Cara Farquhar

Young Stars are newly formed stars that have not yet reached the main sequence phase of their evolution and due to their large convective layers are very active. Young stars are typically surrounded by a protoplanetary disk, which is a rotating disk of dense gas and dust. Material from this disk is often accreted onto the stellar surface of young stars resulting in the formation of active sites. Since young stars have a faster differential rotation than older stars we expect their magnetic poles to flip more often. The duration between the flipping of these poles is known as a magnetic cycle.

The aim was to analyse the long and short-term rotation and activity in a group of young stars, including exploring any potential changes and correlations in their results.

Data from the Kepler 2 Space Mission, Catalina Survey and All Sky Automated Survey (ASAS) were used for a selected group of thirty-two young stars, taken from a base paper [L.M. Rebull et al. (2018). The Astronomical Journal, 155(5):196.]. The three surveys differed in length and in the observational dates they occurred. Data from each survey was used to generate light curves and periodograms, to determine the potential periods for each young star and whether dips or flares (caused by cold spots, protoplanetary disks, binary stars, active sites, or hot spots) were present. Wavelet analyses of the Kepler 2 data were also generated to obtain a more accurate analyse. Phase diagrams, for each survey, were then obtained from the periods to analyse any potential modulations and shifts of stellar spots. Statistical tests of the results were also carried out to determine potential correlations between mass, disks, flares, and Kepler 2 periods. Finally, using a Monte Carlo analysis, confidence intervals were obtained for the periodograms with possible long-term modulation.

Light curves for the Kepler 2 data allowed the presence of dips and flares to be easily detected and distinct period values were obtained from their respective periodograms. Light curves for the Catalina and ASAS data did not allow the presence of dips or flares to be easily detected, and their respective periodograms contained multiple period points. Phase analysis of the Kepler 2 data showed strong modulations, as expected. The ASAS and Catalina data did not show any strong modulation due to large variations in the time between observations and ground sampling (a result of the uneven time intervals). Statistical tests suggested one possible correlation between shorter Kepler 2 periods and the presence of flares, indicating that more active young stars tend to rotate faster. No magnetic cycles were detected in the Catalina or ASAS data.

In conclusion, analysis of the short-term activity showed strong modulations for the young stars, with a potential correlation between the presence of flares and a shorter period. This correlation between periods and the existence of flares is expected if flares are related to the magnetic activity of young stars. The long-term activity did not show any strong modulations, due to the uneven time intervals between observations and ground sampling. No magnetic cycles were detected suggesting, any magnetic cycles were probably longer than 1000 days.