천문학회지 (Journal of The Korean Astronomical Society)

  • 제54권6호
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  • Pages.171-182
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  • 2021
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  • 1225-4614(pISSN)
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  • 2288-890X(eISSN)
한국천문학회 (The Korean Astronomical Society)
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ALMA OBSERVATIONS OF W HYDRAE: IMPACT OF MISSING BASELINES

  • Do, Thi Hoai (Department of Astrophysics, Vietnam National Space Center, Vietnam Academy of Science and Technology) ;
  • Pham, Tuan Anh (Department of Astrophysics, Vietnam National Space Center, Vietnam Academy of Science and Technology) ;
  • Pham, Tuyet Nhung (Department of Astrophysics, Vietnam National Space Center, Vietnam Academy of Science and Technology) ;
  • Darriulat, Pierre (Department of Astrophysics, Vietnam National Space Center, Vietnam Academy of Science and Technology) ;
  • Pham, Ngoc Diep (Department of Astrophysics, Vietnam National Space Center, Vietnam Academy of Science and Technology) ;
  • Nguyen, Bich Ngoc (Department of Astrophysics, Vietnam National Space Center, Vietnam Academy of Science and Technology) ;
  • Tran, Thi Thai (Department of Astrophysics, Vietnam National Space Center, Vietnam Academy of Science and Technology)
  • 투고 : 2021.08.30
  • 심사 : 2021.11.23
  • 발행 : 2021.12.31
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초록

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 flux, 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 29SiO(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.

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과제정보

We thank Dr. Stephane Guilloteau for useful discussions and Dr. Aki Takigawa for clarifications on the maximal recoverable scale used in their article. This paper uses ALMA data ADS/JAO.ALMA#2015.1.01446.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The data are retrieved from the JVO/NAOJ portal. We are deeply indebted to the ALMA partnership, whose open access policy means invaluable support and encouragement for Vietnamese astrophysics. Financial support from the World Laboratory, the Odon Vallet Foundation and VNSC is gratefully acknowledged. This research is funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 103.99-2019.368.

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