Chemistry in disks. I. Deep search for N2H+ in the protoplanetary disks around LkCa 15, MWC 480, and DM Tauri
Chemistry in disks. I. Deep search for N2H+ in the protoplanetary disks around LkCa 15, MWC 480, and DM Tauri
复制标题
磁盘中的化学。
DOI：
--
复制
发表时间：
2006
期刊：
影响因子：
--
通讯作者：
F. Gueth
中科院分区：
文献类型：
--
作者：
A. Dutrey;T. Henning;S. Guilloteau;D. Semenov;V. Piétu;K. Schreyer;A. Bacmann;R. Launhardt;J. Pety;F. Gueth
目的：为了限制原行星盘中的电离分数，我们提出了一种新的高灵敏度干涉观测方法，在DMTau、LkCa15和MWC480周围的三个盘中观测到N2H+。方法：使用IRAM PdBI阵列观察N2H+J=1-0谱线，并应用？^2-最小化技术估计相应的列密度。将这些值与HCO+柱密度与具有垂直温度梯度的稳态圆盘模型的结果进行了比较。结果：我们报道了LkCa15和DM Tau在5？水平和MWC480的上限。根据LkCa15的数据得出的柱密度比以前报道的要低得多。[N2H^+/HCO^+]比值在0.02-0.03量级。到目前为止，HCO+仍然是盘中观测到的最丰富的分子离子。结论：在几百万年的演化阶段(在不确定范围内)，所有的观测值与模拟的圆盘柱密度基本一致，但分子的径向分布不能很好地再现。N2H+在低质量和中等质量年轻恒星周围的三个圆盘中的低推测浓度意味着，这种离子不是整个圆盘电离分数的灵敏示踪剂。根据IRAM Platform de Bure干涉仪进行的观测。IRAM得到INSU/CNRS(法国)、MPG(德国)和IGN(西班牙)的支持。这项研究得到了法国星际介质物理化学国家计划PCMI的部分支持。
Aims.To constrain the ionization fraction in protoplanetary disks, we present new high-sensitivity interferometric observations of N2H+ in three disks surrounding DM Tau, LkCa 15, and MWC 480. Methods: We used the IRAM PdBI array to observe the N2H+ J=1-0 line and applied a ?^2-minimization technique to estimate corresponding column densities. These values are compared, together with HCO+ column densities, to results of a steady-state disk model with a vertical temperature gradient coupled to gas-grain chemistry. Results: We report two N2H+ detections for LkCa 15 and DM Tau at the 5 ? level and an upper limit for MWC 480. The column density derived from the data for LkCa 15 is much lower than previously reported. The [ N2H^+/HCO^+] ratio is on the order of 0.02-0.03. So far, HCO+ remains the most abundant observed molecular ion in disks. Conclusions: .All the observed values generally agree with the modelled column densities of disks at an evolutionary stage of a few million years (within the uncertainty limits), but the radial distribution of the molecules is not reproduced well. The low inferred concentration of N2H+ in three disks around low-mass and intermediate-mass young stars implies that this ion is not a sensitive tracer of the overall disk ionization fraction. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). Research partially supported by PCMI, the French national program for the Physics and Chemistry of the Interstellar Medium.