{"title":"Radio-wave diagnostics of interstellar flares in binary systems","authors":"A.V. Ipatov , A.V. Stepanov","doi":"10.1016/S0083-6656(97)00006-8","DOIUrl":"10.1016/S0083-6656(97)00006-8","url":null,"abstract":"<div><p>The possibilities for radio wave diagnostics of interstellar flares in RS CVn and Algol type binary systems using both VLBI and single dish measurements are discussed. The model for interstellar flares based on the Ohm's generalised law and the circuit analog for a current-carrying filament between two stars of the binary system is proposed. It has been shown that intense “core” radio radiation can exist between two components. Filament oscillations can be a driver for the re-current flares and/or for the quasi-periodic variations of radio emission. The oscillation period depends on the kinetic temperature of a filament. We suggest that the coherent plasma radiation plays an important role in the flare radio emission. Interstellar flare radio emission is a good diagnostic tool for the plasma parameters in a flare.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 2","pages":"Pages 203-206"},"PeriodicalIF":0.0,"publicationDate":"1997-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0083-6656(97)00006-8","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74086568","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"A polarization study of quasar 4C71.07","authors":"J.M. Hutchison, T.V. Cawthorne","doi":"10.1016/S0083-6656(97)00011-1","DOIUrl":"10.1016/S0083-6656(97)00011-1","url":null,"abstract":"<div><p>Parsec-scale observations of quasars have shown that the magnetic fields along the jets do not always lie parallel to the jet direction but there are some cases of misalignment. Preliminary results from dual frequency polarization VLBI are presented for quasar 4C71.07 (0836+710). Our results show that Faraday rotation is not the origin of the misalignment. The magnetic field is found to be misaligned to the structural jet direction by a maximum of 28 ± 4°. The consequences for the magnetic field geometry and the interaction with the narrow line region are discussed.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 2","pages":"Pages 231-235"},"PeriodicalIF":0.0,"publicationDate":"1997-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0083-6656(97)00011-1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79361021","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J.M. Marcaide , A. Alberdi , E. Ros , P. Diamond , I.I. Shapiro , J.C. Guirado , D.L. Jones , F. Mantovani , M.A. Pérez-Torres , R.A. Preston , R.T. Schilizzi , C. Trigilio , A.R. Whitney
{"title":"Expansion of SN 1993J: New λλ6 and 13 cm images","authors":"J.M. Marcaide , A. Alberdi , E. Ros , P. Diamond , I.I. Shapiro , J.C. Guirado , D.L. Jones , F. Mantovani , M.A. Pérez-Torres , R.A. Preston , R.T. Schilizzi , C. Trigilio , A.R. Whitney","doi":"10.1016/S0083-6656(97)00003-2","DOIUrl":"10.1016/S0083-6656(97)00003-2","url":null,"abstract":"<div><p>Radio supernovae are rare events among supernovae, usually taking place in distant galaxies. In recent years, great progress has been made in the study of radio supernovae with high angular resolution, due to advances in the VLBI technique and to the lucky occurrence of the powerful supernova SN 1993J in M81 only 3.6 Mpc distant. Its spatial structure has been unveiled and its expansion rate determined at 3.6 cm. Here we present new preliminary VLBI results on the expansion of this supernova at 6 and 13 cm. We resolve the shell at both wavelengths. The size estimates at 6 cm indicate a lower expansion rate than previously estimated. This may be the first evidence of deceleration.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 2","pages":"Pages 185-191"},"PeriodicalIF":0.0,"publicationDate":"1997-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0083-6656(97)00003-2","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79729298","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D.L. Jones , S.J. Tingay , D.L. Jauncey , R.A. Preston , J.E. Reynolds , D.L. Meier , D.W. Murphyl , A.K. Tzioumis , D.J. McKay , M.J. Kesteven , J.E.J. Lovell , D. Campbell-Wilson , S.P. Ellingsen , R. Gough , R.W. Hunstead , P.M. McCulloch , V. Migenes , J. Quick , M.W. Sinclair , D. Smits
