360 research outputs found
Metrics and spectral triples for Dirichlet and resistance forms
The article deals with intrinsic metrics, Dirac operators and spectral
triples induced by regular Dirichlet and resistance forms. We show, in
particular, that if a local resistance form is given and the space is compact
in resistance metric, then the intrinsic metric yields a geodesic space. Given
a regular Dirichlet form, we consider Dirac operators within the framework of
differential 1-forms proposed by Cipriani and Sauvageot, and comment on its
spectral properties. If the Dirichlet form admits a carr\'e operator and the
generator has discrete spectrum, then we can construct a related spectral
triple, and in the compact and strongly local case the associated Connes
distance coincides with the intrinsic metric. We finally give a description of
the intrinsic metric in terms of vector fields
High Contrast L' Band Adaptive Optics Imaging to Detect Extrasolar Planets
We are carrying out a survey to search for giant extrasolar planets around
nearby, moderate-age stars in the mid-infrared L' and M bands (3.8 and 4.8
microns, respectively), using the Clio camera with the adaptive optics system
on the MMT telescope. To date we have observed 7 stars, of a total 50 planned,
including GJ 450 (distance about 8.55pc, age about 1 billion years, no real
companions detected), which we use as our example here. We report the methods
we use to obtain extremely high contrast imaging in L', and the performance we
have obtained. We find that the rotation of a celestial object over time with
respect to a telescope tracking it with an altazimuth mount can be a powerful
tool for subtracting telescope-related stellar halo artifacts and detecting
planets near bright stars. We have carried out a thorough Monte Carlo
simulation demonstrating our ability to detect planets as small as 6 Jupiter
masses around GJ 450. The division of a science data set into two independent
parts, with companions required to be detected on both in order to be
recognized as real, played a crucial role in detecting companions in this
simulation. We mention also our discovery of a previously unknown faint stellar
companion to another of our survey targets, HD 133002. Followup is needed to
confirm this as a physical companion, and to determine its physical properties.Comment: 8 pages, 4 figure
A Framework for Classifying the Operational Risks of Outsourcing - Integrating Risks from Systems, Processes, People and External Events within the Banking Industry
Diffusion of Helpdesk Systems – The Influence of Personal Networks on the Level of Adoption
The high importance of the availability of end user computing systems raises the need for effective and efficient helpdesk systems. However, research shows that the adoption and diffusion of such systems is surprisingly low. Classical approaches to deal with this problem solely focus on the system itself, especially by focusing on the quality of the helpdesk. But this neglects the fact, that problem solving often takes place in unofficial personal networks. This aspect gains importance due to the increasing relevance of team-based work structures. Motivated by this, we present a model of adoption of helpdesk system that considers the quality of personal networks as influencing factor for the level of adoption
High-Contrast 3.8 Micron Imaging Of The Brown Dwarf/Planet-Mass Companion to GJ 758
We present L' band (3.8 ) MMT/Clio high-contrast imaging data for the
nearby star GJ 758, which was recently reported by Thalmann et al. (2009) to
have one -- possibly two-- faint comoving companions (GJ 758B and ``C",
respectively). GJ 758B is detected in two distinct datasets. Additionally, we
report a \textit{possible} detection of the object identified by Thalmann et al
as ``GJ 758C" in our more sensitive dataset, though it is likely a residual
speckle. However, if it is the same object as that reported by Thalmann et al.
it cannot be a companion in a bound orbit. GJ 758B has a H-L' color redder than
nearly all known L--T8 dwarfs. Based on comparisons with the COND evolutionary
models, GJ 758B has T 560 K and a mass
ranging from 10--20 M if it is 1 Gyr old to 25--40
M if it is 8.7 Gyr old. GJ 758B is likely in a highly eccentric orbit, e
0.73, with a semimajor axis of 44 AU. Though GJ 758B is sometimes discussed within the context of
exoplanet direct imaging, its mass is likely greater than the deuterium-burning
limit and its formation may resemble that of binary stars rather than that of
jovian-mass planets.Comment: 14 pages, 3 figures. Accepted for publication in The Astrophysical
Journal Letter
The Orbit of the Companion to HD 100453A: Binary-Driven Spiral Arms in a Protoplanetary Disk
HD 100453AB is a 10+/-2 Myr old binary whose protoplanetary disk was recently
revealed to host a global two-armed spiral structure. Given the relatively
small projected separation of the binary (1.05", or ~108 au), gravitational
perturbations by the binary seemed to be a likely driving force behind the
formation of the spiral arms. However, the orbit of these stars remained poorly
understood, which prevented a proper treatment of the dynamical influence of
the companion on the disk. We observed HD 100453AB between 2015-2017 utilizing
extreme adaptive optics systems on the Very Large Telescope and Magellan Clay
Telescope. We combined the astrometry from these observations with published
data to constrain the parameters of the binary's orbit to a=1.06"+/-0.09",
e=0.17+/-0.07, and i=32.5+/- 6.5 degrees. We utilized publicly available ALMA
CO data to constrain the inclination of the disk to i~28 degrees, which is
relatively co-planar with the orbit of the companion and consistent with
previous estimates from scattered light images. Finally, we input these
constraints into hydrodynamical and radiative transfer simulations to model the
structural evolution of the disk. We find that the spiral structure and
truncation of the circumprimary disk in HD 100453 are consistent with a
companion-dirven origin. Furthermore, we find that the primary star's rotation,
its outer disk, and the companion exhibit roughly the same direction of angular
momentum, and thus the system likely formed from the same parent body of
material.Comment: 28 pages, 11 figures, Accepted to Ap
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