标题： 确认在650百万年古老的亚海王星HD235088 b（TOI-1430 b）周围存在氦I蒸发大气层，使用CARMENES 显示英文标题

标题： Confirmation of an He I evaporating atmosphere around the 650-Myr-old sub-Neptune HD235088 b (TOI-1430 b) with CARMENES

摘要： HD235088 (TOI-1430) 是一颗年轻的恒星，已知拥有一颗亚海王星大小的行星候选体。 我们通过多波段光度测量验证了HD235088 b的行星性质，优化了其行星参数，并获得了恒星的新年龄估计，将其置于600-800百万年。 之前的光谱观测在一次凌日过程中检测到了与行星候选体凌日时间一致的He I过量吸收。 在这里，我们通过CARMENES观测的一次凌日确认了HD235088 b大气中存在He I。 我们还检测到氦信号强度的变化迹象，吸收率为$-$0.91$\pm$0.11%，比之前的测量值略深（2$\sigma$）。 此外，我们用一个球对称的一维流体动力学模型模拟了He I信号，发现HD235088 b的上层大气以显著的质量损失率(1.5-5)$\times$10$^{10}$g s$^{-1}$进行流体动力学逃逸，在相对冷的流出物中，$T$=3125$\pm$375 K，在光子限制逃逸区域。 HD235088 b ($R_{p}$ = 2.045$\pm$0.075 R$_{\oplus}$) 是迄今为止发现的具有固态大气检测的最小行星——不仅检测到了 He I，还检测到了其他任何原子或分子。 这使其成为进一步分析演化中的年轻亚海王星大气的基准行星。 显示英文摘要

摘要： HD235088 (TOI-1430) is a young star known to host a sub-Neptune-sized planet candidate. We validated the planetary nature of HD235088 b with multiband photometry, refined its planetary parameters, and obtained a new age estimate of the host star, placing it at 600-800 Myr. Previous spectroscopic observations of a single transit detected an excess absorption of He I coincident in time with the planet candidate transit. Here, we confirm the presence of He I in the atmosphere of HD235088 b with one transit observed with CARMENES. We also detected hints of variability in the strength of the helium signal, with an absorption of $-$0.91$\pm$0.11%, which is slightly deeper (2$\sigma$) than the previous measurement. Furthermore, we simulated the He I signal with a spherically symmetric 1D hydrodynamic model, finding that the upper atmosphere of HD235088 b escapes hydrodynamically with a significant mass loss rate of (1.5-5) $\times$10$^{10}$g s$^{-1}$, in a relatively cold outflow, with $T$=3125$\pm$375 K, in the photon-limited escape regime. HD235088 b ($R_{p}$ = 2.045$\pm$0.075 R$_{\oplus}$) is the smallest planet found to date with a solid atmospheric detection - not just of He I but any other atom or molecule. This positions it a benchmark planet for further analyses of evolving young sub-Neptune atmospheres.