Przybylski’s Star IV: Or…

Part IV of III.  Part I is here.

A coda: Howard Bond correctly points out that my three explanations are only necessary if a very plausible and less interesting explanation is wrong (a caveat that I had in an early draft of my posts but edited out unintentionally.)

The identification of short-lived actinides could be a mistake! The Gopka et al. identification of these lines was made in a journal I had not heard of, Kinematics and Physics of Celestial Bodies, apparently originally in Russian. As far as I can tell, the paper has been cited exactly once, by the Dzuba et al. paper that proposed the metastable heavy isotope.

The journal and language of the Gopka et al. paper aren’t necessarily problems, of course, but they do raise eyebrows. The fact that it has not been cited could mean that the paper was simply not read (not surprising, given the journal), or that everyone who studies the star that saw the paper decided it was not worth citing, even to refute it.

[Edit: Steinn is much better at this than I am.  He points me to a 2003 AAS abstract by Crowley et al. supporting the existence of short-lived isotopes, a topic Howard Bond also mentioned on Facebook to me. Steinn also finds this paper and this one which I think I missed because I didn’t realize that promethium, a lanthanide, has no isotopes with half-lives longer than 20 years.

The Mkrtichian paper I linked to in the last post mentions Bidelman et al. PASPC, 336, 309, as supporting the short-lived isotope interpretation, and conference proceedings by Yushchenko, Gopka, & Goriely that ADS doesn’t know. Goriely discusses mechanisms here.

So the claim is stronger than I originally hedged in this post.  It’s put best in this followup paper by Crowley it al., originally shown to be by Brian Davis (but which I only just found again, now that I’m thinking of Pm): “The spectroscopic evidence is strong enough that we would declare promethium to be present without hesitation, if any of its isotopes were stable.”  In their other words, it’s only the strong prior against finding unstable isotopes that makes them hedge.]

The mystery of Przybylski’s Star is still a very good one if there are no short-lived actinides isotopes in the spectrum—the identification of the stable lanthanides seems quite secure and fascinating and it remains the most peculiar of the peculiar A stars—but it would mean that it is much more plausible that technical but mundane explanations for the star exist.

 

5 thoughts on “Przybylski’s Star IV: Or…

  1. AC DeBlanc

    Don’t get me wrong. To paraphrase Gus Grissom from “The Right Stuff”, the issue here ain’t superheavies, it’s curium. Superheavies are, as you pointed out, hard to identify. They may also be very scarce. It looks to me like ground states of nuclides on decay chains which end beta decay in the superheavy region don’t fission, but that tells me very little. I’ve found a little bit about how r-process nuclides grow, but there isn’t much information handy about excited states of superheavy element precursors. We do know that heavy isotopes of Fm fission with millisecond half-lives, and we know that Md260, a doubly-odd nuclide, decays mainly by fission. An r-process path capable of making superheavy elements probably exists, but it’s equally plausible that the path includes some attrition due to fission. I’d more or less expect superheavy elements to be rare.

    Consider curium by contrast. We know curium can form in an r-process, because we’ve done just that. It should be, to a first approximation, nearly as abundant as uranium. Its lines are well characterized. It should be an easy target. Since any process short of black magic which forms superheavies should form curium at the same time and in greater abundance, curium suffices as evidence of one mechanism by which Pm has found its way to the “surface” of Przybylski’s star,

    Thanks.

  2. jtw13 Post author

    AC wrote: “Its spectrum doesn’t show any lines for superheavies, or we would have heard about it, big time.”

    Not at all! There are many unidentified lines in the spectrum, and we don’t know what the spectra of superheavies look like, because we’ve never seen them and the energy levels are too complicated to calculate precisely.

  3. AC DeBlanc

    Sorry about the grammar. Its spectrum doesn’t show any lines for superheavies, or we would have heard about it, big time. Elements anchored by N=184 will probably be around, but not enough of them to make usable lines. What I’m going to have to do is give the literature an amateur-grade scouring for curium, though. If there’s enough Cm in the star’s “surface” to show reliable spectral lines, there will be plenty of fission daughters, including Pm, forming in those same locations.

    Thanks.

  4. jtw13 Post author

    Thanks for that. Why do you write “I know the spectrum of Przybylski’s star doesn’t contain superheavy elements”? I don’t know which elements it contains for sure (I haven’t studied the literature at that detail), but there are many, many unidentified lines.

  5. AC DeBlanc

    I’ve looked at the r process, using KUTY data from a presentation by Dr. Koura and Moller-Nix data from LANL. Unless I’m way off, Z > 113 isn’t likely to form. There’s a fission barrier between fresh r-process nuclides and the zone of beta stability. Superheavy elements will be around for a while, but they’re not necessary. Curium 250 has a half-life of almost 10000 years and decays principally by spontaneous fission. Other r-process actinides also have both strong fission branches and long half lives. Fission products will include promethium. Unless actinide daughter abundances are weird, that’s the tough element to explain. I know the spectrum of Przybylski’s star doesn’t contain superheavy elements, but does it show curium? If curium is there, is it possible Przybylski’s star collided with a fresh supernova remnant some time ago?

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