3,018 research outputs found
Nonextensivity in the solar magnetic activity during the increasing phase of solar Cycle 23
In this paper we analyze the behavior of the daily Sunspot Number from the
Sunspot Index Data Center (SIDC), the mean Magnetic Field strength from the
National Solar Observatory/Kitt Peak (NSO/KP) and Total Solar Irradiance means
from Virgo/SoHO, in the context of the --Triplet which emerges within
nonextensive statistical mechanics. Distributions for the mean solar Magnetic
Field show two different behaviors, with a --Gaussian for scales of 1 to 16
days and a Gaussian for scales longer than 32 days. The latter corresponds to
an equilibrium state. Distributions for Total Solar Irradiance also show two
different behaviors (approximately Gaussian) for scales of 128 days and longer,
consistent with statistical equilibrium and --Gaussian for scales 128
days. Distributions for the Sunspot Number show a --Gaussian independent of
timescales, consistent with a nonequilibrium state. The values obtained
("--Triplet",,)
demonstrate that the Gaussian or --Gaussian behavior of the aforementioned
data depends significantly on timescales. These results point to strong
multifractal behavior of the dataset analyzed, with the multifractal level
decreasing from Sunspot Number to Total Solar Irradiance. In addition, we found
a numerically satisfied dual relation between and .Comment: 6 pages, 4 figure
Power-law statistics and stellar rotational velocities in the Pleiades
In this paper we will show that, the non-gaussian statistics framework based
on the Kaniadakis statistics is more appropriate to fit the observed
distributions of projected rotational velocity measurements of stars in the
Pleiades open cluster. To this end, we compare the results from the
and -distributions with the Maxwellian.Comment: 13 pages, 3 figure
A snapshot of the inner dusty regions of a RCrB-type variable
R Coronae Borealis variable stars are suspected to sporadically eject
optically thick dust clouds causing, when one of them lies on the
line-of-sight, a huge brightness decline in visible light. Mid-infrared
interferometric observations of RYSgr allowed us to explore the circumstellar
regions very close to the central star (~20-40 mas) in order to look for the
signature of any heterogeneities. Using the VLTI/MIDI instrument, five
dispersed visibility curves were recorded with different projected baselines
oriented towards two roughly perpendicular directions. The large spatial
frequencies visibility curves exhibit a sinusoidal shape whereas, at shorter
spatial frequencies visibility curves follow a Gaussian decrease. These
observations are well interpreted with a geometrical model consisting in a
central star surrounded by an extended circumstellar envelope in which one
bright cloud is embedded. Within this simple geometrical scheme, the inner
110AU dusty environment of RYSgr is dominated at the time of observations by a
single dusty cloud which, at 10mic represents ~10% of the total flux of the
whole system. The cloud is located at about 100stellar radii from the centre
toward the East-North-East direction (or the symmetric direction with respect
to centre) within a circumstellar envelope which FWHM is about 120stellar
radii. This first detection of a cloud so close to the central star, supports
the classical scenario of the RCrB brightness variations in the optical
spectral domain
On the link between rotation, chromospheric activity and Li abundance in subgiant stars
The connection rotation-CaII emission flux-lithium abundance is analyzed for
a sample of bona fide subgiant stars, with evolutionary status determined from
HIPPARCOS trigonometric parallax measurements and from the Toulouse-Geneva
code.Comment: 9 pages, 8 figure
Observational constraints for Lithium depletion before the RGB
Precise Li abundances are determined for 54 giant stars mostly evolving
across the Hertzsprung gap. We combine these data with rotational velocity and
with information related to the deepening of the convective zone of the stars
to analyse their link to Li dilution in the referred spectral region. A sudden
decline in Li abundance paralleling the one already established in rotation is
quite clear. Following similar results for other stellar luminosity classes and
spectral regions, there is no linear relation between Li abundance and
rotation, in spite of the fact that most of the fast rotators present high Li
content. The effects of convection in driving the Li dilution is also quite
clear. Stars with high Li content are mostly those with an undeveloped
convective zone, whereas stars with a developed convective zone present clear
sign of Li dilution.Comment: 5 pages, 4 figures. accepted for publicatio
Lithium and magnetic fields in giants. HD 232862 : a magnetic and lithium-rich giant star
We report the detection of an unusually high lithium content in HD 232862, a
field giant classified as a G8II star, and hosting a magnetic field. With the
spectropolarimeters ESPaDOnS at CFHT and NARVAL at TBL, we have collected high
resolution and high signal-to-noise spectra of three giants : HD 232862, KU Peg
and HD 21018. From spectral synthesis we have inferred stellar parameters and
measured lithium abundances that we have compared to predictions from
evolutionary models. We have also analysed Stokes V signatures, looking for a
magnetic field on these giants. HD 232862, presents a very high abundance of
lithium (ALi = 2.45 +/- 0.25 dex), far in excess of the theoretically value
expected at this spectral type and for this luminosity class (i.e, G8II). The
evolutionary stage of HD 232862 has been precised, and it suggests a mass in
the lower part of the [1.0 Msun ; 3.5 Msun ] mass interval, likely 1.5 to 2.0
solar mass, at the bottom of the Red Giant Branch. Besides, a time variable
Stokes V signature has been detected in the data of HD 232862 and KU Peg,
pointing to the presence of a magnetic field at the surface of these two
rapidly rotating active stars.Comment: 11 pages, 9 figures ; accepted by Astronomy and Astrophysic
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