A “matrjoshka” scheme for obscuring vortex torus structure is proposed, which could help to explain the AGN radiation flares, variability and evolution.

We review some recent progresses in semi–analytic kinetic approaches to the problem of non linear particle acceleration at non relativistic shock waves.

Broadening and asymmetry of spectral lines in slowly rotating late A-type stars provide evidence for high-amplitude convective motions. The properties of turbulence observed in the A-star atmospheres are not understood theoretically and contradict results of previous numerical simulations of convection. Here we describe an ongoing effort to understand the puzzling convection signatures of A stars with the help of 3-D hydrodynamic simulations. Our approach combines realistic spectrum synthesis and non-grey hydrodynamic models computed with the CO5BOLD code. We discuss these theoretical predictions and confront them with high-resolution spectra of A stars. Our models have, for the first time, succeeded in reproducing the observed profiles of weak spectral lines without introducing fudge broadening parameters.

In this paper we describe three lines of work that are being developed in the framework of the Spanish Virtual Observatory.

In this paper I shall present ways in which professional astronomers in developing nations can aid basic education by using a few things that have been done in Mexico.

Recently the compulsory education in Mexico was increased from 6 to 12 years. An optional subject on astronomy was included in high school; so there are several ways in which one can contribute to the national education system.

I shall give a practical example on ways to teach and mention the importance of magazines and books dedicated to teachers. I will also address the way we have implemented brief courses for educators and organized conferences for science teachers.

It is important to emphasize that we must find ways to train people in a more effective way.

We have undertaken a multiwavelength project to study the properties of X-ray selected groups at intermediate redshifts (0.2 < z < 0.6). Mulchaey et al. (2006) presented the spectroscopic confirmation of nine groups. Jeltema et al. (2006) presented the X-ray properties of these groups based on observations taken with XMM-Newton. These observations confirm that these systems contain luminous, diffuse gas with luminosities and temperatures consistent with the correlations seen among groups and clusters at low redshift. We find indications of excess entropy in these systems over self-similar predictions out to large radii. We have obtained deeper spectroscopic follow-up of seven groups with the Keck and Gemini telescopes. Along with the HST imaging, we study the galaxy populations in these groups, and our main results are summarized below.

The predictions of the Padoan and Nordlund IMF model are tested using the largest simulations of supersonic hydrodynamic (HD) and magneto-hydrodynamic (MHD) turbulence to date (~10003 computational zones). The striking difference between the HD and MHD regimes, predicted by the model, is recovered.

We report an extensive search for Lyα emitters (LAEs) at z = 6.5 in the Subaru Deep Field (SDF). We carried out spectroscopic observations with Subaru/Keck to identify LAEs at z = 6.5 that were selected by narrow-band excess at 920nm. We have identified eight new LAEs based on their significantly asymmetric Lyα emission profiles. This increases the sample of spectroscopically confirmed z = 6.5 LAEs in the SDF to 17. Based on this spectroscopic sample of 17, complemented by a photometric sample of 58 LAEs, we have derived a more accurate Lyα luminosity function (LF) of LAEs at z = 6.5, which reveals an apparent deficit at the bright end, of ∼0.75 mag fainter L*, compared with that observed at z = 5.7. The difference has 3σ significance, which is reduced to 2σ when cosmic variance is taken into account. Several LAEs with high Lyα luminosity have been actually identified by spectroscopy at z<5.7, while our LAE sample at z = 6.5 has no confirmed object having such a high Lyα luminosity. The LF of the rest UV continuum, which is not sensitive to neutral IGM, of our LAE sample has almost the same as those of LAEs at z = 5.7 and i-dropouts at z≃6, even at their bright ends. This result may imply that the reionization of the universe has not been completed at z = 6.5. The decline of the Lyα LF implies the cosmic neutral fraction xHI=0.45 based on a theoretical IGM model, although this predicted value is strongly model dependent. The spatial distribution of our LAE sample was found to be homogeneous over the field, based on three independent methods to quantify the clustering strength. The composite spectrum of our LAE sample clearly reveals an asymmetric Lyα profile with an extended red wing, which can be explained by either a galactic wind model composed of double Gaussian profiles, or by a reionization model expected from the damping wing profile. Although our result has uncertainties in LAE evolution and large cosmic variance, it can be interpreted that LAEs at z = 6.5 are at the end of the reionization epoch.

