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Multi-epoch VLBA 15 and 43 GHz observations of the gravitational lens PKS 1830-211: Extending VLBI towards the micro-arcsecond scale 引力透镜PKS 1830-211的多历元VLBA 15和43 GHz观测:将VLBI扩展到微弧秒尺度
Vistas in Astronomy Pub Date : 1997-01-01 Epub Date: 1999-11-23 DOI: 10.1016/S0083-6656(97)00020-2
M.A. Garrett , S. Nair , R.W. Porcas , A.R. Patnaik
{"title":"Multi-epoch VLBA 15 and 43 GHz observations of the gravitational lens PKS 1830-211: Extending VLBI towards the micro-arcsecond scale","authors":"M.A. Garrett ,&nbsp;S. Nair ,&nbsp;R.W. Porcas ,&nbsp;A.R. Patnaik","doi":"10.1016/S0083-6656(97)00020-2","DOIUrl":"10.1016/S0083-6656(97)00020-2","url":null,"abstract":"<div><p>We present multi-epoch, VLBA maps of PKS 1830-211 at 15 and 43 GHz. The 43 GHz observations reveal complicated submilliarcsecond radio structure in the cores of both lensed images. This structure appears to change dramatically between the two epochs (separated by 44 days). One explanation for these unusually rapid structural changes is that the lens magnifies each image, such that the nominal submilliarcsecond scale of these maps is enhanced by a factor of between 5 and 10—effectively boosting our resolution towards the micro-arcsecond scale.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 2","pages":"Pages 281-285"},"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)00020-2","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86781275","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}
引用次数: 16
High dynamic range imaging with the EVN 高动态范围成像与EVN
Vistas in Astronomy Pub Date : 1997-01-01 Epub Date: 1999-11-23 DOI: 10.1016/S0083-6656(97)00022-6
K. Leppänen , M. Massi , M. Rioja , H. Sanghera
{"title":"High dynamic range imaging with the EVN","authors":"K. Leppänen ,&nbsp;M. Massi ,&nbsp;M. Rioja ,&nbsp;H. Sanghera","doi":"10.1016/S0083-6656(97)00022-6","DOIUrl":"10.1016/S0083-6656(97)00022-6","url":null,"abstract":"<div><p>It has been claimed that MkIII/EVN experiments do not achieve the expected level of image quality, or dynamic range. An EVN test observation of a strong and compact source, DA193, has allowed us to investigate in detail the possible systematic errors affecting EVN images. Indeed, we have identified two effects which both significantly affect image quality: instrumental polarization and an amplitude error caused by the stepwise delay tracking in XF-correlators. This paper shows how these effects influence total-intensity images and discusses the correction of these non-closing errors. Their removal increased the peak/rms dynamic range from 5000 to 19,000 in our image of DA193.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 2","pages":"Pages 291-295"},"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)00022-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91131113","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}
引用次数: 1
High precision astrometry with closure constraints: The triplet 1803+784/1928+738/2007+777 具有闭合约束的高精度天体测量:三重态1803+784/1928+738/2007+777
Vistas in Astronomy Pub Date : 1997-01-01 Epub Date: 1999-11-23 DOI: 10.1016/S0083-6656(97)00007-X
E. Ros , J.M. Marcaide , J.C. Guirado , T.P. Krichbaum , R.A. Preston , M.I. Ratner , I.I. Shapiro , A. Witzel
{"title":"High precision astrometry with closure constraints: The triplet 1803+784/1928+738/2007+777","authors":"E. Ros ,&nbsp;J.M. Marcaide ,&nbsp;J.C. Guirado ,&nbsp;T.P. Krichbaum ,&nbsp;R.A. Preston ,&nbsp;M.I. Ratner ,&nbsp;I.I. Shapiro ,&nbsp;A. Witzel","doi":"10.1016/S0083-6656(97)00007-X","DOIUrl":"10.1016/S0083-6656(97)00007-X","url":null,"abstract":"<div><p>Improvements in the technique of high precision differential astrometry in VLBI based on the use of triangles of radio sources are reported. Such geometry provides new constraints by taking advantage of “closure”. Results on the relative separations (ranging from 4.6 to 6.8°) of the sources in the triangle 1803+784/1928+738/2007+777 from ionosphere-free delays are shown and “sky closure” verified. A comparison with previous results on the pair 1928+738/2007+777 is also presented.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 2","pages":"Pages 207-211"},"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)00007-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82159571","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}
引用次数: 0
Multiscale data analysis - information fusion and constant-time clustering 多尺度数据分析——信息融合与恒时聚类
Vistas in Astronomy Pub Date : 1997-01-01 Epub Date: 1999-11-23 DOI: 10.1016/S0083-6656(97)00039-1
