A revised catalogue of 294 Galactic supernova remnants (SNRs) is presented, along with some simple statistics. This catalogue has twenty more entries than did the previous version (from 2009), as 21 new remnants have been added, and one object has been removed as it has been identified as an HII region.
We designed and built a new astronomical photo-polarimeter that can measure linear polarization simultaneously in three spectral bands. It has a Calcite beam-displacement prism as the analyzer. The ordinary and extra-ordinary emerging beams in each spectral bands are quasi-simultaneously detected by the same photomultiplier by using a high speed rotating chopper. A rotating superachromatic Pancharatnam halfwave plate is used to modulate the light incident on the analyzer. The spectral bands are isolated using appropriate dichroic and glass filters.We show that the reduction of 50% in the efficiency of the polarimeter because of the fact that the intensities of the two beams are measured alternately is partly compensated by the reduced time to be spent on the observation of the sky background. The use of a beam-displacement prism as the analyzer completely removes the polarization of background skylight, which is a major source of error during moonlit nights, especially, in the case of faint stars.The field trials that were carried out by observing several polarized and unpolarized stars show the performance of the polarimeter to be satisfactory.
The Double Pulsar J0737-3039A/B, discovered with the Parkes radio telescope in 2003, is one of the most intriguing pulsar discoveries of the last decade. With its orbital velocity of similar to 1% of the speed of light, it is the most relativistic system ever found and, thanks to the presence of two active radio pulsars, it has also shown unprecedented mutual interactions between the radio beam of one pulsar and the magnetosphere of the other. Due to these characteristics, the Double Pulsar can be used for a wide variety of experiments, ranging from relativistic gravity, to plasma physics, and to pulsar electrodynamics. Moreover its discovery enhances - by almost an order of magnitude - estimates of merger rates for double neutron stars systems, providing new possibilities for the current generation of ground-based gravitational wave detectors. In this paper we review the main observational properties of the Double Pulsar and their application for physical and astrophysical studies.
This paper presents a detailed study of X-ray emission from the cluster RXC J1252.5-3116, based on an analysis of the Chandra archival data. Here we present radial profiles and maps of X-ray surface-brightness, temperature, electron number density, entropy and pressure of RXC J1252.5-3116. We have also estimated the X-ray luminosity, gas mass, cooling time and mass deposition rate for the cluster. The cluster shows an extremely relaxed X-ray morphology and the radial profiles suggest a drop in the temperature of the central gas. We find an extremely small cool-core and a high mass deposition rate of 43 M⊙ per year. RXC J1252.5-3116 seems to host a possible cool core at its centre.
DE Lac is a high-amplitude delta Scuti variable with a period of 0.253694 days. New CCD photometric monitoring of DE Lac was carried out on 2013 December 18 and 2014 January 5, by using the 1.0-m reflecting telescope at Yunnan Observatories. Photometric observations of DE Lac were also obtained by using the 85-cm telescope at Xinglong Station of National Astronomical Observatory. By using a few new determined times of maximum light together with those collected from the literature, the period changes in Observed-Calculated (O - C) diagram are analyzed. We discover that the pulsating period of DE Lac is increasing continuously at a rate of (P) over dot = + 3.7 x 10(-8) days/year. It is compatible with the prediction from the stellar evolution model calculations. Meanwhile, we collect other delta Scuti stars that have exhibited period changes.
Radio observations serve as a powerful tool to study the physical conditions of the radio emitting sources for understanding the characteristics of solar atmosphere. It is also a useful method for understanding the physical properties and the dynamics of the solar corona. It is evident from various experimental observations that the recent 23-24 solar cycle minimum was elongated for much longer time compared to previous minima. In this paper, the mid-range periodicity (in the range of 50-250 days) for non-magnetic components of solar radio flux at eight discrete frequencies viz. 245, 410, 610, 1415, 2695, 4995, 8800 and 15400 MHz during the extended solar minimum period (2007-2009) have been explored using Lomb-Scargle periodogram technique. The periodicities obtained in the mid range (50-250 days) for different frequencies during this minimum have been identified with the periodicities within the range of standard deviation obtained from different analysis for different time span with different phase of previous solar cycles by different workers. The observations of basal component (non magnetic component of solar radio flux) are interpreted in terms of the internal dynamics of the Sun. The obtained periodicities also provide physical information about the source region of the solar atmosphere.
