Showing papers in "Serbian Astronomical Journal in 2012"

New 6 and 3-cm radio-continuum maps of the Small Magellanic Cloud : Part II - point source catalogue

Abstract: We present two new catalogues of radio-continuum sources in the field of the Small Magellanic Cloud (SMC) These catalogues contain sources found at 4800 MHz (λ=6cm) and 8640 MHz (λ=3cm) Some 457 sources have been detected at 3cm with 601 sources at 6cm created from new high-sensitivity and resolution radio-continuum images of the SMC from Crawford et al (2011)

Multifrequency radio observations of snr j0536-6735 (n 59b) with associated pulsar

Abstract: SUMMARY: We present a study of new Australian Telescope Compact Array(ATCA) observations of supernova remnant, SNR J0536–6735. This remnant ap-pears to follow a shell morphology with a diameter of D =36 × 29 pc (with 1 pcuncertainty in each direction). There is an embedded H ii region on the northernlimb of the remnant which made various analysis and measurements (such as fluxdensity, spectral index and polarisation) difficult. The radio-continuum emissionfollowed the same structure as the optical emission, allowing for extent and fluxdensity estimates at 20 cm. We estimate a surface brightness for the SNR at 1 GHzof 2.55 × 10 −21 Wm −2 Hz −1 sr −1 . Also, we detect a distinctive radio-continuumpoint source which confirms the previous suggestion of this remnant being associ-ated with a pulsar wind nebulae (PWN). The tail of this remnant isn’t seen in theradio-continuum images and is only seen in the optical and X-ray images.Key words. ISM: supernova remnants – Magellanic Clouds – Radio Continuum:ISM – ISM: individual objects – SNR J0536–6735

Radio-continuum observations of small, radially polarised Supernova Remnant J0519-6902 in the Large Magellanic Cloud

Abstract: SUMMARY: We report on new Australian Telescope Compact Array (ATCA)observations of SNR J0519–6902. The Supernova Remnant (SNR) is small in size( ∼ 8 pc) and exhibits a typical SNR spectrum of α = −0.53±0.07 , with steeperspectral indices found towards the northern limb of the remnant. SNR J0519–6902contains a low level of radially orientated polarisation at wavelengths of 3 & 6 cm,which is characteristic of younger SNRs. A fairly strong magnetic field was es-timated of ∼ 171 µ G. The remnant appears to be the result of a typical Type Iasupernovae, sharing many properties as another small and young Type Ia LMCSNR, J0509–6731.Key words. ISM: supernova remnants – Magellanic Clouds – Radio Continuum:ISM – ISM: individual objects – SNR J0519–6902 1. INTRODUCTIONSupernova Remnants (SNRs) play an essen-tial role in the ecology of the universe, enriching theinterstellar medium (ISM) as well as having a signifi-cant impact on the ISM structure and physical prop-erties. The study of SNRs in our own galaxy isn’tideal due to the high level of absorption in additionto difficulties achieving accurate distance measure-ments. Instead, we look to the small dwarf galaxy,the Large Magellanic Cloud (LMC) for our study,which is located at a distance of 50 kpc (Macri et al.2006). This proximity to us is far enough that weare able to assume all objects within the galaxy arelocated at the same distance, making measurementsof extent & surface brightness more reliable. ThereLMC also offers us an environment that is outside ofthe galactic plane at an angle of 35

NEW 20-cm RADIO-CONTINUUM STUDY OF THE SMALL MAGELLANIC CLOUD: PART III { COMPACT HII REGIONS

Abstract: We present and discuss a new catalogue of 48 compact Hii regions in the Small Magellanic Cloud (SMC) and a newly created deep 1420 MHz (λ=20 cm) radio-continuum image of the N19 region located in the southwestern part of the SMC. The new images were created by merging 1420 MHz radiocontinuum archival data from the Australian Telescope Compact Array. The majority of these detected radio compact Hii regions have rather flat spectral indices which indicates, as expected, that the dominant emission mechanism is of thermal nature.

A study of optical observing techniques for extra-galactic supernova remnants: Case of ngc300

Abstract: We present the results of a study of observational and identification techniques used for surveys and spectroscopy of candidate supernova remnants (SNRs) in the Sculptor Group galaxy NGC300. The goal of this study was to investigate the reliability of using [Sii]:Hα ≥ 0.4 in optical SNR surveys and spectra as an identifying feature of extra-galactic SNRs (egSNRs), and also to investigate the effectiveness of the observing techniques (which are hampered by seeing conditions and telescope pointing errors) using this criterion in egSNR surveys and spectrographs. This study is based on original observations of these objects and archival data obtained from the Hubble Space Telescope which contained images of some of the candidate SNRs in NGC300. We found that the reliability of spectral techniques may be questionable and very high-resolution images may be needed to confirm a valid identification of some egSNRs.

