标题： 探索造成潮汐瓦解事件的束缚和非束缚轨道恒星的起源 显示英文标题

标题： Exploring the origin of stars on bound and unbound orbits causing tidal disruption events

摘要： 潮汐瓦解事件（TDEs）为超大质量黑洞（SMBH）及其周围的吸积盘的性质，以及核星团中的恒星密度和速度分布提供了线索。 TDE 光变曲线与标准曲线的偏离取决于恒星轨道是双曲线还是椭圆轨道（Hayasaki 等，2018），以及穿透因子（$\beta$，即潮汐瓦解半径与轨道近日点之比）。 我们通过直接比较 $N$-体模拟数据与解析模型，研究了被潮汐瓦解的束缚星和非束缚星的轨道参数。 从经典的稳态福克-普朗克模型（Cohn & Kulsrud，1978）出发，我们开发了一个解析模型，描述这些恒星的数量密度分布作为轨道偏心率（$e$）和$\beta$的函数。 为此，需要拟合核星团的密度和速度分布以及潮汐瓦解恒星的能量分布，并从$N$-体数据中获得这些拟合结果。 我们证实，在球状核星团中导致 TDEs 的大多数恒星起源于相空间的完整损失锥区域，推导出偏心率-$\beta$空间的解析边界，并发现它们由$N$-体数据所确认。 由于我们的极限偏心率远小于完全吸积或完全逃逸所需的临界偏心率，我们得出结论，这些恒星的轨道只是略微偏心或双曲线，接近抛物线轨道。 显示英文摘要

摘要： Tidal disruption events (TDEs) provide a clue to the properties of a central supermassive black hole (SMBH) and an accretion disk around it, and to the stellar density and velocity distributions in the nuclear star cluster surrounding the SMBH. Deviations of TDE light curves from the standard occurring at a parabolic encounter with the SMBH depends on whether the stellar orbit is hyperbolic or eccentric (Hayasaki et al. 2018) and the penetration factor ($\beta$, tidal disruption radius to orbital pericenter ratio). We study the orbital parameters of bound and unbound stars being tidally disrupted by comparison of direct $N$-body simulation data with an analytical model. Starting from the classical steady-state Fokker-Planck model of Cohn & Kulsrud (1978), we develop an analytical model of the number density distribution of those stars as a function of orbital eccentricity ($e$) and $\beta$. To do so fittings of the density and velocity distribution of the nuclear star cluster and of the energy distribution of tidally disrupted stars are required and obtained from $N$-body data. We confirm that most of the stars causing TDEs in a spherical nuclear star cluster originate from the full loss-cone region of phase space, derive analytical boundaries in eccentricity-$\beta$ space, and find them confirmed by $N$-body data. Since our limiting eccentricities are much smaller than critical eccentricities for full accretion or full escape of stellar debris, we conclude that those stars are only very marginally eccentric or hyperbolic, close to parabolic.