Numerical computations of wave propagation through sunspot-like magnetic field structures are critical to developing and testing methods to deduce the subsurface structure of sunspots and active regions. We show that helioseismic analysis applied to the MHD sunspot simulations of Rempel and collaborators, as well as to translation-invariant models of umbral-like fields, yield wave travel-time measurements in qualitative agreement with those obtained in real sunspots. However, standard inversion methods applied to these data fail to reproduce the true wave-speed structure beneath the surface of the model. Inversion methods which incorporate direct effects of the magnetic field, including mode conversion, may be required.

Observations of plasma and magnetic field fluctuations in the solar wind provide a valuable source of information for the study of turbulence in collisionless astrophysical plasmas. Scientific data collected by various spacecraft over the last few decades has fueled steady progress in this field. Theoretical models, numerical simulations, and comparisons between theory and experiment have also contributed greatly to these advances. This review highlights some recent advances on the observational side including measurements of the anisotropy of inertial range fluctuations as revealed by the different scaling laws parallel and perpendicular to the mean magnetic field, measurements of the normalized cross-helicity spanning the entire inertial range which demonstrate that this quantity is scale invariant, and improved measurements of the spectrum of magnetic field fluctuations in the dissipation range that show a spectral break near the lengthscale of the electron gyro-radius. The theoretical implications of these results and comparisons between theory and observations are briefly summarized.

We present a new model of emission from jets in microquasars, which implements elements from the study of jets in gamma-ray bursts to these objects. By assuming that electrons are accelerated once at the base of the jet to a power law distribution above a low energy Maxwellian, and are cooled by synchrotron emission and possible adiabatic energy losses along the jet, a wealth of spectra can be obtained. We show our theoretical results which can explain some of the key observations. In particular, we show that: (I) a flat radio spectrum, as is frequently seen, is a natural outcome of the model; (II) Strong magnetic field results in a flux decay in the optical/UV band as Fν ~ ν−1/2, irrespective of many of the uncertainties of the model. (III) An increase of the magnetic field above a critical value of ~105 G leads to a sharp decrease in the flux at the radio band, while the flux at higher frequencies saturates to a constant value. We conclude that scatter in the values of the magnetic field may provide a natural explanation to the observed scatter in the radio/X ray luminosity correlation seen in these objects.

We present the status of the BeSS database, which contains a catalogue of all known classical Be stars and a large collection of their spectra obtained at any wavelength, any epoch, and from various sources, from amateur astronomer spectra to professional high-resolution high signal-to-noise echelle spectra. Efficient data retrieval in such a heterogeneous data collection is possible with a wide range of selection criteria thanks to their storage in the fits format and via a web interface (http://basebe.obspm.fr) as well as via the Virtual Observatory. BeSS already contains over 49000 spectra and has allowed the detection of several outbursts.

As part of the Herschel Multi-tiered Extragalactic Survey we have investigated the rest-frame far-infrared (FIR) properties of a sample of more than 4800 Lyman Break Galaxies (LBGs) in the Great Observatories Origins Deep Survey North field. Most LBGs are not detected individually, but we do detect a sub-sample of 12 objects at 0.7 < z < 1.6 and one object at z = 2.0. The LBGs have been selected using color-color diagrams; the ones detected by Herschel SPIRE have redder colors than the others, while the undetected ones have colors consistent with average LBGs at z > 2.5. The spectral energy distributions of the objects detected in the rest-frame FIR are investigated using the code cigale to estimate physical parameters. We include far-UV (FUV) data from GALEX. We find that LBGs detected by SPIRE are high mass, luminous infrared galaxies. It appears that LBGs are located in a triangle-shaped region in the AFUV vs. LogLFUV = 0 diagram limited by AFUV = 0 at the bottom and by a diagonal following the temporal evolution of the most massive galaxies from the bottom-right to the top-left of the diagram. This upper envelop can be used as upper limits for the UV dust attenuation as a function of LFUV. The limits of this region are well explained using a closed-box model, where the chemical evolution of galaxies produces metals, which in turn lead to higher dust attenuation when the galaxies age.

We discuss recent progress in the helioseismic probing of the subsurface structure of solar magnetic regions. To simulate the interaction of helioseismic waves with magnetic fields and thermal perturbations we use a simple model that is translation invariant in the horizontal directions, has a realistic stratification in the vertical direction, and has physically consistent boundary conditions for the waves at the upper and lower boundaries of the computational domain. Using this model we generate synthetic helioseismic data and subsequently measure time-distance travel times. We evaluate a model for the wave-speed perturbation below sunspots that replaces the sound speed in a non-magnetic model by the fast-mode speed from a magnetic model; our results indicate that this approach is unlikely to be useful in modeling wave-speed perturbations in sunspots. We develop and test an inversion algorithm for inferring the sound-speed perturbation in magnetic regions. We show that this algorithm retrieves the correct sound-speed perturbation only when the sensitivity kernels employed account for the effects of the magnetic field on the waves and the subsurface structure.

