020704   Bhalerao V;Vahia M N (NO, Indian Inst of Technol Bombay, Powai, Mumbai-400 076, Email: varunb@iitb.ac.in) : Mass limit of Nemesis. Bull Astr Soc India 2005, 33(1), 27-33.

Authors assumed that if the sun has a companion, it has a period of 27 Myr corresponding to the periodicity seen in cometary impacts on earth. Based on this assumption, it is seen that the inner Lagrangian point of the interaction between the Sun and its companion is in the Oort cloud. From this author has calculated the mass - distance relation for the companion. Authors then computed the expected apparent magnitude (visible and J band) for the companion using the models of Burrows (1993). Authors has also compare this with the catalogue completeness of optical and infrared catalogues to show that the sun cannot have a companion of mass greater than 44 M^jup (0.042 M.).

2 illus, 1 table, 15 ref

020703   Alam M. M;Sattar M. A (Mathematics Discipline, Khulna Univ, Khulna 9208, Bangladesh) : Effect of magnetic field angle and joule heating on MHD free convection and mass transfer flow in a rotating system. J Energy Heat Mass Transfer 2003, 25(4), 293-314.

A steady MHD free convection and mass transfer flow in a rotating system with hall current, viscous dissipation, Joule heating and thermal diffusion of an electrically conducting viscous incompressible fluid past an impulsively started infinite vertical porous plate with variable concentration and suction have been studied analytically. The Governing equations of this problem are reduced to nonlinear differential equations by introducing similarity transformations. The nonlinear similarity equations are then solved analytically by using the perturbation technique. The effects of the various parameters entering into the problem are shown graphically.

17 illus, 20 ref

018509   Banerjee M;Debkumari Sharma B (Laboratory of Algal Biotechnology, Biosci Dep, Barkatullah Univ, Bhopal-462 026, Email: meenakshi_banerjee@indiatimes.com) : Astrobiology - a new emerging field of biological sciences. Curr Sci 2004, 87(10), 1341-4.

Recent advances on the origin and evolution of life have greatly developed understanding of the early stages of life on earth. The claims of signs of extinct life in a meteorite from Mars have prompted much work on how to search for and understand such signs and also address pertinent questions which have baffled man since time immemorial: Where has man come from? Is there life scattered across the solar system or man is truly alone and if so, why? The science, which addresses all these, and many other questions, is the newly coined branch of biological sciences - Astro-biology. It is a type from the are also has an ancillary beneficial effect on the public view of science in general. Discusses some of these aspects.

29 ref

017451   Sujatha N V;Chakraborty P;Murthy J;Henry R C (Indian Institute of Astrophysics, , Bangalore-560 034) : A model of the stellar radiation field in the UV. Bull Astr Soc India 2004, 32(3), 151-8.

This work is the first step in a systematic effort to understand and predict the different components of the UV (912 Angstrum - 3000 Angstrum) radiation field over the entire sky has been developed. A model has been developed to predict the ISRF in the UV within a few hundred parsecs of the Sun using the Hipparcos star catalog. The model has been checked through a comparison with the observations of the Belgian/UK UV sky survey telescope (S2/68) on the ESRO TD-1 satellite.

3 illus, 1 table, 25 ref

017450   Saxena P P (Mathematics and Astronomy Dep, Lucknow Univ, Lucknow-226 007) : On the possibility of nitrous oide (N₂O) as a cometary parent molecule in Comet 1P/Halley. Bull Astr Soc India 2004, 32(3), 185-8.

Nitrous oxide as a possible parent molecule in Comet 1P/Halley is discussed in light of in situ measurements and theoretical considerations. Hitherto undiscussed in cometary context, N₂O could be a trace parent molecule with Q(N₂O)/Q(H₂O) <126> 2 x 10^-4 in Comet 1P/Halley. Having a photo lifetime <62>10⁵ s at 1 au heliocentric distance during solar minimum conditions and with a gas outflow speed of 0.85 km s^-1 in the coma of Comet 1P/Halley, N₂O could reach into the tail of comet where it dissociates into N₂ and O. In this scenario N₂O acts as a camouflage for N₂ and may help solve the puzzle of the presence of N⁺₂ ions only in the tail of Comet 1P/Halley.

16 ref

017449   Roy S (National Centre for Radio Astrophysics, TIFR, Pune Univ Campus, Post Bag No.3, Ganeshkhind, Pune-411 007) : The galactic centre region. Bull Astr Soc India 2004, 32(3), 205-13.

The central 45' region of the Galaxy has been observed at 620 MHz band of the Giant Metrewave Radio Telescope (GMRT) in radio continuum, and the polarisation properties of 64 small diameter background extragalactic sources seen through the -6°<60> l <60>6°, -2°<60> b <60>2° region have been measured with the Australia Telescope Compact Array (ATCA) and the Very Large Array (VLA). The 620 MHz observations show that Sgr A* is located behind the HII region Sgr A West. Using the VLA observations, the Faraday rotation measure (RM) of the polarised sources has been measured. The measured RMs are mostly positive, and show no reversal of sign across the rotation axis of the Galaxy. This rules out any circularly symmetric model of magnetic field in the region. The magnetic field strength in the region is estimated to be <126> 10μG, which raises doubts against an all pervasive mG field in the central few hundred pc of the Galaxy.

5 illus, 22 ref

017448   Rautela B S;Joshi G C;Pandey J C (Aryabhatta Research Institute of Observational Science, , Nainital-263 129) : ARIES imaging polarimeter. Bull Astr Soc India 2004, 32(3), 159-67.

An Imaging Polarimeter has been fabricated for use with liquid-N₂ cooled CCD camera and is designed to suit 104-cm Sampurnanand telescope with an f/13 focus at Aryabhatta Research Institute of Observational Sciences (ARIES), Naini Tal. The instrument measures the linear polarization in broad B, V and R band and has a field of view <126>2' x 2'. Some observations regarding the polarization of some polarized as well as unpolarised stars have been presented with a view to show the performance of the tabricated polarimeter.

