We present a new analysis of galaxy colours and star formation rates as a function of environment, from the Sloan Digital Sky Survey and the 2dF Galaxy Redshift Survey. The galaxy distribution is well characterised by only two distinct populations: one that is blue and star–forming, and one that is red and quiescent. The colour and H$\alpha$ distribution of each of these populations is approximately independent of environment, while their relative abundances depend strongly on local galaxy density. Even in the lowest-density environments, a substantial ($\sim 30$ per cent) population of galaxies have red colours and exhibt no detectable H$\alpha$ emission. We compare these data with theoretical predictions of galaxy formation, properly accounting for observational selection biasses and uncertainties. We conclude that galaxy transformations must either be rapid (with a timescale $\tau\lesssim0.5$ Gyr), or must occur preferentially at high redshift.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A three-dimensional, time-dependent, magnetohydrodynamic (MHD) model is constructed for the study of active region (AR) evolution. The new physics included in this model is differential rotation, meridional flow, effective diffusion and cyclonic turbulence effects, which means, that the photospheric shear is automatically generated instead of prescribed as is usually done for modeling. To benchmark this newly developed model, we have used observed active region NOAA/AR-8100 (October 29 - November 3, 1997) to verify the model by computation of the total magnetic flux and magnetic field maps of that active region. Then, we apply this model to compute the non-potentiality magnetic field parameters for possible coronal mass ejection production. These parameters are: (i) magnetic flux content ($\Phi$), (ii) the length of strong shear, strong-field main neutral line, ($L_{ss}$), (iii) the net electric current ($I_N$) and (iv) the flux normalized measure of the field twist ($\alpha$ = $\mu$$\frac{I_N}{\Phi}$). These parameters are compared with the measured values which showed remarkable agreement.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We observed a sunspot almost exactly at disc centre on 23 September, 2003, with the Tenerife Infrared Polarimeter (TIP; Martínez Pillet et al. 1999) at the $\phi=70$, cm Vacuum Tower Telescope (VTT) on Tenerife. The highly symmetric spot passed the central meridian just at the time of observations; its solar latitude of $9^\circ$ N was almost perfectly compensated by the inclination of the solar axis $B_0=7^\circ$. We took the full Stokes vector through the line profiles of Fe I 10783 Å, Si I 10784.5 Å and Si I 10786.8 Å. The spatial sampling was adapted to the pixel size of 0.4 arcsec width; the VTT correlation tracker largely compensated image motion. The Stokes spectra were corrected for the dark and the gain matrices, as well as for instrumental polarisation and Stokes cross-talk. The spectral resolution finally achieved with TIP and its detector amounts to 32 mÅ.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In this paper I address three topics. The first regards the use of composite spectra as a tool to study the spectral evolution of galaxies in intermediate-redshift clusters. This technique is used to demonstrate the robustness of measurements of strong H$\delta$ absorption, indicative of mild-to-moderate starbursts, in a significant fraction of galaxies in these clusters. Second, I present some spectroscopic data on Abell 851 ($z=0.41$) that suggests that the starbursts in this cluster have been triggered by tidal encounters in infalling groups in the cluster. Third, I briefly describe the IMACS imaging-spectrograph, which has been built for the Magellan-Baade telescope, and, following the idea that the outskirts of clusters are “where the action is,” describe a large spectroscopic program to study “cluster building” using IMACS.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The study of detached eclipsing binaries is one of the most powerful ways to investigate the properties of individual stars and stellar systems. We present preliminary masses, radii and effective temperatures for the eclipsing binary WW Aurigae, which is composed of two metallic-lined A-type stars. We also reanalyse the data on HD 23642, an A-type eclipsing binary member of the Pleiades open cluster with a metallic-lined component, and determine its distance to be $139 \pm 4$ pc. This is in agreement with the traditional Pleiades distance, but in disagreement with distance to the Pleiades, and to HD 23642 itself, derived from Hipparcos trigonometrical parallaxes.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A distinctive characteristic of interplanetary magnetic clouds is their rope-like magnetic structure, i.e., their smoothly-varying helical field lines whose pitch increases from their core to their boundary. Because this regular structure helps to make MCs particularly geo-effective, it is important to understand how it arises.

