003225   Santosh Kumar;Agarwal R;Mishra R;Dubey S K (P G Studies and Research in Physics and Electronics Dep, Rani Durgawati University, Jabalpur-482 001) : Solar poloidal magnetic field orientation causing periodicity in daily variation of cosmic ray intensity. Bull Astr Soc India 2002, 30(2), 451-60.

A detailed analysis of the Deep River neutron monitor (NM) data for four different phases of solar activity cycle and for four groups of days chosen according to their different geomagnetic conditions is being carried out. It is found that the 60 quiet day (QD) in a year serve a better purpose for investigating the short/long term variation in cosmic ray (CR) intensity. Further, data has been harmonically analysed for the period 1964-95 to investigate the effect of solar poloidal magnetic field (SPMF) orientation in daily variation (diurnal/semi-diurnal) of CR on geomagnetically QD. The phase of the diurnal and semi-diurnal anisotropy vectors on QD has shown a significant shift to early hours when the SPMF in the northern hemisphere (NH) is positive during the periods 1971-79 and 1992-95 as compared to that during the periods 1964-70 and 1981-90 when the SPMF in NH is negative, showing a periodic nature of daily variation in CR intensity with SPMF.

7 illus, 27 ref

003224   Sankarasubramanian K;Rangarajan K E;Ramesh K B (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Measurement of solar vector magnetic fields using the Kodaikanal Tower Telescope. Bull Astr Soc India 2002, 30(2), 473-90.

A stokes polarimeter was built as the Kodaikanal Tower Telescope to study the vector field map of active regions like sunspot using the well known Fe I lines 6301.5 <200> lines and 6302.5 <200> lines. The Mueller matrix of the polarimeter was obtained using simple laboratory and field tests. The instrumental polarisation due to the oblique reflections are removed before the observed Stokes profiles were analysed. The advanced Stockes polarimeter data analysis program (ASP code) was used to invert the corrected Stockes profiles to calculate the vector magnetic field parameters of NOAA 8951. The maximum field strength obtained at the umbra of the sunspot was 2500 Gauss. The variation of the field strength, the line-of-sight angle and the azimuthal angle along a cut which passes through the umbra resembles that of a simple round sunspot. The accuracy in the calculation of the vector field is high in the umbra and low in the outer edge of the penumbra of the observed sunspot. The range of errors in the calculation of the field strength, line-of-sight inclination angle, and the azimuthal angle of the magnetic vector are 20-100 Gauas, 1-5°, and 12-20° respectively. Finds a good fit for the observed Stokes profiles of the Ti I line at 6303.78 with a synthetic profile produced using the vecor field parameters derived from the Fe I 6301.5 and 6302.5 lines.

11 illus, 22 ref

003223   Saha S K;Chinnappan V (NO, Indian Institue of Astrophysics, bangalore-560 034) : Performance of the low light level CCD camera for speckle imaging. Bull Astr Soc India 2002, 30(3), 819-20.

A new generation CCD detector called low light level CCD (L3CCD) that performs like an intensified CCD without incorporating a micro channel plate (MCP) for light amplification was procured and tested. A series of short exposure images with millisecond integration time has been obtained. The L3CCD is cooled to about -80° C by Peltier cooling.

5 ref

003222   Saha S K;Chinnappam V;Yeswanth L;Anbazhagan P (NO, Institute of Astrophysics, Bangalore-560 034) : Speckle interferometric observations of close binary stars. Bull Astr Soc India 2002, 30(3), 677-8.

Speckle interferometric technique is employed to record a series of hundreds of short-exposure images of several close binary stars with sub-arcsecond separation through a narrow band filter at the Cassegrain focus of the 2.34 meter (m) Vainu Bappu Telescope (VBT), situated at Vinu Bappu Observatory (VBO), Kavalur, India. The data are recorded sequentially by a Peltier-cooled intensified CCD camera with 10 ms exposure. The auto-correlation method is applied to determine the angular separations and position angles of these binary systems.

1 illus, 6 ref

003221   Rukmini J;Vivekananda Rao P (Centre of Advanced Study in Astronomy, Osmania University, Hyderabad-500 007) : Photometric study of two W Uma-type systems in the intermediate age open cluster Be 33. Bull Astr Soc India 2002, 30(3), 665-70.

Study of eclipsing binaries in open cluster offers information regarding the age of the cluster in addition to the properties of the component stars. Presents the analysis of two W UMa systems discovered in the open cluster Be 33 using the Wilson - Devinney method.

