006219   Sagar R;Pandey S B;Mohan V;Bhattacharya D; Castro-Tirado A J (NO, State Observatory, Manora Peak, Naini Tal-263 129) : GRB 000926 and its optical afterglow : another Possible evidenc for non-isotropic emission. Bull Astr Soc India 2001, 29(1), 1-13.

Steepening in the flux decay seems to have started around 1.7 days after the burst. Negligibe Galactic but relatively large intrinis extinction amounting E(B-V)=0.03 and 0.36±0.02 mag respectively are derived in the direction of GRB 000926. The value of the spectral index in the X-ray-optical-near-infraed region is <126> -0.9. The determination of the redshift z=2.0369. indicates a cosmological origin of the burst at a limnosity distance of 16.6 Gpc. The observed fluence in the energy range 20-100 keV indicates, if istropic, the release of ≥ 10⁵³ ergs of energy. Attributing the observed break in the light curve at 1.7 days to the onset of sideways expansion of a jet-like ejecta, we infer an initial jet opening angle of <126> 0.14 radian. This indicates a large anisotropy in the orignal emission and the amount of released energy is reduced by factor of <126> 100 relative to the isotropic value, which can be understood in terms of the currently popular stellar death models.

3 illus, 2 tables, 60 ref

006218   Richtler T;Sagar R (Fisica de Dep, Universidad de concepcion, Casilla 160-C, Concepcion, Chile) : Old galactic star cluster berkeley 32. Bull Astr Soc India 2001, 29(1), 53-70.

Presents new CCD photometry of the distant old open star cluster Berkeley 32 in Johnson V and Cousins I passbands. A total of <126> 3200 stars have been observed in a field of about 13' x 13'. The colour-magnitude diagram (CMD)in V, (V<126>I) has been generated down to V=22 mag. A broad but well defined main sequence is clearly visible. Some blue stragglers, a well developed subgiant branch and a Red Clump are also seen. By fitting isochromes to this CMD as well as to other CMDs available in the star cluster have been determined. The clustar has a distance of <126> 3.3 kpc, its radius is about 2.4 pc; the reddening E(B-V) is 0.08 mag and the age is <126> 6.3 Gyr. By comparison with theoretical isochrones, a metallicity of [e/H] ≈ <126> 0.2 dex has been estimated. Theoretical isochrones have been used to convert the observed cluster luminosity function into a mass function in the mass range <126> 0.6-1.1 M. Finds a much flatter mass function than what has been for young clusters. If the mass function is a power law dN <126> m^αdm, then get α=0.5±0.3. This may be seen as a signature of the highly evolved dynamical state of the cluster.

6 illus, 8 tables, 33 ref

006217   Raja V;Rajamanickam N (Physics Research Centre, V H N S N College, Virudhunagar-626 001) : Frank-condon factors and r-centroids for the B, C, D-X and d-b band systems of astrophysical molecule BF. Bull Astr Soc India 2001, 29(1), 71-5.

The Frank-Condon factors and r-centroids, which are very closely related to transition probabilities, have been evaluated by the reliable numerical integration procedure for the bands of B¹ε⁺ - X¹ε⁺, C¹⁺ - X¹ε⁺ D¹π-X¹ε⁺ and d³ε-b³ε⁺ systems of asytophysical molecule BF, using Morse potential.

4 tables, 12 ref

006216   Manchanda R K (NO, Tata Institute of Fundamental Research, Mumbai) : Observation of second cyclotron line feature in the spectrum of Her X-1. Bull Astr Soc India 2001, 29(1), 25-37.

Hard X-ray spectrum of Her X-1 was measured during a ballon flight experiment lunched on March 30, 1997 using a large area scintillation counter telescope. The instrument code named LASE, operates in the 20-200 keV energy region and the high spectral and temporal sensitivity for the study of X-ray pulsators. The source observations were made on the 7th day of the 35^d on cycle and at the binary orbital phase of 0.5. The measured source flux in the 20-50 keV region was found to be lower by a factor of about 3, the continuum spectrum was found to be extremely hard ? Apart from the primary cyclotron feature at 48 keV, the persent data provides a clear confirmation of the absorption line feature around 96 keV corresponding to the second harmonic. Discuses the implication of hard X-ray spectrum and the line energy in terms of the properties of the emission region.

5 illus, 2 tables, 29 ref

005325   Yellaiah G;Suresh K;Raghavender B (Astronomy Dep, Osmania University, Hyderabad-500 007) : Study of Es occurrences during meteor shower periods at Hyderabad by using FM radio signals. Bull Astr Soc India 2001, 29(3), 251-7.