We discuss recent work which relates the magnetic and topological parameters of MCs to associated solar active regions. This work strongly supports the notion that MCs associated with active region eruptions are formed by magnetic reconnection between these regions and their larger-scale surroundings, rather than simple eruption or entrainment of pre-existing structures in the corona or chromosphere. We discuss our findings in the context of other recent works on both the solar and interplanetary sides, including ion composition and various MHD models of magnetic cloud formation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We characterize the stellar population of a complete sample of the closest southern radio-galaxies – 12 Fanaroff-Riley I (FR I), 8 FR II and 4 with undefined FRx type – and a comparison sample of 18 non-active elliptical and SO galaxies. We measured equivalent widths and continuum colours and their radial variations, and performed spectral synthesis as a function of distance from the nucleus. Only 4 of the radio-galaxies have more than 10% of the total flux at 4020Å contributed from 100 Myr old or younger stellar population components – including a featureless continuum due to an AGN. All 4 are FRII or FRx. The main difference between the stellar population of the radio-galaxies and that of the non-active ones is that the former have a larger contribution of the intermediate age component, suggesting a relation between the present radio activity and a past episode of star formation which occurred about 1 Gyr ago.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Simulations of cellular magnetoconvection in a compressible fluid reveal the formation of magnetic structures with a substantial bipolar component as an inherent property of the topology of cellular flows.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Analysing mid–infrared ISOCAM images of the cluster of galaxies J1888.16CL, we identified among its members several particularly active galaxies with total infrared luminosities well above $10^{11}~\Lo$. If powered by dust enshrouded starbursts, as suggested by their optical spectra, these Luminous Infrared Galaxies would exhibit star formation rates surprisingly high in the cluster environment. The triggering mechanism is unclear but could be tidal collisions within sub-structures or infalling groups.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Magnetic and acoustic properties of the complex active region AR 486 are analyzed for two consecutive days: October 28 and October 29, 2003 when two large flares of magnitude X17.2 and X10 were produced, respectively. Using the technique of helioseismic holography we detected seismic waves emitted from these flares at 6 mHz. SOHO-MDI white light images, magnetograms, and Dopplergrams are used to study the physics of the acoustic sources.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Coronal heating is an important problem in solar physics. With the development of highly qualified instruments, such as TRACE, SOHO and Yohkoh, more and more observations about coronal loops have been obtained. The coronal loops' heating, being an important ingredient of coronal heating, has been paid particular attentions recently. But there are still some key issues about the structure and mechanism of the loops' heating unresolved. In this paper, after a brief review on the latest progress in both observations and modeling of coronal loops, we emphatically discuss the heating of hydrostatic loops and hydrodynamic loops based on the 1D model. The prospect of the subject is presented.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Both components of the composite-spectrum binary o Leo have Am characteristics, even though the primary is an evolving giant ($\log g=3.25$) with $T_{\rm eff} \sim 6100\,{\rm K}$. This is believed to be the first isolation of such a cool Am star. The finding challenges the theories of diffusion which are widely accepted as the cause of metallicism. The primary component (o Leo A) appears to be deficient in Ca and Sc, as are classical Am stars. Its unusual state may be attributable either to its current state of rapid evolution, or to regular Am-star evolution that is difficult to recognize spectroscopically. A full account of this research appeared in AJ 123, 988-1001, 2002.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In this work we investigate the stellar population, metallicity distribution and ionized gas in the elliptical galaxy NGC 5044, using long-slit spectroscopy and a stellar population synthesis method. We found differences in the slope of FeI and Mg2 lines gradients, which suggests an enhancement of α elements, particularly towards the central region. The stellar population synthesis shows that the contribution, at λ5870, of the most metallic and old stellar population ($Z/Z_\odot \sim 0.0$ and 1010year) is dominant in NGC 5044. The presence of a non-thermal ionization source, such as a low-luminosity AGN and/or shock ionization, is implied by the large values of the ratio [NII]/Hα observed in all sampled regions. However, the emission lines observed in the external regions indicate the presence of an additional ionization source, probably hot, post-AGB stars.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

This investigation is devoted to the study of time variations and spatial peculiarities of radio local radio sources associated with the solar active regions (AR) on the basis of microwave observations in September–October 2002. During this period the most interesting results have been obtained for the AR NOAA 0139. So, in this paper an analysis of this radio source is presented. The observations were made with the radio telescopes RT–22 (Crimea), RATAN–600, the Siberian Solar Radio Telescope (SSRT) and Nobeyama. Observations with the RT–22 (wavelengths 2.0, 2.3, 3.5 cm) were carried out by the quasi–zero method with the flux sensitivity of 0.1 s.f.u and the temporal resolution of about 0.1 s. The typical length of realization was about 6.5 hours. The spatial resolution of few arc minutes allowed to limit the analysis by the particular AR but was not enough to distinguish any details. Nevertheless spectral analysis of the AR made using observations with high one–dimensional resolution of the RATAN–600 shows that at short cm wavelengths for this AR at the period of the RT–22 observations dominated thermal cyclotron emission of above the largest sunspot of the group. This result was also confirmed by radio maps of the Nobeyama at wavelength 1.76 cm.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Recently a formalism for solving the open set of non-local hydrodynamic moment equations has been applied to the envelopes of A-stars by Kupka & Montgomery (2002). Tests on numerical simulations and selected properties derived from stellar spectra such as average surface velocities and velocity skewness have shown the applicability of this RSM approach. In addition, a variety of improvements over existing modeling standards have been developed within and around the AMS group at the Institute for Astronomy in Vienna during the last couple of years. For example, individual elemental abundance patterns (Piskunov & Kupka 2001) or stratification as an observed parameter (Shuliak et al. 2004) can be taken into account in our model atmospheres. Once the underlying programs, which currently operate as stand alone applications, are combined with a model atmosphere code, we will obtain a powerful and efficient tool that will allow us the investigation of a number of open problems in the physics of A-stars, such as more realistic models of the temperature gradients of cool CP2 stars.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The gravitationally lensing clusters A370, A2218, A1689 and Cl0024+1654 were observed with the Infrared Space Observatory (ISO) using ISOCAM at 6.7 $\mu$m and 14.3 $\mu$m (hereafter 7 $\mu$m and 15 $\mu$m respectively).

