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Aims. According to Hubble’s classification scheme, lenticular galaxies represent an intermediate evolutionary step between elliptical and spiral galaxies. This evolutionary path predicts that the aspect ratios of both lenticular and spiral galaxies should be smaller than the aspect ratios of their E6 or E7 elliptical predecessors. In contradiction to this prediction, observation has demonstrated that the aspect ratio of lenticular galaxies is larger than its immediate elliptical predecessor. In this paper, we suggest a novel explanation for this inconsistency. Methods. The approach described in this paper is primarily based on analytical methods; however, some numerical methods are also used. Results. Our idea comes from theoretical and experimental results, which show that a small increase in the equatorial diameter of an oblate spheroid with an aspect ratio ≤0.6 surprisingly causes its minor axis to also increase. We demonstrate that the same phenomenon occurs in the isodensity contours of elliptical galaxies given by Miyamoto & Nagai (Miyamoto M., & Nagai R., 1975, PASJ, 27, 533) and in a Maclaurin spheroidal mass in response to the gravitational force generated by a circumferential equatorial disk. Conclusions. The result of this paper is our explanation for the transformation of a disky elliptical galaxy into a lenticular galaxy which in response to rotation and equatorial diameter expansion evolves into a red spiral galaxy. This evolutionary path is consistent with the common environmental location of disky ellipticals, lenticular and red spiral galaxies and explains why elliptical galaxies are generally ≤E4. The proposed evolutionary path is opposite to the generally accepted formation of lenticular galaxies from the merger of spiral galaxies.

Aims. This is the first paper in a series that deals with solar-physics applications of the equation-of-state formalism based on the formulation of the so-called “Feynman-Kac (FK) representation”. Here, the FK equation of state is presented and adapted for solar applications. Its domain of validity is assessed. The practical application to the Sun will be dealt with in Paper II. Paper III will extend the current FK formalism to a higher order. Methods. A recent rigorous quantum-statistical formalism for Coulomb systems is used to compute the thermodynamical quantities for solar modeling, taking into account the necessary requirements on smoothness and accuracy. The FK formalism being a virial expansion, it suffers from the well-known deficiency that it is limited to nearly full ionization. This point is elaborated in detail, and the quantitative criterion for the domain of validity of the FK equation of state is established. Results. Use of the FK equation of state is limited to physical conditions for which more than 90% of helium is ionized. This includes the inner region of the Sun out to about .98 of the solar radius. Despite this limitation, in the parts of the Sun where it is applicable, the FK equation of state has the power to be more accurate than the equations of state currently used in solar modeling. The FK approach is especially suited to study physical effects such as Coulomb screening, bound states, the onset of recombination of fully ionized species, as well as diffraction and exchange effects. Conclusions. Despite technical difficulties in its application, there are unique features in the FK approach that promise to turn it into the most exact of the available formalisms, provided FK is restricted to the deeper layers of the Sun where more than 90% of helium is ionized. The localizing power of helioseismology allows a test of the FK equation of state. Such a test will be beneficial both for better solar models and for tighter solar constraints of the equation of state.

In this second paper of the sequel of two papers, we further investigate the problem of molecular cloud (MC) collision. Anathpindika (2009) (hereafter paper I) considered highly supersonic cloud collisions and examined the effect of bending and shearing instabilities on the shocked gas slab. We now consider moderately supersonic cloud collisions (precollision cloud velocities of order 1.2 km s$^{-1}$ to 2.4 km s$^{-1}$). In the current paper, we present five SPH simulations of fast head-on and/or off-centre cloud collisions to study the evolution of ram pressure confined gas slabs. The relevant thermodynamics in the problem is simplified by adopting a simple barytropic equation of state. We explore the parameter space by varying the pre-collision velocity and the temperature of the post collision gas slab. The temperature in a pressure compressed gas slab is crucial to its dynamical evolution. The pressure confined gas slabs become Jeans unstable if the average sound crossing time, $t_{cr}$, of putative clumps condensing out of them, is much larger than their free fall time, $t_{ff}$. Self gravitating clumps may spawn multiple/larger $N$-body star clusters. Warmer gas slabs are unlikely to fragment and may end up as diffuse gas clouds., 10pages, 8 figures, 1 table; A&A accepted Typographical errors have been attempted to and the original manuscript has been trimmed. The results however, remain unchanged. The pictures in this version are of considerably lower resolution in order to minimise their sizes

