2,502 research outputs found
Eclipsing binaries in open clusters
Accurate physical parameters have been determined for two early-type detached
eclipsing binaries in the open cluster h Persei (NGC 869). Masses accurate to
1.5% are derived from high-resolution spectroscopy and radii accurate to 4--6%
have been obtained from fitting the existing light curves. The four stars are
placed in the mass radius plane and compared to the theoretical stellar models
of the Granada Group. The best-fitting models have a low metallicity of
approximately Z=0.01 and a high helium abundance of Y=0.34. This is the first
determination of the bulk metallicity of the Perseus Double Cluster. Recent
studies have assumed a solar metallicity so their results should be reviewed.Comment: 4 pages, 5 figures. To appear in Spectroscopically and Spatially
Resolving the Components of Close Binary Stars, ASP Conf. Series, 200
Absolute dimensions of detached eclipsing binaries. I. The metallic-lined system WW Aurigae
WW Aurigae is a detached eclipsing binary composed of two metallic-lined
A-type stars orbiting each other every 2.5 days. We have determined the masses
and radii of both components to accuracies of 0.4 and 0.6 percent,
respectively. From a cross-correlation analysis of high-resolution spectra we
find masses of 1.964 +/- 0.007 Msun for the primary star and 1.814 +/- 0.007
Msun for the secondary star. From an analysis of photoelectric uvby and UBV
light curves we find the radii of the stars to be 1.927 +/- 0.011 Rsun and
1.841 +/- 0.011 Rsun, where the uncertainties have been calculated using a
Monte Carlo algorithm. Fundamental effective temperatures of the two stars have
been derived, using the Hipparcos parallax of WW Aur and published ultraviolet,
optical and infrared fluxes, and are 7960 +/- 420 and 7670 +/- 410 K. The
masses, radii and effective temperatures of WW Aur are only matched by
theoretical evolutionary models for a fractional initial metal abundance, Z, of
approximately 0.06 and an age of roughly 90 Myr. This seems to be the highest
metal abundance inferred for a well-studied detached eclipsing binary, but we
find no evidence that it is related to the metallic-lined nature of the stars.
The circular orbit of WW Aur is in conflict with the circularization timescales
of both the Tassoul and the Zahn tidal theories and we suggest that this is due
to pre-main-sequence evolution or the presence of a circular orbit when the
stars were formed.Comment: Accepted for publication in MNRAS (14 pages, 8 figures). Photometric
data will be made available at the CDS once the final version appear
Raychaudhuri equation in the self-consistent Einstein-Cartan theory with spin-density
The physical implications of the Raychaudhuri equation for a spinning fluid in a Riemann-Cartan spacetime is developed and discussed using the self-consistent Lagrangian based formulation for the Einstein-Cartan theory. It was found that the spin-squared terms contribute to expansion (inflation) at early times and may lead to a bounce in the final collapse. The relationship between the fluid's vorticity and spin angular velocity is clarified and the effect of the interaction terms between the spin angular velocity and the spin in the Raychaudhuri equation investigated. These results should prove useful for studies of systems with an intrinsic spin angular momentum in extreme astrophysical or cosmological problems
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Mechanistic Insights into the Palladium-Catalyzed Aziridination of Aliphatic Amines by C-H Activation.
Detailed kinetic studies and computational investigations have been performed to elucidate the mechanism of a palladium-catalyzed C-H activation aziridination. A theoretical rate law has been derived that matches with experimental observations and has led to an improvement in the reaction conditions. Acetic acid was found to be beneficial in controlling the formation of an off-cycle intermediate, allowing a decrease in catalyst loading and improved yields. Density functional theory (DFT) studies were performed to examine the selectivities observed in the reaction. Evidence for electronic-controlled regioselectivity for the cyclopalladation step was obtained by a distortion-interaction analysis, whereas the aziridination product was justified through dissociation of acetic acid from the palladium(IV) intermediate preceding the product-forming reductive elimination step. The understanding of this reaction mechanism under the synthesis conditions should provide valuable assistance in the comprehension and design of palladium-catalyzed reactions on similar systems.We are grateful to the EPSRC and Pfizer (A.P.S.) for a studentship
and the ERC and EPSRC for fellowships (M.J.G.).
We are also grateful to Dr Alex Thom and Dr David Pryde
(Pfizer) for helpful discussions. The computational work was
performed using the Darwin Supercomputer of the University
of Cambridge High Performance Computing Service
(http://www.hpc.cam.ac.uk/), provided by Dell Inc. using
Strategic Research Infrastructure Funding from the Higher
Education Funding Council for England and funding from
the Science and Technology Facilities Council. Mass spectrometry
data were acquired at the EPSRC UK National Mass
Spectrometry Facility at Swansea University.This is the accepted manuscript. The final version is available at http://pubs.acs.org/doi/abs/10.1021/jacs.5b05529
Minimal coupling of electromagnetic fields in Riemann–Cartan space‐times for perfect fluids with spin density
The electromagnetic field is minimally coupled to gravity in a Riemann–Cartan space‐time containing a charged magnetized spinning fluid. It is required that the overall Lagrangian of the gravitational field, spinning matter, and the electromagnetic field be invariant under a gauge transformation of the vector potential. The theory preserves both charge conservation and particle number conservation. The electromagnetic field, via the vector potential, now interacts directly with the spin energy momentum. The spin transport equation, in addition to the usual Fermi–Walker transport term, contains a contribution due to the torque of the electromagnetic field acting on a magnetic dipole. In the absence of electromagnetism, the field equations reduce to those of the usual self‐consistent Lagrangian formalism for a perfect fluid with spin density.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71126/2/JMAPAQ-33-3-1073-1.pd
The Li Overabundance of J37: Diffusion or Accretion?
