005279   Hiremath K M (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Steady part of rotation and toroidal component of magnetic field in the solar convective envelope. Bull Astr Soc India 2001, 29(3), 169-91.

Solves the toroidal component of the magnetic field. Except near base of the convection zone, both the solutions yield similar field structure for the steady component of the toroidal magnetic field. This consists of a two-zone like field structure of intensity <126> 1 G near the surface and a four-zone like field structure of intensity <126> 10⁴G near base of the convection zone. However, near base of the convective envelope, compared to the field structure obtained from the first solution, the resulting field structure from the second solution is closer to the sites of sunspot formation.

7 illus, 2 tables, 88 ref

005278   Hasan P;Kilambi G C;Baliyan K S (Astronomy Dep, Osmania University, Hyderabad) : Near IR study of the young cluster NGC 2453. Bull Astr Soc India 2001, 29(3), 329-33.

In an attempt to understand early phase of stellar evolution and star formation, study of extremely young star clusters in the near infrared wavebands were taken up. These clusters are deeply embedded inside the molecular gas and dust but radiate substantially in the infrared. One such cluster NGC 2453 was observed from Mt Abu Infrared Observatory (MIRO) operated by the Physical Research Laboratory, using the NICMOS-3 infrared array mounted on the 1.2 m Cassegrain focus telescope. The observations were made in the J, H and K' wavebands in February 2000. The data reduction and the photometry has been performed using IRAF and preliminary results have been presented.

1 illus, 1 table, 8 ref

005277   Gupta S K;Sagar R;Joshi S;Ashoka B N;Babu V C;Seetha S;Girish V (NO, State Observatory, Manora Peak, Naini Tal-263 129) : UPSO three channel fast photometer. Bull Astr Soc India 2001, 29(3), 479-86.

The design and performance of a modular portable three channel fast photometer is described. It can be disassembled as single individual channels such that the system can also be used as a single channel photometer. The instrument is put into operation since November 1999 on the 1-m UPSO telescope at Nainital. Since then, it is used extensively for the survey of roAp stars in the northern sky at UPSO. The discoveries made using this new photometer are also mentioned.

3 illus, 4 ref

005276   Gupta R (NO, IUCAA, Post Bag 4, Ganeshkhind, Pune-411 007) : Small/automated telescopes and backend instrumentation for teaching purpose. Bull Astr Soc India 2001, 29(3), 471-4.

In the past decade, with the inception of UICAA and other similar efforts from Universities and Institutes, several MSc teaching courses at Universities now offer Astronomy & Astrophysics as a specal paper along with a set of laboratory experiments using telescopes and various back-end instruments. Highlights the small and/or automated photoelectric telescopes (APTs) that could be made or procured for the purpose of teaching at University level and the experiments that could be carried out with this kind of set up. At IUCCA's instrumentation laboratory, over the past few years, APTs have been fabricated along with the required light weight back-end instrumentations and these are discussed.

2 ref

005275   Goswami A;Rao N K;Lambert D L (NO, Indian Institute of Astrophysics, Bangalore-560 034) : High resolution spectroscopic study of XX ophiuchi. Bull Astr Soc India 2001, 29(3), 295-9.

The star XX Oph has been known to exhibit peculiar spectral variabilities since the work of Merrill in 1924. A high resolution spectroscopic study of the XX Oph spectra taken in July 1996 and later in June 1997 also exhibit distinctly different line profiles in several spectral regions, the most pronounced variations being in the sodium D and H_α profiles. Estimates the displacement velocities of the strong emission line profiles and their absorption components whenever possible and makes an attempt to examine possible physical scenarios that can account for its peculiar variability.

2 illus, 15 ref

005274   Girish V;Joshi S;Seetha S;Ashoka B N;Martinez P;Chaubey U S;Gupta S K;Kurtz D W;Sagar R (NO, ISRO Satellite Centre (ISAC), Airport Road, Bangalore-560 017) : HD 12098 a new far-norther roAp star. Bull Astr Soc India 2001, 29(3), 305-7.

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 Naini Tal-Cape survey" to search for and study new roAp stars in the northern hemisphere was initiated in 1998 in collaboration between ISAC & UPSO from India and SAAO & UCT from South Africa. HD12098 is the first roAp star discovered in the survey and also the first far northern hemisphere roAp star. During the initial observations the star showed modulation in the pulsation amplitude indicating the multi-periodicity of pulsaitons. The multi-periodicity may be either due to the excitation of different modes or due to the rotation of the star. In order to resolve these frequencies HD12098 was observed extensively in October 2000. The preliminary results of these observations are presented.

