The Intriguing Nature of the Cataclysmic Variable SS Cygni

The classification of SS Cyg as a dwarf nova (DN), a subclass of the non–magnetic (NM) cataclysmic variable (CV) has been considered by most of the community as well established because of a paper appeared in Nature (Bath & van Paradijs, 1983), which was a bandwagon for all the papers discussing SS Cyg behaviour both from experimental and theoretical points of view. This classification has been widely accepted until nowadays, in spite of the many arguments and circumstantial proofs about its possible intermediate polar nature, as claimed by Franco Giovannelli’s group for more than 25 years.The goal of this paper is to present an objective discussion of the problems connected with the controversial nature of SS Cyg, using all the different interpretations of its multifrequency data in order to demonstrate beyond doubt its intermediate polar nature

X-ray Transient Sources (Multifrequency Laboratories) The Case of the Prototype A0535+26/HDE 245770

The goal of this paper is to discuss the behaviour of the X-ray transient source A0535+26 which is considered for historical reasons and for the huge amount of multifrequency data, spread over a period of 35 years, as the prototype of this class of objects. Transient sources are formed by a Be star — the primary — and a neutron star X-ray pulsar — the secondary — and constitute a sub-class of X-ray binary systems. We will emphasize the discovery of low-energy indicators of high-energy processes. They are UBVRI magnitudes and Balmer lines of the optical companion. Particular unusual activity of the primary star — usually at the periastron passage of the neutron star – indicates that an X-ray flare is drawing near. The shape and intensity of X-ray outbursts are dependent on the strength of the activity of the primary. We derive the optical orbital period of the system as 110.856 ± 0.02 days. By using the optical flare of December 5, 1981 (here after 811205-E) that triggered the subsequent X-ray outburst of December 13, 1981, we derive the ephemeris of the system as JD Popt−outb = JD0 (2, 444, 944) ± n(110.856 ± 0.02). Thus the passage of the neutron star at the periastron occurs with a periodicity of 110.856 ± 0.02 days and the different kinds of X-ray outbursts of A0535+26 — following the definitions reported in the review by Giovannelli & Sabau-Graziati (1992) — occur just after ∼ 8 days. The delay between optical and X-ray outbursts is just the transit time of the material coming out from the optical companion to reach the neutron star X-ray pulsar. The occurrence of X-ray “normal outbursts”, “anomalous outbursts” or “casual outbursts” is dependent on the activity of the Be star: “quiet state: steady stellar wind”, “excited state: stellar wind plus puffs of material”, and “expulsion of a shell”, respectively. In the latter case, the primary manifests a strong optical activity and the consequent strong X-ray outburst can occur in any orbital phase, with a preference at the periastron passage of the neutron star, because of its gravitational effects on the Be star

Proxima Centauri b: Infrared detectability in presence of stellar activity

We propose a general method to detect and characterize tidally-locked exoplanets in 1:1 spin/orbit resonance using the information coming from different infrared bands, analyzing the variation in time of the color of exoplanetary systems. We focus on the effects induced on the detectability of the system by the starspots of the active host-stars. The analysis is conducted on the Proxima Centauri system as a case study, comparing the results from a more complex 3D General Circulation Model simulation with a simple toy model. Our toy model includes the black-body emission in the infrared of the host-star, day-side and night-side of the tidally locked planet, as well as the starspots. The results are consistent with the 3D General Circulation Model and suggests that it is possible to disentangle the stellar activity effects from the presence of the planet in the exoplanetary system using the infrared color-color diagram technique

Characterization of the Intra-Unit-Cell magnetic order in Bi2Sr2CaCu2O8+d

As in YBa2Cu3O6+x and HgBa2CuO8+d, the pseudo-gap state in Bi2Sr2CaCu2O8+d is characterized by the existence of an intra-unit-cell magnetic order revealed by polarized neutron scattering technique. We report here a supplementary set of polarized neutron scattering measurements for which the direction of the magnetic moment is determined and the magnetic intensity is calibrated in absolute units. The new data allow a close comparison between bilayer systems YBa2Cu3O6+x and Bi2Sr2CaCu2O8+d and rise important questions concerning the range of the magnetic correlations and the role of disorder around optimal doping.Comment: 12 pages, 8 figures, submitted to physical review

Hormonal signals involved in the regulation of cambial activity, xylogenesis and vessel patterning in trees

The radial growth of plant stem is based on the development of cribro-vascular cambium tissues. It affects the transport efficiency of water, mineral nutrients and photoassimilates and, ultimately, also plant height. The rate of cambial cell divisions for the assembly of new xylem and phloem tissue primordia and the rate of differentiation of the primordia into mature tissues determine the amount of biomass produced and, in the case of woody species, the wood quality. These complex physiological processes proceed at a rate which depends on several factors, acting at various levels: growth regulators, resource availability and environmental factors. Several hormonal signals and, more recently, further regulatory molecules, have been shown to be involved in the induction and maintenance of cambium and the formation of secondary vascular tissues. The control of xylem cell patterning is of particular interest, because it determines the diameter of xylem vessels, which is central to the efficiency of water and nutrient transport from roots to leaves through the stem and may strongly influence the growth in height of the tree. Increasing scientific evidence have proved the role of other hormones in cambial cell activities and the study of the hormonal signals and their crosstalking in cambial cells may foster our understanding of the dynamics of xylogenesis and of the mechanism of vessel size control along the stem. In this article, the role of the hormonal signals involved in the control of cambium and xylem development in trees and their crosstalking are reviewed

Stellar turbulent convection: the multiscale nature of the solar magnetic signature

