Swift UVOT near-UV transit observations of WASP-121 b
Swift UVOT near-UV transit observations of WASP-121 b
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DOI：
10.1051/0004-6361/201732419
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发表时间：
2019-01
影响因子：
6.5
通讯作者：
M. Salz;P. Schneider;Luca Fossati;S. Czesla;J. Schmitt
中科院分区：
文献类型：
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作者：
M. Salz;P. Schneider;Luca Fossati;S. Czesla;J. Schmitt
近距离的气体行星会受到持续的光蒸发作用，这会侵蚀它们挥发性的外壳。今天，通过紫外光谱范围内的凌日观测，已经在少数个别系统中证实了持续的质量损失。我们证明，紫外/光学望远镜（UVOT）板载尼尔Gehrels斯威夫特天文台使测光的相对精度约为0.5%，并提出了第一个近紫外（200-270 nm，NUV）过境观测的WASP-121 B，热木星与最高的预测质量损失率之一。数据涵盖轨道相位0.85-1.15，有三次访问。我们测量了2.10 ± 0.29%的宽带NUV渡越深度。虽然仍与1.55%的光学值一致，但NUV数据表明在1.9σ水平下过量吸收为0.55%。这种过量吸收是从WASP-12系统中已知的，并且这两种热蒸发器预计都将以极高的速率经历质量损失。通过云模拟，我们发现，在稠密的扩展大气中，Fe II的吸收线可以在0.5%的水平上引起宽带近紫外吸收。鉴于低电离金属的大量线，NUV范围是最热气体行星中光蒸发的有希望的示踪剂。
Close-in gas planets are subject to continuous photoevaporation that can erode their volatile envelopes. Today, ongoing mass loss has been confirmed in a few individual systems via transit observations in the ultraviolet spectral range. We demonstrate that the Ultraviolet/Optical Telescope (UVOT) onboard the Neil Gehrels Swift Observatory enables photometry to a relative accuracy of about 0.5% and present the first near-UV (200–270 nm, NUV) transit observations of WASP-121 b, a hot Jupiter with one of the highest predicted mass-loss rates. The data cover the orbital phases 0.85–1.15 with three visits. We measure a broadband NUV transit depth of 2.10 ± 0.29%. While still consistent with the optical value of 1.55%, the NUV data indicate excess absorption of 0.55% at a 1.9σ level. Such excess absorption is known from the WASP-12 system, and both of these hot Jupiters are expected to undergo mass loss at extremely high rates. With a Cloudy simulation, we show that absorption lines of Fe II in a dense extended atmosphere can cause broadband near-UV absorption at the 0.5% level. Given the numerous lines of low-ionization metals, the NUV range is a promising tracer of photoevaporation in the hottest gas planets.