Radiative Transfer (RT) is considered to be one of the four Grand Challenges in Computational Astrophysics aside of Astrophysical Fluid Dynamics, N-Body Problems in Astrophysics, and Relativistic Astrophysics. The high dimensionality (7D instead of 4D for MHD) and the underlying integro-differential transport equation have forced coders to implement approximative RT methods in order to fit spectra and images or to treat RT in their HD and MHD codes.

The central role of RT in star formation (SF) is based on several facts: a) The dense dusty gas in SF regions alters the radiation substantially making SF one of the most complex applications of RT. b) Radiation transports energy within the object and is therefore an essential part of any dynamical SF model. c) RT calculations tell us which of the processes/structures are visible at what wavelength by which telescope/instrument. Hence, RT is the central tool to analyze simulation results or to explore the scientific capabilities of planned instruments. d) With inverse RT, we can obtain the 1D-3D density and temperature structure from observations, completely decoupled from any (M)HD modeling (and the approximations made within).

In this review, we summarize the main difficulties and the currently used computational techniques to calculate the RT in SF regions. Recent applications of 3D continuum RT in molecular clouds and disks around young massive stars are discussed to illustrate the capabilities and limits of current RT modeling.

Preliminary results of a four-week multi-colour photometric campaign on previously identified β Cephei stars as well as newly-discovered variable stars in two respective LMC fields are presented. Besides the two targeted β Cephei stars, at least six further presumed B variables are detected. The strongest identified periods appear to lie on the longward end of the galactic β Cep instability strip, as predicted by model calculations.

Dense wind of a massive star can be partially captured by a companion neutron star (NS) creating a very turbulent and magnetized transition region at some distance from the NS surface. We consider the consequences of electron and hadron acceleration at such a transition region. Electrons lose energy on the synchrotron process and the inverse Compton (IC) scattering of thermal radiation from the NS surface and/or the massive star. We calculate the synchrotron spectra (from X-rays to soft γ-rays) and IC spectra in the case of sources accreting the matter under the accretor and propeller scenarios. It is argued that a population of accreting massive binaries, recently discovered by the INTEGRAL observatory, can be detectable by the Fermi LAT telescope. On the other hand, TeV γ-ray emission from other class of massive binaries can be interpreted in terms of a magnetar accreting matter in the propeller scenario. We also calculate the expected neutrino event rates in a km2 detector produced by relativistic hadrons accelerated in such scenario.

We present preliminary results of the radial velocity survey on going at TNG targeting binaries with similar components.

Based on the three-fluid approximation the influence of the neutral component of hydrogen plasma on Joule dissipation of electric currents are considered. As distinguished from Mestel & Spitzer (1956) and Parker (1963) it has been shown that the magnetic flux may be not conserved in the case of the “ambipolar diffusion” due to collisions between ions and neutrals. This is explained by the ion acceleration under the action of Ampere's force. Joule dissipation is determined by electron and ion collisions in a partially ionized plasma. Plasma evacuation from current sheets is the effective mechanism of its cooling. Thickness of a current sheet can achieve up to hundreds of kilometers in the solar chromosphere. The origin of the solar chromospheric jets observed with the Hinode satellite are discussed.

Jet Emitting Disc (JED) has dynamical properties quite different from both the standard and advection dominated discs. It also exhibits three different thermal equilibrium branches at a given radius: two stable (cold and hot) and one intermediate unstable. The hot solution has all the characteristics of the so-called “hot corona” generally invoked in XrB sytems in the Low/Hard states. We detail the energetics and radiative expectations of our model and show their good agreement with those observed in Cygnus X-1 in terms of jet power, jet velocity and spectral emission.

