论文标题
夏季群集中的质量分离
Mass Segregation in the Hyades Cluster
论文作者
论文摘要
使用Gaia Colour-agnitude图，我们将质量分配给979个确认的hyades群集和尾巴成员的目录。通过拟合累积的质量轮廓，潮汐半径内的恒星具有5.75 pc的plummer状轮廓，带有半质量半径$ r _ {\ rm h} $。尾巴用$ r _ {\ rm h} = 69.35 $ PC扩展，并且掉落的速度比Plummer降低，其密度与距离成正比$^{ - 1.36} $。将簇星分成两组，分为BP-RP $ = 2 $或$ 0.56 m_ \ odot $，以给出高质量（$ {\ bar m} = 0.95 m_ \ odot $）和低质量（$ {\ bar m} = 0.32 m_ \ odot $）。我们表明：（i）高质量人口具有4.88 pc的半质量半径$ r _ {\ rm h} $，而低质量人口的$ r _ {\ rm h} = 8.10 $ pc; （ii）尽管空间范围有所不同，但高质量和低质量种群的运动学和二进制特性却相似。他们的各向同性速度椭圆形分别为0.427和0.415 km s $^{ - 1} $。 Hyades的动态状态远非能源等电位（$σ\ propto {\ bar m}^{ - 1/2} $）。我们为具有逃生速度$ v $的集群确定了新的质量分离不稳定性。 $ v/σ\ Lessim 2 \ sqrt {2} $的种群永远无法达到热平衡和均衡。该机制包括许多银河开放和球状簇。对于hyades，必须有至少$ 9.5 \ times 10^{ - 4} m_ \ odot \，{\ rm km^2 \，s^{ - 2} myr^{ - 1}} $保持其当前配置。目前的质量损失$ 0.26 m_ \ odot {\ rm myr}^{ - 1} $由于潮汐剥离本身而导致的意味着超出了所需幅度的大量能量流。
Using the Gaia colour-magnitude diagram, we assign masses to a catalogue of 979 confirmed members of the Hyades cluster and tails. By fitting the cumulative mass profile, stars within the tidal radius have a Plummer-like profile with half-mass radius $r_{\rm h}$ of 5.75 pc. The tails are extended with $r_{\rm h} = 69.35$ pc and fall off more slowly than Plummer with density proportional to distance$^{-1.36}$. The cluster stars are separated into two groups at BP-RP $=2$ or $0.56 M_\odot$ to give a high mass (${\bar M} = 0.95 M_\odot$) and a low mass (${\bar M} = 0.32 M_\odot$) population. We show that: (i) the high mass population has a half-mass radius $r_{\rm h}$ of 4.88 pc, whilst the low mass population has $r_{\rm h} = 8.10$ pc; (ii) despite the differences in spatial extent, the kinematics and binarity properties of the high and low mass populations are similar. They have isotropic velocity ellipsoids with mean 1d velocity dispersions $σ$ of 0.427 and 0.415 km s$^{-1}$ respectively. The dynamical state of the Hyades is far from energy equipartition ($σ\propto {\bar M}^{-1/2}$). We identify a new mass segregation instability for clusters with escape speed $V$. Populations with $V/σ\lesssim 2\sqrt{2}$ can never attain thermal equilibrium and equipartition. This regime encompasses many Galactic open and globular clusters. For the Hyades, there must be an outward energy flux of at least $9.5 \times 10^{-4} M_\odot\,{\rm km^2\, s^{-2} Myr^{-1}}$ to maintain its current configuration. The present mass loss of $0.26 M_\odot {\rm Myr}^{-1}$ due to tidal stripping by itself implies a substantial energy flow beyond the required magnitude.