In September 2002 the discovery of a super Li-rich F-dwarf (J37) in NGC 6633,
an iron poor analogue of the better studied Hyades and Praecepe open clusters,
was announced. This unique star was thought to be the smoking gun for the
action of diffusion, models of which predict a narrow "Li-peak" at
approximately the correct temperature. However, with more detailed studies into
J37s abundance pattern this star provides firm evidence for the accretion of
planetesimals or other material from the circumstellar environment of new born
stars.
Thanks to the specific predictions made about the behaviour of Be abundances,
(the most striking of which being no Be in super-Li-rich dwarfs subject to
diffusion) the opposing diffusion/accretion predictions can be tested.
Initial modelling of the Be line indicates that J37 is as Be rich as it is Li
rich; log N(Be) = 2.25 +/- 0.25, and so is broadly consistent with an
accretion-fuelled enhancement. However, that both Li and Be are enhanced by
much more than the iron-peak elements (as determined in previous studies)
suggests that diffusion also plays a role in increasing the abundances of Li
and Be specifically.
Furthermore, a new data set from the UVES/UT2 combination has allowed the
elemental abundance of Iron to be measured, and the set of preliminary stellar
parameters determined; Teff ~ 7340 K, log g ~ 4.1, microturbulence ~ 4.3 km/s,
[Fe/H] ~ 0.50. This again provides distinct evidence for the effects of
accretion in J37 and requires a new synthesis of the Be doublet.Comment: 5 pages, 2 figures. Poster presented at IAU Symposium 224 "The A Star
Puzzle", 7-13 July 2004, Poprad, Slovaki
Beryllium Enhancement as Evidence for Accretion in a Lithium-Rich F Dwarf
The early F dwarf star ``J37'' in the open cluster NGC6633 shows an unusual
pattern of photospheric abundances, including an order of magnitude enhancement
of lithium and iron-peak elements, but an under-abundance of carbon. As a
consequence of its thin convection zone these anomalies have been attributed to
either radiative diffusion or the accretion of hydrogen-depleted material. By
comparing high resolution VLT/UVES spectra of J37 (and other F stars in NGC
6633) with syntheses of the Be ii doublet region at 3131 Ang, we establish that
J37 also has a Be abundance (A(Be)=3.0+/-0.5) that is at least ten times the
cosmic value. This contradicts radiative diffusion models that produce a Li
over-abundance, as they also predict photospheric Be depletion. Instead, since
Be is a highly refractory element, it supports the notion that J37 is the first
clear example of a star that has accreted volatile-depleted material with a
composition similar to chondritic meteorites, although some diffusion may be
necessary to explain the low C and O abundances.Comment: Accepted for publication in MNRAS letters, 5 page
Accurate fundamental parameters of eclipsing binary stars
The study of detached eclipsing binaries is one of the most powerful ways to
investigate the properties of individual stars and stellar systems. We present
preliminary masses, radii and effective temperatures for the eclipsing binary
WW Aurigae, which is composed of two metallic-lined A-type stars. We also
reanalyse the data on HD 23642, an A-type eclipsing binary member of the
Pleiades open cluster with a metallic-lined component, and determine its
distance to be 139 +/- 4 pc. This is in agreement with the traditional Pleiades
distance, but in disagreement with distance to the Pleiades, and to HD 23642
itself, derived from Hipparcos trigonometrical parallaxes.Comment: 15 pages, 11 figures, Poster presented at IAU Symposium 224 "The A
Star Puzzle", 7-13 July 2004, Poprad, Slovaki
Spitzer 3.6 micron and 4.5 micron full-orbit lightcurves of WASP-18
We present new lightcurves of the massive hot Jupiter system WASP-18 obtained
with the Spitzer spacecraft covering the entire orbit at 3.6 micron and 4.5
micron. These lightcurves are used to measure the amplitude, shape and phase of
the thermal phase effect for WASP-18b. We find that our results for the thermal
phase effect are limited to an accuracy of about 0.01% by systematic noise
sources of unknown origin. At this level of accuracy we find that the thermal
phase effect has a peak-to-peak amplitude approximately equal to the secondary
eclipse depth, has a sinusoidal shape and that the maximum brightness occurs at
the same phase as mid-occultation to within about 5 degrees at 3.6 micron and
to within about 10 degrees at 4.5 micron. The shape and amplitude of the
thermal phase curve imply very low levels of heat redistribution within the
atmosphere of the planet. We also perform a separate analysis to determine the
system geometry by fitting a lightcurve model to the data covering the
occultation and the transit. The secondary eclipse depths we measure at 3.6
micron and 4.5 micron are in good agreement with previous measurements and
imply a very low albedo for WASP-18b. The parameters of the system (masses,
radii, etc.) derived from our analysis are in also good agreement with those
from previous studies, but with improved precision. We use new high-resolution
imaging and published limits on the rate of change of the mean radial velocity
to check for the presence of any faint companion stars that may affect our
results. We find that there is unlikely to be any significant contribution to
the flux at Spitzer wavelengths from a stellar companion to WASP-18. We find
that there is no evidence for variations in the times of eclipse from a linear
ephemeris greater than about 100 seconds over 3 years.Comment: 17 pages, 10 figures. Accpeted for publication in MNRA
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