This week we have a look at another binary system. The object KH15D near the Christmas Tree Cluster and the Cone Nebula, known as NGC2264. The system shows eclipses, but not in the usual way eclipsing binaries do. This is a young binary which is surrounded by a ring / torus of circumstellar material. The two stars orbit each other with a period of 48.37 days. The orbital plane of the binary is more or less perpendicular to the dust torus and we see the system about edge on, as far as the dust torus is concerned. Thus, the stars move periodically in and out of view, causing brightness changes of the system. The HOYS I-Band data shown in the image, nicely shows the periodic dips in brightness.

Additionally, the dust torus is precessing. Thus, over time this allows us to investigate each of the stars in turn during the bright state, when the other one is not visible. Since the discovery of the system it is now possible for the first time to determine the properties of star B in the system. In particular we can try to measure the rotation period for the first time. Typically, our HOYS data for this target region does not have a daily cadence in all filters as it is a winter target. We have thus applied for, and been given, time to observe this target with the 2m Liverpool Telescope in the next observing season. Starting October 1st 2020, we will observe the object and it’s surroundings in the U, B, V, R, I, and H bands each night until the end of March – weather and the Moon permitting.

These data should allow us to measure the rotation period of star B if there are spots on the surface of the star. It will further allow us to probe the dust structure and properties in the dust torus. With the U-Band data we should also be able to monitor accretion rate changes of the source. We would also like to obtain H-alpha measurements of the source, which are complimentary to the U-Band data. We hence would like to ask all the HOYS participants with a large enough aperture telescope to obtain nightly deep H-alpha observations of the target during next winter. We will remind everybody nearer to the time in a newsletter announcement.