The results of a pilot study on the intrinsic 3D distribution of stars in edge-on disk galaxies are presented. The 3D disk structure of a sample of 12 edge-on galaxies has been reconstructed through a direct deprojection of the observed two-dimensional images. The deprojection method – which utilises the so called Fourier slice theorem and assumes axial symmetry – has been tested with a large set of artificial galaxy models seen under a variety of inclinations (i = 80–90°) and with different spatial dust and optical depths distributions.

We identify disk features (spiral arms, bars, or edge-on disks) in a significant fraction of Virgo cluster early-type dwarfs. These galaxies are disk-shaped and are an unrelaxed cluster population that possibly formed out of infalling progenitors. Some display spiral arms with grand design features that cannot be the mere remainders of potential late-type spiral progenitors.

The luminosity function (LF) is one of the most fundamental quantities to be observed in Astronomy. It is determined by the combined effects of the various physical phenomena that drive galaxy formation and evolution, therefore it is a very useful tool to constrain cosmological models.

Episodic activity in super-massive black holes is shown by radio galaxies exhibiting ‘double-double’ radio morphologies (Subrahmanyan et al. 1996, Schoenmakers et al. 2000). Spectacular examples showing a renewal of beam activity in the form of new beams emerging within relic radio lobes of previous activity have placed the phenomenon of recurrence in AGN outflows on a firm footing.

By using the SUMSS and WENSS GRG samples, we infer that on timescales of order a few million years, low luminosity radio sources are more likely to exhibit episodic behaviour in the accretion on to their supermassive black holes as compared to the more powerful radio galaxies.

The parallax of the Pleiades has been mired in controversy ever since the very first astrometric measures in the late 1880s. Over a century later, the measures from the HIPPARCOS catalogue gave results which were inconsistent with the distance inferred from the fitting of the colour-magnitude diagram. We briefly review here the debate and focus on the various attempts made at solving the problem, and especially those using binary stars. The only double-lined eclipsing binary found so far in the Pleiades, HD 23642, provides not only the final answer to the problem but also, through detailed state-of-the-art analyses, the fundamental calibration for binaries in more distant clusters and hence in the Local Group. We discuss some of the various sources of systematic uncertainties that limit, so far, the accuracy of the measured stellar parameters to about 1% and the progress that is required to break this barrier.

The relation of the surface brightness, a parameter related to the apparent magnitude and the angular diameter of a star, with a colour index is used to determine various stellar parameters. Eclipsing spectroscopic binaries can even be used as a distance indicator. In this work, we use a number of low-mass eclipsing binaries, whose parameters have been accurately determined, to refine the Barnes-Evans–like relation F V − (I c − K) introduced by Amado et al. (1999), a relation more suitable for the low temperature of these cool stars.

It has been shown quite recently (Morales-Rueda et al. 2003) that dB stars, extreme horizontal branch (EHB) objects in high probability all belong to binary systems. We study in detail the mass and angular momentum loss from the giant progenitors of sdB stars in an attempt to clarify why binarity must be a crucial factor in producing EHB objects. Assuming that the progenitors of EHB objects belong to binaries with initial separations of a roughly a hundred solar radii and fill in their critical Roche lobes while close to the tip of red giant branch, we have found that considerable shrinkage of the orbit can be achieved due to a combined effect of angular momentum loss from the red giant and appreciable accretion on its low mass companion on the hydrodynamical timescale of the donor, resulting in formation of helium WD with masses roughly equal to a half solar mass and thus evading the common envelope stage. A simple approximative analytical formula for mass loss rate from Roche lobe filling giant donor has been proposed depending on mass, luminosity and radius of donor.

If the standard disk-blackbody approximation is used to estimate black hole (BH) masses in ultraluminous X-ray sources (ULXs), the inferred masses are ∼ 1000 M⊙. However, we argue that such an approximation cannot be applied to ULXs, because their disks are only radiating a small fraction of the accretion power, and are therefore cooler than they would be in a thermal-dominant state, for a given BH mass. Instead, we suggest that a different phenomenological approximation should be used, based on three observable parameters: disk luminosity, peak temperature, and ratio between thermal and non-thermal emission. This method naturally predicts masses ∼ 50 M⊙, more consistent with other theoretical and observational constraints.