2 illus, 5 ref

005273   Giridhar S;Arellano Ferro A;Mathias P (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Li-rich post-AGB star HD 172481. Bull Astr Soc India 2001, 29(3), 289-93.

Abundance analysis of the post-AGB candidate star #D172481 confirms its status. It belongs to an important, but relatively rare class of post-AGB stars showing Li I features in their spectra. The strength of OI triplet at 7774 A confirms its high luminosity (log, L/L_o) <126> 4). It is moderately metal-poor with [Fe/H] of -0.6 but shows significant enrichment of s-process elements indicating that the star has gone through the third dredge-up. Finds C/O of <126> 0.4 for this star. Hot Bottom Burning scenario can explain the production of Li as well as the destruction of carbon via CN cycle that could prevent C/O ratio from exceeding one.

1 illus, 1 table, 11 ref

005272   Ghosh S K;Mookerjea B;Rengarajan T N;Tandon S N;Verma R P (NO, Tata Institute of Fundamental Research, Bombay-400 005) : Far infrared mapping of three galactic star forming regions. Bull Astr Soc India 2001, 29(3), 335-6.

Three Galactic star forming regions in the northern sky, viz., associated with W3(OH), S209 and S187 have been simultaneously mapped in two trans-IRAS far infrared (FIR) bands centered <126> 140 and 200 μm using the TIFR 100 cm baloon borne FIR telescope. These maps show extended FIR emission with structures. The spatial distribution of cold dust (T <60> 30 K) for two of these sources (W3(OH) & S209), has been generated from these maps. The HIRES processed IRAS maps of these regions at 12, 25, 60 & 100 μm have also been used for comparison. Point-like sources have been extracted from the longest waveband TIFR maps and searched for associations in the other five bands. Their positions, flux densities etc have been determined.

1 illus, 4 ref

005271   Ganesh S;Joshi U C;Baliyan K S;Shah C R;Jain J K;Rajpurohit G S;Sanchawala K;Shah A B (NO, Physical Research Laboratory, Navarangpura, Ahmedabad-380 009) : PRLNIC3 observations of star forming cloud L1340. Bull Astr Soc India 2001, 29(3), 339-42.

Due mainly to high extinction in optical, the structure of our galaxy, Milky Way, is not very well understood. The Galactic disk and bulge contain a host of heavily reddened open clusters which are deeply embedded within dark molecular clouds of dust and gas. The extremely young stellar objects in these clouds can provide important informations for the study of stellar evolution and star formation. Reports near infrared photometric study of one such cloud, Lynds 1340 in the survey mode. The cloud contains several nebulous regions and is shown to harbour a young cluster RN07. The near IR study provides detailed information on the embedded sources.

1 illus, 3 ref

005270   Faruque S B (Physics Dep, Shah Jalal University of Science & Technology, Sylhet 3114, Bangladesh) : Axial oscillation of a planetoid in restricted three body problem: the circular Sitnikov problem. Bull Astr Soc India 2002, 30(4), 895-909.

Two equally massive primaries are assumed to be moving in circular orbits in Cartesian x-y plane. A planetoid is assumed to be on the z-axis. This is a particular case of the restricted three body problem with mass ratio μ=1/2, known as the curcular Sitnikov problem. Motion of the planetoid is calculated using Lindstedt-Ppincare' perturbation and Green's function method. It is found that the planetoid oscillated nonlinearly along the z-axis. Presents analytic solutions up to 2nd order of approximation and compare the solutions with earlier results of other authors. A solution of the exact problem is also discussed.

2 illus, 14 ref

005269   Durgapal A K (NO, U.P. State Observatory, Manora Peak, Naini Tal-263 129) : Photometric studies of intermediate and old age galactic star clusters. Bull Astr Soc India 2001, 29(3), 389-96.

Presents a detailed analysis of five intermediate / old age open star clusters, based on the CCD UBVRI data. Uses a new colour index parameter (CIP), which is the difference in colour index between the blue turn off point (BTO) of the main sequence and the colour at the base of the red giant branch (BRGB), to estimate morphological age of the cluster. This parameter is useful for the clusters which have no noticeable red giant clump. Finds that morphological features of the colour magnitude diagram (CMD) are better understood in terms of convective core overshooting. Age of the cluster sunder study ranges between 0.6-5 Gyr. Studied the mass function and structure of all the clulters. Mass function slopes for three clusters are in agreement with the Salpeter (1955) value. Spatial variation of mass function along the clusters is also studied. Mass segregation is observed in three clusters. Since all these clusters are dynamically relaxed, the observed mass segregation is therefore most likely due to the dynamical evolution processes.

