Towards simulating the photometry, chemistry, mass loss and pulsational properties of AGB star populations in resolved galaxies

Extended and updated grids of TP-AGB tracks have been implemented in the TRILEGAL population synthesis code, which generates mock stellar catalogues for a galaxy given its mass, distance, star formation history and age-metallicity relation, including also the Milky Way foreground population. Among the stellar parameters that are simulated, we now include the surface chemistry, mass-loss rates, pulsation modes and periods of LPVs. This allows us to perform a series of consistency checks between AGB model predictions and observations, that we are just starting to explore. We present a few examples of model--data comparisons, mostly regarding the near-infrared and variability data for AGB stars in the Magellanic Clouds.Comment: 5 pages, 3 figures, contributed talk to the workshop "Why galaxies care about AGB stars", Vienna, August 7-11, 200

The third dredge-up and the carbon star luminosity functions in the Magellanic Clouds

We investigate the formation of carbon stars as a function of the stellar mass and parent metallicity. Theoretical modelling is based on an improved scheme for treating the third dredge-up in synthetic calculations of thermally pulsing asymptotic giant branch (TP-AGB) stars. In this approach, the usual criterion (based on a constant minimum core mass for the occurrence of dredge-up, M_c^min) is replaced by one on the minimum temperature at the base of the convective envelope, T_b^dred, at the stage of the post-flash luminosity maximum. Envelope integrations then allow determination of M_c^min as a function of stellar mass, metallicity, and pulse strength (see Wood 1981), thus inferring if and when dredge-up first occurs. Moreover, the final possible shut down of the process is predicted. Extensive grids of TP-AGB models were computed using this scheme. We present and discuss the calibration of the two dredge-up parameters (lambda and T_b^dred) aimed at reproducing the carbon star luminosity function (CSLF) in the LMC. It turns out that the faint tail is almost insensitive to the history of star formation rate (SFR) in the parent galaxy (it is essentially determined by T_b^dred), in contrast to the bright wing which may be more affected by the details of the recent SFR. Once the faint end is reproduced, the peak location is a stringent calibrator of lambda. The best fit to the observed CSLF in the LMC is obtained with Z=0.008, lambda=0.50, log(T_b^dred)=6.4, and a constant SFR up to 5x10^8 yr ago. A good fit to the CSLF in the SMC is then easily derived from the Z=0.004 models, with a single choice of parameters, and a constant SFR over the entire significant age interval. The results are consistent with the theoretical expectation that the third dredge-up is more efficient at lower Zs.Comment: 22 pages with 15 figures, to appear in A&

Evolutionary models of zero metallicity stars

We present new evolutionary models for zero-metallicity stars, covering a large range of initial masses (from 0.8 to 100 M_sun). Models are computed with overshooting from stellar cores and convective envelopes, and assuming mass-loss from the most massive stars. We discuss the main evolutionary features of these stars, and provide estimates of the amount of newly-synthesized elements dredged-up to the stellar surface, and possibly lost by stellar winds from the most massive stars. Full details of these models will be given in Marigo et al. (2000, in preparation).Comment: 2 pages, to appear in the proceedings of the MPA/ESO Workshop "The first stars

The TP-AGB phase. Lifetimes from C and M star counts in Magellanic Cloud clusters

Using available data for C and M giants with Mbol<-3.6 in Magellanic Cloud clusters, we derive limits to the lifetimes of the corresponding evolutionary phases, as a function of stellar mass. The C-star phase is found to have a duration between 2 and 3 Myr for stars in the mass range from 1.5 to 2.8 Msun. There is also an indication that the peak of C-star lifetime shifts to lower masses (from slightly above to slightly below 2 Msun) as we move from LMC to SMC metallicities. The M-giant lifetimes also peak at 2 Msun in the LMC, with a maximum value of about 4 Myr, whereas in the SMC their lifetimes appear much shorter but, actually, they are poorly constrained by the data. These numbers constitute useful constraints to theoretical models of the TP-AGB phase. We show that several models in the literature underestimate the duration of the C-star phase at LMC metallicities.Comment: 8 pages, to appear in Astronomy & Astrophysic

Mutual Inductance Route to Paramagnetic Meissner Effect in 2D Josephson Junction Arrays

We simulate two-dimensional Josephson junction arrays, including full mutual- inductance effects, as they are cooled below the transition temperature in a magnetic field. We show numerical simulations of the array magnetization as a function of position, as detected by a scanning SQUID which is placed at a fixed height above the array. The calculated magnetization images show striking agreement with the experimental images obtained by A. Nielsen et al. The average array magnetization is found to be paramagnetic for many values of the applied field, confirming that paramagnetism can arise from magnetic screening in multiply-connected superconductors without the presence of d-wave superconductivity.Comment: REVTeX 3.1, 5 pages, 5 figure

