6,646 research outputs found
Magnetic topology and surface differential rotation on the K1 subgiant of the RS CVn system HR 1099
We present here spectropolarimetric observations of the RS CVn system HR 1099
(V711 Tau) secured from 1998 February to 2002 January with the
spectropolarimeter MuSiCoS at the Telescope Bernard Lyot (Observatoire du Pic
du Midi, France). We apply Zeeman-Doppler Imaging and reconstruct brightness
and magnetic surface topologies of the K1 primary subgiant of the system, at
five different epochs. We confirm the presence of large, axisymmetric regions
where the magnetic field is mainly azimuthal, providing further support to the
hypothesis that dynamo processes may be distributed throughout the whole
convective zone in this star. We study the short-term evolution of surface
structures from a comparison of our images with observations secured at
close-by epochs by Donati et al. (2003) at the Anglo-Australian Telescope. We
conclude that the small-scale brightness and magnetic patterns undergo major
changes within a timescale of 4 to 6 weeks, while the largest structures remain
stable over several years. We report the detection of a weak surface
differential rotation (both from brightness and magnetic tracers) indicating
that the equator rotates faster than the pole with a difference in rotation
rate between the pole and the equator about 4 times smaller than that of the
Sun. This result suggests that tidal forces also impact the global dynamic
equilibrium of convective zones in cool active stars.Comment: accepted by MNRA
Analysis of the socio-economic impact of the tobacco CMO reform on italian tobacco sector
The Tobacco CMO (Common Market Organization) is involved in a intense debate between the European tobacco industry and those who are against to a crop whose transformed product is dangerous to the health. European institutions have shown a strong interest in this complex issue introducing two Reforms (1992 and 1998) and one revision in 2004. This paper aims to analyse and investigate the socio-economic impact of the tobacco CMO Reform of 2004 in Italy, across the scenarios proposed by the EC Commission (2004), both on the tobacco production and processing sector. The considered socio-economic indicators are harvested surfaces, farm income and overall employment, while the sample of farms used in this research belong to the FADNâItaly sample.Tobacco CMO, CAP reform, decoupling, Positive Mathematical Programming
Magnetic fields and differential rotation on the pre-main sequence I: The early-G star HD 141943 - brightness and magnetic topologies
Spectroscopic and spectropolarimetric observations of the pre-main sequence
early-G star HD 141943 were obtained at four observing epochs (in 2006, 2007,
2009 and 2010). The observations were undertaken at the 3.9-m Anglo-Australian
Telescope using the UCLES echelle spectrograph and the SEMPOL
spectropolarimeter visitor instrument. Brightness and surface magnetic field
topologies were reconstructed for the star using the technique of least-squares
deconvolution to increase the signal-to-noise of the data.
The reconstructed brightness maps show that HD 141943 had a weak polar spot
and a significant amount of low latitude features, with little change in the
latitude distribution of the spots over the 4 years of observations. The
surface magnetic field was reconstructed at three of the epochs from a high
order (l <= 30) spherical harmonic expansion of the spectropolarimetric
observations. The reconstructed magnetic topologies show that in 2007 and 2010
the surface magnetic field was reasonably balanced between poloidal and
toroidal components. However we find tentative evidence of a change in the
poloidal/toroidal ratio in 2009 with the poloidal component becoming more
dominant. At all epochs the radial magnetic field is predominantly
non-axisymmetric while the azimuthal field is predominantly axisymmetric with a
ring of positive azimuthal field around the pole similar to that seen on other
active stars.Comment: 18 pages, 17 figures, accepted by MNRA
Eosinophilic ulcer of the tongue - Case report.
