An Adaptive Measurement Method for Spectral Lines Based on Local Spectral Trends
WANG Yu-peng1, CAI Jiang-hui2*, YANG Hai-feng2*, ZHOU Li-chan1, SHI Chen-hui1, LI Yan-feng2
1. School of Electronic and Information Engineering, Taiyuan University of Science and Technology, Taiyuan 030024, China
2. School of Computer Science and Technology, Taiyuan University of Science and Technology, Taiyuan 030024, China
Abstract：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.
王玉鹏，蔡江辉，杨海峰，周立婵，史晨辉，李砚峰. 一种基于光谱局部趋势的谱线自适应度量方法[J]. 光谱学与光谱分析, 2025, 45(08): 2259-2265.
WANG Yu-peng, CAI Jiang-hui, YANG Hai-feng, ZHOU Li-chan, SHI Chen-hui, LI Yan-feng. An Adaptive Measurement Method for Spectral Lines Based on Local Spectral Trends. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2025, 45(08): 2259-2265.
[1] Gasparri D, Morelli L, Cuomo V, et al. Monthly Notices of the Royal Astronomical Society, 2024, 530(1): 560.
[2] Rodríguez-Merino L H, Mayya Y D, Coelho P R T, et al. The Astrophysical Journal Letters, 2020, 889(2): L31.
[3] Yang H, Shi C, Cai J, et al. Monthly Notices of the Royal Astronomical Society, 2022, 517(4): 5496.
[4] Yang H, Zhou L, Cai J, et al. Monthly Notices of the Royal Astronomical Society, 2023, 518(4): 5904.
[5] Zhang F, Li L, Han Z, et al. Astronomy & Astrophysics, 2023, 679: A27.
[6] Doorenbos L, Sextl E, Heng K, et al. The Astrophysical Journal, 2024, 977(1): 131.
[7] Ko Y, Lee M G, Park H S, et al. The Astrophysical Journal, 2020, 903(2): 110.
[8] Knowles A T, Sansom A E, Coelho P R T, et al. Monthly Notices of the Royal Astronomical Society, 2019，486(2): 1814.
[9] Gorgas J, Faber S M, Burstein D, et al. The Astrophysical Journal Supplement Series, 1993, 86(1): 153.
[10] Worthey G, Faber S M, Gonzalez J J, et al. The Astrophysical Journal Supplement Series, 1994, 94(2): 687.
[11] Trager S C, Worthey G, Faber S M, et al. The Astrophysical Journal Supplement Series, 1998, 116(1): 1.
[12] Liu C, Cui W Y, Zhang B, et al. Research in Astronomy and Astrophysics, 2015, 15(8): 1137.
[13] QU Cai-xia, YANG Hai-feng, CAI Jiang-hui, et al(屈彩霞，杨海峰，蔡江辉，等). Spectroscopy and Spectral Analysis(光谱学与光谱分析)，2020, 40(4): 1304.
[14] Yang H F, Yin X N, Cai J H, et al. Research in Astronomy and Astrophysics, 2023, 23(5): 055006.
