The shortest period M-dwarf eclipsing system BW3 V38, II: determination of absolute elements

The spectroscopic data for the short-period (0.1984 d)eclipsing binary V38, discovered by the OGLE micro-lensing team in Baade's Window field BW3, are analyzed. Radial velocity curves are derived from mid-resolution spectra obtained with EMMI-NTT at ESO - La Silla, and a simultaneous solution of the existing light curve by OGLE and of the new radial velocity curves is obtained. The system is formed by almost twin M3e dwarf components that are very close, but not yet in contact. The spectra of both dwarfs show signatures of the presence of strong chromospheres. Spectroscopy definitely confirms, therefore, what was suggested on the basis of photometry: BW3 V38 is indeed a unique system, as no other similar binary with M components and in such a tight orbit is known. Within the limits posed by the relatively large errors, due to the combined effect of system faintness and of the constraints on exposure time, the derived physical parameters seem to agree with the relations obtained from the other few known eclipsing binaries with late type components (which indicate a discrepancy between the available evolutionary models and the data at ~ 10% level). A possible explanation is the presence of strong magnetic fields and fast rotation (that applies to the BW3 V38 case as well). A simple computation of the system secular evolution by angular momentum loss and spin orbit synchronization shows that the evolution of a system with M dwarfs components is rather slow, and indicates as well a possible reason why systems similar to BW3 V38 are so rare.Comment: 9 pages, 7 figures, 3 tables, accepted for publication in A&

A-type stars: evolution, rotation and binarity

We discuss the internal structure of stars in the mass range 1.5 to 4 M_sun from the PMS to the subgiant phase with a particular emphasis on the convective core and the convective superficial layers. Different physical aspects are considered such as overshooting, treatment of convection, microscopic diffusion and rotation. Their influence on the internal structure and on the photospheric chemical abundances is briefly described. The role of binarity in determining the observed properties and as a tool to constrain the internal structure is also introduced and the current limits of theories of orbital evolution and of available binary data--sets are discussed. keywords{stars: evolution, stars: binaries: general, stars: rotation}Comment: 11 pages, 7 figures, conference: The A-star Puzzle, IAU Simp. 224, 200

The shortest-period M-dwarf eclipsing system BW3 V38

The photometric data for a short-period (0.1984 day) eclipsing binary V38 discovered by the OGLE micro-lensing team in Baade's W indow field BW3 have been analyzed. The de-reddened color (V-I_C)_0=2.3 and the light-curve synthesis solution of the I-filter light curve suggest a pair of strongly-distorted M-dwarfs, with parameters between those of YY Gem and CM Dra, revolving on a tightest known orbit among binaries consisting of Main Sequence stars. The primary, more massive and hotter, component maybe filling its Roche lobe. The very small amount of angular momentum in the orbital motion makes the system particularly important for studies of angular momentum loss at the faint end of the Main Sequence. Spectroscopic observations of the orbital radial velocity variations as well as of activity indicators are urgently needed for a better understanding of the angular-momentum and internal-structure evolutionary state of the system.Comment: latex aastex4.0, 16 pages, in that 4 figures (.ps inserted by psfig.sty) and one table; submitted to PAS

12 Bootis: a test bed for extra-mixing processes in stars

12 Bootis is a spectroscopic binary whose visual orbit has been resolved by interferometry. Though the physical parameters of the system have been determined with an excellent precision, the theoretical modelling of the components is still uncertain. We study the capability of solar-like oscillations to distinguish between calibrated models of the system obtained by including in the stellar modelling different mixing processes. We consider different scenarios for the chemical transport processes: classical overshooting, microscopic diffusion and turbulent mixing. For each of them we calibrate the stellar models of 12 Boo A and B by fitting the available observational constraints by means of a Levenberg-Marquardt minimization algorithm, and finally, we analyze the asteroseismic properties of different calibrated models. Several solutions with 12 Boo A in (or close to) post-main sequence and 12 Boo B on main sequence are found by assuming a thickness of the overshooting layer between 0.06 and 0.23 the pressure scale height. Solutions with both components on the main sequence can be found only by assuming an overshoot larger in the primary than in the secondary, or a more efficient central mixing for 12 Boo A than for 12 Boo B. We show that the detection of solar-like oscillations expected in these stars would allow to distinguish between different scenarios and provide therefore an estimation of the overshooting parameters and of the properties of extra-mixing processes.Comment: 12 pages, 11 figures. Accepted for publication in MNRA

A CCD photometric study of the late type contact binary EK Comae Berenices

We present CCD photometric observations of the W UMa type contact binary EK Comae Berenices using the 2 metre telescope of $IUCAA$ Girawali Observatory, India. The star was classified as a W UMa type binary of subtype-W by \citet{sam1996}. The new V band photometric observations of the star reveal that shape of the light curve has changed significantly from the one observed by \citet{sam1996}. A detailed analysis of the light curve obtained from the high-precision CCD photometric observations of the star indicates that EK Comae Berenices is not a W-type but an A-type totally eclipsing W UMa contact binary. The photometric mass ratio is determined to be 0.349 $\pm$ 0.005. A temperature difference of $\Delta T = 141 \pm 10$ K between the components and an orbital inclination of $i [^{o}] = 89.800 \pm 0.075$ were obtained for the binary system. Absolute values of masses, radii and luminosities are estimated by means of the standard mass-luminosity relation for zero age main-sequence stars. The star shows O'Connell effect, asymmetries in the light curve shape around the primary and secondary maximum. The observed O'Connell effect is explained by the presence of a hot spot on the primary component.Comment: 26 pages, 9 figures, 5 tables. Accepted for publication in New Astronom