2 illus, 2 tables, 12 ref

003220   Roy S (NO, National Centre for Radio Astrophysics (TIFR, Pune University Campus, Post Bag No 3, Gameshkhind, Pune-411 007) : Radio study of the galactic centre environment. Bull Astr Soc India 2002, 30(3), 637-42.

The central region of our milky way Galaxy still eludes a comprehensive understanding. With new observations, however, are being able to know manyof the observable properties of the sources, which allow to better understand the actual physical processes operating in the region. Discuss about the present status and the new observations in the radio wavelengths to constrain the source properties in this comlex region.

3 illus, 16 ref

003219   Rannot R C at al (Bhabha Atomic Research Centre, Nuclear Research Laboratory, Mumbai-400 085) : Search for pulsed TeV gamma- rays from Crab pulsar with the TACTIC imaging gamma-ray telescope. Bull Astr Soc India 2002, 30(3), 699-700.

The TACTIC Imaging Element has observed Crab Nebula/pulsar for a total of about 40 hours during Jan - Mar. 2001. Preliminary results do not show any evidence of the 33 ms pulsations from the pulsar direction at an energy threshold of 1 TeV. The 99.9% confidence level upper limit for pulsed emission has been derived to be ≤ 22% of the steady flux from the Crab Nebula.

1 illus, 6 ref

003218   Poonam Chandra;Ray A;Bhatnagar S (NO, IISc, Bangalore-560 012) : Radio studies of young core collapse supernovae. Bull Astr Soc India 2002, 30(3), 755-8.

Multi-frequency observations of two radio bright SNe (SN1993J, SN1979C) carried out over a year with GMRT are presented. Their radio light curves trace the evolution of the mass loss in the stellar wind before the presupernova star exploded. Their spectra at low frequencies distinguish between the synchrotron self-absorption and free-free absorption based models. Two very similar type IIp SN1999gi and SN1999em were also observed and comnent on their progenitor mass. These observations of different subclasses of core-collapse supernovae will aid in defining their progenitors.

2 illus, 3 tables, 6 ref

003217   Patil M K;Sahu D K;Pandey S K;Kembhavi A K; Joshi U C;Baliyan K S;Mahendra Singh (School of Physical Sciences, S R T M University, Nanded-431 606) : Dust properties in early-type galaxies. Bull Astr Soc India 2002, 30(3), 759-60.

1 illus, 1 table, 6 ref

003216   Pandey V N;Oozeer N;Udaya Shanker;Somanah R (NO, Raman Research Institute, Sadashivanagar, Bangalore-560 080) : Full resolution deconvolved images from the Mauritus Radio Telescope. Bull Astr Soc India 2002, 30(3), 773-4.

2 ilus

003215   Omar A;Dwarakanath K S;Anantharamaiah K R (NO, Raman Research Institute, Bangalore-560 080) : A GMRT H I imaging survey of the ERIDANUS group of galaxies. Bull Astr Soc India 2002, 30(3), 749-50.

Aims to image a subset of galaxies in the nearby Eridanus group in H I emission and in radio continuum using the GMRT. The typical resolution of H I images well be <126> 1 kpc with a 3σ sensitivity to H I mass of a few times 10⁷ M. The rotation curves obtained using the H I velocity field together with the 2MASS magnitudes in the near infrared will be used to construct the Tully-Fisher relation for this group. High resolution (sub-kpc) multi-frequency radio continuum images will be used to study star-formation rates, radio morphologies and spectral indices of Eridanus galaxies. About half of the galaxies have already been observed and further observations on some late type galaxies are proposed with the GMRT. Presents here the H I image and the rotation curve for a member of this group viz. NGC 1385.

1 illus, 1 ref

003214   Omar A;Chengalur J N;Roshi D A (NO, Raman Research Institute, Bangalore) : The electron temperatures of HII regions S 201, S 206 and S 209 : multi-frequency GMRT observations. Bull Astr Soc India 2002, 30(3), 705-6.

Three Galactic HII regions, viz.,S 201, S 206 and S 209 have been imaged at three frequencies, viz., 232, 327, and 610 MHz using the GMRT. The resolutions of these images are typically 15" at 232, 10" at 327, and 6" at 610 MHz. These are the highest resolution low frequency images of these HII regions. Finds that all three HII regions have core-envelope morphologies. Uses the high resolution afforded by the data to estimate the electron temperatures of the compact cores of these HII regions. These estimates of the electron temperatures are consistent with an increase in the temperature with Galacto-centric distance; an effect attributed to a decrease in the heavy elements abundances at large galacto-centric distances.