We perform a 3D-MHD simulation of a self-gravitating isothermal gas layer that is initially penetrated by a uniform magnetic field. The strength of the initial magnetic field is such that the cloud is slightly subcritical. In this system, we input random supersonic turbulence initially. Ion-neutral friction is also introduced in the magnetized gas so that the magnetic diffusion allows gas to go across the magnetic field and form self-gravitating cores. We found that self-gravitating cores are formed in the dense region enhanced by the shock waves if ion-neutral friction is introduced. The time scale of core formation is on the order of the 106 years, which is faster than the usual magnetic diffusion time (107 years) estimated from the initial condition. Our result is consistent with the results of 2D-MHD simulations by Li & Nakamura (2004).

We present a spectrophotometric study of circumnuclear star forming regions (CNSFR) in the galaxies: NGC 2903, NGC 3351 and NGC 3504, all of them of over solar metallicity according to standard empirical calibrations. A detailed determination of their abundances is made after careful subtraction of the prominent underlying stellar absorption. It is found that most regions show the highest abundances in HII region-like objects. It is also shown that CNSFR, as a class, segregate from the disk HII region family, clustering around smaller η' values, and therefore higher ionizing temperatures.

From [Sii],λλ 6717,6731 Å lines, we have derived an electron density range from 180 to 650 −3, with average values of around 350 cm−3, higher than that found in Giant Extragalactic HII Regions (GEHR). The very low intensity of the [Oiii] lines (λλ 4959, 5007 Å implies high metallicity. Measurement of line temperature of [Oiii] (t[Oiii]) requires detection of auroral [Oiii]λ 4363 Å lines a few percent of [Oiii]λ 5007 Å which is impossible.

Therefore, abundances for most of the regions require the use of empirical methods. CNSFRs show values of O23 (=([Oii]3727+[Oiii]4959, 5007)/Hβ; Pagel et al., 1979. MNRAS.189.95) which indicate oversolar metallicities, but the actual values are difficult to estimate since O23 levels off. At times [Oiii] lines are very difficult to measure. The combined parameter S23/O23 (S23 = ([Sii]6717, 6731+[Siii]9069, 9532)/Hβ; Vílchez & Esteban, 1996. MNRAS.280.720) yields values of the oxygen abundances higher than twice solar. Also the N2 parameter (log([Nii]/Hβ; Denicoló, Terlevich & Terlevich, 2002. MNRAS.330.69) renders oversolar abundances. Furthermore, the CNSFRs of our sample show the highest values of the ratio N/O known for the HII region-like objects.

When we study the relation between the metallicity and the ionisation degree parametrized by the ratio [Sii]6717, 6731[Siii]9069, 9532 we find that the CNSFRs of our sample are among the HII region-like objects with the lowest ionisation parameter. Moreover, we estimate that the S23 parameter is, in this case, better than N2 to discriminate between different metallicities.

The temperature of the ionising stars can be parametrized by the “softness parameter” η' (=([Oii]3727/[Oiii]4959, 5007)/([Sii]6717, 6731/[Siii]9069, 9532); Vílchez & Pagel, 1988. MNRAS.231.257). This parameter can be used as an ionising temperature indicator. Analysing N2 vs. η' we find that the CNSFR of our sample have, in general, lower values of η' than those of the GEHRs, implying higher temperatures. In an Eta Prime Plot (log([Oii]3727/[Oiii]4959, 5007) vs. log([Sii]6717, 6731/[Siii]9069, 9532)) we can see that the CNSFRs follow the behaviour of HII galaxies rather than that of GEHR implying, again, higher temperatures.

Some general conclusions are: CNSFR spectra are difficult to analyse; they show prominent underlying stellar populations so a careful subtraction of the absorption spectrum can be critical; abundance determination mostly comes from empirical calibrations. Furthermore, some conclusions derived from line diagnostics are that CNSFR can show very high metal abundances and N/O overabundances too; they show indications of low ionization parameter; regarding the temperature of ionizing stars, CNSFRs seem to share more properties with HII galaxies than with disk GEHR, which is puzzling.

Basic properties of equipotential surfaces in test perfect fluid tori with uniform distribution of the specific angular momentum orbiting KdS black holes are summarized. The central mass-densities of adiabatic non-relativistic tori, for which the approximation of test fluid is adequate, are given and compared with the typical densities of Giant Molecular Clouds.

