613 research outputs found
CHARA/MIRC observations of two M supergiants in Perseus OB1: temperature, Bayesian modeling, and compressed sensing imaging
Two red supergiants of the Per OB1 association, RS Per and T Per, have been
observed in H band using the MIRC instrument at the CHARA array. The data show
clear evidence of departure from circular symmetry. We present here new
techniques specially developed to analyze such cases, based on state-of-the-art
statistical frameworks. The stellar surfaces are first modeled as limb-darkened
discs based on SATLAS models that fit both MIRC interferometric data and
publicly available spectrophotometric data. Bayesian model selection is then
used to determine the most probable number of spots. The effective surface
temperatures are also determined and give further support to the recently
derived hotter temperature scales of red su- pergiants. The stellar surfaces
are reconstructed by our model-independent imaging code SQUEEZE, making use of
its novel regularizer based on Compressed Sensing theory. We find excellent
agreement between the model-selection results and the reconstructions. Our
results provide evidence for the presence of near-infrared spots representing
about 3-5% of the stellar flux
Magnetospheric Accretion and Ejection of Matter in Resistive Magnetohydrodynamic Simulations
The ejection of matter in the close vicinity of a young stellar object is
investigated, treating the accretion disk as a gravitationally bound reservoir
of matter. By solving the resistive MHD equations in 2D axisymmetry using our
version of the Zeus-3D code with newly implemented resistivity, we study the
effect of magnetic diffusivity in the magnetospheric accretion-ejection
mechanism. Physical resistivity was included in the whole computational domain
so that reconnection is enabled by the physical as well as the numerical
resistivity. We show, for the first time, that quasi-stationary fast ejecta of
matter, which we call {\em micro-ejections}, of small mass and angular momentum
fluxes, can be launched from a purely resistive magnetosphere. They are
produced by a combination of pressure gradient and magnetic forces, in presence
of ongoing magnetic reconnection along the boundary layer between the star and
the disk, where a current sheet is formed. Mass flux of micro-ejection
increases with increasing magnetic field strength and stellar rotation rate,
and is not dependent on the disk to corona density ratio and amount of
resistivity.Comment: 18 pages, many revisions from previous version, accepted in Ap
Rationality as the Rule of Reason
The demands of rationality are linked both to our subjective normative perspective (given that rationality is a person-level concept) and to objective reasons or favoring relations (given that rationality is non-contingently authoritative for us). In this paper, I propose a new way of reconciling the tension between these two aspects: roughly, what rationality requires of us is having the attitudes that correspond to our take on reasons in the light of our evidence, but only if it is competent. I show how this view can account for structural rationality on the assumption that intentions and beliefs as such involve competent perceptions of downstream reasons, and explore various implications of the account
Modelling of particulate matter concentrations and source contributions in the Helsinki Metropolitan Area in 2008 and 2010
We refined an urban-scale dispersion modelling system by adding a road dust suspension model, FORE. The deterministic modelling includes both vehicular exhaust emissions (including cold start and cold driving) and suspended road dust. The urban scale modelling system was used in combination with the regional scale chemical transport model LOTOSEUROS, for 2008, and the measured regional background concentrations, for 2010. The predictions were compared against measured concentrations of PM2.5 and PM10. PM2.5 concentrations were slightly and the PM10concentrations substantially under-predicted in 2008, mainly due to the under-predicted regional background concentration. Source contributions of suspended road dust varied from 2% to 8% and from 12% to 38% for PM2.5 and PM10, respectively. Long-range transported contributions at the urban traffic stations were 72% to 92% for PM2.5 and 50% to 83% for PM10. © 2016
Irregular dust features around intermediate-mass young stars with GPI: signs of youth or misaligned disks?
This is the final version. Available from the American Astronomical Society via the DOI in this recordWe are undertaking a large survey of over thirty disks using the Gemini Planet Imager (GPI) to
see whether the observed dust structures match spectral energy distribution (SED) predictions and
have any correlation with stellar properties. GPI can observe near-infrared light scattered from dust
in circumstellar environments using high-resolution Polarimetric Differential Imaging (PDI) with coronagraphy and adaptive optics. The data have been taken in J and H bands over two years, with inner
working angles of 0.08 ” and 0.11 ” respectively. Ahead of the release of the complete survey results,
here we present five objects with extended and irregular dust structures within 2 ” of the central star.
These objects are: FU Ori; MWC 789; HD 45677; Hen 3-365; and HD 139614. The observed structures are consistent with each object being a pre-main-sequence star with protoplanetary dust. The
five objects’ circumstellar environments could result from extreme youth and complex initial conditions, from asymmetric scattering patterns due to shadows cast by misaligned disks, or in some cases
from interactions with companions. We see complex Uφ structures in most objects that could indicate
multiple scattering or result from the illumination of companions. Specific key findings include the
first high-contrast observation of MWC 789 revealing a newly-discovered companion candidate and arc,
and two faint companion candidates around Hen 3-365. These two objects should be observed further
to confirm whether the companion candidates are co-moving. Further observations and modeling are
required to determine the causes of the structures.Science and Technology Facilities Council (STFC
Imaging the disc rim and a moving close-in companion candidate in the pre-transitional disc of V1247 Orionis
This is the author accepted manuscript. The final version is available from EDP Sciences via the DOI in this record.Context. V1247 Orionis harbours a pre-transitional disc with a partially cleared gap. Earlier interferometric and polarimetric observations
revealed strong asymmetries both in the gap region and in the outer disc. The presence of a companion was inferred to explain
these asymmetric structures and the ongoing disc clearing.
