ESO091111:研究太阳内部化学元素之系外行星法

辛苦，翻译后看的很明白！

The straight line log N(Li)=1.5 matches the upper envelope of the lower limits corresponding to a minimum S/N = 200 in a typical solar twin.
图中直线代表最小信噪比为200的类似太阳的恒星，Li的含量对数的上限。upper envelope是上包络，我想此处译为上限是无误的。另外“无行星”的恒星系统，是空心黑圈的。
log N(Li)应该在论文中有定义或说明的，我刚刚看了那段PDF，你最好引用一下那个定义。后面一句我也看不懂，但我看了原先的PDF，那是你转档时错误了，其实它是T[sub]eff [/sub] averaged over all stars are 0.06 dex and 30K, respectively[sup]12[/sup]，eff不过是T的下缀而已，12则是上缀，代表第12条参考文献。

建议其祥把这段翻译了，否则我想你说不清插图1的

嗯，我努力认真把文章读懂再来补充吧，今天晚上看看能否读懂。

学习了，谢谢楼主～

学习了，谢谢楼主～
Black★Star 发表于 2009-11-15 13:13

                               
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客气了，O(∩_∩)O~。

为同好们能更好的理解论文中所附插图，所以我打算努力将那篇在Nature发表的论文全文进行翻译。
由于本人能力有限，所学知识范围较窄，翻译不当之处，请指正。谢谢。
关于论文作者联系信息（前面已译）及所引用文献的翻译，本人省略了。

论文题目：
Enhanced lithium depletion in Sun-like stars with orbiting planets.
对于含有行星绕转的类太阳恒星系统中锂损耗的研究




The surface abundance of lithium on the Sun is 140 times less than protosolar[sup]1[/sup], yet the temperature at the base of the surface convective zone is not hot enough to burn Li[sup] 2,3[/sup]. A large range of Li abundances in solar type stars of the same age, mass and metallicity is observed[sup] 4,5[/sup], but theoretically difficult to understand [sup]3,6,7[/sup]. An earlier suggestion [sup]8,9,10[/sup] that Li is more depleted in stars with planets was weakened by the lack of a proper comparison sample of stars without detected planets. Here we report Li abundances for an unbiased sample of solar-analogue stars with and without detected planets. We find that the planet-bearing stars have less than 1 per cent of the primordial Li abundance, while about 50 per cent of the solar analogues without detected planets have on average 10 times more Li. The presence of planets may increase the amount of mixing and deepen the convective zone to such an extent that the Li can be burned.

太阳表面所蕴含的锂的丰度不到原始太阳的1/140（参考文献1），但是在太阳表面对流层的底部，尚达不到Li燃烧所需的温度（参考文献2，3）。理论上很难说清楚（参考文献3，6，7）为何一系列无论年龄、质量还是金属丰度（参考文献4，5）都与太阳极其类似的恒星却含有大量的锂元素。一项早期缺乏合适实验对照组的研究（参考文献8，9，10）表明，”有行星“恒星中锂更容易被消耗。我们的报告中有关锂丰度的样本真实可靠，样本中既含有”有行星“恒星同时具有”无行星“恒星。通过研究，我们发现”有行星“恒星所含的锂不及原始锂丰度的1%，但是，大约50%的”无行星但是类太阳“恒星却含有是平均情况下10倍之多的锂元素。因此，行星的存在有可能加剧了对流层的深度和混合程度，以至于锂被燃烧掉。

We obtained Li abundances from high resolution, high signal-to-noise (S/N) spectra for a sample of 451 stars in the HARPS high precision (better than 1 m/s) radial velocity exoplanet survey [sup]11[/sup] spanning the effective temperature range between 4900 and 6500 K. These are unevolved, slowly rotating non-active stars from a CORALIE catalogue. These stars have been monitored with high precision spectroscopic observations for years in order to detect planetary systems. Of these 451 stars, 70 are reported to host planets and the rest, which we will designate as a comparison sample, (we often call them “single” stars) have no detected planets so far. If there are planets around these “single” stars, their masses and orbital parameters will be different from those already known. We use this comparison sample to show that the reason for this extra Li depletion is not related to high metallicity (characteristic of planet-host stars) or to old ages.