In this paper we consider the effects of resonance and electron scattering on the escape of Lyman alpha photons during cosmological hydrogen recombination. We pay particular attention to the influence of atomic recoil, Doppler boosting and Doppler broadening using a Fokker-Planck approximation of the redistribution function describing the scattering of photons on the Lyman alpha resonance of moving hydrogen atoms. We extend the computations of our recent paper on the influence of the 3d/3s-1s two-photon channels on the dynamics of hydrogen recombination, simultaneously including the full time-dependence of the problem, the thermodynamic corrections factor, leading to a frequency-dependent asymmetry between the emission and absorption profile, and the quantum-mechanical corrections related to the two-photon nature of the 3d/3s-1s emission and absorption process on the exact shape of the Lyman alpha emission profile. We show here that due to the redistribution of photons over frequency hydrogen recombination is sped up by DN_e/N_e~-0.6% at z~900. For the CMB temperature and polarization power spectra this results in |DC_l/C_l|~0.5%-1% at l >~ 1500, and therefore will be important for the analysis of future CMB data in the context of the PLANCK Surveyor, SPT and ACT. The main contribution to this correction is coming from the atomic recoil effect (DN_e/N_e~-1.2% at z~900), while Doppler boosting and Doppler broadening partially cancel this correction, again slowing hydrogen recombination down by DN_e/N_e~0.6% at z~900. The influence of electron scattering close to the maximum of the Thomson visibility function at z~1100 can be neglected. (abridged), 11 pages, 13 figures, submitted to A&A

The knowledge of accurate stellar parameters is a key stone in several fields of stellar astrophysics, such as asteroseismology and stellar evolution. Although the parameters can be derived both via spectroscopy and multicolor photometry, the obtained results are sometimes affected by systematic uncertainties. In this paper we present a self-consistent spectral analysis of the solar-type star HD49933, which is a primary target for the CoRoT satellite. We used high-resolution and high signal-to-noise ratio spectra to carry out a consistent parameter estimation and abundance analysis of HD49933. The LLmodels code was employed for model atmosphere calculations, while Synth3 and Width9 codes were used for line profile calculation and LTE abundance analysis. In this paper we provide a detailed description of the methodology adopted to derive the fundamental parameters and the abundances. Although the obtained parameters differ from the ones previously derived by other authors, we show that only the set obtained in this work is able to fit the observed spectrum accurately. In particular, the surface gravity was adjusted to fit pressure-sensitive spectral features. We confirm the importance of a consistent analysis of relevant spectroscopic features, application of advanced model atmospheres, and the use of up-to-date atomic line data for the determination of stellar parameters. These results are crucial for further studies, e.g. detailed theoretical modelling of the observed pulsation frequencies., Accepted by A&A, 11 pages, 5 figures, 4 tables

This paper is a follow-up of the vast effort to collect radial velocity data for stars belonging to the Hipparcos survey. We aim at extending the orbital data available for binaries with M giant primaries. The data will be used in the companion papers of this series to (i) derive the binary frequency among M giants and compare it to that of K giants (Paper II), and (ii) analyse the eccentricity-period diagram and the mass-function distribution (Paper III). Keplerian solutions are fitted to radial-velocity data. However, for several stars, no satisfactory solution could be found, despite the fact that the radial-velocity standard deviation is larger than the instrumental error, because M giants suffer from intrinsic radial-velocity variations due to pulsations. We show that these intrinsic radial-velocity variations can be linked with both the average spectral-line width and the photometric variability. We present an extensive collection of spectroscopic orbits for M giants, with 12 new orbits, plus 17 from the literature. Moreover, to illustrate the fact that the large radial-velocity jitter present in Mira and semi-regular variables may easily be confused with orbital variations, we also present examples of pseudo-orbital variations (in S UMa, X Cnc and possibly in HD 115521, a former IAU radial-velocity standard). Because of this difficulty, M giants involving Mira variables were excluded from our monitored sample. We finally show that the majority of M giants detected as X-ray sources are actually binaries., Comment: 17 pages, 15 figures, accepted for publication in A&A, language editing changes only

