Astrophysical Bulletin ( IF 1.2 ) Pub Date : 2021-04-08 , DOI: 10.1134/s1990341321010065 V. M. Danilov
We estimated a number of parameters for small groups of stars in the open Pleiades star cluster using Gaia DR2 coordinate and proper motion data for stars in the region of radius d = 2.5° relative to the center of the cluster on the celestial sphere. We selected 36 wide pairs of stars with magnitudes mG < 15m and velocities of the stars in these pairs with respect to their geometric centers close to the circular velocity relative to their centers of mass. The average mass ratio of the components in such pairs is q \( \simeq \) 0.67 ± 0.04, and the median ratio is q \( \simeq \) 0.78. The number of such pairs increases with q and has a maximum near q \( \simeq \) 0.8–0.9. The mutual distances r1,2 between individual stars in the pairs increase with distance r from the cluster center, and a maximum number of such pairs are located in the r = 3–4 pc interval (median r \( \simeq \) 3.64). We note the absence of dynamically active binaries in the cluster. The formulas for the potential energy of a binary star are written with account for the force fields of the cluster and Galaxy. Only one of the identified wide binaries has a negative total energy. The “(BP–RP) color index—\(~{{m}_{{\text{G}}}}\)” diagram for mG < 15m was used to select 62–70 unresolved multiple stars in the Pleiades. The spatial-kinematic parameters of the considered groups of wide binaries and unresolved multiple stars coincide within the margin of error, which indicates a common origin of these groups in this cluster for mG < 15m. For unresolved multiple stars of arbitrary multiplicity, we derived formulas for estimating the masses of the components from the luminosity of the star, considered as a single star on the main sequence (MS). Using these formulas for unresolved multiple stars in the Pleiades leads to an average increase in the masses of such “single MS stars” in binary, triple, quadruple stars by factors of 1.61, 2.19, 2.74 correspondingly. The shape of the stellar velocity dispersion \(\sigma _{v}^{2}\) dependence on r in the small groups is determined by a combined influence of gravitational instability and violent relaxation in the cluster. We determined the sizes of such groups (several pc) and decay times (several million years). The degree of correlation of \(\sigma _{v}^{2}\) in small groups of stars increases near the center of the cluster and in the 2 < r < 5.7 pc interval.
中文翻译:
基于Gaia DR2的the中多颗恒星的运动
我们使用Gaia DR2坐标和相对于天球上星团中心的半径d = 2.5°范围内的恒星的适当运动数据,估计了开放P宿星团中小群恒星的许多参数。我们选择了36对宽大的恒星,它们的大小为m G <15 m,并且这些恒星中的恒星相对于其几何中心的速度接近于相对于其质心的圆周速度。这些对中组件的平均质量比为q \(\ simeq \) 0.67±0.04,中位数比率为q \(\ simeq \) 0.78。此类对的数量随着q的增加而增加,并且在q附近具有最大值 \(\ simeq \) 0.8-0.9。成对的单个恒星之间的相互距离r 1,2随着距星团中心的距离r而增加,并且此类对的最大数量位于r = 3-4 pc区间(中位数r \(\ simeq \) 3.64 )。我们注意到集群中没有动态活动的二进制文件。编写双星恒星势能的公式时要考虑星团和银河系的力场。所识别的宽二进制文件中只有一个具有负的总能量。m G <15 m的“(BP – RP)颜色索引— \(〜{{m} _ {{\ text {G}}}} \) ”图被用来在select宿星中选择62–70个未解析的多颗恒星。考虑的宽双星群和未解析多星群的空间运动学参数在误差范围内重合,这表明这些群在m G <15 m时是该星团的共同起源。对于任意多重性的未解析多颗恒星,我们推导了用于根据恒星的光度估计分量质量的公式,该恒星的光度被视为主序列(MS)上的单颗恒星。对these宿星中未解析的多颗星使用这些公式会导致这种“单MS星”在双星,三星,四星中的质量平均增加,分别增加1.61、2.19、2.74倍。恒星速度色散的形状\(\ sigma _ {v} ^ {2} \)对小组中r的依赖性由重力不稳定和群集中的暴力松弛的综合影响确定。我们确定了此类群的大小(数个pc)和衰减时间(数百万年)。小群恒星中\(\ sigma _ {v} ^ {2} \)的相关度在星团中心附近和2 < r <5.7 pc间隔内增加。