6,330 research outputs found
Electrode Glow During Electrolysis and Liberation of Hydrogen and Oxygen Together on the Electrodes
The Horizontal Branch in the UV Colour Magnitude Diagrams. II. The case of M3, M13 and M79
We present a detailed comparison between far-UV/optical colour Magnitude
Diagrams obtained with high-resolution Hubble Space Telescope data and suitable
theoretical models for three Galactic Globular Clusters: M3, M13 and M79. These
systems represents a classical example of clusters in the intermediate
metallicity regime that, even sharing similar metal content and age, show
remarkably different Horizontal Branch morphologies. As a consequence, the
observed differences in the colour distributions of Horizontal Branch stars
cannot be interpreted in terms of either first (metallicity) or a second
parameter such as age. We investigate here the possible role of variations of
initial Helium abundance (Y). Thanks to the use of a proper setup of far-UV
filters, we are able to put strong constraints on the maximum Y (Y_{max})
values compatible with the data. We find differences Delta Y_{max} ~ 0.02-0.04
between the clusters with M13 showing the largest value (Y_{max} ~ 0.30) and M3
the smallest (Y_{max} ~ 0.27). In general we observe that these values are
correlated with the colour extensions of their Horizontal Branches and with the
range of the observed Na-O anti-correlations.Comment: Accepted for publication by MNRAS. 15 pages, 15 figures, 1 tabl
Liberation of Hydrogen and Oxygen Together on the Electrodes During Electrolysis Accompanied by Electrode Glow
Positive-Negative Sign Rule for Ion-Terms on E.M.F of Electrochemical Cells and its Application to Potentiometric Titration
On the very long term evolutionary behavior of hydrogen-accreting Low-Mass CO white dwarfs
Hydrogen-rich matter has been added to a CO white dwarf of initial mass 0.516
\msun at the rates and \msun \yrm1, and results are
compared with those for a white dwarf of the same initial mass which accretes
pure helium at the same rates. For the chosen accretion rates, hydrogen burns
in a series of recurrent mild flashes and the ashes of hydrogen burning build
up a helium layer at the base of which a He flash eventually occurs. In
previous studies involving accretion at higher rates and including initially
more massive WDs, the diffusion of energy inward from the H shell-flashing
region contributes to the increase in the temperature at the base of the helium
layer, and the mass of the helium layer when the He flash begins is
significantly smaller than in a comparison model accreting pure helium; the He
shell flash is not strong enough to develop into a supernova explosion. In
contrast, for the conditions adopted here, the temperature at the base of the
He layer becomes gradually independent of the deposition of energy by H shell
flashes, and the mass of the He layer when the He flash occurs is a function
only of the accretion rate, independent of the hydrogen content of the accreted
matter. When the He flash takes place, due to the high degeneracy at the base
of the He layer, temperatures in the flashing zone will rise without a
corresponding increase in pressure, nuclear burning will continue until nuclear
statistical equilibrium is achieved; the model will become a supernova, but not
of the classical type Ia variety.Comment: 14 pages and 3 Postscript figures, Accepted for publication on ApJ
Letter
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