Undersampling effects on observed periods of coronal oscillations

IF 5.4 2区 物理与天体物理 Q1 ASTRONOMY & ASTROPHYSICS Astronomy & Astrophysics Pub Date : 2024-10-09 DOI:10.1051/0004-6361/202451684
Daye Lim, Tom Van Doorsselaere, Valery M. Nakariakov, Dmitrii Y. Kolotkov, Yuhang Gao, David Berghmans
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Abstract

Context. Recent observations of decayless transverse oscillations have revealed two branches in the relationship between period and loop length. One is a linear relationship, interpreted as a standing mode, while the other shows almost no correlation and has not yet been interpreted conclusively.Aims. We investigated the undersampling effect on observed periods of decayless oscillations.Methods. We considered oscillating coronal loops that closely follow the observed loop length distribution. Assuming that all oscillations are standing waves, we modelled a signal that represents decayless oscillations where the period is proportional to the loop length and the amplitude and phase are randomly drawn. We generated a downsampled signal from the original signal by considering different sample rates that mimic temporal cadences of telescopes, and analysed the periods for sampled signals using the fast Fourier transform.Results. When the sampling cadence approaches the actual oscillation period, there is a greater tendency to overestimate the periods in short loops. We find the same two branches in the relationship between loop length and period of the sampled signals as those seen in the observations.Conclusions. We find that long periods of decayless oscillations occurring in short loops could be the result of undersampling.
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日冕振荡观测周期的欠采样效应
背景最近对无衰减横向振荡的观察发现,周期与环长之间的关系有两个分支。一个是线性关系,被解释为驻留模式,而另一个则几乎没有相关性,尚未得到最终解释。我们研究了取样不足对观测到的无衰减振荡周期的影响。我们考虑了与观测到的环长分布密切相关的振荡日冕环。假设所有振荡都是驻波,我们模拟了一个代表无衰减振荡的信号,其中周期与环长成正比,振幅和相位是随机绘制的。我们通过考虑不同的采样率(模拟望远镜的时间节奏),从原始信号中生成了下采样信号,并使用快速傅里叶变换分析了采样信号的周期。当采样频率接近实际振荡周期时,短环路中的周期更容易被高估。我们发现环路长度与采样信号周期之间的关系中存在与观测结果相同的两个分支。我们发现,短环路中出现的长周期无衰减振荡可能是采样不足的结果。
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来源期刊
Astronomy & Astrophysics
Astronomy & Astrophysics 地学天文-天文与天体物理
CiteScore
10.20
自引率
27.70%
发文量
2105
审稿时长
1-2 weeks
期刊介绍: Astronomy & Astrophysics is an international Journal that publishes papers on all aspects of astronomy and astrophysics (theoretical, observational, and instrumental) independently of the techniques used to obtain the results.
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