We present a few results of a low-frequency southern sky survey carried out using the Mauritius Radio Telescope (MRT).

It is widely accepted that the Doppler de-boosting effects exist in counter relativistic jets. However, people often neglect another important fact that both Doppler boosting and de-boosting effects could happen in forward relativistic jets. Such effects might be used to explain some strange phenomena, such as the invisible gaps between the inner and outer jets of AGNs, and the rapid initial decays and re-brightening bumps in the light curves of GRBs.

The analysis of the R-band luminosity function of galaxies in substructures of 21 Abell clusters shows that the characteristic magnitude M* for dominant substructure is brighter than in the second substructure and the magnitude gap between two brightest galaxies in dominant substructure is larger than in the second one.

Young brown dwarfs have been identified in a significant population in various star forming regions. Some deep surveys have yielded less massive objects with planetary-mass (e.g., Oasa et al. 1999; Lucas & Roche 2000). Nevertheless, it is not yet clear how abundant these very low-mass objects are formed. S106 is one of the nearest massive star-forming regions associated with prominent bipolar nebulae and an HII region. We have conducted near-infrared photometric and spectroscopic observations of very low-mass young stellar objects (YSOs) in the S106 region.

The radio astronomical approach is applied to 2D and 3D Doppler tomography for close binary central stars in planetary nebulae. It is more effective than the traditional one.

We present first results from an HST/ACS imaging survey of stars and star clusters in five nearby spiral galaxies. This contribution concentrates on NGC 1313, a highly distorted late-type barred spiral. We compare the field star and cluster formation histories in our three ACS pointings for this galaxy. In one pointing, both the cluster and field star age distributions show clear evidence for a ramp-up in the star formation rate about 108 years ago.

We present preliminary results from a new wide-field photometric investigation of the globular cluster system of NGC 5128. NGC 5128 is the nearest giant elliptical and thus its globular cluster system serves as prototype for those of this important galaxy type. We have obtained images from IMACS at the Magellan telescope in excellent seeing that allow us to not only resolve globular clusters but derive their structural parameters. This extensive database provides a wealth of data to study the globular clusters in unprecedented detail. We discuss here the resolution of the clusters and their preliminary structural parameters.

In the present work the results of an optical spectroscopy study of 8 galaxies projected in the central part of the A1367 cluster are reported. The observations were made using the 2.2 m. Guillermo Haro Telescope in Cananea (Mexico), and the Boller and Chivens spectrograph. A catalog of the optical positions of more than 100 galaxies in the cluster is presented. The redshifts of 7 galaxies were determined from their absorption systems, while for the remaining galaxy was obtained from its strong emission lines of H-alpha, S II, O III and H-beta. For one of the galaxies the emission redshift is z= 0.015, not showing absorptions lines at the cluster redshifts (z = 0.026), which argues that it is located between the observer and the A1367 cluster.

LOFAR (Low Frequency Array) is an innovative radio telescope optimized for the frequency range 30–240 MHz. The telescope is realized as a phased aperture array without any moving parts. Digital beam forming allows the telescope to point to any part of the sky within a second. Transient buffering makes retrospective imaging of explosive short-term events possible. The scientific focus of LOFAR will initially be on four key science projects (KSPs): (i) Detection of the formation of the very first stars and galaxies in the universe during the so-called epoch of reionization by measuring the power spectrum of the neutral hydrogen 21-cm line (Shaver et al. 1999) on the ∼ 5′ scale; (ii) Low-frequency surveys of the sky with of order 108 expected new sources; (iii) All-sky monitoring and detection of transient radio sources such as γ-ray bursts, X-ray binaries, and exo-planets (Farrell et al. 2004); and (iv) Radio detection of ultra-high energy cosmic rays and neutrinos (Falcke & Gorham 2003) allowing for the first time access to particles beyond 1021 eV (Scholten et al. 2006). Apart from the KSPs open access for smaller projects is also planned. Here we give a brief description of the telescope.

The total number of Galactic planetary nebulae (GPNe) is highly uncertain; the most inclusive current catalog contains only $\sim$ 1,500. We will use the PRISM wide-field imager on the 1.83 m Perkins Telescope to conduct a pilot survey of the Galactic plane in search of [S III] emission from PNe obscured by dust and missed by surveys of H$\,\alpha$. We are employing the method of Jacoby & Van de Steene (JVS), who surveyed the bulge for [S III] $\lambda$9532. In addition to seeing through more of the extinction, use of the [S III] emission line will a priori reject the most troublesome catalog contaminants: ultracompact H II regions.