我们所获得的锂丰度的样本来自于高分辨率，高信噪比的光谱分析，在高精度（高于1m/s）的利用径向速度法探测系外行星的HARPS样本（参考文献11）有451颗恒星，它们的有效温度介于4900K~~6500K之间。这些都是来自CORALIE星表中演化稳定、低自转率、非活动性的恒星，它们已被高精度光谱仪跟踪了很长一段时间来确定其是否拥有行星系统。在这451颗恒星中，70颗被行星绕转，剩下的那些尚未发现有行星绕转的恒星（我们称之为”单星“）将作为对照组进行分析。假如这些”单星“有行星绕转，他们的质量以及相关参数将与已知的恒星会十分不同。（其祥注：直接说请读者相信我们的实力不得了，O(∩_∩)O~）我们应用这批对照组样本来表明锂元素的额外消耗和恒星的高金属丰度以及年老无关。 （其祥注：恒星演化后期，即年老恒星由于轻核元素逐渐燃尽并形成质量稍微大一些的金属元素（小于铁），所以其金属丰度会相对较高。）

Our abundance analysis, which followed standard prescriptions for stellar models, spectral synthesis code and stellar parameter determination[sup]12[/sup], confirm the peculiar behaviour of Li in the effective temperature range 5600–5900 K for the 30 planet-bearing stars with respect to the 103 stars without planets in the comparison sample. To put this on a more solid statistical foundation these two samples in the T[sub]eff[/sub] = 5600–5900 K window were extended by adding 16 and 13 planet-host and comparison sample stars respectively, for which we have obtained new Li abundances from high quality spectroscopic observations using the same spectral synthesis tools. We found that the immense majority of planet-host stars have severely depleted lithium whereas in the comparison sample a large fraction has only partially inhibited depletion. At higher and lower temperatures planet-host stars do not appear to show any peculiar behaviour in their Li abundance. The explanation of lithium survival at T[sub]eff[/sub] (>=)5850 K is that the convective layers of stars more massive than the Sun are shallow and too remote to reach the Li burning layers. However, lower mass stars with T[sub]eff[/sub] (<=) 5700 K have deeper convective layers that transport surface material to high temperature regions in the interior where Li can be destroyed more efficiently.

通过对恒星模型、光谱合成辨认、以及恒星参数的确认（参考文献12）等大量分析后，在有效温度介于5600~~5900K的30颗”有行星“恒星与103颗”无行星“恒星的实验对照组中，我们可以确定锂元素的确表现出独特的性质。在此温度范围中，通过利用同样的光谱合成手段，我们得到一批新的样本，它们的锂丰度同样由高质量光谱分析仪得出。这样，我们为这两组样本分别各增加16颗”有行星“恒星和13颗”无行星“恒星，使得统计结果更具有可靠性。如此，我们发现大量的”有行星“恒星相比对照组，它们锂元素严重损耗，然而，大部分的”无行星“恒星却仅有部分损耗。在更高或更低的温度范围中，”有行星"恒星在锂的含量中却没有表现出丝毫的独特性。当恒星表面的有效温度高于5850K时，关于锂依然存在的解释是此类恒星的对流层深度相比太阳而言较浅，这些恒星有着较高的质量，但其对流深度却没有达到锂燃烧层。然而，低质量且有效温度低于5700K的恒星，由于其对流层较深，可以将恒星表面的物质运输到恒星内部的高温度区域，这样就致使锂元素被快速的燃烧掉。

The Li abundance of some 20% of stars with exoplanets in the temperature range 5600–5900 K is log N(Li) ≥ 1.5 (in standard notation, log N(Li) = log [n(Li)/n(H)] + 12, where n is the number density of atoms), while for the 116 comparison stars the Li abundance shows a rather high dispersion with some 43% of the stars displaying Li abundances log N(Li) ≥ 1.5. This result becomes more obvious in solar analogue stars where some 50% of 60 “single” stars in the narrow window of T[sub]sun[/sub]± 80 K (T[sub]sun[/sub]=5777 K)appear with log N(Li) ≥ 1.5 while only two planet hosts out of 24 have log N(Li) ≥ 1.5 (Fig 1). We performed different two-sample statistical tests using ASURV[sup]13[/sup] (version 1.2). All tests consistently confirm (at the 3σ level) that the planet-host and single star populations are not drawn from the same parent population. We note that subgiants were not included in this study because they undergo dramatic changes in their internal structure that alters the surface abundance of Li. The Li over-depletion in planetbearing main sequence stars is a generic feature over the Teff-restricted range T[sub]sun[/sub]±80 K and is independent of T[sub]eff[/sub] (or mass). These stars have very similar masses and similar surface convective zone depth, therefore there should be additional reasons for the over-depletion of lithium. We now discuss the impact of age and metallicity on the Li abundance of solar analogue stars.

