131 research outputs found
Magnetism, rotation and accretion in Herbig Ae-Be stars
Studies of stellar magnetism at the pre-main sequence phase can provide
important new insights into the detailed physics of the late stages of star
formation, and into the observed properties of main sequence stars. This is
especially true at intermediate stellar masses, where magnetic fields are
strong and globally organised, and therefore most amenable to direct study.
This talk reviews recent high-precision ESPaDOnS observations of pre-main
sequence Herbig Ae-Be stars, which are yielding qualitatively new information
about intermediate-mass stars: the origin and evolution of their magnetic
fields, the role of magnetic fields in generating their spectroscopic activity
and in mediating accretion in their late formative stages, and the factors
influencing their rotational angular momentum.Comment: 8 page
Somatostatin receptors in human adrenal gland tumors--immunohistochemical study.
Somatostatin receptors subtypes (SSTR 1-5) were demonstrated in surgically obtained adrenal gland tumors by means of immunohistochemistry (IHC). Results of the present study demonstrate that somatostatin receptors are expressed in adrenal tumors in a varied manner which is specific in each case. It provides different diagnostic and therapeutic possibilities
Magnetic deformation of the white dwarf surface structure
The influence of strong, large-scale magnetic fields on the structure and
temperature distribution in white dwarf atmospheres is investigated. Magnetic
fields may provide an additional component of pressure support, thus possibly
inflating the atmosphere compared to the non-magnetic case. Since the magnetic
forces are not isotropic, atmospheric properties may significantly deviate from
spherical symmetry. In this paper the magnetohydrostatic equilibrium is
calculated numerically in the radial direction for either for small deviations
from different assumptions for the poloidal current distribution. We generally
find indication that the scale height of the magnetic white dwarf atmosphere
enlarges with magnetic field strength and/or poloidal current strength. This is
in qualitative agreement with recent spectropolarimetric observations of
Grw+10\degr8247. Quantitatively, we find for e.g. a mean surface poloidal
field strength of 100 MG and a toroidal field strength of 2-10 MG an increase
of scale height by a factor of 10. This is indicating that already a small
deviation from the initial force-free dipolar magnetic field may lead to
observable effects. We further propose the method of finite elements for the
solution of the two-dimensional magnetohydrostatic equilibrium including
radiation transport in the diffusive approximation. We present and discuss
preliminary solutions, again indicating on an expansion of the magnetized
atmosphere.Comment: 14 pages with 14 figure
Period and period change measurements for 143 SuperWASP eclipsing binary candidates near the short-period limit and discovery of a doubly eclipsing quadruple system
Building on previous work, a new search of the SuperWASP archive was carried out to identify eclipsing binary systems near the short-period limit. 143 candidate objects were detected with orbital periods between 16 000 and 20 000 s, of which 97 are new discoveries. Period changes significant at 1σ or more were detected in 74 of these objects, and in 38 the changes were significant at 3σ or more. The significant period changes observed followed an approximately normal distribution with a half-width at half-maximum of ~0.1 s yr-1. There was no apparent relationship between period length and magnitude or direction of period change. Amongst several interesting individual objects studied, 1SWASP J093010.78+533859.5 is presented as a new doubly eclipsing quadruple system, consisting of a contact binary with a 19 674.575 s period and an Algol-type binary with a 112 799.109 s period, separated by 66.1 AU, being the sixth known system of this type
Genetic profile and clinical implications of hepatoblastoma and neuroblastoma coexistence in a child
A dominant magnetic dipole for the evolved Ap star candidate EK Eridani
EK Eri is one of the most slowly rotating active giants known, and has been
proposed to be the descendant of a strongly magnetic Ap star. We have performed
a spectropolarimetric study of EK Eri over 4 photometric periods with the aim
of inferring the topology of its magnetic field. We used the NARVAL
spectropolarimeter at the Bernard Lyot telescope at the Pic du Midi
Observatory, along with the least-squares deconvolution method, to extract high
signal-to-noise ratio Stokes V profiles from a timeseries of 28 polarisation
spectra. We have derived the surface-averaged longitudinal magnetic field Bl.
We fit the Stokes V profiles with a model of the large-scale magnetic field and
obtained Zeeman Doppler images of the surface magnetic strength and geometry.