International audience; Aims: This paper investigates the rotation rate of solar activity from a global point of view, considering daily index or flux, instead of individual structures. It determines the rotation rate variations inside the cycle by two-year sequences and the comprehensive study of the cycle. Methods: The method consists of harmonic analysis of series of daily monitoring of solar activity. One is the sunspot number covering cycles 9 to 23 (over 157 years) and the second the flux of the corona at 2800 MHz from cycle 19 to 25 (over 53 years). These long series were analysed by the maximum entropy method for the measurement of rotation frequency. Results: The findings displayed in this paper are: i) sunspots and coronal flux show the same global rotation rates; ii) the solar rotation unfolding during the cycle is complex, without any systematic pattern; iii) the analysis of cyclic solar activity rotation leads to variation of the rotation rate with a period of 52.4 years; iv) the present result supports the existence of high-level cycles made of five eleven-year cycles; the global rotation rate also has this periodicity; v) no asymmetry was found in the northern and southern hemisphere rotation rates.

Aims. In a previous paper, the volumetric plasma filling factor of coronal bright points was determined from spectra obtained with the Extreme ultraviolet Imaging Spectrometer (EIS). The analysis of these data showed that the median plasma filling factor was 0.015. One interpretation of this result was that the small filling factor was consistent with a single coronal loop with a width of 1–2 �� , somewhat below the apparent width. In this paper, higher spatial resolution observations with the Transition Region and Corona Explorer (TRACE) are used to test this interpretation. Methods. Rastered spectra of regions of the quiet Sun were recorded by the EIS during operations with the Hinode satellite. Many of these regions were simultaneously observed with TRACE. Calibrated intensities of Fe xii lines were obtained and images of the quiet corona were constructed from the EIS measurements. Emission measures were determined from the EIS spectra and geometrical widths of coronal bright points were obtained from the TRACE images. Electron densities were determined from density-sensitive line ratios measured with EIS. A comparison of the emission measure and bright point widths with the electron densities yielded the plasma filling factor. Results. The median electron density of coronal bright points is 3 × 10 9 cm −3 at a temperature of 1.6 × 10 6 K. The volumetric plasma filling factor of coronal bright points was found to vary from 3 × 10 −3 to 0.3 with a median value of 0.04. Conclusions. The current set of EIS and TRACE coronal bright-point observations indicate the median value of their plasma filling factor is 0.04. This can be interpreted as evidence of a considerable subresolution structure in coronal bright points or as the result of a single completely filled plasma loop with widths on the order of 0.2–1.5 �� that has not been spatially resolved in these measurements.

Aims: Pointed observations with XMM-Newton provide the basis for creating catalogues of X-ray sources detected serendipitously in each field. This paper describes the creation and characteristics of the 2XMM catalogue. Methods: The 2XMM catalogue has been compiled from a new processing of the XMM-Newton EPIC camera data. The main features of the processing pipeline are described in detail. Results: The catalogue, the largest ever made at X-ray wavelengths, contains 246,897 detections drawn from 3491 public XMM-Newton observations over a 7-year interval, which relate to 191,870 unique sources. The catalogue fields cover a sky area of more than 500 sq.deg. The non-overlapping sky area is ~360 sq.deg. (~1% of the sky) as many regions of the sky are observed more than once by XMM-Newton. The catalogue probes a large sky area at the flux limit where the bulk of the objects that contribute to the X-ray background lie and provides a major resource for generating large, well-defined X-ray selected source samples, studying the X-ray source population and identifying rare object types. The main characteristics of the catalogue are presented, including its photometric and astrometric properties ., Comment: 27 pages (plus 8 pages appendices), 15 figures. Minor changes following referee's comments; now accepted for publication in A & A. Note that this paper "V", not paper "VI" in the series. Previous posting was incorrect in this regard

