111 research outputs found
Absolute Dimensions and Apsidal Motion of the Young Detached System LT Canis Majoris
New high resolution spectra of the short period (P~1.76 days) young detached
binary LT CMa are reported for the first time. By combining the results from
the analysis of new radial velocity curves and published light curves, we
determine values for the masses, radii and temperatures as follows: M_1= 5.59
(0.20) M_o, R_1=3.56 (0.07) R_o and T_eff1= 17000 (500) K for the primary and
M_2=3.36 (0.14) M_o, R_2= 2.04 (0.05) R_o and T_eff2= 13140 (800) K for the
secondary. Static absorbtion features apart from those coming from the close
binary components are detected in the several spectral regions. If these
absorbtion features are from a third star, as the light curve solutions
support, its radial velocity is measured to be RV_3=70(8) km s^-1. The orbit of
the binary system is proved to be eccentric (e=0.059) and thus the apsidal
motion exists. The estimated linear advance in longitude of periastron
corresponds to an apsidal motion of U=694+/-5 yr for the system. The average
internal structure constant log k_2,obs=-2.53 of LT CMa is found smaller than
its theoretical value of log k_2,theo=-2.22 suggesting the stars would have
more central concentration in mass. The photometric distance of LT CMa
(d=535+/-45 pc) is found to be much smaller than the distance of CMa OB1
association (1150 pc) which rules out membership. A comparison with current
stellar evolution models for solar metallicity indicates that LT CMa (35 Myr)
is much older than the CMa OB1 association (3 Myr), confirming that LT CMa is
not a member of CMa OB1. The kinematical and dynamical analysis indicate LT CMa
is orbiting the Galaxy in a circular orbit and belongs to the young thin-disk
population.Comment: 19 pages, 6 figures and 6 tables, accepted for publication in
Publication of the Astronomical Society of Japa
Study of Eclipsing Binary and Multiple Systems in OB Associations II. The Cygnus OB Region: V443 Cyg, V456 Cyg and V2107 Cyg
Three presumably young eclipsing binary systems in the direction of the
Cygnus OB1, OB3 and OB9 associations are studied. Component spectra are
reconstructed and their orbits are determined using light curves and spectra
disentangling techniques. V443 Cyg and V456 Cyg have circular orbits, while the
light curve of V2107\,Cyg imposes a slightly eccentric orbit
(. V443 Cyg harbours F-type stars, and not young early-A stars
as previously suggested in the literature based on photometry solely. It
appears to be situated in the foreground (distance kpc) of the
young stellar populations in Cygnus. V456 Cyg, at a distance of
kpc consists of a slightly metal-weak A--type and an early--F star. The age of
both systems, on or very near to the main sequence, remains uncertain by an
order of magnitude. V2107 Cyg is a more massive system ( and
) at kpc and, also kinematically, a strong
candidate-member of Cyg OB1. The more massive component is slightly evolved and
appears to undergo non-radial -type pulsations. The Doppler signal
of the secondary is barely detectable. A more extensive study is important to
fix masses more precisely, and an asteroseismological study would then become
appropriate. Nevertheless, the position of the primary in the HR-diagram
confines the age already reasonably well to Myr, indicating for Cyg
OB1 a similar extent of star formation history as established for Cyg OB2.Comment: 27 pages, including 9 figures and 6 tables, accepted for publication
in Astronomical Journa
Study of Eclipsing Binary and Multiple Systems in OB Associations: I. Ori OB1a - IM Mon
All available photometric and spectroscopic observations were collected and
used as the basis of a detailed analysis of the close binary IM Mon. The
orbital period of the binary was refined to 1.19024249(0.00000014) days. The
Roche equipotentials, fractional luminosities (in (B, V) and H_p bands) and
fractional radii for the component stars in addition to mass ratio q,
inclination i of the orbit and the effective temperature T_eff of the secondary
cooler less massive component were obtained by the analysis of light curves. IM
Mon is classified to be a detached binary system in contrast to the contact
configuration estimations in the literature. The absolute parameters of IM Mon
were derived by the simultaneous solutions of light and radial velocity curves
as M_1,2=5.50(0.24)M_o and 3.32(0.16)M_o, R1,2=3.15(0.04)R_o and 2.36(0.03)R_o,
T_eff1,2=17500(350) K and 14500(550) K implying spectral types of B4 and B6.5
ZAMS stars for the primary and secondary components respectively. The modelling
of the high resolution spectrum revealed the rotational velocities of the
component stars as V_rot1=147(15) km/s and V_rot2=90(25) km/s. The photometric
distance of 353(59) pc was found more precise and reliable than Hipparcos
distance of 341(85) pc. An evolutionary age of 11.5(1.5) Myr was obtained for
IM Mon. Kinematical and dynamical analysis support the membership of the young
thin-disk population system IM Mon to the Ori OB1a association dynamically.