Disk scale length rd and central surface brightness μ0 for a sample of 29955 bright disk galaxies from the Sloan Digital Sky Survey have been analyzed. Cross correlation of the SDSS sample with the LEDA catalogue allowed us to investigate the variation of the scale lengths for different types of disk/spiral galaxies and present distributions and typical trends of scale lengths all the SDSS bands with linear relations that indicate the relation that connect scale lengths in one passband to another. We use the volume corrected results in the r-band and revisit the relation between these parameters and the galaxy morphology, and find the average values 〈rd〉 = 3.8 ± 2.1 kpc and 〈μ0〉 = 20.2 ± 0.7 mag arcsec−2. The derived scale lengths presented here are representative for a typical galaxy mass of 1010.8 M⊙, and the RMS dispersion is larger for more massive galaxies. We analyse the rd–μ0 plane and further investigate the Freeman Law and confirm that it indeed defines an upper limit for μ0 in bright disks (rmag < 17.0), and that disks in late type spirals (T ≥ 6) have fainter central surface brightness. Our results are based on a sample of galaxies in the local universe (z < 0.3) that is two orders of magnitudes larger than any sample previously studied, and deliver statistically significant results that provide a comprehensive test bed for future theoretical studies and numerical simulations of galaxy formation and evolution.

We present a study of the temporal changes in the sensitivities of the frequencies of the solar p-mode oscillations to corresponding changes in the levels of solar activity during Solar Cycle 23. From MDI and GONG++ full-disk Dopplergram three-day time series obtained between 1996 and 2008 we have computed a total of 221 sets of m-averaged power spectra for spherical harmonic degrees ranging up to 1000. We have then fit these 284 sets of m-averaged power spectra using our WMLTP fitting code and both symmetric Lorentzian profiles for the peaks as well as the asymmetric profile of Nigam and Kosovichev to obtain 568 tables of p-mode parameters. We then inter-compared these 568 tables, and we performed linear regression analyses of the differences in p-mode frequencies, widths, amplitudes, and asymmetries as functions of the differences in as many as ten different solar activity indices. From the linear regression analyses that we performed on the frequency difference data sets, we have discovered a new signature of the frequency shifts of the p-modes. Specifically, we have discovered that the temporal shifts of the solar oscillation frequencies are positively correlated with the changes in solar activity below a limiting frequency. They then become anti-correlated with the changes in activity for a range of frequencies before once again becoming positively-correlated with the activity changes at very high frequencies. We have also discovered that the two frequencies where the sensitivities of the temporal frequency shifts change sign also change in phase with the average level of solar activity.

Information of astronomical objects is obtained mainly through their radiation. Thus, the radiative transfer problem has a central role in all astrophysical research. Basic radiative transfer analysis or more complex modeling is needed both to interpret observations and to make predictions on the basis of numerical models. In this paper I will discuss radiative transfer in the context of interstellar molecular clouds where the main scientific questions involve the structure and evolution of the clouds and the star formation process. The studies rely on the analysis of spectral line and dust continuum observations. After a discussion of the corresponding radiative transfer methods, I will examine some of the current challenges in the field. Finally, I will present three studies where radiative transfer modeling pays a central role: the polarized dust emission, the Zeeman effect in emission lines, and the continuum emission from dense cloud cores.

We present a unified three-dimensional model of the convection zone and upper atmosphere of the Sun in spherical geometry. In this model, magnetic fields, generated by a helically forced dynamo in the convection zone, emerge without the assistance of magnetic buoyancy. We use an isothermal equation of state with gravity and density stratification. Recurrent plasmoid ejections, which rise through the outer atmosphere, is observed. In addition, the current helicity of the small–scale field is transported outwards and form large structures like magnetic clouds.

A report of a systematic search for Be star candidates in the Small Magellanic Cloud using statistical selection criteria is presented. The results are compared with those obtained with a standard photometric method to search for Be star candidates.

To form meter-sized pre-planetesimals in protoplanetary discs, dust aggregates have to decouple from the gas at a distance far enough from the central star so they are not accreted. Dust grains are affected by gas drag, which results in a vertical settling towards the mid-plane, followed by radial migration. To have a better understanding of the influence of growth on the dust dynamics, we use a simple grain growth model to determine the dust distribution in observed discs. We implement a constant growth rate into a gas+dust hydrodynamics SPH code and vary the growh rate to study the resulting effect on dust distribution. The growth rate allows us to determine the relative importance between friction and growth.We show that depending on the growth rate, a range of dust distribution can result. For large enough growth rates, grains can decouple from the gas before being accreted onto the central star, thus contributing as planetary building rocks.

Accreting neutron stars can produce jets only if they are weakly magnetized (B ~ 108 G). On the other hand, neutron stars are compact objects born with strong surface magnetic fields (B ~ 1012 G). In this work we study the conditions for jet formation in a binary system formed by a neutron star and a massive donor star once the magnetic field has decayed due to accretion. We solve the induction equation for the magnetic field diffusion in a realistic neutron star crust and discuss the possibility of jet launching in systems like the recently detected Supergiant Fast X-ray Transients.