We present a study of 413 early-type dwarf (dE) galaxies in the Virgo Cluster with SDSS multicolour imaging. Several dE subclasses show systematic differences in shape, clustering properties, and stellar content. We find different colour-magnitude relations for nucleated and non-nucleated dEs, as well as for dE samples populating regions of different densities.

We dicuss new Galactic ISM results and progress towards low-frequency spectroscopy

Solar coronal heating is a complex problem due to the variety of scales and physical phenomena involved, and intricacy of “boundary conditions”. Lattice models and self-organized criticality provide means to model phenomenologically some of the physics involved over a wide range of scales, and reproduce certain statistical features of solar flares. Furthermore, these models offer a basis for the study of Parker's hypothesis of coronal heating by nanoflares. We provide a short review of this approach pioneered by Lu & Hamilton (1991) and related more recent works involving lattice models.

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.

We present results of a quantitative spectral analysis of a sample comprising eleven hydrogen deficient post-AGB stars of the spectral type PG 1159 with state-of-the-art NLTE model atmospheres. For all objects high resolution spectra obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) are available. The FUV spectra of PG 1159 stars are dominated by lines of helium, carbon and oxygen, and for the first time we also identified lines of several trace elements as sulfur and silicon which allow to determine the abundances of light metals in the atmospheres of these stars. As these stars show nuclear processed former intershell matter on their surface, the determined abundances also allow us to constrain the predictions of evolutionary models and element abundances in AGB stars.

A sample of optically Bright-Rimmed Clouds (BRC) at the edge of HII regions has been observed at multiple wavelengths in order to investigate the possibility that star-formation is present. Such activity may be related to photoionisation induced shocks caused by the massive stars powering the HII regions.

The sample has been observed at radio, infrared and submillimetre wavelengths. Both molecular line studies and continuum observations have been made of the larger cloud structures and embedded sources within.

Radio and infrared continuum observations show the presence of ionised boundary layers coincident with the optically bright rims. These are responsible for the propagation of shocks into the clouds interiors, possibly triggering the collapse of cores into protostars.

Molecular line studies and submillimetre continuum observations show the presence of centrally condensed cores within the clouds, these cores have high densities and have submillimetre luminosities indicative of class 0 protostars. The total luminosities of the embedded sources reveal a set of forming intermediate to high-mass stars.

The identification of these regions as star-forming has important consequences for studies of triggered star-formation, not only does the high incidence of star formation in BRC suggest a high efficiency for Galactic triggered star-formation but the masses of the sources suggest a preferred process for the formation itself.

In the daily RATAN-600 monitoring of the radio variability of the microquasar GRS1915+105 we detected a clear correlation of the flaring radio emission and X-rays “spikes” at 2–12 keV emission (1–2 Crab) detected with RXTE (ASM data) during nine bright (200–600 mJy) radio flares in October 2005. The spectra of these flares in maximum were optically thick at ν<2.3 GHz and optically thin at ν≥2.3 GHz. During radio flares the spectra of the X-ray spikes became definitely softer than those of a quiescent radio state. Thus these data indicated transitions from very high/hard states to high/soft ones during which massive ejections are probably happened, and the ejections are detected as the radio flares.

Clusters of galaxies contain several types of diffuse radio sources with very steep radio spectra which are associated with the cluster environment, including central radio bubbles, cluster radio relics, and cluster radio halos. Radio halos and relics are found only in merging clusters. Cluster radio relics may be produced by particle acceleration in merger shocks, while radio halos, may result from electron re-acceleration by turbulence produced by mergers. Secondary production of electrons and positrons by hadronic interactions also plays a role. If cluster radio halos and relics are related to mergers, then deep low frequency radio surveys could detect 1000's of clusters. Long-wavelength radio observations have a great potential to help us understand clusters and large scale structure, and can provide a diagnostic of cluster mergers, which affect the use of clusters in cosmological and dark energy studies.