5 illus, 3 tables, 7 ref

017447   Pandey U S (Physics Dep, D D U Gorakhpur Univ, Gorakhpur-273 009) : On gravitating stellar system I. formulation using distribution function method. Bull Astr Soc India 2004, 32(3), 141-50.

An interesting work on self-gravitating gaseous disks has concerned the behaviour of the precursor of massive central dark object that might be the energy source existing at centers of galaxies and powering quasars. With this view, a model of self gravitating gas flattened in a disk has been presented. The following assumptions have been made: (i) the interaction force between individual pairs of particles is negligibly small, (ii) the distribution function f in phase space satisfies collision-free Boltzmann equation and (iii) the system is conservative. A third order linear differential equation satisfied by the disk has been set up for axisymmetnc case. A particular solution for the disk in steady state has been obtained. The expression for gravitational potential W and surface mass density of the disk have been derived. The velocity profiles have been calculated..

9 ref

017446   Omar A (Raman Research Institute, , Sadashivanagar, Bangalore-560 080) : H_{I deficiency in groups : what can we learn from Eridanus.} Bull Astr Soc India 2004, 32(3), 239-45.

The H_{I,D> content of the Eridanus group of galaxies is studied using the GMRT observations and the HIPASS data. A significant HI deficiency up to a factor of 2 - 3 is observed in galaxies in the Eridanus group. The deficiency is found to be directly correlated with the projected galaxy density and inversely correlated with the line of sight radial velocity. It is suggested that the HI deficiency is due to tidal interactions. An important implication is that significant evolution of galaxies can take place in a group environment.}

4 illus, 1 table, 22 ref

017445   Nejad-Asghar M;Ghanbari J (Physics Dep, School of Sciences, Ferdowsi Univ of Mashhad, Mashhad, Iran) : Occurrence of thermal instability in molecular clouds. Bull Astr Soc India 2004, 32(3), 169-83.

Linear perturbation is used on the complete MHD equations of the magnetic molecular clouds. A comparison of characteristic time-scales has been carried out, and conditions which linear thermal instability causes to form the small-scale condensations in the local expanding/contracting medium of a molecular cloud have been presented. Ambipolar diffusion, or ion-neutral friction on the perturbed states have been considered. In this way, a non-dimensional characteristic equation that reduces to the prior characteristic equation in the non-gravitating stationary background have been obtained. By manipulation of this characteristic equation, it has been concluded that there are, not only oblate formation regions, but also prolate condensation forming solutions, according to expansion or contraction of the background. Some typical data that correspond to the real observed magnetic molecular clouds is presented.

5 illus, 31 ref

017444   Narasimha D (Tata Institute of Fundamental Research, , Mumbai-400 005) : PKS1830-211: the strongest lensed radio source. Bull Astr Soc India 2004, 32(3), 257-65.

The Ooty lens PKS1830-211 is a bright, variable radio source at a redshift of 2.507 consisting of a compact flat-spectrum core, associated knot and jet, which are lensed by an intervening spiral galaxy at a redshift of 0.886. It forms two images separated by 0".98 with a ring passing through them. Multi-epoch Very Large Array (VLA), Multi-Element Radio Linked Interferometer Network (MERLIN), Very Long Baseline Interferometer (VLBI) and Very Long Baseline Array (VLBA). observations have shown variability of the source by more than a factor of two, over time scales of less than a day to years, some of which mimic superluminality. Absorption lines of neutral hydrogen and many molecules have been observed in front of both the images. The molecular lines appear to dominate the image passing near the central part of the lens while the image farther away is dominated by HI 21 cm. Overall, the column density of various species appears to be similar to that found in the Milky Way. But isotopic ratios estimated from the line ratios of several isotopomers appear to indicate that the lens galaxy is less evolved than the Milky Way. The differential Faraday rotation between the images (upwards of 2000 rad m^-2) is suggestive of a large-scale magnetic field of a few microgauss in the lens galaxy. The time-delay between the images is estimated to be 26⁺⁴_-5 days. Multi-epoch VLB imaging as well as absorption line monitoring have provided rich information on the source property as well as tools for studying high-redshift objects.

1 ilus, 2 tables, 28 ref

017443   Mondal N K (Tata Institute of Fundamental Research, , Homi Bhabha Road, Mumbai-400 005) : Status of India-based neutrino observatory (INO). Proc Indian Natn Sci Acad-Pt A 2004, 70(1), 71-7.

Reports on the current status of an Indian based Neutrino observatory. Reviews the goals of INO, its physics potential and on-going efforts to prepare a detailed feasibility report.

3 illus, 9 ref

017442   Lal D V;Rao A P (National Centre for Radio Astrophysics, TIFR, Pune Univ Campus, Ganeshkhind, Pune-411 007) : Spectral structure of X-shaped radio sources. Bull Astr Soc India 2004, 32(3), 247-55.

Analysis of Giant Metrewave Radio Telescope low frequency data for an X-shaped source, 3C 223.1 has revealed an unusual result as discussed earlier by Lal & Rao (2004). The radio morphologies of it at 240 and 610 MHz show a well-defined X-shaped structure with a pair of active jets along the north-south axis and a pair of wings along the east-west axis, that pass symmetrically through the undetected radio core. The wings (or low surface brightness jet) seem to have flatter spectral index with respect to the high surface brightness jet. This clearly show the value of mapping the sample of X-shaped sources at low frequencies. Here preliminary results for two more such sources have been presented.

3 illus, 11 ref

017441   Joshi B C etal (National Centre for Radio Astrophysics, TIFR, Pune-411 007) : Double pulsar system J0737-3039 and its low-frequency observations with GMRT. Bull Astr Soc India 2004, 32(3), 191-203.

