Speaker: Marcel Agüeros (Columbia University)

Title: The Factory & The Beehive: Stellar Rotations at 600 Myr

Time: 12:00, Tuesday 19 April 2011

Place: SAAO Auditorium

Abstract:
In a classic 1972 paper, Andrew Skumanich showed that stellar rotation decreases over time — as does chromospheric activity, a proxy for magnetic field strength. This relationship between age, rotation, and activity has been a cornerstone of stellar evolution work for over 40 years. However, rotation periods are scarce for stars with ages greater than 500 Myr, complicating the calibration of an age-rotation-activity relation that can be applied to field stars. The Columbia/Cornell/Caltech Palomar Transient Factory (CCCP) survey of open clusters is an effort to systematically map stellar rotation in open clusters. I will present the first CCCP results for Praesepe, a rich, nearby, 600 Myr open cluster. With light curves containing >150 measurements over more than three months, we have measured rotation periods for ~40 K & M-type cluster members. These rotation periods span the gap between the periods measured for the solar-type and lowest-mass Praesepe members, and indicate that the orderly mass-rotation relation seen for higher mass Praesepe members begins to break down at ~0.6 Msun. In addition, I will discuss our on-going effort to complete the portrait of the 600
Myr age-activity-rotation by measuring Halpha emission for cluster stars.