We have conducted deep near-infrared surveys of the Sh-2 255, W3 Main and NGC 7538 massive star forming regions using simultaneous observations of the JHKs-band with the near-infrared camera SIRIUS on the UH 88-inch telescope and with SUBARU. The near-infrared surveys cover a total area of ~ 72 arcmin2 of three regions with 10-σ limiting magnitudes of ~ 19.5, 18.4 and 17.3 in J, H and Ks-band, respectively. Based on the color-color and color-magnitude diagrams and their clustering properties, the candidate young stellar objects are identified and their luminosity functions are constructed in Sh-2 255, W3 Main and NGC 7538 star forming regions. A large number of previously unreported red sources (H-K > 2) have also been detected around these regions. We argue that these red stars are most probably pre-main-sequence stars with intrinsic color excesses. The detected young stellar objects show a clear clustering pattern in each region: the Class I-like sources are mostly clustered in molecular cloud region, while the Class II-like sources are in or around more evolved optical HII regions. We find that the slopes of the Ks-band luminosity functions of Sh-2 255, W3 Main and NGC 7538 are lower than the typical values reported for the young embedded clusters, and their stellar populations are primarily composed of low mass pre-main-sequence stars. From the slopes of the Ks-band luminosity functions, we infer that Sh-2 255, W3 Main and NGC 7538 star forming regions are rather young (age ≤ 1 Myr).

Understanding the stellar populations of extragalactic globular cluster (GC) systems and, in particular, determining their ages, provide essential clues to constrain the star formation histories of their host galaxies. We here summarize the most relevant results derived from a detailed, spectroscopic study of 20 GCs in the E0 NGC 1407. We find most GCs are old (~11 Gyr), follow a tight metallicity sequence reaching values slightly above solar, and exhibit mean [α/Fe] ratios of ~0.3 dex. Blue horizontal branch effects are detected for 3 GCs. We also report the existence of two families of metal-rich (MR) GCs, as some of them exhibit significantly larger [Mg/Fe] and [C/Fe] ratios, what might be interpreted in terms of different star formation time-scales. Striking CN overabundances are found over the entire GC metallicity range. In particular, for MR GCs, N increases dramatically while C essentially saturates. This may be interpreted as a consequence of the increasing importance of the CNO cycle with increasing metallicity.

We present our recent work on the conditions under which star formation occurs in a metal-poor environment, the Large Magellanic Cloud ([Fe/H] ~ −0.4). Water masers are used as beacons of the current star formation in H II regions. Comparing their location with the dust morphology imaged with the Spitzer Space Telescope, and additional Hα imaging and groundbased near-infrared observations, we conclude that the LMC environment seems favourable to sequential star formation triggered by massive star feedback (Oliveira et al. 2006). Good examples of this are 30 Doradus and N 113. There are also H II regions, such as N 105A, where feedback may not be responsible for the current star formation although the nature of one young stellar object (YSO) suggests that feedback may soon start making an impact. The chemistry in one YSO hints at a stronger influence from irradiation effects in a metal-poor environment where shielding by dust is suppressed (van Loon 2005).

We describe the mid- (MIR) and far- (FIR) infrared properties of a large (~1000) sample of the most isolated galaxies in the local Universe. This sample is intended as a “nurture-free” zero point against which more environmentally influenced samples can be compared. We reprocess IRAS MIR/FIR survey data using the ADDSCAN/SCANPI utility for 1030 out of 1050 galaxies from the Catalogue of Isolated Galaxies (CIG) as part of the AMIGA project. We focus on diagnostics (FIR luminosity LFIR, R = log(LFIR/LB) and IRAS colours) thought to be sensitive to effects of environment or interaction. The distribution of log(LFIR) is sharply peaked from 9.0–10.5 with very few (<2%) galaxies above 10.5. Review of available optical images of the most FIR luminous galaxies finds the majority to be, likely, interacting systems missed in our earlier morphological reevaluation. The optically normalised luminosity diagnostic R = log(LFIR/LB) shows a distribution sharply peaked between 0.0 and −1.0. These results were compared to the magnitude limited CfA sample that was selected without environmental discrimination. This modestly (e.g. compared to cluster, binary galaxy and compact group samples) environmentally affected sample shows significantly higher mean log(LFIR) and R, whereas the mean log(LB) is the same. Our sample shows a strong LFIR vs. LB correlation, with a slope steeper than one (LFIR ∝ L1.41B). Interacting galaxies were found above this correlation, showing an enhancement in LFIR. With respect to the IRAS colours, we found higher F60/F100 value for ellipticals and late-type galaxies than for spirals, indicating a higher dust temperature. The mean value of F60/F100 was found to be lower than for interacting samples from the literature. The results indicate that the FIR emission is a variable enhanced by interaction, and that our sample probably shows the lowest possible mean value. This attests to the utility of our sample for defining a nurture-free zero point. More details can be found in the paper (The AMIGA sample of isolated galaxies, III. IRAS data and infrared diagnositics, U. Lisenfeld et al.) which is accepted for publication in Astronomy & Astrophysics.