The Virtual Solar Observatory (VSO) is a lightweight web service unifying twelve major solar data archives. With the VSO, users can simultaneously search for data from 50 space- and ground-based instruments covering the time period from 1915 to the present.

The products of optical wide-field survey are very valuable for their own purposes like the studies of large scale structure of galaxies, evolution of galaxies, Galactic structure and so on. At the same time optical view of sky will provide basic reference for the observation at other wavelength ranges. For this reason Palomar all sky survey has been used for various astronomical studies over 50 years. Now in the era of electronic devices, digital archives, and powerful computer systems, modern observation will replace the Palomar all sky survey.

For a long time it was believed that thermal convection could serve as the driving mechanism for turbulence and angular momentum transport in accretion disks. Even it is meanwhile accepted that convection had to leave that role to the magneto rotational instability, it is still an important effect arising in a realistic treatment of accretion disks, i.e. with proper thermodynamics and radiation transport. We review the history of thermal convection in astrophysical disks and show the relevant analytic and numerical work, including energy transport by convection and the effect of “negative” Reynolds stresses. We will also place the convective instability into the context of the magnetorotational instability and planet–disk interaction.

Stellar winds from O and WR stars transfer large amounts of mechanical energy and momentum into the interstellar medium. They sweep up and compress the interstellar material, creating interstellar bubbles. These structures are detected as optical ring nebulae, as thermal radio continuum sources, as infrared shells, as neutral gas voids and expanding shells in the HI line emission distribution, and as molecular shells.

We summarize recent numerical results on the control of the star formation efficiency (SFE), addressing the effects of turbulence and the magnetic field strength. In closed-box numerical simulations, the effect of the turbulent Mach number depends on whether the turbulence is driven or decaying: In driven regimes, increasing with all other parameters fixed decreases the SFE, while in decaying regimes the converse is true. The efficiencies in non-magnetic cases for realistic Mach numbers 10 are somewhat too high compared to observed values. Including the magnetic field can bring the SFE down to levels consistent with observations, but the intensity of the magnetic field necessary to accomplish this depends again on whether the turbulence is driven or decaying. In this kind of simulations, a lifetime of the molecular cloud (MC) needs to be assumed, being typically a few free-fall times. Further progress requires determining the true nature of the turbulence driving and the lifetimes of the clouds. Simulations of MC formation by large-scale compressions in the warm neutral medium (WNM) show that the generation of the clouds' initial turbulence is built into the accumulation process that forms them, and that the turbulence is driven for as long as accumulation process lasts, producing realistic velocity dispersions and also thermal pressures in excess of the mean WNM value. In simulations including self-gravity, but neglecting the magnetic field and stellar energy feedback, the clouds never reach an equilibrium state, but rather evolve secularly, increasing their mass and gravitational energy until they engage in generalized gravitational collapse. However, local collapse events begin midways through this process, and produce enough stellar objects to disperse the cloud or at least halt its collapse before the latter is completed. Simulations of this kind including the missing physical ingredients should contribute to a final resolution of the MC lifetime and the origin of the low SFE problems.

At the centre of the Milky Way is Sgr A*, a putative 3 million solar mass black hole with an observed luminosity that is orders of magnitude smaller than that expected from simple accretion theories. The number density of early-type stars is quite high near Sgr A*, so the ensemble of their stellar winds has a significant impact on the black hole's environment.

We present results of 3D hydrodynamic simulations of the accretion of stellar winds onto Sgr A*. Using the LANL/SAIC code, RAGE, we model the central arc-second of the Galaxy, including the central cluster stars (the S-stars) with orbits and wind parameters that match observations. A significant fraction of the winds from the S stars becomes gravitationally bound to the black hole and thus could provide enough hot gas to produce the X-ray emission seen by Chandra. We perform radiative transfer calculations on the 3D hydrodynamic data cubes and present the resulting synthetic X-ray spectrum.

