2022ApJ...925...76A

Morphological and chemical structures of M33 are investigated with the LAMOST DR7 survey. Physical parameters; extinction; chemical composition of He, N, O, Ne, S, Cl, and Ar (where available); and radial velocities were determined for 110 nebulae (95 H II regions and 15 planetary nebulae) in M33. Among them, 8 planetary nebulae and 55 H II regions in M33 are newly discovered. We obtained the following O abundance gradients: -0.199_–0.030^+0.030 dex R₂₅^–1 (based on 95 H II regions), -0.124_–0.036^+0.036 dex R₂₅^–1 (based on 93 H II regions), and -0.207_–0.174^+0.160 dex R₂₅^–1 (based on 21 H II regions), utilizing abundances from N2 at O3N2 diagnostics and the T _e -sensitive method, respectively. The He, N, Ne, S, and Ar gradients resulted in slopes of -0.179_–0.146^+0.145, -0.431_–0.281^+0.282, -0.171_–0.239^+0.234, -0.417_–0.182^+0.174, and -0.340_–0.157^+0.156, respectively, utilizing abundances from the T _e -sensitive method. Our results confirm the existence of the negative axisymmetric global metallicity distribution that is assumed in the literature. We noticed one new WC star candidate and one transition W-R WN/C candidate. The grand-design pattern of the spiral structure of M33 is presented.