1,486 research outputs found
Recurrent shell infall events in a B0.5e star: HD 58978 1979-1988
Infall from the circumstellar envelope onto the bright B0.5 IVe star, HD 58978 was studied. The IUE data indicate that the star was surrounded by a low and moderately ionized circumstellar shell at least 12 times between 1979 and 1988. During 6 of these episodes, the signatures of cool circumstellar material were redshifted with respect to the photosphere by 20 to 80 km/sec. The data indicate that the transition from infall to minimal shell absorption can occur in under 10 days, and are consistent either with infall phases lasting up to 6 months, or with infall episodes shorter than 10 to 15 days. The long term behavior of the shell episodes is compared with variability in the stellar wind
The constant magnetic field of xi 1 CMa: geometry or slow rotation?
We report recent observations of the sharp-lined magnetic beta Cep pulsator
xi 1 CMa (= HD 46328). The longitudinal magnetic field of this star is detected
consistently, but it is not observed to vary strongly, during nearly 5 years of
observation. In this poster we evaluate whether the nearly constant
longitudinal field is due to intrinsically slow rotation, or rather if the
stellar or magnetic geometry is responsible
Marine ecosystem services: Linking indicators to their classification
© 2014 Elsevier Ltd. All rights reserved. There is a multitude of ecosystem service classifications available within the literature, each with its own advantages and drawbacks. Elements of them have been used to tailor a generic ecosystem service classification for the marine environment and then for a case study site within the North Sea: the Dogger Bank. Indicators for each of the ecosystem services, deemed relevant to the case study site, were identified. Each indicator was then assessed against a set of agreed criteria to ensure its relevance and applicability to environmental management. This paper identifies the need to distinguish between indicators of ecosystem services that are entirely ecological in nature (and largely reveal the potential of an ecosystem to provide ecosystem services), indicators for the ecological processes contributing to the delivery of these services, and indicators of benefits that reveal the realized human use or enjoyment of an ecosystem service. It highlights some of the difficulties faced in selecting meaningful indicators, such as problems of specificity, spatial disconnect and the considerable uncertainty about marine species, habitats and the processes, functions and services they contribute to
Search for the magnetic field of the O7.5 III star xi Persei
Cyclical wind variability is an ubiquitous but as yet unexplained feature
among OB stars. The O7.5 III(n)((f)) star xi Persei is the brightest
representative of this class on the Northern hemisphere. As its prominent
cyclical wind properties vary on a rotational time scale (2 or 4 days) the star
has been already for a long time a serious magnetic candidate. As the cause of
this enigmatic behavior non-radial pulsations and/or a surface magnetic field
are suggested. We present a preliminary report on our attempts to detect a
magnetic field in this star with high-resolution measurements obtained with the
spectropolarimeter Narval at TBL, France during 2 observing runs of 5 nights in
2006 and 5 nights in 2007. Only upper limits could be obtained, even with the
longest possible exposure times. If the star hosts a magnetic field, its
surface strength should be less than about 300 G. This would still be enough to
disturb the stellar wind significantly. From our new data it seems that the
amplitude of the known non-radial pulsations has changed within less than a
year, which needs further investigation.Comment: 2 pages, 6 figures, contributed poster at IAU Symposium 259 "Cosmic
Magnetic Fields: from Planets, to Stars and Galaxies", Tenerife, Spain,
November 3-7, 200
Calculation of the average Green's function of electrons in a stochastic medium via higher-dimensional bosonization
The disorder averaged single-particle Green's function of electrons subject
to a time-dependent random potential with long-range spatial correlations is
calculated by means of bosonization in arbitrary dimensions. For static
disorder our method is equivalent with conventional perturbation theory based
on the lowest order Born approximation. For dynamic disorder, however, we
obtain a new non-perturbative expression for the average Green's function.
Bosonization also provides a solid microscopic basis for the description of the
quantum dynamics of an interacting many-body system via an effective stochastic
model with Gaussian probability distribution.Comment: RevTex, no figure
Investigating the origin of cyclical wind variability in hot, massive stars - I. On the dipolar magnetic field hypothesis
OB stars exhibit various types of spectral variability associated with wind
structures, including the apparently ubiquitous discrete absorption components
(DACs). These are proposed to be caused by either magnetic fields or non-radial
pulsations (NRPs). In this paper, we evaluate the possible relation between
large-scale, dipolar magnetic fields and the DAC phenomenon by investigating
the magnetic properties of a sample of 13 OB stars exhibiting well-documented
DAC behaviour.
