3,756 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
Overview of methods used to evaluate the adequacy of nutrient intakes for individuals and populations
The objective of the present paper is to review the methods of measuring micronutrient intake adequacy for individuals and for populations in order to ascertain best practice. A systematic review was conducted to locate studies on the methodological aspects of measuring nutrient adequacy. The results showed that for individuals, qualitative methods (to find probability of adequacy) and quantitative methods (to find confidence of adequacy) have been proposed for micronutrients where there is enough data to set an average nutrient requirement (ANR). If micronutrients do not have ANR, an adequate intake (AI) is often defined and can be used to assess adequacy, provided the distribution of daily intake over a number of days is known. The probability of an individual's intake being excessive can also be compared with the upper level of safe intake and the confidence of this estimate determined in a similar way. At the population level, adequacy can be judged from the ANR using the probability approach or its short cut â the estimated average requirement cut-point method. If the micronutrient does not have an ANR, adequacy cannot be determined from the average intake and must be expressed differently. The upper level of safe intake can be used for populations in a similar way to that of individuals. All of the methodological studies reviewed were from the American continent and all used the methodology described in the Institute of Medicine publications. The present methodology should now be adapted for use in Europe
Identification of transitional disks in Chamaeleon with Herschel
Transitional disks are circumstellar disks with inner holes that in some
cases are produced by planets and/or substellar companions in these systems.
For this reason, these disks are extremely important for the study of planetary
system formation. The Herschel Space Observatory provides an unique opportunity
for studying the outer regions of protoplanetary disks. In this work we update
previous knowledge on the transitional disks in the Chamaeleon I and II regions
with data from the Herschel Gould Belt Survey. We propose a new method for
transitional disk classification based on the WISE 12 micron-PACS 70 micron
color, together with inspection of the Herschel images. We applied this method
to the population of Class II sources in the Chamaeleon region and studied the
spectral energy distributions of the transitional disks in the sample. We also
built the median spectral energy distribution of Class II objects in these
regions for comparison with transitional disks. The proposed method allows a
clear separation of the known transitional disks from the Class II sources. We
find 6 transitional disks, all previously known, and identify 5 objects
previously thought to be transitional as possibly non-transitional. We find
higher fluxes at the PACS wavelengths in the sample of transitional disks than
those of Class II objects. We show the Herschel 70 micron band to be an
efficient tool for transitional disk identification. The sensitivity and
spatial resolution of Herschel reveals a significant contamination level among
the previously identified transitional disk candidates for the two regions,
which calls for a revision of previous samples of transitional disks in other
regions. The systematic excess found at the PACS bands could be a result of the
mechanism that produces the transitional phase, or an indication of different
evolutionary paths for transitional disks and Class II sources.Comment: Accepted for publication in A&A: 11 March 2013 11 pages, 15 figure
An analysis of the transit times of CoRoT-1b
I report the results from a study of the transit times for CoRoT-1b, which
was one of the first planets discovered by CoRoT. Analysis of the pipeline
reduced CoRoT light curve yields a new determination of the physical and
orbital parameters of planet and star, along with 35 individual transit times
at a typical precision of 36 s. I estimate a planet-to-star radii ratio of
0.1433 +/- 0.0010, a ratio of the planet's orbital semimajor axis to the host
star radius of 4.751 +/- 0.045, and an orbital inclination for the planet of
83.88 +/- 0.29 deg. The observed transit times are consistent with CoRoT-1b
having a constant period and there is no evidence of an additional planet in
the system. I use the observed constancy of the transit times to set limits on
the mass of a hypothetical additional planet in a nearby, stable orbit. I
ascertain that the most stringent limits (4 M_earth at 3 sigma confidence) can
be placed on planets residing in a 1:2 mean motion resonance with the
transiting planet. In contrast, the data yield less stringent limits on planets
near a 1:3 mean motion resonance (5 M_jup at 3 sigma confidence) than in the
surrounding parameter space. In addition, I use a simulation to investigate
what sensitivity to additional planets could be obtained from the analysis of
data measured for a similar system during a CoRoT long run (100 sequential
transit times). I find that for such a scenario, planets with masses greater
than twice that of Mars (0.2 M_earth) in the 1:2 mean motion resonance would
