标题： 金牛座中的17个新的极低质量成员。 重新审视褐矮星的缺失问题 显示英文标题

标题： 17 new very low-mass members in Taurus. The brown dwarf deficit revisited

摘要： 近期关于金牛座分子云次恒星族群的研究揭示，与梯形星团相比，金牛座分子云中的褐矮星数量存在不足（Briceno等 1998；Luhman 2000；Luhman等 2003a；Luhman 2004）。然而，这些研究主要集中在金牛座分子云的高恒星密度区域。 我们对该区域进行了大规模光学巡天，覆盖总面积达30平方度，包括云团最密集的部分及其周边环境，探测极限质量达到15个木星质量（MJ）。 本文介绍了对97个通过测光方法选出的潜在新低质量金牛座成员的光学光谱后续观测，其中27个是强晚型M星（SpT < M4V）候选体。 这些观测发现了5个新的超低质量（VLM）金牛座成员和12个新的褐矮星。 结合我们的观测数据与之前发表的结果，我们得到了金牛座分子云中次恒星与恒星比例的更新值Rss = 0.23 ± 0.05。 这一比例现在看起来与在梯形星团中得出的值（假设条件相似时为0.26 ± 0.04）一致。 我们发现，在聚合体的中心区域，褐矮星相对于恒星的数量比在分布更广的群体中减少了约2倍。 我们的发现最好用胚胎排斥模型来解释，在该模型中，褐矮星起源于小型N不稳定多星系统中的动力学相互作用。 显示英文摘要

摘要： Recent studies of the substellar population in the Taurus cloud have revealed a deficit of brown dwarfs (BD) compared to the Trapezium cluster population (Briceno et al 1998; Luhman 2000; Luhman et al 2003a; Luhman 2004). However, these works have concentrated on the highest stellar density regions of the Taurus cloud. We have performed a large scale optical survey of this region, covering a total area of 30 deg^2, and encompassing the densest part of the cloud as well as their surroundings, down to a mass detection limits of 15 Jupiter Masses (MJ). In this paper, we present the optical spectroscopic follow-up observations of 97 photometrically selected potential new low-mass Taurus members, of which 27 are strong late-M (SpT < M4V) candidates. These observations reveal 5 new very low mass (VLM) Taurus members and 12 new BDs. Combining our observations with previously published results, we derive an updated substellar to stellar ratio in Taurus of Rss =0.23 +/- 0.05. This ratio now appears consistent with the value previously derived in the Trapezium cluster under similar assumptions of 0.26 +/- 0.04. We find strong indication that the relative numbers of BDs with respect to stars is decreased by a factor 2 in the central regions of the aggregates with respect to the more distributed population. Our findings are best explained in the context of the embryo-ejection model where brown dwarfs originate from dynamical interactions in small N unstable multiple systems.