945 research outputs found
Theoretical isochrones for the Delta a photometric system
We have calculated theoretical isochrones for the photometric Delta a system
to derive astrophysical parameters such as the age, reddening and distance
modulus for open clusters. The Delta a system samples the flux depression at
520 nm which is highly efficient to detect chemically peculiar (CP) objects of
the upper main sequence. The evolutionary status of CP stars is still a matter
of debate and very important to test, for example, the dynamo and diffusion
theories. In fact, the dynamo or fossil origin of the magnetic fields present
in this kind of stars it still not clear. Using the stellar evolutionary models
by Claret (1995), a grid of isochrones with different initial chemical
compositions for the Delta a system was generated. The published data of 23
open clusters were used to fit these isochrones with astrophysical parameters
(age, reddening and distance modulus) from the literature. As an additional
test, isochrones with the same parameters for Johnson UBV data of these open
clusters were also considered. The fits show a good agreement between the
observations and the theoretical grid. We find that the accuracy of fitting
isochrones to Delta a data without the knowledge of the cluster parameters is
between 5 and 15%.Comment: 5 pages, 4 figures, accepted by A&
Absolute dimensions of eclipsing binaries. XVII. A metal-weak F-type system, perhaps with preference for Y = 0.23-0.24
V1130 Tau is a bright (m_V = 6.56), nearby (71 +/- 2 pc) detached system with
a circular orbit (P = 0.80d). The components are deformed with filling factors
above 0.9. Their masses and radii have been established to 0.6-0.7%. We derive
a [Fe/H] abundance of -0.25 +/- 0.10. The measured rotational velocities, 92.4
+/- 1.1 (primary) and 104.7 +/- 2.7 (secondary) km/s, are in fair agreement
with synchronization. The larger 1.39 Msun secondary component has evolved to
the middle of the main-sequence band and is slightly cooler than the 1.31 Msun
primary. Yonsai-Yale, BaSTI, and Granada evolutionary models for the observed
metal abundance and a 'normal' He content of Y = 0.25-0.26, marginally
reproduce the components at ages between 1.8 and 2.1 Gyr. All such models are,
however, systematically about 200 K hotter than observed and predict ages for
the more massive component, which are systematically higher than for the less
massive component. These trends can not be removed by adjusting the amount of
core overshoot or envelope convection level, or by including rotation in the
model calculations. They may be due to proximity effects in V1130 Tau, but on
the other hand, we find excellent agreement for 2.5-2.8 Gyr Granada models with
a slightly lower Y of 0.23-0.24. V1130 Tau is a valuable addition to the very
few well-studied 1-2 Msun binaries with component(s) in the upper half of the
main-sequence band, or beyond. The stars are not evolved enough to provide new
information on the dependence of core overshoot on mass (and abundance), but
might - together with a larger sample of well-detached systems - be useful for
further tuning of the helium enrichment law.Comment: Accepted for publication in Astronomy & Astrophysic
Chemically peculiar stars in the Large Magellanic Cloud
The detection of magnetic chemically peculiar (CP2) stars in open clusters of
extragalactic systems can give observational answers to many unsolved
questions. The mean percentage of CP2 stars in the Milky Way is of the order of
5% for the spectral range from early B- to F-type, luminosity class V objects.
The origin of the CP2 phenomenon seems to be closely connected to the overall
metallicity and global magnetic field environment. The theoretical models are
still only tested by observations in the Milky Way. It is therefore essential
to provide high quality observations in rather different global environments.
The young clusters NGC 2136/7 were observed in the Delta a photometric system.
This intermediate band photometric system samples the depth of the 520nm flux
depression by comparing the flux at the center with the adjacent regions with
bandwidths of 11nm to 23nm. The Delta a photometric system is most suitable for
detecting CP2 stars with high efficiency, but is also capable of detecting a
small percentage of non-magnetic CP objects. We present high precision
photometric Delta a observations of 417 objects in NGC 2136/7 and its
surrounding field, of which five turned out to be bona fide magnetic CP stars.
In addition, we discovered two Be/Ae stars. From our investigations of NGC
1711, NGC 1866, NGC 2136/7, their surroundings, and one independent field of
the LMC population, we derive an occurrence of classical chemically peculiar
stars of 2.2(6)% in the LMC, which is only half the value found in the Milky
Way. The mass and age distribution of the photometrically detected CP stars is
not different from that of similar objects in galactic open clusters.Comment: 5 pages, 4 figures, accepted by A&
Tidal and rotational effects in the perturbations of hierarchical triple stellar systems. II. Eccentric systems - the case of AS Camelopardalis
We study the perturbations of a relatively close third star on a tidally
distorted eccentric eclipsing binary. We consider both the observational
consequences of the variations of the orbital elements and the interactions of
the stellar rotation with the orbital revolution in the presence of
dissipation. We concentrate mainly on the effect of a hypothetical third
companion on both the real, and the observed apsidal motion period. We
investigate how the observed period derived mainly from some variants of the
O-C relates to the real apsidal motion period. We carried out both analytical
and numerical investigations and give the time variations of the orbital
elements of the binary both in the dynamical and the observational reference
frames. We give the direct analytical form of an eclipsing O-C affected
simultaneously by the mutual tidal forces and the gravitational interactions
with a tertiary. We also integrated numerically simultaneously the orbital and
rotational equations for the possible hierarchical triple stellar system AS
Camelopardalis. We find that there is a significant domain of the possible
hierarchical triple system configurations, where both the dynamical and the
observational effects tend to measure longer apsidal advance rate than is
expected theoretically. This happens when the mutual inclination of the close
and the wide orbits is large, and the orbital plane of the tertiary almost
coincides with the plane of the sky. We also obtain new numerical results on
the interaction of the orbital evolution and stellar rotation in such triplets.
