70 research outputs found
The change in the inclination angle of the non-eclipsing binary SS Lacertae: future eclipses
Eclipses in the 14.4-day period double-lined binary SS Lac were observed
photographically and visually early in the 20th century, but stopped some 50 or
60 years ago. This has been explained by the presence of a distant third star
in the system, which has now been detected spectroscopically with a period of
679 days. The plane of the orbit of the binary is changing relative to the line
of sight in response to perturbations from this third object. A recent analysis
by Milone et al. (M00) of all photometric material available for the system,
including a re-measurement of original Harvard plates, has confirmed earlier
reports of changes in the depth of the eclipses as a function of time, which
are due to the third star. In this paper we discuss our detailed analysis of
the eclipse amplitude measurements, and extract from them information on the
change in the inclination angle of the binary over the last century. Our use of
a much improved ephemeris for the system by Torres & Stefanik was found to be
crucial, and prompted us to re-determine all the amplitudes from the historical
data at our disposal, including the Harvard material used by M00.
Systematically lower measurements on the branches of the minima were properly
accounted for, and we made use of both a linear approximation to the time
variation of the inclination angle and a more realistic model based on the
theory of three-body interactions ("regression of the nodes" effect). The nodal
cycle is found to be about 600 yr, within which TWO eclipse "seasons" occur,
each lasting about 100 yr. The non-eclipsing status of the system is expected
to continue until the beginning of the 23rd century.Comment: 32 pages, including figures and tables. Accepted for The Astronomical
Journal, April 200
HAT Variability Survey in the High Stellar Density "Kepler Field" with Millimagnitude Image Subtraction Photometry
The Hungarian-made Automated Telescope network (HATnet) is an ongoing project
to detect transiting extra-solar planets using small aperture (11 cm diameter),
robotic telescopes. In this paper we present the results from using image
subtraction photometry to reduce a crowded stellar field observed with one of
the HATnet telescopes (HAT-5). This field was chosen to overlap with the
planned Kepler mission. We obtained I-band light curves for 98,000 objects in a
8.3x8.3 square degree field of view, near the Galactic plane in the
constellations Cygnus and Lyra. These observations include 788 5-minute
exposures over 30 days. For the brightest stars (I~8.0) we achieved a precision
of 3.5 millimagnitudes, falling to 0.1 magnitudes at the faint end (I~14). From
these light curves we identify 1617 variable stars, of which 1439 are newly
discovered. The fact that nearly 90% of the variables were previously
undetected further demonstrates the vast number of variables yet to be
discovered even among fairly bright stars in our Galaxy. We also discuss some
of the most interesting cases. These include: V1171 Cyg, a triple system with
the inner two stars in P=1.462 day period eclipsing orbit and the outer star a
P=4.86 day Cepheid; HD227269, an eccentric eclipsing system with a P=4.86 day
period that also shows P=2.907 day pulsations; WW Cyg, a well studied eclipsing
binary; V482 Cyg, an RCB star; and V546 Cyg, a PV Tel Variable. We also detect
a number of small amplitude variables, in some cases with full amplitude as low
as 10 mmag.Comment: 44 pages, 19 figures. Accepted for publication in the Astronomical
Journal. Revised version, including updated matches to existing catalogs.
Data available at http://cfa-www.harvard.edu/~gbakos/HAT/LC/199
Accurate masses and radii of normal stars: modern results and applications
This paper presents and discusses a critical compilation of accurate,
fundamental determinations of stellar masses and radii. We have identified 95
detached binary systems containing 190 stars (94 eclipsing systems, and alpha
Centauri) that satisfy our criterion that the mass and radius of both stars be
known to 3% or better. To these we add interstellar reddening, effective
temperature, metal abundance, rotational velocity and apsidal motion
determinations when available, and we compute a number of other physical
parameters, notably luminosity and distance. We discuss the use of this
information for testing models of stellar evolution. The amount and quality of
the data also allow us to analyse the tidal evolution of the systems in
considerable depth, testing prescriptions of rotational synchronisation and
orbital circularisation in greater detail than possible before. The new data
also enable us to derive empirical calibrations of M and R for single (post-)
main-sequence stars above 0.6 M(Sun). Simple, polynomial functions of T(eff),
log g and [Fe/H] yield M and R with errors of 6% and 3%, respectively.