The recent discovery of two radio pulsars, with periods of 23 ms and 2.8 s, in a tight 2.4 hour highly reiativistic double neutron star binary, is one of the most significant discoveries of pulsar astronomy. The sharp pulses of the millisecond pulsar, the detection of its long period companion as a pulsar and an almost edge-on orbit make this system a unique laboratory for relativistic physics. The line of sight to the millisecond pulsar passes through the magnetosphere of the long period pulsar giving a unique probe of the pulsar magnetosphere. The relatively small separation between the two pulsars, a 17° per year advance in its angle of periastron and a mild eccentricity leads to a varying interaction between the pulsars, observed as a rich phenomenology in their emission. The status of research on this system since its discovery is reviewed and its low frequency observations using Giant Metrewave Radio Telescope (GMRT) are described.

4 illus, 35 ref

017440   Dwarakanath K S (Raman Reserch Institute, , Bangalore-560 080) : Kinematis of diffuse interstellar clouds: recent GMRT results. Bull Astr Soc India 2004, 32(3), 215-21.

A high latitude HI 21 cm-line absorption survey towards extragalactic sources was recently completed using the Giant Meterwave Radio Telescope (GMRT). A total of 104 sources with | b |<62> 15 ° and with a 21 cm flux density greater than 1 Jy were observed for 120 hours. With an optical depth detection limit of <126> 0.01 this is the most sensitive high-latitude survey as yet. Most of the detected Hi 21 cm-line absorption features belong to a population with a velocity dispersion of <126> 7.6 km s^-1. These are the 'standard' HI clouds and have been well-studied for decades. However, a second population of absorbing clouds with a velocity dispersion of <126> 21 km s^-1 have been deteded. About 20% of the total population of absorbing clouds belong to this population. This new population of 'fast' clouds can be identified with a similar velocity dispersion Ca II absorbing clouds and with the Halo clouds recently detected in HI emission from Green Bank.

6 illus, 21 ref

017439   Chandra P;Ray A (Joint Astronomy Programme, IISc, Bangalore-560 012) : Baby supernovae through the looking glass at long wavelengths. Bull Astr Soc India 2004, 32(3), 223-30.

The importance of observations of young supernovae in wide radio band has been emphasized. It has been argued that on the basis of observational results that only high- or only low-frequency data is not sufficient to get full physical picture of the shocked plasma. In SN 1993J, the composite spectrum obtained with Very Large Array (VLA) and Giant Metrewave Radio Telescope (GMRT), around day 3200. Shows observational evidence of synchrotron cooling, which leads is to the direct determination of the magnetic field independent of the equipartition assumption, as well as the relative strengths of the magnetic field and relativistic particle energy densities. The GMRT low-frequency light curves of SN 1993J suggest the modification in the radio emission models developed on the basis of VLA data alone. The composite radio spectrum of SN 2003bg on day 350 obtained with GMRT plus VLA strongly supports internal synchrotron self absorption as the dominant absorption mechanism.

3 illus, 2 tables, 12 ref

017438   Bhattacharjee P (Indian Institute of Astrophysics, , Bangalore-560 034) : Neutrinos and origin of ultrahigh energy cosmic rays. Proc Indian Natn Sci Acad-Pt A 2004, 70(1), 135-44.

Ultra High Energy Cosmic Ray (UHECR) particles with energies exceeding 10²⁰ eV have been detected. The sources as well as the physical mechanism(s) responsible for endowing particles with such enormous energies are unknown. The existence of these extremely energetic particles is difficult to explain within the standard scenario in which charged particles are accelerated in powerful astrophysical sources and their interactions are governed by the Standard Model of particle physics. Here, after a brief review of the basic problems associated with the question of UHECR, author summarize some of the proposed ideas in the literature regarding the possible role of neutrinos in solving some of the problems associated with the question of UHECR origin. Two possible scenarios and constraints on those from UHECR are examined: The so-called "Z-burst" scenario involving massive neutrinos in the sub-eV mass range, and the scenario involving possible new (almost) strong interaction of neutrinos attributed to possible new fundamental physics (such as extra dimensions) at the highest energies of interest. The highest energy end of the cosmic ray spectrum can thus be used as a probe of possible new fundamental physics beyond Standard Model.

1 illus, 47 ref

017437   Begum a;Chengalur J N (National Centre for Radio Astrophysics, , Post Bag 3, Ganeshkhind, Pune-411 007) : GMRT study of extremely faint dwarf irregular galaxies. Bull Astr Soc India 2004, 32(3), 231-8.

Results of deep, high velocity resolution (<126>1.6 km s^-1) Giant Metrewave Radio Telescope (GMRT) HI 21 cm-line observations of a sample of extremely faint (M_B <62> -12.5) dwarf irregular galaxies have been presented. Unlike previous studies, large-scale velocity gradients have been found in even the faintest galaxies of the sample i.e. their velocity fields are not "chaotic". For some of the sample galaxies, where the velocity fields are in fact completely consistent with ordered rotation, rotation curves have been derived and the structure of the dark matter halos of the galaxies have been derived from mass modelling. using the "asymmetric drift" corrected rotation velocities. Finally, from literature a sample of galaxies with known dark matter distribution, estimated from HI synthesis observations have been compiled, and the results and their implications for hierarchical galaxy formation models have been discussed.

5 illus, 11 ref

015348   Subramanian P;Pujari B S;Becker P A (NO, Inter-Univ Center for Astronomy and Astrophysics, P.O Bag 4, Ganeshkhind, Pune-411 007, Email: psubrama@iucaa.ernet.in) : Angular momentum transport in Quasi-Keplerian Accretion disks. J Astrophys Astr 2004, 25(1-2), 81-91.

Authors re-examine arguments advanced by Hayashi & Matsuda (2001), who claim that several simple, physically motivated derivations based on mean free path theory for calculating the viscous torque in a Quasi-Keplerian accretion disk yield results that are inconsistent with the generally accepted model. If correct, the ideas proposed by Hayashi & Matsuda would radically alter our understanding of the nature of the angular momentum transport in the disk, which is a central feature of accretion disk theory. However, points out several fallacies in their arguments and show that there indeed exists a simple derivation based on mean free path theory that yields an expression for the viscous torque that is proportional to the radial derivative of the angular velocity in the accretion disk, as expected. The derivation is based on the analysis of the epicyclic motion of gas parcels in adjacent eddies in the disk.

