5,029 research outputs found
The V471 Tauri System: A Multi-datatype Probe
V471 Tauri, a white dwarf--red dwarf eclipsing binary in the Hyades, is well
known for stimulating development of common envelope theory, whereby novae and
other cataclysmic variables form from much wider binaries by catastrophic orbit
shrinkage. Our evaluation of a recent imaging search that reported negative
results for a much postulated third body shows that the object could have
escaped detection or may have actually been seen. The balance of evidence
continues to favor a brown dwarf companion about 12 AU from the eclipsing
binary. A recently developed algorithm finds unified solutions from three
datatypes. New radial velocities (RVs) of the red dwarf and BV RCIC light
curves are solved simultaneously along with white dwarf and red dwarf RVs from
the literature, uvby data, the MOST mission light curve, and 40 years of
eclipse timings. Precision-based weighting is the key to proper information
balance among the various datasets. Timewise variation of modeled starspots
allows unified solution of multiple data eras. Light curve amplitudes strongly
suggest decreasing spottedness from 1976 to about 1980, followed by
approximately constant spot coverage from 1981 to 2005. An explanation is
proposed for lack of noticeable variation in 1981 light curves, in terms of
competition between spot and tidal variations. Photometric spectroscopic
distance is estimated. The red dwarf mass comes out larger than normal for a
K2V star, and even larger than adopted in several structure and evolution
papers. An identified cause for this result is that much improved red dwarf RVs
curves now exist
A BVRcIc Survey of W Ursae Majoris Binaries
We report on a BVRcIc survey of field W Ursae Majoris binary stars and
present accurate colors for 606 systems that have been observed on at least
three photometric nights from a robotic observatory in southern Arizona.
Comparison with earlier photometry for a subset of the systems shows good
agreement. We investigate two independent methods of determining the
interstellar reddening, although both have limitations that can render them
less effective than desired. A subset of 101 systems shows good agreement
between the two reddening methods.Comment: 10 pages, 6 figures, accepted for publication in A
Design of a 30 GHz Damped Detuned Accelerating Structure
Within the framework of the SLAC/CERN studies of 30 GHz linear colliders, an attempt has been made to scale as closely as possible the existing X-band NLC damped detuned accelerating structure to 30 GHz. A simple scaling was not possible because of mechanical and RF constraints. The 30 GHz design has 101 cells and a minimum aperture of 3.4 mm. In order to obtain acceptably small values for both the single-bunch transverse wakefield and the long-range multibunch wakefield a relatively large non-linear variation of the iris thickness was introduced in addition to the iris diameter variation. The resulting wakefield has a short-range value of 1290 V/pC/mm/m and a long range value below 10 V/pC/mm/m
Skeletal muscle metabolic abnormalities in congestive heart failure are not due to muscle atrophy
The antiderivative understanding by students in the first university courses
ABSTARCT: In this article, we present the results of a questionnaire designed to evaluate college students’ understanding of the antiderivative. Specifically, by civil engineering students when answering the questionnaire’ tasks, in order to identify and characterize the meanings on the antiderivative that are mobilized by them. In order to analyse the answers given, we used some theoretical and methodological notions provided by the theoretical model known as the Onto-Semiotic Approach (OSA) of mathematics cognition and instruction. The results show knowledge of antiderivative by the Civil Engineering students. Furthermore, the comparison between the mathematical activity of students provides information that allows concluding that the meanings that they mobilized might be shared among their communities
Evidence of strong quasar feedback in the early Universe
Most theoretical models invoke quasar driven outflows to quench star
formation in massive galaxies, this feedback mechanism is required to account
for the population of old and passive galaxies observed in the local universe.
The discovery of massive, old and passive galaxies at z=2, implies that such
quasar feedback onto the host galaxy must have been at work very early on,
close to the reionization epoch. We have observed the [CII]158um transition in
SDSSJ114816.64+525150.3 that, at z=6.4189, is one of the most distant quasars
known. We detect broad wings of the line tracing a quasar-driven massive
outflow. This is the most distant massive outflow ever detected and is likely
tracing the long sought quasar feedback, already at work in the early Universe.
The outflow is marginally resolved on scales of about 16 kpc, implying that the
outflow can really affect the whole galaxy, as required by quasar feedback
models. The inferred outflow rate, dM/dt > 3500 Msun/yr, is the highest ever
found. At this rate the outflow can clean the gas in the host galaxy, and
therefore quench star formation, in a few million years.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
Quasi-periodic flares in EXO 2030+375 observed with INTEGRAL
Context: Episodic flaring activity is a common feature of X-ray pulsars in
HMXBs. In some Be/X-ray binaries flares were observed in quiescence or prior to
outbursts. EXO 2030+375 is a Be/X-ray binary showing "normal" outbursts almost
every ~46 days, near periastron passage of the orbital revolution. Some of
these outbursts were occasionally monitored with the INTEGRAL observatory.
Aims: The INTEGRAL data revealed strong quasi-periodic flaring activity during
the rising part of one of the system's outburst. Such activity has previously
been observed in EXO 2030+375 only once, in 1985 with EXOSAT. (Some indications
of single flares have also been observed with other satellites.) Methods: We
present the analysis of the flaring behavior of the source based on INTEGRAL
data and compare it with the flares observed in EXO 2030+375 in 1985. Results:
Based on the observational properties of the flares, we argue that the
instability at the inner edge of the accretion disk is the most probable cause
of the flaring activity.Comment: Accepted for publication in A&A Lette
Generalized Numerical Renormalization Group for Dynamical Quantities
In this paper we introduce a new approach for calculating dynamical
properties within the numerical renormalization group. It is demonstrated that
the method previously used fails for the Anderson impurity in a magnetic field
due to the absence of energy scale separation. The problem is solved by
evaluating the Green function with respect to the reduced density matrix of the
full system, leading to accurate spectra in agreement with the static
magnetization. The new procedure (denoted as DM-NRG) provides a unifying
framework for calculating dynamics at any temperature and represents the
correct extension of Wilson's original thermodynamic calculation.Comment: 4 pages RevTeX, 6 eps figures include
A possible magnetar nature for IGR J16358-4726
We present detailed spectral and timing analysis of the hard X-ray transient IGR J16358-4726 using multisatellite archival observations. A study of the source flux time history over 6 yr suggests that lower luminosity transient outbursts can be occurring in intervals of at most 1 yr. Joint spectral fits of the higher luminosity outburst using simultaneous Chandra ACIS and INTEGRAL ISGRI data reveal a spectrum well described by an absorbed power-law model with a high-energy cutoff plus an Fe line. We detected the 1.6 hr pulsations initially reported using Chandra ACIS also in the INTEGRAL ISGRI light curve and in subsequent XMM-Newton observations. Using the INTEGRAL data, we identified a spin-up of 94 s ( = 1.6 × 10-4), which strongly points to a neutron star nature for IGR J16358-4726. Assuming that the spin-up is due to disk accretion, we estimate that the source magnetic field ranges between 1013 and 1015 G, depending on its distance, possibly supporting a magnetar nature for IGR J16358-4726
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