The Asteroseismological Richness of RCB and dLHdC Stars. (arXiv:2311.10158v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Wong_T/0/1/0/all/0/1">Tin Long Sunny Wong</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bildsten_L/0/1/0/all/0/1">Lars Bildsten</a>
RCB stars are $Lapprox10^4,L_{odot}$ solar-mass objects that can exhibit
large periods of extinction from dust ejection episodes. Many exhibit
semiregular pulsations in the range of $30-50$ days with semi-amplitudes of
$0.05-0.3$ magnitude. Space-based photometry has discovered that solar-like
oscillations are ubiquitous in hydrogen-dominated stars that have substantial
outer convective envelopes, so we explore the hypothesis that the pulsations in
RCB stars and the closely related dustless hydrogen-deficient carbon (dLHdC)
stars, which have large convective outer envelopes of nearly pure helium, have
a similar origin. Through stellar modeling and pulsation calculations, we find
that the observed periods and amplitudes of these pulsations follows the
well-measured phenomenology of their H-rich brethren. In particular, we show
that the observed modes are likely of angular orders $l=0,1$ and $2$ and
predominantly of an acoustic nature (i.e. $p$-modes with low radial order). The
modes with largest amplitude are near the acoustic cut-off frequency
appropriately rescaled to the helium-dominated envelope, and the observed
amplitudes are consistent with that seen in high luminosity
($L>10^3,L_{odot}$) H-rich giants. We also find that for
$T_{mathrm{eff}}gtrsim5400,mathrm{K}$, an HdC stellar model exhibits a
radiative layer between two outer convective zones, creating a $g$-mode cavity
that supports much longer period ($approx 100$ days) oscillations. Our initial
work was focused primarily on the adiabatic modes, but we expect that
subsequent space-based observations of these targets (e.g. with TESS or Plato)
are likely to lead to a larger set of detected frequencies that would allow for
a deeper study of the interiors of these rare stars.
RCB stars are $Lapprox10^4,L_{odot}$ solar-mass objects that can exhibit
large periods of extinction from dust ejection episodes. Many exhibit
semiregular pulsations in the range of $30-50$ days with semi-amplitudes of
$0.05-0.3$ magnitude. Space-based photometry has discovered that solar-like
oscillations are ubiquitous in hydrogen-dominated stars that have substantial
outer convective envelopes, so we explore the hypothesis that the pulsations in
RCB stars and the closely related dustless hydrogen-deficient carbon (dLHdC)
stars, which have large convective outer envelopes of nearly pure helium, have
a similar origin. Through stellar modeling and pulsation calculations, we find
that the observed periods and amplitudes of these pulsations follows the
well-measured phenomenology of their H-rich brethren. In particular, we show
that the observed modes are likely of angular orders $l=0,1$ and $2$ and
predominantly of an acoustic nature (i.e. $p$-modes with low radial order). The
modes with largest amplitude are near the acoustic cut-off frequency
appropriately rescaled to the helium-dominated envelope, and the observed
amplitudes are consistent with that seen in high luminosity
($L>10^3,L_{odot}$) H-rich giants. We also find that for
$T_{mathrm{eff}}gtrsim5400,mathrm{K}$, an HdC stellar model exhibits a
radiative layer between two outer convective zones, creating a $g$-mode cavity
that supports much longer period ($approx 100$ days) oscillations. Our initial
work was focused primarily on the adiabatic modes, but we expect that
subsequent space-based observations of these targets (e.g. with TESS or Plato)
are likely to lead to a larger set of detected frequencies that would allow for
a deeper study of the interiors of these rare stars.
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