1 illus, 12 ref

015347   Stalin C S;Gopal-Krishna;Sagar R;Wiita P J (NO, Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak Nainital-263 12) : Optical variability properties of high luminosity AGN classes. J Astrophys Astr 2004, 25(1-2), 1-55.

Presents the results of a comparative study of the intra-night optical variability (INOV) characteristics of radio-loud and radio-quiet quasars, which involves a systematic intra-night optical monitoring of seven sets of high luminosity AGNs. The sample, matched in the optical luminosity - redshift (M_B - <90>) plane, consists of seven radio-quiet quasars (RQQs), eight radio lobe-dominated quasars (LDQs), five radio core-dominated quasars (CDQs) and six BL Lac objects (BLs). Systematic CCD observations, aided by a careful data analysis procedure, have allowed us to detect INOV with amplitudes as low as about 1%. Present observations cover a total of 113 nights (720 hours) with only a single quasar monitored as continuously as possible on a given night. Considering the cases of only unambiguous detections of INOV we have estimated duty cycles (DCs) of 17%, 12%, 20% and 61% for RQQs, LDQs, CDQs, and BLs, respectively. The much lower amplitude and DC of INOV shown by RQQs compared to BLs may be understood in terms of their having optical synchrotron jets which are modestly misdirected from us. From fairly extensive dataset, no general trend of a correlation between the INOV amplitude and the apparent optical brightness of the quasar is noticed. This suggests that the physical mechanisms of INOV and long term optical variability (LTOV) do not have a one-to-one relationship and different factors are involved. Also, the absence of a clear negative correlation between the INOV and LTOV characteristics of blazars of our sample points toward an inconspicuous contribution of accretion disk fluctuations to the observed INOV. The INOV duty cycle of the AGNs observed in this program suggests that INOV is associated predominantly with the highly polarized optical emission components. Also reports new VLA imaging of two RQQs (1029 + 329 & 1252 + 020) in our sample which has yielded a 5 GHz detection in one of them (1252 + 020; S_{5 GHz} ≈ 1 mJy).

9 illus, 4 tables, 85 ref

015346   Chandra P;Govind Swarup;Kulkarni V K; Kantharia G (NO, Tata Institute of Fundamental Research, Mumbai-400 005) : Associated HI absorption in the z = 3.4 radio galaxy B2 0902 + 343 observed with the GMRT. J Astrophys Astr 2004, 25(1-2), 57-65.

Oservations were made of the associated HI absorption of a high redshift radio galaxy 0902+34 at z = 3.395 with the Giant Meterwave Radio Telescope in the 323 ± 1 MHz band. Authors finds narrow absorption line with a flux density of 11.5 mJy at a redshift of 3.397 consistent with that observed by Uson et al. (1991), Briggs et al. (1993) and de Bruyn (1996). A weak broad absorption feature reported by de Bruyn (1996) has not been detected in authors observations, also places an upper limit of 4 mJy (2σ) on emission line strength at the position where Uson et al. (1991) claimed to have found a narrow emission line.

4 illus, 3 tables, 14 ref

015345   Chakrabarty T N (Applied Physics Dep, Fr. Conceicao Rodrigeues College of Engineering, Fr. Agnel Ashram, Bandstand, Bandra (W), Mumbai-400 050, Email: tn_chakrabarty@yahoo.com) : Radial matrix elements of hydrogen atom and the correspondence principle. J Astrophys Astr 2004, 25(1-2), 93-101.

Radial dipole matrix elements having astrophysical importance have been computed for highly excited states of hydrogen atom. Computation is based on Heisenberg's form of correspondence principle for Coulomb potential. Particular attention has been paid to the choice of classical analogue (n_c) of principal quantum number (n). The computed radial matrix elements are in good agreement with quantum mechanical results. Further, radial matrix elements for few transitions involving high n neighboring states of hydrogen atom are presented.

4 tables, 11 ref

015344   Bharadwaj S;Srikant P S (Physics and Meteorology Dep and Center for Theoretical Studies, I.I.T., Kharagpur-721 302) : HI fluctuations at large redshifts: III - Simulating the signal expected at GMRT. J Astrophys Astr 2004, 25(1-2), 67-80.

Simulates the distribution of neutral hydrogen (HI) at the redshifts z = 1.3 and 3.4 using a cosmological N-body simulation along with a prescription for assigning HI masses to the particles. The HI is distributed in clouds whose properties are consistent with those of the damped Lyman-α absorption systems (DLAs) seen in quasar spectra. The clustering properties of these clouds are identical to those of the dark matter. Authors use this to simulate the redshifted HI emission expected at 610 MHz and 325 MHz, two of the observing bands at the GMRT. These are used to predict the correlations expected between the complex visibilities measured at different baselines and frequencies in radio-interferometric observations with the GMRT. The visibility correlations directly probe the power spectrum of HI fluctuations at the epoch when the HI emission originated, and this holds the possibility of using HI observations to study large-scale structures at high z.

6 illus, 2 tables, 27 ref

014281   Sharma U;Shrivastava P K (Physics Dep, A.P.S. University, Rewa-486 003) : Long-term cosmic ray modulation during odd and even solar cycles. Ultra Scient phys Sci 2004, 16(3), 399-402.

The relationship of cosmic ray intensity and sunspot number (Rz) are investigated by using their yearly mean values for the period of 1958 to 2003, covering the solar cycles 19 to 32. Systematic differences are noticed from results obtained for odd and even solar cycles. Correlation between cosmic rays and sunspot number (Rz) generate wider loops for odd solar cycles and narrow loops for even solar cycles.