Bl variations of up to about 80 G are observed without any reversal of its
sign, and which are in phase with photometric ephemeris. The activity
indicators are shown to vary smoothly on a timescale compatible with the
rotational period inferred from photometry (308.8 d.), however large deviations
can occur from one rotation to another. The surface magnetic field variations
of EK Eri appear to be dominated by a strong magnetic spot (of negative
polarity) which is phased with the dark (cool) photometric spot. Our modeling
shows that the large-scale magnetic field of EK Eri is strongly poloidal. For a
rotational axis inclination of i = 60{\deg}, we obtain a model that is almost
purely dipolar. In the dipolar model, the strong magnetic/photometric spot
corresponds to the negative pole of the dipole, which could be the remnant of
that of an Ap star progenitor of EK Eri. Our observations and modeling
conceptually support this hypothesis, suggesting an explanation of the
outstanding magnetic properties of EK Eri as the result of interaction between
deep convection and the remnant of an Ap star magnetic dipole.Comment: 8 pages, 6 figures, accepted for publication in Astronomy &
Astrophysic
Improved pulsating models of magnetic Ap stars I: exploring different magnetic field configurations
Magnetic perturbations to the frequencies of low degree, high radial order,
axisymmetric pulsations in stellar models permeated by large scale magnetic
fields are presented. Magnetic fields with dipolar, quadrupolar and a
superposition of aligned dipolar and quadrupolar components are considered.
The results confirm that the magnetic field may produce strong anomalies in
the power spectra of roAp stars. It is shown for the first time that anomalies
may result both from a sudden decrease or a sudden increase of a mode
frequency. Moreover, the results indicate that the anomalies depend essentially
on the geometry of the problem, i.e., on the configuration of the magnetic
field and on the degree of the modes. This dependence opens the possibility of
using these anomalies as a tool to learn about the magnetic field configuration
in the magnetic boundary layer of pulsating stars permeated by large scale
magnetic fields
Stokes IQUV Magnetic Doppler Imaging of Ap stars I. ESPaDOnS and NARVAL Observations
In this paper we describe and evaluate new spectral line polarisation
observations obtained with the goal of mapping the surfaces of magnetic Ap
stars in great detail. One hundred complete or partial Stokes IQUV sequences,
corresponding to 297 individual polarised spectra, have been obtained for 7
bright Ap stars using the ESPaDOnS and NARVAL spectropolarimeters. The targets
span a range of mass from approximately 1.8 to 3.4 solar mass, a range of
rotation period from 2.56 to 6.80 days, and a range of maximum longitudinal
magnetic field strength from 0.3 to over 4 kG. For 3 of the 7 stars, we have
obtained dense phase coverage sampling the entire rotational cycle. These
datasets are suitable for immediate magnetic and chemical abundance surface
mapping using Magnetic Doppler Imaging (MDI). For the 4 remaining stars,
partial phase coverage has been obtained, and additional observations will be
required in order to map the surfaces of these stars. The median
signal-to-noise ratio of the reduced observations is over 700 per 1.8 km\s
pixel. Spectra of all stars show Stokes V Zeeman signatures in essentially all
individual lines, and most stars show clear Stokes QU signatures in many
individual spectral lines. The observations provide a vastly improved data set
compared to previous generations of observations in terms of signal-to-noise
ratio, resolving power and measurement uncertainties. Measurement of the
longitudinal magnetic field demonstrates that the data are internally
consistent within computed uncertainties typically at the 50 to 100 sigma
level. Data are also shown to be in excellent agreement with published
observations and in qualitative agreement with the predictions of published
surface structure models. This study establishes the performance and stability
of the ESPaDOnS and NARVAL high-resolution spectropolarimeters during the
period 2006-2010.Comment: 31 pages, 35 figures, 4 tables Accepted in MNRA
Orbital period changes and the higher-order multiplicity fraction amongst SuperWASP eclipsing binaries
Orbital period changes of binary stars may be caused by the presence of a third massive body in the system. Here we have searched the archive of the Wide Angle Search for Planets (SuperWASP) project for evidence of period variations in 13 927 eclipsing binary candidates. Sinusoidal period changes, strongly suggestive of third bodies, were detected in 2% of cases; however, linear period changes were observed in a further 22% of systems. We argue on distributional grounds that the majority of these apparently linear changes are likely to reflect longer-term sinusoidal period variations caused by third bodies, and thus estimate a higher-order multiplicity fraction of 24% for SuperWASP binaries, in good agreement with other recent figures for the fraction of triple systems amongst binary stars in general
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