1 illus, 4 ref

003213   Ojha D K;Ghosh S K;Verma R P;Chakraborti A; Anandarao B G (NO, Tata Institute of Fundamental Research, Mumbai-400 005) : First light observations with TIFR near-infrared camera. Bull Astr Soc India 2002, 30(3), 827-8.

The TIFR near-infrared camera (TIRCAM) is based on the SBRC InSb focal plane array (58x62 pixels) sensitive between 1-5 μm. TIRCAM had it s first engineering run at Gurusikhar 1.2 meter PRL telescope at Mount Abu during March-April 2001. The first light observations with TIRCAM were quite successful. Several infrared standard stars and the Trapezium Cluster in Orion region were observed in the J, H and K bands. In a narrow band at 3.9 μm (nbL), some bright stars could be detected from the Gurusikhar site. The performance of TIRCAM is discussed in the light of preliminary observations in nbL band.

1 illus, 1 table

003212   Ojha D K;Ghosh S K;Verma R P (NO, Tata Institute of undamental Research, Mumbai-400 005) : Far-infrared study of a few southern Galactic star forming regions. Bull Astr Soc India 2002, 30(3), 647-8.

Simultaneous far-infrared observations at 130 and 200 μm of the southern Galactic star forming regions (associated with IRAS 12326-6245, IRAS 17059-4132, IRAS 17160-3707 and IRAS 17233-3606) have been carried out using the TIFR 100 cm balloon-borne telescope. These far-infrared maps have a resolution of <126> 1 arc min and show extended emission. Nearly identical beams in the two far-infrared bands have enabled us to determine the dust temperature and optical depth distribution in the star forming regions. The TIR bands are sensitive to the distribution of cold (<60> 30 K) dust. HIRES processed images in four IRAS bands at 12, 25, 60 and 100 μm and the mid-infrared images from the MSX mission at 8.3, 12.1, 14.7 and 21.3 μm have also been compared. Radiative transfer models have been explored to fit available observations (viz. SED, angular size, etc) to extract various physical parameters of these star forming regions.

1 illus, 4 ref

003211   Narayan C A;Jog C J (Physics Dep, Indian Institute of Science, Bangalore-560 012) : Vertical scaleheights of stars and gas in the galaxy. Bull Astr Soc India 2002, 30(3), 703-4.

The vertical scaleheight of atomic hydrogen gas in observed to be nearly constant with radius in the iner Galaxy (<60> 8.5 kpc). This has been a long-standing puzzle (Oort 1962) because the gas scaleheight should increase exponentially with radius as a response to the decreasing gravitational potential of the stellar disk alone. Treats the stars, H I and H₂ as three gravitationally coupled components in the Galactic disk and find their scaleheights as a function of galactocentric radius. This approach not only explains the near-constancy of H I scaleheight but also reproduces the observed scaleheight variation for H2 and stars in the Galaxy.

2 illus, 7 ref

003210   Narasimha D (NO, Tata Institute of Fundamental Research, Mumbai-400 005) : Time delay in gravitational lens systems and cosmological parameters. Bull Astr Soc India 2002, 30(3), 723-8.

The time delay between the multiple images in gravitational lens systems is affected by large scale mass distribution in the lens, even though it might not have observable effects on the macro images. Inhomogeneity at very small scale will not directly affect the time delay but will influence the models of mass distribution in the lens galaxy. how this degeneracy can be eliminated is described. A method to determine time delay based on smoothed cubic splines is explained. The value of the Hubble Constant, inferred from the time delay in 5 well-constrained lens systems is 56±8 km s^-1 Mpc^-1.

1 table, 18 ref

003209   Mondal S;Chandrasekhar T;Kikani P K (NO, Physical Research laboratory, Ahmedabad-380 009) : A remote-controlled fast infrared photometer for simultaneous lunar occultation observations in K and L bands - successful observations of two M3 giants. Bull Astr Soc India 2002, 30(3), 811-3.

Details of successful use of a new high speed infrared photometer for recording lunar occultation light curves simultaneously in K (2.2 μm) and L (3.6 μm) bands are presented. The photometer has also a provision to incorporate a CCD in its light path for quick monitoring and positioning of the optical/IR sources. A motorized flip mirror arrangement for 45° angular movement using stepper motor controlled drive has been put into operation. The change from optical to IR channels can also be triggered by remote control using a radio frequency transmitter-receiver system. lunar occulation observation of two M3 giants η Gem and μ Gem in K and L bands heve been successfully observed.

