024434   Mazumdar A;Narasimha D (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-400 005) : Cepheid distance estimation for Virgo cluster. Curr Sci 2001, 80(3), 361-8.

Measurement of distance to the Virgo cluster and a few of its member galaxies by direct method is clearly important for a reliable determination of the Hubble constant as well as for studying the dynamics of a nearby rich galaxy cluster. Cepheid variables in a few galaxies in the Virgo cluster were observed with the Hubble Space Telescope (HST) over the last few years. This work is a reanalysis of the HST data following study of the Galactic and Magellanic Cloud Cepheids. The log (period) vs V-magnitude relation is re-calibrated using the Galactic, LMC as well as the HST observations. The number density of Cepheid variables as a function of their period is used to determine the role of flux-limited incompleteness and a prescription is given to correct for this bias in the sample. The extinction correction is carried out using period vs mean <193>V - I<209>0 colour and V-amplitude vs (V - I) colour at the brightest phase relations. The distance and error estimation is based on L1 minimization. The mean distance to Virgo cluster is estimated to be 20.5±1.8 (random) ± 2.5 (systematic) Mpc.

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023273   Singh O P;Khan T M A;Rahman M S (NO, SAARC Meteorological Research Centre, Abhawa Bhaban, Agargaon, Dhaka 1207, Bangladesh) : Has the frequency of intense tropical cyclones increased in the north Indian ocean. Curr Sci 2001, 80(4), 575-80.

Results of the study, which has considered the entire existing data of 122 years of tropical cyclone frequency over the north Indian ocean from 1877 to 1998, have shown that there is indeed a trend in the enhanced cyclogenesis during November and May. These months account for the maximum number of severe cyclones over the north Indian Ocean. The increasing trend in the cyclone frequency during these months has been primarily due to the significant positive trends over the Bay of Bengal, where the majority of north Indian Ocean cyclones develop. Thus the coastal regions of Bangladesh, India and Myanmar have indeed become more prone to the incidence of severe cyclones during November and May. There has been a two-fold increase in the tropical cyclone frequency over the Bay of Bengal during November in the past 122 years. There has been a 17% increase in the intensification rate of cyclonic disturbances to the cyclone stage, and a 25% increase to severe cyclone stage over the north Indian Ocean during November, which accounts for highest monthly average of severe cyclone frequency. All these linear trends are statistically significant at 99% level. The increasing trend in the cyclone frequency during May is also highly significant but the intensification rates to cyclone and severe cyclone stages have registered only slight increasing tendencies.

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023272   Manohar G K;Kandalgaonkar S S;Tinmaker M I R (NO, Indian Institute of Tropical Meterorology, Pune-411 008) : Cloud liquid water content responses to hygroscopic seeding of warm clouds. Curr Sci 2001, 80(4), 555-60.

The cloud liquid water content (CLWC) data in time and space from a total of 96 pairs of target (T) and control (C) experiments were analysed in this study to compare the responses of CLWC to hygroscopic seeding of warm clouds. Results of various approaches taken for this analysis have indicated significant modifications in the CLWC for the T clouds as against C clouds. Analysis of changes in CLWC in the T clouds after and before seeding has pointed out their increasing trend of values with increment in the number of seeded traverses in most cases. These results have shown that CLWC in the T clouds increases following the seeding treatment in the range 9-26%. Similar comparisons in the C clouds have indicated obvious diminution in CLWC that lies in the range 5-11%. These results clearly indicate the influence on microphysical growth and decay of such clouds that arises from hygroscopic seeding and not seeding of warm clouds. Analysis of spatial responses of CLWC to seeding has shown that the optimum effect of seeding may be achieved for a suitable cloud in the altitude range 5750-6250 ft (asl) in the Pune area. It is believed that this study has provided adequate support in favour of the hypothesis of hygroscopic seeding of warm clouds.

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023271   Abbas A (NO, Institute of Physics, Bhubaneswar-751 005) : Signals of supersymmetric dark matter. Indian J pure appl Phys 2000, 38(6), 377-82.

