coefficients and sky brightness values at the location of the 3.6m DOTsite basedon the imaging data taken between 2016 and 2021. For the 4K$\times$4K CCD imager, all given combinations of gains (1, 2, 3, 5 and 10 e$^-$/ADU) and readout noise values for the three readout speeds (100 kHz, 500 kHz and 1 MHz) are verified using the sky flats and bias frames taken during early 2021; measured values resemble well with the theoretical ones. Using color–color and color–magnitude transformation equations, color coefficients ($\alpha$) and zero-points ($\beta$) are determined to constrain and examine their long-term consistencies and any possible evolution based on UBVRI observations of several Landolt standard fields observed during 2016–2021. Our present analysis exhibits consistency among estimated a values within the 1$\sigma$ and does not show any noticeable trend with time. We also found that the photometric errors and limiting magnitudes computed using the data taken using the CCD imager follow the simulated ones published earlier. The average extinction coefficients, their seasonal variations and zenith night-sky brightness values for the moon-less nights for all ten Bessell and SDSS filters are also estimated and found comparable to those reported for other good astronomical sites.

    • Optical observations of star clusters NGC 1513 and NGC 4147; white dwarf WD 1145$+$017 and K band imaging of star-forming region Sh 2-61 with the 3.6-m Devasthal optical telescope

      RAM SAGAR R. K. S. YADAV S. B. PANDEY SAURABH SHARMA SNEH LATA SANTOSH JOSHI

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      The UBVRI CCD photometric data of open star cluster NGC 1513 are obtained with the 3.6-m Indo-Belgian Devasthal optical telescope (DOT). Analyses of the GAIA EDR3 astrometric data have identified 106 possible cluster members. The mean proper motion of the cluster is estimated as $\mu_{\alpha}\cos\delta=1.29\pm 0.02$ and $\mu_{\delta}=-3.74\pm0.02$ mas yr$^{-1}$. Estimated values of reddening $E(B-V)$ and distance to the NGC 1513 are $0.65 \pm 0.03$ mag and $1.33 \pm 0.1$ kpc, respectively. Age of $225 \pm 25$ Myr is assigned to the cluster by comparing theoretical isochrones with deeply observed cluster sequences. Using observations taken with the 3.6-m DOT, values of distance and age of the galactic globular cluster NGC 4147 areestimated as $18.2 \pm 0.2$ Kpc and $14 \pm 2$ Gyr, respectively. The optical observations of planetary transit around white dwarf WD $1145\pm 017$ and $K$-band imaging of star-forming region Sharpless Sh 2-61 demonstrate observing capability of 3.6-m DOT. Optical and near-infrared observations of celestial objects and events are being carried out routinely with the 3.6-m DOT. They indicate that the performance of the telescope is at par with those of other similar telescopes located elsewhere in the world. We, therefore, statethat this observing facility augurs well for multi-wavelength astronomy including the study of astrophysical jets.

  • Journal of Astrophysics and Astronomy | News

    • Continuous Article Publication

      Posted on January 27, 2016

      Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

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