2 illus, 1 table, 1 ref

003208   Mondal S;Chandrasekhar T (NO, Physical Research Laboratory, Ahmedabad-380 009) : High angular resolution structures in the dust shell surronding WR 104 from lunar occultation observations at 2.2 μm. Bull Astr Soc India 2002, 30(3), 661-4.

A rare event of lunar occulation of a Wolf-Rayet star (WR 104) in the near IR K-band (2.2 mcron) is reported. Analysis of the occulation light curve shows a fully resolved dust envelope departing significantly from a uniform disk profile. Reports three major peaks in derived brightness profile. Results of the dust structure are in good agreement with contemporaneous aperture masking interferometry carried out at the Keck I 10m telescope which shows a pinwheel dust structure around WR 104.

1 illus, 7 ref

003207   Mohan A;Dwivedi B N (Applied Physics Dep, Institute of Technology, Banaras Hindu University, Varanasi-221 005) : EUV diagnostics for boron-like ions from spectra obtained by SUMER/SOHO. Bull Astr Soc India 2002, 30(3), 589-90.

1 illus, 9 ref

003206   Mishra S;Anandarao B G;Ojha D K (NO, Physical Research Laboratory, Ahmedabad-380 009) : A near-infrared study of the massive young star IRAS 02230+6202 and its surroundings. Bull Astr Soc India 2002, 30(3), 643-5.

^ssc1 illus, 8 ref

003205   Mekkaden M V (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Search for activity signature in T Tauri stars. Bull Astr Soc India 2002, 30(3), 613-22.

T Tauri stars are young, low mass, pre-main sequence stars. They exhibit a large variety of properties characteristic of earlier as well as later evolutionary phases and represent an important phase in the stellar evolutionary sequence that lies between the low luminosity sources which are deeply embbedded in dust and solar type stars. T Tauri stars show uv and IR excesses, and strong and variable emissions in the optical, ultraviolet and x-ray regions. The exotic behaviour of Classical T Tauri stars are primarily due to the active circumstellar disk and its interaction with the star and the properties of Weak Emission T Tauri stars are mainly attributed to the enhanced stellar activity. I have carried out a systematic study of a group of T Tauri stars using photometric, spectroscopic and polarimetric observations. I will summarize the important signatures of activity in T Tauri stars. I will also present the results of my observations and interpretations based on them.

3 illus, 30 ref

003204   Manoj P;Maheswar G;Bhatt H C (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Circumstellar environment around young stars in nearby OB associations. Bull Astr Soc India 2002, 30(3), 657-60.

Studies the circumstellar environment around intermediate mass young stars in nearby OB associations of different ages. Finds that a significant fraction of stars in these associations have cool circumstellar dust around them. Very few of these stars show any emission line activity. These are young Vega-like systems with tenuous dusty disks made of material left over from a more active pre-main sequence phase.

2 illus, 1 table, 4 ref

003203   Maheswar G;Manoj P;Bhatt H C (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Intermediate galactic latitude sarforming region-CG 12. Bull Astr Soc India 2002, 30(3), 651-2.

Optical linear polarization measurements of stars seen projected towards CG 12, an intermediate latitude (b=21°.1) starforming cloud, have been made. The results show that the polarization vectors of the majority of the stars seem to be oriented parallel to the tail of CG 12, implying that the magnetic field in the cloud is parallel to the tail. Spectroscopic observations of each component of the double star Her 4636 show that pnly the northern component has Hα in emission.

1 illus, 3 ref

003202   Konar S;Choudhuri A R (NO, Inter University Centre for Astronomy and Astrophysics, Pune-411 007) : Diamagnetic screening of the magnetic field in accreting neutron stars. Bull Astr Soc India 2002, 30(3), 697-8.

A possible mechanism for screening of the surface magnetic field of an accreting neutron star, by the accreted material, is investigated. In particular, investigates the nature of the evolution of the internal field configuration in the case of a polar cap accretion and spherical accretion.

2 illus, 5 ref

003201   Kharb P;Gabuzda D;Shastri P (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Polarization study of BL lacertae objects on pc-scales. Bull Astr Soc India 2002, 30(3), 761-4.

Presents results of the VLBA³ polarization observations of "X-ray selected" BL Lac objects from the HEAO-1 survey and also a few from the ROSAT0Green Bank (RGB) sample. These primarily high energy peaked BL Lacs (HBLs) have "core-jet" morphologies with modestly polarized pc-scale cores and jet components, similar to their radio-selected counterparts (Primarily low energy peaked BL Lacs, LBLs). However, finds that the jets in HBLs show preferentially longitudinal magnetic fields, as opposed to the jets in LBLs, which tend to have transverse magnetic fields.

