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Description
TOPSEGI is a Python-based program developed to calculate the excitation temperature ($T$) and total column density ($N$) of molecules and isotopologs observed in various astrophysical environments, such as planetary atmospheres, satellites, comets, and carbon-rich stars. The program utilizes high-resolution infrared spectral data, such as those from the Stratospheric Observatory for Infrared Astronomy (SOFIA), to precisely analyze $T$ and $N$. To overcome the limitations of the conventional rotation diagram (RD) method, where the inferred $N$ depends on $T$, TOPSEGI estimates both variables by employing a quadtree and $\chi^2$ minimization, thereby improving precision and reducing computational cost. Additionally, the program can extend its capabilities to isotopologs not covered in molecular spectroscopic databases, including HITRAN, ExoMol, and GEISA, by supplementing rotational and centrifugal distortion constants through density functional theory calculations, such as B3LYP. Moreover, it is applicable to any molecules or isotopologs as long as appropriate spectral data are provided. For example, we present a TOPSEGI-based analysis of hydrogen cyanide (HCN) and hydrogen isocyanide (HNC) molecular isotopologs in Orion IRc2. In the Integral Shape Filament (ISF) in Orion, the HCN/HNC intensity ratio investigated through the emission of the ground-state transitions is known as a chemical thermometer for the $15-40$ K range. However, we analyze the spectra of the Orion IRc2 region at higher temperatures of about $100-200$ K. Using $\chi^2$ minimization for the HCN and H$^{13}$CN lines, we derive a $^{12}$C/$^{13}$C ratio of $12.43^{+1.23}_{-1.20}$, with the uncertainty reduced by about 42% compared to the RD result of $12.61 \pm 2.07$. This program offers a robust and flexible tool for the precise analysis of interstellar molecules, enabling the straightforward calculation of molecular properties from high-resolution spectroscopic data, with wide potential for future astrophysical research.
