White dwarf orbiting a blue straggler star detected
The ACS / SBC images watered in the F165LP filter of the Five BSS studied in this study. The positions of the 5 targets are marked by circles of green color: from left to right, BSS1, BSS2, BSS3, BSS4 and BSS5. The scale is indicated in the lower left corner of each frame. Credit: arxiv (2025). DOI: 10.48550 / Arxiv. 2008.21118
Using the Hubble space telescope (HST), Italian astronomers observed five staggler blue stars in the globular cluster 47 Tucanae. Their results show that one of these stars has a white dwarf companion. The discovery is presented in an article published on August 28 on the arxiv pre -printed server.
Located at around 15,300 light years away from the earth, 47 Tucanae is a massive globular bunch and not stuck in the constellation constellation. This cluster shows low extinction, has a high interaction rate and has the most X -ray sources identified so far among the other globular clusters. These properties make 47 Tucanae an excellent target to study close binary systems.
Now, a team of astronomers led by Elisabetta Reggiani from the University of Florence in Italy, discovered a new binary in 47 Tucanae, after that, they identified the presence of a complementary star at one of the stars of Blue Straggler of the Cluster (BSSS), designed BSS4. In general, BSS are main oil combustion objects more massive than the main sequences (MS) and the post-MS stars. 47 Tucanae is known to accommodate at least five stars of Straggler Blue.
“Analysis of the extraviolement photometric data acquired with ACS / SBC in HRTs unambiguously reveals the presence of a hot companion from BSS4”, wrote the researchers in the article.
Based on the data collected, astronomers have found that the BS4 companion object is probably a warm white dwarf (WD). They assume that WD probably formed by mass transfer less than 12 million years ago.
Left panel: Sed observed from BSS1 (blue circles) compared to the expected flows (cyan squares) calculated from the best suitable synthetic SED convolution (black line) with the photometric filters adopted. The uncertainties on the observed flows are marked with vertical error bars (unless they are smaller than the size of the blue circles). Cyan’s shaded horizontal rectangles mark the wavelength of each photometric filter. For the sake of clarity, they were not associated with the expected flows but, of course, they also hold for the points observed. The vertical error bar of Cyan squares corresponds to the 1σ error on the expected flows. The temperature and the surface radius of the best adjustment are labeled with their 1σ uncertainty in the legend of the upper right corner. The residues between the observed and expected flows are drawn in the lower panel. Right panel: χ2 card for BSS1 showing the distribution of χ2 Values (color coded as in the sidebar) obtained for all the explored combinations of R and T. The black lines refer to the 1σ, 2σ and 3σ χ2 contours of minimum values (χ20), which is marked with a black cross and labeled in the lower right corner. Credit: arxiv (2025). DOI: 10.48550 / Arxiv. 2008.21118
Regarding the properties of the new white dwarf, scientists estimate that it has a mass between 0.2 and 0.55 solar masses, while its radius is probably solar rays of 0.016-032. The effective temperature of this star is estimated at more than 20,000 K.
The authors of the article noted that at the time at the very young WD cooling age and at the significant speed of rotation of BSS4 suggest that this is a recently formed system. They added that this binary is perhaps about to complete the mass transfer process. Consequently, it is expected that over the next million years, the bare companion will increase its surface temperature due to the complete loss of the envelope around its nucleus.
Summarizing the results, the researchers stressed that BSS4 is one of the youngest BSS-WD systems detected. According to them, a more in -depth investigation by BSS4 could provide important information on the evolution of these rare binary people.
“In particular, the determination of the radial speed curve of the system (and also of the BSSs without any evidence of an ultraviolet excess) could add other precious details for the physical characterization of these confusing objects and their evolutionary processes, providing crucial constraints to the theoretical modeling of the mass transfer training channel”, concluded astronomers.
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More information:
Elisabetta Reggiani et al, detection of a white dwarf in orbit around a carbon carbon carbon in 47 Tucanae, arxiv (2025). DOI: 10.48550 / Arxiv. 2008.21118
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