1,664 research outputs found
Extensions of tempered representations
Let be irreducible tempered representations of an affine Hecke
algebra H with positive parameters. We compute the higher extension groups
explicitly in terms of the representations of analytic
R-groups corresponding to and . The result has immediate
applications to the computation of the Euler-Poincar\'e pairing ,
the alternating sum of the dimensions of the Ext-groups. The resulting formula
for is equal to Arthur's formula for the elliptic pairing of
tempered characters in the setting of reductive p-adic groups. Our proof
applies equally well to affine Hecke algebras and to reductive groups over
non-archimedean local fields of arbitrary characteristic. This sheds new light
on the formula of Arthur and gives a new proof of Kazhdan's orthogonality
conjecture for the Euler-Poincar\'e pairing of admissible characters.Comment: This paper grew out of "A formula of Arthur and affine Hecke
algebras" (arXiv:1011.0679). In the second version some minor points were
improve
Spitzer Mid-Infrared Photometry of 500 - 750 K Brown Dwarfs
Mid-infrared data, including Spitzer warm-IRAC [3.6] and [4.5] photometry, is
critical for understanding the cold population of brown dwarfs now being found,
objects which have more in common with planets than stars. As effective
temperature (T_eff) drops from 800 K to 400 K, the fraction of flux emitted
beyond 3 microns increases rapidly, from about 40% to >75%. This rapid increase
makes a color like H-[4.5] a very sensitive temperature indicator, and it can
be combined with a gravity- and metallicity-sensitive color like H-K to
constrain all three of these fundamental properties, which in turn gives us
mass and age for these slowly cooling objects. Determination of mid-infrared
color trends also allows better exploitation of the WISE mission by the
community. We use new Spitzer Cycle 6 IRAC photometry, together with published
data, to present trends of color with type for L0 to T10 dwarfs. We also use
the atmospheric and evolutionary models of Saumon & Marley to investigate the
masses and ages of 13 very late-type T dwarfs, which have H-[4.5] > 3.2 and
T_eff ~ 500 K to 750 K.Comment: To be published in the on-line version of the Proceedings of Cool
Stars 16 (ASP Conference Series). This is an updated version of Leggett et
al. 2010 ApJ 710 1627; a photometry compilation is available at
http://www.gemini.edu/staff/slegget
Extending the Canada-France brown Dwarfs Survey to the near-infrared: first ultracool brown dwarfs from CFBDSIR
We present the first results of the ongoing Canada-France Brown Dwarfs
Survey-InfraRed, hereafter CFBDSIR, a Near InfraRed extension to the optical
wide-field survey CFBDS. Our final objectives are to constrain ultracool
atmosphere physics by finding a statistically significant sample of objects
cooler than 650K and to explore the ultracool brown dwarf mass function
building on a well defined sample of such objects. Candidates are identified in
CFHT/WIRCam J and CFHT/MegaCam z' images using optimised psf-fitting, and we
follow them up with pointed near infrared imaging with SOFI at NTT. We finally
obtain low resolution spectroscopy of the coolest candidates to characterise
their atmospheric physics. We have so far analysed and followed up all
candidates on the first 66 square degrees of the 335 square degrees survey. We
identified 55 T-dwarfs candidates with z'-J > 3:5 and have confirmed six of
them as T-dwarfs, including 3 that are strong later-than-T8 candidates, based
on their far-red and NIR colours. We also present here the NIR spectra of one
of these ultracool dwarfs, CFBDSIR1458+1013 which confirms it as one of the
coolest brown dwarf known, possibly in the 550-600K temperature range. From the
completed survey we expect to discover 10 to 15 dwarfs later than T8, more than
doubling the known number of such objects. This will enable detailed studies of
their extreme atmospheric properties and provide a stronger statistical base
for studies of their luminosity function.Comment: A&A, Accepte
The SPHERE data center: a reference for high contrast imaging processing
The objective of the SPHERE Data Center is to optimize the scientific return
of SPHERE at the VLT, by providing optimized reduction procedures, services to
users and publicly available reduced data. This paper describes our motivation,
the implementation of the service (partners, infrastructure and developments),
services, description of the on-line data, and future developments. The SPHERE
Data Center is operational and has already provided reduced data with a good
reactivity to many observers. The first public reduced data have been made
available in 2017. The SPHERE Data Center is gathering a strong expertise on
SPHERE data and is in a very good position to propose new reduced data in the
future, as well as improved reduction procedures.Comment: SF2A proceeding
Meson Condensation in Dense Matter Revisited
The results for meson condensation in the literature vary markedly depending
on whether one uses chiral perturbation theory or the current-algebra-plus-PCAC
approach. To elucidate the origin of this discrepancy, we re-examine the role
of the sigma-term in meson condensation. We find that the resolution of the
existing discrepancy requires a knowledge of terms in the Lagrangian that are
higher order in density than hitherto considered.Comment: 10pages, USC(NT)-94-
Extrasolar planets and brown dwarfs around A--F type stars. VIII. A giant planet orbiting the young star HD113337
In the frame of the search for extrasolar planets and brown dwarfs around
early-type main-sequence stars, we present the detection of a giant planet
around the young F-type star HD113337. We estimated the age of the system to be
150 +100/-50 Myr. Interestingly, an IR excess attributed to a cold debris disk
was previously detected on this star. The SOPHIE spectrograph on the 1.93m
telescope at Observatoire de Haute-Provence was used to obtain ~300 spectra
over 6 years. We used our SAFIR tool, dedicated to the spectra analysis of A
and F stars, to derive the radial velocity variations. The data reveal a 324.0
+1.7/-3.3 days period that we attribute to a giant planet with a minimum mass
of 2.83 +- 0.24 Mjup in an eccentric orbit with e=0.46 +- 0.04. A long-term
quadratic drift, that we assign to be probably of stellar origin, is
superimposed to the Keplerian solution.Comment: 7 pages, 4 figure
A Markovian event-based framework for stochastic spiking neural networks
In spiking neural networks, the information is conveyed by the spike times,
that depend on the intrinsic dynamics of each neuron, the input they receive
and on the connections between neurons. In this article we study the Markovian
nature of the sequence of spike times in stochastic neural networks, and in
particular the ability to deduce from a spike train the next spike time, and
therefore produce a description of the network activity only based on the spike
times regardless of the membrane potential process.
