Variable X-ray emission from the accretion shock in the classical T Tauri star V2129 Ophiuchi
Variable X-ray emission from the accretion shock in the classical T Tauri star V2129 Ophiuchi
复制标题
DOI：
10.1051/0004-6361/201016321
复制
发表时间：
2011-06-01
影响因子：
6.5
通讯作者：
Walter, F. M.
中科院分区：
文献类型：
--
作者：
Argiroffi, C.;Flaccomio, E.;Walter, F. M.
上下文在几个CTTS观测到的高密度等离子体软X射线辐射通常与吸积过程有关。然而，目前还不清楚这种高密度的“冷”等离子体是否在吸积激波中被加热，或者它是否是由吸积过程提供或修改的日冕等离子体。我们进行了协调的准同时光学和X射线观测活动的CTTS V2129 Oph。在本文中，我们分析了钱德拉光栅光谱仪的数据，并试图将观测到的X射线发射等离子体成分与吸积过程的特征和同时光学观测约束的恒星磁场相关联。我们分析了一个200 ks钱德拉/HETGS观测，细分为两个100 ks的部分，CTTS V2129 Oph。在一个恒星自转周期内对应两个不同相位的两个观测段，我们测量了冷等离子体成分的密度和发射测度分布。X射线发射等离子体覆盖广泛的温度范围：从2到34 MK。V2129 Oph的冷等离子体组件（T近似于3-4 MK）在钱德拉观测的两个部分之间变化：在第一个观测段期间，（log N-e = 12（-1.1））（+0.6）），具有类似于3-4 MK的高EM，而在第二段期间，该血浆成分具有较低的EM和较低的密度（logN-e < 11.5），尽管这些差异的统计显著性是边际的。较热的等离子体成分，T >= 10 MK，在短时间尺度（类似于10 k）上变化，这是典型的日冕等离子体。在第一段观测到的一个清晰的耀斑可能位于一个大的冕环（半长> 3颗R星）内。我们的观察提供了额外的确认，在CTTS中的几个MK的稠密冷等离子体是在吸积激波加热的材料。V2129 Oph上这种冷等离子体成分的变化可以用吸积激波中发射的X射线来解释，并在我们的观察所探测的两个旋转相位处用不同的视角观察。特别是，在第一个时间间隔内，可以直接看到激波区域，而在第二个时间间隔内，吸积漏斗本身与激波区域的视线相交，阻止我们观察吸积驱动的X射线。
Context. The soft X-ray emission from high density plasma observed in several CTTS is usually associated with the accretion process. However, it is still unclear whether this high density "cool" plasma is heated in the accretion shock, or if it is coronal plasma fed or modified by the accretion process.Aims. We conducted a coordinated quasi-simultaneous optical and X-ray observing campaign of the CTTS V2129 Oph. In this paper, we analyze Chandra grating spectrometer data and attempt to correlate the observed X-ray emitting plasma components with the characteristics of the accretion process and the stellar magnetic field constrained by simultaneous optical observations.Methods. We analyze a 200 ks Chandra/HETGS observation, subdivided into two 100 ks segments, of the CTTS V2129 Oph. For the two observing segments corresponding to two different phases within one stellar rotation, we measure the density of the cool plasma component and the emission measure distribution.Results. The X-ray emitting plasma covers a wide range of temperatures: from 2 up to 34 MK. The cool plasma component of V2129 Oph (T approximate to 3-4 MK) varies between the two segments of the Chandra observation: during the first observing segment high density plasma (log N-e = 12(-1.1)(+0.6) ) with high EM at similar to 3-4 MK is present, whereas, during the second segment, this plasma component has lower EM and lower density (log N-e < 11.5), although the statistical significance of these differences is marginal. Hotter plasma components, T >= 10 MK, vary on short timescales (similar to 10 ks), which are typical of coronal plasma. A clear flare, detected during the first segment, might be located in a large coronal loop (half length > 3 R-star).Conclusions. Our observation provides additional confirmation that the dense cool plasma at a few MK in CTTS is material heated in the accretion shock. The variability of this cool plasma component on V2129 Oph may be explained in terms of X-rays emitted in the accretion shock and seen with different viewing angles at the two rotational phases probed by our observation. In particular, during the first time interval a direct view of the shock region is possible, while, during the second, the accretion funnel itself intersects the line of sight to the shock region, preventing us from observing the accretion-driven X-rays.