Aims. Using an extensive set of multi-wavelength and multi-epoch observations we aimed to identify the origin of the previously
detected asymmetries.
Methods. We observed V1247 Ori at three epochs spanning ∼ 678 days using sparse aperture masking interferometry with
Keck/NIRC2 and VLT/NACO. In addition, we search for signs of accretion through VLT/SPHERE-ZIMPOL spectral differential
imaging in Hα and R-band continuum. Our SMA sub-millimetre interferometry in 880 µm continuum and in the CO(3-2) line allows
us to constrain the orientation and direction of rotation of the outer disc.
Results. We find the L’-band emission to be dominated by static features which trace forward-scattered dust emission from the
inner edge of the outer disc located to the north-east. In H- and K-band, we see evidence for a companion candidate that moved
systematically by 45◦ within the first ∼345 days. The separation of the companion candidate is not well constrained, but the observed
position angle change is consistent with Keplerian motion of a body located on a 6 au orbit. From the SMA CO moment map, the
location of the disc rim, and the detected orbital motion, we deduced the 3-dimensional orientation of the disc. We see no indication
of accretion in Hα and set upper limits for an accreting companion.
Conclusions. The measured contrast of the companion candidate in H and K is consistent with an actively accreting protoplanet.
Hence, we identify V1247 Ori as a unique laboratory for studying companion-disc interactions and disc clearing.We acknowledge support from an ERC
Starting Grant (Grant Agreement No. 639889), STFC Rutherford Fellowship
Article number, page 14 of 17
M. Willson et al.: Imaging the disc rim and companion candidate in V1247 Ori
(ST/J004030/1), STFC Rutherford Grant (ST/K003445/1), Marie SklodowskaCurie
CIG grant (Ref. 618910), and Philip Leverhulme Prize (PLP-2013-110).
We additionally acknowledge support from NASA KPDA grants (JPL-1452321,
1474717, 1485953, 1496788). The Submillimeter Array is a joint project between
the Smithsonian Astrophysical Observatory and the Academia Sinica Institute
of Astronomy and Astrophysics and is funded by the Smithsonian Institution
and the Academia Sinica. The authors wish to recognize and acknowledge
the very significant cultural role and reverence that the summit of Mauna Kea
has always had within the indigenous Hawaiian community. We are most fortunate
to have the opportunity to conduct observations from this mountain.Some
of the data presented herein were obtained at the W.M. Keck Observatory, which
is operated as a scientific partnership among the California Institute of Technology,
the University of California and the National Aeronautics and Space
Administration. The Observatory was made possible by the generous financial
support of the W.M. Keck Foundation. J. Kluska acknowledges support from the
research council of the KU Leuven under grant number C14/17/082. M. Curé
and S. Kanaan acknowledge financial support from Centro de Astrofísica de Valparaiso.
S. Kanaan thank the support of Fondecyt iniciacíon grant No. 11130702.
T. Muto is partially supported by JSPS KAKENHI grant No. 26800106
Non-Minimal Supersymmetric Higgs Bosons at LEP2
We discuss the discovery reach of LEP2 for the Higgs sector of a general
extension of the MSSM including a single gauge singlet field. This change
introduces a new quartic Higgs boson self-coupling which can increase the
masses of the CP-even states, and also allows mixing between singlet and
non-singlet states which can reduce the couplings of the mass eigenstates to
the . The lightest CP-even Higgs boson is bounded by a parameter
which takes a maximum value GeV for top mass
GeV. We generalise the discussion of the bound to include the entire
CP-even spectrum and show how experiment may exclude values of
smaller than some . CP-even Higgs boson searches at LEP2 will be
able to exclude GeV, depending on the machine
parameters. We also present exclusion plots in the plane, based
on an analysis of CP-even, CP-odd and charged Higgs production processes at
LEP2.Comment: Plain LaTeX, 33 pages, figures uuencoded and gzipped. Trivial changes
and typos corrected for publication in Rhys Rev
Modelling the dispersion of particle numbers in five European cities
We present an overview of the modelling of particle number concentrations (PNCs) in five major European cities, namely Helsinki, Oslo, London, Rotterdam, and Athens, in 2008. Novel emission inventories of particle numbers have been compiled both on urban and European scales. We used atmospheric dispersion modelling for PNCs in the five target cities and on a European scale, and evaluated the predicted results against available measured concentrations. In all the target cities, the concentrations of particle numbers (PNs) were mostly influenced by the emissions originating from local vehicular traffic. The influence of shipping and harbours was also significant for Helsinki, Oslo, Rotterdam, and Athens, but not for London. The influence of the aviation emissions in Athens was also notable. The regional background concentrations were clearly lower than the contributions originating from urban sources in Helsinki, Oslo, and Athens. The regional background was also lower than urban contributions in traffic environments in London, but higher or approximately equal to urban contributions in Rotterdam. It was numerically evaluated that the influence of coagulation and dry deposition on the predicted PNCs was substantial for the urban background in Oslo. The predicted and measured annual average PNCs in four cities agreed within approximatelyPeer reviewe
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