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Browsing by Author "Sagar, R"

Browsing by Author "Sagar, R"

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  • Non-uniform extinction in ten young open clusters 
    Sagar, R (Science Press & Pergamon Journals Ltd., 1988)
  • Non-uniform extinction in young open star clusters 
    Yadav, R. K. S; Sagar, R (Royal Astronomical Society, 2001-12)
    The extinction law and the variation of colour excess with position, luminosity and spectral class in young open star clusters NGC 663, NGC 869, NGC 884, NGC 1502, NGC 1893, NGC 2244, NGC 2264, NGC 6611, Tr 14, Tr 15, Tr ...
  • Observations of GRB afterglows from Nainital : Evidence in favour of jet model 
    Sagar, R (Astronomical Society of India, 2002)
    Broad band optical photometric observations of five Gamma-ray burst (GRB) afterglows (GRB 990123, GRB 991208, GRB 991216, GRB 000301c and GRB 000926) are taken from Nainital during 1999 and 2000. These in combination with ...
  • Observations with the 3.6-meter Devasthal optical telescope 
    Sagar, R; Kumar, B; Sharma, S (Indian Academy of Sciences, 2020-12)
    The 3.6-meter Indo–Belgian Devasthal optical telescope (DOT) has been used for optical and near-infrared (NIR) observations of celestial objects. The telescope has detected stars of B=24.5±0.2,R=24.6±0.12 and g=25.2±0.2 ...
  • On mass and velocity distributions in members of star clusters: An analytical approach 
    Chatterjee, S; Kumar, B; Sagar, R (Astronomical Society of India, 2002-12)
    Dynamical evolution of stellar mass distribution in star clusters is analysed by considering simultaneously the effects of dynamical friction, stochastic heating and the gravitational potential due to mass distribution ...
  • On the determination of age and mass functions of stars in young open star clusters from the analysis of their luminosity functions 
    Piskunov, A. E; Belikov, A. N; Sagar, R; Subramaniam, A (Royal Astronomical Society, 2004-04-21)
    We construct the observed luminosity functions of the remote young open clusters NGC 2383, 2384, 4103, 4755, 7510 and Hogg 15 from CCD observations of them. The observed LFs are corrected for field star contamination ...
  • On the Photometric Error Calibration for the Differential Light Curves of Point-like Active Galactic Nuclei 
    Goyal, Arti; Mhaskey, Mukul; Gopal-Krishna; Witta, P. J; Stalin, C. S; Sagar, R (Indian Academy of Sciences, 2013-09)
    It is important to quantify the underestimation of rms photometric errors returned by the commonly used APPHOT algorithm in the IRAF software, in the context of differential photometry of point-like AGN, because of the ...
  • The optical afterglow of the not so dark GRB 021211 
    Pandey, S. B; Anupama, G. C; Sagar, R; Bhattacharya, D; Castro-Tirado, A. J; Sahu, D. K; Parihar, P. S; Prabhu, T. P (The European Southern Observatory, 2003-09)
    We determine Johnson B,V and Cousins R,I photometric CCD magnitudes for the afterglow of GRB 021211 during the first night after the GRB trigger. The afterglow was very faint and would have been probably missed if no prompt ...
  • Optical and near-infrared photometric study of the open cluster NGC 637 and 957 
    Yadav, R. K. S; Kumar, B; Subramaniam, A; Sagar, R; Mathew, B (Royal Astronomical Society, 2008-11)
    We present UBVRI CCD photometry in the region of the open clusters NGC 637 and 957. The radii are found to be 4.2 and 4.3 arcmin. Their reddenings E(B - V) are 0.64 +/- 0.05 and 0.71 +/- 0.05 mag and their distances, from ...
  • Optical and radio observations of the bright GRB 010222 afterglow: evidence for rapid synchrotron cooling ? 
    Sagar, R; Stalin, C. S; Bhattacharya, D; Pandey, S. B; Mohan, V; Castro-Tirado, A. J; Pramesh Rao, A; Trushkin, S. A; Nizhelskij, N. A; Bremer, M; Castro Ceron, J. M (Astronomical Society of India, 2001)
    We report photometric observations of the optical afterglow of GRB 010222 in V, R and I passbands carried out between 22-27 February 2001 at Nainital. We determine the CCD Johnson BV and Cousins RI photometric magnitudes ...