Lightest supersymmetric particle predicted in most of the supersymmetric scenarios is an ideal candidate for the dark matter of cosmology. Recently there have been intriguing signals of 59 Gev neutralino dark matter at DAMA in Gran Sasso. The passage of the earth through dense clumps of dark matter would produce large quantities of heat in the interior of this planet through the capture and subsequent annihilation of dark matter particles. This heat would lead to large-scale volcanism which could in turn have caused mass extinctions. The periodicity of such volcanic outbursts agrees with the frequency of palaeontological mass extinctions as well as the observed periodicity in the occurrence of the largest flood basalt provinces on the globe. Binary character of these extinctions is another unique aspect of this signature of dark matter. In addition dark matter annihilations appear to be a new source of heat in the planetary systems.

020151   Sivakumar C;John M V;Babu Joseph K (Department of Physics, Cochin University of Science and Technology, Kochi-682 022) : Stochastic evolution of cosmological parameters in the early universe. Pramana J Phys 2001, 56(4), 477-86.

Develops a stochastic formulation of cosmology in the early universe, after considering the scatter in the redshift-apparent magnitude diagram in the early epochs as an observational evidence for the non-deterministic evolution of early universe. Consider the stochastic evolution of density parameter in the early universe after the inflationary phase qualitatively, under the assumption of fluctuating ω factor in the equation of state, in the Fokker-Planck formalism. Since the scale factor for the universe depends on the energy density, from the coupled Friedmann equations calculated the two variable probability distribution function assuming a flat space geometry.

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020150   Sen S;Banerjee N (NO, Harish Chandra Research Institute, Chhatnag Road, Jhusi, Allahabad-211 019) : On the absence of scalar hair for charged rotating black holes in non-minimally coupled theories. Pramana J Phys 2001, 56(4), 487-50.

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020149   Sathyaprakash B S (Department of Physics and Astronomy, Cardiff University, Cardiff CF2 3YB, Great Britain) : Gravitational wave symphony of the universe. Pramana J Phys 2001, 56(4), 457-75.

The new millennium will see the upcoming of several ground-based interferometric gravitational wave antennas. Within the next decade a space-based antenna may also begin to observe the distant Universe. These gravitational wave detectors will together operate as a network taking data continuously for several years, watching the transient and continuous phenomena occurring in the deep cores of astronomical objects and dense environs of the early Universe where gravity was extremely strong and highly nonlinear. The network will listen to the waves from rapidly spinning non-axisymmetric neutron stars, normal modes of black holes, binary black hole inspiral and merger, phase transitions in the early Universe, quantum fluctuations resulting in a characteristic background in the early Universe. The gravitational wave antennas will open a new window to observe the dark Universe unreachable via other channels of astronomical observations.

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020148   Raj Bali;Dave S (Department of Mathematics, University of Rajasthan, Jaipur-302 004) : Bianchi type IX string cosmological model in general relativity. Pramana J Phys 2001, 56(4), 513-8.

Bianchi type IX string cosmological models in general relativity has been investigated. To get a determinate solution, assumed a condition ρ = λ i.e. rest energy density for a cloud of strings is equal to the string tension density. The various physical and geometrical aspects of the models are also discussed.

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020147   Patil K D;Ghate S H;Saraykar R V (NO, B.D. College of Engineering, Sewagram, Wardha) : Spherically symmetric inhomogeneous dust collapse in higher dimensional space-time and cosmic censorship hypothesis. Pramana J Phys 2001, 56(4), 503-11.

Consider a collapsing spherically symmetric inhomogeneous dust cloud in higher dimensional space-time. And shows that the central singularity of collapse can be a strong curvature or a weak curvature naked singularity depending on the initial density distribution.

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015983   Varricatt W P (Physical Research Laboratory, , Ahmedabad-380 009) : Photometric studies of close binary systems. Bull Astr Soc India 2000, 28(2), 321-7.

Two factors are considered as the indication of the presence of a dark spot on the back side of the secondary star and the values of the spot parameter are derived using the model. For R CMA, T2 was found to increase towards the near IR wavelengths, from the optical bands. This is interpreted as due to the presence of localized gas in the system. Also T2 derived from the Hα light curves is found to be higher than that derived from the neighbouring bands. This is explained as due to the difference in the photospheric absorption of Hα in the photospheres of the primary and the secondary. The moments of primary minima follows the periodic O-C curve observed for R CMa, giving more faith in the presence of a third body in the system, which was proposed before. But the nature of the third body, if present, is still uncovered.

