• R. Sagar

      Articles written in Journal of Astrophysics and Astronomy

    • Photometric variability of four coronally active stars

      J. C. Pandey K. P. Singh R. Sagar S. A. Drake

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      We present photometric observations of four stars that are optical counterparts of soft X-ray/EUV sources, namely 1ES 0829+15.9, 1ES0920-13.6, 2RE J1 10159+223509 and 1ES 1737+61.2. We have discovered periodic variability in two of the stars, viz., MCC 527 (1ES 0829+15.9; Period = 0d.828 ± 0.0047) and HD 81032 (1ES 0920-13.6; Period = ∼ 57.02 ± 0.560 days). HD 95559 (2RE J1 10159+223509) is found to show a period of 3d. HD 160934 (1ES1737+61.2) also shows photometric variability but needs to be monitored further for finding its period. These stars most likely belong to the class of chromospherically active stars.

    • Unravelling the nature of HD 81032 — A new RS CVn binary

      J. C. Pandey K. P. Singh S. A. Drake R. Sagar

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      BVR photometric and quasi-simultaneous optical spectroscopic observations of the star HD 81032 have been carried out during the years 2000-2004. A photometric period of 18.802 ± 0.07d has been detected for this star. A large group of spots with a migration period of 7.43 ± 0.07 years is inferred from the first three years of the data. Hα and CaII H and K emissions from the star indicate high chromospheric activity. The available photometry in the BVRIJHK bands is consistent with the spectral type of K0IV previously found for this star. We have also examined the spectral energy distribution of HD 81032 for the presence of an infrared colour excess using the 2MASS JHK and IRAS photometry, but found no significant excess in any band above the normal values expected for a star with this spectral type. We have also analyzed the X-ray emission properties of this star using data obtained by the ROSAT X-ray observatory during its All-Sky Survey phase. An X-ray flare of about 12 hours duration was detected during the two days of X-ray coverage obtained for this star. Its X-ray spectrum, while only containing 345 counts, is inconsistent with a single-temperature component solar-abundance coronal plasma model, but implies either the presence of two or more plasma components, nonsolar abundances, or a combination of both of these properties. All of the above properties of HD 81032 suggest that it is a newly identified, evolved RS CVn binary.

    • 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.

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    • Continuous Article Publication

      Posted on January 27, 2016

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      Posted on July 25, 2019

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