A total of 178 sources were detected in the whole set, 70 of them being cluster objects. The spectral energy distribution of a subset of sources was calculated using GRASIL. The results for the total infrared luminosity and the estimation of the star formation rate are presented for the non stellar objects for which the SED has been determined. The majority of the cluster galaxies in A2218 are best fit by models of quiescent ellipticals. In Cl0024+1654, most of the galaxies lying on the Butcher-Oemler region of the colour-magnitude diagram are best fit by disk galaxies, while those on the main sequence area have in general SEDs corresponding to post-starburst galaxies.

The population of each cluster is compared with the field population, as well as with the population of other clusters. A significant number of Luminous IR Galaxies (LIRGs) is detected in Cl0024+1654, while only one LIRG has been observed in total in A370, A1689, and A2218. This result supports the link between LIRGs in clusters and recent or ongoing cluster merger activity as well as the need for extending the observations to the outer parts of clusters.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The kinematics of black hole and neutron star X-ray binaries in the Galaxy should help to know their birth place and constrain their evolution. We have used multiple tools of modern astronomy to determine the trajectories in the Galaxy and track the origins of black hole and neutron star X-ray binaries that are of topical interest in astrophysics. We find three distinct classes of black hole and neutron star X-ray binaries: (1) low mass X-ray binaries that move at high velocities on galactocentric orbits similar to the most ancient stars born in the Galactic bulge and the halo, (2) those that move in the Galactic disk along paths that resemble the circular orbits of massive stars formed in the disk, and (3) high and intermediate mass X-ray binaries running away from their parent regions of star formation. Here we discuss some of the cases studied.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

This work reports direct observations of the magnetic reconnection site during an eruptive process occurring on November 18, 2003. The event started with a rapid expansion of a few magnetic arcades located over the east limb of the Sun and developed an energetic partial halo coronal mass ejection (CME), a long current sheet and a group of bright flare loops in the wake of the CME. It was observed by several instruments both in space and on ground, including the EUV Imaging Telescope, the Ultraviolet Coronagraph Spectrometer, and the Large Angle and Spectrometric Coronagraph experiment on board the Solar and Heliospheric Observatory, the Reuven Ramaty High Energy Solar Spectroscopic Imager, as well as the Mauna Loa Solar Observatory Mark IV K-coronameter. We combine the data from these instruments to investigate various properties of the eruptive process, including those around the current sheet. The composite of images from different instruments and the corresponding results specify explicitly how the different objects developed by a single eruptive process are related to one another.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the initial results of a deep submillimeter survey of ten $z\sim 1$ galaxy clusters with the SCUBA bolometer array on the JCMT. Recently, an excess number of dust enshrouded starbursts in high-redshift galaxy cluster fields was reported (Best 2002) and has been interpreted as increased star-formation within young clusters. An alternative explanation is that these starbursts are background objects behind clusters with enhanced lensing cross-sections, over that predicted from simple lensing models, so-called “super-lenses” seen in recent optical cluster surveys. To investigate this issue, we are studying a set of clusters which show strong optical arcs (super-lenses) and a set of clusters of equal redshift and richness but which are not super-lenses. The preliminary results, based on 50% of the sample, tentatively suggest that, while the dusty starbursts are limited to the super-lensing cluster fields, they are not background objects but lie within the clusters themselves. Cluster-cluster merging offers a means of increasing both the lensing cross-section, thereby accounting for the multiple strong optical arcs, and increasing the star formation within the clusters through galaxy interactions.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We examine the energetics of the best examples of flux-rope CMEs observed by LASCO in 1996-2001. We find that 69% of the CMEs in our sample experience a driving power in the LASCO field of view. For these CMEs which are driven, we examine if they might be deriving most of their driving energy by coupling to the solar wind. We do not find conclusive evidence to support this hypothesis. We adopt two different methods to estimate the energy that can possibly be released by the internal magnetic fields of the CMEs. We find that the internal magnetic fields are a viable source of driving power for these CMEs.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html