3 illus, 8 ref

014280   Sharaf M A;Nouh M I;Sadd A S (Astronomy Dep, Faculty of Science, King Abdul Aziz University, Jeddah, Saudi Arabia) : Relation between a function of the right ascension and the angular distance to the vertex for hyades stars. J Astrophys Astr 2004, 25(3&4), 213-20.

In the paper, relation was developed for Hyades stars between a function of the right ascensions and the angular distances from the vertex. The precision criteria of this relation are very satisfactory and a correlation coefficient value of ~_- 1 was found which proves that the attributes are completely related linearly. The importance of this relation was illustrated through its usages as a criterion for membership of the cluster, a generating function for evaluating some parameters of the cluster, and a generating function for the initial values of the vertex equatorial coordinates which could then be improved iteratively using the procedure of differential corrections.

11 ref

014279   Rekhesh Mohan;Dwarakanath K S;Srinivasan G (NO, Indian Institute of Astrophysics, Bangalore-560 034, Email: reks@iiap.res.in) : A high galactic latitude HI 21 cm-line absorption survey using the GMRT: II. Results and interpretation. J Astrophys Astr 2004, 25(3&4), 185-201.

Sensitive high-latitude (|b|<62>15°) HI 21 cm-line absorption survey have been carried out towards 102 sources using the GMRT. With a 3σ detection limit in optical depth of ~0.01, this is the most sensitive HI absorption survey. Detected 126 absorption features most of which also have corresponding HI emission features in the Leiden Dwingeloo Survey of Galactic neutral Hydrogen. The histogram of random velocities of the absorption features is well-fit by two Gaussians centered at V_lsr~0 km s^-1 with velocity dispersions of 7.6 ± 0.3km s^-1 and 21 ± 4km s^-1 respectively. About 20% of the HI absorption features form the larger velocity dispersion component. The HI absorption features forming the narrow Gaussian have a mean optical depth of 0.20 ± 0.19, a mean HI column density of (1.46 ± 1.03) x 10²⁰cm^-2, and a mean spin temperature of 121 ± 69 K. These HI concentrations can be identified with the standard HI clouds in the cold neutral medium of the Galaxy. The HI absorption features forming the wider Gaussian have a mean optical depth of 0.04±0.02, a mean HI column density of (4.3±3.4)xl0¹⁹cm^-2, and a mean spin temperature of 125±82 K. The HI column densities of these fast clouds decrease with their increasing random velocities. These fast clouds can be identified with a population of clouds detected so far only in optical absorption and in HI emission lines with a similar velocity dispersion. This population of fast clouds is likely to be in the lower Galactic Halo.

10 illus, 40 ref

014278   Rekhesh Mohan;Dwarakanath K S;Srinivasan G (NO, Indian Institute of Astrophysics, Bangalore-560 034, Email: reks@iiap.res.in) : A high galactic latitude HI 21 cm-line absorption survey using the GMRT: I. Observations and spectra. J Astrophys Astr 2004, 25(3&4), 143-83.

The Giant Meterwave Radio Telescope (GMRT) was used to measure the Galactic HI 21-cm line absorption towards 102 extragalactic radio continuum sources, located at high (lbl<62> 15°) Galactic latitudes. The Declination coverage of the survey is δ<62>~-45°. With a mean rms optical depth of ~0.003, this is the most sensitive Galactic HI 21-cm line absorption survey to date. To supplement the absorption data, HI 21-cm line emission profiles towards these 102 lines of sight from the Leiden Dwingeloo Survey of Galactic neutral hydrogen. Gaussian fitting analysis was carried out to identify the discrete absorption and emission components in these profiles. In the paper, the spectra and the components are presented.

2 illus, 1 table, 24 ref

014277   Ray S (NO, Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad-211 019, Email: surya@mri.emet.in) : TreePM method for two-dimensional cosmological simulations. J Astrophys Astr 2004, 25(3&4), 103-13.

Two dimensional TreePM method has been described. The 2d TreePM code is an accurate and efficient technique to carry out large two-dimensional N-body simulations in cosmology. This hybrid code combines the 2d Barnes and Hut Tree method and the 2d Particle-Mesh method. Splitting of force between the PM and the Tree partsand Estimate error in force for a realistic configuration have been discussed including some tests of the code.

3 illus, 25 ref

014276   Lin-sen Li (Physics Dep, Northeast Normal University, Changchun-130 024) : An apparent descriptive China method for judging the synchronization of rotation of binary stars. J Astrophys Astr 2004, 25(3&4), 203-11.

The problem of the synchronous rotation of binary stars is judged by using a synchronous parameter Q introduced in an apparent descriptive method. The synchronous parameter Q is defined as the ratio of the rotational period to the orbital period. The author suggests several apparent phenomenal descriptive methods for judging the synchronization of rotation of binary stars. The first method is applicable when the orbital inclination is well-known. The synchronous parameter is defined by using the orbital inclination i and the observable rotational velocity (V_1,2 sin i)_M The method is mainly suitable for eclipsing binary stars. Several others are suggested for the cases when the orbital inclination is unknown. The synchronous parameters are defined by using a_1,2 sin i, m_1,2 sin³ i, the mass function f(m) and semi-amplitudes of the velocity curve, K_1,2 given in catalogue of parameters of spectroscopic binary systems and (V_1,2 sin i)_M. These methods are suitable for spectroscopic binary stars including those that show eclipses and visual binary stars concurrently. The synchronous parameters for fifty-five components in thirty binary systems are calculated by using several methods. The numerical results are listed in Tables 1 and 2. The statistical results are listed in Table 3. In addition, several apparent descriptive methods are discussed.

3 tables, 16 ref

014275   Kundt W;Gopal Krishna (NO, IfA of Bonn University, Auf dem Huegel-71, D-53121, Bonn, Email: wkundt@ astro.uni-bonn.de) : The physics of E x B-Drifting Jets. J Astrophys Astr 2004, 25(3&4), 115-27.