Sporadic-E occurrences are found to be more during meteor shower periods when compared to non-shower periods. Meteor activity can be estimated by recording the radio signals reflected by meteor trails. The results of the data obtained from recording of the radio signals of a distant FM radio broadcasting station, received after reflection from meteoric ionisation trails, are presented. From these results, it is observed that the radio echoes are found to be more during shower periods and early morning hours, when the meteor activity is expected to be more. Present observations show that the occurrence of Es is found to be more during Geminid meteor shower period compared to other periods. This shows a clear evidence of occurrence of Es due to meteoric ionization.

5 illus, 13 ref

005324   Yadav K K;Bhatt N;Kaul S R;Koul R (Nuclear Research Laboratory, Bhabha Atomic Research Centre, Mumbai-400 085) : Multinode data acquisition and control system for the Vertex Elements of the TACTIC telescope array. Bull Astr Soc India 2001, 29(3), 497-9.

An interrupt based multinode data acquisition and control system has been developed for the three Vertex Elements of the TACTIC telescope array. Describes the salient design features of the hardware and software of the system.

1 illus, 1 ref

005323   Yadav J S (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-400 005) : Multiwavelength studies of galactic black-hole candidates. Bull Astr Soc India 2001, 29(3), 271-6.

One of the Galactic Black-hole Candidates (GRS 1915 + 105 has shown spectacular variability on various time scales in X-ray, Infrared (IR) and Radio wavelengths and has been extensively studied in multiwavelengths during last few years. This X-ray transient source has earned the name "microquasar" as it is known to emit superluminal relativistic radio jets. Since microquasars are much smaller, closer and show faster variability than the extragalactic systems (quasars and other active galactic nuclei (AGNs), they are supposed to be potential "laboratories" for the study of black hol accretion relativistic jet systems. Summarises some of the exciting multiwavelength studies of this source and discus the progress made in understanding the accretion disk - jet connection.

3 illus, 24 ref

005322   Wahab Uddin;Prasad L (NO, State Observatory, Manora Peak, Naini Tal-263 129) : Dynamical properties of flare loops of 27 November 1996. Bull Astr Soc India 2001, 29(3), 241-3.

Observes a post-flare loop system in H_α on the west limb on 27 November 1996 which started earlier than 05:07:20 UT in NOAA active region 7997 (N04, W89). The post-flare loops were associated with long duration x-ray flare of important class B9.0. Studies the evolution of post-flare loop system which display complex, fan like structure with multi bright loop tops in H_α as well as in x-ray/Yohkoh and SOHO observations. This event shows the characteristics of long duration event (LDE). The main aim of this is to study the morphological changes of post-flare loops to understand the prolonged post eruption energy release process in decay phase in H_α, x-ray, radio wave and in microwave regions. The results of investigation has been discussed in the light of existing models.

1 illus, 8 ref

005321   Venkatakrishnan P (NO, Udaipur Solar Observatory, P.B. No. 198, Udaipur-313 004) : Multi-aperture solar telescope. Bull Astr Soc India 2001, 29(3), 467-70.

A proposal for a new ground based solar telescope of very high angular resolution is presented. The science goals that drive the need for this facility are enumerated. The proposed strategy, of combining several smaller aperture telescopes to provide the desired angular resolution, is out-lined.

1 illus, 14 ref

005320   Umapathy C N;Sharma M R;Solanky C;Kulkarni R; Shah A B;Vadher N M;Jain R;Jain A K;Sreekumar P (Technical Physics Div, ISRO Satellite Centre, Airport Road, Bangalore-560 017) : Processing electronics instrumentation for the low energy detector of solar x-ray spectrometer (SOXS) experiment. Bull Astr Soc India 2001, 29(3), 475-8.

005319   Thakur P;Chakraborty D K (School of Studies in Physics, Pt. Ravishankar Shukla University, Raipur-492 010) : Correlated projected properties of triaxial mass models. Bull Astr Soc India 2001, 29(3), 443-5.

Triaxial mass models producing ellipticity variations and isophote twists are investigated. The spherical mass distributions are made triaxial by adding two more terms, each consisting of a radial function multiplied by a low order spherical harmonic. Modified Hubble mass model and γ-models of Dehnen are investigated. It is found that the projected properties are correlated when a model with a given set of intrinsic parameters, is viewed in all possible orientations. Proposes that these correlation patterns carry the signature of intrinsic shape parameters of the triaxial mass model.

1 illus, 7 ref

005318   Subramanian P;Becker P A;Kazanas D (NCRA, TIFR, Pune-411 007) : Relativistic outflows from advection-dominated accretion disks around black holes. Bull Astr Soc India 2001, 29(3), 369-70.

^ssc8 ref

005317   Subramaniam A;Anupama G C (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Study of the local environment of novae in the large magellanic cloud. Bull Astr Soc India 2001, 29(3), 379-80.

8 ref

005316   Srivastava N (NO, Udaipur Observatory, Physical Research Laboratory, PO Box No. 198, Udaipur-313 001) : Solar and interplanetary signatures of intense geomagnetic storms during 1997-2000. Bull Astr Soc India 2001, 29(3), 249-50.

