HD 87240 is a chemically peculiar star with an overabundance of heavy elements, study suggests

October 22, 2018 by Tomasz Nowakowski, Phys.org report
HD 87240 is a chemically peculiar star with an overabundance of heavy elements, study suggests
HD 87240. Credit: Digitized Sky Survey.

European astronomers have conducted a chemical study of the star HD 87240, a member of the open cluster NGC 3114. The new research, which determined the abundances of several elements in HD 87240's atmosphere, suggests that the object is a chemically peculiar star showcasing an overabundance of heavy elements. The finding is reported in a paper published October 10 on arXiv.org.

Located some 7,200 light years away in the constellation Carina, NGC 3114 is a sparse, young (about 160 million years old) open cluster. Although the cluster is very difficult to study, due to the high number of field stars from the Galactic disc, it has been a subject of numerous observations since 1963.

Now, a team of astronomers from Paris Observatory and Space Research Institute of Austrian Academy of Sciences, has performed a chemical study of one of NGC 3114's , namely HD 87240, which was classified by previous observations as an Ap Si star – a magnetic chemically peculiar star (CP star) with an overabundance of silicon (Si).

For their research, the astronomers used the data collected by European Southern Observatory's (ESO) Very Large Telescope (VLT) in Chile. HD 87240 was observed by VLT's Ultraviolet and Visual Echelle Spectrograph (UVES) in its high-resolution mode on October 26, 2017.

"We have used the code ATLAS9 to compute a model atmosphere for HD 87240 for the effective temperature and surface gravity derived from Stromgren's photometry A grid of synthetic spectra has been computed using SYNSPEC49 and adjusted to the UVES spectrum of HD 87240 to determine the abundances of several chemical elements using the latest critically evaluated atomic data from NIST," the researchers wrote in the paper.

Analysis of UVES data allowed the team to determine chemical abundances for 39 elements in the atmosphere of HD 87240. The astronomers found that this star is significantly overabundant in , especially when it comes to platinum (Pt) and mercury (Hg) – about 10,000 times the solar abundances.

Moreover, HD 87240 was found to be unusually rich in silicon (around 10 times the solar abundance) an in the so-called rare-earth elements like cerium (Ce), praseodymium (Pr) and neodymium (Nd) – at a level of at least five times the solar abundances.

HD 87240 also displays solar abundances of carbon, nitrogen and oxygen, as well as scandium (Sc) and vanadium (V). However, the star turns out to be underabundant in light elements such as helium or sulfur.

According to the paper, the derived chemical abundances suggest that HD 87240 should be reclassified as a chemically peculiar late B star with overabundances of silicon, platinum and mercury.

"The derived abundance pattern of HD 87240 departs strongly from the solar composition which definitely shows that HD 87240 is not a superficially normal late B star but is definitely a new CP star. (…) Hence we propose that HD 87240 be reclassified as a Bp SiPtHg star (not as an Ap Si as it currently is)," the researchers concluded.

Explore further: Chemically peculiar star HR8844 could be a hybrid object

More information: Elemental abundances of HD 87240, member of the young open cluster NGC 3114, arXiv:1810.04540 [astro-ph.SR] arxiv.org/abs/1810.04540

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9 comments

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Benni
1.7 / 5 (14) Oct 22, 2018
OK, great, but what does this tell us about the % quantity of hydrogen available for fusion to helium?

It only states that the star has a greater abundance of certain elements versus that for other kinds of stars, so what if anything does this tell us bout the thermonuclear processes of transforming mass to energy? Nothing. With no comparison of it's energy output to gassy stars we don't actually know what this means in the evolution of stars do we?
Nik_2213
4 / 5 (4) Oct 22, 2018
IMHO, either it caught a supernova's enriched blast, or it swallowed a rocky planet...
MrBojangles
3.8 / 5 (10) Oct 22, 2018
The purpose of the paper was not to answer your questions.
https://arxiv.org...4540.pdf
jonesdave
3.8 / 5 (17) Oct 22, 2018
OK, great, but what does this tell us about the % quantity of hydrogen available for fusion to helium?


It tells us that there is sufficient H at sufficient temperature and density to start the p-p fusion chain. Obviously, otherwise it wouldn't be a star, and we wouldn't see it.

Nik_2213
5 / 5 (4) Oct 22, 2018
@MrB: Thank you for the arxiv link !!
rrwillsj
2.1 / 5 (7) Oct 22, 2018
BEMi, that was an interesting way to put into perspective the research described in this article.

Nahh, who am I kidding?
BEMi's comment was a total infantile rant.

BEMi, if you want my respect for your comment?

Then you are required to provide, in complete detail, the minutia of your life.

Listing, without fail! The dream that woke you up in the morning. How often you yawned and scratched yourself, Then details of your toiletries and other morning routines.

What do you mean. I am being unreasonable? I am just reiterating your childish whinge against the research project described in this article.

Do not forget to include, in excruciating detail, all that you will be experiencing for the next ten years.

Otherwise your life has no meaning and is a total fail! Just as you concluded of these researchers in your comment.
Benni
1.6 / 5 (7) Oct 22, 2018
OK, great, but what does this tell us about the % quantity of hydrogen available for fusion to helium?


It tells us that there is sufficient H at sufficient temperature and density to start the p-p fusion chain. Obviously, otherwise it wouldn't be a star, and we wouldn't see it.


You're not qualified to answer questions I'm not asking, or even if I were asking that question.
Cryptodiamond
5 / 5 (2) Oct 22, 2018
They re-classify this star as Bp star! These stars tend to rotate more slowly than others and have very strong magnetic feilds, the current best guess is the magnetic fields "levitate" the heavy metals to near the surface and differentiate the star, which mus be hard to do given all that thermal mixing. Although I like Nix-2213 suggestions as well.
barakn
4.6 / 5 (9) Oct 23, 2018
OK, great, but what does this tell us about the % quantity of hydrogen available for fusion to helium? -Benni

A nuclear engineer simply would have looked up the solar abundances conveniently included in the paper and realized that Hg, for example, in the Sun is 10^-10.91 times (1.23 x10-^11 x) less abundant than H, and in HD 87240, it's 10^-6.87 = 1.35 x 10^-7 x less abundant. Hydrogen is still by far the the most abundant element and fusion is not going to be significantly affected. That's what a nuclear engineer would have concluded, but Benni had to ask the crowd.

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