1 illus, 10 ref

003200   Kapoor R C;Shukre C S (NO, Indian Institute of Astrophysics, Koramangala, Bangalore-560 034) : Radio pulsar emission altitudes. Bull Astr Soc India 2002, 30(3), 695-6.

By attributing the often seen longitude offsets between the core and conal component centres of pulsar radio pulses to different emission altitudes, presents a new method for investigating these altitudes. Method can explain these offsets and also shed light on them.

1 ref

003199   Kameswara Rao N;Goswami A;Lambert D L (NO, Indian Institute of Astropysics, Bangalore-560 034) : High resolution spectroscopy of QY Sge. Bull Astr Soc India 2002, 30(3), 671-4.

High resolution spectral analysis of QY Sge, a post AGB star is presented here. The spectrum of QY Sge is characterized by three major components: absorption lines representative of a G supergiant, sharp emission lines from resonance and low excitation transitions of abundant neutral atoms, and broad emission lines of Na D and K lines at 7665 Å and 7699 Å. The star is a velocity variable. The radial velocities of the star as measured from a set of unblended absorption line are estimated as <126> -21 kms^-1 for 199 and <126> -23 km^-1 for 2000 spectrum. An abundance analysis shows that the star is of approximately solar composition but with the highly condensable elements (e.g, Sc and Ti), depleted by factors of 5 to 10.

2 illus, 1 table

003198   Kamath U S;Anupama G C (NO, Indian Institute of Astrophysics, Koramangala, bangalore-560 034) : Optical spectroscopy of the nova-like variable V445 puppis. Bull Astr Soc India 2002, 30(3), 679-81.

V445 Puppis is a peculiar variable had a nova-like eruption in December 2000. The early spectra did not show any emission lines of hydrogen or helium. Fe II lines were very dominant during this phase. Presents optical spectra of the early-decline phase of V445 Pu obtained from the Vainu Bappu Observatory during Feb-April 2001.

2 illus, 4 ref

003197   Joshi B C;Lyne A G;Jordan C;Krawczyk A;Gil J A (NO, Jodrell Bank Observatory, UK) : Observations of rotational instabilities in radio pulsars. Bull Astr Soc India 2002, 30(3), 691-3.

Two kinds of irregularities are observed in the rotation rates of pulsars - timing noise and glitches. A study of these irregularities is useful as a probe for the internal structure of these stars. Presents the distribution of fractional change in the rotation rate of pulsars as obtained from all available data.

2 illus, 8 ref

003196   Joshi B C;Burgay M;Lyne A G;Manchester R N; Possenti A;Camilo F;Amico N D;Kramer M (Jodrell Bank Observatory, University of Manchester, UK) : A high Galactic latitude search for pulsars. Bull Astr Soc India 2002, 30(3), 687-9.

Millisecond pulsars (MSPs) are an important class of radio pulsars. Their observed spatial distribution is flux limited and is nearly isotropic. Many such pulsars have been observed at high galactic latitudes. The preliminary results of a new survey with Parkes radio telescope using the 20 cm multibeam receiver are reported. The survey covers a region around the southern Galactic plane between longitudes 220° and 260° and latitudes [b] <60>60°. Discovered two new pulsars and detected 15 known pulsars so far.

2 illus, 2 tables, 8 ref

003195   Javaraiah J (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Study of Sun's rotation and solar activity. Bull Astr Soc India 2002, 30(3), 605-12.

Presented many interesting properties of Sun's rotation and magnetic activity derived from extensive analysis of over 100 year photoheliographic data on sunspot activity and 26 year's data on photospheric motions from Mt Wilson, and supporting data from GONG and SOHO.

16 ref

003194   Javaraiah J (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Short-term periodicities in the north-south asymmetry of the Sun's surface rotation. Bull Astr Soc India 2002, 30(3), 587-8.

Power spectra of N-S asymmetries of the coefficients A^- and C^- of the Sun's surface differential rotation determined from the Mt. Wilson velocity data during 1982-1994 suggest the existence of a period at 474±30 day in the N-S asymmetries of A^- and C^- with<62> 99.9% confidence level. The spectrum of the N-S asymmetry of the coefficient B^- suggests existence of the periods at 374±30 day, 78±2 day and 49±1 day in the N-S asymmetry of B^- with ≥ 99% confidence level.

2 ref

003193   Iyer B R (NO, Raman Research Institute, Bangalore-560 080) : Gravitational wave astronomy probing physics and unravelling astrophysics. Bull Astr Soc India 2002, 30(3), 735-40.