20 cm VLA RADIO-CONTINUUM STUDY OF M31 - IMAGES AND POINT SOURCE CATALOGUES

Abstract: We present a series of new high-sensitivity and high-resolution radio-continuum images of M31 at λ=20 cm (ν=1.4 GHz). These new images were produced by merging archived 20 cm radio-continuum observations from the Very Large Array (VLA) telescope. Images presented here are sensitive to rms=60 μJy and feature high angular resolution (<10’’). A complete sample of discrete radio sources have been catalogued and analyzed across 17 individual VLA projects. We identified a total of 864 unique discrete radio sources across the field of M31. One of the most prominent regions in M31 is the ring feature for which we estimated total integrated flux of 706 mJy at λ=20 cm. We compare here detected sources to those listed in Gelfand et al. (2004) at λ=92 cm and find 118 sources in common to both surveys. The majority (61%) of these sources exhibit a spectral index of α <-0.6 indicating that their emission is predominantly non-thermal in nature, that is more typical for background objects.

Focal length determination for the 60cm telescope at Astronomical station Vidojevica

Abstract: SUMMARY: The focal length of a telescope is an important parameter in determining the angular pixel size. This parameter is used for the purpose of determining the relative coordinates (angular separation and positional angle) of double and multiple stars, and the precise coordinates of extragalactic radio sources (ERS) that are visible at optical wavelengths. At the Astronomical Station Vidojevica we have collected observations of these objects using two CCD cameras, Apogee Alta U42 and SBIG ST-10ME, attached to the 60 cm telescope. Its nominal focal length is 600 cm as given by the manufacturer. To determine the telescope focal length more precisely for both attached detectors, we used angular-separation measurements from CCD images taken at Astronomical Station Vidojevica. The obtained focal lengths are: F42 = (5989 ± 7) mm using the CCD camera Apogee Alta U42 attached to the telescope, and F10 = (5972 ± 4) mm with the CCD camera SBIG ST-10ME attached to the telescope.

WASP light curve of the eclipsing binary VZ CVn

Abstract: The WASP light curve of the eclipsing binary VZ CVn, consisting of more than 14000 individual observations, is analyzed for photometric elements using the modeling code of Đurasevic (1992). The spectroscopic parameters are adopted from the recent radial velocity work by Pribulla et al. (2009). The results of the study include new times of minimum light, an improved ephemeris, and the updated physical and orbital parameters of the system.

Heating in Collisions of Solids: Possible Application to Impact Craters

Abstract: Due to the importance of collisions and impacts in early phases of the evolution of the planetary system, it is interesting to estimate the heating of a solid target due to an impact on it. A physically simple calculation of the temperature to which a solid target heats up after the impact of a projectile with mass m and speed v is performed, and possibilities for the application of this result in planetology are pointed out.

Investigation of some galactic and extragalactic gravitational phenomena

Abstract: SUMMARY: Here we present a short overview of the most important results of our investigations of the following galactic and extragalactic gravitational phenomena: supermassive black holes in centers of galaxies and quasars, supermassive black hole binaries, gravitational lenses and dark matter. For the purpose of these investigations, we developed a model of a relativistic accretion disk around a supermassive black hole, based on the ray-tracing method in the Kerr metric, a model of a bright spot in an accretion disk and three difierent models of gravitational microlenses. All these models enabled us to study physics, spacetime geometry and efiects of strong gravity in the vicinity of supermassive black holes, variability of some active galaxies and quasars, difierent efiects in the lensed quasars with multiple images, as well as the dark matter fraction in the Universe. We also found an observational evidence for the flrst spectroscopically resolved sub-parsec orbit of a supermassive black hole binary system in the core of active galaxy NGC 4151. Besides, we studied applications of one potential alternative to dark matter in the form of a modifled theory of gravity on Galactic scales, to explain the recently observed orbital precession of some S-stars, which are orbiting around a massive black hole at the Galactic center.