Context. Photon orbital angular momentum (POAM) has been created in the laboratory, yet it is still relatively unknown. How does POAM manifest itself in astronomy? Are there any applications for measuring astrophysical POAM? Aims. In this paper, I 1) explain POAM in an astronomical context; 2) define the POAM observables for astronomy; 3) create generic systems-based calculi that describe how POAM propagates from celestial sphere to detector; 4) use the calculi with several astronomical instruments as examples of their utility; 5) demonstrate an application for astrophysical POAM measurements; and 6) relate POAM to existing astronomical instruments and concepts. Methods. Electric fields are expanded into azimuthal Fourier components, and the intensities are expanded into correlations or rancors. The source electric fields are spatially incoherent. In the systems-based calculi, the inputs are located on the celestial sphere, the system is represented by propagation through free space and instrument, and the outputs are located in a specific plane. The diffraction and point-spread function expansions are very generic and can be used with any type of instrument. I employ these examples to demonstrate the calculi (in order of increasing difficulty): free space, single telescopes, interferometers, coronagraphs, and rancorimeters. Results. The azimuthal Fourier components of the electric field correspond to POAM vortex states. Rancors contain less information than correlations, yet they are easier to measure and can be used in many applications. Propagation through an aberrated telescope applies external torque, which may be expressed in terms of Zernike polynomials. I prove that a sectored phase mask in a focal-plane coronagraph applies torque to the low-order states, producing a null. Also, I prove that a Michelson interferometer is inherently capable of filtering POAM; e.g., tracking 180 ◦ from the central fringe eliminates even states, producing a null. A limited rancorimeter can be created by placing a focal-plane wedge mask in a coronagraph. The resulting rancors can be used to perform super-Rayleigh observations of unresolved unresolved objects, such as binary stars. There are three types of source POAM: intrinsic, structure, and pointing. Instrumental POAM, which must be calibrated, includes optical aberrations and atmospheric turbulence. Conclusions. This paper represents the starting point for future research: 1) making a priori predictions about the intrinsic POAM of astronomical sources; 2) designing ground- and space-based POAM-measuring instruments; 3) understanding existing instruments in terms of POAM; 4) minimizing the effects of random noise on POAM; and 5) calibrating all types of instrumental POAM.

This paper presents morphological type, membership, and U−V color for a sample of galaxies in the Coma cluster direction, complete down to MB = −15.00 mag and extending down to MB = −14.25 mag. We have examined 1155 objects from the GMP 1983 catalog on B and V images of the CFH12K camera, and obtained the Hubble type in most cases. Coma cluster membership for 473 galaxies was derived using morphology, apparent size, and surface brightness, and, afterward, redshift. The comparison among morphologyand redshift- memberships and among luminosity functions derived from this morphologically-selected sample, or by using statistical members or spectroscopic members, all show that the morphological membership provided here can be trusted. For the first time, the morphological classification of Coma galaxies reaches magnitudes that are faint enough to observe the whole magnitude range of the giant types, E, S0, and spiral stages. The data presented in this paper makes our sample the richest environment where membership and morphology for complete samples down to faint magnitudes (MB ∼− 15 mag) are available, thereby enlarging the baseline of environmental studies.

Context. The intensity of the YORP (Yarkovsky, O'Keefe, Radzievskii, and Paddack) effect and its ability to affect the rotational properties of asteroids depend mainly on the size of the body and on its shape. At present, we have a database of about 30 well-defined shapes of real minor bodies (most of them asteroids, but also planetary satellites and cometary nuclei).Aims. In this paper we perform a statistical analysis of how the YORP effect depends on the shape.Methods. We used the Rubincam approximation (i.e. neglecting the effects of a finite thermal conductivity).Results. We show that, among real bodies, the distribution of the YORP types, according to the classification of Vokrouhlický and Capek, is significantly different from the one obtained in the same paper from theoretical modeling of shapes. A new “type” also comes out. Moreover, we show that the types are strongly correlated with the intensity of the YORP effect (when normalized to eliminate the dependence on the size, and thus only related to the shape).

