313 research outputs found
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 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 0.005. A temperature
difference of K between the components and an orbital
inclination of 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 (). 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 (). No strict mass ratio - luminosity
ratio relation of contact binary stars exists.Comment: 5 pages, 4 figures, accepted for publication in A&
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