3 illus, 2 tables, 22 ref

005268   Dewangan G C;Singh K P;Jones L R;McHardy I M; Newsam A M;Mason K O (NO, Tata Institute of Fundamental Research, Mumbai-400 005) : Discovery of a new NLQSO: RX J1334.2+3759. Bull Astr Soc India 2001, 29(3), 417-20.

A new narrow-line QSO, RX J1334.2+3759, has been identified at a redshift of 0.3858. The QSO has intrinsic soft X-ray luminosity <126> 2.8 x 10⁴⁴ erg s^-1. Soft X-ray emission from the QSO is highly variable. Rapid variability (change in intensity by a factor of <126> 4 within <126> 400 s) has also been found. The soft X-ray spectra of the QSO is well described by a power-law of photon index, Γx <126> 3.8. The optical spectrum of RX J1334.2+3759 is typical of narrow-line Seyfert 1 galaxies. The NLR of RX J1334.2+3759 appears to be significantly different from those of normal Seyfert 1 galaxies.

1 illus, 13 ref

005267   Dewangan G C;Singh K P (NO, Tata Institute of Fundamental Research, Mumbai-400 005) : Soft x-ray properties of a complete sample of QSOs. Bull Astr Soc India 2001, 29(3), 413-5.

In order to study systematically the soft X-ray emission of AGNs, have been ROSAT PSPC spectra of 22 QSOs. The QSOs form a complete sample with soft X-ray flux ≥ 1.4 x 10^-14 erg cm^-2 s^-1 in the energy band of 0.1-2.0 keV in a circular region of radius 15 arcmin in the sky. The highest redshift QSO in the sample has z = 3.4. The average photon index (Γ) of te QSOs is 2.39 with a dispersion of 0.57. There are only 3 QSOs with Γx ≥ 3.0. The average slope of the soft-X-ray spectra of the QSOs flattens at higher redshifts. Only three out of 22 QSOs show the presence of a significant excess absorption over the Galactic value.

11 ref

005266   Dewangan G C (Astronomy & Astrophysics Dep, Tata Institute of Fundamental Research, Mumbai-400 005) : Narrow-line Seyfert 1 galaxies. Bull Astr Soc India 2001, 29(3), 463-6.

Narrow-line Seyfert 1 (NLS1) galaxies form a distinct subclass of Seyfert 1 galaxies. Optical spectroscopic and X-ray spectral and timing results on NLS 1 and the plausible underlying physical parameters thought to be responsible for the observed properties are discussed.

26 ref

005265   Das M;Chakraborty D K (School of Studies in Physics, Pt. Ravishankar Shukla University, Raipur-492 010) : Family of triaxial mass models : analytical study of its projected properties. Bull Astr Soc India 2001, 29(3), 439-42.

Triaxial modified Hubble mass models are studied. The models are more general than those studied by earlier workers. The potential and the projected surface density of the mass models can be calculated analytically. The shapes of the isophotes and the profiles of ellipticity and position angles are studied. The inclusion of large number of terms in density function, allows one to produce a large variety of these profiles, which can be compared with observations.

1 illus, 5 ref

005264   Cowsik R;Prabhu T P;Anupama G C;Bhatt B C; Sahu D K;Ambika S;Padmakar;Bhargavi S G (NO, Indian Institute of Astrophysics, II Block, Koramangala, Bangalore-560 034) : Optical photometry of the GRB 010222 afterglow. Bull Astr Soc India 2001, 29(3), 157-68.

The optical afterglow of GRB 010222 was observed using the recently installed 2-m telescope at the Indian Astronomical Observatory, Hanle, and the telescopes at the Vainu Bappu Observatory, Kavalur, beginning <126> 0.6 day after the detection of the event. The results based on these photometric observations combined with others reported in the literature are presented. The R band light curve shows an initial decline of intensities proportional to t^0.542 which steepens, after 10.3 hours, to t^1.263. Following the model of collimated outflow, the early break in the light curve implies a very narrow beam angle (<126> 2° - 3°). The two decay rates are consistent with the standard jet model in a uniform density ambient medium, but require a hard spectrum of electron powder density with p <126> 1.5. The R band light between 14 and 17 hours since outburst departs from the power law fit by 0.1 mag and shows some evidence for fluctuations over time scales of an hour in the observer's frame. Such deviations are expected due to density inhomogeneities if the ambient medium is similar to the local interstellar medium. GRB 010222 is thus an example of a highly collimated outflow with a hard spectrum of electron energy distribution in normal interstellar environment.