The multiscale dynamics associated with turbulent convection present in physical systems governed by very high Rayleigh numbers still remains a vividly disputed topic in the community of astrophysicists, and in general, among physicists dealing with heat transport by convection. The Sun is a very close star for which detailed observations and estimations of physical properties on the surface, connected to the processes of the underlying convection zone, are possible. This makes the Sun a unique natural laboratory in which to investigate turbulent convection in the hard turbulence regime, a regime typical of systems characterized by high values of the Rayleigh number. In particular, it is possible to study the geometry of convection using the photospheric magnetic voids (or simply voids), the quasi-polygonal quiet regions nearly devoid of magnetic elements, which cover the whole solar surface and which form the solar magnetic network. This work presents the most extensive statistics, both in the spatial scales studied (1-80 Mm) and in the temporal duration (SC 23 and SC 24), to investigate the multiscale nature of solar magnetic patterns associated with the turbulent convection of our star. We show that the size distribution of the voids, in the 1-80 Mm range, for the 317, 870 voids found in the 692 analyzed magnetograms, is basically described by an exponential function

Hormonal responses to water deficit in cambial tissues of Populus alba L.

Changes of the concentration of bioactive gibberellins and abscisic acid in the cambial region of white poplar (Populus alba L.) were investigated in one-year-old plants, to highlight how these phytohormone signals are modulated in response to water deficit. Plants were cultivated in pots outdoor and, at the time of maximum cambial growth (T0), irrigation was withdrawn for 8 d, inducing a mild water deficit, thus mimicking a condition that is recurrent in mediterranean climates when white poplar attains its maximum growth rate. The water deficit was suspended by resuming irrigation (Tmax), throughout a recovery period of two weeks (Trec). Cambial tissues were sampled at T0, Tmax and Trec. Significant changes of leaf and stem relative water content, leaf water potential, stomatal conductance, transpiration, carbon assimilation, stem shrinkage and leaf number were induced by soil water shortage, which also negatively affected cambium development. Nevertheless, these responses were almost fully reversed following the resumption of irrigation. Water deficit induced the accumulation of large amounts of abscisic acid in cambial tissues, but the hormone was brought back to pre-stress levels after the recovery period. With regard to bioactive gibberellins, GA1 was several fold more abundant than GA4 and reached the greatest level in the plants recovering from the water status imbalance. The possible functions of gibberellins and abscisic acid in the response of cambial tissues to water deficit are discussed in view of the known physiological roles and molecular mechanisms of action of these hormonal signals

Biopsy vs. brushing: comparison of two sampling methods for the detection of HPV-DNA in squamous cell carcinoma of the oral cavity

Background: HR HPV infection was proposed as aetiological factor of oral squamous cell carcinomas (OSCC). HPV frequency in OSCC is highly variable, due to the discrepancy in oral sampling procedures, HPV testing methods and inclusion criteria regarding tumour site (strictly oral cavity vs. nearby structures). Our aim was to compare HPV DNA frequency and type-specific distribution in paired cytological and histological samples of SCC strictly located in oral cavity. The correlation between HPV detection rate by each method of sampling and demographical, behavioural and clinical-pathological variables was also examined. Patients and methods: HPV DNA was detected in brushed cells and formalin-fixed paraffin-embedded biopsies obtained from 83 consecutive unselected immunocompetent adults with OSCC. HPV DNA detection was performed in all samples by nPCR followed by direct DNA sequencing and the assay INNO-LiPA HPV Genotyping. Univariate and multivariate statistics were used, including Cohen κ index to evaluate agreement between two methods and association between HPV infection and demographical, behavioural and clinical-pathological variables for each method of sampling (p < 0.05 statistically significant). Results: HPV DNA was detected in 15.7% (13/83) of brushings and 12.1% (10/83) of biopsies (p > 0.05). High risk HPV 51, 16 and 39 were genotypes more frequently detected, especially among biopsies; no concordance between two methods was found (Cohen κ index = 0.04, p = 0.34). Conclusion: A fraction of OSCC could be linked to HR HPV infection in the Mediterranean area. Although without a statistical significance, biopsy specimen demonstrated more accurate for HR HPV detection than brushing in OSCC

Neutrinos from Accreting Neutron Stars

The magnetospheres of accreting neutron stars develop electrostatic gaps with huge potential drops. Protons and ions, accelerated in these gaps along the dipolar magnetic field lines to energies greater than 100 TeV, can impact onto a surrounding accretion disc. A proton-induced cascade so develops, and $\nu$-emission is produced from charged pion decays. Using GEANT4, a computer code that tracks particles produced in high energy collisions, we have calculated the resulting $\nu$-spectrum with extensive disc shower simulations. We show that the $\nu$-spectrum produced out of the proton beam is a power law. We use this result to propose accretion-powered X-ray binaries (with highly magnetized neutron stars) as a new population of point-like $\nu$-sources for km-scale detectors, such as ICECUBE. As a particular example we discuss the case of A0535+26. We show that ICECUBE should find A0535+26 to be a periodic $\nu$-source: one for which the formation and loss of its accretion disc can be fully detected. Finally, we briefly comment on the possibility that smaller telescopes, like AMANDA, could also detect A0535+26 by folding observations with the orbital period.Comment: 7 pages, 5 figures. Updates to match accepted version in Astrophys.

The Golden Age of Cataclysmic Variables and Related Objects (Old and News)

In this paper we review cataclysmic variables (CVs) discussing several hot points about the renewing interest of today astrophysics about these sources. We will briefly discuss also about classical and recurrent novae, as well as the intriguing problem of progenitors of the Type Ia supernovae. This paper is an extended and updated version of the review by Giovannelli (2008). Because of limited length of the paper and our knowledge, this review does not pretend to be complete. However, we would like to demonstrate that the improvement on knowledge of the physics of our Universe is strictly related also with the multifrequency behaviour of CVs, which apparently in the recent past lost to have a leading position in modern astrophysics