对于大约20%左右的有效温度范围分布在5600-5900K的“有行星”恒星，对于它们锂丰度而言，有此关系式：log N(Li) ≥ 1.5（在标准记数法中，log N(Li) = log [n(Li)/n(H)] + 12，其中n代表原子的数密度），而对于对照组中的116颗恒星而言，它们的锂丰度却呈现出一种相当高的离散程度，其中大约43%的样本，其log N(Li) ≥ 1.5。如此，结果就显而易见了：有约50%的60颗有效温度介于T[sub]sun[/sub]± 80 K (T=5777 K，此为太阳光球层表面温度，下同)的狭窄区间内的“单星”中，其log N(Li) ≥ 1.5；而在24颗“有行星”恒星中只有2颗恒星的log N(Li) ≥ 1.5（见图表1）。我们针对这两种不同的样本进行了ASURV（参考文献13）统计分析.所有的分析结果（取值在3σ内） 【其祥注：对于正态分布，尽管其取值范围是（-∞，+∞），但是它的值落在（μ-3σ，μ+3σ）内几乎是肯定的事情，即人们常说的“3σ”法则】都证实了“有行星”恒星及“无行星”恒星不是来源于同一母体。同时，我们注意到亚巨星未包含在这个研究中，因为它们的内部结构经历了巨大的变化，会影响其表面的Li丰度。（意为：经历过程不同，所以不具有样本意义）。在有效温度介于T[sub]sun[/sub]± 80 K “有行星”主序星中锂的过度消耗很具有普遍性，而且此现象基本上和恒星的有效温度或质量无关。这些恒星都具有极其相似的质量和对流层深度，因此对于锂燃烧它们有其它额外的原因。现在我们主要讨论的是：“类太阳”恒星中，与锂含量有关的恒星年龄和金属性效应问题。
【注：按当前的恒星演化理论，主序星温度与其质量正相关。】

The lithium abundance of solar-type stars is expected to decrease progressively with age [sup]14，15[/sup]. It is in principle possible that solar analogue planet-host stars are on average older than the comparison sample and have depleted more lithium. If that were the case, we should also expect a correlation between lithium and stellar age indicators. Chromospheric activity is a reliable age indicator for solar-type stars from young ages to about [sup]15，16 [/sup]1 Gyr, or perhaps even to the age of the Sun [sup]17[/sup]. Abundances of Li versus chromospheric activity indices [sup]17[/sup], R[sub]HK[/sub], for the solar analogue stars with and without detected planets are shown in Fig. 2a. The comparison of the RHK values for the stars in our sample and for stars in the 625 Myr old [sup]15[/sup] Hyades cluster [sup]18[/sup] indicates a much older age for our stars. We find no correlation between Li and the activity index in both samples (Fig 2a). This suggests that age is not the main parameter governing Li depletion in our targets. It is known [sup]19[/sup] that chromospheric activity correlates with stellar rotation (vsini). If the planet hosts were older than the comparison sample, their rotational velocities would be smaller than in the comparison sample. This is not observed either (Fig 2b), adding support to our previous conclusion.

