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Thread: Pulsation in Faint Blue Stars

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    Pulsation in Faint Blue Stars

    The authors use the Mesa Code which follows the sequential development of isotopic species in the the evolving nucleosynthesis in stars, to identify a new class of pulsating variables....faint blue stars. BLAPs, blue large amplitude pulsators, were recently discovered, and now these faint blue stars are added as a new class. It is proposed that these are low mass, pre-white dwarf stars and that the pulsations are driven by iron-group elements' opacity.
    SEE:https://arxiv.org/pdf/1912.04129.pdf


    pete
    Last edited by trinitree88; 2019-Dec-10 at 04:01 PM. Reason: clarify

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    Care to convert it to "georgeeze"? I'll try...

    1) Wimpy stars destined to WD retirement, and wimpier than normal, can have more of its shell remain after the puffing stage of its outer envelope.
    2) The inner remaining hydrogen shell burns brightly, perhaps re-ignites?, increasing the radiation flux.
    3) The increase in radiation pushes radially outward the heavier metals (e.g. 5 cent kind) known here as radiative levitation.
    4) Opacity increases and, thus, so do the temperatures.
    5) Just a guess, and I admit to not reading all of it, a point is reached during the outward propagation of the metals where the opacity drops since, for one reason, the gap between metals
    increases.
    6) This is observed as a blue light pulsation.
    7) The pulsation period (not the interval between pulses) would be restricted to this hydrogen fusion time frame, maybe?
    8) Eventually it becomes a lower mass WD, though we know it will appear bluish white until it's older.
    9) Binarity may be essential to cause these circumstances.
    10) WD stands for White Dwarf.

    So what's my grade out of 10?
    Last edited by George; 2019-Dec-10 at 05:18 PM.
    We know time flies, we just can't see its wings.

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    Quote Originally Posted by George View Post
    Care to convert it to "georgeeze"? I'll try...

    1) Wimpy stars destined to WD retirement, and wimpier than normal, can have more of its shell remain after the puffing stage of its outer envelope.
    2) The inner remaining hydrogen shell burns brightly, perhaps re-ignites?, increasing the radiation flux.
    3) The increase in radiation pushes radially outward the heavier metals (e.g. 5 cent kind) known here as radiative levitation.
    4) Opacity increases and, thus, so do the temperatures.
    5) Just a guess, and I admit to not reading all of it, a point is reached during the outward propagation of the metals where the opacity drops since, for one reason, the gap between metals
    increases.
    6) This is observed as a blue light pulsation.
    7) The pulsation period (not the interval between pulses) would be restricted to this hydrogen fusion time frame, maybe?
    8) Eventually it becomes a lower mass WD, though we know it will appear bluish white until it's older.
    9) Binarity may be essential to cause these circumstances.
    10) WD stands for White Dwarf.

    So what's my grade out of 10?
    George. That's pretty good. It's similar to classical Cepheid pulsations, but the time evolution for the opacity is a little different, hence their graphs. Better ingredients do make better pizzas, and better data from better instrumentation, enable discoveries of new classes of stars. pete

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    Quote Originally Posted by trinitree88 View Post
    George. That's pretty good. It's similar to classical Cepheid pulsations, but the time evolution for the opacity is a little different, hence their graphs. Better ingredients do make better pizzas, and better data from better instrumentation, enable discoveries of new classes of stars. pete
    I thought they might be similar but the "radiative levitation" sounded almost magical, and its novelty got my interest. I don't think metals play a similar role for Cepheids, not that I really understand their role for these bluish WDs.
    We know time flies, we just can't see its wings.

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    If I am not mistaken, helium in the envelope is the active ingredient in Cepheids.

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    Quote Originally Posted by Hornblower View Post
    If I am not mistaken, helium in the envelope is the active ingredient in Cepheids.
    Yes, my limited understanding is that the massive Cepheid will increase the double ionization level for the helium in its envelope which causes destabilization because of the compounding storing of energy due to the fact double ionization increases opacity. The star doesn't have time to expand quick enough to deal with the temperature rise. Once it has expanded, its size increase plus all that retained energy being released will greatly increase its luminosity until cooling and shrinking takes place. This gets it back to where it was and the cycle begins anew.

    Are metals for the blue WDs serving analogous to the double ionization of He?
    We know time flies, we just can't see its wings.

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    George. The first ionization energy for iron group elements is relatively low, such that a second and third may occur. This frees up extra electrons, which contribute to the overall radiation pressure, which for massive stars, exceeds the gas pressure and controls the pulsations. The numbers are crunched some here:https://jila.colorado.edu/~pja/astr3730/lecture16.pdf


    pete

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    Quote Originally Posted by trinitree88 View Post
    George. The first ionization energy for iron group elements is relatively low, such that a second and third may occur. This frees up extra electrons, which contribute to the overall radiation pressure, which for massive stars, exceeds the gas pressure and controls the pulsations. The numbers are crunched some here:https://jila.colorado.edu/~pja/astr3730/lecture16.pdf
    Yeah, and I think nickel is a similar story. Having so many more electrons available to play with (compared to He) likely means it wouldn't take a lot of extra heat to get a lot of free electrons running around batting back those photons as they only half-heartedly think they can finally get out of town. Thus, opacity gets bumped. But it's that phrase, "radiative levitation" that is so intriguing. Does this cause a concentration of metals as pressure pushes on them outward, thus concentrating the scattering-hungry free electrons, thus increase opacity, thus retain radiation, thus swell, and act like a Cepheid? Is it that simple?
    Last edited by George; 2019-Dec-11 at 10:16 PM.
    We know time flies, we just can't see its wings.

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