The most important fact is that resonances might occur as the stellar
rotational rate varies during the dissipation-driven synchronization process...Comment: 33 pages, 12 figures (reduced quality!), accepted for publication for
Astronomy and Astrophysic
Spectral and temporal luminescent properties of Eu(III) in humic substances solutions from different origins
International audienceAlthough a high heterogeneity of composition is awaited for humic substances, their complexation properties do not seem to greatly depend on their origins. The information on the difference in the structure of these complexes is scarce. To participate in the filling of this lack, a study of the spectral and temporal evolution of the Eu(III) luminescence implied in humic substance (HS) complexes is presented. Seven different extracts, namely Suwannee River fulvic acid (SRFA) and humic acid (SRHA), and Leonardite HA (LHA) from the International Humic Substances Society (USA), humic acid from Gorleben (GohyHA), and from the Kleiner Kranichsee bog (KFA, KHA) from Germany, and purified commercial Aldrich HA (PAHA), were made to contact with Eu(III). Eu(III)-HS time-resolved luminescence properties were compared with aqueous Eu at pH 5. Using an excitation wavelength of 394 nm, the typical bi-exponential luminescence decay for Eu(III)-HS complexes is common to all the samples. The components 1 and τ2 are in the same order of magnitude for all the samples, i.e., 40 1 (s) 60, and 145 2 (s) 190, but significantly different. It is shown that different spectra are obtained from the different groups of samples. Terrestrial extract on the one hand, i.e. LHA/GohyHA, plus PAHA, and purely aquatic extracts on the other hand, i.e., SRFA/SRHA/KFA/KHA, induce inner coherent luminescent properties of Eu(III) within each group. The D0 F transition exhibits the most striking differences. A slight blue shift is observed compared to aqueous Eu ( = 615.4 nm), and the humic samples share almost the same 614.5 nm. The main differences between the samples reside in a shoulder around 612.5 nm, modelled by a mixed Gaussian–Lorentzian band around 612 nm. SRFA shows the most intense shoulder with an intensity ratio of / = 1.1, KFA/KHA/SRHA share almost the same ratio / = 1.2–1.3, whilst the LHA/GohyHA/PAHA group has a / = 1.5–1.6. This shows that for the two groups of complexes, despite comparable complexing properties, slightly different symmetries are awaited
The LMC eclipsing binary HV 2274: fundamental properties and comparison with evolutionary models
We are carrying out an international, multi-wavelength program to determine
the fundamental properties and independent distance estimates of selected
eclipsing binaries in the LMC and SMC. Eclipsing binaries with well-defined
double-line radial velocity curves and light curves provide valuable
information on orbital and physical properties of their component stars. The
study of stars in the LMC and SMC where the metal abundances are significantly
lower than solar provides an important opportunity to test stellar atmosphere,
interior and evolution models, and opacities. For the first time, we can also
measure direct M-L relations for stars outside our Galaxy. In this paper we
concentrate on the determination of the orbital and physical properties of HV
2274 from analyses of light curves and new radial velocity curves formed from
HST/GHRS observations. From UV/optical spectrophotometry of HV 2274 obtained
with HST/FOS, the temperatures and the metallicity of the stars were found, as
well as the interstellar extinction of the system. The values of mass, absolute
radius, and effective temperature, for the primary and secondary stars are:
12.2(7) Mo, 9.9(2) Ro, 23000(180) K, and 11.4(7) Mo, 9.0(2) Ro, 23110(180) K,
respectively. The age of the system (17(2) Myr), helium abundance (Y=0.26(3))
and a lower limit of the convective core overshooting parameter of 0.2 were
obtained from fitting the stellar data with evolution models. The apsidal
motion analysis corroborates that some amount of convective overshooting
(0.2-0.5) is needed.Comment: 39 pages, 9 figures, accepted for publication in Ap
A Strict Test of Stellar Evolution Models: The Absolute Dimensions of Massive Benchmark Eclipsing Binary V578 Mon
We determine the absolute dimensions of the eclipsing binary V578 Mon, a
detached system of two early B-type stars (B0V + B1V, P2.40848 d) in the
star-forming region NGC 2244 of the Rosette Nebula. From the light curve
analysis of 40 yr of photometry and the analysis of HERMES spectra, we find
radii of Rsun and Rsun, and temperatures of ~K and K respectively. We find that our
disentangled component spectra for V578 Mon agree well previous spectral
disentangling from the literature. We also reconfirm the previous spectroscopic
orbit of V578 Mon finding that masses of Msun and Msun are fully compatible with the new analysis. We compare the absolute
dimensions to the rotating models of the Geneva and Utrecht groups and the
models of Granada group. We find all three sets of models marginally reproduce
the absolute dimensions of both stars with a common age within uncertainty for
gravity-effective temperature isochrones. However - there are some apparent age