Eosinophilic ulcer of the oral mucosa is a rare, self-limiting, chronic and benign lesion of unknown pathogenesis that affects the oral mucosa. We present the case of a 65 year-old Caucasian female with a fivemonth history of a painful ulcer on the lateral side of her tongue. The ulcer was not adhered to the underlying structures and there was no evidence of regional lymph node involvement. Laboratory examinations and X-rays revealed no abnormalities. Topical treatments had been performed without any improvement. Histopathological examination showed an ulcerated surface and mixed inflammatory infiltrate with several eosinophils extending into the mucosa and submucosa. No cellular atypia was observed. Based on the patient-s history and mucosal biopsy, a final diagnosis of eosinophilic ulcer of the oral mucosa was made
Magnetic field, differential rotation and activity of the hot-Jupiter hosting star HD 179949
HD 179949 is an F8V star, orbited by a giant planet at ~8 R* every 3.092514
days. The system was reported to undergo episodes of stellar activity
enhancement modulated by the orbital period, interpreted as caused by
Star-Planet Interactions (SPIs). One possible cause of SPIs is the large-scale
magnetic field of the host star in which the close-in giant planet orbits.
In this paper we present spectropolarimetric observations of HD 179949 during
two observing campaigns (2009 September and 2007 June). We detect a weak
large-scale magnetic field of a few Gauss at the surface of the star. The field
configuration is mainly poloidal at both observing epochs. The star is found to
rotate differentially, with a surface rotation shear of dOmega=0.216\pm0.061
rad/d, corresponding to equatorial and polar rotation periods of 7.62\pm0.07
and 10.3\pm0.8 d respectively. The coronal field estimated by extrapolating the
surface maps resembles a dipole tilted at ~70 degrees. We also find that the
chromospheric activity of HD 179949 is mainly modulated by the rotation of the
star, with two clear maxima per rotation period as expected from a highly
tilted magnetosphere. In September 2009, we find that the activity of HD 179949
shows hints of low amplitude fluctuations with a period close to the beat
period of the system.Comment: Accepted for publication in Monthly Notices of The Royal Astronomical
Societ
Dynamo models and differential rotation in late-type rapidly rotating stars
Increasing evidence is becoming available about not only the surface
differential rotation of rapidly rotating cool stars but, in a small number of
cases, also about temporal variations, which possibly are analogous to the
solar torsional oscillations. Given the present difficulties in resolving the
precise nature of such variations, due to both the short length and poor
resolution of the available data, theoretical input is vital to help assess the
modes of behaviour that might be expected, and will facilitate interpretation
of the observations. Here we take a first step in this direction by studying
the variations in the convection zones of such stars, using a two dimensional
axisymmetric mean field dynamo model operating in a spherical shell in which
the only nonlinearity is the action of the azimuthal component of the Lorentz
force of the dynamo generated magnetic field on the stellar angular velocity.
We consider three families of models with different depths of dynamo-active
regions. For moderately supercritical dynamo numbers we find torsional
oscillations that penetrate all the way down to the bottom of the convection
zones, similar to the case of the Sun. For larger dynamo numbers we find
fragmentation in some cases and sometimes there are other dynamical modes of
behaviour, including quasi-periodicity and chaos. We find that the largest
deviations in the angular velocity distribution caused by the Lorentz force are
of the order of few percent, implying that the original assumed `background'
rotation field is not strongly distorted.Comment: Astronomy and Astrophysics, in pres
Magnetic cycles of the planet-hosting star Tau Bootis: II. a second magnetic polarity reversal
In this paper, we present new spectropolarimetric observations of the
planet-hosting star Tau Bootis, using ESPaDOnS and Narval spectropolarimeters
at Canada-France-Hawaii Telescope (CFHT) and Telescope Bernard Lyot (TBL),
respectively. We detected the magnetic field of the star at three epochs in
2008. It is a weak magnetic field of only a few Gauss, oscillating between a
predominant toroidal component in January and a dominant poloidal component in
June and July. A magnetic polarity reversal was observed relative to the
magnetic topology in June 2007. This is the second such reversal observed in
two years on this star, suggesting that Tau Boo has a magnetic cycle of about 2
years. This is the first detection of a magnetic cycle for a star other than
the Sun. The role of the close-in massive planet in the short activity cycle of
the star is questioned.