cause high-significance transit time deviations. Therefore, such planets could
be detected or ruled out using CoRoT long run data. I conclude that CoRoT data
will indeed be very useful for searching for planets with the transit timing
method.Comment: accepted for publication in A&A; v2 replaces with accepted versio
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
-Primitive -Normal elements in Arithmetic Progressions over Finite Fields
Let be a finite field with elements. For a positive
divisor of , the element is called
\textit{-primitive} if its multiplicative order is . Also, for a
non-negative integer , the element is
\textit{-normal} over if in
has degree . In this paper we discuss the existence of
elements in arithmetic progressions with
being -primitive and at least one of the elements in the arithmetic
progression being -normal over . We obtain asymptotic results
for general and concrete results when for .Comment: arXiv admin note: substantial text overlap with arXiv:2210.1150
Progressive loss functions for speech enhancement with deep neural networks
The progressive paradigm is a promising strategy to optimize network performance for speech enhancement purposes. Recent works have shown different strategies to improve the accuracy of speech enhancement solutions based on this mechanism. This paper studies the progressive speech enhancement using convolutional and residual neural network architectures and explores two criteria for loss function optimization: weighted and uniform progressive. This work carries out the evaluation on simulated and real speech samples with reverberation and added noise using REVERB and VoiceHome datasets. Experimental results show a variety of achievements among the loss function optimization criteria and the network architectures. Results show that the progressive design strengthens the model and increases the robustness to distortions due to reverberation and noise
Orbit determination of Transneptunian objects and Centaurs for the prediction of stellar occultations
The prediction of stellar occultations by Transneptunian objects and Centaurs
is a difficult challenge that requires accuracy both in the occulted star
position as for the object ephemeris. Until now, the most used method of
prediction involving tens of TNOs/Centaurs was to consider a constant offset
for the right ascension and for the declination with respect to a reference
ephemeris. This offset is determined as the difference between the most recent
observations of the TNO and the reference ephemeris. This method can be
successfully applied when the offset remains constant with time. This paper
presents an alternative method of prediction based on a new accurate orbit
determination procedure, which uses all the available positions of the TNO from
the Minor Planet Center database plus sets of new astrometric positions from
unpublished observations. The orbit determination is performed through a
numerical integration procedure (NIMA), in which we develop a specific
weighting scheme. The NIMA method was applied for 51 selected TNOs/Centaurs.
For this purpose, we have performed about 2900 new observations during
2007-2014. Using NIMA, we succeed in predicting the stellar occultations of 10
TNOs and 3 Centaurs between 2013 and 2015. By comparing the NIMA and JPL
ephemerides, we highlighted the variation of the offset between them with time.
Giving examples, we show that the constant offset method could not accurately
predict 6 out of the 13 observed positive occultations successfully predicted
by NIMA. The results indicate that NIMA is capable of efficiently refine the
orbits of these bodies. Finally, we show that the astrometric positions given
by positive occultations can help to further refine the orbit of the TNO and
consequently the future predictions. We also provide the unpublished
observations of the 51 selected TNOs and their ephemeris in a usable format by
the SPICE library.Comment: 12 pages, 9 figures, accepted in A&
Radiopurity of Micromegas readout planes
Micromesh Gas Amplification Structures (Micromegas) are being used in an
increasing number of Particle Physics applications since their conception
fourteen years ago. More recently, they are being used or considered as readout
of Time Projection Chambers (TPCs) in the field of Rare Event searches (dealing
with dark matter, axions or double beta decay). In these experiments, the
radiopurity of the detector components and surrounding materials is measured
and finely controlled in order to keep the experimental background as low as
possible. In the present paper, the first measurement of the radiopurity of
Micromegas planes obtained by high purity germanium spectrometry in the low
background facilities of the Canfranc Underground Laboratory (LSC) is
presented. The obtained results prove that Micromegas readouts of the microbulk
type are currently manufactured with radiopurity levels below 30 microBq/cm2
for Th and U chains and ~60 microBq/cm2 for 40K, already comparable to the
cleanest detector components of the most stringent low background experiments
at present. Taking into account that the studied readouts were manufactured
without any specific control of the radiopurity, it should be possible to
improve these levels after dedicated development.Comment: 15 pages, 2 figure
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