F. Murtagh , A. Aussem , J.-L. Starck
{"title":"Multiscale data analysis - information fusion and constant-time clustering","authors":"F. Murtagh ,&nbsp;A. Aussem ,&nbsp;J.-L. Starck","doi":"10.1016/S0083-6656(97)00039-1","DOIUrl":"10.1016/S0083-6656(97)00039-1","url":null,"abstract":"<div><p>We describe the use of the wavelet transform for multivariate data analysis problems. In prediction, a multiscale transform of time-varying data can allow forecasts of each scale, followed by a combining of the individual forecasts. The use of a wavelet transform with noise modeling for point pattern clustering can lead to the result, which initially appears counterintuitive, of clustering in constant computational time, <em>O</em> (1).</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 3","pages":"Pages 359-364"},"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)00039-1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81792218","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}
引用次数: 1
Concentration of information by transforms 通过变换来集中信息
Vistas in Astronomy Pub Date : 1997-01-01 Epub Date: 1999-11-23 DOI: 10.1016/S0083-6656(97)00050-0
Gotthard M. Richter , Rob Assendorp , Petra Böhm , Stefan Bogun
{"title":"Concentration of information by transforms","authors":"Gotthard M. Richter ,&nbsp;Rob Assendorp ,&nbsp;Petra Böhm ,&nbsp;Stefan Bogun","doi":"10.1016/S0083-6656(97)00050-0","DOIUrl":"10.1016/S0083-6656(97)00050-0","url":null,"abstract":"<div><p>The concentration of information is a general problem in image processing. We illustrate this in a particularly simple case, the ISO Serendipity Survey, where a detector of 2 × 2 pixels slews through the sky and the task is to detect point sources. There is a theoretically optimal solution for information concentration: the Eigenvalue Transform. The practical shortcomings of the ET are solved by the Karhunen-Loèv Transform concept; and the application of the KLT to our particular problem yields the first-order two-dimensional Haar Transform. The above mentioned transform concentrates the information of the point sources and the glitches in different coefficients (gradient and curvature respectively). A one-dimensional (along the slew) Adaptive Filtering of the gradient is used to detect the point sources.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 3","pages":"Pages 447-453"},"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)00050-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84574630","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}
引用次数: 0
Southern radio emitting X-ray binary stars 发射x射线双星的南方无线电
Vistas in Astronomy Pub Date : 1997-01-01 Epub Date: 1998-05-20 DOI: 10.1016/S0083-6656(96)00060-8
R.E. Spencer , A.K. Tzioumis , L.R. Ball , S.J. Newell , V. Migenes
{"title":"Southern radio emitting X-ray binary stars","authors":"R.E. Spencer ,&nbsp;A.K. Tzioumis ,&nbsp;L.R. Ball ,&nbsp;S.J. Newell ,&nbsp;V. Migenes","doi":"10.1016/S0083-6656(96)00060-8","DOIUrl":"10.1016/S0083-6656(96)00060-8","url":null,"abstract":"<div><p>A survey of southern X-ray binary stars from the van Paradijs catalogue has been made using the Australia Telescope Compact Array. Detection sensitivities of under 1 mJy were achieved for each of the 91 fields of declinations &lt; −30° observed at 6 and 3 cm wavelength. Eight objects were detected within the inner imaged field of 128<sup>2</sup> arc-sec<sup>2</sup> at flux densities of ≥ 1 mJy. Preliminary work on improving the sensitivity of the survey by mapping the whole primary field of the ATCA antennas is reported.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 1","pages":"Pages 37-41"},"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)00060-8","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87117514","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}
引用次数: 3
Multichannel image restoration in astronomy 天文学中的多通道图像恢复
Vistas in Astronomy Pub Date : 1997-01-01 Epub Date: 1999-11-23 DOI: 10.1016/S0083-6656(97)00041-X
Rafael Molina, Javier Mateos
{"title":"Multichannel image restoration in astronomy","authors":"Rafael Molina,&nbsp;Javier Mateos","doi":"10.1016/S0083-6656(97)00041-X","DOIUrl":"10.1016/S0083-6656(97)00041-X","url":null,"abstract":"<div><p>Over the last few years quite a lot of research has been devoted to restoring astronomical images, but not much work has been reported on the use of multichannel techniques to restore such images. In this work, we apply the Bayesian paradigm to restore multichannel astronomical images. We compare classical methods which are formulated as Bayesian deconvolution techniques and propose a new method based on a multichannel prior distribution that preserves the flux within each channel. The methods are compared on real multichannel astronomical images.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 3","pages":"Pages 373-378"},"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)00041-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79880434","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}