discrepancies for the corresponding mass-radius isochrones. Models with larger
convective overshoot worked best. Combined with our previously
determined apsidal motion of deg cycle,
we compute the internal structure constants (tidal Love number) for the
newtonian and general relativistic contribution to the apsidal motion,
and respectively. We find
the relativistic contribution to the apsidal motion of be small . We find
that the prediction of of the Granada
models fully agrees with our observed .Comment: accepted for publication in AJ 05/02/201
CCD photometric search for peculiar stars in open clusters VIII. King 21, NGC 3293, NGC 5999, NGC 6802, NGC 6830, Ruprecht 44, Ruprecht 115, and Ruprecht 120
Context. We continue our survey of magnetic chemically peculiar (CP2) stars in galactic open clusters to shed more light on their origin and evolution. Aims. To study the group of CP2 stars, it is essential to find these objects in different galactic environments and at a wide range of evolutionary stages. The knowledge of open cluster ages and metallicities can help for finding a correlation between these parameters and the (non-)presence of peculiarities, which has to be taken into account in stellar evolution models. Methods. The intermediate band Δa photometric system samples the depth of the 5200 Å flux depression by comparing the flux at the centre with the adjacent regions with bandwidths of 110 A to 230 A. It is capable of detecting magnetic CP2 and CP4 stars with high efficiency, but also the groups of (metal-weak) λBootis and classical Be/shell stars can be successfully investigated. In addition, it allows the age, reddening, and distance modulus to be determined with appropriate accuracy by fitting isochrones. Results. From the 1677 observed members of the eight open clusters, one Ae and twenty-five CP2 stars were identified. Furthermore nineteen deviating stars are designated as questionable for several reasons. The estimated age, reddening, and distance for the programme clusters were compared with published values of the literature and discussed in this context. Conclusions. The current paper shows that CP2 stars are continuously present in very young (7 Myr) to intermediate age (500 Myr) open clusters at distances greater than 2 kpc from the Sun. © ESO 2007.Fil: Netopil, M.. Universidad de Viena; AustriaFil: Paunzen, E.. Universidad de Viena; AustriaFil: Maitzen, H.M.. Universidad de Viena; AustriaFil: Pintado, Olga Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Claret, A.. Instituto de Astrofísica de Andalucía - Csic;Fil: Miranda, L.F.. Instituto de Astrofísica de Andalucía - Csic;Fil: Hiev, I.Kh.. National Astronomical Observatory Rozhen; BulgariaFil: Casanova, V.. Instituto de Astrofísica de Andalucía - Csic
On the apsidal motion of BP Vulpeculae
BP Vulpeculae is a bright eclipsing binary system showing apsidal motion. It
was found in an earlier study that it shows retrograde apsidal motion which
contradicts theory. In this paper we present the first light curve of the
system and its light curve solution as well as seven new times of the minima
from the years 1959-1963. This way we could expanded the baseline of the
investigation to five decades. Based on this longer baseline we concluded that
the apsidal motion is prograde agreeing with the theoretical expectations and
its period is about 365 years and the determined internal structure constant is
close to the theoretically expected one.Comment: accepted for New Astronomy; two figure
Observational Tests and Predictive Stellar Evolution
We compare eighteen binary systems with precisely determined radii and masses
from 23 to 1.1 M_sol, and stellar evolution models produced with our newly
revised code TYCHO. ``Overshooting'' and rotational mixing were suppressed in
order to establish a baseline for isolating these and other hydrodynamic
effects. Acceptable coeval fits are found for sixteen pairs without optimizing
for heavy element or helium abundance. The precision of these tests is limited
by the accuracies of the observed effective temperatures. High dispersion
spectra and detailed atmospheric modeling should give more accurate effective
temperatures and heavy element abundances. PV Cas, a peculiar early A system,
EK Cep B, a known post-T Tauri star, and RS Cha, a member of a young OB
association, are matched by pre-main sequence models. Predicted mass loss
agrees with upper limits from IUE for CW Cep A and B. Relatively poor fits are
obtained for binaries having at least one component in the mass range 1.7 <
M/M_sol <2.6, whose evolution is sensitive to mixing. These discrepancies are
robust and consistent with additional mixing in real stars. The predicted
apsidal motion implies that massive star models are systematically less
centrally condensed than the real stars. If these effects are due to
overshooting, then the overshooting parameter alpha_OV increases with stellar
mass. The apsidal motion constants are controlled by radiative opacity under
conditions close to those directly measured in laser experiments, making this
test more stringent than possible before.Comment: 38 pages, 9 figures (color versions of figures 1,2,3,4, and 9 are
available separately). Accepted for publication in the Astrophysical Journa
- …