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RISS 인기검색어
- 검색키워드
- 저자 : Darriulat, P. (검색결과 2 건)
- 무료
- 기관 내 무료
- 유료
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QUADRUPLY-IMAGED QUASARS: SOME GENERAL FEATURES
Tuan-Anh, P.,Thai, T.T.,Tuan, N.A.,Darriulat, P.,Diep, P.N.,Hoai, D.T.,Ngoc, N.B.,Nhung, P.T.,Phuong, N.T. The Korean Astronomical Society 2020 Journal of The Korean Astronomical Society Vol.53 No.6
Gravitational lensing of point sources located inside the lens caustic is known to produce four images in a configuration closely related to the source position. We study this relation in the particular case of a sample of quadruply-imaged quasars observed by the Hubble Space Telescope. Strong correlations between the parameters defining the image configuration are revealed. The relation between the image configuration and the source position is studied. Some simple features of the selected data sample are exposed and commented upon. In particular, evidence is found for the selected sample to be biased in favor of large magnification systems. While having no direct impact on practical analyses of specific systems, our results have pedagogical value and deepen our understanding of the mechanism of gravitational lensing.
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ALMA OBSERVATIONS OF W HYDRAE: IMPACT OF MISSING BASELINES
Do Thi Hoai,Tuan-Anh Pham,Pham Tuyet Nhung,Pierre Darriulat,Pham Ngoc Diep,Nguyen Bich Ngoc,Tran Thi Thai 한국천문학회 2021 Journal of The Korean Astronomical Society Vol.54 No.6
The lack of short baselines, referred to as the short-spacing problem (SSP), is a well-known limitation of the performance of radio interferometers, causing a reduction of the flux detected from source structure on large angular scales. The very large number of antennas operated in the Atacama Large Millimeter/sub-millimeter Array (ALMA) generates situations for which the impact of the SSP takes a complex form, not simply measurable by a single number, such as the maximal recoverable scale. In particular, extended antenna configurations, complemented by a small group of closeby antennas at the centre of the array, may result in a double-humped baseline distribution with a significant gap between the two groups. In such cases one should adopt as the effective maximal recoverable scale the one associated with the extended array and use only the central array to recover missing ux, as one would do with single dish or ACA (Atacama Compact Array) observations. The impact of the missing baselines can be very important and may easily be underestimated, or even overlooked. The present study uses ALMA archival data of the ^{29}SiO(8-7) line emission of the AGB star W Hydrae for a demonstration. A critical discussion of the reliability of the observations away from the star is presented together with comments of a broader scope. Properties of the circumstellar envelope of W Hya within ~15 au from the star, many of which are not mentioned in the published literature, are briefly described and compared with R Doradus, an AGB star having properties very similar to W Hya.
ScienceON
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