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Browsing Publications of Astronomical Society of India by Author "Sagar, R"

Browsing Publications of Astronomical Society of India by Author "Sagar, R"

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  • GRB 000926 and its optical afterglow : Another possible evidence for non-isotropic emission 
    Sagar, R; Pandey, S. B; Mohan, V; Bhattacharya, D; Castro-Tirado, A. J (Astronomical Society of India, 2001)
    The CCD Johnson BV and Cousins RI photomertric magnitudes are determined for 20 stars in the field of GRB 000926. They are used to calibrate the present R as well as published BVRI photometric magnitudes of the GRB 000926 ...
  • HD 12098 a new far-northern roAp star 
    Girish, V; Joshi, S; Seetha, S; Ashoka, B. N; Martinez, P; Chaubey, U. S; Gupta, S. K; Kurtz, D. W; Sagar, R (Astronomical Society of India, 2001)
    The rapidly oscillating Ap (roAp) stars are cool, magnetic, chemically peculiar stars which pulsate in non-radial p-modes in the period range 4-16 min and have Johnson B amplitudes less than 8 mmag. "The NainiTal-Cape ...
  • Influence of a third body on the luminosity of a contact binary system 
    Barman, S. K; Sagar, R (Astronomical Society of India, 1996)
  • Integrated photometric parameters of open and globuler clusters 
    Sagar, R; Joshi, U. C; Sinvhal, S. D (Astronomical Society of India, 1983-03)
    In this work we have discussed UBV parameters of 142 galactic clustes and 32 globular clusters. Comparison of the integrated parameters of galactic clusters with the theoretical ones confirms the validity of the basic ...
  • Internal motions in the open star clusters NGC 654 and 6087 
    Sagar, R; Bhatt, H. C (Astronomical Society of Indian, 1989-03)
    Proper motion measurements are used to study the internal kinematics in the open star clusters NGC 654 and 6087. It is found that intrinsic dispersions are independent of stellar mass and radial distance in both clusters. ...
  • Intracluster extinction in young open star clusters 
    Sagar, R; Qian, Z. Y (Astronomical Society of India, 1993)
    An analysis of near-infrared data in combination with optical observations, indicates a normal interstellar extinction law around hot O and B stars at wavelengths greater than or = 0.9 micrometers. At shorter wavelengths, ...
  • Naini Tal-Cape survey for pulsating chemically peculiar stars - A status report 
    Seetha, S; Chaubey, U. S; Girish, V; Joshi, S; Ashoka, B. N; Gupta, S. K; Kurtz, D. W; Martinez, P; Sagar, R (Astronomical Society of India, 2001)
    The "Naini Tal-Cape survey for rapidly oscillating Ap stars", to search the northern hemi-sphere sky for pulsating stars was initiated in 1997. This is a collaboration between India and South Africa. So far about 70 stars ...
  • New pulsating variables discovered from the Naini Tal-Cape survey 
    Seetha, S; Ashoka, B. N; Joshi, S; Girish, V; Sagar, R; Chaubey, U. S; Gupta, S. K (Astronomical Society of India, 2002-09)
    The Naini Tal-Cape survey has been initiated to search for pulsations in chemically peculiar A and F type stars. Many of the magnetic A peculiar type stars exhibit rapid oscillations with periods ranging from 4-16 minutes. ...
  • 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 ...
  • 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 ...
  • 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 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 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 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 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 ...
  • Performance of the IIA mosaic CCD camera system 
    Naidu, B. N; Srinivasan, R; Mohan, V; Sagar, R (Astronomical Society of India, 2001)
    We evaluate performance of the 4K x 4K mosaic CCD camera system developed at the Indian Institute of Astrophysics using four Thomson CCDs in a buttable configuration. The camera system consists of a mosaic CCD dewar developed ...
  • Photometric Performance of the CCD Detector at the Kavalur 102-CM Reflector 
    Sagar, R; Pati, A. K (Astronomical Society of Indian, 1989-03)
    A CCD detector system built around the Thomson TH 7882 chip has recently been acquired for use at the 102 cm telescope at the Vainu Bappu Observatory (VBO). The chip has a coating for enhanced ultraviolet sensitivity, ...
  • Possible Microlensing Event in the direction of M31 
    Joshi, Y. C; Pandey, A. K; Narasimha, D; Sagar, R (Astronomical Society of India, 2003)
    The Cousin R and I band photometric observations of ~ 13 x 13 field in the direction of M31 galaxy have been carried out during 1999-2001 to search for microlensing events using pixel technique. Here we report a microlensing-like ...
  • A possible scenario for the formation of the composite Large Magellanic Cloud star cluster NGC 2214 
    Bhatt, H. C; Sagar, R (Astronomical Society of India, 1992)
    The total masses and relaxation times for the two stellar populations (old and young) in the star cluster NGC 2214 are estimated. The total masses are found to be comparable. While the older population may be dynamically ...

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