Using high-precision spectropolarimetric data acquired in part in the context
of the Magnetism in Massive Stars (MiMeS) project, we find no evidence for
surface dipolar magnetic fields in any of these stars. Using Bayesian
inference, we compute upper limits on the strengths of the fields and use these
limits to assess two potential mechanisms by which the field may influence wind
outflow: magnetic wind confinement and local photospheric brightness
enhancements. Within the limits we derive, both mechanisms fail to provide a
systematic process capable of producing DACs in all of the stars of our sample.
Therefore, this implies that dipolar fields are highly unlikely to be
responsible for these structures in all massive stars, meaning that some other
mechanism must come into play.Comment: 17 pages, 6 figures, accepted for publication in MNRA
The magnetic characteristics of Galactic OB stars from the MiMeS survey of magnetism in massive stars
The Magnetism in Massive Stars (MiMeS) project represents the largest
systematic survey of stellar magnetism ever undertaken. Based on a sample of
over 550 Galactic B and O-type stars, the MiMeS project has derived the basic
characteristics of magnetism in hot, massive stars. Herein we report
preliminary results.Comment: Proceedings of IAUS 302: Magnetic fields throughout stellar evolutio
Scar sarcoidosis on a finger mimicking a rapidly growing soft tissue tumour: a case report
Background: Scar sarcoidosis is a rare and uncommon but specific cutaneous manifestation of sarcoidosis. In general it arises in pre-existing scars deriving from mechanical traumas. As most surgeons dealing with scars might not be aware of cutaneous sarcoidosis and its different types of appearance the appropriate staging and treatment might be missed or at least delayed. To our knowledge this is the first case in literature of scar sarcoidosis on a finger. Case presentation: We present a case of a 33-year-old carpenter who developed scar sarcoidosis on his right index finger 4 years after the tendon of the long digital flexor got accidentally cut by an angle grinder. He was referred due to a swelling of the finger suspected to be a malignant soft tissue tumour. The circumference of the affected finger had almost doubled, adding up to 94 mm. Incision biopsy revealed typical noncaseating granulomas. Further investigation showed a systemic extent of the disease with involvement of the lung. A systemic treatment with oral steroids led to an almost full regression of the swelling with restoration of function and resolution of lung infiltrates. Conclusion: In case of a suspicious and/or progressive swelling a definite diagnosis should be achieved by biopsy within a short time to enable a proper treatment. If scar sarcoidosis is proven further investigation is necessary to exclude a systemical involvement. A surgical treatment of the swelling is not indicated.</p
Magnetic field measurements and wind-line variability of OB-type stars
Context. The first magnetic fields in O- and B-type stars that do not belong
to the Bp-star class, have been discovered. The cyclic UV wind-line
variability, which has been observed in a significant fraction of early-type
stars, is likely to be related to such magnetic fields. Aims. We attempt to
improve our understanding of massive-star magnetic fields, and observe
twenty-five carefully-selected, OB-type stars. Methods. Of these stars we
obtain 136 magnetic field strength measurements. We present the UV wind-line
variability of all selected targets and summarise spectropolarimetric
observations acquired using the MUSICOS spectropolarimeter, mounted at the TBL,
Pic du Midi, between December 1998 and November 2004. From the average Stokes I
and V line profiles, derived using the LSD method, we measure the magnetic
field strengths, radial velocities, and first moment of the line profiles.
Results. No significant magnetic field is detected in any OB-type star that we
observed. Typical 1{\sigma} errors are between 15 and 200 G. A possible
magnetic-field detection for the O9V star 10 Lac remains uncertain, because the
field measurements depend critically on the fringe- effect correction in the
Stokes V spectra. We find excess emission in UV-wind lines, centred about the
rest wavelength, to be a new indirect indicator of the presence of a magnetic
field in early B-type stars. The most promising candidates to host magnetic
fields are the B-type stars {\delta} Cet and 6 Cep, and a number of O stars.
Conclusions. Although some O and B stars have strong dipolar field, which cause
periodic variability in the UV wind-lines, such strong fields are not
widespread. If the variability observed in the UV wind-lines of OB stars is
generally caused by surface magnetic fields, these fields are either weak
(<~few hundred G) or localised.Comment: A&A publishe
The MiMeS Project: Magnetism in Massive Stars
The Magnetism in Massive Stars (MiMeS) Project is a consensus collaboration
among the foremost international researchers of the physics of hot, massive
stars, with the basic aim of understanding the origin, evolution and impact of
magnetic fields in these objects. The cornerstone of the project is the MiMeS
Large Program at the Canada-France-Hawaii Telescope, which represents a
dedication of 640 hours of telescope time from 2008-2012. The MiMeS Large
Program will exploit the unique capabilities of the ESPaDOnS spectropolarimeter
to obtain critical missing information about the poorly-studied magnetic
properties of these important stars, to confront current models and to guide
theory.Comment: 6 pages, 3 figures, proceedings of IAUS 259: Cosmic Magnetic Field
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