2 illus, 3 tables, 42 ref

005263   Chatterjee S;Brijesh Kumar;Ram Sagar (NO, Indian Institute of Astrophysics, Bangalore-560 034) : On mass and velocity distributions in members of star clusters: an analytical approach. Bull Astr Soc India 2002, 30(4), 951-71.

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 in the clusters. A simple expression is suggested for the dynamical friction which adequately describes it in both high and low velocity ranges and the effect of mass distribution in the cluster on the dynamics of a test mass can be described by an anharmonic potential. With the help of energy considerations, describes the dispersions in position and in velocity for stars of different masses showing how the slowing down and mass segregaiton of stars evolve in the cluster. Results are presented with the parameters for the star clusters of Galaxy.

6 illus, 28 ref

005262   Bhatnagar S (NO, National Centre for Radio Astrophysics (TIFR), Post Bag No. 3, Ganeshkhind, Pune-411 007) : Supernova remnants: GMRT based results. Bull Astr Soc India 2001, 29(3), 277-81.

3 illus, 12 ref

005261   Bhat C K;Kaul R K;Sapru M L;Bhat C L (Nuclear Research Lab, Bhabha Atomic Research Centre, Mumbai-400 085) : Cosmic-ray mass composition investigations through atmospheric Cerenkov technique - a simulation study. Bull Astr Soc India 2001, 29(3), 491-5.

The 4-element TACTIC Cerenkov telescope array at Mt. Abu comprises a central Imaging Element equipped with a 349- pixel Cerenkov imaging camera and three Vertex Elements, each of which is equipped with a special duplex detector array for recording spectral, temporal and polarization characteristics of the atmospheric Cerenkov pulses initiated by primary gamma-rays and cosmic-ray hadrons. It is proposed to use the array for cosmic-ray mass-composition studies above 10 TeV energy during partially moonlit conditions. In order to assess the capability of the TACTIC array for these studies, detailed Monte Carlo simulations, using the CORSIKA code, are being carried out for four primary species (gamma-rays, protons, Neon and Iron), in the energy range <126> 10 - 400 TeV, to estimate the spectral parameters like UV (λ <126> 250 - 310 nm) to Visible (F128><108> <126> 310 - 600 nm) intensity ratio, energy dependence of U/V ratio for each species and the lateral distribution of Cerenkov light for primaries of different energies.

2 illus, 6 ref

005260   Barman S K;Kariyappa R (NO, IGNOU and Centre for Space Physics, Malda, Puratuli, J.P. Lane, WB-732 101) : Change of level population density with time in the solar quiet chromospheric atmosphere. Bull Astr Soc India 2001, 29(3), 245-7.

Employing a law of weak acoustic wave, the ratio of population density N₂/N₁ with time for the Ca II H and K lines appropriate for the solar quiet chromosphere have been calculated. This has been done by solving the equations of radiative transfer and statistical equilibrium for two level plus continuum atom simultaneously. From the calculation it has been shown that even a small deposit of weak acoustic wave energy can enhance the emission peak of resonance lines.

1 illus, 6 ref

005259   Baliyan K S;Ganesh S;Joshi U C;Shah C R; Vadher N M;Deshpande M R (NO, Physical Research Laboratory, Ahmedabad-380 009) : Study of variability in BL Lac objects. Bull Astr Soc India 2001, 29(3), 421-4.

Monitors some of the BL Lac objects, such as OJ287, Mrk 421, Mrk 501 etc from Mt Abu Infrared Observatory, using optical photopolarimeter, CCD and NICMOS-3 IR array mounted at the Cassegrain focus of the 1.2 m telescope. The data obtained indicate existence of variability at various time scales. Some of the results on OJ 287 Mrk 421 are presented.

2 illus, 2 ref

005258   Baliyan K S (NO, Physical Research Laboratory, Ahmedabad-380 009) : Multiwavelength study of the variability in blazars. Bull Astr Soc India 2001, 29(3), 397-405.