During the ascending phase of the recent solar cycle, the solar and interplanetary signatures of coronal mass ejections (CMEs) observed by Large Angle Spectrometric Coronagraphs (LASCO) aboard SOHO, have been examined. These CMEs were responsible for causing intense geomagnetic storms (Dst ≤ -100 nT) on the earth. The relationship of these CMEs with halos, long-duration events, flares and eruptive prominences have been studied. In addition, investigation of the role of the initial expansion speeds of halos in determining the time of their arrival at the earth has also been made.

1 ref

005315   Srikanth R;Jagdev Singh;Bagare S P (Center for Theoretical Studies, Indian Institute of Science, Bangalore-560 012) : Distribution of the quiet sun photospheric magnetic flux. Bull Astr Soc India 2002, 30(4), 871-9.

Finds that the field is not uniformly distributed, but parcelled into flux concentrations. Both the flux and size of the concentrations are found to be described by broad, asymmetric distribution functions. Their mean absolute flux and size are found to be about 1.4 x 10¹⁸ mx and 6.1 Mm for both polarities in unsmoothed magnetograms at 5 gauss threshold. These values represent a weighted average for both network- and intranetwork magnetic fields, since the present method cannot currently distinguish between the two regions. Both flux and size distributions become more symmetric and less peaked in response to smoothing of images. Extrapolating this trend to sub-resolution scale, a linear decrease in size but a rapid increase in the mean absolute field strength, with asymptotic values of about 400 km and 50 gauss. This exercise shows that the true field strengths of quiet magnetic elemets are higher and their size smaller than usually inferred from observations. This is because observation of mixed polarity regions under finite resolution causes the observed flux to be smeared out and apparently modified. Therefore, this flux cannot be interpreted independently of the geometric structure and flux distribution of the concentrations.

4 illus, 2 tables, 15 ref

005314   Sinha S;Sreekumar P;Kasturirangan K (NO, ISRO Satellite Centre, Bangalore) : Gamma ray burst experiment on the Indian SROSS C-2 satellite. Bull Astr Soc India 2001, 29(3), 505-8.

The SROSS C-2 satellite launched by the ASLV carried aloft a CsI gamma ray burst detector. To date, 51 GRB events have been detected unambiguously with 22 being common with BATSE. The experiment with its 2 ms time resolution provides good light curves in the 20 KeV - 1 MeV range. In addition, simultaneous light curves are also available in 3 broad energy bands. Presents the current status and summary of GRB events from SROSS C-2.

2 illus, 6 ref

005313   Singh N S;Singh K Y;Naik S;Paul B;Agrawal P C;Rao A R;Seetha S;Kasturirangan K (NO, Manipur University, Canchipur, Imphal-795 003) : Observation of x-ray binary Cygnus X-3 Indian x-ray astronomy experiment. Bull Astr Soc India 2001, 29(3), 351-4.

The X-ray binary Cygnus X-3 was observed with the Indian X-ray Astronomy Experiment (IXAE) on Board the Indian Remote Sensing Satellite IRS-P3 during July 3-13, 1999 and October 11-24, 1999 with total useful exposure time of 31244.64 seconds in 1 sec integration mode. The short and long time variability of the X-ray source has been studied. Orbital period to be was found 17254.273 ± 0.890 seconds.

3 illus, 18 ref

005312   Singh M;Sanwal B B;Stalin C S (NO, U.P. State Observatory, Manora Peak, Nani Tal-263 129) : Surface photometry of three Wolf-Rayet galaxies. Bull Astr Soc India 2001, 29(3), 447-8.

CCD photometric observations of the Wolf-Rayet galaxies NFC 1741, IIZ240 and IRAS 01003-2238 were taken with 104 cm telescope of the U.P. State Observatory Naini Tal using1024 x 1024 CCD camera in B V R I and H_α filters. Processing based on the analyses is discussed.

10 ref

005311   Sharma M;Prabhu T P (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Photometric catalogs of four EMSS poor clusters of galaxies. Bull Astr Soc India 2002, 30(4), 911-41.

2.3-meter Vainu Bappu Telescope was used to perform CCD imaging of X-ray-selected poor clusters of galaxies. Sample consisted of four X-ray luminous clusters in the Einstein Observatory Extended Medium Sensitivity Survey (EMSS) and noted by Gioia & Luppino (1994) to be optically less rich than Abell clusters. The sample spaned a redshift range of 0.08≤ z ≤0.22. Catalogs of galaxies detected were assembled in the cluster fields to a magnitude limit mv ≈ 22. Data reduction performed on the CCD images, methods used to construct the extended object catalogs, the photometric calibrations, and some understanding of their completeness and contamination have been described.

4 illus, 10 tables, 36 ref

005310   Seetha S;Chaubey U S;Girish V;Joshi S;Ashoka B N;Gupta S K;Kurtz D W;Martinez P;Sagar R (NO, ISRO Satellite Centre (ISAC), Airport Road, Bangalore-560 017) : Naini Tal - Cape survey for pulsating chemically peculiar stars - a status report. Bull Astr Soc India 2001, 29(3), 309-12.

