672 research outputs found
The Best Brown Dwarf Yet?: A Companion to the Hyades Eclipsing Binary V471 Tau
We have carried out an analysis of about 160 eclipse timings spanning over 30
years of the Hyades eclipsing binary V471 Tauri that shows a long-term
quasi-sinusoidal modulation of its observed eclipse arrival times. The O-Cs
have been analyzed for the ``light-time'' effect that arises from the
gravitational influence of a tertiary companion. The presence of a third body
causes the relative distance of the eclipsing pair to the Earth to change as it
orbits the barycenter of the triple system. The result of the analysis of the
eclipse times yields a light-time semi-amplitude of 137.2+/-12.0 s, an orbital
period of P_3 = 30.5+/-1.6 yr and an eccentricity of e_3 = 0.31+/-0.04. The
mass of the tertiary component is M_3 sin i_3 = 0.0393+/-0.0038 Mo when a total
mass of 1.61+/-0.06 Mo for V471 Tau is adopted. For orbital inclinations i_3 >
35 deg, the mass of the third body would be below the stable hydrogen burning
limit of M = 0.07 Mo and it thus would be a brown dwarf. In the next several
years (near maximum elongation), it should be feasible to obtain IR images and
spectra of V471 Tau C that, when combined with the known mass, age, distance,
and [Fe/H], will serve as a benchmark for understanding the physical properties
and evolution of brown dwarfs.Comment: 9 pages, 3 figures, accepted for publication in ApJ Letter
Stimulus Frequency Otoacoustic Emission Delays and Generating Mechanisms in Guinea Pigs, Chinchillas, and Simulations
According to coherent reflection theory (CRT), stimulus frequency otoacoustic emissions (SFOAEs) arise from cochlear irregularities coherently reflecting energy from basilar membrane motion within the traveling-wave peak. This reflected energy arrives in the ear canal predominantly with a single delay at each frequency. However, data from humans and animals indicate that (1) SFOAEs can have multiple delay components, (2) low-frequency SFOAE delays are too short to be accounted for by CRT, and (3) âSFOAEsâ obtained with a 2nd (âsuppressorâ) tone â„2 octaves above the probe tone have been interpreted as arising from the area basal to the region of cochlear amplification. To explore these issues, we collected SFOAEs by the suppression method in guinea pigs and time-frequency analyzed these data, simulated SFOAEs, and published chinchilla SFOAEs. Time-frequency analysis revealed that most frequencies showed only one SFOAE delay component while other frequencies had multiple components including some with short delays. We found no systematic patterns in the occurrence of multiple delay components. Using a cochlear model that had significant basilar membrane motion only in the peak region of the traveling wave, simulated SFOAEs had single and multiple delay components similar to the animal SFOAEs. This result indicates that multiple components (including ones with short delays) can originate from cochlear mechanical irregularities in the SFOAE peak region and are not necessarily indicative of SFOAE sources in regions â„2 octaves basal of the SFOAE peak region. We conclude that SFOAEs obtained with suppressors close to the probe frequency provide information primarily about the mechanical response in the region that receives amplification, and we attribute the too-short SFOAE delays at low frequencies to distortion-source SFOAEs and coherent reflection from multiple cochlear motions. Our findings suggest that CRT needs revision to include reflections from multiple motions in the cochlear apex.United States. National Institute for Deafness and other Communicative Disorders (RO1 DC000235)United States. National Institute for Deafness and other Communicative Disorders (R01 DC003687)United States. National Institute for Deafness and other Communicative Disorders (T32 DC00038)United States. National Institute for Deafness and other Communicative Disorders (P30 DC005209)National Science Foundation (U.S.) (NSF Graduate Research Fellowship Program
Searching for Weak or Complex Magnetic Fields in Polarized Spectra of Rigel
Seventy-eight high-resolution Stokes V, Q and U spectra of the B8Iae
supergiant Rigel were obtained with the ESPaDOnS spectropolarimeter at CFHT and
its clone NARVAL at TBL in the context of the Magnetism in Massive Stars
(MiMeS) Large Program, in order to scrutinize this core-collapse supernova
progenitor for evidence of weak and/or complex magnetic fields. In this paper
we describe the reduction and analysis of the data, the constraints obtained on
any photospheric magnetic field, and the variability of photospheric and wind
lines.Comment: IAUS272 - Active OB Stars: Structure, Evolution, Mass Loss and
Critical Limit
The Distance to the Large Magellanic Cloud from the Eclipsing Binary HV2274
