INVESTIGADORES
MILLER BERTOLAMI Marcelo Miguel
congresos y reuniones científicas
Título:
Testing the hot-flasher scenario with asteroseismological tools. First Results
Autor/es:
M. M. MILLER BERTOLAMI; CORSICO, A.; ALTHAUS, L. G.
Lugar:
Rio de Janeiro
Reunión:
Taller; XXVIIth General Assembly; 2009
Institución organizadora:
International Astronomical Union
Resumen:
A core helium flash after the departure from the red giant branch (i.e.
"hot-flasher scenario") offers one of the most promising explanations
for the origin of He-sdO stars. Recently, Miller Bertolami et al. (2008)
have shown that many surface properties of H-deficient sdO stars (the
He-sdO stars) could be explained through this scenario if chemical
diffusion is taken into account. In this context the He-sdO stars formed
during a hot-flasher event would transform into H-rich hot-sdB stars
(33000-38000 K) as a consequence of diffusion of the remaining H towards
the surface of the star. Thus, some hot sdBs might be the descendants of
He-sdO stars that have previously burnt most of their H-content and,
thus, a very thin H envelope should be expected (10‑9
to 10‑10 Mȯ, see Miller Bertolami et
al. 2008 for details). Interestingly enough, the location of these sdB
stars in the logg - Teff diagram should overlap
with the domain of the rapidly pulsating (p-mode) EC 14026 stars. This
fact opens the interesting possibility of employing asteroseismology to
investigate the existence of hot-sdB stars characterized by such very
thin H envelopes. In this preliminary investigation, we explore the
sensitivity of the acoustic pulsation spectrum of EC 14026 stars to the
thickness of the H envelope.
The pulsation analysis presented in this work was performed with the
help of the adiabatic radial and nonradial pulsation code employed by
our group in numerous asteroseismological studies of white dwarfs and
pre-white dwarfs (see Córsico et al. 2008 and references
therein). The stellar models adopted in the present study where
extracted from the 0.48150 Mȯ (Z= 0.001) sequence of
Miller Bertolami et al. (2008). Given the exploratory nature of this
work, in order to analyze the effects of different thicknesses of the
H-rich envelope on the pulsation spectrum of sdB stars we have
artificially added a H-rich envelope in the outermost layers of our
initial model. We have considered four different thicknesses of the H
envelope (log Menv/Mȯ ~ ‑4, ‑6,
‑8, ‑10) in addition to the self-consistent model (which
lacks a H envelope). Next, we have pursued the evolution of the five
sequences during the evolution on the HB. For each stellar model, we
have computed the radial and nonradial p-modes with periods longer than
20 seconds, thus comfortably covering the observed period range of EC
14026 stars (80 - 400 sec).
Our results show that the cycle of trapping is markedly smaller for the
case of thick H-envelope models (Menv >
10‑7 Mȯ) than for the thin H-envelope
models (Menv < 10‑7 Mȯ).
We find that sdB stars with very thin H envelopes (Menv <
10‑7 Mȯ) would not display almost any
kind of trapping features in their frequency distribution at the
observed range in EC 14026 stars (ν < 13 mHz). Consequently their
frequency spectra should be significantly different from that of normal
sdB stars. We plan to explore in future works to which extent the shape
of the chemical transitions (here adopted as simple gaussian profiles)
affects the mode-trapping features.