Research investigates 47 Tucanae’s brightest star

Astronomers have inspected the brightest star in a globular cluster known as 47 Tucanae (another designation NGC 104). The results of the study, published Aug. 3 on arXiv.org, provide important information about the properties and chemical makeup of this star, which could improve our understanding of the nature of the cluster.

Globular clusters (GC) are collections of closely related stars orbiting galaxies. Astronomers see them as natural laboratories for studies of the evolution of stars and galaxies. In particular, globular clusters could help researchers better understand the history of the formation and evolution of early-type galaxies, as the origin of GC appears to be closely related to periods of intense star formation.

Located some 13,000 light years away in the constellation Tucana, 47 Tucanae, or 47 Tuc for short, is a globular cluster with a diameter of about 120 light years. It is the second brightest GC in the sky and can be seen with the naked eye.

The brightest star of 47 Tuc at ultraviolet and optical wavelengths is the so-called “Bright Star” (BS). It is a spectral type B8 III blue giant star with an effective temperature of around 11,000 K. In addition, the Bright Star is a post-asymptotic (post-AGB) giant branch star that moves on the color diagram. -magnitude towards the tip. of the white dwarf cooling sequence.

Although many studies on the bright star have been carried out, its chemical composition is still poorly understood. Since the bright star represents a unique window into the chemistry of 47 Tuc, a team of astronomers led by William V. Dixon of the Space Telescope Science Institute in Baltimore, Maryland, studied this star using the Far Ultraviolet. Spectroscopic Explorer (FUSE), the Hubble Space Telescope (HST) and the Magellan Telescope.

The observations allowed the team to determine the photospheric abundances of 26 elements of the bright star. The data shows that the elements of intermediate mass generally flake with iron, while the heavier elements have roughly solar abundances. The star was found to have a relatively low carbon-to-nitrogen ratio, which suggests that it belongs to the second generation of cluster stars. In addition, it turns out that it also has a low carbon / oxygen ratio, which indicates that it did not undergo a third dredging on the AGB.

The study determined the fundamental parameters of the bright star. According to research, it has a radius of about 9.63 solar rays, a mass of about 0.54 solar mass, and an effective temperature at a level of 10,850 K. The mass derived from the bright star suggests that the Individual stars of 47 Tuc lose between 0.1 and 0.2 solar mass on the AGB, which is only slightly less than the mass that the same stars lose on the branch of the red giant (RGB).

Summarizing the results, the researchers concluded that the bright star did not experience any significant change in its photospheric abundances during its AGB ascent.

“If so, then its heavy element abundances are typical of cluster values,” added the authors of the article.

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