The distance to the Large Magellanic Cloud (LMC) is crucial for the
calibration of the Cosmic Distance Scale. We derive a distance to the LMC based
on an analysis of ground-based photometry and HST-based spectroscopy and
spectrophotometry of the LMC eclipsing binary system HV2274. Analysis of the
optical light curve and HST/GHRS radial velocity curve provides the masses and
radii of the binary components. Analysis of the HST/FOS UV/optical
spectrophotometry provides the temperatures of the component stars and the
interstellar extinction of the system. When combined, these data yield a
distance to the binary system. After correcting for the location of HV2274 with
respect to the center of the LMC, we find d(LMC) = 45.7 +/- 1.6 kpc or DM(LMC)
= 18.30 +/- 0.07 mag. This result, which is immune to the metallicity-induced
zero point uncertainties that have plagued other techniques, lends strong
support to the ``short'' LMC distance scale as derived from a number of
independent methods.Comment: 6 pages, including 2 pages of figures. Newly available optical (B and
V) photometry has revealed -- and allowed the elimination of -- a systematic
error in the previously reported determination of E(B-V) for HV2274. The new
result is E(B-V) = 0.12 mag (as compared to the value of 0.083 reported in
the original submission) and produces a DECREASE in the distance modulus of
HV2274 by 0.12 mag. ApJ Letters, in pres
Evidence of major fisheries impact on cold-water corals in the deep waters off the Porcupine Bank, west coast of Ireland: are interim management measures required?
Artificial Intelligence Approach to the Determination of Physical Properties of Eclipsing Binaries. I. The EBAI Project
Achieving maximum scientific results from the overwhelming volume of
astronomical data to be acquired over the next few decades will demand novel,
fully automatic methods of data analysis. Artificial intelligence approaches
hold great promise in contributing to this goal. Here we apply neural network
learning technology to the specific domain of eclipsing binary (EB) stars, of
which only some hundreds have been rigorously analyzed, but whose numbers will
reach millions in a decade. Well-analyzed EBs are a prime source of
astrophysical information whose growth rate is at present limited by the need
for human interaction with each EB data-set, principally in determining a
starting solution for subsequent rigorous analysis. We describe the artificial
neural network (ANN) approach which is able to surmount this human bottleneck
and permit EB-based astrophysical information to keep pace with future data
rates. The ANN, following training on a sample of 33,235 model light curves,
outputs a set of approximate model parameters (T2/T1, (R1+R2)/a, e sin(omega),
e cos(omega), and sin i) for each input light curve data-set. The whole sample
is processed in just a few seconds on a single 2GHz CPU. The obtained
parameters can then be readily passed to sophisticated modeling engines. We
also describe a novel method polyfit for pre-processing observational light
curves before inputting their data to the ANN and present the results and
analysis of testing the approach on synthetic data and on real data including
fifty binaries from the Catalog and Atlas of Eclipsing Binaries (CALEB)
database and 2580 light curves from OGLE survey data. [abridged]Comment: 52 pages, accepted to Ap
Magnetic field and wind of Kappa Ceti: towards the planetary habitability of the young Sun when life arose on Earth
We report magnetic field measurements for Kappa1~Cet, a proxy of the young
Sun when life arose on Earth. We carry out an analysis of the magnetic
properties determined from spectropolarimetric observations and reconstruct its
large-scale surface magnetic field to derive the magnetic environment, stellar
winds and particle flux permeating the interplanetary medium around Kappa1~Cet.
Our results show a closer magnetosphere and mass-loss rate of Mdot = 9.7 x
10^{-13} Msol/yr, i.e., a factor 50 times larger than the current solar wind
mass-loss rate, resulting in a larger interaction via space weather
disturbances between the stellar wind and a hypothetical young-Earth analogue,
potentially affecting the planet's habitability. Interaction of the wind from
the young Sun with the planetary ancient magnetic field may have affected the
young Earth and its life conditionsComment: 6 pages, 5 figures, Published at the Astrophysical Journal Letters
(ApJL): Manuscript #LET3358
Communications Biophysics
Contains a summary of research publications and reports on four research projects.National Science Foundation (Grant GP-2495)National Institutes of Health (Grant MH-04737-04)National Aeronautics and Space Administration (Grant NsG-496
- âŠ