标题： 使用SCUBA-2 850-$μ$米波段对猎户座$λ$星团中的恒星盘进行巡天调查 显示英文标题

标题： A SCUBA-2 850-$μ$m survey of circumstellar disks in the $λ$ Orionis cluster

摘要： We present results from an 850-$\mu$m survey of the $\sim$ 5 Myr old $\lambda$ Orionis star-forming region. We used the SCUBA-2 camera on the James Clerk Maxwell Telescope to survey a $\sim$0.5-diameter circular region containing 36 (out of 59) cluster members with infrared excesses indicative of circumstellar disks. 我们仅在$>3\sigma$显著性水平上检测到一个目标，即Herbig Ae星HD 245185，其流量密度为$\sim74$毫焦耳/束$^{-1}$，对应于$\sim150$M$_{\oplus}$的尘埃质量。 将单独未被探测到的源叠加在一起并没有产生显著的平均信号，但给出了猎户座盘中平均尘埃质量的一个上限，即$\lambda$ 的尘埃质量小于$\sim3$ M$_{\oplus}$。 Our follow-up observations of HD 245185 with the Submillimeter Array found weak CO 2--1 line emission with an integrated flux of $\sim170$ mJy km s$^{-1}$ but no $^{13}$CO or C$^{18}$O isotopologue emission at 30 mJy km s$^{-1}$ sensitivity, suggesting a gas mass of $\lesssim1$ M$_{\rm Jup}$. 由此推断的气体与尘埃比例比星际介质的标准值低了$\gtrsim50$倍，这使得 HD 245185 有别于其他年龄相近的赫比格Ae星盘，那些星盘被发现富含气体；由于HD 245185也显示出吸积的迹象，我们或许正在观测它在清除盘的最后阶段。我们对猎户座星团中$\lambda$的研究对行星形成的时间尺度进行了定量限制，表明在$\sim5$百万年时，平均盘不再有足够的尘埃和气体来形成巨型行星，甚至可能无法形成超级地球；大部分物质已经分散或者以毫米大小以上的砾石/星子形式存在。 显示英文摘要

摘要： We present results from an 850-$\mu$m survey of the $\sim$ 5 Myr old $\lambda$ Orionis star-forming region. We used the SCUBA-2 camera on the James Clerk Maxwell Telescope to survey a $\sim$0.5-diameter circular region containing 36 (out of 59) cluster members with infrared excesses indicative of circumstellar disks. We detected only one object at $>3\sigma$ significance, the Herbig Ae star HD 245185, with a flux density of $\sim74$ mJy beam$^{-1}$ corresponding to a dust mass of $\sim150$ M$_{\oplus}$. Stacking the individually undetected sources did not produce a significant mean signal but gives an upper limit on the average dust mass for $\lambda$ Orionis disks of $\sim3$ M$_{\oplus}$. Our follow-up observations of HD 245185 with the Submillimeter Array found weak CO 2--1 line emission with an integrated flux of $\sim170$ mJy km s$^{-1}$ but no $^{13}$CO or C$^{18}$O isotopologue emission at 30 mJy km s$^{-1}$ sensitivity, suggesting a gas mass of $\lesssim1$ M$_{\rm Jup}$. The implied gas-to-dust ratio is thus $\gtrsim50$ times lower than the canonical interstellar medium value, setting HD 245185 apart from other Herbig Ae disks of similar age, which have been found to be gas rich; as HD 245185 also shows signs of accretion, we may be catching it in the final phases of disk clearing. Our study of the $\lambda$ Orionis cluster places quantitative constraints on planet formation timescales, indicating that at $\sim5$ Myr the average disk no longer has sufficient dust and gas to form giant planets and perhaps even super Earths; the bulk material has been mostly dispersed or is locked in pebbles/planetesimals larger than a few mm in size.