From the Gaia-ESO Survey, the analysis of the rotational velocity of the B stars in 8 stellar clusters of the Carena Complex presented in “The Gaia-ESO Survey: projected rotational velocities of B stars in the Carina Nebula” of W Santos (Observatorio Nacional MCTI, Brazil)

Rotation velocities measured for 330 B-type stars in eight stellar clusters of the Carina complex, thanks to the Gaia-ESO Survey.

Stars rotate on their axes. Some, such as young stars, spin very rapidly, with rotation periods as short as one or two days. In other cases, like red giant stars, rotation is much slower, with periods lasting several months.

The study of stellar rotation is far from a mere intellectual exercise: rotation rates can vary significantly even among stars that are otherwise very similar. This happens for several reasons—some still not fully understood—including evolutionary processes. Among these are binarity (that is, whether a star is or has been part of a system of two or more stars orbiting each other) and the dispersal of the protoplanetary disk, a structure of gas and dust that surrounds stars during their first few million years of life and regulates the evolution of their angular momentum. Moreover, stellar rotation can affect the duration of the main-sequence phase, promote the mixing of internal stellar layers, and—especially in lower-mass stars—play a key role in generating magnetic fields.

Large star-forming regions, such as the Carina Nebula, provide an important opportunity to investigate how stellar evolution and environment influence stellar rotation. This nebula is a vast star-forming complex, spanning between 800 and 1000 light-years. It hosts several stellar clusters of different ages and stellar populations, including regions of active star formation and some of the most massive stars known, such as Eta Carinae.

A team led by astrophysicist W. Santos (Observatório Nacional, Brazil, and Universidade Estadual de Santa Cruz) analyzed spectroscopic data obtained with the FLAMES instrument at the European Southern Observatory, as part of the Gaia-ESO Survey. The study focused on 330 B-type stars associated with eight stellar clusters in the Carina Nebula. By examining absorption lines due to neutral helium in stellar atmospheres, the team measured the stars’ rotation velocities—in 220 cases for the first time—and studied their distribution.

For the entire sample, rotation velocities typically range between 100 and 150 km/s. When restricting the analysis to stars of spectral types B0–B3 (effective temperatures between 18000 and 30000 K), the distribution shows three prominent peaks at 100 km/s, 200 km/s, and 350 km/s.

Furthermore, the average rotation velocity of stars in the various analyzed clusters shows a clear correlation with cluster age, with older clusters hosting faster rotators on average.

The study is described in the article “The Gaia-ESO Survey: projected rotational velocities of B stars in the Carina Nebula”, published in Monthly Notices of the Royal Astronomical Society. Among the co-authors is astronomer F. Damiani from INAF – Osservatorio Astronomico di Palermo.

The cover image (click here to view in full) shows an infrared view of the Carina Complex, captured by the WISE satellite.