  • Optical CCD imaging of some Herbig Ae/Be stars 
    Bhatt, H. C; Sagar, R (EDP Sciences, 1992-02)
    Results of V, R, and H-alpha CCD imaging for 15 Herbig Ae/Be stars are presented. Light variations of more than about 2 mag in V have been noticed in stars T Ori, RR Tau, and LH-alpha 25. The nature of the variations in ...
  • Optical follow up of the GRB 990123 sources from UPSO, Naini Tal 
    Sagar, R; Pandey, A. K; Mohan, V; Yadav, R. K. S; Nilakshi; Bhattacharya, D; Castro-Tirado, A. J (Astronomical Society of India, 1999)
    The CCD magnitudes in Johnson $BV$ and Cousins $R$ photometric passbands are determined for the optical transient of GRB 990123. These observations have been taken approximately 12 hours after trigger of the gamma-ray ...
  • Optical follow-up of GRB afterglows from UPSO, Naini Tal 
    Pandey, S. B; Sagar, R; Mohan, V; Pandey, A. K; Bhattacharya, D; Castro-Tirado, A. J (Astronomical Society of India, 2001)
    Successful optical photometric observations of five GRB afterglows namely GRB 990123, GRB 991208, GRB 991216, GRB 000301c and GRB 000926 have been carried out from State Observatory Naini Tal till 2000. The results and ...
  • Optical microvariability in radio quiet quasars 
    Wiita, P. J; Gopal-Krishna; Sagar, R (Kluwer Academic Publishers, 1994)
    We have observed 11 radio quiet QSOs (RQQSOs) to see if they exhibit intranight variability in the optical. The detection of such microvariability would support models in which flutuations on accretion disks are dominant, ...
  • Optical observations and multiband modelling of the afterglow of GRB041006 : Evidence of a hard electron energy spectrum 
    Misra, K; Resmi, L; Pandey, S. B; Bhattacharya, D; Sagar, R (Astronomical Society of India, 2005-12)
    We present the CCD Cousins R band photometric observations of the afterglow of GRB 041006. The multiband afterglow evolution is modelled using an underlying `hard' electron energy spectrum with a p1 ~ 1.3. The burst appears ...
  • Optical observations of GRB 060124 afterglow: a case for an injection break 
    Misra, K; Bhattacharya, D; Sahu, D. K; Sagar, R; Anupama, G. C; Castro-Tirado, A. J; Guziy, S. S; Bhatt, B. C (EDP Sciences, 2007-03)
    Aims.We present broad band optical afterglow observations of a long duration GRB 060124 using the 1.04-m Sampurnanand Telescope at ARIES, Nainital and the 2.01-m HCT at IAO, Hanle, including the earliest ground-based ...
  • Optical observations of GRB afterglows from India 
    Sagar, R; Misra, K (Astronomical Society of India, 2005-06)
    Optical observations of GRB afterglows provide information about GRB distances as well as their isotropic/non-isotropic nature of emission. More than 30 GRB fields have been probed by us during 1999 to 2003, out of which ...
  • Optical observations of star clusters NGC 1513 and NGC 4147; white dwarf WD 1145þ017 and K band imaging of star-forming region Sh 2-61 with the 3.6-m Devasthal optical telescope 
    Sagar, R; Yadav, R. K. S; Pandey, S. B; Sharma, Saurabh; Lata, Sneh; Joshi, Santosh (Indian Academy of Sciences, 2022-06)
    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 ...
  • Optical observations of the bright long duration peculiar GRB 021004 afterglow. 
    Pandey, S. B; Sahu, D. K; Resmi, L; Sagar, R; Anupama, G. C; Bhattacharya, D; Mohan, V; Prabhu, T. P; Bhatt, B. C; Pandey, J. C; Parihar, P. S; Castro-Tirado, A. J (Astronomical Society of India, 2003)
    The CCD magnitudes in Johnson B,V and Cousins R and I photometric passbands are determined for the bright long duration GRB 021004 afterglow from 2002 October 4 to 16 starting ~ 3 hours after the γ - ray burst. Light curves ...
  • Optical variability of radio-intermediate quasars 
    Goyal, Arti; Gopal-Krishna; Joshi, S; Sagar, R; Wiita, Paul J; Anupama, G. C; Sahu, D. K (Blackwell Publishing, 2010-02)
    We report the results of our intensive intranight optical monitoring of eight optically bright `radio-intermediate quasars' (RIQs) having flat or inverted radio spectra. The monitoring was carried out in R band on 25 nights ...

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