015982   Vadher N M;Shah A B;Shroff A J;Joshi U C (Physical Research Laboratory, , Ahmedabad-380 009) : Simultaneous imaging in optical and near-IR bands. Bull Astr Soc India 2000, 28(2), 445.

Authors have developed an imaging system with two channels - one channel for visual band and other for the near infrared. A beam splitter splits the light from telescope into two components. The visual light beam (reflected) goes to CCD camera and near IR beam (transmitted) to IR camera (NICMOS3), enabling both to be recorded simultaneously. The software to control two instruments simultaneously is developed in house. Test runs have already been conducted.

015981   Vadawale S V;Rao A R;Malkar J P (NO, Tata Institute of Fundamental Research, Mumbai-400 005) : Position sensitive proportional counter. Bull Astr Soc India 2000, 28(2), 447-9.

Position Sensitive Proportional Counter for X-rays in the energy range from 2 keV to 20 keV has been developed. With the sensitive circular area of 30 mm diameter, it can be used as an imaging detector at the focal plane of a soft X-ray optics. For two demensional position determination of an X-ray event, two multi wire cathode grids of 50 μm wire spaced at 0.5 mm are used. The final position of the event is obtained by calculating the center of gravity of the charge spread. Accuracy of the order 50 μm can be achieved by this method. The main anode grid made up of 25 μm wire spaced at 1 mm gives the standard energy resolution of the proportional counter. Another anode grid is used as an anti-coincidence counter to achieve high degree of background rejection.

015980   Tickoo A K;Kaul S K;Kaul I K;Koul R;Bhat C L (Nuclear Research Laboratory, Bhabha Atomic Research Centre, , Mumbai-400 085) : DSO-based system for temporal-profile extraction of atomspheric cerenkov events. Bull Astr Soc India 2000, 28(2), 465-9.

The TACTIC array of Cerenkov telescopes, being set up at Mt. Abu, proposes to record time-profiles of atmospheric Cerenkov pulses with a view to exploit apparent differences in the associated time-parameters for a possible characterisation of the progenitor particles. Discusses here a cost-effective hardware scheme for deployment in the TACTIC for recording the Cerenkov pulse profiles.

015979   Subramaniam A;Gorti U;Sagar R;Bhatt H C (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Binary star clusters in galaxies : our galaxy. Bull Astr Soc India 2000, 28(2), 257-9.

015978   Subramaniam A;Bhatt H C (NO, Indian Institute of Astrophysics, Bangalore-560 034) : New look at the OB associations and star clusters in the Puppis-Vela region using HIPPARCOS data. Bull Astr Soc India 2000, 28(2), 255-6.

015977   Seetha S;Ashoka B N;Raj E;Kasturirangan K (Technical Physics Division, ISRO Satllite Centre, , Airport Road, Bangalore-560 017) : Photometric observations of the AM CVn star EC 15330-1403. Bull Astr Soc India 2000, 28(2), 247-50.

015976   Salter C J;Banhatti D G (NO, School of Physics, Madurai Kamaraj University, Madurai-625 021) : Some home-truths about small samples and counting statistics. Bull Astr Soc India 2000, 28(2), 363-5.

Assessing a fluctuation in the sky density of astronomical objects uses counting (i.e. Poisson) statistics for estimating the errors. For a finite sample, there is a limit to the maximum possible fluctuation from the mean in units of the rms. This maximum is derived, and an example is used to illustrate these concepts.

015975   Saha S K;Morel S (Indian Institute of Astrophysics, , Bangalore-560 034) : Perspective of long baseline optical interferometry. Bull Astr Soc India 2000, 28(2), 175-209.

The current status of interferometers are enumerated. The data analysis being carried out using the working interferometers are also described. The space interferometry programmes are advancing very fast. Among the notable ones are the space technology 3 (ST3), Space interferometry mission (SIM), and Darwin; they have already received funds. The technical details of these inteferometers and their objectives are highlighted.

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015974   Sagar R et al (Uttar Pradesh State Observatory, , Manora Peak, Naini Tal-263 129) : Site characterization for the UPSO-TIFR telescope. Bull Astr Soc India 2000, 28(2), 429-35.