E x B-drifting jets have been generally ignored for the past 25 years even though they may well describe all the astrophysical jet sources, both on galactic and stellar scales. Here author present closed-form solutions for their joint field-and-particle distribution, argue that the observed jets are near equipartition, with extremely relativistic, monoenergetic e^±-pairs of bulk Lorentz factor χ~<60>10⁴, and are first-order stable. Authors describe plausible mechanisms for the jets' formation, propagation, and termination. Wherever a beam meets with resistance, its frozen-in Poynting flux transforms the delta-shaped energy distribution of the pairs into an almost white power law, E²Ne~<62> E^ε with ε0, via single-step falls through the huge convected potential.

3 illus, 53 ref

014274   Dwarakanath K S;Goss W M;Zhao J H;Lang C C (NO, Raman Research Institute, Sadashivanagar, Bangalore-560 080, Email: dwaraka@rri.res.in) : On the origin of the wide HI absorption line towards Sgr A. J Astrophys Astr 2004, 25(3&4), 129-41.

A region has been imagined of ~5' extent surrounding Sgr A* in the HI 21 cm-line absorption using the Very Large Array. A Gaussian decomposition of the optical depth spectra at positions within ~2' ~5 pc at 8.5 kpc) of Sgr A* detects a wide line underlying the many narrow absorption lines. The wide line has a mean peak optical depth of 0.32 ± 0.12 centered at a mean velocity of V_lsr = -4± 15km s^-1. The mean full width at half maximum is 119 ± 42 km s^-1. Such a wide line is absent in the spectra at positions beyond ~2' from Sgr A*. The position-velocity diagrams in optical depth reveal that the wide line originates in various components of the circumnuclear disk (radius ~1.3 ) surrounding Sgr A*. These components contribute to the optical depth of the wide line in different velocity ranges. The position-velocity diagrams do not reveal any diffuse feature which could be attributed to a large number of HI clouds along the line of sight to Sgr A*. Consequently, the wide line has no implications either to a global population of shocked HI clouds in the Galaxy or to the energetics of the interstellar medium as was earlier thought.

9 illus, 18 ref

013214   Souradeep T (NO, Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune-411 007, Email: tarun@iucaa.emet.in) : Summary of cosmology workshop. Pramana J Phys 2004, 63(4), 891-903.

Cosmology is passing through a golden phase of rapid advance. The cosmology workshop at ICGC-2004 attracted a large number of research contributions to diverse topics of cosmology. I attempt to classify and summarize the research work and results of the oral and poster presentations made at the meeting.

4 illus, 34 ref

013213   Sood N K;Singh K (Physics Dep, Guru Nanak Dev University, Amritsar-143 005) : Equilibrium of self gravitating polytropes. Proc Natn Acad Sci India-Sect A 2004, 74(Pt III), 353-60.

The equilibrium of a self gravitating cylindrical polytrope with a general magnetic field and rotation has been discussed.

5 illus, 7 ref

013212   Shrivastava P;Shrivastava P (Physics Dep, Government New Science College, Rewa-486 001) : Relationship between cosmic rays and geomagnetic activity during Forbush decrease events of February and August, 1999. Proc Natn Acad Sci India-Sect A 2004, 74(Pt III), 361-7.

Transient decrease in cosmic ray intensity followed by a slow recovery is called a Forbush decrease event in cosmic ray studies. Such two Forbush decrease events were noted first in August 19 to 29, 1999 another in February 15 to 23, 1999, which occured during high solar activity period of solar cycle 23. It is noteworthy that both the events were accompanied with several intense solar flares and geomagnetic storms, Systematic study has been carried out to derive relationship between cosmic ray decrease and increase in geomagnetic activity. Significant relationship between cosmic ray intensity and decreasing profile of Dst values. Results of analysis indicate a strong relationship between geomagnetic activity and cosmic ray intensity on short-term basis.

5 illus, 9 ref

013211   Sharan A M;Balasubramaniam R (NO, Memorial Newfoundland Univ, Newfoundland, Canada A1B 3X5) : Data of sanakanika inseription and its astronomical significance for archaeological structures at Udayagiri. Curr Sci 2004, 87(11), 1562-6.

The historical importance of the original location of the Delhi Iron Pillar, namely Udayagiri, has been briefly introduced. The specific date mentioned in the Sana-kanika inscription of cave 6 has been analysed and its date determined according to modern calendar. This day was 26 June 402 AD, close to the summer solstice of that year (22 June). The angle of cut of the most important passageway at Udayagiri was specially designed based on astronomical calculations. There is no shadow along the passageway at noon only in the period around summer solstice. The early morning sunlight falls along the passageway, only in the time period around the summer solstice. This study proves the advanced state of astronomical knowledge that existed during the time of Chandragupta II Vikramaditya (AD 375-414).

2 tables, 17 ref

013210   Rahman M M;Zakaria M (Physics Dep, Solar Radiation Lab, University of Rajshahi, Rajshahi-6205, Bangladesh) : Modified Angstrom coefficients for the sunshine-irradiation Correlation. Indian J Radio Space Phys 2005, 34(1), 33-41.

Model parameters are achieved very often by the least square method (LSM) and regression technique between irradiation and bright sunshine data. A new variance method (VRM) is used for finding the modified Angstrom coefficients (a, b) using the same set of data. Some other methods (such as latitude method {LM), Reitveld method (RVM) etc.), which are dependent on geographical as well as meteorological parameters, are also employed in this work. The study of levels of performance of these methods shows that the VRM and LSM predict the global solar radiation H with better accuracy than other methods. The index of agreement d indicates a little better performance of VRM over LSM. Latitude method (LM) does not give satisfactory results at lower latitude φ of the site. Analysis shows that the LM might be applicable for the latitudes ≥10°N safely with a maximum deviation of 6 % where only the sunshine data are available. Polynomial behaviour of the sunshine-irradiation relationship along with the linear form is also studied to know actually which form belongs to them.