We investigate the energy dependencies of X-ray quasi-periodic oscillations in black hole X-ray binaries. We analyze RXTE data on both the low- and high-frequency QPO. We construct the low-f QPO energy spectra, and demonstrate that they do not contain the thermal disk component, even though the latter is present in the time averaged spectra. The disk thus does not seem to participate in the oscillations. Moreover the QPO spectra are harder than the time averaged spectra when the latter are soft, which can be modeled as a result of modulations occurring in the hot plasma. The QPO spectra are softer than the time averaged spectra when the latter are hard. The absence of the disk component in the QPO spectra is true also for the high-frequency (hecto-Hz) QPO observed in black hole binaries. We compute the QPO spectra expected from the model of disk resonances.

Methanol masers and UCHII regions trace massive star formation sites. We have undertaken a mid-IR survey of 17 regions containing methanol masers and UCHIIs in order to locate the young stellar sources associated with them. The images were obtained from 8.7 to 18.8 μm with the mid-IR camera CID (Salas et al. 2003) on the 2.1m telescope of the Observatorio Astronomico Nacional at San Pedro Martir (Baja California, Mexico). The images were taken with a scale 0.55″/pix and the mean PSF was 1.5-2.0″(FWHM) close to the diffraction limit. We report as an example in Fig. 1 (left panel) our 18.8μm contours of IRAS 06061+2151 superimposed to the 2MASS Ks image. A young cluster of at least 4 sources has been found centered on the IRAS source (Anandarao et al. 2004). We have found two mid-IR sources coinciding with the source #2 and #4 of Anandarao et al. (2004). The source #4 is at the center of two H2 knots and a high velocity molecular outflow. The mid-IR emission from #2 is extended and coincides with the UCHII and MSX source. The methanol maser is approximately 10″ south of the source #2. The SEDs of both sources are illustrated in Fig. 1 (right panel). The IR spectral indices of source #2 and #4 are α(IR)=1.9 and 2.2 respectively.

The non-local, time-dependent convection theory of Kuhfuß (1986) in both its one- and three-equation form has been implemented in the Garching stellar evolution code. We present details of the implementation and the difficulties encountered. Specific test cases have been calculated, among them a 5 M⊙ star and the Sun. These cases point out deficits of the theory. In particular, the assumption of an isotropic velocity field leads to too extensive overshooting and has to be modified at convective boundaries. Some encouraging aspects are indicated as well.

The outer surface layers of the sun show a clear deceleration at low latitudes. This is generally thought to be the result of a strong dominance of vertical turbulent motions associated with strong downdrafts. This strong negative radial shear should not only contribute to amplifying the toroidal field locally and to expelling magnetic helicity, but it may also be responsible for producing a strong prograde pattern speed in the supergranulation layer. Using simulations of rotating stratified convection in cartesian boxes located at low latitudes around the equator it is shown that in the surface layers patterns move in the prograde direction on top of a retrograde mean background flow. These patterns may also be associated with magnetic tracers and even sunspot proper motions that are known to be prograde relative to the much slower surface plasma.

We present a detailed comparison between high resolution observations of a quiet solar region and simulated spectra in several 3-D snapshots of a realistic radiation-hydrodynamical simulation of the solar atmosphere. We find excellent agreement between the two data sets, thus providing strong support to the realism of the simulations, and confirming the high quality of the instrumentation. We propose that spatially resolved spectral data can be employed as a complementary tool to more classic analysis for investigating the hotly debated topic of solar abundances.

The VVDS Surveys aim at understanding the combined evolution of galaxies and large scale structure and have by now collected more than 35000 redshifts in four sky areas covering a total of 4.3 square degrees. They are the only surveys of this kind using a purely apparent magnitude selection, thus avoiding the intrinsic biases present in most of the high redshift color based surveys.