The Uttar Pradesh State Observatory, Naini Tal and Tata Institute of Fundamental Research, Mumbai plan to install jointly a 3 metre size optical telescope at Devasthal located east of Naini Tal about 50 km by road. The site has been selected after a decade of survey in Kumaon and Garhwal hills. The altitude of the peake is 2450±5 meters, while longitude and latitude are 79° 40' 57 E and 29° 22' 46' N respectively. The loation of the site is such that logistics of access and transportation are not too difficult and at the same time, it is far from urban development, has more than 200 astronomically useful nights, dark sky, low atmospheric extinction and most importantly seeing better than 1 arcsec for about 40% of the time. Extensive efforts are going on to characterize the site more precisely.

015973   Ray M K;Chaudhuri S;Banerji S (Physics Department, Jadavpur University, , Calcutta-700 032) : Collapse of voids in a Robertson-Walker universe with nonzero spatial curvature. Bull Astr Soc India 2000, 28(2), 419-21.

Considers the model of a spherical void (or its precursor) with heat conducting perfect fluid in Region I with Maiti metric (1982) surrounded by a spherical shell filled with radiation (Region II) having Vaidya metric. The combination is embedded in Robertson-Walker (RW) Universe in Region III. Earlier. Mandal and Banerji (1998) took RW Universe with zero spatial curvature and showed that to an observer, a little away from the boundary in Region III, the void appears to collapse provided the arrow of time is future directed in all the regions. Same result holds also for the case of non-zero spatial curvature of Region III. The rate of collapse is the fastest for k = +1, moderate for k = 0, and the slowest k = -1.

015972   Ravindranath S;Prabhu T P (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Study of the emission line spectra and the stellar populations of starburst galaxies. Bull Astr Soc India 2000, 28(2), 407-8.

Based on the optical-NIR spectra, discusses the nebular properties and stellar populations of starburst nuclei. Starburts are found to have higher electron densities and higher excitations compared to HII nuclei. Finds evidence for a composite population of young, ionizing massive stars (less than 3 Myr old) co-existing with the evolved RSG populations (about 5 to 7 Myr old) in most of sample starburst nuclei.

015971   Ramesh Bhat N D (National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune) : Pulsar scintillation and the local interstellar medium. Bull Astr Soc India 2000, 28(2), 335-41.

Ever since their discovery, pulsars have been proved to be excellent tools to study the Interstellar Medium. Results from new observations using the Ooty Radio Telescope at 327 MHz are used to investigate the properties of the Local Interstellar Medium; in particular, the distribution of radio wave scattering material and the spatial power spectrum of plasma density fluctuations. The morphology of the scattering structure inferred from the observations shows a striking similarity with that of the Local Bubble. The observations suggest that the overall nature of the spectrum is Kolmogorov-like in the spatial scale range <126> 10⁶ m to 10¹¹ m, with excess power at larger scales (<126> 10¹² - 10¹³ m). Data are also used to test the quantitative predictions from refractive scintillation theory.

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015970   Prabhu T P (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Indian astronomical observatory, Hanle. Bull Astr Soc India 2000, 28(2), 233-4.

The high-altitude astronomical station of Indian Institute of Astrophysics at Mt. Saraswati, Hanle, function as a full-fledged observatory with one 2-m and one 50-cm telescopes. The telescope is operated in robotic or remote operation mode using a dedicated satellite communication link from the control station at Hosakote near Bangalore. The current status and schedule are described.

015969   Parthasarathy M (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Birth and early evolution of planetary nebulae. Bull Astr Soc India 2000, 28(2), 217-24.

Birth and early evolution of planetary nebulae is described. The study of the young planetary nebula Hen 1357 (Stingray Nebula) with HST is discussed. The observed characteristics of few interesting PPNe and PNe are described. The presence of multiple arcs or rings, knots, jets collimated and bipolar out flows and disks shows the complex nature of mass loss process during the AGB and post-AGB phases of evolution.

015968   Pandey G;Kameswara Rao N;Lambert D L;Jeffery C S;Asplund M (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Abundance analysis of extreme helium stars. Bull Astr Soc India 2000, 28(2), 303-4.

