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In Wikipedia it defines "chemically peculiar stars (CP stars)" as,

In astrophysics, chemically peculiar stars (CP stars) are stars with distinctly unusual metal abundances, at least in their surface layers.

HD 222925 has been making a lot of news lately. In this video by Anton Petrov, "Groundbreaking Image of the Most Element Rich Star Found to Date " he says,

[HD 222925] was always classified as "chemically peculiar" or basically unusual or somewhat strange and there is a really important reason for that. [...] With the exception of our own Sun this particular star seems to be extremely rich in various elements. A relatively recent study identified 65 various elements, chemical elements, including Gold with an overabundance of a lot of other metal that's never been seen before anywhere except in our own Sun.

It sounds like HD 222925 is "chemically peculiar" because of the composition of the star. If so, is our Sun also "chemically peculiar"? And if not, what is the definition of "chemically peculiar" such that our Sun is NOT and HD 222925 is?

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    $\begingroup$ My guess is that we can get a lot more spectrographic data from sunlight than from starlight, simply due to the brightness. $\endgroup$
    – PM 2Ring
    Jul 27, 2022 at 23:44
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    $\begingroup$ Interesting, but I think this is a matter of subjective, rather than objective, classification. $\endgroup$
    – Carl Witthoft
    Jul 28, 2022 at 13:58
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    $\begingroup$ I don't think this question should be closed and answer blocked because it is "likely to be answered with opinions rather than facts and citations". The OP found something that sounds authoritative yet feels subjective, and has come here to Astronomy SE to clear this up. Instead of preventing anyone from posting an answer because the quoted bit from the link sounds subjective, let's allow answers to be posted so we can get to the bottom of this! $\endgroup$
    – uhoh
    Jul 29, 2022 at 12:29
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    $\begingroup$ I agree with @uhoh I previously upvoted this question because it is interesting and I was hoping to see a good answer. As well, the new echelle spectrograph at Gemini South targeted this particular star for its initial tests: “Gemini South telescope's GHOST spectrograph captures first light observations of a bright, chemically rich star phys.org/news/….” So what gives with this star? $\endgroup$
    – Ed V
    Jul 30, 2022 at 15:30
  • $\begingroup$ Very poor video. $\endgroup$
    – ProfRob
    Jul 31, 2022 at 23:12

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No, the Sun is not "chemically peculiar". (I'm not sure most astronomers would call HD 222925 chemically peculiar, either, certainly not in any of the ways discussed on the Wikipedia page.)

The video you link to is rather confused. What makes HD 222925 special is not that it is, overall, "rich in elements". In fact, it is relatively metal-poor, with only about 3% of the Sun's iron abundance. The key things about it are: 1) the r-process elements are enhanced relative to other elements in that star; 2) it is relatively hot -- and thus produces significant UV light; and 3) it is -- because it is metal-poor -- lacking in iron-group elements. The latter fact means that the UV signatures of many r-process elements (including, yes, gold) are discernible in the UV spectrum in a way that would not be possible in a more metal-rich, hot star, where the UV spectrum is dominated by absorption lines from iron-group elements. (It is also bright enough to make high-signal-to-noise UV spectra possible.)

The Sun is relevant not because it is especially enhanced in r-process elements, but because we can know the abundances of all the r-process elements in the Solar System really well from analysis of meteorites. (The video's claim that the Solar System's r-process elements must have come from a single nearby neutron-star collision is erroneous, as is the attempt to suggest that r-process elements are important for life.)

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Not chemically peculiar. Local Group stars appear similar in composition. At least, to the extent that spectroscopy (“squiggly-line interpretation”) can nail down one star, let alone star-to-Sun differences.

The solar composition is measured as much (or more) from exceptional meteorites (CI chondrites) than spectroscopy:

https://en.wikipedia.org/wiki/CI_chondrite

See also review article, The future of Genesis science, Meteoritics and Planetary Science, 2019 May

Happy squiggling.

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