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Besançon Astronomers Finds intriguing chemical anomalies in a giant star wandering among the Milky Way

par Edith Burgey -

An international group of astronomers led by J. G. Fernández Trincado (PhD student at The Université de Franche-Comté), Annie C. Robin and Céline Reylé of the Observatory of Besançon, working in a detailed analysis of hundreds of thousands of spectra of stars observed in the near infrared with the Sloan 2.5 meters telescope at Apache Point Observatory in New Mexico, United States, have found some unexpected results in a giant star wandering among the Milky Way disk, which shows a chemical composition very atypical.

The team, in collaboration with researchers from the Sloan Digital Sky Surveys (SDSS) consortium (USA) found a large reservoir of chemical elements in this star.

“When we looked at the new spectrum, much to our surprise, we found strong Light-element abundance variations from strong absorption lines of carbon, aluminium, magnesium, and nitrogen”. This phenomenon has been observed only on dense star clusters such as globular clusters, i.e., in extremely dense agglomerates of stars, formed very early in the Universe, which have very low metal content, said team members.

Astronomers think that the star could have “escaped” from some of these dense stellar systems, and could be part of fossil relics of disrupted clusters. “In the meantime about another dozen have been found, but none has an extreme abundance variations as this star. Such galactic fossils allow astronomers to reconstruct an important piece of the history of our Milky Way.

“This star is an important laboratory for discovering heavy-element lines” said Sten Hasselquist, a PhD student at New Mexico State University, USA, has confirmed the findings using optical high-resolution spectrum obtained using the FEROS (Fiberfed Extended Range Optical Spectrograph) spectrograph installed at the 2.2 m telescopes of ESO at La Silla (Chile), and strikingly has also found potential Neodymium (Nd II) lines, which reveal that this star is also enhanced in the neutron-capture (r-process) elements.

This finding is helping astronomers in the quest to find these anomalies through the Milky Way, as well as to improve the characterization of astrophysical atomic lines.

The results have been recently published in the Astrophysical Journal.

See article online

PNG - 2.5 Mo
The central square shows the anomalous star in the middle of the stellar field observed by the NASA’s Wide-Field Infrared Survey Explorer (WISE) space telescope. At the bottom, the observed spectrum of the star with absorption magnesium lines (Mg) and aluminum (Al). © NASA / JPL-Caltech / and SDSS collaboration

References  :

· “Discovery of a Metal-Poor Field Giant with a Globular Cluster Second-Generation
Abundance Pattern” J. G. Fernández-Trincado et al. (2016),
http://adsabs.harvard.edu/abs/2016arXiv160401279F
· “Identification of Neodymium in the APOGEE H-band spectra” Sten Hasselquist et al.
(2016), In press.


Contacts :

  • José Gregorio Fernàndez Trincado – jfernandez chez obs-besancon.fr - Phone : 03.81.66.69.45
  • Annie Robin - Mail : annie.robin chez obs-besancon.fr - Phone : + (33) 03 81 66 69 41
  • Céline Reylé - Mail : celine.reyle chez obs-besancon.fr - Phone : + (33) 03 81 66 69 01