The intermediate-age open cluster NGC 2158

We report on $UBVRI$ CCD photometry of two overlapping fields in the region of the intermediate-age open cluster NGC 2158 down to V=21. By analyzing Colour-Colour (CC) and Colour-Magnitude Diagrams (CMD) we infer a reddening $E_{B-V}= 0.55\pm0.10$, a distance of $3600 \pm 400$ pc, and an age of about 2 Gyr. Synthetic CMDs performed with these parameters (but fixing $E_{B-V}=0.60$ and $[{\rm Fe/H}]=-0.60$), and including binaries, field contamination, and photometric errors, allow a good description of the observed CMD. The elongated shape of the clump of red giants in the CMD is interpreted as resulting from a differential reddening of about $\Delta E_{B-V}=0.06$ across the cluster, in the direction perpendicular to the Galactic plane. NGC 2158 turns out to be an intermediate-age open cluster with an anomalously low metal content. The combination of these parameters together with the analysis of the cluster orbit, suggests that the cluster belongs to the old thin disk population.Comment: 11 pages, 12 figures, in press in MNRA

Drosophila melanogaster, un modelo animal emergente en el estudio de enfermedades cardíacas humanas

Background: The need to work with model organisms in medical research has revealed the usefulness of the fruit fly Drosophila melanogaster, considering its advantages to perform classic genetic studies and modern techniques of genome edition. Several human genes are similar to those of the fruit fly. We have developed for the first time in the country a cardiovascular line of research to study the genetics of aging, addictions and chronic consumption of substances in humans like caffeine. Objective: The aim of this study was to provide experimental evidence that validates Drosophila melanogaster as a model to study human cardiomyopathies related to the pharmacological action of caffeine on the heart. Methods: Cardiac function and the effect of caffeine were studied in semi-intact preparations of Drosophila melanogaster. Heart rate and the intracellular calcium transient were recorded and analyzed in 3, 7 and 40-day-old adult flies harboring one genetically encoded reporter system. Hearts of adult flies were dissected to show the myofibrillar structural organization and specific proteins such as SERCA. Results: Aging and caffeine alter contraction rate and intracellular calcium handling in the adult heart of Drosophila melanogaster in a similar way as mammals Conclusion: The study supports the use of this model of fast and easy reproductive cycle to identify the genes involved in the mechanisms through which aging, caffeine (and other substances) and environmental factors affect the heart.Introducción: La necesidad de trabajar con modelos de organismos en la investigación sobre salud ha revelado las utilidades de la mosca de la fruta Drosophila melanogaster considerando sus ventajas para realizar genética clásica y modernas técnicas de edición del genoma. Muchos genes humanos son homólogos a los genes de la mosca. Hemos desarrollado por primera vez en el país una línea de investigación cardiovascular para estudiar la genética del envejecimiento, las adicciones y sustancias de consumo crónico en el humano como la cafeína. Objetivo: Aportar evidencia experimental que valida el modelo de Drosophila melanogaster para el estudio de miocardiopatías humanas en relación con la acción farmacológica de la cafeína sobre el corazón. Material y métodos: Se analizaron la función cardíaca y el efecto de la cafeína en preparados semiintactos de Drosophila melanogaster. Se registró la frecuencia cardíaca y se analizó el transitorio de calcio intracelular en moscas adultas de 3, 7 y 40 días mediante un reportero codificado genéticamente. Corazones de moscas adultas se disecaron para mostrar la organización estructural de las miofibrillas y proteínas específicas como la SERCA. Resultados: La cafeína y el envejecimiento afectan la frecuencia de contracción y el manejo de calcio intracelular en el corazón adulto de Drosophila melanogaster en forma similar a lo que ocurre en mamíferos. Conclusión: El estudio abre la posibilidad de usar este modelo de fácil y rápida reproducción en busca de genes que permitan conocer los mecanismos por los cuales el envejecimiento, la cafeína (u otros compuestos) y factores ambientales actúan sobre el corazón.Facultad de Ciencias Médicas (FCM)Facultad de Ciencias Veterinarias (FCV

EFFICIENT SIMULATION TOOL TO CHARACTERIZE THE RADAR CROSS SECTION OF A PEDESTRIAN IN NEAR FIELD

none4A simulation tool to characterize the radar cross section of a pedestrian in near field is presented in the paper. The tool has been developed in order to predict and optimize the performance of the short-range radar systems employed in autonomous vehicle operations. It is based on an analytical model which joins the modeling of the human body with the theory of the physical optics. Our studies first focused on the implementation of the electromagnetic code where the human body, the radiation properties of the antenna and the scenario to be analyzed have been analytically expressed. Then, the proposed model has been validated in terms of accuracy comparing simulated and experimental data regarding the radar cross section of a metal sphere and of an adult, in the frequency range 23-28 GHz. In the end, an evaluation of the performance in terms of required computer memory and execution time has been carried out, comparing the proposed simulation tool with other numerical computational methods.openManfredi, Giovanni; Russo, Paola; De Leo, Alfredo; Cerri, GrazianoManfredi, Giovanni; Russo, Paola; De Leo, Alfredo; Cerri, Grazian