367 research outputs found
Kinematics of W UMa-type binaries and evidences on the two types of formation
The kinematics of 129 W UMa binaries is studied and its implications on the
contact binary evolution is discussed. The sample is found to be heterogeneous
in the velocity space that kinematically younger and older contact binaries
exist in the sample. Kinematically young (0.5 Gyr) sub-sample (MG) is formed by
selecting the systems which are satisfying the kinematical criteria of moving
groups. After removing the possible MG members and the systems which are known
to be members of open clusters, the rest of the sample is called Field Contact
Binaries (FCB). The FCB has further divided into four groups according to The
orbital period ranges. Then a correlation has been found in the sense that
shorter period less massive systems have larger velocity dispersions than the
longer period more massive systems. Dispersions in the velocity space indicates
5.47 Gyr kinematical age for the FCB group. Comparing with the field
chromospherically active binaries (CAB), presumably detached binary progenitors
of the contact systems, the FCB appears to be 1.61 Gyr older. Assuming an
equilibrium in the formation and destruction of CAB and W UMa systems in the
Galaxy, this age difference is treated as empirically deduced lifetime of the
contact stage. Since the kinematical ages of the four sub groups of FCB are
much longer than the 1.61 Gyr lifetime of the contact stage, the pre-contact
stages of FCB must dominantly be producing the large dispersions. The
kinematically young (0.5 Gyr) MG group covers the same total mass, period and
spectral ranges as the FCB. But, the very young age of this group does not
leave enough room for pre-contact stages, thus it is most likely that those
systems were formed in the beginning of the main-sequence or during the
pre-main-sequence contraction phase.Comment: 19 pages, including 11 figures and 5 tables, accepted for publication
in MNRA
Extragalactic Objects in Basle Fields
We discriminated the extragalactic objects (galaxies and quasars) from stars
for Basle star fields, Plaut I, SA 54, and SA 82 by comparison of Basle fields
and APS POSS I finder charts. Their numbers are 187, 70, and 93 for Plaut I, SA
54, and SA 82, respectively. Most of these objects are apparently faint in V,
and they cause an overestimated local luminosity function for absolutely faint
magnitudes, M(V) > 5. This effect is more conspicious for the field Plaut I.Comment: 13 pages, including 3 Tables and 5 figures; accepted for publication
in Turkish Journal of Physic
Kinematics of the chromospherically active binaries and evidence of an orbital period decrease in binary evolution
Kinematics of 237 Chromospherically Active Binaries (CAB) were studied. The
sample is heterogeneous with different orbits and physically different
components from F to M spectral type main sequence stars to G and K giants and
super giants. The computed , , space velocities indicate the sample
is also heterogeneous in the velocity space. That is, both kinematically
younger and older systems exist among the non-evolved main sequence and the
evolved binaries containing giants and sub giants. The kinematically young
(0.95 Gyr) sub-sample (N=95), which is formed according to the kinematical
criteria of moving groups, was compared to the rest (N=142) of the sample (3.86
Gyr) in order to investigate observational clues of the binary evolution.
Comparing the orbital period histograms between the younger and older
sub-samples, evidences were found supporting Demircan's (1999) finding that the
CAB binaries lose mass (and angular momentum) and evolve towards shorter
orbital periods. The evidence of mass loss is noticeable on the histograms of
the total mass (), which is compared between the younger
(available only N=53 systems) and older sub-samples (available only N=66
systems). The orbital period decrease during binary evolution is found to be
clearly indicated by the kinematical ages of 6.69, 5.19, and 3.02 Gyr which
were found in the sub samples according to the period ranges of ,
, and among the binaries in the older sub
sample.Comment: 26 pages, including 11 figures and 5 tables, 2004, MNRAS, 349, 106
A CCD Study of High Latitude Galactic Structure: Testing the Model Parameters
We interpret published CCD UBVI data to deduce the stellar density
distribution and metallicity distribution function in the region from 2-8 kpc
from the Galactic Plane, and compare our results to several star count models.
A feature of extant star count models is degeneracy between the adopted scale
heights of the thin and thick disks, and their local normalisation. We
illustrate the utility of this small data set, and future larger sets (e.g.
SDSS), by explicitly considering consistency between the derived density laws,
and the implied solar neighbourhood luminosity function. Our data set, from
Hall et al.(1996) (l=52, b=-39) contains 566 stars, selected to be consistent
with stellar loci in colour-colour diagrams. Our analysis supports the
parameterisation of the recent SDSS galaxy model of Chen et al.(2001), except
in preferring the stellar halo axis ratio to be 0.84. Photometric
metal-abundances have been derived for 329 stars using a new calibration. The
vertical distance-dependent metallicity distribution function, if parameterised
by a single mean value, can be described by a metallicity gradient -0.2 dex/kpc for the inner halo.
