As promised in last weeks post, we have another look at the old friend of the project, KH15D this week. In the two images above we compare the I-band light curves for the object for the observing season 2022-23 and 2024-25 (current). In both cases we see three of the dimming events with the 48.4d period.
However, the shape of the light curve has changed quite a bit in the two years. In the first picture, the maxima are rounded off and the dimming lasts slightly in excess of 20d. In the last year, the brightness maxima are more of less flat, and the dimming has shortened to about 2weeks. Furthermore, the maxima vary in brightness by more than 0.1mag.
These changes are due to the nature of the source. We have a binary system surrounded by a dust torus. The binary orbit is almost perpendicular to the torus plane. Thus, the stars move in and out of the line of sight through the torus as they orbit each other. However, the torus is also precessing. Thus, over time, we see the stars at different parts of their orbit, explaining the changes in the light curves. Modelling by another group is underway, to better describe this system and the properties and distribution of material in the dust torus. Thus, at some stage we will have a full paper to share and discuss … stay tuned! 🙂