Despite many studies, the post-AGB phase is still not well understood. To make progress in this field, we searched for information about proto-planetary nebulae and built a catalogue of post-AGB objects. Based on collected data we were able to trace the evolution of stars in their late stages making a distinction between carbon and oxygen-rich objects. We focused our attention on spectral features seen in ISO data and clues for AGB nucleosynthesis. Together with the newest HST images of post-AGB objects we can study correlations between morphological types and chemical and physical properties of stars to improve our understanding of stellar evolution.

The Long Wavelength Array (LWA) will be a new, open, user-oriented astronomical instrument operating in the relatively unexplored window from 20–80 MHz near arcsecond angular resolution and milliJansky sensitivity. Operated by the University of New Mexico on behalf of the Southwest Consortium (SWC) the LWA will provide a unique training ground for the next generation of radio astronomers. Students may also put skills learned on the LWA to work in computer science, electrical engineering, and the communications industry, among others. The development of the LWA will follow a phased build which benefits from lessons learned at each phase. Four university-based Scientific Testing and Evaluation (ST&E) teams with different areas of concentration: (i) high-resolution imaging and particle acceleration; (ii) wide-field imaging and large scale structures; (iii) ionospheric physics; and (iv) radio frequency interference (RFI) suppression and transient detection will provide the feedback needed to assure that science objectives are met as the build develops. Currently in its first year of construction funding, the LWA team is working on the design for the first station (see also Ray et al. 2006).

We investigate the dependence of galaxy populations on environment. Our samples are selected from the follow-up of Red-Sequence Cluster Survey (RCS) catalogs using wide-field BVRz' imaging for 60 intermediate redshift (0.3 < z < 0.6) clusters. Galaxy redshifts are estimated using an empirical photometric redshift technique with a training set of 3996 galaxies to z 1.4. To obtain photometric redshift probability density for each galaxy, we bootstrap the training set galaxies to estimate the fitting uncertainties and apply Monte-Carlo method to simulate galaxy magnitudes errors. In order to find galaxy groups using photometric redshift, we develop a modified friends-of-friends algorithm, ‘Probability Friends-of-Friends Algorithm (pFOF)’, where photometric redshift redshift probability densities of individual galaxies are used to determine member galaxies of a group. We calculate the red galaxy fraction to infer the evolutionary status of cluster galaxies and also for galaxies in groups selected in the same redshift space as the clusters.

The Square Kilometre Array SKA is intended to be the centimeter- and meter-wavelength telescope for the 21st century. At long wavelengths, the SKA's key science projects include the search for highly redshifted hydrogen, including the signal from the epoch of re-ionization, and the search for the first supermassive black holes.

Photometric studies on globular cluster systems in early-type galaxies are widely used to resolve stellar populations in these galaxies. The knowledge of the age and metalicity structure within the globular cluster systems allows to set constraints on the major star formation episodes in the galaxy. Here we present our method of detecting age sub-populations in globular cluster systems based on optical/near-infrared observations and Monte-Carlo simulations. It is based on the determination of the cumulative age distribution and its comparison to simulated globular cluster systems. On various galaxies we will demonstrate the ability of our method to detect age sub-populations and show how we use the derived age structure to find correlations between various galaxy parameters and the formation/evolution of a given galaxy.

High-resolution 905-1187Å spectra of the central star of NGC 7009 obtained with the FUSE satellite provide new constraints on the mass loss and atmosphere parameters. The most prominent spectral feature is a very strong P-Cygni profile of O VI 1032-1038. The only other wind lines are S VI 933-44 (FUSE) and N V 1238-42 and O V 1371 from IUE spectra. C IV 1548-50 and P V 1118-28 are not present, indicating that the wind is very highly ionized. A lower limit on the mass loss rate ($\dot{M}>10^{-8} M_{\odot} $y$^{-1}, v_{\infty}=2450$ km s$^{-1}$) has been derived from an SEI analysis of these wind lines. Preliminary identification of several photospheric spectral features include several strong Fe VII and O VI lines between 1100 and 1170 Å.