Orientation of the rotation axis and the location of water-ice sublimation activity of the main-belt comet 313P/Gibbs

Context. The dust ejection activity of main-belt comet 313P/Gibbs is driven by water-ice sublimation, and the distribution of water-ice sublimation activity is nonuniform around perihelion, which may be related to seasonal modulation driven by the orientation of the rotation axis. Aims. We aim to estimate the orientation of the rotation axis of 313P and the location of water-ice sublimation on the surface of the nucleus. Methods. We used a thermophysical model of the nucleus to calculate its surface temperature distribution under various orientations of the rotation axis, aiming to identify the orientation that best matches the observational data. The position of water-ice sublimation on the surface of the cometary nucleus was estimated by fitting the simulated full width at half maximum of the dust tail to the observed data. Results. The water-ice sublimation rate of 313P is estimated to be about QH2O ≈ 4.2 × 1020 molecules m−2 s−1 (corresponding to 1.3 × 10−5 kg m−2 s−1). The spin vector of the rotation axis of 313P is located approximately at an ecliptic longitude of 70° with an ecliptic latitude in the range of [0°, 25°], or at an ecliptic longitude of 250° with an ecliptic latitude in the range of [0°, 45°]. The local latitude of water-ice sublimation activity on the surface of the nucleus is 50° (corresponding to an ecliptic longitude of the rotation axis of 70°) or −53° (corresponding to an ecliptic longitude of the rotation axis of 250°).