Globular clusters (GCs) are collections of tightly bound stars orbiting galaxies.
At a distance of about 8,150 lightyears, the galaxy NGC 6544 is a poorly studied medium-density galactic GC. Although NGC 6544 is located relatively close to the Sun, very little is known about its internal chemical composition.
A group of astronomers led by Felipe Gran fromThe Pontifical Catholic University of Chile in Santiago has conducted a high-resolution spectroscopic study of NGC 6544. Analyzing data from the APO Galactic Evolution Experiment (APOGEE), they selected 23 stars from this cluster to characterize the chemical properties of NGC 6544 and compare it with other GCs.
The study showed that the analyzedRed giant branch stars (RGB) NGC 6544 have an average metallicity of about -1.44 and an alpha element of 0.2. As for the stars with the asymptotic giant branch (AGB), these values were -1.66 and 0.25, respectively.
Let's remember the red giant branch (RGB) -stage of evolution of small and medium mass stars. These stars are giants of late spectral types, and therefore occupy a certain region on the Hertzsprung-Russell diagram, also called the red giant branch. In turn, the asymptotic giant branch is a late stage in the evolution of stars of small and medium mass. Stars at the evolutionary stage of the asymptotic giant branch have low temperatures and large sizes and luminosities.
According to the study, 14 out of 23 studiedThe stars of NGC 6544 exhibit different chemical structures. This indicates that they are so-called second generation stars. In general, multiple populations (MP) within GCs belong mainly to the first (FG) and second generation (SG) stars. The composition of SG stars varies almost at the level of individual clusters.
Second generation stars emergedfrom a substance enriched with heavy elements (heavier than helium). These elements were synthesized in stars and were ejected into interstellar space, mainly during supernova explosions. By the way, the Sun is a second generation star. At the same time, the stars of the first generation were born from the primary matter formed during the Big Bang, i.e., almost exclusively from hydrogen and helium. Second generation stars arose from matter enriched in heavy elements (heavier than helium).
In addition, the study showed thatThe stars described in the paper in NGC 6544 show significant variation in metallicity and aluminum-to-iron ratios that are larger than expected. Finally, after analyzing data sets from the APOGEE survey, astronomers noted that there are no chemically peculiar (CP) stars in the cluster.
Read more
Ingenuity helicopter successfully takes off on Mars
The first accurate map of the world was created. What's wrong with everyone else?
NASA told how they will deliver samples of Mars to Earth
APOGEE — APO Galactic Evolution Experiment.
Peculiar stars are different from ordinary starsthe same spectral class by some significant features in the spectra, and sometimes by other properties (for example, strong and variable magnetic fields). The reasons are anomalies in the chemical composition, the presence of a strong magnetic field, etc.
Chemically peculiar stars (CP stars) are common among hot main sequence stars.