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Stellar rotation periods determined from simultaneously measured Ca?II H&K and Ca?II IRT lines

机译：根据同时测量的Ca？II H＆K和Ca？II IRT谱线确定的恒星旋转周期

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Aims. Previous studies have shown that, for late-type stars, activity indicators derived from the Ca? ii infrared-triplet (IRT) lines are correlated with the indicators derived from the Ca? ii H&K lines. Therefore, the Ca? ii IRT lines are in principle usable for activity studies, but they may be less sensitive when measuring the rotation period. Our goal is to determine whether the Ca? ii IRT lines are sufficiently sensitive to measure rotation periods and how any Ca? ii IRT derived rotation periods compare with periods derived from the “classical” Mount Wilson S -index. Methods. To analyse the Ca? II IRT lines’ sensitivity and to measure rotation periods, we define an activity index for each of the Ca? II IRT lines similar to the Mount Wilson S -index and perform a period analysis for the lines separately and jointly. Results. For eleven late-type stars we can measure the rotation periods using the Ca? ii IRT indices similar to those found in the Mount Wilson S -index time series and find that a period derived from all four indices gives the most probable rotation period; we find good agreement for stars with already existing literature values. In a few cases the computed periodograms show a complicated structure with multiple peaks, meaning that formally different periods are derived in different indices. We show that in one case, this is due to data sampling effects and argue that denser cadence sampling is necessary to provide credible evidence for differential rotation. However, our TIGRE data for HD?101501 shows good evidence for the presence of differential rotation.
机译：目的以前的研究表明，对于晚型恒星，其活动指标来源于Ca?。 ii红外三重谱系（IRT）与Ca？ ii H＆K线。因此，钙？ ii IRT线原则上可用于活动研究，但在测量轮换期时可能不太敏感。我们的目标是确定是否含有Ca？ ii IRT线足够敏感，可以测量旋转周期以及Ca值如何？ ii IRT得出的旋转周期与“经典” Mount Wilson S指数得出的周期进行比较。方法。分析钙？ II IRT线的敏感性并测量旋转周期，我们为每个Ca？ II IRT线类似于威尔逊山S指数，并分别和共同对这些线进行周期分析。结果。对于11个晚型恒星，我们可以使用Ca？来测量自转周期。 ii IRT索引类似于在Mount Wilson S索引时间序列中发现的那些，发现从所有四个索引得出的周期给出了最可能的旋转周期;对于已经具有现有文学价值的恒星，我们找到了很好的协议。在少数情况下，计算出的周期图显示出具有多个峰的复杂结构，这意味着在不同的索引中会得出形式上不同的周期。我们表明，在一种情况下，这是由于数据采样效应所致，并认为更密集的节奏采样对于为差分旋转提供可靠的证据是必要的。但是，我们针对HD？101501的TIGRE数据显示出存在差速旋转的良好证据。

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