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arXiv 1210.8136astro-ph.GA
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星际介质中的小尺度结构:向κ Velorum的时变星际吸收

Small-scale structure in the interstellar medium: time-varying interstellar absorption towards κ Velorum

Keith T. Smith, Stephen J. Fossey, Martin A. Cordiner, Peter J. Sarre, Arfon M. Smith, Tom A. Bell, Serena Viti

摘要:

本文报道了利用英澳望远镜上的超高分辨率设备对随时间变化的星际吸收向κ Vel方向的超高光谱分辨率观测。得到了星际Ca I、Ca II、K I、Na I和CH的探测值,同时报道了C_2的柱密度上限。结果显示,自4年前观测以来,K I和Ca I的柱密度持续增加,因为恒星的横向运动使其垂直于视线约10 AU。谱线轮廓模型拟合的光谱和两个主要的窄组分(A和B)被确定为所有物种除了CH。柱密度N(KI)被发现增加了82 + 10 - 9%之间1994年和2006年,而N(Ca I)被发现增加了32 +-5%,在较短的时间内2002-2006年。谱线宽度用于限制动力学温度T_k,A < 671 + 18 - 17 K和T_k,B < 114 + 15 - 14 K。电子密度由Ca I / Ca II比值决定,而Ca I / Ca II比值又将总数密度的下限设为n_A > 7 * 10^3 cm^-3和n_B > 2 * 10^4 cm^-3。根据Ca I / K I比值估计钙消耗。与贝尔等人(2005)的化学模型进行比较,证实了高的数密度,最佳拟合模型的数密度为n = 5 * 10^4 cm^-3。对这颗恒星的弥漫星际带(DIB)的第一次测量是在两个时期进行的,但在大约9年的时间里,它们的变化只有<40%的上限。DIBs对于测量的E(B-V)来说异常微弱,似乎表现出与猎户座相似的行为。λ5780与λ5797 DIB的等效宽度之比是已知的最高之一,这可能表明λ5797的载体对紫外辐射比对局部密度更敏感。

英文摘要:

Ultra-high spectral resolution observations of time-varying interstellar absorption towards κ Vel are reported, using the Ultra-High Resolution Facility on the Anglo-Australian Telescope. Detections of interstellar Ca I, Ca II, K I, Na I and CH are obtained, whilst an upper limit on the column density is reported for C_2. The results show continued increases in column densities of K I and Ca I since observations ~ 4 yr earlier, as the transverse motion of the star carried it ~ 10 AU perpendicular to the line of sight. Line profile models are fitted to the spectra and two main narrow components (A & B) are identified for all species except CH. The column density N(K I) is found to have increased by 82 +10-9 % between 1994 and 2006, whilst N(Ca I) is found to have increased by 32 +- 5 % over the shorter period of 2002-2006. The line widths are used to constrain the kinetic temperature to T_k,A < 671 +18-17 K and T_k,B < 114 +15-14 K. Electron densities are determined from the Ca I / Ca II ratio, which in turn place lower limits on the total number density of n_A > 7 * 10^3 cm^-3 and n_B > 2 * 10^4 cm^-3. Calcium depletions are estimated from the Ca I / K I ratio. Comparison with the chemical models of Bell et al. (2005) confirms the high number density, with n = 5 * 10^4 cm^-3 for the best-fitting model. The first measurements of diffuse interstellar bands (DIBs) towards this star are made at two epochs, but only an upper limit of < 40 % is placed on their variation over ~ 9 years. The DIBs are unusually weak for the measured E(B-V) and appear to exhibit similar behaviour to that seen in Orion. The ratio of equivalent widths of the λ5780 to λ5797 DIBs is amongst the highest known, which may indicate that the carrier of λ5797 is more sensitive to UV radiation than to local density.

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