Lick线指数是一种衡量谱线强度的重要指标。 目前计算Lick线指数的方法中谱线轮廓的波长范围是通过对固定区间求取均值来实现的, 这种方法获取的轮廓范围难以准确反映单条光谱谱线的实际强弱, 从而影响Lick线指数的准确性与可靠性。 为此, 本文介绍了一种基于光谱局部趋势特征的谱线强度自适应度量方法。 首先, 根据谱线的特征定义一个边界因子n, 用于限定谱线轮廓的极限范围。 其次, 计算谱线线芯波长左右两侧的斜率以捕捉趋势信息, 根据趋势增减性的变化, 分别获取两侧距离线芯波长最近的 n个流量峰(或谷)值。 随后, 选取其中的最大(小)流量值及对应波长作为谱线轮廓的边界点。 最后, 基于此边界点使用等值宽度(EW)或星等(Mag)公式分别计算线指数值, 以此数值来度量谱线特征的强弱。 通过对F、 G与K型恒星光谱中的Ca4227, Hβ, Mgb及Hα吸收线的强弱进行度量, 分别从三个角度对比分析了自适应度量方法与固定区间度量方法的差异。 首先, 自适应方法获取的Adaptive EW值与固定区间法获取的EW值的二维散点分布图显示, 绝大部分数据点呈现一定聚集趋势, 但并非完全沿对角线分布, 表明两种方法均具有一定的稳定性, 但在计算结果上存在系统性差异。 其次, 两者的统计结果显示Adaptive EW的均值与标准差均高于EW的, 说明自适应方法在捕获光谱细节变化方面更为敏感, 能够捕捉到因恒星个体差异、 观测条件波动等因素引起的谱线变化, 进而更真实地反映谱线强弱。 最后, 通过人眼检测两种方法获取的谱线轮廓范围表明, 自适应方法能够根据谱线的实际情况, 动态调整边界点的位置, 从而更准确地确定谱线的轮廓范围。 因此, 自适应获取谱线轮廓范围的方法为度量个例谱线强弱提供了一种有效途径。

Lick indices are an important metrics for measuring spectral line strength. In the current methods for calculating the Lick index, the wavelength range of the spectral line profile is determined by taking the mean over a fixed interval. This approach often fails to accurately capture the actual strength of individual spectral lines, thereby compromising the accuracy and reliability of the Lick index. To address this problem, this paper introduces an adaptive spectral line measurement method based on local trend characteristics. Firstly, a boundary factor n is defined according to the spectral line characteristics to limit the extreme range of the spectral line profile. Secondly, the slopes on blue and red bands of the core wavelength of the spectral line are calculated to capture the trend information. According to the increasing or decreasing trends changes, n flux peaks (or valleys) closest to the core wavelength on both sides are obtained respectively. Subsequently, the maximum (minimum) flux values and the corresponding wavelengths are selected as the boundary points of the spectral line profile. Finally, based on these boundary points, the line index is calculated through either Equivalent Width (EW) or Magnitude (Mag) formulations, and this value is used to measure the strength of the spectral line feature. By measuring the strength of Ca4227, Hβ, Mgb, and H alpha absorption lines in F, G, and K-type stellar spectra, this paper compares and analyzes the differences between the adaptive and fixed interval measurement methods from three perspectives. First, the scatter distribution map of the Adaptive EW values obtained by the adaptive method and the EW values obtained by the fixed interval method shows that most data points exhibit certain aggregation trends, but are not completely distributed along the diagonal, indicating that both methods are stable. Still, there are systematic differences in the calculation results. Second, the statistical results of two methods show that the mean and standard deviation of Adaptive EW are higher than those of EW, indicating that the adaptive method is more sensitive in capturing spectral detail changes, can capture spectral line changes caused by factors such as stellar individual differences and observational condition fluctuations, and thus more truly reflects the strength of the spectral line. Finally, by visually inspecting the spectral line profile range obtained by the two methods, it is shown that the adaptive method can dynamically adjust the position of the boundary points according to the actual situation of the spectral line, thereby more accurately determining the profile range of the spectral line. Therefore, the adaptive profile boundary detection method establishes an effective approach for quantifying line strengths in individual spectra.