标题： 阿塔卡马大型毫米/亚毫米阵列揭示了日晒伤：球状星团 47 天鹅座中渐近巨星分支星周围的 CO 分子离解 显示英文标题

标题： ALMA reveals sunburn: CO dissociation around AGB stars in the globular cluster 47 Tucanae

摘要： 阿塔卡马大型毫米/亚毫米阵列（ALMA）的观测结果显示，在半人马座ω星团中最亮的四颗渐近巨星分支（AGB）恒星周围未探测到一氧化碳。 恒星演化模型和恒星计数表明，这些恒星的质量损失率应为~1.2-3.5 × 10⁻⁷太阳质量每年。 我们天真地认为以这个距离（4.5千秒差距），这样的恒星应该是可以被探测到的。 通过建模半人马座ω星团中的后渐近巨星分支恒星和白矮星的紫外辐射场，我们得出结论，一氧化碳应该在异常靠近这些恒星的地方被分解。 我们估计，这些恒星的一氧化碳包层将在距离它们宿主恒星几百个恒星半径处被截断，并且这些谱线的强度大约比我们目前的探测极限低两个数量级。 一氧化碳包层的截断对于密集星团中的AGB恒星来说应该是重要的。 观测更高能级的一氧化碳（3-2）以及其他跃迁，并将目标锁定在远离星团中心的恒星上，应当能够得到所需的探测结果，从而测量出这些恒星的外流速度。 显示英文摘要

摘要： ALMA observations show a non-detection of carbon monoxide around the four most luminous asymptotic giant branch (AGB) stars in the globular cluster 47 Tucanae. Stellar evolution models and star counts show that the mass-loss rates from these stars should be ~1.2-3.5 x 10^-7 solar masses per year. We would naively expect such stars to be detectable at this distance (4.5 kpc). By modelling the ultraviolet radiation field from post-AGB stars and white dwarfs in 47 Tuc, we conclude CO should be dissociated abnormally close to the stars. We estimate that the CO envelopes will be truncated at a few hundred stellar radii from their host stars and that the line intensities are about two orders of magnitude below our current detection limits. The truncation of CO envelopes should be important for AGB stars in dense clusters. Observing the CO (3-2) and higher transitions and targeting stars far from the centres of clusters should result in the detections needed to measure the outflow velocities from these stars.