A DOUBLE MAIN SEQUENCE IN THE GLOBULAR CLUSTER NGC 6397

作者：Milone A P^*; Marino A F; Piotto G; Bedin L R; Anderson J; Aparicio A; Cassisi S; Rich R M

来源：Astrophysical Journal, 2012, 745(1): 27.

DOI：10.1088/0004-637X/745/1/27

• globular clusters: individual (NGC 6397)
• stars: Population II

High-precision multi-band Hubble Space Telescope (HST) photometry reveals that the main sequence of the globular cluster NGC 6397 splits into two components, containing similar to 30% and similar to 70% of the stars. This double sequence is consistent with the idea that the cluster hosts two stellar populations: (1) a primordial population that has a composition similar to field stars, containing similar to 30% of the stars, and (2) a second generation with enhanced sodium and nitrogen, depleted carbon and oxygen, and a slightly enhanced helium abundance (Delta Y similar to 0.01). We examine the color difference between the two sequences across a variety of color baselines and find that the second sequence is anomalously faint in m(F336W). Theoretical isochrones indicate that this could be due to NH depletion.

• 出版日期2012-1-20