Blazars are the radio-loud AGNs with polarized, highly luminous and rapidly variable non-thermal continuum emission ranging from radio to γ rays, from a relativistic jet. These features are interpreted in terms of the synchrotron radiation produced in the jet and beamed in the direction close to the line of sight. Thus, the study of blazars provides an opportunity to understand the mechanism of energy extraction from the central black hole where jets are formed. A multi-wavelength study of variability is the only way to obtain information on the geometry of the jets and to constrain the parameters characterizing the spectral energy distribution (SED). Radio through γ-ray SED of blazars exhibits two broad humps-first at UV/optical and second one extending from X-ray to γ-rays whose origin is less understood. Variability in blazars has been studied in a number of objects using satellite borne detectors in X, UV and γ-ray bands, sometimes co-ordinated with ground based observations in optical, IR and radio. The variability time scales obtained vary from minutes to years. Such studies will be reviewed and the emerging scenario will be discussed.

3 illus, 36 ref

005257   Ashok N M;Banerjee D P K (Astronomy & Astrophysics Div, Physical Research Laboratory, Ahmedabad-380 009) : Limited seeing measurements at Mount Abu infrared observatory. Bull Astr Soc India 2002, 30(4), 851-8.

Measurements of atmospheric seeing for the Mount Abu Infrared Observatory, Gurusikhar are presented. Observations made with a differential image motion monitor, between 6 December 1999 to 28 April 2000, give an error-corrected, median value of 0.91 arc second for the seeing during this period. Due to certain constraints, seeing measurements were possible only during a substantial fraction of, but not the complete observing season. The results therefore, may be considered to give, a qualitative idea of the seeing conditions at Mt. Abu.

3 illus, 6 ref

005256   Anupama G C;Sahu D K;Mayya Y D (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Optical spectroscopy of nova V1494 Aquilae 1999. Bull Astr Soc India 2001, 29(3), 375-7.

2 illus, 4 ref

005255   Ananthasubramanian P G;Yamamoto S;Prabhu T P (NO, Raman Research Institute, Bangalore-560 080) : 220 GHz tipping radiometer for monitoring atmospheric opacity at Hanle. Bull Astr Soc India 2001, 29(3), 487-90.

Describes the working principle, data acquisition method and data reduction scheme of a 220 GHz tipping a radiometer. Also presents the preliminary 220 GHz zenith optical depth results at Mt. Saraswati, Digpa Ratsa Ri, Hanle.

3 illus

005254   Agrawal V K;Seekumar P;Seetha S;Agrawal P C (NO, ISRO Satellite Centre, Airport Road, Bangalore-560 017) : Study of type I X-ray bursts from 4U 1705-44 using IXAE and PCA data. Bull Astr Soc India 2001, 29(3), 361-3.

2 illus, 1 table, 6 ref

005253   Abraham L;Agrawal V;Sreekumar P;Seetha S (NO, ISRO Satellite Centre, Airport Road, Bangalore-560 017) : Timing and spectral studies of the 1999 outburst of 4U 1630-47. Bull Astr Soc India 2001, 29(3), 365-7.

3 illus, 1 table, 9 ref

004183   Thieberger R;Spiegel E A (Astronomy Dep, Columbia University, New York, 10021, USA) : Luminosity effects in projected fractals. Bull Astr Soc India 2002, 63(2), 461-71.

Portant Bridge/Jetty at Mumbai severely affected by environmental effects had to be rehabilitied by dismanting the complete original superstructure and reconstructing a new supwestructure on existing piers without disruption to vehicular traffic over it. Discusses details of planning and executon of this project.

3 tables, 44 ref

004182   Prithivikumaran N;Rajamanickam N (Physics Research Centre, V.H.N.S.N. College, Virudhunagar-626 001) : Tranisition probablity parameters for the D-X and D'-X band systems of GeF molecule. Asian J Spectrosc 2002, 6(2), 85-9.

The Franck-Condon (FC) factors (transition probabilities) and r-centeroids have been evaluated by the reliable numerical integration procedure for the D-X and D'-X band systems of GeF molecule, using a suitable potential.

5 tables, 14 ref

004181   Balachandra Kumar K;Rajamanickam N;Bagare S P (Physics Research Centre, V.H.N.S.N. College, Virudhunagar-626 001) : Franck-Condon factors and r-centroids for the band systems F, G and H-X of astrophysical molecule AlF. Asian J Spectrosc 2002, 6(2), 81-4.