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 have been observed and 4 variables have been discovered. The variables are HD 13079, HD 13038, HD 12098 and HD 98851. Of these HD 12098 is a likely rapidly oscillating Ap star. Gives a status report on the survey. The methodology of this survey and an evaluation of observing time vis-a-vis the chance of discovering a new variable are discussed.

2 illus, 7 ref

005309   Sathyabama N;Dhar V K;Koul M K;Bhat C L (Nuclear Research Lab, Bhabha Atomic Research Centre, Mumbai-400 085) : Energy resolution of the TACTIC imaging element. Bull Astr Soc India 2001, 29(3), 501-3.

Explores here the possibility of using artificial neural network (ANN) for characterization of atmospheric Cerenkov events (progenitor type and energy) detected by the imaging γ-ray telescope array, TACTIC.

4 illus, 4 ref

005308   Sanwal B B;Brijesh Kumar;Mahendra Singh (NO, State Observatory, Manora Peak, Nainital-263 129) : Spectrophotometry of the comets C/2000 WM1 (LINEAR) and C/2001 C1 (Ikeya-Zhang). Bull Astr Soc India 2002, 30(4), 943-50.

Spectrophotometric observations of the coma of the comets C/2000 WM1 (LINEAR) and C/2002 C1 (Ikeya-Zhang) were taken during Nov, Dec 2001 and Mar, Apr 2002 respectively with 104-cm telescope of the State Observatory, Nainital. CN (F128><108> 3883 Angstrom) and C₂ swan bands have been identified in both the comets. Na I emission was detected in comet Ikeya-Zhang. An estimate of CN and C₂ abundance and their production rates have been derived. Dust production rates have also been determined.

5 illus, 3 tables, 6 ref

005307   Sanwal B B (NO, U.P. State Observatory, Manora Peak, Naini Tal-263 129) : Wolf-Rayet galaxies and their CCD photometry. Bull Astr Soc India 2001, 29(3), 407-11.

Galaxies with Wolf-Rayet star features in their spectra have long been known. They are characterised by a broad emission feature at λ 4686 Angstrom. This is attributed to stellar HeII emission from a large population of WR stars. Broad CIV λ 5808 Angstrom emission has also been detected in about 30 WR galaxies. The WR galaxies are thought to be undergoing present or very recent star formation that produces massive stars evolving the the WR stage. More than 130 WR galaxies are now known and most of them have been studied on the basis of spectroscopic observations. Therefore, a CCD surface photometry programme has been initiated at the U.P. State Observatory, Naini Tal using B V R I and H_α filters. NGC 1741, IIZw40, IRAS01003-2238 have been observed and their morphology is discussed.

6 ref

005306   Santosh Kumar;Yadav M P (P.G. Studies & Research in Physics and Electronics Dep, R.D. University, Jodhpur-482 001) : Geomagnetic storms with H ≥ 400nT during 1979-99. Bull Astr Soc India 2002, 30(4), 859-70.

Magnitude of GMSs is associated with different properties of H_α, X-ray solar flares and APDFs i.e., NOAA region, location (helio-longitude/latitude), duration and area of solar events. It is observed statistically that 77.2%, 62.8% and 68.5% GMSs are associated with H_α, X-ray solar flares and APDFs respectively. It is observed that coronal mass ejection (CMEs) ralated storm sudden commencements (SSCs) are not always associated with high speed solar wind streams (HSSWS). Associated solar activity of CME events near the Sun are eruptive prominences, long duration solar events, impulsive X-ray events, optical flares, type II and IV radio burst leading to SSCs. The travel time between the explosion on the solar disc and maximum geomagnetic activity has been observed in the range 53-114 Hrs.

5 illus, 53 ref

005305   Sahayanathan S;Bhattacharyya S;Kaul C L;Bhat C L (Nuclear Research Lab, Bhabha Atomic Research Centre, Mumbai-400 085) : Adiabatic cooling and nonthermal spectrum of blazars. Bull Astr Soc India 2001, 29(3), 457-8.

Studies the effect of adiabatic cooling on the non-thermal synchrotron spectra of blazars from radio to resulting X-ray region when blazars are in the flaring state.

2 illus, 4 ref

005304   Rukmini J;Vivekananda Rao P;Ausekar B D (NO, Centre of Advanced Study in Astronomy, Hyderabad-500 007) : Photometric study of the short period W UMa system - FZ orionis. Bull Astr Soc India 2001, 29(3), 323-7.

Photoelectric B, V observations of the eclipsing biary system FZ Orionis obtained from the Japal-Rangapur Observatory during the years 1981 to 1992 are presented and studied. No period changes in the system are detected. The light curves are analysed using the Wilson-Devinney method and the system parameters are derived.