The paper reports about several actual problems of the solar wind and solar energetic particle studies. Primary focus is on unsolved questions. The clear and sharp boundary in the phase space between solar wind plasma particle populations and “solar energetic particles” does not exist. Because of this separate consideration of “solar energetic particles” has only limited applicability and needs some reservations, which should be clearly stated and not forgotten to avoid possible errors and misinterpretations, which sometimes happen in the literature. In any case, the solar wind particles often serve as a big reservoir for acceleration (or cooling) of less abundant energetic particles. Solar wind and solar energetic particles are just two selected populations (big and small) in their joint distribution functions. It is very difficult and even impossible in many instances to have demarcation between particle populations in the energy space or indicate their ultimate “origins” in the coordinate space. It is because of the absence of localized “accelerators”, “heaters” or “sources” of particles. All these three categories mentioned above often have very limited physical meaning, but sometimes they can be useful and localized in the momentum and coordinate space. We are still too far from complete knowledge and understanding of many relevant questions in this regard.

From the sample of 613 PNe used in the paper ‘Revised Diagnostic Diagrams for Planetary Nebulae’ (Riesgo & López, 2006) we have isolated a subsample of 51 PNe defined by log [H$\alpha$/[N II]]$<0$ and log [H$\alpha$/[S II]] $<0.4$. These objects have extremely intense [N II] and [S II] lines with respect to H$\alpha$ and are indicative of either very low excitation and/or high optical depth conditions, abundance effects in the case of N or cooling effects in shock excited regions, such as those expected in high velocity, collimated outflows. We have undertaken an imaging and detailed kinematic study of all the members of the subsample visible from the northern hemisphere. In this work we discuss the results and some correlations found between the anomalous line ratios in these objects and their morphological and kinematic characteristics.

The MAGPOP-ITP is a large observational project of the EU MAGPOP Network. In order to study the star formation history of dwarf galaxies, a total of 60 nights was allocated on the 4 large La Palma telescopes in the framework of an International Time Programme. The programme comprises continuum, Hα and near-infrared imaging and optical spectroscopy of quiescent and star-forming dwarfs in the field and in the Virgo Cluster. All galaxies in the sample are selected to have imaging in the UV (by GALEX) and in the optical (by SDSS), and many have additional data available in the GOLDMine database.

The aim of the programme is to study the star formation of dwarf galaxies in function of their environment and dwarf type. In this contribution, I will focus on the results obtained for dwarf elliptical galaxies (dEs) using long-slit optical spectroscopy obtained with the NOT. We derive mean luminosity-weighted ages and metallicities using Lick indices for 25 dEs.

The dEs show a large spread in both ages and metallicities, but overall they are younger and less metal-rich than normal ellipticals (Es). The [α/Fe] ratios of the dEs are compatible with solar ratios, or are even slightly underabundant, pointing at prolonged star formation histories for dEs.

We explore the thermal Sunyaev-Zel'dovich (SZ) effect of a sample of 31 clusters in the three-year data of the Wilkinson Microwave Anisotropy Probe (WMAP), and detect strong SZ signal at the ~10 σ level. By comparing the co-added SZ profile of the sample clusters with the prediction based on the X-ray observations of ROSAT and XMM-Newton, we find the SZ profiles are consistent with the isothermal β-model of intracluster medium (ICM), but the central region (<0°.2) may be contaminated by the central radio sources in the clusters. We derive a mean outer radius of the ICM distribution at ~1.2 ± 0.4rvir (68% CL). The existence of the ICM outer edge could be the first evidence of ICM accretion shock, which is important for understanding the formation and evolution of clusters. We also estimate the mean gas mass fraction of the ICM from the overall amplitude of the SZ signals as fgas = 0.10 ± 0.05, which is consistent with the X-ray observation and lower than the cosmic average baryon fraction.