High resolution spectra were obtained for a sample of hydrogen-deficient stars which are hotter than the R CrB stars and cooler among the extreme helium stars (EHe). These stars are transition objects evolving either to EHe stars or R CrB stars. Explores the evolutionary link between the program stars, R CrB stars and EHe stars. Distribution of these stars in the log g - log Teff plane shows similar L/M ratios (≈4.0). These objects have an abundance pattern like R CrB stars and EHe stars.

015967   Padmakar;barway S;Pandey S K (NO, School of Studies in Physics, Pt. Ravishankar Shukla University, Raipur-492 010) : Study of sky condition at Raipur and calibration of the photometer telescope system. Bull Astr Soc India 2000, 28(2), 437-40.

To investigate local sky condition for valuable astronomical observation, authors obtained values of atmospheric extinction coefficients in BVR filters for over 150 nights during the period of 1994 to 1997. Observation over nearly three years indicates that although the sky condition at the observing site is not steady, the observing facility can be fully exploited for differential photometric studies on bright variable stars. Several times during each observing season on clear photometric nights authors also carried out observation for calibration and checked reliability of the system calibration.

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015966   Ojha D K;Omont A;Simon G;Blommaert J (NO, , T.I.F.R., Homi Bhabha Road, Colaba, Mumbai-400 005) : Asymptotic giant branch stars in the ISOGAL survey. Bull Astr Soc India 2000, 28(2), 241-2.

Presents and analyses the data of a field at 1 = 0°, b = 1° from the ISOGAL survey of selected areas of the inner Galactic bulge at 15 and 7 μm. In combination with IJKs data from the near-infrared southern sky survey DENIS, the ISOCAM data allow the first detailed study of infrared stellar populations in very obscured regions of the inner Galaxy. The K/J-K magnitude-color diagram for the sources detected in the ISOGAL field shows a remarkably well-defined tip of the bulge red giant sequence. A few stars clearly show an excess in the value of J-K with respect to the red giant sequence. Most of them are probably AGB stars with large mass-loss rates. The other color-color and magnitude-color diagrams are also discussed. About half of the source have observed K-[15] colors. Thus these data suggest that these are masslosing stars.

015965   Narasimhan K S V S;Alladin S M;Sastry K S (NO, Inter-University Centre for Astronomy and Astrophysics, Pune-411 007) : Classification of colliding galaxies. Bull Astr Soc India 2000, 28(2), 385-8.

Authors had classified galaxies in increasing order of the intensity of tidal effects on the basis of transfer of energy from the motion of galaxies to the internal motions. This work has been refined by presenting the classification on the basis of the velocity of collision, which is an observable parameter. Analytic expressions are obtained for Vdis, the maximum velocity required for the disruption of one of the galaxies and Vcap, the maximum velocity required for mutual capture of the galaxies, in terms of collision parameters. Examples of some observed pairs of galaxies for the classification types are given.

015964   Narasimha D;Srinand R (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-400 005) : Study of quasar broad emission region from spectroscopy of multiple images. Bull Astr Soc India 2000, 28(2), 395-6.

Using the high resolution radio observations and analysis of the broad emission lines as well as continum in the optical spectra of the multiple images of quasars, authors provide a method to probe the structure and dynamics of the broad emission region of AGNs. From the study of the system 1422+231 they establish that the optical and radio emission of the source originate from two different regions.

015963   Narasimha D;Singh K P (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-400 005) : Probes of superclusters at moderate redshifts. Bull Astr Soc India 2000, 28(2), 381-3.

Detection of superclusters at z = 0.2 - 1.0 and determination of their mass provide constraints on the theories of structure formation in the Universe. A combination of the study of hot gas observed in X-rays, and the distribution of arcs (weak lensing of background galaxies) in optical can proble clusters of galaxies as well as superclusters. Authors analyse the available X-ray and optical maps of a cluster pair of Abell 222 and Abell 223 at redshift ≈ 0.2, separated by <126> 15' and where at least one arc has been reported. X-ray temperature of the gas in the two clusters is 4±2 keV and a bridge of hot gas at temperature of ≈ 2 keV connects them. The bridge is also seen in the optical indicating the presence of a supercluster structure.

015962   Namboodiri P M S (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Tidal interactions in spherical galaxies. Bull Astr Soc India 2000, 28(2), 397-9.