引用次数: 6
The calendar of the future. A world calendar with leap week 未来的日历。带有闰周的世界日历
Vistas in Astronomy Pub Date : 1997-01-01 Epub Date: 1999-11-23 DOI: 10.1016/S0083-6656(97)00033-0
Josef Šuráň
{"title":"The calendar of the future. A world calendar with leap week","authors":"Josef Šuráň","doi":"10.1016/S0083-6656(97)00033-0","DOIUrl":"https://doi.org/10.1016/S0083-6656(97)00033-0","url":null,"abstract":"<div><p>There exists a unique perpetual (solar) calendar with leap week that could become the basis for an eventual world calendar reform. Unlike the Universal Calendar considered for such a reform by the UN in 1956, rejected in a vote, it does not interrupt the continuity of weeks, which was the chief objection against this calendar. Except for the mentioned serious chronological defect, the Universal Calendar would otherwise have had many advantages. The leap week concept had been suggested earlier, but was never elaborated properly. Relevant theoretical questions and a suitable form of the calendar based on this concept are discussed. There is also a glimpse of the possible form of our calendar in a very distant future and of a calendar in cosmic space. The new calendar proposed is an optimum compromise for a solar calendar. While preserving advantages of the Universal Calendar, it fulfills all modern requirements: constancy, uniformity, continuity, simplicity and accuracy. With the leap rule derived (with regard to uniform time) an error of one day would occur in the new calendar in an interval longer than 10000 years. It could obtain a global acceptance, because there would be no discordance in the day of the week with respect to other existing calendars having a weekly cycle (such as, e.g., Jewish, Muslim, etc.).</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 4","pages":"Pages 493-506"},"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)00033-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91694756","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}
引用次数: 0
Search for radio jets in Cygnus X-1 搜寻天鹅座X-1的射电喷流
Vistas in Astronomy Pub Date : 1997-01-01 Epub Date: 1998-05-20 DOI: 10.1016/S0083-6656(96)00059-1
J. Martí , I.F. Mirabel , L.F. Rodríguez , J.M. Paredes
{"title":"Search for radio jets in Cygnus X-1","authors":"J. Martí ,&nbsp;I.F. Mirabel ,&nbsp;L.F. Rodríguez ,&nbsp;J.M. Paredes","doi":"10.1016/S0083-6656(96)00059-1","DOIUrl":"10.1016/S0083-6656(96)00059-1","url":null,"abstract":"<div><p>We present very deep VLA radio maps of the field around the Cyg X-1 radio counterpart. These images were obtained in an attempt to search for radio jets emanating from this black hole candidate.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 1","pages":"Pages 33-36"},"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)00059-1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73373772","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}
引用次数: 1
Object-based image coding 基于对象的图像编码
Vistas in Astronomy Pub Date : 1997-01-01 Epub Date: 1999-11-23 DOI: 10.1016/S0083-6656(97)00051-2
Montse Pardàs
{"title":"Object-based image coding","authors":"Montse Pardàs","doi":"10.1016/S0083-6656(97)00051-2","DOIUrl":"10.1016/S0083-6656(97)00051-2","url":null,"abstract":"<div><p>Object-based compression methods describe images in terms of a set of regions (a partition), and of some information for each region to be used by the receiver to reconstruct the image (its texture). Different techniques can be used to define the partition as well as for coding it and its texture. In this paper we propose a general multi-resolution segmentation algorithm which can deal with many different types of images selecting the appropriated criteria. We also review most outstanding techniques for coding in this context.</p></div>","PeriodicalId":101275,"journal":{"name":"Vistas in Astronomy","volume":"41 3","pages":"Pages 455-461"},"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)00051-2","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78984996","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}
引用次数: 0
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