对于“类太阳”恒星，锂含量会随着其年龄的增加而日益衰减（参考文献14，15） 。原则上，类太阳“有行星”恒星很有可能起平均年龄大于其对照组，因此燃烧了更多的锂。若真是这样的话，我们有必要找出恒星年龄与Li含量间的相互关系式。从年龄较小的至大约10亿岁的（参考文献14，15） ，甚至达到太阳（参考文献17）年龄的“类太阳”恒星，色球层的活动性都是一个可以信赖的年龄指标。在图表2a中，对于“类太阳”恒星中的“有行星”恒星以及“无行星”恒星，用Rhk来表示锂丰度相对色球层活动指数（参考文献17）。R[sub]HK[/sub]值的比较是针对我们样本中的恒星以及年龄较大的约6.25亿岁的毕星团（参考文献18）。我们没有发现锂丰度和活动指数有相关性（图表2a）。这表明在我们的样本中，年龄不会成为锂衰减的主要影响因素。我们知道恒星的自转速度（vsini）和色球层的活动二者是相关的（参考文献19）。若在年龄上”有行星“恒星比对照组恒星大一些，它们的旋转速度就会小一些。但这也没有观察到（图表2b），从而增加了我们先前结论的可靠性。
【其祥注：毕星团是著名的银河星团之一，位于金牛座。它的几颗亮星构成二十八宿中的毕宿，因此称为毕星团。但是毕宿中最亮的毕宿五并不是星团的成员。毕星团几乎是球形的，它有300多个成员星，总质量约300个太阳质量。它的直径约15°，线直径约10秒差距。这是一个中心聚度很高的星团，约有一半的质量位于半径为6 秒差距的球内，中心附近的恒星密度达每立方秒差距0.5个恒星,比太阳附近的恒星密度大好几倍。毕星团还是一个移动星团，它的成员星的自行的辐射点在猎户座α星(中国名称是“参宿四”)以东5°处。大约在8万年以前，毕星团离太阳最近，只有现在的距离的一半。现在它正以每秒43公里的速度离开我们。6,000万年以后，毕星团将成为一个普通的银河星团，那时最亮的成员星为12等。在毕星团中，光谱型最早的恒星为A1型，所有早于A5型的恒星都已离开主星序，此外，还有四个光谱型为K的红巨星。因此,毕星团的年龄要比昴星团老,估计约为6亿年。毕星团的中心同太阳的距离为44秒差距约130光年，是离我们最近的成员星较多的星团。】

Most of the planet-host stars discovered to date are metal rich [sup]20[/sup]. The metallicity excess could result from either the accretion of planets/planetesimals on to the star or the protostellar molecular cloud. This metallicity excess is also present in the solar analogue planet-bearing stars (see Fig. 2c). Can high metallicity be responsible for enhanced Li depletion in these stars? The increase of metal opacities in solar-type stars is responsible for the transition between radiative and convective energy transport. The main contributors to the total opacity at the base of the convective zone are oxygen and iron [sup]21[/sup]. Our data (Fig 2c) show that the fraction of single stars with log Li > 1.5 is 50% at both [Fe/H] < 0 and [Fe/H] > 0. This suggests that the Li depletion mechanism does not depend on the metallicity in the range -0.5 < [Fe/H] < +0.5. We have investigated the dependence of log N(Li) on [O/Fe] for planet-host stars, using oxygen data from the literature[sup] 22[/sup], and again found no correlation. Comparison with field stars then leads to the conclusion that neither age nor metallicity is responsible for the excess Li depletion. This is reinforced by observations of Li in solar-type stars in old clusters, which indeed show a wide dispersion of Li abundances with values ranging from log N(Li) = 2.5 down to 1.0 and lower [sup]5,23[/sup]. This is the case for M67 (age 3.5–4.8 Gyr and [Fe/H] = 0.06)[sup] 23 [/sup]and NGC 6253 (age 3 Gyr and [Fe/H] = 0.35) [sup]24,25[/sup], as is clearly seen in Fig 2d. These two clusters offer a homogeneous sample of solar analogues in terms of age and metallicity. Both high and low Li abundance solar analogues are present in these two clusters. The high Li abundance in a large fraction of old metal rich stars in NGC 6253 and M67 leads us to conclude that high metallicity and/or age may not be the main cause for the systematic low Li abundances in solar-analogue planet-host stars. Our observations do not suggest that Li is unaffected by metallicity and/or age. They only imply that these parameters are not important enough in order to make the enhanced Li depletion that we observe in solar-analogues with exoplanets.

