5,053 research outputs found
On the white dwarf cooling sequence with extremely large telescopes
We present new diagnostics of white dwarf (WD) cooling sequences and
luminosity functions (LFs) in the near-infrared (NIR) bands that will exploit
the sensitivity and resolution of future extremely large telescopes. The
collision-induced absorption (CIA) of molecular hydrogen causes a clearly
defined blue turn-off along the WD (WDBTO) cooling sequences and a bright
secondary maximum in the WD LFs. These features are independent of age over a
broad age range and are minimally affected by metal abundance. This means that
the NIR magnitudes of the WDBTO are very promising distance indicators. The
interplay between the cooling time of progressively more massive WDs and the
onset of CIA causes a red turn-off along the WD (WDRTO) cooling sequences and a
well defined faint peak in the WD LFs. These features are very sensitive to the
cluster age, and indeed the K-band magnitude of the faint peak increases by
0.2--0.25 mag/Gyr for ages between 10 and 14 Gyr. On the other hand, the faint
peak in the optical WD LF increases in the same age range by 0.17 (V band) and
0.15 (I band) mag/Gyr. Moreover, we also suggest to use the difference in
magnitude between the main sequence turn-off and either the WDBTO (optical) or
the WDRTO (NIR). This age diagnostic is also independent of distance and
reddening. Once again the sensitivity in the K band (0.15-0.20 mag/Gyr) is on
average a factor of two higher than in the optical bands (0.10 [V band], 0.07
[I band] mag/Gyr). Finally, we also outline the use of the new diagnostics to
constrain the CO phase separation upon crystallization.Comment: 6 pages, 5 figures, accepted on A&
Cepheid Mass-loss and the Pulsation -- Evolutionary Mass Discrepancy
I investigate the discrepancy between the evolution and pulsation masses for
Cepheid variables. A number of recent works have proposed that non-canonical
mass-loss can account for the mass discrepancy. This mass-loss would be such
that a 5Mo star loses approximately 20% of its mass by arriving at the Cepheid
instability strip; a 14Mo star, none. Such findings would pose a serious
challenge to our understanding of mass-loss. I revisit these results in light
of the Padova stellar evolutionary models and find evolutionary masses are
()% greater than pulsation masses for Cepheids between 5<M/Mo<14. I
find that mild internal mixing in the main-sequence progenitor of the Cepheid
are able to account for this mass discrepancy.Comment: 15 pages, 3 figures, ApJ accepte
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