Kilometer scale Laser Interferometer Gravitational Wave Detectors like LIGO (VIRGO) are expected to go online in 2002 (2003). Space interferometers like LISA are scheduled for 2011. The possible Science payoffs of these experiments are explored. Starting from the basic properties of implications of gravitational wave observations for basic physics, astrophysics and cosmology. The current status of theoretical computation of waveforms and templates for data analysis is breiefly discussed.

14 ref

003192   Ishwara Chandra C H;Anantharamaiah K R; Dwarakanath K S (Space Astronomy and Instrumentation Div, ISRO Satellite Centre, Bangalore-560 017) : GMRT detection of H I absorption in the high-redshift red quasar 3C 190. Bull Astr Soc India 2002, 30(3), 747-8.

Reports the GMRT detection of H I absorption in the high-redshift red quasar 3C 190 at a redshift of 1.1946. The most interesting result is that the peak of the H I absorption is blueshifted by <126> 250 kms^-1 with respect to the optical emission lines. The H I absorption profile indicates the presence of multiple components and the pea absorption is at 647.728 MHz. The FWHM of this absorption feature is 185±7 kms^-1 and the peak optical depth is 0.012. The corresponding atomic hydrogen column density is 3.98 x 10²⁰ (T_s/100K) cm^-2.

1 illus, 3 ref

003191   Hasan P;Kilambi G C;Baliyan K S (Astronomy Dep, Osmania University, Hyderabad-500 007) : Near infrared photometry of the young open cluster NGC 1960. Bull Astr Soc India 2002, 30(3), 653-5.

Presents the preliminary results of observations of NGC 1960 which was observed from the Mt Abu Infrared Observatory, using the NICMOS3 infrared arrary monted on the 1.2 m Cassegrain focus telescope. The observations were made in February 2000. The data reduction has been performed using IRAF. The distance has been estimated to be 1000 pc.

1 illus, 11 ref

003190   Gupta R;Burse M;Das H K;Kohok A;Ramaprakash A N;Engineer S;Tandon S N (NO, IUCAA, Post Bag 4, Ganeshkhind, Pune-411 007) : IUCAA 2 meter telescope and its first light instrument IFOSC. Bull Astr Soc India 2002, 30(3), 785-90.

The various features of the IUCAA 2-meter telescope, its site parameters and considerations made for preserving the local seeing in terms of ventilation, thermal emissivity of the dome etc are described. The first light back-end instrument for this telescope, i.e. Iucaa Faint Object Spectrometer and Camera (IFOSC), too is described in some detail.

2 illus, 1 table, 1 ref

003189   Gosain S;Choudhary D P (Udaipur Solar Observatory, Physical Research Laboratory, Udaipur-313 001) : Magnetic and velocity fields over active regions. Bull Astr Soc India 2002, 30(3), 579-81.

In order to understand the nature of dynamics over an active region (AR), it is necessary to study the velocity and magnetic fields simultaneously. Presents the preliminary results from analysis of spectro-polarimetric observations of active region NOAA-8426 over two days. These observations were done using Advanced Stokes polarimeter (ASP) instrument of HAO-NSO (Elmore et al. 1992, Lites 1996) with the Richard Dunn Vacuum Tower Telescope, USA. The line-of-sight (LOS) magnetic field information is derived using least squares fitting of the Stokes-V profiles, in a weak field approximation. Simultaneous LOS velocity information over these AR is obtained in two ways : Zero-crossing (ZC) velocities using Stokes-V profiles, and centre of gravity (COG) velocities using Stokes-I profiles. The former corresponds to the magnetised plasma whereas the latter to be gross plasma over the AR. Average relative velocities of isolated polarity regions of the AR are presented.

6 ref

003188   Giridhar S;Goswami A (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Spectroscopic survey of field stars: a search for metal-poor stars. Bull Astr Soc India 2002, 30(2), 501-16.

Observations are carried out using OMR spectrograph attached to VBT, Kavalur. The sample of candidate stars are chosen from priosmatic survey of Beers and his collaborators covering a large part of the Galaxy. At the first phase of this project, the analysis is completed for a set of 19 relatively hot stars (T_eff in 6000 to 8000K range). The metallicities of the program stars are derived by synthesizing the spectrum in the wavelength range 4900 to 5400 for different metallicities and matching them with the observed spectra. This spectral region contains strong feature of Fe I at 5269 and one moderately strong Fe I blend at 5228. These features were generally relied upon for Fe/H determination. More than half of the candidate stars were found to show [Fe/H] om -0.7 to -1.2 range. Two most metal-poor stars have [Fe/H] values of -1.3 and -1.8. It appears that metal-poor candidates suggested by Beers et al. from their prismatic survey has a very significant fraction of metal-poor stars. The significantly metal-poor stars found so far would be studied in detail using high resolution spectra to understand incleosynthesis processes that might have occurred in early Galaxy.