截至目前为止，我们所发现的大多数”有行星“恒星都富含金属性（参考文献20）。含金属过多是由行星/行星原质或原始恒星分子云的吸积引起的。同时，这种过金属性质也表现在类太阳”有行星“恒星中（参见图表2c）。这些恒星的高金属性也可能加剧锂的衰减吗？在类太阳恒星中金属不透明度的增加也可能致使辐射层及对流层之间能量的交换。影响整体不透明度的主要因子是对流层底部的氧元素和铁元素（参考文献21）。我们的数据（图表2c）显示，无论在[Fe/H] < 0 还是 [Fe/H] > 0（无法理解，怎么会小于0？若[...]代表取对数，怎么会大于0？）的情况下，对于log Li > 1.5的”单星“所占的比例都是50%。这表明锂衰减机制在−0.5 < [Fe/H] <+0.5范围内和恒星的金属性基本无关。通过相关文献（参考文献22）中氧的数据，我们同时也在”有行星“恒星的[O/Fe]比例上对log N(Li)做了调查，也没有发现相关性。通过以上分析，我们可以说锂的过度消耗无论和恒星年龄还是其金属丰度都没有相关性。通过对老年星团里对类太阳恒星中锂的观测（log N(Li)的值离散较大，从2.5到1甚至更小的值），此观点的可靠性也被加强。举例说明，对于M67（年龄分布在35亿至48亿年之间，[Fe/H] = 0.06)） （参考文献23）和NGC 6253（年龄约30亿年，[Fe/H] = 0.35)，这在图表2d中可以很清楚地看到。这两个星团为我们提供了在年龄和金属性商同种性质的类太阳样本。无论锂丰度含量高还是低的类太阳恒星在这两个星团中都有体现。NGC 6253 和 M67中老年且富含金属恒星的锂丰度含量较高，说明高金属性和年龄不是类太阳”有行星“恒星中锂含量低的主要原因。但是我们的观测不能锂一点也不受恒星金属性或年龄的的影响。在我们所观测的类太阳”有行星“恒星中，这些参数的重要性较小，不能很好的解释锂的过度衰减。

We propose that the low Li abundance of planet-host solar-analogue stars is directly associated with the presence of planets. The presence of a planetary system may affect the angular momentum evolution of the star and the surface convective mixing. Planet migration will probably increase the angular momentum of the star. Various theoretical studies [sup]3,6,7[/sup] show how magnetic braking scales with rotational velocity leading to turbulent diffusion mixing and enhanced lithium depletion. If that were the case we would expect severely Li-depleted stars to host planets with shorter orbital periods. There is no indication for such a correlation in the data, but we also note that in most cases we can only impose upper limits on the Li abundance, so that such correlations with orbital parameters could still be masked in the current data.


我们假设类太阳”有行星“恒星中较低的锂含量直接原因来自于行星的存在。行星绕转系统可能影响到恒星的角动量演化以及其表面对流层的混合程度。行星的移动很有可能增加恒星的角动量。不同的理论研究（参考文献3，6，7）既展示了在旋转导致湍流扩散与混合下恒星磁场是如何减速的，同时也表明了锂的加剧衰减。若情况属实，我们则可以大胆推测锂被过度消耗的恒星是一些轨道周期较小的”有行星“恒星。在数据方面，当然还没有表明二者间存在联系，但是可以看到在多数情况下，我们可以仅仅依据锂丰度的上限，以此，说明和旋转参数有关的内容依然被掩盖在当前的数据下。

Alternatively, a long-lasting star–disc interaction during the pre-main sequence may cause planet-host stars to be slow rotators and develop a high degree of differential rotation between the radiative core and the convective envelope, also leading to enhanced lithium depletion[sup] 26 [/sup]. Revealing the relationships between protoplanetary discs and stellar structure in the early phases of the evolution of solar-type stars is a challenge for evolutionary models and simulations. It is possible that the enhanced Li depletion already takes place in the pre-main sequence stage of planet-host stars. Exoplanet searches in very young stars will be crucial to elucidate this. Asteroseismological observations of solar twins with and without known planets may reveal peculiarities in the inner structure of planet-host stars that could be the key to ascertaining the impact of planetary systems on the structure and angular momentum history of these stars.


