90 research outputs found
Grid Databases for Shared Image Analysis in the MammoGrid Project
The MammoGrid project aims to prove that Grid infrastructures can be used for
collaborative clinical analysis of database-resident but geographically
distributed medical images. This requires: a) the provision of a
clinician-facing front-end workstation and b) the ability to service real-world
clinician queries across a distributed and federated database. The MammoGrid
project will prove the viability of the Grid by harnessing its power to enable
radiologists from geographically dispersed hospitals to share standardized
mammograms, to compare diagnoses (with and without computer aided detection of
tumours) and to perform sophisticated epidemiological studies across national
boundaries. This paper outlines the approach taken in MammoGrid to seamlessly
connect radiologist workstations across a Grid using an "information
infrastructure" and a DICOM-compliant object model residing in multiple
distributed data stores in Italy and the UKComment: 10 pages, 5 figure
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
Rotation and Macroturbulence in Metal-poor Field Red Giant and Red Horizontal Branch Stars
We report the results for rotational velocities, Vrot sin i, and
macroturbulence dispersion, zeta(RT), for 12 metal-poor field red giant branch
stars and 7 metal-poor field red horizontal branch stars. The results are based
on Fourier transform analyses of absorption line profiles from high-resolution
(R ~ 120,000), high-S/N (~ 215 per pixel) spectra obtained with the Gecko
spectrograph at CFHT. We find that the zeta(RT) values for the metal-poor RGB
stars are very similar to those for metal-rich disk giants studied earlier by
Gray and his collaborators. Six of the RGB stars have small rotational values,
less than 2.0 km/sec, while five show significant rotation, over 3 km/sec. The
fraction of rapidly rotating RHB stars is somewhat lower than found among BHB
stars. We devise two empirical methods to translate the line-broadening results
obtained by Carney et al. (2003, 2008) into Vrot sin i for all the RGB and RHB
stars they studied. Binning the RGB stars by luminosity, we find that most
metal-poor field RGB stars show no detectable sign, on average, of rotation.
However, the most luminous stars, with M(V) <= -1.5, do show net rotation, with
mean values of 2 to 4 km/sec, depending on the algorithm employed, and these
stars also show signs of radial velocity jitter and mass loss.Comment: accepted for publication in the Astronomical Journa
Discovery of a strong magnetic field in the rapidly rotating B2Vn star HR 7355
We report the detection of a strong, organized magnetic field in the
helium-variable early B-type star HR 7355 using spectropolarimetric data
obtained with ESPaDOnS on the 3.6-m Canada-France-Hawaii Telescope within the
context of the Magnetism in Massive Stars (MiMeS) Large Program. HR 7355 is
both the most rapidly rotating known main-sequence magnetic star and the most
rapidly rotating helium-strong star, with = 300 15 km s
and a rotational period of 0.5214404 0.0000006 days. We have modeled our
eight longitudinal magnetic field measurements assuming an oblique dipole
magnetic field. Constraining the inclination of the rotation axis to be between
and , we find the magnetic obliquity angle to be
between and , and the polar strength of the magnetic
field at the stellar surface to be between 13-17 kG. The photometric light
curve constructed from HIPPARCOS archival data and new CTIO measurements shows
two minima separated by 0.5 in rotational phase and occurring 0.25 cycles
before/after the magnetic extrema. This photometric behavior coupled with
previously-reported variable emission of the H line (which we confirm)
strongly supports the proposal that HR 7355 harbors a structured magnetosphere
similar to that in the prototypical helium-strong star, Ori E.Comment: 6 pages, 3 figures. Accepted for publication in MNRAS Letter
Confirmation of the Luminous Blue Variable status of MWC 930
We present spectroscopic and photometric observations of the emission-line
star MWC 930 (V446 Sct) during its long-term optical brightening in 2006--2013.
Based on our earlier data we suggested that the object has features found in
Luminous Blue Variables (LBV), such as a high luminosity (~3 10^5 Lsun, a low
wind terminal velocity (~ 140 km/s), and a tendency to show strong brightness
variations (~1 mag over 20 years). For the last ~7 years it has been exhibiting
a continuous optical and near-IR brightening along with a change of the
emission-line spectrum appearance and cooling of the star's photosphere. We
present the object's --band light curve, analyze the spectral variations,
and compare the observed properties with those of other recognized Galactic
LBVs, such as AG Car and HR Car. Overall we conclude the MWC 930 is a bona fide
Galactic LBV that is currently in the middle of an S Dor cycle.Comment: 12 pages, 7 figure
Simultaneous monitoring of the photometric and polarimetric activity of the young star PV Cep in the optical/near-infrared bands
We present the results of a simultaneous monitoring, lasting more than 2
years, of the optical and near-infrared photometric and polarimetric activity
of the variable protostar PV Cep. During the monitoring period, an outburst has
occurred in all the photometric bands, whose declining phase (J
3 mag) lasted about 120 days. A time lag of 30 days between
optical and infrared light curves has been measured and interpreted in the
framework of an accretion event. This latter is directly recognizable in the
significant variations of the near-infrared colors, that appear bluer in the
outburst phase, when the star dominates the emission, and redder in declining
phase, when the disk emission prevails. All the observational data have been
combined to derive a coherent picture of the complex morphology of the whole PV
Cep system, that, in addition to the star and the accretion disk, is composed
also by a variable biconical nebula. In particular, the mutual interaction
between all these components is the cause of the high value of the polarization
( 20%) and of its fluctuations. The observational data concur to
indicate that PV Cep is not a genuine EXor star, but rather a more complex
object; moreover the case of PV Cep leads to argue about the classification of
other recently discovered young sources in outburst, that have been considered,
maybe over-simplifying, as EXor.Comment: Accepted for publication on Ap
The Polarizing Power of the Interstellar Medium in Taurus
We present a study of the polarizing power of the dust in cold dense regions
(dark clouds) compared to that of dust in the general interstellar medium
(ISM). Our study uses new polarimetric, optical, and spectral classification
data for 36 stars to carefully study the relation between polarization
percentage (p) and extinction (A_V) in the Taurus dark cloud complex. We find
two trends in our p-A_V study: (1) stars background to the warm ISM show an
increase in p with A_V; and (2) the percentage of polarization of stars
background to cold dark clouds does not increase with extinction. We detect a
break in the p-A_V relation at an extinction 1.3 +/- 0.2 mag, which we expect
corresponds to a set of conditions where the polarizing power of the dust
associated with the Taurus dark clouds drops precipitously. This breakpoint
places important restrictions on the use of polarimetry in studying
interstellar magnetic fields.Comment: 17 pages, 2 figures, to appear in ApJLett, AASTeX was use
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