Characterising the properties and evolution of surface spots on young stellar objects with citizen science photometry

Young stellar objects (YSOs) display variability on the timescale of the rotational period due to surface spots rotating in and out of the observer’s line of sight. The fast rotation of young stars results in photometric variability on the order of days. In this thesis, a methodology has been developed that uses the peak-to-peak amplitude of variation in multi filter broad band photometry to characterise surface spots on YSOs. This methodology was then applied to data obtained through the Hunting Outbursting Young Stars citizen science project. Firstly, to YSOs in IC 5070 with high cadence data, and then to long duration light curves in the same field. Finally, all YSOs in HOYS fields were searched for periodicity and spot proper ties were established for all suitable sections of light curves. Across all YSO samples, two thirds of spot-induced variability is due to cold spots, and one third is due to warm/hot spots. The majority of all spots detected have surface coverage values below 30 percent. Most cold spots are 300 – 1500 K below the stellar temperature. The threshold of detection is around 300 K above or below the stellar temperature, dependent on coverage. A significant distribution of large, low temperature contrast warm spots (300 – 2500 K above stellar temperature) has been observed, alongside a small population of high temperature (>2500 K above stellar temperature), low coverage hot spots attributed to accretion. Spot properties have been related to stellar properties, particularly inner disc excess. Cold spots appear on objects with no preference to inner disc excess, while warm/hot spots have been observed as more or equally common on objects without an inner disc excess depending on the sample. The observed warm spots are hence either related to accretion as low-density accretion structures, or plages as have been observed on non-accreting YSOs.