The Phase Equilibrium in a Lennard-Jones Fluid: Possible Applications in Astrophysics

Abstract: Using standard thermodynamics and previous results of the author, this paper aims to discuss the conditions for phase equilibrium in a Lennard-Jones fluid. Possibilities for astrophysical applications of the obtained results are discussed to some extent, including an unexpected application - in physics of extremely dense matter concerning studies of neutron stars.

An investigation of mass composition of ultra-high energy cosmic rays with energies above 1019 eV via the study of extensive air showers

Abstract: The electron and muon components of extensive air shower (EAS) with energies above 1019 eV are analyzed via various giant EAS arrays. A varying property of showers is observed for two energy ranges; higher and lower than (3 − 4) x 1019 eV. The age parameter, zenith angle, shower size dependence on muon size and shower size dependence on primary energy show an increment of mass composition (MC) above (3−4)x 1019eV. Comparison of the observed EAS results with the simulations of Capdevielle et al. (2000) and Shinozaki et al. (2005) gives at most 20% photon fraction for primary energies above 1019 eV. The arrival directions of showers above 4x1019 eV indicate an increasing concentration towards the super galactic plane.

Simple MCBR Models of Chemical Evolution: An Application to the Thin and the Thick Disk

Abstract: 0 • ‡O • (‡O)1 for in∞owing gas and (‡O)1 • ‡O • 1:2 for out∞owing gas, with a single exception related to the thin disk (A stage), where the range of fltting curves is restricted to 0:35 • ‡O • (‡O)1. The F stage may safely be described by a steady in∞ow regime (• = i1), implying a ∞at TDOD, in agreement with the results of hydrodynamical simulations. Finally, (1) the change of fractional mass due to the extension of the linear flt to the EDOD, towards both the (undetected) low-metallicity and high-metallicity tail, is evaluated and (2) the idea of a thick disk - thin disk collapse is discussed, in the light of the model.

Hyperbolic normal forms and invariant manifolds: Astronomical applications

Abstract: In recent years, the study of the dynamics induced by the invariant manifolds of unstable periodic orbits in nonlinear Hamiltonian dynamical systems has led to a number of applications in celestial mechanics and dynamical astronomy. Two applications of main current interest are i) space manifold dynamics, i.e. the use of the manifolds in space mission design, and, in a quite different context, ii) the study of spiral structure in galaxies. At present, most approaches to the computation of orbits associated with manifold dynamics (i.e. periodic or asymptotic orbits) rely either on the use of the so-called Poincare - Lindstedt method, or on purely numerical methods. In the present article we briefly review an analytic method of computation of invariant manifolds, first introduced by Moser (1958), and developed in the canonical framework by Giorgilli (2001). We use a simple example to demonstrate how hyperbolic normal form computations can be performed, and we refer to the analytic continuation method of Ozorio de Almeida and co-workers, by which we can considerably extend the initial domain of convergence of Moser’s normal form.

Astronomical Station Vidojevica: In Situ Test of the Alta Apogee U42 CCD Camera

Abstract: Currently, the CCD camera most used by observers of the Astronomical Observatory of Belgrade is the ALTA Apogee U42. It is used for both photometric and astrometric observations. Therefore, it is very important to know different measurable parameters which describe the condition of the camera - linearity, gain, readout noise etc. In this paper, we present a thorough test of this camera.

The Intergalactic Newtonian Gravitational Field and the Shell Theorem

Abstract: The release of the 2MASS Redshift Survey (2MRS), with it’s 44599 galaxiesallows the deduction of the galaxy’s masses in nearly complete sample. Acubic box with side of 37 Mpc containing 2429 galaxies is extracted and theNewtonian gravitational eld is evaluated both at the center of the box aswell in 101 x 101 x 101 grid points of the box. The obtained results are thendiscussed at the light of the shell theorem which states that at the internalof a sphere the gravitational eld is zero.keywordsmethods: statistical; cosmology: observations; (cosmology): large-scale struc-ture of the Universe

Maximum mass ratio of am CVn-type binary systems and maximum white dwarf mass in ultra-compact x-ray binaries (addendum - Serb. Astron. J. No. 183 (2011), 63)

Abstract: We recalculated the maximum white dwarf mass in ultra-compact X-ray binaries obtained in an earlier paper (Arbutina 2011), by taking the effects of super-Eddington accretion rate on the stability of mass transfer into account. It is found that, although the value formally remains the same (under the assumed approximations), for white dwarf masses M2 >~0.1MCh mass ratios are extremely low, implying that the result for Mmax is likely to have little if any practical relevance.