Red sequence galaxies form with an intense burst of star formation in the early universe to evolve passively into massive, metal rich, old galaxies at z 0. But Abell 1314 (z=0.034) is found to host almost all red sequence galaxy members - iden- tified using the mz index, classified using the Principle Component Analysis technique and SDSS colour correlations - some of which show properties of low-mass, star form- ing, and metal rich galaxies. The variably spread Intra-Cluster Medium (ICM) near the core forms a vital part in influencing the evolution of these members. To study their evolution, I correlated di erent parameters of the rest-frame narrowband photometry and the derived luminosity-weighted mean Single Stellar Population model ages and metallicities. The study finds the member galaxies evolve di erently in three di erent sec- tions of the cluster: 1. the region of 200 kpc hosts passively evolving old, massive systems which accumulate mass by dry, minor mergers, 2. the zone between 200-500 kpc shows stripped systems (or in the process of being gas stripped) by ram pressure with moderate star formation history, 3. the outer regions ( 500 kpc) show low-mass red objects with blue, star forming Butcher-Oemler galaxy like colours. This sort of environmental condition is known to harbour hybrid systems, like, the pseudo bulges, blue sequence E/S0 and Butcher-Oemler like satellite cluster galaxies. Overall, the cluster is found to be poor, quiescent with galaxies to have formed by the monolithic structure formation in the early universe and are now evolving with mergers and gas stripping processes by ram pressure.
We present the results obtained from timing and spectral studies of high mass X-ray binary pulsar OAO 1657-415 using a Suzaku observations in 2011 September. X-ray pulsations were detected in the light curves up to $\sim$70 keV. The continuum spectra during the high- and low-flux regions in light curves were well described by high energy cutoff power-law model along with a blackbody component and iron fluorescent lines at 6.4 keV and 7.06 keV. Time resolved spectroscopy was carried out by dividing the entire observations into 18 narrow segments. Presence of additional dense matter at various orbital phases was confirmed as the cause of low-flux regions in the observations. Presence of additional matter at several orbital phases of the pulsar was interpreted as due to the inhomogeneously distributed clumps of matter around the neutron star. Using clumpy wind hypothesis, the physical parameters of the clumps causing the high- and low-flux episodes in the pulsar light curve were estimated. The equivalent width of iron emission lines was found to be significantly large at certain orbital phases of low-flux segments. We investigated the iron line emitting regions and suggest the existence of neutral and ionized iron atoms in emission sites that are located within the accretion radius.
We study the coupled disc-jet system around the black hole where the outflow solutions are obtained in terms of the inflow parameters. We observe that an advective accretion disc can eject outflows/jets for wide range of viscosity parameter. However, such possibility is reduced if the cooling is active as the energy dissipative process inside the disc. For mass outflow, we obtain the parameter space spanned by the inflow angular momentum and the viscosity in terms of cooling and quantify the limits of viscosity parameter.
Singularities in general relativity such as the big bang and big crunch, and exotic singularities such as the big rip are the boundaries of the classical spacetimes. These events are marked by a divergence in the curvature invariants and the breakdown of the geodesic evolution. Recent progress on implementing techniques of loop quantum gravity to cosmological models reveals that such singularities may be generically resolved because of the quantum gravitational effects. Due to the quantum geometry, which replaces the classical differential geometry at the Planck scale, the big bang is replaced by a big bounce without any assumptions on the matter content or any fine tuning. In this manuscript, we discuss some of the main features of this approach and the results on the generic resolution of singularities for the isotropic as well as anisotropic models. Using effective spacetime description of the quantum theory, we show the way quantum gravitational effects lead to the universal bounds on the energy density, the Hubble rate and the anisotropic shear. We discuss the geodesic completeness in the effective spacetime and the resolution of all of the strong singularities. It turns out that despite the bounds on energy density and the Hubble rate, there can be divergences in the curvature invariants. However such events are geodesically extendible, with tidal forces not strong enough to cause inevitable destruction of the in-falling objects.
Quasar lensing offers an important diagnostic of masses and mass distributions in foreground objects, and is sensitive to both baryonic and dark matter. In addition, strong lensing also magnifies the brightness of background objects, allowing one to probe regions with potentially interesting cosmological information. In this review I present individual theoretical results, and discuss possible future applications of quasar lensing, and the observational programmes which will develop the subject in the coming years.
Observations of the transit of Venus were made from the Kodaikanal Observatory on 2012 June 06 in Ca-K wavelengths. Only half of the event was visible from India. We utilized this unique opportunity to compute the contribution of the scattered light within the Twin Telescope optics at Kodaikanal. The instrumental and atmospheric scattered light are derived from the model point spread function which is a combination of four Gaussians with different widths and weights. The restoration procedure has significantly improved the rms contrast of the images. The rms contrast of the stray light corrected images are almost two fold larger than that those of the uncorrected images. The derived network element sizes matches well with previous observations.