El rol del Profesor en Educación Física en un Programa de Rehabilitación Cardiovascular

Las Enfermedades CardioVasculares son la principal causa de muerte en el mundo. Los Factores de Riesgo, ayudan a incrementar la enfermedad, como por ejemplo: Diabetes, HTA, dislipemia, Tabaquismo y el Sedentarismo. Como Profesores en Educación Física, es en la temática que más debemos participar activamente, modificando y creando en el paciente de RHCV, conciencia de Prevención e introducción de hábitos saludables, y la regularidad de la Actividad Física a la vida cotidiana, pudiendo descender significativamente los riesgos y eventos de la ECV. De acuerdo a los informes de la OMS, expresan que uno de los flagelos queprovocan una situación crítica en la vida de los habitantes del mundo, es el SEDENTARISMO. Al cual, lo podemos definir de manera muy sencilla como "una forma de vida con poco movimiento". En nuestro espacio institucional, privado como público, de acuerdo a nuestra formación y decisión profesional, tenemos como objetivo general, mejorar la Calidad de Vida, delineando metódicamente, las acciones necesarias para que se incorporen, junto con la actividad física, hábitos higiénicos y alimenticios, siendo herramientas claves para combatir la vida sedentaria. El movimiento, ayuda a incrementar y mantener la Capacidad Funcional. Utilizamos metodología propia de nuestra formación, más conocimientosnuevos que diversifican y amplían la misma, construyendo parte del campo, hasta ahora poco conocido y reconocido de la Educación Física. La ausencia de actividad es un factor importante que contribuye a alimentar el campo de las enfermedade

CoRoT 102918586: a Gamma Dor pulsator in a short period eccentric eclipsing binary

Pulsating stars in eclipsing binary systems are powerful tools to test stellar models. Binarity enables to constrain the pulsating component physical parameters, whose knowledge drastically improves the input physics for asteroseismic studies. The study of stellar oscillations allows us, in its turn, to improve our understanding of stellar interiors and evolution. The space mission CoRoT discovered several promising objects suitable for these studies, which have been photometrically observed with unprecedented accuracy, but needed spectroscopic follow-up. A promising target was the relatively bright eclipsing system CoRoT 102918586, which turned out to be a double-lined spectroscopic binary and showed, as well, clear evidence of Gamma Dor type pulsations. We obtained phase resolved high-resolution spectroscopy with the Sandiford spectrograph at the McDonald 2.1m telescope and the FEROS spectrograph at the ESO 2.2m telescope. Spectroscopy yielded both the radial velocity curves and, after spectra disentangling, the component effective temperatures, metallicity and line-of-sight projected rotational velocities. The CoRoT light curve was analyzed with an iterative procedure, devised to disentangle eclipses from pulsations. We obtained an accurate determination of the system parameters, and by comparison with evolutionary models strict constraints on the system age. Finally, the residuals obtained after subtraction of the best fitting eclipsing binary model were analyzed to determine the pulsator properties. We achieved a quite complete and consistent description of the system. The primary star pulsates with typical {\gamma} Dor frequencies and shows a splitting in period which is consistent with high order g-mode pulsations in a star of the corresponding physical parameters. The value of the splitting, in particular, is consistent with pulsations in l = 1 modes.Comment: 12 pages, 10 figures. Accepted for publication in Astronomy and Astrophysic

On the properties of contact binary stars

A catalogue of light curve solutions of contact binary stars has been compiled. It contains the results of 159 light curve solutions. Properties of contact binary stars were studied by using the catalogue data. As it is well known since Lucy's (1968a,b) and Mochnacki's (1981) works, primary components transfer their own energy to the secondary star via the common envelope around the two stars. This transfer was parameterized by a transfer parameter (ratio of the observed and intrinsic luminosities of the primary star). We proved that this transfer parameter is a simple function of the mass and luminosity ratio. This newly found relation is valid for all systems except H type systems which have a different relation. We introduced a new type of contact binary stars: H subtype systems which have a large mass ratio ($q>0.72$). These systems show highly different behaviour on the luminosity ratio - transfer parameter diagram from other systems and according to our results the energy transfer rate is less efficient in them than in other type of contact binary stars. We also show that different types of contact binaries have well defined locations on the mass ratio - luminosity ratio diagram. All contact binary systems do not follow Lucy's relation ($L_2/L_1 = (M_2/M_1)^{0.92}$). No strict mass ratio - luminosity ratio relation of contact binary stars exists.Comment: 5 pages, 4 figures, accepted for publication in A&