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 $q$--Triplet which emerges within nonextensive statistical mechanics. Distributions for the mean solar Magnetic Field show two different behaviors, with a $q$--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 $q$--Gaussian for scales $<$ 128 days. Distributions for the Sunspot Number show a $q$--Gaussian independent of timescales, consistent with a nonequilibrium state. The values obtained ("$q$--Triplet"$\equiv$$\{$$q$$_{stat}$,$q$$_{sen}$,$q$$_{rel}$$\}$) demonstrate that the Gaussian or $q$--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 $q_{stat}$ and $q_{sen}$.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 $\kappa$ and $q$-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