Our BVI photometric observations reveal that GSC 2701-2527 is a high-amplitude delta Scuti star with quite low temperature. The frequency analysis exhibits that it is multiperiodic pulsator. The obtained period ratio f(1)/f(2)=0.791 is higher than the canonical value. The large value of the period ratio f(1)/f(3)=0.813 implies nonradial nature of the third mode. Using empirical relations for the ffi Scuti stars we determined the global parameters of GSC 2701-2527: luminosity 26.2 L-circle dot, radius 3.95 R-circle dot, mass 2.18 M-circle dot,and distance 506 pc.
Quasar spectra, apart from showing the broad, redshifted emission lines, often show narrow as well as broad absorption lines. The presence of absorption lines has been known since shortly after the discovery of these objects. The spectrum of a single quasar can have more than one group of absorption lines, termed absorption line systems, each system having its characteristic redshift. Most of these systems are believed to be produced by galactic or intergalactic clouds, while those having redshifts close to that of the quasar may be produced by material intrinsic to the quasar. These systems thus offer a sensitive probe to understand the evolutionary history of the Universe over 90% of its age as well as the quasar environment. In recent times, the commissioning of large telescopes, high resolution spectrographs, space telescopes, large sky digital surveys and progress in hydro-simulations have resulted in rapid progress in this field. In this article, I will summarize some of our current understanding of these systems and the information that has been obtained about various aspects of the Universe from their study.
In this paper we present the analysis of twenty hot contact binary systems in the Small Magellanic Cloud using the Wilson-Devinney method and their properties are discussed in context of TRO model.
The surface gravitational redshift of the neutron star PSR B2303+ 46 is investigated within the framework of relativistic mean field theory for the baryon octet system through adjusting the hyperon coupling constants. We obtain any models for the neutron star B2303+ 46 by choosing suitable hyperon coupling constants chi(sigma h) and chi(omega h) with chi(rho h) being determined by SU(6) symmetry and the nucleon coupling constant being chosen as CZ11. Our calculations show that the radius and the surface gravitational redshift of the neutron star PSR B2303+ 46 are determined as R = 12: 477 similar to 12: 493 km and z = 0: 2184 similar to 0: 2187, respectively. Our results are not consistent with the recent discovery of the massive neutron star PSR J1614 2230 and PSR J0348+0432.
Stark width regularities within homologous spectral series of neutral atoms of alkaline earth metals were found and discussed. The emphasis is on: (i) the Stark width dependence on the upper level ionization potential (chi); and (ii) term structure influence on the found Stark parameter dependences. The relations found for particular electron temperature and density were of the form ! = a chi(-b), where a, b are constants, for particular homologous spectral series. Published Stark widths data are used to demonstrate the existence of these kinds of regularities for the electron impact contributions to the Stark widths. The obtained functions were used to predict the electron impact Stark widths data for 37 lines of strontium and 29 for barium neither calculated nor measured so far.
We present deep Johnson UBV and Cousins RI CCD photometry of three young open clusters, namely, NGC 2129, NGC 1502 and King 12 reaching down to V similar to 22 mag. For the first time, we have reported optical CCD data for King 12. Fundamental parameters for these clusters have been determined by comparing colourcolour and colour-magnitude diagrams (CMDs) with the theoretical models. The cluster radii have been estimated to be 3.3, 1.7 and 3.9 pc for NGC 2129, NGC 1502 and King 12 respectively. The reddenings E(B-V) have been determined to be 0.77 +/- 0.05, 0.68 +/- 0.05 and 0.63 +/- 0.05 while the corresponding distances have been found to be 2.1 +/- 0.1, 1.0 +/- 0.1 and 2.5 +/- 0.1 kpc respectively. The ages of the clusters have been obtained after fitting theoretical stellar evolutionary models for solar metallicity Z = 0.019 isochrones with the observed CMDs. This gives an age of 10.0 +/- 0.1 Myr for all the three clusters. The analysis shows that there is differential interstellar reddening in the direction of all clusters.
I review the current status of quasar black hole (BH) mass estimations. Spectroscopic methods have been developed to estimate BH mass in broad line quasars to an accuracy of ~0.5 dex. Despite their popularity, significant issues and confusion remain regarding these mass estimators. I provide an in-depth discussion on the merits and caveats of the single-epoch (SE) virial BH mass estimators, and a detailed derivation of the statistical biases of these SE mass estimates resulting from their errors. I show that error-induced sample biases on the order of a factor of several are likely present in the SE mass estimates for flux-limited, statistical quasar samples, and the distribution of SE masses in finite luminosity bins can be narrower than the nominal uncertainty of these mass estimates. I then discuss the latest applications of SE virial masses in quasar studies, including the early growth of supermassive black holes, quasar demography in the mass-luminosity plane, and the evolution of the BH-host scaling relations, with specific emphases on selection effects and sample biases in the SE masses. I conclude that there is a pressing need to understand and deal with the errors in these BH mass estimates, and to improve these BH weighing methods with substantially more and better reverberation mapping data.