1 illus, 5 tables, 33 ref

013209   Ostriker J P;Souradeep T (Astrophysical Sciences Dep, Peyton Hall, Princeton University, Princeton, NJ 08544, USA, Email: jpo@astro.princeton.edu) : The current status of observational cosmology. Pramana J Phys 2004, 63(4), 817-28.

Observational cosmology has indeed made very rapid progress in recent years. The ability to quantify the universe has largely improved due to observational constraints coming from structure formation. The transition to precision cosmology has been spearheaded by measurements of the anisotropy in the cosmic microwave background (CMB) over the past decade. Observations of the large scale structure in the distribution of galaxies, high red-shift supernova, have provided the required complementary information. We review the current status of cosmological parameter estimates from joint analysis of CMB anisotropy and large scale structure (LSS) data. We also sound a note of caution on overstating the successes achieved thus far.

3 illus, 2 tables, 38 ref

013208   Mishra V K;Tiwari D P;Agrawal S P (Physics Dep, A P S University, Rewa-486 003, Email: vkmishra74@yahoo.com) : Comparative study of different solar parameters with sunspot numbers. Indian J Radio Space Phys 2005, 34(1), 13-6.

Based on the monthly data of various solar parameters e.g. sunspot numbers (SSN), sunspot area, grouped solar flares (GSF) and solar flare index (SFI) for the last four solar cycles (19 to 22) as well as for the present cycle 23 (up to year 2003), a detailed correlative study has been performed. It has been found that, on monthly average basis, the SSN are highly correlated with other solar parameters and hence, SSN can be safely used as a solar parameter for any correlative study, until and unless there are some specific reasons to use other easily available solar parameters (or indices). Moreover, it was found that with the progression of solar cycle, from cycle 20 to 23 the slope of the regression line between SSN and GSF or SFI decreases continuously. However, no such unidirectional change is observed in the correlation coefficient.

2 illus, 17 ref

013207   Majumdar S (CITA, University of Toronto, Toronto, ON, M5S 3H8, Canada, Email: subha@cita.utoronto.ca) : Cosmology with cluster surveys. Pramana J Phys 2004, 63(4), 871-5.

Surveys of clusters of galaxies provide us with a powerful probe of the density and nature of the dark energy. The red-shift distribution of detected clusters is highly sensitive to the dark energy equation of state parameter ω. Upcoming Sunyaev-Zel'dovich (SZ) surveys would provide us large yields of clusters to very high red-shifts. Self-calibration of cluster scaling relations, possible for such a huge sample, would be able to constrain systematic biases on mass estimators. Combining cluster red-shift abundance with limited mass follow-up and cluster mass power spectrum can then give constraints on ω, as well as on σ₈ and Ω_M to a few per cents.

2 illus, 21 ref

013206   Kaplinghat M (Physics Dep, University of California, One Shields Ave, Davis, CA 95616, USA, Email: kaplinghat@ucdavis.edu) : Early reionization and its cosmological implications. Pramana J Phys 2004, 63(4), 865-9.

We discuss how future CMB polarization measurements will provide detailed information about the reionization history and the implications of early reionization for cosmology.

1 illus, 16 ref

013205   Kane R P (NO, Instituto Nacional de Pesquisas Espacias, Sao Jose dos Campos, Sao Paulo, Brazil, Email: kane@laser.inpe.br) : Proxies for solar RUV in cycle 23. Indian J Radio Space Phys 2004, 33(4), 215-22.

For daily values in a strong 27-day sequence, lasting for more than 8 months, correlations of solar EUV with solar FG₁₀ radio emision were, sometimes, found to be lower than those with solar Mg II core-to-wing index, sometimes higher, and sometimes almost the same. Correlations of EUV with the UC Si III and Lyman-α were found to be mostly higher than those with F₁₀ and Mg II. In contrast to the correlations for long-term changes (0.95 or more), the maximum correlations for short-term changes (daily values) were only -0.80, implying an explained variance of only -65%, leaving -35% unexplained. Hence, estimates of daily EUV using F₁₀ and Mg II as proxies could have uncertainties of several tens of percent. For intermediate and long-term changes, EUV was very highly correlated with F₁₀, Mg II and Lyman-α (and to some extent even with sunspots) during years of low and medium sunspot activity (1996-1999) of cycle 23. The Mg II had a slight supriority over F₁₀, but both could be considered as good proxies for EUV. However, for the sunspot maximum years 2000-2002, the EUV evolution differed from the evolutions of F₁₀

3 illus, 3 tables, 21 ref

013204   Harada T (Astronomy Unit, School of Mathematical Sciences, Queen Mary, University of London, Mile End Road, London El 4NS, UK, Email: T.Harada@qmul.ac.uk) : Gravitational collapse and naked singularities. Pramana J Phys 2004, 63(4), 741-53.

Gravitational collapse is one of the most striking phenomena in gravitational physics. The cosmic censorship conjecture has provided strong motivation for research in this field. In the absence of a general proof for censorship, many examples have been proposed, in which naked singularity is the outcome of gravitational collapse. Recent developments have revealed that there are examples of naked singularity formation in the collapse of physically reasonable matter fields, although the stability of these examples is still uncertain. We propose the concept of 'effective naked singularities', which will be quite helpful because general relativity has limitation in its application at the high-energy end. The appearance of naked singularities is not detestable but can open a window for the new physics of strongly curved space-times.

8 illus, 45 ref

013203   Gupta P D (Physics and Astrophysics Dep, University of Delhi, Delhi-110 007, Email: patrickdasgupta@yahoo.co.uk) : Workshop on gravitational waves and relativistic astrophysics. Pramana J Phys 2004, 63(4), 877-82.

Discussions related to gravitational wave experiments viz. LIGO and LISA as well as to observations of supermassive black holes dominated the workshop sessions on gravitational waves and relativistic astrophysics in the ICGC-2004. A summary of seven papers that were presented in these workshop sessions has been provided in this article.

