The Not So Simple Globular Cluster ω Cen. I. Spatial Distribution of the Multiple Stellar Populations^∗

Abstract

We present a multi-band photometric catalog of ≈ 1.7 million cluster members for a field of view of ≈ 2×2• across ω Cen. Photometry is based on images collected with the Dark Energy Camera on the 4m Blanco telescope and the Advanced Camera for Surveys on the Hubble Space Telescope. The unprecedented photometric accuracy and field coverage allowed us for the first time to investigate the spatial distribution of ω Cen multiple populations from the core to the tidal radius, confirming its very complex structure. We found that the frequency of blue main-sequence stars is increasing compared to red main-sequence stars starting from a distance of ≈ 25' from the cluster center. Blue main-sequence stars also show a clumpy spatial distribution, with an excess in the North-East quadrant of the cluster pointing towards the direction of the Galactic center. Stars belonging to the reddest and faintest redgiant branch also show a more extended spatial distribution in the outskirts of ω Cen, a region never explored before. Both these stellar sub-populations, according to spectroscopic measurements, are more metal-rich compared to the cluster main stellar population. These findings, once confirmed, make ω Cen the only stellar system currently known where metal-rich stars have a more extended spatial distribution compared to metal-poor stars. Kinematic and chemical abundance measurements are now needed for stars in the external regions of ω Cen to better characterize the properties of these sub-populations.

Evolutionary and pulsation properties of Type II Cepheids

“…The haloes of giant galaxies are, indeed, marginally affected by crowding problems. Moreover, ELTs will provide the unique opportunity to trace old stellar populations (Fiorentino et al 2017) Pritzl et al 2003) and ω Cen, characterized by a very broad metallicity distribution (Johnson & Pilachowski 2010;Calamida et al 2017). The top panel of Fig.…”

The STREGA survey – II. Globular cluster Palomar 12★

“…To check this behaviour, we use an innovative and more complex approach to perform a more accurate separation of field and cluster stars. In particular, we adopt a procedure similar to that suggested by Di Cecco et al (2015) and Calamida et al (2017) that we call a "3D procedure" to distinguish it from the previous one.…”

Homogeneous analysis of globular clusters from the APOGEE survey with the BACCHUS code – III. ω Cen

“…Pancino et al (2000Pancino et al ( , 2003 found that the three main stellar sub-populations of ω Cen have different spatial distributions making it one of the very few clusters currently known in which metal-rich stars have a more extended spatial distribution than metal-poor stars. This spatial coverage was studied in detail by Calamida et al (2017), who concluded that merging scenario is a viable explanation for the formation of ω Cen. Evidence of interaction with the Milky Way was eventually discovered by Ibata et al (2019b) who proved with N-body simulations that the 'Fimbulthul' structure, a stream of 309 stars that surround the inner Galaxy (Ibata et al 2019a), is the tidal stream of ω Cen.…”