标题： 类似太阳恒星的光球和色球丰度：Tau宝瓶座的特殊案例 显示英文标题

标题： Photospheric and coronal abundances in solar-type stars: the peculiar case of Tau Bootis

摘要： 太阳型恒星中的化学丰度是一个备受争议的话题。已知拥有行星的恒星富含金属，但这种特性是否也适用于恒星外层大气的化学组成仍有待澄清。更普遍地说，在晚型恒星中，日冕和光球的丰度在许多情况下似乎不同，但要理解恒星大气中的化学分层效应如何运作，需要比目前更大的观测基础。 我们获得了Tau Bootis（一颗已知的附近恒星，有一颗类似木星的近距离行星）的XMM-Newton高分辨率X射线光谱。我们分析了这些数据，目的是进行详细的基于线的发射量分析，并独立应用两种方法分别推导日冕中各元素的丰度。 我们将Tau Bootis的日冕丰度与基于高分辨率光学光谱的发表的光球丰度以及其它具有不同磁活动水平的晚型恒星（包括太阳）的日冕丰度进行了比较。 我们发现，这两种方法对于高温等离子体的发射量分布和日冕丰度的一致性结果在统计不确定性范围内是可靠的，但在2σ水平上的差异仅限于3-4百万开尔文温度下的等离子体量以及O和Ni的丰度上。 在这两种情况下，对于同时有日冕和光球测量值的元素（C、N、O、Si、Fe和Ni），其日冕中的丰度系统地比光球低3倍以上，例外的是日冕中的Ni丰度与光球值相似。 与其他具有相似活动水平的晚型恒星相比，这些日冕/光球丰度比是Tau Bootis特有的，可能与其作为行星宿主恒星的超金属特性有关。 显示英文摘要

摘要： Chemical abundances in solar-type stars are a much debated topic. Planet-hosting stars are known to be metal-rich, but whether or not this peculiarity applies also to the chemical composition of the outer stellar atmospheres is still to be clarified. More in general, coronal and photospheric abundances in late-type stars appear to be different in many cases, but understanding how chemical stratification effects work in stellar atmospheres requires an observational base larger than currently available. We obtained XMM-Newton high-resolution X-ray spectra of Tau Bootis, a well known nearby star with a Jovian-mass close-in planet. We analyzed these data with the aim to perform a detailed line-based emission measure analysis and derive the abundances of individual elements in the corona with two different methods applied independently. We compared the coronal abundances of Tau Bootis with published photospheric abundances based on high-resolution optical spectra and with those of other late-type stars with different magnetic activity levels, including the Sun. We find that the two methods provide consistent results within the statistical uncertainties for both the emission measure distribution of the hot plasma and for the coronal abundances, with discrepancies at the 2-sigma level limited to the amount of plasma at temperatures of 3-4 MK and to the O and Ni abundances. In both cases, the elements for which both coronal and photospheric measurements are available (C, N, O, Si, Fe, and Ni) result systematically less abundant in the corona by a factor 3 or more, with the exception of the coronal Ni abundance, which is similar to the photospheric value. Comparison with other late-type stars of similar activity level shows that these coronal/photospheric abundance ratios are peculiar to Tau Bootis and possibly related to the characteristic over-metallicity of this planet-hosting star.