1 illus, 1 table, 13 ref

005303   Ram Sagar (State Observatory, , Manora Peak, Naini Tal-263 129) : Emission from GRBs and their afterglows: Indian observations. Bull Astr Soc India 2001, 29(3), 215-29.

Study of Gamma-ray bursts, electromagnetically the most luminous events in the Universe though only for a few seconds, was revolutionized in 1997 when the Italian-Dutch X-ray satellite BeppoSAX started providing the positions of some events with an accuracy of a few arcminutes within a few hours after the burst. Indian contributions in this area are summarized. While mainly ISRO contributed to studies of GRB emission, a number of research organizations contributed to the optical observations of GRB afterglows. So far successful optical observations have been obtained for five afterglows namely GRB 990123, GRB 991208, GRB 991216, GRB 000301C and GRB000926. The light curves, spectral energy distributions and energetics of these are discussed in the light of recent fireball plus blast wave theoretical models of GRBs. Their early-time flux decay constant is <126> 1.1 which become <126> 2.4 at later times. All are having relatively flat spectral index with its value ranges from 0.73 to 0.95. Observations of these afterglows support the model of non-isotropic synchrotron emission from the centre of the GRBs which reduces the budget of isotropic energy emission from ≥ 10⁵³ ergs to <60> 10⁵² ergs, a value which is compatible with the current popular model of the origin of GRBs.

5 illus, 2 tables, 58 ref

005302   Radhika P;Vivekananda Rao P (Centre of Advanced Study in Astronomy, Osmania University, Hyderabad-500 007) : Long-term study of the starspot activity on the eclipsing short-period RS Canum Venaticorum binary UV piscium. Bull Astr Soc India 2001, 29(3), 317-22.

Presents optical photometry of the short-period eclipsing RS CVn system, UV Piscium for the years 1966-1984. For each light curve, models the distortion waves in order to study the behaviour of starspots in this system. After removing the spot effects from the light curves, models the cleaned data to obtain system parameters. Also notes changes in the luminosity of the primary star that are not explained by the spot variation.

1 illus, 30 ref

005301   Piskunov A E (NO, Institute of Astronomy Russian Acad Sci, 48 Pyatnitskaya Str., Moscow-109 017, Russia) : Young open clusters and star formation. Bull Astr Soc India 2001, 29(3), 259-62.

3 illus, 2 ref

005300   Patil M K;Pandey S K;Kembhavi A K;Mahendra Singh (School of Physical Sciences, S.R.T.M. University, Nanded-431 606) : Dust in an extragalactic environment: the case of NGC 2907. Bull Astr Soc India 2001, 29(3), 453-5.

Carries out a detailed CCD surface photometric analysis of the lenticular galaxy NGC 2907, containing multiple dust lanes, with the objective of studying properties of dust in an extragalactic environment. Measurements of extinction in the optical B, V, R, and I bands indicate that the wavelength dependence of dust extinction is similar to that of the Milky Way. However, the R_v value for NGC 2907 turns out to be smaller than the canonical Galactic value of 3.1, suggesting that the dust grains responsible for the optical extinction are smaller than that in the Milky Way.

1 illus, 1 table, 6 ref

005299   Pandey S K;Sahu D K;Kembhavi A K;McCarthy P J (School of Studies in Physics, Pt. Ravishankar Shukla University, Raipur and IUCAA, Pune) : Optical and near-IR imaging of dusty ellipticals. Bull Astr Soc India 2001, 29(3), 449-52.

Presents some of the results of imaging observations of dusty ellipticals in the optical B & R bands as well as in near IR K'-band taken at the Las Campanas Observatory, Chile. Derives radical profiles of surface brightness, position angle, ellipticity as well as profiles of higher order Fourier coefficients by fitting ellipses to isophotes for each band. As the effect of dust obscuration is very much reduced in the near-IR, a comparison of isophotal profiles in the K'band with those of optical bands permits analysis of the effects of dust extinction in the dusty ellipticals. Examines optical & optical-IR color maps, color profiles, color gradients and discuss the results.

2 illus, 2 tables, 7 ref

005298   Pandey S B;Sagar R;Mohan V;Pandey A K; Bhattacharya D;Castro-Tirado A J (NO, State Observatory, Manora Peak, Naini Tal-263 129) : Optical follow-up of GRB afterglows from UPSO, Naini Tal. Bull Astr Soc India 2001, 29(3), 459-61.

Successful optical photometric observaitons 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 light curve parameters of these GRBs are summarised here. The optical light curves of these GRBs exhibit break (i.e., early and late time power law decay with different indices) generally around 2 days after the burst. The observed steepening in the afterglow light curves may be due to non-isotropic emission from the burst ejecta in the course of time. The non-isotropic energy emission from these GRBs is ≤ 10⁵² ergs and can be understood in terms of current popular models for the origin of GRBs.