Excellent agreement is found with independent determinations for host stars of
transiting extrasolar planets, and good agreement with determinations of M and
R from stellar models as constrained by trigonometric parallaxes and
spectroscopic values of T(eff) and [Fe/H]. Finally, we list a set of 23
interferometric binaries with masses known to better than 3%, but without
fundamental radius determinations (except alpha Aur). We discuss the prospects
for improving these and other stellar parameters in the near future.Comment: 56 pages including figures and tables. To appear in The Astronomy and
Astrophysics Review. Ascii versions of the tables will appear in the online
version of the articl
Individual caspase-10 isoforms play distinct and opposing roles in the initiation of death receptor-mediated tumour cell apoptosis
The cysteine protease caspase-8 is an essential executioner of the death receptor (DR) apoptotic pathway. The physiological function of its homologue caspase-10 remains poorly understood, and the ability of caspase-10 to substitute for caspase-8 in the DR apoptotic pathway is still controversial. Here, we analysed the particular contribution of caspase-10 isoforms to DR-mediated apoptosis in neuroblastoma (NB) cells characterised by their resistance to DR signalling. Silencing of caspase-8 in tumour necrosis factor-related apoptosis-inducing ligand (TRAIL)-sensitive NB cells resulted in complete resistance to TRAIL, which could be reverted by overexpression of caspase-10A or -10D. Overexpression experiments in various caspase-8-expressing tumour cells also demonstrated that caspase-10A and -10D isoforms strongly increased TRAIL and FasL sensitivity, whereas caspase-10B or -10G had no effect or were weakly anti-apoptotic. Further investigations revealed that the unique C-terminal end of caspase-10B was responsible for its degradation by the ubiquitin–proteasome pathway and for its lack of pro-apoptotic activity compared with caspase-10A and -10D. These data highlight in several tumour cell types, a differential pro- or anti-apoptotic role for the distinct caspase-10 isoforms in DR signalling, which may be relevant for fine tuning of apoptosis initiation
Lattice Boltzmann simulations of soft matter systems
This article concerns numerical simulations of the dynamics of particles
immersed in a continuum solvent. As prototypical systems, we consider colloidal
dispersions of spherical particles and solutions of uncharged polymers. After a
brief explanation of the concept of hydrodynamic interactions, we give a
general overview over the various simulation methods that have been developed
to cope with the resulting computational problems. We then focus on the
approach we have developed, which couples a system of particles to a lattice
Boltzmann model representing the solvent degrees of freedom. The standard D3Q19
lattice Boltzmann model is derived and explained in depth, followed by a
detailed discussion of complementary methods for the coupling of solvent and
solute. Colloidal dispersions are best described in terms of extended particles
with appropriate boundary conditions at the surfaces, while particles with
internal degrees of freedom are easier to simulate as an arrangement of mass
points with frictional coupling to the solvent. In both cases, particular care
has been taken to simulate thermal fluctuations in a consistent way. The
usefulness of this methodology is illustrated by studies from our own research,
where the dynamics of colloidal and polymeric systems has been investigated in
both equilibrium and nonequilibrium situations.Comment: Review article, submitted to Advances in Polymer Science. 16 figures,
76 page
The Properties of X-Ray and Optical Light Curves of X-Ray Novae
We have collected the available data from the literature and from public data
archives covering the past two decades for the long-term X-ray and optical
light curves of X-ray nova (XN) outbursts, and carry out for the first time a
systematic, statistical study of XN light curves which are classified into 5
morphological types. Basic light curve parameters, e.g., the outburst peak
flux, amplitude, luminosity, rise and decay timescales, the observed and
expected outburst durations, and total energy radiated, are tabulated and
discussed. The rise timescales are found to have a flat distribution while the
decay timescales have a much narrower and near-Gaussian distribution, centered
around 30 days and dominated by the strongest outbursts. The peak luminosity is
also distributed like a Gaussian, centered around 0.2 in Eddington units, while
the total energy released has a much broader distribution around 10E44 ergs.
We identify and discuss additional light curve features, such as precursors,
plateaus, and secondary maxima. The plateaus exhibited in the light curves of
black hole sources are found to have, on average, longer durations and they are
followed by longer decays. The identified secondary maxima seem to occur mostly
in black hole systems. For the frequency of outbursts, we find that the average
XN outburst rate is about 2.6 per year for events >0.3 Crab, and that the mean
recurrence time between outbursts from a single source is 6 years. The spatial
and logN-logS distribution of the XN sources, with limited statistics, agrees
with a source population in the Galactic disk, as observed from a point at a
distance of 8.5 kpc from the Galactic center. Finally, we point out that the
observed XN light curve properties can in general be explained by a disk
thermal instability model, although some important problems still remain.Comment: 68 pages including 27 Postscript figures and 12 tables. To be
published in the Astrophysical Journal, Part
AE Aquarii represents a new subclass of Cataclysmic Variables
We analyze properties of the unique nova-like star AE Aquarii identified with
a close binary system containing a red dwarf and a very fast rotating
magnetized white dwarf. It cannot be assigned to any of the three commonly
adopted sub-classes of Cataclysmic Variables: Polars, Intermediate Polars, and
Accreting non-magnetized White Dwarfs. Our study has shown that the white dwarf
in AE Aqr is in the ejector state and its dipole magnetic moment is . It switched into this state due to intensive mass
exchange between the system components during a previous epoch. A high rate of
disk accretion onto the white dwarf surface resulted in temporary screening of
its magnetic field and spin-up of the white dwarf to its present spin period.
Transition of the white dwarf to the ejector state had occurred at a final
stage of the spin-up epoch as its magnetic field emerged from the accreted
plasma due to diffusion. In the frame of this scenario AE Aqr represents a
missing link in the chain of Polars evolution and the white dwarf resembles a
recycled pulsar.Comment: accepted for publication in Astronomy Reports (July 2012
Determination of a saliva cotinine cut-off to distinguish pregnant smokers from pregnant non-smokers
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