Struttura ed evoluzione degli ammassi nell’associazione Vela OB2. Pubblicato su A&A: “The Gaia DR2 view of the Gamma Velorum cluster: resolving the 6D structure” di E. Franciosini (INAF-Arcetri)

of Mario Giuseppe Guarcello    ( follow mguarce)

 

We are living a golden age for the research on stellar clusters and their structure, formation and evolution. This thanks to the satellite Gaia of the European Space Agency, which will provide position and radial velocity of over one billion stars with unprecedented precision, and the project Gaia-ESO Survey, an ambitious spectroscopic survey of over 100000 stars in the Milky Way observed with the spectrograph “Fibre Large Array Multi Element Spectrograph” (FLAMES) of the European Southern Observatory. These two projects allow astronomers to select stars associated with stellar clusters, study their properties such as age, dynamic, rotation, and distance, and to understand how stellar clusters form and evolve.

 

One of the clusters which has been studied in details thanks to these two projects is the Gamma Velorum cluster. This cluster has been discovered in 2000 thanks to X-ray observations around the Wolf-Rayet binary system γ2 Vel in the Vela OB2 Association (Pozzo et al. 2000)). Later, thanks to the observations of the Gaia-ESO Survey, it has been discovered that the cluster is formed by two distinct stellar populations: Gamma Vel A, clustered around γ2 Vel, and Gamma Vel B, more dispersed. Several studies have focused on the nature of these two clusters and their physical connection. Two studies (Jeffries et al. (2014) and Sacco et al. (2015)) suggest that Gamma Vel A is the remnant of a dense cluster formed around γ2 Vel, or that both populations formed in a dense cluster caught in the act of dispersion after the removal of the parental cloud. The theoretical study of Mapelli et al. (2015) suggests instead that the two clusters formed in different epochs from the same parental cloud and that now they are merging into a single cluster.

 

In the study “The Gaia DR2 view of the Gamma Velorum cluster: resolving the 6D structure” of E. Franciosini, which has been recently published by Astronomy & Astrophysics, the nature of this cluster and its two stellar populations is unveiled thanks to Gaia observations. The main result of this study is that the two populations lie at different distances from us: about 1125 light years for Gamma Vel A and about 1250 light years for Gamma Vel B, with a difference of about 125 light years. Besides, Gamma Vel B is expanding, and the two populations have similar age. Considered together, these properties suggests that the two populations are two not connected clusters: Gamma Vel A being closer and more compact around γ2 Vel and Gamma Vel B more distant and in an expansion phase. The astronomer F. Damiani of the Astronomical Observatory of Palermo is one of the coauthors of this study.

 

The figure (link) shows an optical image of the 1-square degree area around γ2 Vel.