1 table, 12 ref

005297   Pandey K;Narain U (NO, Udaipur Solar Observatory, Devali, Bari Road, Udaipur) : On solar coronal heating. Bull Astr Soc India 2001, 29(3), 231-8.

Reviews heating of solar corona by magnetic fields/currents with emphasis on micro- and nano-flares. In case of a microflare the energy release is <126> 10²⁶ ergs whereas in a nanoflare <126> 10²³ - 10²⁵ ergs of energy is released. Flares have a distribution law over total radiated energy with exponent α = 1.8. Extending the same power law to micro and nano-flares and assuming that they constitute a dominant heating mechanism for solar corona α must be grater than 2. Many investigation lead to α <60> 2 where as a few yielded α <62> α <62> 2. The verdict remains inconclusive. More observational analyses and numerical simulations are needed to discriminate between the two cases.

1 illus, 31 ref

005296   Namboodiri P M S;Sastry K S;Narasimhan K S V S (NO, Indian Institute of Astrophysics, Bangalore-560 034) : N-body simulations of galaxy collisions. Bull Astr Soc India 2001, 29(3), 435-7.

The tidal effects of close collisions between two spherical galaxies of different mass and mass distributions are studied by numerical simulations. The galaxies are represented by polytropes of indices n = 4 and n = 0 which represent a wide range in mass distribution of high central concentration and uniform mass distribution respectively. The initial relative velocity of the galaxies in a hyperbolic orbit is taken to be 700 kms^-1. It is found that the tidal effects are quite sensitive to the mass ratio and the mass distribution of the galaxies. The results show that in a collision between identical centrally concentrated galaxies, relatively more spin is imparted to the galaxies compared to collision between identical homogeneous galaxies. The dependence of tidal capture and tidal disruption on the choice of the model and mass ratio is also investigated.

1 table, 5 ref

005295   Muthu C (NO, Physical Research Laboratory, Navrangpura, Ahmedabad-380 009) : Spectroscopic investigations of planetary nebulae. Bull Astr Soc India 2001, 29(3), 381-8.

The morphologies of three selected asymmetrical planetary nebulae (PNe), namely NGC 4361, NGC 1514 and NGC 246, were studied using spatio-kinematic observations made with an Imaging Fabry-Perot Spectrometer. From the 3D spatio-kinematic models, plaussible nebular formation scenarios were proposed for NGC 4361 and NGC 1514 based on the interacting binary progenitor model. A few parameters regarding the binary, viz. the progenitor's mass the binary separation, were suggested from the study. The elemental concentration of N and He in the nebulae were used to get some information regarding their progenitors. It is suggested from that the binary progenitor hypothesis gives more consistent explanation of the observed structures of the PNe than the single star hypothesis. The physical condition of a PNe interacting with the ambient interstellar medium has been investigated in NGC 246. Its distorted morphology is attributed to its interaction with the Interstellar Medium (ISM).

3 illus, 1 table, 28 ref

005294   Murthy J (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Multiwavelength observaitons of interstellar dust. Bull Astr Soc India 2001, 29(3), 263-70.

Interstellar dust is important in virtually every aspect of Galactic and extragalactic astronomy - whether one simply wants to correct for its effects or to study galactic dynamics and processes. Interstellar dust is found in every line of sight and is responsible for much of the radiation emited by a galaxy. Multiwavelength studies of interstellar dust are critical to an understanding of the nature and evolution of interstellar dust. The dust absorbs strongly in the near and far ultraviolet where the stellar radiation field is most energetic and re-emits in the infrared. Describs observations of interstellar dust ranging from the limited data sets in the UV and visible, where dust scattering and extinction are observed, to the all-sky survey data of IRAS and COBE. Concludes with the importance of ASTROSAT to studies of interstellar dust.

32 ref

005293   Moojerjea B;Ghosh S K;Kaneda H;Nakagawa T; Ojha D K;Rengarajan T N;Shibai H;Verma R P (NO, Tata Institute of Fundamental Research, Mumbai-400 005) : Mapping of the orion molecular cloud in the [CII] line and continuum at 158 μm. Bull Astr Soc India 2001, 29(3), 337-8.

A fabry Perot Spectrometer (FPS) tuned to the astrophysically interesting (CII) line at 157.7409 μm, developed at ISAS (Japan) has been successfully interfaced to the TIFR 100 cm far-infrared balloon borne telescope. A region (30' x 15') of the Orion molecular cloud was mapped with a spectral resolution of 1700 and angular resolution of <126> 1'. The spatial distribution of (CII) line emission at 157.7409 μm and the neighboring dust continuum are presented.

1 illus, 3 ref

005292   Manoj P;Bhatt H C (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Kinematics of Vega-like stars. Bull Astr Soc India 2001, 29(3), 313-6.