Finally, we derived the distance, age and metallicity information of Ori OB1a
sub-group using the information of IM Mon parameters.Comment: 26 pages, 5 figures and 6 tables, accepted for publication in
Publication of the Astronomical Society of Japa
Modelling the components of binaries in Hyades: The dependence of the mixing-length parameter on stellar mass
We present our findings based on a detailed analysis for the binaries of the
Hyades, in which the masses of the components are well known. We fit the models
of components of a binary system to the observations so as to give the observed
total V and B-V of that system and the observed slope of the main-sequence in
the corresponding parts. According to our findings, there is a very definite
relationship between the mixing-length parameter and the stellar mass. The
fitting formula for this relationship can be given as , which is valid for stellar masses greater than
0.77 M_sun. While no strict information is gathered for the chemical
composition of the cluster, as a result of degeneracy in the colour-magnitude
diagram, by adopting Z=0.033 and using models for the components of 70 Tau and
theta^2 Tau we find the hydrogen abundance to be X=0.676 and the age to be 670
Myr. If we assume that Z=0.024, then X=0.718 and the age is 720 Myr. Our
findings concerning the mixing length parameter are valid for both sets of the
solution. For both components of the active binary system V818 Tau, the
differences between radii of the models with Z=0.024 and the observed radii are
only about 4 percent. More generally, the effective temperatures of the models
of low mass stars in the binary systems studied are in good agreement with
those determined by spectroscopic methods.Comment: 11 pages, 7 figures, accepted for publication in MNRA
The Spectroscopic Orbits of Three Double-lined Eclipsing Binaries: I. BG Ind, IM Mon, RS Sgr
We present the spectroscopic orbit solutions of three double-lines eclipsing
binaries, BG Ind, IM Mon and RS Sgr. The first precise radial velocities (RVs)
of the components were determined using high resolution echelle spectra
obtained at Mt. John University Observatory in New Zealand. The RVs of the
components of BG Ind and RS Sgr were measured using Gaussian fittings to the
selected spectral lines, whereas two-dimensional cross-correlation technique
was preferred to determine the RVs of IM Mon since it has relatively short
orbital period among the other targets and so blending of the lines is more
effective. For all systems, the Keplerian orbital solution was used during the
analysis and also circular orbit was adopted because the eccentricities for all
targets were found to be negligible. The first precise orbit analysis of these
systems gives the mass ratios of the systems as 0.894, 0.606 and 0.325,
respectively for BG Ind, IM Mon and RS Sgr. Comparison of the mass ratio
values, orbital sizes and minimum masses of the components of the systems
indicates that all systems should have different physical, dynamical and
probable evolutionary status.Comment: 17 pages, 6 figures and 4 tables, accepted for publication in New
Astronom
Testing robustness of relative complexity measure method constructing robust phylogenetic trees for Galanthus L. Using the relative complexity measure
Background: Most phylogeny analysis methods based on molecular sequences use multiple alignment where the quality of the alignment, which is dependent on the alignment parameters, determines the accuracy of the resulting trees. Different parameter combinations chosen for the multiple alignment may result in different phylogenies. A new non-alignment based approach, Relative Complexity Measure (RCM), has been introduced to tackle this problem and proven to work in fungi and mitochondrial DNA.
Result: In this work, we present an application of the RCM method to reconstruct robust phylogenetic trees using sequence data for genus Galanthus obtained from different regions in Turkey. Phylogenies have been analyzed using nuclear and chloroplast DNA sequences. Results showed that, the tree obtained from nuclear ribosomal RNA gene sequences was more robust, while the tree obtained from the chloroplast DNA showed a higher degree of variation.