Franck-Condon factors and r-centroids, which are very closely related to transition probabilities, have been evaluated by the more reliable numerical integration procedure for the bands of F^<207>Π, G ^<207>Σ⁺ - X ^<207>Σ⁺ systems of AlF molecule. The species has been observed in circumstellar envelope around AGB stars and is likely to be present in umbral atmosphere. The molecular parameters evaluated are necessary for studying the physical and dynamical properties of these sources.

3 tables, 15 ref

003245   Tripathy S C;Jain K;Bhatnagar A (Udaipur Solar Observatory, Physical Research laboratory, PO Box No 198, Udaipur-313 001) : Temporal variations of solar p-mode frequencies on time scales of 27 days. Bull Astr Soc India 2002, 30(3), 577-8.

Studied variations in the frequencies of intermediate degree solar oscillation modes on a time cadence of 18 and 27 days. Reports that the pmodes adjust to changes in the activity measures on time scales as short as 18 days.

1 illus, 2 ref

003244   Tickoo A K et al (NO, Bhabha Atomic Research Centre, Nuclear Research Laboratory, Mumbai-400 085) : Recent observations of 1ES2344+514 and PSR 0355+54 with TACTIC imaging element. Bull Astr Soc India 2002, 30(3), 775-6.

The TACTIC Imaging Element has observed the active galaxy 1ES 2344+514 and the pulsar PSR 0355+54 during Oct-Nov, 2001. Analysis of the recorded events, collected for a period of 70 hours on both these sources reveals absence of any steady emission from these sources.

2 illus, 6 ref

003243   Thieberger R;Spiegel E A (Astronomy Dep, Columbia University, New York, 10021, USA) : Luminosity effects in projected fractals. Bull Astr Soc India 2002, 30(2), 461-71.

The use of two-dimensional catalogues in unraveling the large scale distribution of extra-galactic objects can reveal more information than has been supposed if the objects have approximate scaling properties such as observations suggest. Discusses examples of projected fractals for the case where the objects studied have a Schechter luminosity function. Ananyzes the effects of projection on the characteristics of such a fractal distribution. Results indicate that two-dimensional catalogues of sources could be of value in detecting the effects of luminosity functions as well as of large-scale structure.

3 tables, 44 ref

003242   Swarup G;Sarkar A (NO, National Centre for Radio Astrophysics, TIFR, Pune-411 007) : Observations of associated H I absorption in radio galaxics and quasars using GMRT. Bull Astr Soc India 2002, 30(3), 743-6.

Describes observations and preliminary results of absorption by cold hydrogen gas (H I) associated with six radio galaxies and quasars (Table I) which may provide valuable information about their host galaxies and their surroundings. Observations were made using GMRT.

2 illus, 1 table, 5 ref

003241   Suresh Chandra (NO, School of Physical Sciences, S R T M University, Nanded-431 606) : Search for molecules in cool cosmic objects. Bull Astr Soc India 2002, 30(3), 741-2.

1 illus, 2 ref

003240   Subramanian K R;Ebenezer E (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Quasi - periodic pulsations at decameter wavelengths in the November 24, 2000 solar flare. Bull Astr Soc India 2002, 30(3), 595-7.

Spectral observations of the Sun in the frequency range of 54 to 78 MHz in the November 24, 2000 solar flare showed quasi - periodic pulsations with periods in the range of 11 - 19 seconds. YOHKOH images of this flare in the active region AR 9236 showed loop structures. Assuming an impulsively generated propagating MHD wave for the pulsations, the coronal magnetic field at 1.6 R© height is derived as <126> 8 Gauss.

1 illus, 6 ref

003239   Subramanian K (NO, Inter University Centre for Astronomy and Astrophysics, Post bag 4, pune University Campus, Ganeshkind, Pune-411 007) : Magnetic helicity in galactic dynamos. Bull Astr Soc India 2002, 30(3), 715-21.

Magnetic fields correlated on kiloparsec scales are seen in spiral galaxies. Their origin could be due to amplification of a small seed field by a turbulent galactic dynamo. Reviews the current status of the galactic dynamo, especially the constraints imposed by magnetic helicity conservation. Estimates the minimal strength of the large-scale magnetic field which could arise in spite of the helicity constraint.