{"title":"VLBI imaging of GRO J1655-40 with the sheve array","authors":"D.L. Jones , S.J. Tingay , D.L. Jauncey , R.A. Preston , J.E. Reynolds , D.L. Meier , D.W. Murphyl , A.K. Tzioumis , D.J. McKay , M.J. Kesteven , J.E.J. Lovell , D. Campbell-Wilson , S.P. Ellingsen , R. Gough , R.W. Hunstead , P.M. McCulloch , V. Migenes , J. Quick , M.W. Sinclair , D. Smits","doi":"10.1016/S0083-6656(96)00058-X","DOIUrl":"10.1016/S0083-6656(96)00058-X","url":null,"abstract":"<div><p>On 27 July 1994 the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory detected an outburst of high energy X-rays from a previously unknown source in the constellation Scorpius. This source was designated GRO J1655-40. Approximately 12 days after the start of the X-ray outburst, a strong outburst of radio emission occurred. Here we present very long baseline interferometry (VLBI) observations of GRO J1655-40 made with an array of telescopes in Australia, South Africa, and the western United States. These observations show that the radio source which appeared two weeks after the initial X-ray outburst consisted of two prominent components which separated with an apparent speed of 1.5 ± 0.4c. When the various possibilities for the geometry of the radio source are taken into account the apparent speed implies an intrinsic speed between 0.5c and 0.9c. Our results and those of other investigators imply a strong link between the accretion of material onto a highly compact object and the ejection of relativistic components of radio emission.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 1","pages":"Pages 27-31"},"PeriodicalIF":0.0,"publicationDate":"1997-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0083-6656(96)00058-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75141244","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Space VLBI—Today and tomorrow","authors":"L.I. Gurvits","doi":"10.1016/S0083-6656(97)00027-5","DOIUrl":"10.1016/S0083-6656(97)00027-5","url":null,"abstract":"<div><p>Ground-based VLBI is a front-running technique in studying the Universe with the sharpest angular resolution. However, many astrophysical problems require even higher angular resolution and the only way to achieve this, for a given wavelength, is to create an interferometer with a baseline larger than the diameter of the Earth by placing at least one telescope in space. In this contribution the scientific rationale and technical aspects of the present and future generations of Space VLBI missions are briefly discussed.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 2","pages":"Pages 317-322"},"PeriodicalIF":0.0,"publicationDate":"1997-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0083-6656(97)00027-5","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79426377","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Massi , M. Rioja , D. Gabuzda , K. Leppänen , H. Sanghera , K. Ruf , L. Moscadelli
{"title":"Non-closing errors in EVN data","authors":"M. Massi , M. Rioja , D. Gabuzda , K. Leppänen , H. Sanghera , K. Ruf , L. Moscadelli","doi":"10.1016/S0083-6656(97)00021-4","DOIUrl":"10.1016/S0083-6656(97)00021-4","url":null,"abstract":"<div><p>We show how the total intensity data acquired with the European VLBI telescopes are affected by a systematic error, the physical origin of which lies in the instrumental polarization of the telescopes. The effect on the data can be modeled and therefore removed by data processing.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 2","pages":"Pages 287-290"},"PeriodicalIF":0.0,"publicationDate":"1997-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0083-6656(97)00021-4","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86390359","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
L. Lara , G. Giovannini , W.D. Cotton , L. Feretti , T. Venturi , S.A. Baum , C.P. O'Dea , S. De Koff , W.B. Sparks
{"title":"EVN and MERLIN observations of the FR 1 radio galaxy 3C 264","authors":"L. Lara , G. Giovannini , W.D. Cotton , L. Feretti , T. Venturi , S.A. Baum , C.P. O'Dea , S. De Koff , W.B. Sparks","doi":"10.1016/S0083-6656(97)00013-5","DOIUrl":"10.1016/S0083-6656(97)00013-5","url":null,"abstract":"<div><p>We present results from simultaneous EVN and MERLIN observations of the FR 1 radio galaxy 3C 264 at 5 GHz. The combination of these two arrays allows us to obtain radio images with resolutions ranging from 4.6 to 118 mas. Moreover, we compare similar resolution images from MERLIN and the HST, compute the spectral index along the jet between optical and radio wavelengths, and confirm the synchrotron nature of the optical jet in 3C 264.