Conclusions: Phylogenies generated by Relative Complexity Measure were found to be robust and results of RCM were more reliable than the compared techniques. Particularly, to overcome MSA-based problems, RCM seems to be a reasonable way and a good alternative to MSA-based phylogenetic analysis. We believe our method will become a mainstream phylogeny construction method especially for the highly variable sequence families where the accuracy of the MSA heavily depends on the alignment parameters
Testing robustness of relative complexity measure method constructing robust phylogenetic trees for \u3ci\u3eGalanthus\u3c/i\u3e L. Using the relative complexity measure
Background: Most phylogeny analysis methods based on molecular sequences use multiple alignment where the quality of the alignment, which is dependent on the alignment parameters, determines the accuracy of the resulting trees. Different parameter combinations chosen for the multiple alignment may result in different phylogenies. A new non-alignment based approach, Relative Complexity Measure (RCM), has been introduced to tackle this problem and proven to work in fungi and mitochondrial DNA.
Result: In this work, we present an application of the RCM method to reconstruct robust phylogenetic trees using sequence data for genus Galanthus obtained from different regions in Turkey. Phylogenies have been analyzed using nuclear and chloroplast DNA sequences. Results showed that, the tree obtained from nuclear ribosomal RNA gene sequences was more robust, while the tree obtained from the chloroplast DNA showed a higher degree of variation.
Conclusions: Phylogenies generated by Relative Complexity Measure were found to be robust and results of RCM were more reliable than the compared techniques. Particularly, to overcome MSA-based problems, RCM seems to be a reasonable way and a good alternative to MSA-based phylogenetic analysis. We believe our method will become a mainstream phylogeny construction method especially for the highly variable sequence families where the accuracy of the MSA heavily depends on the alignment parameters
Experimental bond behaviour of GFRP and masonry bricks under impulsive loading
Fibre Reinforced Polymers have become a popular material for strengthening of masonry structures. The performance of this technique is strongly dependent on the bond between the FRP and the substrate. Understanding the strain rate effect on these materials and strengthening techniques is important for proper design and proper modelling of these systems under impacts or blast loads. This work aims to study the behaviour of the bond between GFRP and brick at different strain rates. A Drop Weight Impact Machine specially developed for pull-off tests (single shear tests) is used with different masses and different heights introducing different deformation rates. The strain rate effect on the failure mode, shear capacity and effective bond length is determined from the experimental results. Empirical relations of dynamic increase factors (DIF) for these materials and techniques are also presented.This work was performed under Project CH-SECURE (PTDC/EMC/120118/2010)
funded by the Portuguese Foundation of Science and Technology – FCT. The authors
acknowledge the support. The first author also acknowledges the support from his PhD
FCT grant with the reference SFRH/BD/45436/2008
Absolute properties of the spotted eclipsing binary star CV Bootis
We present new V-band differential brightness measurements as well as new
radial-velocity measurements of the detached, circular, 0.84-day period,
double-lined eclipsing binary system CV Boo. These data along with other
observations from the literature are combined to derive improved absolute
dimensions of the stars for the purpose of testing various aspects of
theoretical modeling. Despite complications from intrinsic variability we
detect in the system, and despite the rapid rotation of the components, we are
able to determine the absolute masses and radii to better than 1.3% and 2%,
respectively. We obtain M(A) = 1.032 +/- 0.013 M(Sun) and R(B) = 1.262 +/-
0.023 R(Sun) for the hotter, larger, and more massive primary (star A), and
M(B) = 0.968 +/- 0.012 M(Sun) and R(B) = 1.173 +/- 0.023 R(Sun) for the
secondary. The estimated effective temperatures are 5760 +/- 150 K and 5670 +/-
150 K. The intrinsic variability with a period about 1% shorter than the
orbital period is interpreted as being due to modulation by spots on one or
both components. This implies that the spotted star(s) must be rotating faster
than the synchronous rate, which disagrees with predictions from current tidal
evolution models according to which both stars should be synchronized. We also
find that the radius of the secondary is larger than expected from stellar
evolution calculations by about 10%, a discrepancy also seen in other (mostly
lower-mass and active) eclipsing binaries. We estimate the age of the system to
be approximately 9 Gyr. Both components are near the end of their main-sequence
phase, and the primary may have started the shell hydrogen-burning stage.Comment: 17 pages in emulateapj format, including figures and tables. To
appear in The Astronomical Journa
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