4 ref

013202   Faber J;Grandclement P;Rasio F (Physics and Astronomy Dep, Northwestern University, Evanston, IL 60208-0834, USA, Email: rasio@mac.com) : Relativistic calculations of coalescing binary neutron stars. Pramana J Phys 2004, 63(4), 837-43.

We have designed and tested a new relativistic Lagrangian hydrodynamics code, which treats gravity in the conformally flat approximation to general relativity. We have tested the resulting code extensively, finding that it performs well for calculations of equilibrium single-star models, collapsing relativistic dust clouds, and quasi-circular orbits of equilibrium solutions. By adding a radiation reaction treatment, we compute the full evolution of a coalescing binary neutron star system. We find that the amount of mass ejected from the system, much less than a per cent, is greatly reduced by the inclusion of relativistic gravitation. The gravity wave energy spectrum shows a clear divergence away from the Newtonian point-mass form, consistent with the form derived from relativistic quasi-equilibrium fluid sequences.

4 illus, 19 ref

013201   Engavale B;Bhattacharyya A (NO, Indian Institute of Geomagnetism, New Panvel, New Mumbai-410 218) : Spatial Correlation function of intensity variations in the ground scintillation pattern produced by equatorial spread-F irregularities. Indian J Radio Space Phys 2005, 34(1), 22-32.

A theoretical model is used to relate the spatial variations found in intensity scintillation patterns formed on the ground due to scattering of VHF radio waves by equatorial ionospheric irregularities, with the spatial structure of these irregularities. As equatorial ionospheric irregularities are closely aligned with the geomagnetic field, they may be considered to constitute a two-dimensional dispersive random medium. Electron density variations, which produce refractive index irregularities in the medium, are assumed to be characterized by a power law spectrum. A numerical solution of the equation satisfied by the fourth moment of intensity variations, in the plane of the receiver, is obtained using the split step method. The S₄-index, which is the standard deviation of normalized intensity variations as well as spatial correlation function of intensity, is obtained by considering special cases of the fourth moment of intensity variations. Variation of S₄-index with the standard deviation of phase fluctuations imposed by the ionospheric irregularities is studied for irregularities with different power spectral indices. Effect of varying phase fluctuations on the 50% de-correlation scale length is also studied for weak as well as strong scintillations. The S₄-index and spatial scale lengths in the ground scintillation pattern depend on parameters like thickness and height of the irregularity layer, background plasma density, standard deviation of electron density fluctuation and irregularity power spectrum. The theoretical model is used to understand the roles of these parameters in determining the S₄-index and spatial correlation function of intensity in the ground scintillation pattern.

8 illus, 17 ref

013200   Crittenden R G (NO, Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth PO1 2EG, UK, Email: robert.crittenden@port.ac.uk) : What have we learnt from Wilkinson microwave anisotropy probe?. Pramana J Phys 2004, 63(4), 829-36.

It has been a little over a year since WMAP produced its dramatic new glimpse of the cosmic microwave background. I review the results of the WMAP mission and the science that has arisen from it, focusing on the qualitatively new features of the data: the temperature-polarization correlation, correlations with large scale structure, the large-scale power deficit and its implications, and the search for non-Gaussianity.

35 ref

009162   Indumathi D (Institute of Mathematical Sciences, , Chennai-600 113) : From neutrons to neutrinos: On the trail of solar fusion and terrestrial fission. Curr Sci 2003, 85(12), 1662-4.

7 ref

007198   Singh N;Tiwari D P;Tiwari C M;Shrivastava P K (Department of Physics, A P S University, Rewa 486 003) : Solar longitudinal distribution of solar flares in association with forbush decreases. Acta Cienc Indica-Phys 2004, 30(2), 209-12.

Solar flare events have been utilized to study the longitudinal frequency distribution of solar flares in eastern and western hemisphere of sun. A statistical study has been performed to obtain their relationship with Sudden Storms Commencements (SSCs) and Forbush decreases (Fds). Almost equal distribution of solar flares in both the eastern and western are found in association with SSCs. In further analysis, it has been noted that larger number solar flares located in western hemisphere are found responsible in producing Fds alongwith SScs in comparison to western hemisphere.

4 illus, 4 ref

006240   Ramasubramanian k;Sriram M S (Theoretical Phys Dep, Univ of Madras, Guindy Campus, Channai-600 025) : Corrections to the terrestrial latitude in tantrasangraha. Indian J Hist Sci 2003, 38(2), 129-44.

The terrestrial latitude of an observes location is equal to the zenith distance of the sun at noon on the equinoctial day. The effect of solar parallax on the zenith distance of the sun was known to the Indian astronomers right from Aryabhata, but none of the astronomers prior to Nilakantha Somayaji (c. 1500 AD) discussed its effect on the measurement of the observers latitude. In his Tantrasangraha Nilakantha states not only about this correction but also explicity gives its magnitude. He also prescribes a correction due to the finite size of the sun. A detailed explanation of these corrections appears in Yuktidipika, a commentary on the Tantrasan graha by Sankara Varier.

3 ills

006239   Iyengar R N (Civil Engg Dep, Indian Inst of Sci, Bangalore-560 012) : Internal consistency of eclipses and planetary positions of Mahabharata. Indian J Hist Sci 2003, 38(2), 77-115.

The ancient intellectual tradition of India holds that the epic Mahabharata reports part of its national history. However historicity of key personalities like Krsna has dependent more on an unbroken tradition, rather than on archaeological evidences. The single most important physical source available for present-day study is the text of Mahabharata itself. It is unlikely that later reciters and copyists of the epic would have tampered with descriptions of natural phenonena like eclipses, even though transcription and transmission errors cannot be rules out. Hence, such celestial observations would become the most important physical evidences if they can be scientifically investigated and dated. Planetarium softwares are powerful tools for computer-based searching of thousands of possibilities and for sifting through obscure texts on celestial events. Such an exercies in archaeo-astronomy leads us to the conclusion that the eclipses and planetary observations of Mahabharata should belong to the period 1493 BC-1443 BC of Indian history.

4 illus, 7 tables, 10 ref