Rotation of young stars studied in “Near-Infrared Time-Series Photometry in the Field of Cygnus OB2 Association” by J. Roquette (ICEx – UFMG)

Conservation of angular momentum is one of the fundamental laws of physic that every student must deal with. Let’s make an example: if we consider a rotating cloud of dust  and gas of our Galaxy and we let it collapse under its own gravity, and then form stars, the conservation of its angular momentum dictates a faster and faster rotation while the cloud is collapsing. At the end of the collapse, the newborn stars will have a rotation velocity close to their break-up value… Instead, we observe that angular momentum of young stars is only a fraction of their break-up value. Thus, where is all the angular momentum gone?

 

This is only one of the open questions about stellar angular momentum, whose evolution is connected to stellar winds, the evolution of stellar internal structure, the presence of protoplanetary disks, and likely to the surrounding environment. The study of stellar angular momentum is thus of great interest for stellar physics.

 

This is the field of “Near-Infrared Time-Series Photometry in the Field of Cygnus OB2 Association. I – Rotational Scenario For Candidate Members“, a paper recently published on Astronomy and Astrophysics by J. Roquette (young astronomer of the Department of Physics of the University of Minas Gerais – Brazil), with the collaboration of M. G. Guarcello of the Astronomical Observatory of Palermo. The paper is based on the analysis of a long time-series of infrared observations of 5083 stars associated with Cygnus OB2, with the aim of calculating their rotation periods. The obtained values of 1224 stars, ranging from 0.8 to 32.5 days, are analysed as a function of stellar mass, the presence of a protoplanetary disk and stellar local environment. Among the results of the paper, it must be cited the further evidence that stars with protoplanetary disks rotate on average slower than stars without disks (disk-locking phenomenon), as a consequence of stellar-disk interaction, and the evidence that also the local environment, in particular the local UV field, can affect the evolution of stellar angular momentum.

 

In Figure (link) an infrared image of the area around Cygnus OB2.