33 ref

003238   Stalin C S;Gopal Krishna;Ram Sagar;Wiita P J (NO, State Observatory, Manora Peak, Nanital-263 129) : A comparative study of the intra-night optical variability of powerful AGNs. Bull Astr Soc India 2002, 30(3), 765-6.

In order to address a currently much debated issue, are carrying out a systematic search for intra-night optical micro-variability in major classes of poweful (M_v ≥ -23.0 mag) active galactic nuclei (AGBs). Sample includes 7 sets of Agns, covering narrow redshift bins across the range 0.18 ≤ z ≤ 2.2. Each set consists of a radio-quiet quasar, a radio lobe-dominatedquasar, a BL Lac object and/or a radio core-dominated quasar (blazar), all having m_v <126> 16 mag. The observations were made primarily using the 104-cm telescope of State Observatory, Nainital. The monitoring completed so far (<126> 90 nights) clearly indicates that, compared to the other AGN types, BL Lacs are distinctly more prone to exhibit intra-night optical variations.

1 illus, 2 ref

003237   Srivastava N (Udaipur Solar Observatory, Physical Research Laboratory, Udaipur-313 001) : Can geoeffectiveness of CMEs be predicted. Bull Astr Soc India 2002, 30(3), 557-62.

Coronal mass ejections or CMEs are well known as the drivers of enhanced interplanetary and geomagnetic activity. Large expulsions of material from the Sun, which travel into the interplanetary (IP) medium and, if directed towards the earth, can reach the earth in 3-5 days. It is therefore, necessary to track a CME from the solar surface through the IP medium till it reaches the earth. Recent observations from different instruments aboard SOHO, which simultaneously image the solar atmosphere in different layers up to a distance of 32 R©, have enabled to study the initiation and the propagation of CMEs outward in the helosphere. These observations reveal that the halo CMEs are the potential sources of geomagnetic activity at the earth. However, not all halo CMEs give rise to the geoeffective IP shocks, which adds to the problem of space weather forecasting. Here I propose to examine the characteristics of the geoeffective CMEs observed by LASCO/SOHO and discuss their role in the prediction of intense geomagnetic storms.

6 illus, 21 ref

003236   Srinivasan G (NO, Raman Research Institute, Bangalore-560 080) : The maximum mass of neutron stars. Bull Astr Soc India 2002, 30(3), 523-47.

^iia11 illus, 30 ref

003235   Srinivasa Rao M (NO, Indian Institute of Astrophysics, Koramangala, bangalore-560 034) : Atomspheres of components of the close binary stars. Bull Astr Soc India 2002, 30(3), 707-14.

For theoretical modeling of binary systems, one has to consider realistic models which takes into account the radiative transfer, hydrodynamics, and the effect of irradiation from the secondary component on the atmosphere of primary component. Since the problem is complex, studied in the thesis idealized models which will help us in understanding the important physical processes in close binaries. As a first step to understand the reflection effect developed a method of obtaining radiation field from the spherical surface irradiated by an external point source extended source of radiation in close binary systems. The method has been extended in the case of atmospheres distorted due to self rotation of the component and tidal effects due to the presence of its companion. In all the cases used two-levelatom approximation with complete redistribution in calculating the spectral lines formed in the atmosphere of the primary sar. The effects of irradiation from the secondary component on the atmosphere of the primary is calculated depending upon the geometrical shape of the illuminated surface, proximity of the secondary component to the primary and ratio of the luminosities of the primary and the secondary. Calculated the line profiles with various parameters like density and velocity variations.

2 illus, 9 ref

003234   Sridharan R (NO, Udaipur Solar Observatory, Udaipur-313 001) : Techniques for achieving higher spatial resolution. Bull Astr Soc India 2002, 30(3), 837-45.

The application of speckle and interferometric techniques for imaging small scale solar features is studied in detail. A computer program(speckle code) was developed to analyze the speckle data. The capability of the code to obtain a `good' reconstruction from a few selected best frames has been demonstrated. It is found that the interferometric imaging technique can probably be used for imaging bright isolated point-like objects that ride on a bright or locally depressed background.

5 illus, 15 ref

003233   Srianand R;Gupta R;Kembhavi A;Ramaprakash A N;Tandon S N (NO, IUCAA, Post Bag 4, Ganeshkhind, Pune-411 007) : Science with IUCAA telescope. Bull Astr Soc India 2002, 30(3), 797-8.

Presents a brief overview of the proposed astronomical observations using the first light instrument IFOSC for the IUCAA 2 m telescope.