We performed numerical simulation including UV radiation transfer, and investigated effects of radiation driven implosion on star formation processes. We also observed two bright-rimmed clouds with C12O(J=1-0) and C13O(J=1-0) in order to compare density distributions between numerical results and observational results. Density profiles of bright-rimmed clouds are consistent with those of numerical simulations. These facts insist that star formations in bright-rimmed clouds are triggered by radiation driven implosion.

The energetic shock waves associated with the violent large-scale structure formation process are able to accelerate relativistic electrons and protons. The induced non-thermal emission, especially at long radio wavelength, provides a fascinating perspective into structure formation, the relativistic Universe, and cosmic magnetic fields.

Based on FORS2-VLT long-slit spectroscopy, the analysis of the central absorption line indices of 9 S0 galaxies in the Fornax Cluster is presented. Central indices correlate with central velocity dispersions (σ0) as observed in ellipticals (E). However, the stellar population properties of these S0s indicates that the observed trends are produced by relative differences in age and α-element abundances and not in metallicity ([Fe/H]) as previous studies have found in E galaxies. The observed scatter in the line indices versus σ0 relations can be partially explained by the rotationally-supported nature of many of these systems. The presence of tighter line indices vs. maximum (circular) rotational velocity (VMAX) relations confirms this statement. It was also confirmed that the dynamical mass is the driving physical property of all these correlations and in our Fornax S0s it has to be estimated assuming rotational support.

We report about the multi-frequency (1–30 GHz) daily monitoring of the radio flux variability of the three microquasars: SS433, GRS1915+105 and Cyg X-3 during 2005–2006. After a quiescent radio emission we have detected a drop down of the fluxes (∼20 mJy) from Cyg X-3, a sign of the following bright flare, and indeed a 1 Jy flare was detected on 2 February 2006 after 18 days of quenched radio emission. The daily spectra of the flare in the maximum was found flat from 2 to 110 GHz, using the quasi-simultaneous observations at 109 GHz with the RT45m telescope and the NMA millimeter array of Nobeyama Radio Observatory in Japan. Several bright radio flaring events (1–15 Jy) followed during the state of highly variable and intense 1–12 keV X-ray emission (∼0.5 Crab), monitored in the RXTE ASM program. We discussed various spectral and temporal characteristics of the detected 180 day light curves from three microquasars in comparison with the Rossi XTE ASM data.

From a survey of PNs in NGC 300 we obtain its PNLF. We use it to derive a distance estimate, and briefly discuss the PNLF shape.

A brief overview of upcoming total solar eclipses in 2008–2010 is presented. Global maps illustrate the geographic region of visibility for each eclipse. In addition, preliminary weather prospects are discussed.

Smoothed Particle Hydrodynamics (SPH) simulations are a powerful tool to investigate hydrodynamical processes in astrophysics such as the formation of galactic disks. Dense gas clouds raining on the forming disk are possibly disrupted by Kelvin-Helmholtz-Instabilities (KHI). To understand the evolution of the halo clouds, we have to ascertain the capability of SPH to treat the KHI correctly, since SPH-methods tend to suffer from an innate surface tension and viscosity effects, both of which could dampen the KHI. We analytically derive a growth rate of the KHI including surface tension and viscosity in the linear regime, and compare this growth rate to results of numerical simulations by an SPH method and a grid-based method. We find that SPH in some cases suppresses the KHI (Junk et al., in prep).

Everybody understands what is meant by an eclipse: a body that covers another one. However, the general audience and the students in particular do not know exactly “What the relative positions of the Earth, the Sun and the Moon have to be in order for an eclipse to take place?”

You can read a newspaper or watch TV and observe that the information about an eclipse is not correct. In my country, it was stated, in a very important newspaper, that “the solar eclipse will take place tomorrow because there will be a Full Moon”.

Teaching this topic in schools or in educational sessions in observatories, it is a good idea to introduce a simple model that maintains the proportion between the diameters and distances of these three bodies. This contribution will introduce this model, showing their applications in the playgrounds of the school, for sunny days or in the classroom for cloudy days.