论文标题
HST对H $ _2 $ O 1.4 $ $ M $ M吸收频段的HST调查：II。替代国际货币基金组织降低到行星质量
HST survey of the Orion Nebula Cluster in the H$_2$O 1.4 $μ$m absorption band: II. The substellar IMF down to planetary masses
论文作者
论文摘要
我们利用哈勃太空望远镜在低质量恒星，棕色矮人和行星质量物体的大气中探测近红外吸水物的能力，以创建一个非常纯净的猎户座星云群（ONC）成员的样本，而不会受到缺乏吸水的背景星和星系的污染影响。多亏了这些数据，我们将ONC的初始质量函数（IMF）推断为$ 0.005-1.4 $ m $ _ {\ odot} $制度，即降至几个木星质量。 ONC的年轻年龄，$ \ sim1 $ myr，为典型的银河系磁盘分子云的当今条件（金属性，温度，压力）提供了恒星形成结果的快照。我们证明，ONC的IMF通过对数正态函数或破碎的幂律很好地描述，参数值定性地与乳白色磁盘IMF的规范Chabrier或Kroupa形式一致。质量分布的这种连续性为以下事实提供了线索，即相同的物理过程可能是调节恒星，棕色矮人和行星质量对象的形成。这两种规范IMF表格被预测的低质量成员的数量（低于$ $ M $ _ \ odot $），我们的数据允许更精确的约束。然而，我们没有观察到棕矮星或行星质量制度中的上升或次要峰值。因此，我们的研究与基于近频段近红外地面光度法的发现相矛盾，该发现预测了极高数量的自由浮动行星，但可能会遭受未计算的背景污染。
We exploit the ability of the Hubble Space Telescope to probe near infrared water absorption present in the atmosphere of low-mass stars, brown dwarfs and planetary mass objects to create a very pure sample of Orion Nebula Cluster (ONC) members, not affected by contamination from background stars and galaxies which lack water absorption. Thanks to these data we infer the Initial Mass Function (IMF) of the ONC in the $0.005 - 1.4$M$_{\odot}$ regime, i.e. down to few Jupiter masses. The young age of the ONC, $\sim1$ Myr, provides a snapshot of the outcome of star formation for the present-day conditions (metallicity, temperature, pressure) of typical Milky Way disk molecular clouds. We demonstrate that the IMF of the ONC is well described by either a log-normal function or a broken power-law, with parameter values qualitatively in agreement with the canonical Chabrier or Kroupa forms for the Milky Way disk IMF. This continuity in the mass distribution provides clues to the fact that the same physical processes may be regulating formation of stars, brown dwarfs, and planetary mass objects. Both the canonical IMF forms under-predict the observed number of very low mass members (below $0.1$ M$_\odot$), a regime where our data allows more precise constraints. Nevertheless, we do not observe a rise or secondary peak in the brown dwarfs or planetary mass regimes. Our study thus contradicts findings based on broad-band near infrared ground-based photometry, which predict an extremely high number of free-floating planets, but likely suffer from unaccounted background contamination.