We investigate the effect of solar wind and solar electromagnetic radiation on the dynamics of spherical cosmic dust particles. We also consider the non-radial component of the solar wind velocity, in the reference frame of the Sun. We apply the equation of motion to the motion of dust grains near commensurability resonances with a planet – mean motion orbital resonance (MMR; a particle is in resonance with a planet when the ratio of their mean motions is approximately the ratio of two small integers) – and possible capture of the grains in the resonances. Up to now, only nonspherical grains, under action of the electromagnetic radiation of the central star, were known to exhibit an increase of semimajor axis before capture into the MMR. This paper shows that the same result can be generated by the non-radial component of the solar wind even for spherical dust particles. Spherical dust grains enable the treatment of the problem in an analytic way (at least partially), which is not the case for the effect of electromagnetic radiation on nonspherical dust grains. The situation treated in the paper presents the second known case when resonant trapping of a cosmic body occurs for diverging orbits. The paper presents the first case of secular evolution of the eccentricity of a body captured in the resonance derived in an analytic way for a body characterized by a diverging orbit.

In a companion paper we studied the detailed evolution of stellar collision products that occurred in an $N$-body simulation of the old open cluster M67 and compared our detailed models to simple prescriptions. In this paper we extend this work by studying the evolution of the collision products in open clusters as a function of mass and age of the progenitor stars. We calculated a grid of head-on collisions covering the section of parameter space relevant for collisions in open clusters. We create detailed models of the merger remnants using an entropy-sorting algorithm and follow their subsequent evolution during the initial contraction phase, through the main sequence and up to the giant branch with our detailed stellar evolution code. We compare the location of our models in a colour-magnitude diagram to the observed blue straggler population of the old open clusters M67 and NGC 188 and find that they cover the observed blue straggler region of both clusters. For M67, collisions need to have taken place recently. Differences between the evolution tracks of the collision products and normal main sequence stars can be understood quantitatively using a simple analytic model. We present an analytic recipe that can be used in an $N$-body code to transform a precomputed evolution track for a normal star into an evolution track for a collision product., To be published in A&A

The XMM-Large Scale Structure survey field (XMM-LSS) is an extragalactic window surveyed in the X-ray with the XMM-Newton satellite. It has also been observed in the optical with the Canada-France Hawai Telescope (CFHTLS survey), and in the infrared with the Spitzer Space Telescope (SWIRE survey). These surveys have been carried out to study the structure and evolution of both baryonic and dark matter on cosmological scales. In two previous papers, we presented deep low frequency radio surveys of the XMM-LSS field, with limiting flux density levels of ~4 and ~1.5 mJy/beam at 325 and 610 MHz respectively (5 σ ). These radio surveys were motivated by the need to understand the various connections between the host galaxies of radio sources and their environments. In this paper, we identify optical counterparts to the low frequency radio sources, using the CFHTLS optical catalogue and images, that have an i -band limiting magnitude of $i_{\rm AB}\sim 25$. We use a likelihood ratio method and estimate that ~75% of the radio sources have a detected optical counterpart. Using the CFHTLS and SWIRE data, we derive photometric redshifts for the galaxies that are identified with a radio source, as well as for those that are not; we demonstrate the reliability of these photometric redshifts by deriving the stellar mass function for galaxies at different redshifts, and showing that it is consistent with previous determinations. We classify the radio sources as type-1 AGN, radio galaxies, or star-forming galaxies, and show that the radio luminosity function of the radio galaxies agrees with previous measurements.

