Yu-Han Ling (Department of Atmospheric Sciences, National Central University, Taoyuan, Taiwan); Wen-Ping Chen(Graduate Institute of Astronomy, National Central University, Taoyuan, Taiwan)
A star spins down as it ages. The effect may be particularly exacerbated toward the lower main sequence with elevated magnetic braking. The mid-aged Sun, for example, rotates slowly with an equatorial speed of ~2 km/s. We propose to study the angular momentum evolution of the Sun by tracing the rotational periods of solar analogs in star clusters with well determined ages. Here we present our diagnosis of the Praesepe (M44, or Beehive) star cluster. With a heliocentric distance of less than 200 pc, and an age of some 600 Myr, the cluster, according to magnetic breaking theories, should be rapidly slowing down, making it suitable to measure the rotation of solar analog members. We present refined parameters of the cluster, such as the distance, age, and kinematics of the cluster members using Gaia eDR3 data. In addition, a total of 15 solar solar analogs are identified in the cluster. The cluster was well in the footprint of the Kepler/K2 mission. We present preliminary result of using the K2 light curves, as well as our own observations to measure possible periodicity caused by rotational modulation by starspots, as the proxy of the solar rotation rate at this age.