003232   Singh K P (Astronomy and Astrophysics Dep, Tata institute of Fundamental Research, Mumbai-400 005) : Science from astrosat. Bull Astr Soc India 2002, 30(3), 803-10.

ASTROSAT is an X-ray and UV observatory that is planned to be launched in 2006 A.D. it will cover the entire X-ray spectral band from .3 to 150 keV in one mission, with simultaneous UV oservations in the 1350 - 3000 <199>. A Scanning Survey Monitor will look for transient X-ray sources in the Sky. ASTROSAT will thus be a unique mission in the time frame of 2006 - 2010 A.D.

3 illus, 1 table, 13 ref

003231   Singh K P (Astronomy and Astrophysics Dep, Tata Institute of Fundamental Research, Mumbai-400 005) : Soft X-ray imaging telescope on ASTROSAT. Bull Astr Soc India 2002, 30(3), 799-801.

A Soft X-ray focusing Telescope (SXT) with an X-ray sensitive CCD camera at the focal plane is being developed for the ASTROSAT. Made from conical foil mirrors with a CCD detector in the focal plane, SXT will have a reflecting area of <126>200 cm² below 1.5 keV, angular resolution of <126>3'-4'(WHM) at 1.5 keV, energy bandwidth of 0.3 - 8 keV and energy resolution of about 150 eV. A brief description of the SXT design and development and science expected from it after its launch is given.

9 ref

003230   Singh G N;Shrivastava P K (Physics Dep, Sudarshan Degree College, Rewa-486 115) : Effect of solar wind streams on interplanetary features and on geomagnetic field.. Bull Astr Soc India 2002, 30(3), 599-600.

High speed solar wind stream are separated into two categories Corotating Flare-generated streams. Results based on this analysis indicate the occurrence of large geomagnetic and interplanetary disturbances during flare-generated streams in comparison to period of corotating streams.

2 illus, 4 ref

003229   Shylaja B S;Ashok N M (Bangalore Association for Science Education, Jawaharlal Nehru Planetarium, Sri T Chowdaiah Road, High Grounds, Bangalore-560 001) : IR observations of Am stars. Bull Astr Soc India 2002, 30(2), 491-500.

The IR observations of chemically peculiar stars are carried out and compared with the previous data in IR and far IR from IRAS. The flux redistribution appears to be a common phenomenon in all the stars of this class. The observed energy distribution and a model fit based on effective temperature estimates show slight excess in the IR.

4 illus, 2 tables, 30 ref

003228   Seetha S;Ashoka B N;Joshi S;Girish V;Sagar R; Chaubey U S;Gupta S K (NO, ISRO Satelite Centre, Airport Road, Bangalore-560 017) : New pulsating variables discovered from the Naini Tal-Cape survey. Bull Astr Soc India 2002, 30(3), 623-9.

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. These stars are termed as rapidly oscillating Ap stars (roAp) stars. The oscillations are attributed to low order, high overtone p modes. In addition to the Ap stars, this region of the HR diagram also encompasses the non-magnetic `Am' or metallic lined stars. Some of these Am stars exhibit low overtone δ Scuti type pulsations. The scientific motivation for a study of these oscillations is discussed along with the results on the variables discovered from the survey.

2 illus, 13 ref

003227   Seetha S (NO, ISRO Satelite Centre, Airport Road, Bangalore-560 017) : Scanning sky monitor (SSM) on ASTROSAT. Bull Astr Soc India 2002, 30(3), 829-31.

The scanning sky monitor (SSM) on the ASTROSAT is an instrument to be used for dectecting and locating new x-ray transients and to study the long term behaviour of the known bright x-ray sources in the celestial sphere. The SS is very similar in design to the ASM on RXTE. The first phase of the hardware development for this experiment is to design, fabricate and test an engineering model. Describes the principle of operation and the design specifications of the SSM and highlights the current status of the testing the detector.

3 illus

003226   Satya Narayanan A;Ramesh R (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Interfacial hydromagnetic waves with shear and inclined magnetic fields. Bull Astr Soc India 2002, 30(3), 573-6.

The combined effect of non-parallel propagation, steady flow and inclined magnetic field on the propagation characteristics of hydromagnetic surface waves is examined. The fluid is assumed to be perfectly conducting, infinite in extent with an interface which supports body modes as well as surface modes. This model also supports fast, Alfven and slow modes depending on the parametric values of the system. These modes have interesting applications in the solar corona and solar wind.

5 ref