Researchers conduct chemical analysis of globular cluster NGC 5824

April 2, 2018 by Tomasz Nowakowski, Phys.org report
NGC 5824 imaged by the Hubble Space Telescope. Credit: NASA/ESA

Italian researchers have investigated the chemical composition of NGC 5824, a massive globular cluster in the Milky Way galaxy. Their analysis, based on observational data provided by the Very Large Telescope array, offers some hints into the nature of this cluster. The study was published March 26 in a paper on arXiv.org.

Located some 105,000 light years away in the constellation Lupus, NGC 5824 is a massive globular in the outer halo of the Milky Way galaxy. The cluster's is still puzzling astronomers; thus, many studies are focused on determining elemental abundances of the sample of its stars.

In May 2015, NGC 5824 was observed with the Fibre Large Array Multi Element Spectrograph (FLAMES) mounted on ESO's Very Large Telescope (VLT) in Chile. Using FLAMES a team of researchers led by Alessio Mucciarelli of the University of Bologna in Italy, obtained high-resolution spectra of 117 giant stars of the cluster. The collected data allowed the scientists to determine chemical abundances of these stars, revealing important information about chemical composition of NGC 5824.

"In this paper we investigate the chemical composition of NGC 5824 using a sample of high-resolution spectra collected with FLAMES at the Very Large Telescope for a total of 117 member stars," the astronomers wrote in the paper.

Previous studies suggested that NGC 5824 has an intrinsic spread in its iron content, but the research conducted by Mucciarelli's team does not confirm this assumption. They found that the cluster has an average iron abundance of –2.14 dex and shows no evidence of intrinsic spread. Therefore, the researchers classified it as a normal globular cluster, not showing any evidence of internal self-enrichment in terms of iron.

The astronomers also found evidence of chemical anomalies like sodium-oxygen (Na-O) and magnesium-aluminum (Mg-Al) anticorrelations, which are typical for globular clusters. The study emphasizes that a very small star-to-star scatter in their iron abundance and the presence of star-to-star variations in the chemical abundances of some light elements (like Na-O and Mg-Al) are the two key features confirming that a stellar system is, indeed, a globular cluster.

Moreover, they found that NGC 5824 showcases a huge range of magnesium to iron abundance ratio observed only in a few metal-poor and massive clusters. This could be due to an efficient self-enrichment driven by massive asymptotic giant branch stars.

The derived chemical abundances allowed the scientists to conclude that NGC 5824 is a standard globular cluster with one peculiarity.

"We conclude that NGC 5824 is a standard globular cluster, without spread in [Fe/H] and with the presence of usual anomalies (both Na-O and Mg-Al anticorrelations), but showing a large (and rare) spread in Mg," the paper reads.

Explore further: Researchers investigate chemical composition of globular cluster NGC 6362

More information: The chemical composition of NGC5824, a globular cluster without iron spread but with an extreme Mg-Al anticorrelation, arXiv:1803.09759 [astro-ph.SR] arxiv.org/abs/1803.09759

Abstract
NGC5824 is a massive Galactic globular cluster suspected to have an intrinsic spread in its iron content, according to the strength of the calcium triplet lines. We present chemical abundances of 117 cluster giant stars using high-resolution spectra acquired with the multi-object spectrograph FLAMES. The metallicity distribution of 87 red giant branch stars is peaked at [Fe/H]=-2.11+-0.01 dex, while that derived from 30 asymptotic giant branch stars is peaked at [Fe/H]=-2.20+-0.01 dex. Both the distributions are compatible with a null spread, pointing out that this cluster did not retain the ejecta of supernovae. The small iron abundance offset between the two groups of stars is similar to those already observed among red and asymptotic giant branch stars in other clusters. The lack of intrinsic iron spread rules out the possibility that NGC5824 is the remnant of a disrupted dwarf galaxy, as previously suggested. We also find evidence of the chemical anomalies usually observed in globular clusters, namely the Na-O and the Mg-Al anticorrelations. In particular, NGC5824 exhibits a huge range of [Mg/Fe] abundance, observed only in a few metal-poor and/or massive clusters. We conclude that NGC5824 is a normal globular cluster, without spread in [Fe/H] but with an unusually large spread in [Mg/Fe], possibly due to an efficient self-enrichment driven by massive asymptotic giant branch stars.

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Hyperfuzzy
1 / 5 (2) Apr 02, 2018
There are a few translations unaccounted! Since there is no limit to light speed. Light originates at a charge center, or its field and field updates therefore is it possible to receive visual information as located also in space and time, or an image could be reversed in time. So time parity. I prefer scale as c=1 then T=lambda! Don't even try, you already reconcile this as depth. But the deeper you peer into an infinite Universe it's nice if we can locate in space and time. No time isn't changing, we are observing these changes due to the vastness of space.

So there should be a presort or unk
Hyperfuzzy
1 / 5 (2) Apr 02, 2018
Other words what is the "attack" I like backward and forward.
Hyperfuzzy
1 / 5 (2) Apr 03, 2018
In other words, focus with Logic not Nonsense!
Hyperfuzzy
1 / 5 (2) Apr 03, 2018
We validate chemistry by the frequency lines observed. But we observe a lot of lines at the same time. The curvature of the wave front defines the center, The amplitude the radius; however, like lightening bugs, some fake in order to win the mate and then that almost confusing signal, until logic is applied Yeah hard to believe the world is old enough for a wavelet that passed our local galaxy cluster, long ago, is now a wave front we see as ahead of us, not only that, how far back in time is this? Some signals traveling further back! WTH! Captain I need a bigger computer and multiple multi-directional sensors, everywhere!

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