Numerical simulations of equal mass galaxies, moving initially on a parabolic orbit, have been performed to see how the total energy of the system changes in close and wide encounters. The results are compared with those obtained using impulse approximation.

015961   Nair S;Garrett M A (NO, Raman Research Institute, Bangalore-560 080) : Fresh results from modelling the gravitationally lensed system PKS 1830-211. Bull Astr Soc India 2000, 28(2), 401-2.

Fresh modelling of PKS 1830-211 points to a perturbation in the NE image by a lens of globular cluster scale.

015960   Naik S;Agrawal P C;Paul B;Rao A R;Seetha S; Kasturirangan K (NO, Tata Institute of Fundamental Research, Mumbai-400 005) : X-ray observation of newly discovered transient XTE J1748-288 by the Indian X-ray astronomy experiment. Bull Astr Soc India 2000, 28(2), 289-91.

The observations of X-ray transient XTE J1748-288 were made in the energy band 2-18 keV with the Indian X-ray astronomy experiment (IXAE) during 1998, June 14-25 with total useful exposure of 27,100 second for 1 sec integration mode and 15,440 sec for the 0.1 sec mode. The X-ray light curves showed no significant intensity variations on short time scale (<62>10s). The power density spectrum obtained from timing analysis of the data show no quasi-periodic oscillations in the frequency range of 0.001 Hz to 5 Hz. From the observed X-ray characteristics it is difficult to infer the nature of the X-ray source.

015959   Mukherjee K;Agrawal P C;Paul B;Rao A R;Yadav J S;Seetha S;Kasturirangan K (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-400 005) : Study of two pulsars with the Indian x-ray astronomy experiment. Bull Astr Soc India 2000, 28(2), 293-4.

The X-ray pulsar Cep X-4 4U 1907+09 were observed with the Indian X-ray Astronomy Experiment (IXAE). Observations of Cep-X4 were made during the declining phase of its latest 30 days outburst in 1997, July-August. The X-ray pulse profiles obtained during IXAE observations show inter-pulse dominated double-peak pulse. The second X-ray pulsar 4U 1907+09 with a period of 440s was observed in August 1996 and again in June 1998. The X-ray profile shows a double-peak pulse shape. The P obtained from these two observations indicate that the pulsar is in monotonically spin-down phase, at the rate of 0.23 s yr-1.

015958   Manchanda R K (NO, Tata Institute of Fundamental Research, Colaba, Bombay-400 005) : Near absence of hard x-ray pulsation from GS 1843+00 in the middle of burst phase. Bull Astr Soc India 2000, 28(2), 277-80.

Hard X-ray transient pulsar GS 1843+00 was observed in the 20-200keV region using a higher sensitivity large area scintillation counter instrument during its 1997 flare on March 30. The data indicates a near absence of 29.5^s pulsation in the hard X-ray energy band of 30-70 keV, even though observations correspond near to intensity maximum in the burst phase. Along with the RXTE and Compton observatory data taken during this burst present results in terms of geometrical constraints and the X-ray emission mechanism are discussed.

015957   Manchanda R K (NO, Tata Institute of Fundamental Research, Colaba, Bombay-400 005) : 20-200 keV observations of binary X-ray sources with a balloon-borne payload. Bull Astr Soc India 2000, 28(2), 281-7.

The spectral information in the hard X-ray energy region above 30 keV is available only for a small number of X-ray objects even though hard X-ray flux has been observed from about 80 of the 200,000 X-ray sources catalogued so far. Paper attempts spectral observations of binary X-ray sources in the 20-200 keV band using a newly developed balloon-borne large area scintillation counter telescope. Presents the hard X-ray spectra of some of these sources obtained during various experiments.

015956   Mahendra Singh;Sanwal B B;Stalin C S (Uttar Pradesh State Observatory, , Manora Peak, Naini Tal-263 129) : CCD photometry of the wolf rayet galaxy mink. Bull Astr Soc India 2000, 28(2), 393-4.

Presents the results from B and V photometric observations of the Wolf Rayet galaxy Mink which was observed through the 104 cm telescope of U.P. State Observatory using 1 K x 1 K CCD. The surface brightness profiles in B and V filters and the contour map in B filter are given.

015955   Madhwani P P;Manchanda R K (NO, Tata Institute of Fundamental Research, Mumbai-400 005) : New automatic star tracker for balloon-borne astronomy instruments. Bull Astr Soc India 2000, 28(2), 451-4.

