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行星形成尺度上具有ALMA的分子(MAPS)II:CLEAN合成原行星盘中分子谱线发射图像的策略

Molecules with ALMA at Planet-forming Scales (MAPS) II: CLEAN Strategies for Synthesizing Images of Molecular Line Emission in Protoplanetary Disks

Ian Czekala, Ryan A. Loomis, Richard Teague, Alice S. Booth, Jane Huang, Gianni Cataldi, John D. Ilee, Charles J. Law, Catherine Walsh, Arthur D. Bosman, Vivian… 展开作者

Ian Czekala, Ryan A. Loomis, Richard Teague, Alice S. Booth, Jane Huang, Gianni Cataldi, John D. Ilee, Charles J. Law, Catherine Walsh, Arthur D. Bosman, Viviana V. Guzmán, Romane Le Gal, Karin I. Öberg, Yoshihide Yamato, Yuri Aikawa, Sean M. Andrews, Jaehan Bae, Edwin A. Bergin, Jennifer B. Bergner, L. Ilsedore Cleeves, Nicolas T. Kurtovic, François Ménard, Hideko Nomura, Laura M. Pérez, Chunhua Qi, Kamber R. Schwarz, Takashi Tsukagoshi, Abygail R. Waggoner, David J. Wilner, Ke Zhang

摘要:

行星形成尺度下的分子与ALMA大型计划(MAPS LP)以高角分辨率调查了五个原行星盘的化学结构,跨越40多条不同的谱线(对于频带6和3分别为0.15”和0.30”梁)和灵敏度(对于频带6和3分别为0.3 - 1.3 mJy/梁和0.4 - 1.9 mJy/梁)。在本文中,我们描述了我们的多阶段工作流程-围绕CASA tclean图像反卷积程序构建-我们用于生成MAPS LP的核心数据产品:每条谱线的位置-位置-速度图像立方体。由于调查的广泛性,我们遇到了一系列的成像挑战;一些是亚毫米原行星盘社区熟悉的,如使用精确的CLEAN掩模的好处,和其他不太知名的,如Jorsater和van Moorsel 1995年首次描述的CLEAN残差图的错误默认通量缩放(“JvM效应”)。我们将学到的经验教训提炼成推荐的工作流程,用于合成分子发射的图像立方体。特别是,我们描述了如何通过“JvM校正”产生具有准确通量的图像立方体,该过程通常适用于通过CLEAN反卷积合成的任何图像,但对于低S/N发射尤其重要。我们进一步解释了我们如何使用可见度逐渐变细,以促进一个共同的,基准光束的大小和上下文的信噪比的解释时,检测分子发射从原行星盘。本文是《天体物理学杂志增刊》MAPS特刊的一部分。

英文摘要:

The Molecules with ALMA at Planet-forming Scales large program (MAPS LP) surveyed the chemical structures of five protoplanetary disks across more than 40 different spectral lines at high angular resolution (0.15" and 0.30" beams for Bands 6 and 3, respectively) and sensitivity (spanning 0.3 - 1.3 mJy/beam and 0.4 - 1.9 mJy/beam for Bands 6 and 3, respectively). In this article, we describe our multi-stage workflow -- built around the CASA tclean image deconvolution procedure -- that we used to generate the core data product of the MAPS LP: the position-position-velocity image cubes for each spectral line. Owing to the expansive nature of the survey, we encountered a range of imaging challenges; some are familiar to the sub-mm protoplanetary disk community, like the benefits of using an accurate CLEAN mask, and others less well-known, like the incorrect default flux scaling of the CLEAN residual map first described in Jorsater & van Moorsel 1995 (the "JvM effect"). We distill lessons learned into recommended workflows for synthesizing image cubes of molecular emission. In particular, we describe how to produce image cubes with accurate fluxes via the "JvM correction," a procedure that is generally applicable to any image synthesized via CLEAN deconvolution but is especially critical for low S/N emission. We further explain how we used visibility tapering to promote a common, fiducial beam size and contextualize the interpretation of signal to noise ratio when detecting molecular emission from protoplanetary disks. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.

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