The kinematics of Vega-like stars in the solar neighbourhood. Space velocities was studied computed for 80 Vega-like stars. Space velocities of these stars were analysed in connection with the young stellar associations and star forming regions in the solar neighbourhood. Preliminary analysis suggested that many of the Vega-like stars were kinematically connected with the members of the mentioned associations and star forming regions. This places a strong constraint on the ages of Vega-like stars which are generally believed to be an older population. Details of the analysis and preliminary results have been presented.

3 illus, 15 ref

005291   Manchanda R K (NO, T.I.F.R., Colaba, Bombay-400 005) : Observation of hard X-ray emission from extragalactic sources 3C 273 and NGC 5506 in 20-200 keV band. Bull Astr Soc India 2001, 29(3), 429-33.

Reports spectral measurements of the bright QSO 3C273 and the AGN source NGC 5506 made during a balloon flight experimet using high sensitivity scintillation counter telescope LASE, operating in the 20-200 keV energy band. The observations were made on Nov. 20, 1998 from Hyderabad, S. India. The observed spectrum for 3C 273 and is best fitted with a power law of the form dN/dE - KE^-α and the measure luminosity compares with earlier measurements by SIGMA and OSSE satellites. The observed spectra of NGC 5506 was found to be very hard although the total luminosity was much lower than the earlier observations and is consistent with the time variability of the AGN sources, Spectral data is discussed in terms of non-thermal emission models and X-ray emission geometry.

3 illus, 8 ref

005290   Manchanda R K (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Bombay-400 005) : Pulse profiles of binary x-ray pulsars in 20-200 keV band. Bull Astr Soc India 2001, 29(3), 355-60.

Hard X-ray observations of the binary X-ray pulsars were made using a balloon-borne large area scintillation counter telescope in the 20-200 keV band. Apart from many other galactic and extragalactic X-ray sources, three X-ray pulsars namely Her X-1, GS 1843+00 and 4U 1907+09 were tracked during two flights launched in March 1997 and Nov. 1998. The observations of the transient sources GS 1843+00 correspond to near intensity maximum in its burst phase. Discusses the morphology of the pulse profiles in terms of geometrical constraints and the X-ray emission mechanism.

3 illus, 13 ref

005289   Kundt W (NO, Institut fur Astrophysik der Universitat, Auf Dem Hugel 71, D-53121 Bonn, Germany) : Neutron stars: seen my way. Bull Astr Soc India 2001, 29(3), 283-7.

Unconventional survey is presented of the observable properties of neutron stars and of all astrophysical phenomena possibly related to them, such as their pulsing, clock irregularities, bursting, flickering, and occasional super-Eddington brightness, the generaiton of cosmic rays, of gamma-ray bursts, of jets, and of synchrotron nebulae, their birth, and their occasional transient appearance as `supersoft' X-ray sources. The msec pulsars are argued to be born fast, the black-hole candidates to be neutron stars inside of massive disks, and the gamma-ray bursts to be sparks from dense `blades' accreting spasmodically onto the surfaces of (generally old) neutron stars within ≤ 0.3 Kpc from the Sun. Supernovae - the likely birth events of neutron stars - are thick-walled explosions, not to be described by Sedov-Taylor waves, which illuminate their gaseous environs via collisions of their `splinters'.

1 illus, 13 ref

005288   Kharb P;Shastri P (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Relativistic beaming and central components of radio galaxies. Bull Astr Soc India 2001, 29(3), 425-7.

Presents results of study of the parsec-scale components of radio galaxies as observed at radio and optical wavelengths, in the framework of the Unified Scheme.

1 illus, 7 ref

005287   Kaul R K (NO, Bhabha Atomic Research Centre, Nuclear Research Laboratory, Mumbai-400 085) : TeV gamma-ray flux estimates from EGRET supernova remnant sources. Bull Astr Soc India 2001, 29(3), 371-4.

The EGRET experiment, onboard the Compton Gamma-Ray Observatory (CGRO) satellite, has provided evidence of possible ≥ 100 MeV gamma-ray emission from <126><126> 10¹⁴ eV in these remnants, the TeV gamma-ray fluxes likely to result from these sources through the π⁰ - decay and the inverse Compton processes have been estimated, involving shock - accelerated relativistic protons and electrons.

1 illus, 9 ref

005286   Kapoor R C;Shukre C S (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Are pulsars strange?. Bull Astr Soc India 2001, 29(3), 347-9.

Pulsar radio pulses are made up of the so called core and conal components. A remarkably precise relation for core component widths, found observationally, in effect specifies the size of the polar cap on pulsars. Inclusion of general relativistic effects makes the theoretical size dependent on the pulsar mass. The observed core width relation thus provides constraints on masses and radii of pulsars leading to a very stringent selection from the available equations of state for the pulsar matter, strongly indicating that pulsars are strange stars rather than neutron stars.

