57 research outputs found
Direct detection of a magnetic field in the photosphere of the single M giant EK Boo: How common is magnetic activity among M giants?
We study the fast rotating M5 giant EK Boo by means of spectropolarimetry to
obtain direct and simultaneous measurements of both the magnetic field and
activity indicators, in order to infer the origin of the activity in this
fairly evolved giant. We used the new spectropolarimeter NARVAL at the Bernard
Lyot Telescope (Observatoire du Pic du Midi, France) to obtain a series of
Stokes I and Stokes V profiles for EK Boo. Using the Least Square Deconvolution
technique we were able to detect the Zeeman signature of the magnetic field. We
measured its longitudinal component by means of the averaged Stokes V and
Stokes I profiles. The spectra also permitted us to monitor the CaII K&H
chromospheric emission lines, which are well known as indicators of stellar
magnetic activity. From ten observations obtained between April 2008 and March
2009, we deduce that EK Boo has a magnetic field, which varied in the range of
-0.1 to -8 G. We also determined the initial mass and evolutionary stage of EK
Boo, based on up-to-date stellar evolution tracks. The initial mass is in the
range of 2.0-3.6 M_sun, and EK Boo is either on the asymptotic giant branch
(AGB), at the onset of the thermal pulse phase, or at the tip of the first (or
red) giant branch (RGB). The fast rotation and activity of EK Boo might be
explained by angular momentum dredge-up from the interior, or by the merging of
a binary. In addition, we observed eight other M giants, which are known as
X-ray emitters, or to be rotating fast for their class. For one of these, beta
And, presumably also an AGB star, we have a marginal detection of magnetic
field, and a longitudinal component Bl of about 1G was measured. More
observations like this will answer the question whether EK Boo is a special
case, or whether magnetic activity is, rather, more common among M giants than
expected.Comment: Accepted for publication in Astronomy & Astrophysics, 10 pages, 8
figure
Uncertain groupings: probabilistic combination of grouping data
Probabilistic approaches for data integration have much potential. We view data integration as an iterative process where data understanding gradually increases as the data scientist continuously refines his view on how to deal with learned intricacies like data conflicts. This paper presents a probabilistic approach for integrating data on groupings. We focus on a bio-informatics use case concerning homology. A bio-informatician has a large number of homology data sources to choose from. To enable querying combined knowledge contained in these sources, they need to be integrated. We validate our approach by integrating three real-world biological databases on homology in three iterations
EK Eridani: the tip of the iceberg of giants which have evolved from magnetic Ap stars
We observe the slowly-rotating, active, single giant, EK Eri, to study and
infer the nature of its magnetic field directly. We used the spectropolarimeter
NARVAL at the Telescope Bernard Lyot, Pic du Midi Observatory, and the Least
Square Deconvolution method to create high signal-to-noise ratio Stokes V
profiles. We fitted the Stokes V profiles with a model of the large-scale
magnetic field. We studied the classical activity indicators, the CaII H and K
lines, the CaII infrared triplet, and H\alpha line. We detected the Stokes V
signal of EK Eri securely and measured the longitudinal magnetic field Bl for
seven individual dates spanning 60% of the rotational period. The measured
longitudinal magnetic field of EK Eri reached about 100 G and was as strong as
fields observed in RSCVn or FK Com type stars: this was found to be
extraordinary when compared with the weak fields observed at the surfaces of
slowly-rotating MS stars or any single red giant previously observed with
NARVAL. From our modeling, we infer that the mean surface magnetic field is
about 270 G, and that the large scale magnetic field is dominated by a poloidal
component. This is compatible with expectations for the descendant of a
strongly magnetic Ap star.Comment: 8 pages, 6 figures. Accepted for publication in A&
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Health âBrexternalitiesâ: The Brexit effect on health and health care outside the UK
The principal effects of Brexit on health and health care will fall within the United Kingdom, and all forms of Brexit have overwhelmingly negative implications for health care and health within the UK. This article focuses on the external effects of Brexit (âBrexternalitiesâ) for health and health care. The EU is a particularly powerful institutional and legal arrangement for managing economic and political externalities, in health policy as in any other policy. Equally, when a state leaves the EU, the manner of leaving will result in better or worse management of relevant externalities. âBrexternalitiesâ thus involve questions about policy legitimacy and accountability. Health âBrexternalitiesâ do not fall equally in all EU countries. They are felt more distinctly in the context of those elements of health policy that are most closely entwined with the UKâs health policy: for instance, on the island of Ireland; certain areas of Spain and other parts of southern Europe. Some health âBrexternalitiesâ, such as in medicines safety, will be imposed on the whole population of the EU. And some health âBrexternalitiesâ, such as communicable disease control, will be felt globally
Supporting User-Defined Functions on Uncertain Data