The data are however better described as the sum of three discrete distribution
functions, each of which has a small or zero internal gradient. The changing
mix of thin disk, thick disk and halo populations with distance from the plane
generates an illusion of a smooth gradient.Comment: 14 pages, 43 gif figures, accepted for publication in MNRA
Reaching the boundary between stellar kinematic groups and very wide binaries. II. alpha Lib + KU Lib: a common proper motion system in Castor separated by 1.0 pc
Aims: I investigate the gravitational binding of a nearby common proper
motion system in the young Castor moving group (tau ~ 200 Ma), formed by the
bright quadruple star alpha Lib (Zubenelgenubi) and the young solar analog KU
Lib. The system has an exceptionally wide angular separation, of about 2.6 deg,
which corresponds to a projected physical separation of about 1.0 pc. Methods:
I compile basic information of the system and compare its binding energy with
those of other weakly bound systems in the field, and study the physical
separations of resolved multiple systems in Castor. Results: KU Lib has roughly
the same proper motion, parallactic distance, radial velocity, and metallicity
than the young hierarchical quadruple system alpha Lib. Besides, KU Lib also
displays youth features. The resemblance between these basic parameters and the
relatively large estimated binding energy point out that the five stars are
gravitationally bound. KU Lib and alpha Lib constitute the widest known
multiple system at all mass domains, and likely represent the most extreme
example of young wide binaries on the point of being disrupted. Besides, I make
a comprehensive compilation of star candidates in Castor, including new ones.Comment: A&A, in press (v2: language edited
MnOx-Promoted PdAg Alloy Nanoparticles for the Additive-Free Dehydrogenation of Formic Acid at Room Temperature
Formic acid (HCOOH) has a great potential as a safe and a convenient hydrogen carrier for fuel cell applications. However, efficient and CO-free hydrogen production through the decomposition of formic acid at low temperatures (<363 K) in the absence of additives constitutes a major challenge. Herein, we present a new heterogeneous catalyst system composed of bimetallic PdAg alloy and MnOx nanoparticles supported on amine-grafted silica facilitating the liberation of hydrogen at room temperature through the dehydrogenation of formic acid in the absence of any additives with remarkable activity (330 mol H2·mol catalyst-1·h-1) and selectivity (>99%) at complete conversion (>99%). Moreover this new catalytic system enables facile catalyst recovery and very high stability against agglomeration, leaching, and CO poisoning. Through a comprehensive set of structural and functional characterization experiments, mechanistic origins of the unusually high catalytic activity, selectivity, and stability of this unique catalytic system are elucidated. Current heterogeneous catalytic architecture presents itself as an excellent contender for clean hydrogen production via room-temperature additive-free dehydrogenation of formic acid for on-board hydrogen fuel cell applications. © 2015 American Chemical Society
Transumbilical Totally Laparoscopic Single-Port Nissen Fundoplication: A New Method of Liver Retraction: The Istanbul Technique
Mustafa Kemal Ataturk, founder of the Turkish Republic, had guarded many German scientists of a Jewish descent before the Second World War. Dr. Rudolf Nissen was one of the outstanding surgeons who had served in the Turkish university hospitals. He had created an antireflux procedure which is named after his own name while he was working in our clinic, the CerrahpaAYa Hospital. From a laparoscopic approach, the Nissen fundoplication was the gold standard intervention for the surgical treatment of gastroesophageal reflux disease (GERD). Currently, video laparoscopic surgery is evolving quickly with the guidance of new technology. Single-port (SP) laparoscopic transumbilical surgery is one of the newest branches of advanced laparoscopy
Rotation, activity, and lithium abundance in cool binary stars
We have used two robotic telescopes to obtain time-series high-resolution
spectroscopy and V I and/or by photometry for a sample of 60 active stars.
Orbital solutions are presented for 26 SB2 and 19 SB1 systems with
unprecedented phase coverage and accuracy. The total of 6,609 R=55,000 echelle
spectra are also used to systematically determine effective temperatures,
gravities, metallicities, rotational velocities, lithium abundances and
absolute H{\alpha}-core fluxes as a function of time. The photometry is used to
infer unspotted brightness, V - I and/or b - y colors, spot-induced brightness
amplitudes and precise rotation periods. Our data are complemented by
literature data and are used to determine rotation-temperature-activity
relations for active binary components. We also relate lithium abundance to
rotation and surface temperature. We find that 74% of all known
rapidly-rotating active binary stars are synchronized and in circular orbits
but 26% are rotating asynchronously of which half have Prot > Porb and e > 0.
Because rotational synchronization is predicted to occur before orbital
circularization active binaries should undergo an extra spin-down besides tidal
dissipation. We suspect this to be due to a magnetically channeled wind with
its subsequent braking torque. We find a steep increase of rotation period with
decreasing effective temperature for active stars. For inactive, single giants
with Prot > 100 d, the relation is much weaker. Our data also indicate a
period-activity relation for H{\alpha} of the form RH{\alpha} \propto P - 0.24
for binaries and RH{\alpha} \propto P -0.14 for singles. Lithium abundances in
our sample increase with effective temperature. On average, binaries of
comparable effective temperature appear to exhibit 0.25 dex less surface
lithium than singles. We also find a trend of increased Li abundance with
rotational period of form log n(Li) \propto - 0.6 log Prot
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