Variations in the far-UV local radiation in the Cygnus OB2 association. FUV fluxes were estimated using the luminosities of massive stars and 2D projections for the distances between OB stars an low mass stars.

where I identified 1224 periodic variable stars among the members of the Cygnus OB2 association. I found that 894 of these periodic variables could be characterised as spot-variability, which means their periods reflect the stars' rotational period. I explored this distribution of spin-rates in the context of the general scenario for the rotational evolution of young stars seen in other similarly aged regions. However, Cygnus OB2 association is a very particular young region. First, it is an OB association and shows no signs that it suffered significant dynamical evolution (Wright et al. 2014 MNRAS 438,639-464). Second, it has a very rich massive population with more than 169 OB stars (Wright et al. 2015 MNRAS 449, 741-760). Third, previous observations show that the fractions of stars with disks is shorter close to the massive stars (Guarcello et al. 2016 ArXiv). These three points motivated us looking beyond the comparison of rotational period distributions with the literature by further investigating possible observational evidence of environmental feedback on rotation. For that, we used the position and luminosity of the O-type stars in Cygnus OB2 to build far-UV maps of the association, using 2D projections of the distances between the stars (see plot on the left). We used the estimations of local far-UV flux obtained with these maps to compare the rotational properties of stars in regions of low and high far-UV. We found different statistical properties in the correlation between rotation and the presence of a disk and rotation for stars in high and low far-UV regions. Additionally to the paper, you can also read more about this project in my PhD thesis.