3 ref

005285   Joshi S;Girish V;Martinez P;Sagar R;Ashoka B N;Gupta S K;Seetha S;Chaubey U S;Kurtz D W (NO, Uttar Pradesh State Observatory, Manora Peak, Naini Tal-263 129) : Discovery of pulsations in HD 98851. Bull Astr Soc India 2001, 29(3), 301-3.

Using the UPSO 1-m Sampurnanand reflector telescope equipped with a fast photometer, chemically peculiar (CP) star HD 98851 for a total of around 30 hours on 5 different nights between January to April 2000. From the Fourier analysis of the data it was found that HD 98851 pulsated with periods of 75.76 min and 151.52 min and amplitudes ≈ 25 mmag and 12 mmag respectively. The star appeared to be a δ Scuti variable.

1 illus, 1 table, 4 ref

005284   John M V;Sivakumar C;Joseph K B (Department of Physics, St. Thomas College, Kozhencherri-689 641) : Classical stochastic approach to cosmology revisited. Pramana J Phys 2003, 60(1), 1-10.

The classical stochastic model of cosmology recently develoed is reconsidered. In that approach the parameter w defined by the equation of state p=wρ was taken to be fluctuating with mean zero and the theoretical probability distribution function (PDF) was compared for the Hubble parameter with observational data corresponding to a universe with matter and vacuum energy. Evan though qualitiative agreement between the two was obtained, an attempt is made to introduce a more realistic assumption for the mean of w and use it for the calculations. The mean values of both p and w are taken to be nonzero. The theoretical and observational PDFs are compared for different epochs and values of the Hubble parameter. The corresponding values of the diffusion constant D obtained are approximately constant. The scatter in the observed redshift-magnitude data of Type Ia supernova is used to place limits on the stochastic variation in expansion rate and consequently, on the stochastic variation of the equation of state.

2 illus, 1 table, 11 ref

005283   Jog C J;Narayan C A (Physics Dep, IISc, Bangalore-560 012) : Dynamical effects of a cloud complex on stellar and HI components in a galaxy. Bull Astr Soc India 2001, 29(3), 343-5.

Investigates the dynamical effects of a molecular cloud complex with a mass <126> 10⁷M and a size of <126> few 100 pc, on the vertical distribution of stars and HI in a galactic disc. The complex has a strong local confining effect reducing the vertical scale-heights of stars and HI to less than 1/3 of their initial values.

2 illus, 5 ref

005282   Jain K;Tripathy S C;Bhatnagar A;Brajesh Kumar (NO, Udaipur Solar Observatory, Physical Research Laboratory, PO Box No. 198, Udaipur-313 001) : Solar rotation rate from minimum to maximum of activity cycle. Bull Astr Soc India 2001, 29(3), 239-40.

Reports on the temporal variation of the rotation rate. Using helioseismic data from SOI/MDI and GONG for the current solar cycle 23, from solar minimum to near maximum phase.

1 illus, 6 ref

005281   Jagdev Singh;Sakurai T;Ichimoto K (NO, Indian Institute of Astrophysics, Koramangala, Bangalore-560 034) : On the disappearance of H-alpha filaments and soft x-ray enhancements as seen from Yohkoh SXT. Bull Astr Soc India 2001, 29(3), 193-202.

H-alpha images of the sun taken at Kodaikanal and Mitaka observatories were studied and soft-X-ray images obtained by SXT onboard Yohkoh for the years 1993 and 94. From events of disappearing quiescent H-alpha filaments and associated soft X-ray brightenings it was found that in some cases H-alpha filament appeared broken and diffused about a day earlier than beginning of the soft X-ray transient brightening which lasted for 7 - 10 hours. Further, enhancements began along filament channels and then moved along arches which were inclined to the filament direction. From the observations it is poltulated that heating of plasma in the filament begins when it appears broken and less dark and continues till it triggers some physical process, responsible to begin soft X-ray enhancement. It is not possible to say that if the H-alpha filament disappears earlier than the beginning of soft-X-ray enhancement or vice versa as there is time difference between H-alpha and soft X-ray observations.

7 illus, 2 tables, 18 ref

005280   Huisong Tan;Xue-fen Cen;Tong-ling Qian; Jian-cheng Wang (NO, National Astronomical Observatories, Yunnan Observatory, CAS, Kunming-650 011, China) : Evaluation of Lijiang Gaomeigu site for astrophysical observation. Bull Astr Soc India 2002, 30(4), 881-93.

The work on the site testing at the Gaomeigu village Lijiang county in the northwest of Yunnan province, was started in 1994 after the completion of the investigation on optical astronomical observatory site survey over Yunnan Province. From six years of systematic study of astro-climate conditions, the average viewing was found to be about 0.9 arcsec from 32636 DIMM observations of 426 nights. The number of useful nights were more than 200. The sky brightness and the extinction coefficients were acceptable and the climate conditions were suitable for an astrophysical observational station. A 2.4m and some 1-m class telescopes would be installed there in the coming years.

9 illus, 3 tables, 11 ref