124 research outputs found
Spectral Decomposition of the Tent Map with Varying Height
The generalized spectral decomposition of the Frobenius-Perron operator of
the tent map with varying height is determined at the band-splitting points.
The decomposition includes both decay onto the attracting set and the approach
to the asymptotically periodic state on the attractor. Explicit compact
expressions for the polynomial eigenstates are obtained using algebraic
techniques.Comment: 39 pages, 7 figures, in LATeX with embedded PS figure
The rapidly pulsating sdO star, SDSS J160043.6+074802.9
A spectroscopic analysis of SDSS J160043.6+074802.9, a binary system
containing a pulsating subdwarf-O (sdO) star with a late-type companion, yields
Teff = 70 000 +/- 5000 K and log g = 5.25 +/- 0.30, together with a most likely
type of K3V for the secondary star. We compare our results with atmospheric
parameters derived by Fontaine et al. (2008) and in the context of existing
evolution models for sdO stars. New and more extensive photometry is also
presented which recovers most, but not all, frequencies found in an earlier
paper. It therefore seems probable that some pulsation modes have variable
amplitudes. A non-adiabatic pulsation analysis of uniform metallicity sdO
models show those having log g > 5.3 to be more likely to be unstable and
capable of driving pulsation in the observed frequency range.Comment: 14 pages, 12 figures, accepted for publication in MNRAS, 2009
September
The Excitation of Extended Red Emission: New Constraints on its Carrier From HST Observations of NGC 7023
The carrier of the dust-associated photoluminescence process causing the
extended red emission (ERE) in many dusty interstellar environments remains
unidentified. Several competing models are more or less able to match the
observed broad, unstructured ERE band. We now constrain the character of the
ERE carrier further by determining the wavelengths of the radiation that
initiates the ERE. Using the imaging capabilities of the Hubble Space
Telescope, we have resolved the width of narrow ERE filaments appearing on the
surfaces of externally illuminated molecular clouds in the bright reflection
nebula NGC 7023 and compared them with the depth of penetration of radiation of
known wavelengths into the same cloud surfaces. We identify photons with
wavelengths shortward of 118 nm as the source of ERE initiation, not to be
confused with ERE excitation, however. There are strong indications from the
well-studied ERE in the Red Rectangle nebula and in the high-|b| Galactic
cirrus that the photon flux with wavelengths shortward of 118 nm is too small
to actually excite the observed ERE, even with 100% quantum efficiency. We
conclude, therefore, that ERE excitation results from a two-step process. While
none of the previously proposed ERE models can match these new constraints, we
note that under interstellar conditions most polycyclic aromatic hydrocarbon
(PAH) molecules are ionized to the di-cation stage by photons with E > 10.5 eV
and that the electronic energy level structure of PAH di-cations is consistent
with fluorescence in the wavelength band of the ERE. Therefore, PAH di-cations
deserve further study as potential carriers of the ERE. (abridged)Comment: Accepted for Publication in the Ap
Brownian motion and diffusion: from stochastic processes to chaos and beyond
One century after Einstein's work, Brownian Motion still remains both a
fundamental open issue and a continous source of inspiration for many areas of
natural sciences. We first present a discussion about stochastic and
deterministic approaches proposed in the literature to model the Brownian
Motion and more general diffusive behaviours. Then, we focus on the problems
concerning the determination of the microscopic nature of diffusion by means of
data analysis. Finally, we discuss the general conditions required for the
onset of large scale diffusive motion.Comment: RevTeX-4, 11 pages, 5 ps-figures. Chaos special issue "100 Years of
Brownian Motion
Formation and evolution of a 0.242 Msun helium white dwarf in presence of element diffusion
A 0.242 Msun object that finally becomes a helium white dwarf is evolved from
Roche lobe detachment down to very low luminosities. In doing so, we employ our
stellar code to which we have added a set of routines that compute the effects
due to gravitational settling, and chemical and thermal diffusion. Initial
model is constructed by abstracting mass to a 1 Msun red giant branch model up
to the moment at which the model begins to evolve bluewards. We find that
element diffusion introduces noticeable changes in the internal structure of
the star. In particular, models undergo three thermonuclear flashes instead of
one flash as we found with the standard treatment. This fact has a large impact
on the total mass fraction of hydrogen left in the star at entering the final
cooling track. As a result, at late stages of evolution models with diffusion
are characterized by a much smaller nuclear energy release, and they evolve
significantly faster compared to those found with the standard treatment.
