Rotation Modulations and Distributions of the Flare Occurrence Rates on the Surface of Five UV Ceti Type Stars

In this study, we considered stellar spots, stellar flares, and also the relation between these two magnetic proccesses that take place on UV Cet stars. In addition, the hypothesis about slow flares described by Gurzadyan (1986 Ap&SS, 125, 127) was investigated. All of these discussions were based on the results of three years of observations of UV Cet-type stars: AD Leo, EV Lac, V1005 Ori, EQ Peg, and V1054 Oph. First of all, the results show that stellar spot activity occurs on the stellar surface of EV Lac, V1005 Ori, and EQ Peg, while AD Leo does not show any short-term variability and V1054 Oph does not exhibit any variability. We report on new ephemerides for EV Lac, V1005 Ori, and EQ Peg, obtained from time-series analyses. The phases, computed at intervals of 0.10 phase length, where the mean flare occurence rates to obtain maximum amplitude; also, the phases of rotational modulation were compared in order to investigate whether there is any longitudinal relation between stellar flares and spots. Although the results show that flare events are related with spotted areas on stellar surfaces during some of the observing seasons, we did not find any clear correlation among them. Finally, it was tested whether slow flares are fast flares occurring on the opposite side of the stars according to the direction of the observers, as mentioned in a hypothesis developed by <A >Gurzadyan (1986). The flare occurence rates reveal that both slow and fast flares can occur in any rotational phases. The flare occurence rates of both fast and slow flares vary in the same way along the longitudes for all program stars. These results are not expected based on the case mentioned in the hypothesis.Comment: 24 pages, 15 figures, 6 tabels, 2011PASJ...63..427

V1135 Herculis: a double-lined eclipsing binary with an Anomalous Cepheid

BVR light curves and radial velocities for the double-lined eclipsing binary V1135\,Her were obtained. The brighter component of V1135\,Her is a Cepheid variable with a pulsation period of 4.22433$\pm$0.00026 days. The orbital period of the system is about 39.99782$\pm$0.00233 days, which is the shortest value among the known Type\,II Cepheid binaries. The observed B, V, and R magnitudes were cleaned for the intrinsic variations of the primary star. The remaining light curves, consisting of eclipses and proximity effects, are obtained. Our analyses of the multi-colour light curves and radial velocities led to the determination of fundamental stellar properties of both components of the interesting system V1135\,Her. The system consists of two evolved stars, G1+K3 between giants and supergiants, with masses of M$_1$=1.461$\pm$0.054 \Msun ~and M$_2$=0.504$\pm$0.040 {\Msun} and radii of R$_1$=27.1$\pm$0.4 {\Rsun} and R$_2$=10.4$\pm$0.2 {\Rsun}. The pulsating star is almost filling its corresponding Roche lobe which indicates the possibility of mass loss or transfer having taken place. We find an average distance of d=7500$\pm$450 pc using the BVR magnitudes and also the V-band extinction. Location in the Galaxy and the distance to the galactic plane with an amount of 1300 pc indicate that it probably belongs to the thick-disk population. Most of the observed and calculated parameters of the V1135\,Her and its location on the color-magnitude and period-luminosity diagrams lead to a classification of an Anomalous Cepheid.Comment: 25 pages, 9 Tables, 9 Figures, Accepted Revista Mexicana de Astronom\'ia y Astrof\'isica. arXiv admin note: substantial text overlap with arXiv:1211.120

Evaluating the impact of Hymenoscyphus fraxineus in Trentino (Alps, Northern Italy): first investigations

The spread of Hymenoscyphus fraxineus has been causing great concern regarding the survival of European ash (Fraxinus excelsior) throughout Europe since the 1990s. The disease was first recorded in Trentino (southern Alps, Italy) in 2012 and has spread throughout the mountain landscape, where ash trees are scattered in small and isolated stands in different valleys. The status of the disease was checked by monitoring the damage to natural regeneration and adult trees in 90 sites spread over the whole region. The survey confirmed the complete colonization by the pathogen of the whole investigated area, with high levels of damage to both young and adult ash trees. Regeneration (both seedlings and saplings) was observed to be affected by the fungus in 88 plots out of 90. Out of 4486 examined young European ashes, 2261 (50.4%) were affected and 789 (17.6%) were already dead. Ten of the 384 assayed flowering ashes (Fraxinus ornus) showed symptoms on branches and apical stems, similar to those observed for European ash. Isolation and molecular analysis proved the presence of the fungus on both symptomatic European and flowering ashes. The examined 386 adult trees showed different levels of damage, sometimes reaching more than 75% of the crown. Some individual trees (42) growing close to severely damaged trees appeared fully healthy, which suggests the possible existence of some resistant/tolerant individuals in the examined populations

Magnetic Field Effects on the Head Structure of Protostellar Jets

We present the results of 3-D SPMHD numerical simulations of supermagnetosonic, overdense, radiatively cooling jets. Two initial magnetic configurations are considered: (i) a helical and (ii) a longitudinal field. We find that magnetic fields have important effects on the dynamics and structure of radiative cooling jets, especially at the head. The presence of a helical field suppresses the formation of the clumpy structure which is found to develop at the head of purely hydrodynamical jets. On the other hand, a cooling jet embedded in a longitudinal magnetic field retains clumpy morphology at its head. This fragmented structure resembles the knotty pattern commonly observed in HH objects behind the bow shocks of HH jets. This suggests that a strong (equipartition) helical magnetic field configuration is ruled out at the jet head. Therefore, if strong magnetic fields are present, they are probably predominantly longitudinal in those regions. In both magnetic configurations, we find that the confining pressure of the cocoon is able to excite short-wavelength MHD K-H pinch modes that drive low-amplitude internal shocks along the beam. These shocks are not strong however, and it likely that they could only play a secondary role in the formation of the bright knots observed in HH jets.Comment: 14 pages, 2 Gif figures, uses aasms4.sty. Also available on the web page http://www.iagusp.usp.br/preprints/preprint.html. To appear in The Astrophysical Journal Letter