6 illus, 4 tables, 19 ref

003187   Ghosh S K;Ojha D K (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-400 005) : Spatial distribution of unidentified infrared emission bands in star forming regions. Bull Astr Soc India 2002, 30(3), 649-50.

Midcourse Space Experiment (MSX) has surveyed the Galactic plane in four infrared bands between 6 and 25 μm, two of which cover several Unidentified Infrared emission bands (UIBs). A scheme has been developed to extract the spatial distribution of the UIB emission using the MSX data. The observatins have been modelled by two components : the emission in UIBs and an underlying thermal continuum (gray body) from the interstellar dust. The reliability of the scheme has been successfully verified by comparing the results for a sample of five Galactic compact H II regions (Sh-61, Sh-138, Sh-152, Sh-156, Sh-186) for which ISOCAM images in some individual UIBs are available. Scheme demonstrates the usefulness of the MSX database doe study of large scale spatial distribution of UIB emission (and the carriers of UIBs) in the entire Galactic plane.

1 illus, 2 ref

003186   Dwivedi B N (Applied Physics Dep, Institute of Technology, Banaras Hindu University, Varanasi-221 005) : Probing sun's hot atmosphere : views from Yohkoh, SOHO and TRACE. Bull Astr Soc India 2002, 30(3), 549-55.

Reviews some recent progress of the Sun's hot atmosphere, using data from spacecraft (Yohkoh, SOHO and TRACE) and from ground-based eclipse experiments.

^iia2 illus, 10 ref

003185   Dhurandhar S V (NO, UCAA, Pune-411 007) : Gravitational wave astronomy: recent advances. Bull Astr Soc India 2002, 30(3), 729-34.

Several groundbased gravitational wave (GW) laser interferometric projects have completed construction and are currently involved in conducting engineering runs. The spacebased NASA-ESA mission. LISA is expected to be launched in ten years' time. With the data around the corner exciting times lie ahead for GW astronmy. A brief introduction based detectors, the space based detector LISA, GW sources and the data analysis necessary to extract the weak GW signal from the detector noise will be presented.

1 illus, 5 ref

003184   Dharam Vir Lal (NO, Indian Institute of Astrophysics, Koramangala, Bangalore-560 034) : Seyfert galaxies : nuclear radio structure and unification. Bull Astr Soc India 2002, 30(3), 777-83.

Observed a sample of Seyfert (Sy) galaxies with global Very Long Baseline Interferometry (VLBI) to test predictions of the unification scheme which hypothesize that Sys of Type 1 and Type 2 constitute a single population of objects. If Sy 1 and Sy 2 galaxies differ only in the orientation of the axisymmetric active nucleus with respect to the observe, then, the parsec-scle radio structures of the two types should be similar. Choses a sample of Sy 1s and Sy 2s such that the two subsamples were intrinsically similar within the framework of the unified scheme. This was done by matching them as far as possible in orientation-independent parameters viz. host galaxy properties and measures of intrinsic power of the active nucleus. Presents the results obtained from these observations and their implications for the unification scheme. Also discusses the results obtained from the measurements at all IRAS and 2-10 keV X-ray wavebands for Sy galaxy sample using data from the literature.

2 illus, 9 ref

003183   Deep A;Ramaprakash A N;Tandon S N;Gupta R; Burse M P;Chordia P A;Das H K;Engineer S;Kohok A A;Mestry V B (NO, Inter University Centre for Astronomy and Astrophysics, Pune-411 007) : Near infrared PICNIC imager (NIPI) for UCAA telescope. Bull Astr Soc India 2002, 30(3), 791-5.

Presents the current status of development of the Near Infrared PICNIC Imager (NIPI), which will be the first near-IR instrument on IUCAA telescope. When used at one of the Cassegrain side ports of the telescope, it gives a plate scale of 0.8 arcsec per pixel at the PICNIC detector array with a field of view of 2.5 arc minutes. It offers imaging capabilities in J, H and K filter bands, with the reimager optimized in H-band for which almost 90encircled energy of a point source is contained in a pixel. Hardware and software for infrared readout are being developed at IUCAA.