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 2","pages":"Pages 241-245"},"PeriodicalIF":0.0,"publicationDate":"1997-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0083-6656(97)00013-5","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77148207","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Jets from radio pulsars","authors":"Jon Bell","doi":"10.1016/S0083-6656(96)00067-0","DOIUrl":"10.1016/S0083-6656(96)00067-0","url":null,"abstract":"<div><p>The observational evidence for jets and phenomena arising from rotation powered radio pulsars is reviewed, including many recent and exciting discoveries at X-ray wavelengths. The well studied jets of the Crab pulsar are summarised, including recent results from the HST. The evolutionary links between the known binary radio pulsars and jets sources in X-ray binaries are discussed.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 1","pages":"Pages 87-93"},"PeriodicalIF":0.0,"publicationDate":"1997-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0083-6656(96)00067-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75062943","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"EVN maps of 5 cm line OH emission from star-forming regions","authors":"J.-F. Desmurs , A. Baudry , D.A. Graham","doi":"10.1016/S0083-6656(97)00001-9","DOIUrl":"10.1016/S0083-6656(97)00001-9","url":null,"abstract":"<div><p>We have used three antennas of the EVN (Effelsberg, Medicina and Jodrell Bank) to observe in W3(OH) and in five other star-forming regions, simultaneously, and for the first time, the two main lines of the <span><math><msup><mi></mi><mn>2</mn></msup><mtext>φ</mtext><msub><mi></mi><mn><mtext>3</mtext><mtext>2</mtext></mn></msub></math></span>, <span><math><mtext>J</mtext><mtext>=</mtext><mtext>5</mtext><mtext>2</mtext></math></span> excited state of OH with right and left circularly polarized feeds. The data were correlated with the MkIII MPIfR correlator in Bonn and processed with the AIPS package at the Observatoire de Bordeaux. In W3(OH) we made cleaned maps of all individual channels for each line and polarization. These maps made with a 5×6.5 mas beam reveal complex kinematics and spatial structure with both extended emission and unresolved features. This fact and polarization properties demon-strate the masing nature of the emission. Maser features are identified by searching for emission over adjacent channels, and adjacent positions (within about one synthesized beam) in both polarizations after we had mapped and selected one channel as a phase reference. We have been able to identify OH Zeeman pairs and to estimate the magnetic field strength across W3(OH); the field varies from about 1 to 10 mG. At the time of this conference, three other star-forming regions (M17, ON1 and W51) show fringes while two other regions are still incompletely processed.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 2","pages":"Pages 169-173"},"PeriodicalIF":0.0,"publicationDate":"1997-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0083-6656(97)00001-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73677717","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"High quality astronomical image compression","authors":"J.-L. Starck , F. Murtagh , M. Louys","doi":"10.1016/S0083-6656(97)00049-4","DOIUrl":"10.1016/S0083-6656(97)00049-4","url":null,"abstract":"<div><p>We present a new image compression method, for very high quality lossy compression. This method caters for image data in regimes of (i) detector imperfections, which motivates a robust approach based on the median transform, and (ii) noise, which is explicitly sought and separated out, since noise is inherently non-compressible. An in-depth assessment is carried out on real data, relative to the standard JPEG compression method. Comparable visual quality is based on 260:1 compression with the new method, and 40:1 compression with JPEG. The assessment procedure, based on the astronomical images used, is an objective approach for determining very high quality visual reconstructions.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 3","pages":"Pages 439-445"},"PeriodicalIF":0.0,"publicationDate":"1997-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0083-6656(97)00049-4","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73745409","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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