To study this question in a rigorous manner, we introduce and study an
event-based description of networks of noisy integrate-and-fire neurons, i.e.
that is based on the computation of the spike times. We show that the firing
times of the neurons in the networks constitute a Markov chain, whose
transition probability is related to the probability distribution of the
interspike interval of the neurons in the network. In the cases where the
Markovian model can be developed, the transition probability is explicitly
derived in such classical cases of neural networks as the linear
integrate-and-fire neuron models with excitatory and inhibitory interactions,
for different types of synapses, possibly featuring noisy synaptic integration,
transmission delays and absolute and relative refractory period. This covers
most of the cases that have been investigated in the event-based description of
spiking deterministic neural networks
The SOPHIE search for northern extrasolar planets VIII. A warm Neptune orbiting HD164595
High-precision radial velocity surveys explore the population of low-mass
exoplanets orbiting bright stars. This allows accurately deriving their orbital
parameters such as their occurrence rate and the statistical distribution of
their properties. Based on this, models of planetary formation and evolution
can be constrained. The SOPHIE spectrograph has been continuously improved in
past years, and thanks to an appropriate correction of systematic instrumental
drift, it is now reaching 2 m/s precision in radial velocity measurements on
all timescales. As part of a dedicated radial velocity survey devoted to search
for low-mass planets around a sample of 190 bright solar-type stars in the
northern hemisphere, we report the detection of a warm Neptune with a minimum
mass of 16.1 +- 2.7 Mearth orbiting the solar analog HD164595 in 40 +- 0.24
days . We also revised the parameters of the multiplanetary system around
HD190360. We discuss this new detection in the context of the upcoming space
mission CHEOPS, which is devoted to a transit search of bright stars harboring
known exoplanets.Comment: 11 pages, 9 figure
Numerical Solution of Differential Equations by the Parker-Sochacki Method
A tutorial is presented which demonstrates the theory and usage of the
Parker-Sochacki method of numerically solving systems of differential
equations. Solutions are demonstrated for the case of projectile motion in air,
and for the classical Newtonian N-body problem with mutual gravitational
attraction.Comment: Added in July 2010: This tutorial has been posted since 1998 on a
university web site, but has now been cited and praised in one or more
refereed journals. I am therefore submitting it to the Cornell arXiv so that
it may be read in response to its citations. See "Spiking neural network
simulation: numerical integration with the Parker-Sochacki method:" J. Comput
Neurosci, Robert D. Stewart & Wyeth Bair and
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2717378
The SOPHIE search for northern extrasolar planets VIII. Follow-up of ELODIE candidates: long-period brown-dwarf companions
Long-period brown dwarf companions detected in radial velocity surveys are
important targets for direct imaging and astrometry to calibrate the
mass-luminosity relation of substellar objects. Through a 20-year radial
velocity monitoring of solar-type stars that began with ELODIE and was extended
with SOPHIE spectrographs, giant exoplanets and brown dwarfs with orbital
periods longer than ten years are discovered. We report the detection of five
new potential brown dwarfs with minimum masses between 32 and 83 Jupiter mass
orbiting solar-type stars with periods longer than ten years. An upper mass
limit of these companions is provided using astrometric Hipparcos data,
high-angular resolution imaging made with PUEO, and a deep analysis of the
cross-correlation function of the main stellar spectra to search for blend
effects or faint secondary components. These objects double the number of known
brown dwarf companions with orbital periods longer than ten years and reinforce
the conclusion that the occurrence of such objects increases with orbital
separation. With a projected separation larger than 100 mas, all these brown
dwarf candidates are appropriate targets for high-contrast and high angular
resolution imaging.Comment: 17 pages, 9 figures, accepted in A&
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