The infrared eye of the Wide-Field Camera 3 on the Hubble Space Telescope reveals multiple main sequences of very low-mass stars in NGC 2808

TL;DR

Using Hubble's infrared imaging, the study uncovers multiple main sequences in NGC 2808, revealing complex stellar populations and their chemical compositions, especially among very low-mass stars.

Contribution

This work provides new infrared observations of NGC 2808's multiple main sequences, linking photometric features to stellar generations and chemical abundances, expanding understanding of globular cluster complexity.

Findings

Identification of three main sequences in infrared CMD

Association of faint MS with primordial stellar generation

Detection of abundance anticorrelation signatures in low-mass stars

Abstract

We use images taken with the infrared channel of the Wide Field Camera 3 on the Hubble Space Telescope (HST) to study the multiple main sequences (MSs) of NGC 2808. Below the turn off, the red, the middle, and the blue MS, previously detected from visual-band photometry, are visible over an interval of about 3.5 F160W magnitudes. The three MSs merge together at the level of the MS bend. At fainter magnitudes, the MS again splits into two components containing ~65% and ~35% of stars, with the most-populated MS being the bluest one. Theoretical isochrones suggest that the latter is connected to the red MS discovered in the optical color-magnitude diagram (CMD), and hence corresponds to the first stellar generation, having primordial helium and enhanced carbon and oxygen abundances. The less-populated MS in the faint part of the near-IR CMD is helium-rich and poor in carbon and oxygen, and it can be associated with the middle and the blue MS of the optical CMD. The finding that the photometric signature of abundance anticorrelation are also present in fully convective MS stars reinforces the inference that they have a primordial origin.