Authors have developed a new microprocessor controlled stnad-alone star tracker with a built-in GPS receiver for use in the X-ray astronomy experiments using balloons. GPS receiver provides a highly accurate (<126> arcsec) instant longitude of the balloon platform on continuous basis. Present hardware design is restricted to 12-bit resolutions (<126>'-). This paper presents some of the technical details of the new system.

015954   Lokanadham B;Babu G S D;Ravi Kiron Y (Centre for Advanced study in Astronomy, Osmania University, Hyderabad-500 007) : CCD imaging of Seyfert galaxy NGC 1068. Bull Astr Soc India 2000, 28(2), 413-8.

CCD observations of NGC 1068 have been obtained in BVRI filters with 2.34 meter Vainu Bappu Telescope of Kavalur in India. The contours of the indices B-V, B-I and V-I of the galaxy indicate the presence of the star-forming region in the circumnuclear ring. The excitation mechanism of the star forming complexes is explained in the light of multi-wavelength observations of the galaxy.

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015953   Lal D V;Shastri P;Gabuzda D (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Seyferts at milli-arcsec scales. Bull Astr Soc India 2000, 28(2), 403-5.

Observes a sample of Seyfert galaxies using Global Very Long Baseline Interferometry at 5 GHz. The goal is to investigate the systematics fo their nuclear radio morphology on milli-arsecond scales. Choses the objects so as to be able to test the predictions of the Unified Schemes for Seyfert galaxies. Presents preliminary results of the VLBI observations.

015952   Konar S (NO, Inter-University Centre for Astronomy and Astrophysics, Pune-411 007) : Whither strange pulsars. Bull Astr Soc India 2000, 28(2), 299-301.

It has been argued that some of the pulsars could be strange stars because these too are capable of supporting fast rotations observed in pulsar. Examines this claim from the point of veiw of the evolution of magnetic field in pulsars and find that there is no compelling reason for the existence of strange pulsars.

015951   Konar S (NO, Raman Research Institute, Bangalore-560 080) : Evolution of the magnetic field in accreting neutron stars. Bull Astr Soc India 2000, 28(2), 343-9.

015950   Kaul I K;Kaul S R;Tickoo A K;Koul R;Bhat C L (Nuclear Research Laboratory, , Trombay, Mumbai-400 085) : Spectral-ratio based trigger generator for TACTIC vertex elements. Bull Astr Soc India 2000, 28(2), 459-63.

An unconventional hardware trigger-generator, based on an on-line estimation of the spectral-ratio of the Cerenkov radiation, has been developed for the three Vertex Elements of the TACTIC γ-ray telescope array. The paper discusses the operational principle of the trigger - generator and the test results from a prototype circuit developed for demonstration purposes.

015949   Kashyap V;Drake J J (Centre for Astrophysics, , Cambridge, MA 02138) : PINTofALE : package for the interactive analysis of line emission. Bull Astr Soc India 2000, 28(2), 475-6.

PINTofALE was developed to analyze spectroscopic data from coronal sources in the 1-1500A range. It is based on a modular set of IDL tools that interact with an atomic database and with observational data. The tools allow to easily identify spectral lines, measure fluxes, and carry out more detailed modeling. The package has been extended to handle analysis of high-resolution X-ray spectra that will be obtained with the Chandra X-ray Observatory.

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015948   Kamath U S (Physical Research Laboratory, , Navrangpura, Ahmedabad-380 009) : Studies of classical novae and related objects. Bull Astr Soc India 2000, 28(2), 329-33.

This thesis is based on studies of two classical novae - V1425 Aquilae (J H K photometry and optical spectroscopy) and V723 Cassiopeiae (J H K photometry) and a sample of symbiotic stars (J H K photometry and Circular Variable Filter spectroscopy). The infrared data have been obtained from Mt. Abu IR observatory of Physical Research Laboratory, Ahmedabad, and the optical spectral from Vainu Bappu Observatory of Indian Institute of Astrophysics, Bangalore.

015947   Joshi U C;Baliyan K S;Ganesh S;Deshpande M R (Physical Research Laboratory, , Ahmedabad-380 009) : Coordinated TeV gamma-ray and optical polarization study of BL lac object Mkn 501. Bull Astr Soc India 2000, 28(2), 409-11.

