Rotation period of C/2006 P1 (McNaught) through morphological analysis with narrowband imaging

ABSTRACT This study presents findings from narrowband imaging of comet C/2006 P1 (McNaught) using the 3.6-meter New Technology Telescope (NTT) at La Silla, Chile. Observations commenced on 2007 January 27, 15 d after perihelion, and continued until February 4, with additional sessions from February 25 to 28. Imaging was conducted using the ESO Multi-Mode Instrument (EMMI) in both broad band (B, V, R) and six comet-specific narrowband filters (CN, C$_3$, C$_2$, NH$_2$, blue and red continuum). Various image processing techniques were employed to enhance structural features, including azimuthal mean/median division and subtraction, azimuthal renormalization, and division by a 1/$\rho$ profile as well as Larson–Sekanina technique. These enhancements revealed dynamic coma structures, with jets transitioning from spiral patterns to linear or fan-like shapes over time. The consistency of morphological patterns across different processing methods validated their authenticity. The periodic recurrence and temporal evolution of CN coma features in narrowband images indicate a nucleus rotation period of 11.8 $\pm$ 0.5 h, consistent with stable active regions and rotationally modulated outgassing near perihelion.