We find that models in which diffusion is considered predict evolutionary
ages for the white dwarf companion to the millisecond pulsar PSR B1855+09 in
good agreement with the spin-down age of the pulsar.Comment: 6 pages, 3 figures, 12th European Workshop on White Dwarf
First AMBER/VLTI observations of hot massive stars
AMBER is the first near infrared focal instrument of the VLTI. It combines
three telescopes and produces spectrally resolved interferometric measures.
This paper discusses some preliminary results of the first scientific
observations of AMBER with three Unit Telescopes at medium (1500) and high
(12000) spectral resolution. We derive a first set of constraints on the
structure of the circumstellar material around the Wolf Rayet Gamma2 Velorum
and the LBV Eta Carinae
Transmission of MethicillinâResistant Staphylococcus aureus Infection Through Solid Organ Transplantation: Confirmation Via Whole Genome Sequencing
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109324/1/ajt12898.pd
Trajectory versus probability density entropy
We study the problem of entropy increase of the Bernoulli-shift map without
recourse to the concept of trajectory and we discuss whether, and under which
conditions if it does, the distribution density entropy coincides with the
Kolmogorov-Sinai entropy, namely, with the trajectory entropy.Comment: 24 page
Tracing the young massive high-eccentricity binary system Theta 1 Orionis C through periastron passage
The nearby high-mass star binary system Theta 1 Orionis C is the brightest
and most massive of the Trapezium OB stars at the core of the Orion Nebula
Cluster, and it represents a perfect laboratory to determine the fundamental
parameters of young hot stars and to constrain the distance of the Orion
Trapezium Cluster. Between January 2007 and March 2008, we observed T1OriC with
VLTI/AMBER near-infrared (H- and K-band) long-baseline interferometry, as well
as with bispectrum speckle interferometry with the ESO 3.6m and the BTA 6m
telescopes (B'- and V'-band). Combining AMBER data taken with three different
3-telescope array configurations, we reconstructed the first VLTI/AMBER
closure-phase aperture synthesis image, showing the T1OriC system with a
resolution of approx. 2 mas. To extract the astrometric data from our
spectrally dispersed AMBER data, we employed a new algorithm, which fits the
wavelength-differential visibility and closure phase modulations along the H-
and K-band and is insensitive to calibration errors induced, for instance, by
changing atmospheric conditions. Our new astrometric measurements show that the
companion has nearly completed one orbital revolution since its discovery in
1997. The derived orbital elements imply a short-period (P=11.3 yrs) and
high-eccentricity orbit (e=0.6) with periastron passage around 2002.6. The new
orbit is consistent with recently published radial velocity measurements, from
which we can also derive the first direct constraints on the mass ratio of the
binary components. We employ various methods to derive the system mass
(M_system=44+/-7 M_sun) and the dynamical distance (d=410+/-20 pc), which is in
remarkably good agreement with recently published trigonometric parallax
measurements obtained with radio interferometry.Comment: 15 pages, 15 figures, accepted by A&
Direct constraint on the distance of y2 Velorum from AMBER/VLTI observations
In this work, we present the first AMBER observations, of the Wolf-Rayet and
O (WR+O) star binary system y2 Velorum. The AMBER instrument was used with the
telescopes UT2, UT3, and UT4 on baselines ranging from 46m to 85m. It delivered
spectrally dispersed visibilities, as well as differential and closure phases,
with a resolution R = 1500 in the spectral band 1.95-2.17 micron. We interpret
these data in the context of a binary system with unresolved components,
neglecting in a first approximation the wind-wind collision zone flux
contribution. We show that the AMBER observables result primarily from the
contribution of the individual components of the WR+O binary system. We discuss
several interpretations of the residuals, and speculate on the detection of an
additional continuum component, originating from the free-free emission
associated with the wind-wind collision zone (WWCZ), and contributing at most
to the observed K-band flux at the 5% level. The expected absolute separation
and position angle at the time of observations were 5.1±0.9mas and
66±15° respectively. However, we infer a separation of
3.62+0.11-0.30 mas and a position angle of 73+9-11°. Our analysis thus
implies that the binary system lies at a distance of 368+38-13 pc, in agreement
with recent spectrophotometric estimates, but significantly larger than the
Hipparcos value of 258+41-31 pc
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