Panchromatic fits to the Globular Cluster NGC 6366

We present panchromatic isochrone fits to the color magnitude data of the globular cluster NGC 6366, based on HST ACS/WFC and SOAR photometric data. Before performing the isochrone fits, we corrected the photometric data for differential reddening and calculated the mean ridge line of the color magnitude diagrams. We compared the isochrones of Dartmouth Stellar Evolution Database and PAdova and TRieste Stellar Evolution Code (with microscopic diffusion starting on the main sequence). Based on previous determinations of the metallicity of this cluster we test it from [Fe/H]=-1.00 to [Fe/H]= -0.50, and the age from 9 to 13 Gyrs. The uncertainties do not decrease when we fit simultaneous colors. We also find that the Dartmouth Stellar Evolution Database isochrones have a better fit in the sub giant branch and low main sequence than the PAdova and TRieste Stellar Evolution Code. Considering the most recent spectroscopic determination of the metallicity ([Fe/H]= -0.67), we find E(B-V)=0.69+/-0.02, (m-M)_V=15.02+/-0.07 and 11+/-2 Gyr for NGC 6366.Comment: 4 pages, 2 figures. Proceedings of the conference "Reading the book of globular clusters with the lens of stellar evolution", to be published in Memorie della Societ\'a Astronomica Italian

The age-metallicity dependence for white dwarfs

We present a theoretical study on the metallicity dependence of the initial$-$to$-$final mass relation and its influence on white dwarf age determinations. We compute a grid of evolutionary sequences from the main sequence to $\sim 3\, 000$ K on the white dwarf cooling curve, passing through all intermediate stages. During the thermally-pulsing asymptotic giant branch no third dredge-up episodes are considered and thus the photospheric C/O ratio is below unity for sequences with metallicities larger than $Z=0.0001$. We consider initial metallicities from $Z=0.0001$ to $Z=0.04$, accounting for stellar populations in the galactic disk and halo, with initial masses below $\sim 3M_{\odot}$. We found a clear dependence of the shape of the initial$-$to$-$final mass relation with the progenitor metallicity, where metal rich progenitors result in less massive white dwarf remnants, due to an enhancement of the mass loss rates associated to high metallicity values. By comparing our theoretical computations with semi empirical data from globular and old open clusters, we found that the observed intrinsic mass spread can be accounted for by a set of initial$-$to$-$final mass relations characterized by different metallicity values. Also, we confirm that the lifetime spent before the white dwarf stage increases with metallicity. Finally, we estimate the mean mass at the top of the white dwarf cooling curve for three globular clusters NGC 6397, M4 and 47 Tuc, around $0.53 M_{\odot}$, characteristic of old stellar populations. However, we found different values for the progenitor mass, lower for the metal poor cluster, NGC 6397, and larger for the younger and metal rich cluster 47 Tuc, as expected from the metallicity dependence of the initial$-$to$-$final mass relation.Comment: Accepted for publication in MNRA

Anomalous reaction-transport processes: the dynamics beyond the Mass Action Law

In this paper we reconsider the Mass Action Law (MAL) for the anomalous reversible reaction $A\rightleftarrows B$ with diffusion. We provide a mesoscopic description of this reaction when the transitions between two states $A$ and $B$ are governed by anomalous (heavy-tailed) waiting-time distributions. We derive the set of mesoscopic integro-differential equations for the mean densities of reacting and diffusing particles in both states. We show that the effective reaction rate memory kernels in these equations and the uniform asymptotic states depend on transport characteristics such as jumping rates. This is in contradiction with the classical picture of MAL. We find that transport can even induce an extinction of the particles such that the density of particles $A$ or $B$ tends asymptotically to zero. We verify analytical results by Monte Carlo simulations and show that the mesoscopic densities exhibit a transient growth before decay.Comment: 4 pages, 3 figure

White Dwarfs In Ngc6397 And M4: Constraints On The Physics Of Crystallization

We explore the physics of crystallization in the dense Coulomb plasma of the deep interiors of white dwarf stars using the color-magnitude diagram and luminosity function constructed from Hubble Space Telescope photometry of the globular cluster M 4 and compare it with our results for proper motion cleaned Hubble Space Telescope photometry of the globular cluster NGC 6397. We demonstrate that the data are consistent with a binary mixture of carbon and oxygen crystallizing at a value of Gamma higher than the theoretical value for a One Component Plasma (OCP). We show that this result is in line with the latest Molecular Dynamics simulations for binary mixtures of C/O. We discuss implications for future work.Astronom