或许，在主序前期，长期存在的星盘间相互作用可能导致”有行星“恒星自转变地慢下来，并演化为辐射核心层与对流层自转速度差别巨大的恒星，这种情况下当然会产生巨大的湍流而导致更快速的上下混合，Li就消耗得更快了。（参考文献26）。在类太阳恒星的早期演化中，弄清楚行星盘与恒星结构之间的关系对于模拟演化模型来说是极具挑战性的。很有可能锂的加剧消耗在”有行星“恒星的主序前期已经发生了。而在年轻恒星中对于系外行星的探索研究对于它的阐释无疑是决定性的。星震学对于”有行星“恒星和”无恒星“行星的观测可能揭示”有行星“恒星的内部结构中的独特性，这对于解释恒星演化长河中，行星系统的存在是否的确影响这些恒星的结构以及其角动量起到关键性作用。

It is known that solar-type stars with high metallicity have a high probability of hosting planets. Those solar analogues with low Li content (which is extremely easy to detect with simple spectroscopy) have an even higher probability of hosting exoplanets. Understanding the long-lasting mystery of the low Li abundance in the Sun appears to require proper modelling of the impact of planetary systems on the early evolution of solar analogue stars.


因此，高金属性的类太阳恒星很有可能被行星绕转。这些含锂较少的、光谱又极容易被探测的类太阳恒星更有可能有行星绕转。弄清楚太阳中长期存在的锂谜团事件后，看似在类太阳恒星的早期演化过程中，有必要建立合适的行星系统对其主星影响的模型了。

参考文献：

Acknowledgements This research has been supported by The Spanish Ministry of Science
and Innovation (MICINN). N.C.S. and S.G.S. acknowledge the support from the Fundacao
para a Ciencia e a Tecnologia, Portugal, through the programme Ciencia 2007.


致谢：此论文得到西班牙科学创新部N.C.S和S.G.S的支持，我们也感谢在2007科学项目中，葡萄牙科技学会的资金赞助。

Author Contributions All authors participated in data collection, analysis, interpretation and
commented on the manuscript. G. I. led the project and wrote the paper.

The authors declare that they have no competing financial interests.

作者贡献：论文所有的作者都参与了数据采集，分析，解释和对原稿的评论。G.I.是团队的一把手，撰写了此文。所有作者声明他们之间没有对经济利益的竞争。

Author Information Correspondence and requests for materials should be addressed to G. I.
(e-mail: gil@iac.es).

作者信息：有关论文材料的询问和通信请邮寄至G.I.

Figure 1.

Lithium abundance against effective temperature in solar-analogue stars with and without detected planets.

图表一：“无行星”恒星与“类太阳”恒星锂含量对比图。（有效温度与太阳接近）

The planet hosts and “single” stars are red filled and empty circles, respectively. The red circle with the black point at its center indicates the Sun. The minimum detectable Li abundance varies among the stars used in this study because their spectra have different signal-to-noise ratios. The straight line log N(Li)=1.5 matches the upper envelope of the lower limits corresponding to a minimum S/N = 200 in a typical solar twin. We employ this line as a cut-off for selecting Li-depleted stars in our sample. Note that the two planet host stars with the highest Li abundance also have nearly the highest effective temperatures and therefore the thinner convective zones, which help to preserve this element. Apart from these stars, log N(Li)=1.5 is the highest value found in a planet-host star. The mean statistical errors (1σ) for the log N(Li) and T[sub]eff[/sub] averaged over all stars are 0.06 dex and 30 K, respectively[sup]12[/sup] . Errors in log N(Li) (bottom right corner) include uncertainties in T[sub]eff[/sub] and equivalent width measurement.

图中：“有行星”恒星用实心红圈表示；“无行星”恒星用空心圆圈表示；太阳用空心红圈中含有黑点表示。在这项研究中所分析的恒星锂丰度的最小值不同，是因为它们的光谱有不同的信噪比。图中直线log N(Li)=1.5代表最小信噪比为200的类太阳恒星中Li含量对数的上限。 我们用这条直线作为样本中选择“锂耗尽”恒星的分界线。既然两颗具有最高锂丰度的“有行星”恒星的有效温度同时也几乎是最高的，因此，对流层越薄，锂元素就会被燃烧的越少。除了这些被研究的恒星以外，log N(Li)=1.5也是目前所发现“有行星”恒星的最大值。对于log N(Li)以及所有恒星的有效温度平均值，它们的平均统计误差（1σ范围内）分别为：0.06底什和30K（参考文献12）。log N(Li)中 右下角处的的错误包含有效温度以及等效宽度测量的不确定性。
【其祥注：dex——底什，任意比值以10为底的对数表示时称底什】