Tau Boo has strong differential rotation, a common trend for stars with
shallow convective envelope. At latitude 40 deg., the surface layer of the star
rotates in 3.31 d, equal to the orbital period. Synchronization suggests that
the tidal effects induced by the planet may be strong enough to force at least
the thin convective envelope into corotation. Tau Boo shows variability in the
Ca H & K and Halpha throughout the night and on a night to night time scale. We
do not detect enhancement in the activity of the star that may be related to
the conjunction of the planet. Further data is needed to conclude about the
activity enhancement due to the planet.Comment: 9 pages, 5 figures, 3 tables Accepted to MNRA
Critical evaluation of magnetic field detections reported for pulsating B-type stars in the light of ESPaDOnS, Narval and reanalyzed FORS1/2 observations
Recent spectropolarimetric studies of 7 SPB and Cep stars have
suggested that photospheric magnetic fields are more common in B-type pulsators
than in the general population of B stars, suggesting a significant connection
between magnetic and pulsational phenomena. We present an analysis of new and
previously published spectropolarimetric observations of these stars. New
Stokes observations obtained with the high-resolution ESPaDOnS and Narval
instruments confirm the presence of a magnetic field in one of the stars
( Lup), but find no evidence of magnetism in 5 others. A re-analysis
of the published longitudinal field measurements obtained with the
low-resolution FORS1/2 spectropolarimeters finds that the measurements of all
stars show more scatter from zero than can be attributed to Gaussian noise,
suggesting the presence of a signal and/or systematic under-estimation of error
bars. Re-reduction and re-measurement of the FORS1/2 spectra from the ESO
archive demonstrates that small changes in reduction procedure lead to
substantial changes in the inferred longitudinal field, and substantially
reduces the number of field detections at the 3 level. Furthermore, we
find that the published periods are not unique solutions to the time series of
either the original or the revised FORS1/2 data. We conclude that the reported
field detections, proposed periods and field geometry models for Pyx,
15 CMa, 33 Eri and V1449 Aql are artefacts of the data analysis and reduction
procedures, and that magnetic fields at the reported strength are no more
common in SPB/ Cep stars than in the general population of B stars.Comment: 10 pages, 5 figures, accepted for publication in ApJ, 2012, typo
correcte
On the Response Function Technique for Calculating the Random-Phase Approximation Correlation Energy
We develop a scheme to exactly evaluate the correlation energy in the
random-phase approximation, based on linear response theory. It is demonstrated
that our formula is completely equivalent to a contour integral representation
recently proposed by Donau et al. being numerically more efficient for
realistic calculations. Numerical examples are presented for pairing
correlations in rapidly rotating nuclei.Comment: 4 pages, 4 figure
Radial dependence of line profile variability in seven O9--B0.5 stars
Massive stars show a variety of spectral variability: presence of discrete
absorption components in UV P-Cygni profiles, optical line profile variability,
X-ray variability, radial velocity modulations. Our goal is to study the
spectral variability of single OB stars to better understand the relation
between photospheric and wind variability. For that, we rely on high spectral
resolution, high signal-to-noise ratio optical spectra collected with the
spectrograph NARVAL on the Telescope Bernard Lyot at Pic du Midi. We
investigate the variability of twelve spectral lines by means of the Temporal
Variance Spectrum (TVS). The selected lines probe the radial structure of the
atmosphere, from the photosphere to the outer wind. We also perform a
spectroscopic analysis with atmosphere models to derive the stellar and wind
properties, and to constrain the formation region of the selected lines. We
show that variability is observed in the wind lines of all bright giants and
supergiants, on a daily timescale. Lines formed in the photosphere are
sometimes variable, sometimes not. The dwarf stars do not show any sign of
variability. If variability is observed on a daily timescale, it can also (but
not always) be observed on hourly timescales, albeit with lower amplitude.
There is a very clear correlation between amplitude of the variability and
fraction of the line formed in the wind. Strong anti-correlations between the
different part of the temporal variance spectrum are observed. Our results
indicate that variability is stronger in lines formed in the wind. A link
between photospheric and wind variability is not obvious from our study, since
wind variability is observed whatever the level of photospheric variability.
Different photospheric lines also show different degrees of variability.Comment: 13 pages, 9 figures + appendix. A&A accepted. Figures degraded for
arxiv submissio
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