We report on a high-spatial-resolution survey for binary stars in the periphery of the Orion Nebula Cluster, at 5–15 arcmin (0.65 – 2 pc) from the cluster center. We observed 228 stars with adaptive optics systems, in order to find companions at separations of 0.13 – 1.12 arcsec (60 – 500 AU), and detected 13 new binaries. Combined with the results of Petr (1998), we have a sample of 275 objects, about half of which have masses from the literature and high probabilities to be cluster members. We used an improved method to derive the completeness limits of the observations, which takes into account the elongated point spread function of stars at relatively large distances from the adaptive optics guide star. The multiplicity of stars with masses >2 M⊙ is found to be significantly larger than that of low-mass stars. The companion star frequency of low-mass stars is comparable to that of main-sequence M-dwarfs, less than half that of solar-type main-sequence stars, and 3.5 to 5 times lower than in the Taurus-Auriga and Scorpius-Centaurus star-forming regions. We find the binary frequency of low-mass stars in the periphery of the cluster to be the same or only slightly higher than for stars in the cluster core (< 3′ from θ1C Ori). This is in contrast to the prediction of the theory that the low binary frequency in the cluster is caused by the disruption of binaries due to dynamical interactions. There are two ways out of this dilemma: Either the initial binary frequency in the Orion Nebula Cluster was lower than in Taurus-Auriga, or the Orion Nebula Cluster was originally much denser and dynamically more active. A detailed report of this work has been published in Astronomy & Astrophysics (Köhler et al. 2006).

The super-massive black hole in the Galactic Center (Sagittarius A*) is one of the most exciting targets in the sky. At a distance of ∼ 8 kpc it is about one hundred times closer than the second nearest nucleus of a similar galaxy, M31, and therefore the closest galactic nucleus that we can study. Here we report on the modeling of polarized near-infrared flare emission from SgrA* using a model in which a hot spot is moving on a relativistic orbit around the massive black hole. We also summarize the results from simultaneous radio/near-infrared/X-ray measurements of flare emission.

Poor groups are common and interactive environments for galaxies, and thus are important laboratories for studying galaxy evolution. Unfortunately, little is known about groups at z ≥ 0.1, because of the difficulty in identifying them in the first place. Here we present results from our ongoing survey of the environments of strong gravitational lenses, in which we have so far discovered six distant (z ≥ 0.5) groups of galaxies. As in the local Universe, the highest velocity dispersion groups contain a brightest member spatially coincident with the group centroid, whereas lower-dispersion groups tend to have an offset brightest group galaxy. This suggests that higher-dispersion groups are more dynamically relaxed than lower-dispersion groups and that at least some evolved groups exist by z ~ 0.5. We also compare the galaxy and hot gas kinematics with those of similarly distant clusters and of nearby groups.

One of the most interesting constraints on star formation models comes from the study of multiplicity of young stars as a function of mass. While multiplicity studies of low-mass T Tauri stars have been quite exhaustive, an unbiased and systematic investigation of multiplicity among intermediate-mass Herbig Ae/Be (HAEBE) stars is still lacking. We are therefore conducting a photometric and spectroscopic survey of HAEBE stars to detect companions, establish their physical association with the primary and investigate their properties. The frequency and degree of multiplicity of HAEBE systems will provide new constraints on their formation mechanisms. In this paper we present preliminary results of the high resolution imaging part of the survey, carried out with the adaptive optics system Altair-NIRI on Gemini North. Of 72 stars observed, we find 44 possible binaries or multiples, including at least 25 not previously known.

We use sticky-particle simulations to estimate the bar pattern speeds in disk galaxies over a wide range of Hubble types. For early types our results agree with the fast rotation found in previous kinematical measurements, while for later types significantly slower bars are found. Slow bars tend to be small, and favor less luminous galaxies, for a given bulge-to-total ratio.

Interaction and merging are the two most important driving forces of galaxy evolution. In contrast to the well studied major mergers of two large gas-rich disk galaxies, which may lead to Ultraluminous Infrared Galaxies (ULIRGs, LFIR>1012 L⊙), mergers between galaxies of unequal mass or a spiral and an elliptical (S+E mergers) are still poorly understood. These moderate luminosity mergers typically have LFIR > 1011 L⊙. Here, we present the results of our multiwavelength study of a sample of such kind of mergers, including interferometric HI and single-dish CO observations, optical and near-infrared imaging as well as optical spectroscopy.

We construct an exact and simple general relativistic model to describe a galactic disc based on a Schwarzschild disc immersed in a six dimensional space-time. The stability of this configuration is studied and we present results for the calculation of circular geodesic orbits.

Recent observations suggest that dissipationless mergers of elliptical galaxies build up the population of massive early-type galaxies (Bell et al. 2004; Faber et al. 2006). This type of merger is observed in galaxy clusters (Tran et al. 2005) and predicted by semi-analytic models which find mass assembly times significantly later than star-formation times for the most massive elliptical galaxies (de Lucia & Blaizot 2006). Here, we use a semi-analytic model of minor mergers of dark matter halos to examine the role of dry minor mergers in elliptical galaxy formation.