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003182   Das P K (NO, Indian Institute of Astrophysics, Koramangala, Bangalore-560 034) : Ejection of quasars from galaxies and the variable mass hypothesis. Bull Astr Soc India 2002, 30(3), 767-72.

Investigates the dynamics of ejection of quasars from galaxies in the Variable Mass Hypothesis (VMH), originally discussed by Narlikar and Das to provide a theroretical interpretation of the observed alignments of quasars with active galaxies. According to the VMH a typical quasar is ejected from the parent galaxy with zero rest mass which groves with time through a Machian interaction whereas its speed decreases from its initial value which equals the speed of light. A consistent picture emerges from the calculations, based on the recent observational data from X-ray astronomy, in which the quasar passes through a continuous sequence of decreasing redshifts and increasing masses as it grows old. The calculations also provide a method for distinguishing between quasars which can escape the gravitational influence of the parent galaxies and the ones which are bound.

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003181   Choudhary D P;Gosain S (Udaipur Solar Observatory, Physical Research Laboratory, Udaipur-313 001) : Three dimensional structure of active regions. Bull Astr Soc India 2002, 30(3), 583-5.

Presents the preliminary results of the modelling of the three dimensional structure of the magnetic field above the active regions observed with Advanced Stokes polarimeter and Dick Dunn telescope at National Solar Observatory, USA. The observed photospheric magnetograms are extrapolated to chromospheric heights using the Fourier expansion technique to compute the potential (Current-free) magnetic field in Cartesian geometry. The photospheric surface is assumed to be flat, but the tilt of the boundary plane with respect to the plane of the sky is taken int account, depending on the location of the active region. The best fit of the observed and computed scatter plot is achieved by considering the height of the chromospheric emission at 800 km.

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003180   Chinnappan V;Saxsena A A;Sreenivasan A (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Characterization of MOEMS-based adaptive mirror for wavefront correction. Bull Astr Soc India 2002, 30(3), 823-5.

In real-time wavefront compensation techniques, a conjugate surface of the incoming aberrated wavefront is to be created in real-time. Two types of mirrors are used for this purpose. The first one is a tip-tilt mirror and the second one is a deformable mirror. Conducted experiments using piezo-electric actuator-based tip-tilt mirror and micro-opto-electromechanical systems(MOEMS)-based membrane mirror. Explains the experimental results of tip-tilt mirror and theoretical and experimental characteristics of the membrane mirror.

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003179   Chinnappan V;Saxena A K;Sreenivasan A (NO, Indian Institute of Astrophysics, Bangalore-560 034) : Performance evaluation of high-speed camera system for adaptive optics. Bull Astr Soc India 2002, 30(3), 815-7.

Atmospheric turbulence distorts the incoming wavefront from the star light, thus severely limiting the resolution of the groundbased optical telescopes (Fried 1966). Adaptive optics is being implemented in all big telescopes to remove the distortion created by the atmosphere. Dealing with the selection and testing of three types of high-speed imaging systems, a crucial component for wavefront sensing.

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003178   Chatterjee S;Vani V C (NO, Indian Institute of Astrophysics, Koramangala, Bangalore-560 034) : Scattering of light periodic structure with randomness. Bull Astr Soc India 2002, 30(3), 835-6.

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003177   Chandrasekhar T;Ashok N M;Anandarao B G (Astronomy and Astrophysics Div, Physical Research Laboratory, Ahmedabad-380 009) : Imaging Fabry-Perot observations of green coronal line during the total solar eclipse of 21 June 2001. Bull Astr Soc India 2002, 30(3), 591-3.

A Fabry-Perot interferometric experiment on the Green Coronal line was successfully performed during the total solar eclipse of 21 June 2001 from Lusaka, Zambia. Use of a cooled CCD camera permitted 17 separate exposures during the totality which lasted 194 sec. Green line fringes could be traced up to and beyond 1.5 R©. Details of the experiment and emerging results are presented.

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003176   Chakrabarti S K;Bhattacharyya A (NO, S N Bose National Centre for Basic Sciences, Salt Lake, Kolkata-700 098) : How thick are the saturn's rings. Bull Astr Soc India 2002, 30(3), 563-72.

It has been long thought that the rings of saturn are probably not thicker than a few hundreds of meters. By actually following the motion of particles inside the decaying bending waves of the Saturn's rings and matching the resulting damping length of the bending waves launched by a number of moons with the actual damping lengths observed by Voyagar-II, shows that the thickness of the rings need not be larger than a few meters at the most. Presents a few results.

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