Coordinated TeV gamma-ray and optical polarization observations of the BL Lac object Mkn 501, carried out during 1997 with the TACTIC imaging Cerenkov telescope of the BARC and the 1.2 m Gurushikhar optical/IR telescope at Mt. Abu, have revealed a significant increase in the degree of polarization of the optical radiation in association with a TeV gamma-ray flare. The observations indicate a possible leptonic origin of the TeV gamma-ray signal as against a hadronic origin proposed in some models.

015946   Jog C J (Department of Physics, Indian Institute of Science, Bangalore-560 012) : Lopsided spiral galaxies. Bull Astr Soc India 2000, 28(2), 351-5.

Recent observations show that 30% of spiral galaxies have significant lopsidedness in both old stars and gas, indicating asymmetry in the disk mass distribution. This is a new and exciting area in galactic structure and dynamics. Reports the dynamics of particles in closed orbits, the isophotes, and the local disk stability in a axisymmetric galactic disk perturbed by a lopsided halo potential. The results obtained are shown to be valid for both stars and gas in the same region of the disk. The results naturally explain a number of observations of these galaxies, including the non-axisymmetric (m=1) surface density distribution, the isophotal elongation, and the azimuthally asymmetric formation of HII regions. From the observed disk lopsidedness, the degree of halo lopsidedness is obtained to be <126> 5%. Our calculation of the self-consistent disk response shows that the resulting disk lopsidedness is important only beyond 1.4 disk scale-lengths and its magnitude increases with radius - this is exactly in agreement with the recent near-IR observations in the literature.

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015945   Jog C J (Department of Physics, Indian Institute of Science, Bangalore-560 012) : Local stability criterion for a two component galactic disk. Bull Astr Soc India 2000, 28(2), 309-10.

The criterion for stability against local, axisymmetric perturbations in gravitationally coupled stars and gas in a galactic disk is obtained. The new feature is the inclusion of both stars and gas in the study, and a two-component analog of the standard one-component Q-criterion is obtained which is applicable to realistic galaxies consisting of stars and gas. The Qs-g value is shown to be always less than the Q values for the stars-alone and the gas-alone cases, thus a two-component system is more unstable than either component by itself. Hence, future studies of galaxies must use Qs-g as a measure of disk stability. The results obtained are general, and several applications for the stability, structure, and evolution of galaxies are discussed.

015944   Jain D;Panchapakesan N;Mahajan S;Bhatia V B (Department of Physics & Astrophysics, University of Delhi, Delhi-110 007) : Limit on the average redshift of gamma ray bursts from evolving galaxies. Bull Astr Soc India 2000, 28(2), 377-9.

Identification of gravitationally lensed Gamma Ray Bursts (GRBs) in the BATSE 4B catalog can be used to constrain the average redshift <60>z<62> of the GRBs. Calculates an upper limit to <60>z<62>, independent of the physical model for GRBs, using a filled beam approximation to compute the lensing rate for GRBs at high z for a variety of cosmologies. The upper limit on <60>z<62> depends directly on the cosmological parameters Ω and Δ. The other factor which can change the <60>z<62> of GRBs is the evolution of the lensing galaxies. It is found that merging of lensing galaxies puts the GRBs at higher redshift as compared to non evolving model of galaxies.

015943   Hiremath K M (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Internal rotation and toroidal part of the magnetic field of AB Doradus. Bull Astr Soc India 2000, 28(2), 243-5.

MHD equations for the steady parts of internal rotation and toroidal component of the magnetic field of the AB Doradus have been analytically solved. By taking observed surface rotation as the boundary condition and assuming that the base of the convection zone rotates rigidly, estimates the size of the convective envelope to be 40% of the radius and the rotation velocity at the base to be not less than 1.42 x 10^-4 rad/sec. The toroidal magnetic field is distributed throughout the convective envelope. By taking the average density of 1.78 gm cm^-3 and radius 5.95 x 10¹⁰ cms (Allen 1972), obtains a Mega gauss field near base of the convective envelope. Presents rotational and toroidal magnetic field prifiles in the interior, and conjecture on the time dependent part of the magnetic field.