Uncertain data management has become crucial in many sensing and scientific applications. As user-defined functions (UDFs) become widely used in these applications, an important task is to capture result uncertainty for queries that evaluate UDFs on uncertain data. In this work, we provide a general framework for supporting UDFs on uncertain data. Specifically, we propose a learning approach based on Gaussian processes (GPs) to compute approximate output distributions of a UDF when evaluated on uncertain input, with guaranteed error bounds. We also devise an online algorithm to compute such output distributions, which employs a suite of optimizations to improve accuracy and performance. Our evaluation using both real-world and synthetic functions shows that our proposed GP approach can outperform the state-of-the-art sampling approach with up to two orders of magnitude improvement for a variety of UDFs. 1
Discovery of a weak magnetic field in the photosphere of the single giant Pollux
Aims: We observe the nearby, weakly-active single giant, Pollux, in order to
directly study and infer the nature of its magnetic field. Methods: We used the
new generation spectropolarimeters ESPaDOnS and NARVAL to observe and detect
circular polarization within the photospheric absorption lines of Pollux. Our
observations span 18 months from 2007-2009. We treated the spectropolarimetric
data using the Least-Squares Deconvolution method to create high
signal-to-noise ratio mean Stokes V profiles. We also measured the classical
activity indicator S-index for the Ca H&K lines, and the stellar radial
velocity (RV). Results: We have unambiguously detected a weak Stokes V signal
in the spectral lines of Pollux, and measured the related surface-averaged
longitudinal magnetic field Bl. The longitudinal field averaged over the span
of the observations is below one gauss. Our data suggest variations of the
longitudinal magnetic field, but no significant variation of the S-index. We
observe variations of RV which are qualitatively consistent with the published
ephemeris for a proposed exoplanet orbiting Pollux. The observed variations of
Bl appear to mimic those of RV, but additional data for this relationship to be
established. Using evolutionary models including the effects of rotation, we
derive the mass of Pollux and we discuss its evolutionary status and the origin
of its magnetic field. Conclusions: This work presents the first direct
detection of the magnetic field of Pollux, and demonstrates that ESPaDOnS and
NARVAL are capable of obtaining sub-G measurements of the surface-averaged
longitudinal magnetic field of giant stars, and of directly studying the
relationships between magnetic activity, stellar evolution and planet hosting
of these stars.Comment: 8 pages, 6 figures, accepted for publication in Astronomy and
Astrophysic
Systematic detection of magnetic fields in massive, late-type supergiants
We report the systematic detection of magnetic fields in massive (M > 5
M) late-type supergiants, using spectropolarimetric observations
obtained with ESPaDOnS at the Canada-France-Hawaii Telescope. Our observations
reveal detectable Stokes V Zeeman signatures in Least-Squares Deconvolved mean
line profiles in one-third of the observed sample of more than 30 stars. The
signatures are sometimes complex, revealing multiple reversals across the line.
The corresponding longitudinal magnetic field is seldom detected, although our
longitudinal field error bars are typically 0.3 G (). These
characteristics suggest topologically complex magnetic fields, presumably
generated by dynamo action. The Stokes V signatures of some targets show clear
time variability, indicating either rotational modulation or intrinsic
evolution of the magnetic field. We also observe a weak correlation between the
unsigned longitudinal magnetic field and the CaII K core emission equivalent
width of the active G2Iab supergiant ~Dra and the G8Ib supergiant
~Gem.Comment: 8 pages, 1 table, 6 figures, accepted for publication in MNRA
Identification of red high proper-motion objects in Tycho-2 and 2MASS catalogues using Virtual Observatory tools
Aims: With available Virtual Observatory tools, we looked for new M dwarfs in
the solar neighbourhood and M giants with high tangential velocities. Methods:
From an all-sky cross-match between the optical Tycho-2 and the near-infrared
2MASS catalogues, we selected objects with proper motions >50mas/yr and very
red V-Ks colours. For the most interesting targets, we collected
multi-wavelength photometry, constructed spectral energy distributions,
estimated effective temperatures and surface gravities from fits to atmospheric
models, performed time-series analysis of ASAS V-band light curves, and
assigned spectral types from low-resolution spectroscopy obtained with CAFOS at
the 2.2m Calar Alto telescope. Results: We got a sample of 59 bright red high
proper-motion objects, including fifty red giants, four red dwarfs, and five
objects reported in this work for the first time. The five new stars have
magnitudes V~10.8-11.3mag, reduced proper motions midway between known dwarfs
and giants, near-infrared colours typical of giants, and effective temperatures
Teff~2900-3400K. From our time-series analysis, we discovered a long secondary
period in Ruber 4 and an extremely long primary period in Ruber 6. With the
CAFOS spectra, we confirmed the red giant nature of Ruber 7 and 8, the last of
which seems to be one of the brightest metal-poor M giants ever identified.Comment: Accepted in Astronomy & Astrophysic
Spectropolarimetry of stars across the H-R diagram
The growing sample of magnetic stars shows a remarkable diversity in the
properties of their magnetic fields. The overall goal of current studies is to
understand the origin, evolution, and structure of stellar magnetic fields in
stars of different mass at different evolutionary stages. In this chapter we
discuss recent measurements together with the underlying assumptions in the
interpretation of data and the requirements, both observational and
theoretical, for obtaining a realistic overview of the role of magnetic fields
in various types of stars.Comment: 23 pages, 3 figures, chapter 7 of "Astronomical Polarisation from the
Infrared to Gamma Rays", published in Astrophysics and Space Science Library
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