具有行星形成尺度（MAPS）的ALMA的分子。VII。行星供气中的亚恒星O/H和C/H以及超恒星C/O
Molecules with ALMA at Planet-forming Scales (MAPS). VII. Sub-stellar O/H and C/H and super-stellar C/O in planet feeding gas
摘要：
原行星盘中气体和尘埃的元素组成影响着形成于其中的行星的组成，我们利用分子与行星形成尺度的ALMA（MAPS）数据来约束潜在形成行星位置的气体元素组成。元素丰度推断源特定的气体颗粒热化学模型进行比较，可变的C/O比和小颗粒丰度，从DALI代码与CO和C2 H柱密度来自高分辨率的观测磁盘AS 209，HD 163296，和MWC 480。升高的C/O比（~2.0），即使在CO冰线，是必要的，以配合推断的C2 H柱密度，在大多数卵石盘。结合这些系统中CO丰度的限制，这意味着气体中的O/H和C/H比都是亚恒星的4-10倍，O/H消耗了20-50倍，导致高C/O比。这使得即使在CO冰线内，大部分挥发性碳和氧仍然被捕获在中平面的颗粒上。因此，在AS 209、HD 163296和MWC 480盘的间隙中吸积气体的行星在到达卵石隔离质量后将获得非常少的碳和氧。在没有大气富集事件的情况下，这些行星将因此具有强烈的亚恒星O/H和C/H以及超恒星C/O大气成分。
英文摘要：
The elemental composition of the gas and dust in a protoplanetary disk influences the compositions of the planets that form in it. We use the Molecules with ALMA at Planet-forming Scales (MAPS) data to constrain the elemental composition of the gas at the locations of potentially forming planets. The elemental abundances are inferred by comparing source-specific gas-grain thermochemical models, with variable C/O ratios and small-grain abundances, from the DALI code with CO and C2H column densities derived from the high-resolution observations of the disks of AS 209, HD 163296, and MWC 480. Elevated C/O ratios (~2.0), even within the CO ice line, are necessary to match the inferred C2H column densities, over most of the pebble disk. Combined with constraints on the CO abundances in these systems, this implies that both the O/H and C/H ratios in the gas are substellar by a factor of 4-10, with the O/H depleted by a factor of 20-50, resulting in the high C/O ratios. This necessitates that even within the CO ice line, most of the volatile carbon and oxygen is still trapped on grains in the midplane. Planets accreting gas in the gaps of the AS 209, HD 163296, and MWC 480 disks will thus acquire very little carbon and oxygen after reaching the pebble isolation mass. In the absence of atmosphere-enriching events, these planets would thus have a strongly substellar O/H and C/H and superstellar C/O atmospheric composition.
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