The Delta-variance analysis is an efficient tool for measuring the structural scaling behaviour of interstellar turbulence in astronomical maps. In paper I we proposed essential improvements to the Delta-variance analysis. In this paper we apply the improved Delta-variance analysis to i) a hydrodynamic turbulence simulation with prominent density and velocity structures, ii) an observed intensity map of rho Oph with irregular boundaries and variable uncertainties of the different data points, and iii) a map of the turbulent velocity structure in the Polaris Flare affected by the intensity dependence on the centroid velocity determination. The tests confirm the extended capabilities of the improved Delta-variance analysis. Prominent spatial scales were accurately identified and artifacts from a variable reliability of the data were removed. The analysis of the hydrodynamic simulations showed that the injection of a turbulent velocity structure creates the most prominent density structures are produced on a scale somewhat below the injection scale. The new analysis of a rho Oph continuum map reveals an intermediate stage in the molecular cloud evolution showing both signatures of the typical molecular cloud scaling behaviour and the formation of condensed cores. When analysing the velocity structure of the Polaris Flare we show that a universal power law connects scales from 0.03 pc to 3 pc. However, a plateau in the Delta-variance spectrum around 5 pc indicates that the visible large-scale velocity gradient is not converted directly into a turbulent cascade., Comment: Accepted for publication in A&A, Section 6

10 pages.-- arXiv:0804.1913 astro-ph pre-print supplied.-- Final full-text version of the paper available at: http://dx.doi.org/10.1051/0004-6361:200809653., We analyse high-resolution Hubble Space Telescope/Advanced Camera for Surveys imaging of the nuclear starburst region of M 82, obtained as part of the Hubble Heritage mosaic made of this galaxy, in four filters (Johnson-Cousins equivalent B, V, and I broad bands, and an H narrow-band filter), as well as subsequently acquired U-band images. We find a complex system of ~150 star clusters in the inner few 100 pc of the galaxy. We do not find any conclusive evidence of a cluster-formation epoch associated with the most recent starburst event, believed to have occurred about 4-6 Myr ago. This apparent evidence of decoupling between cluster and field-star formation is consistent with the view that star cluster formation requires special conditions. However, we strongly caution, and provide compelling evidence, that the "standard" simple stellar population analysis method we have used significantly underestimates the true uncertainties in the derived ages due to stochasticity in the stellar initial mass function and the corresponding sampling effects., MC is supported by the Spanish MCyT and by FEDER funding of project AYA2007-64712, and by a Ramón y Cajal fellowship. This paper is based on archival observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), under NASA contract NAS5-26555. This research project was funded by the Nuffield Foundation through Undergraduate Summer Bursary URB/34412.

This Comment is in response to an Erratum to the paper entitled "The shape and composition of interstellar silicate grains" (Min et al., A&A, 462, 667-676 (2007). The Erratum corrects erroneously cited data but upholds the paper's original conclusions that GEMS are not remnant interstellar grains and that most GEMS formed in the early solar system. In our Comment, we show that the correct data in fact strengthen the relationship between GEMS and interstellar silicates, contrary to the conclusions of Min et al. in their Erratum. We also explore the validity of the isotopic and bulk chemical bases for comparison and present additional indicators of past ISM radiation processing of silicates., 4 pages; Accepted for publication April 4, 2008 by Astronomy & Astrophysics; added missing subscript in table footnote

This is the third of a series of papers presenting the first attempt to analyze the growth of the bar instability in a consistent cosmological scenario. In the previous two articles we explored the role of the cosmology on stellar disks, and the impact of the gaseous component on a disk embedded in a cosmological dark matter halo. The aim of this paper is to point out the impact of the star formation on the bar instability inside disks having different gas fractions. We perform cosmological simulations of the same disk-to-halo mass systems as in the previous works where the star formation was not triggered. We compare the results of the new simulations with the previous ones to investigate the effect of the star formation by analysing the morphology of the stellar components, the bar strength, the behaviour of the pattern speed. We follow the gas and the central mass concentration during the evolution and their impact on the bar strength. In all our cosmological simulations a stellar bar, lasting 10 Gyr, is still living at z=0. The central mass concentration of gas and of the new stars has a mild action on the ellipticity of the bar but is not able to destroy it; at z=0 the stellar bar strength is enhanced by the star formation. The bar pattern speed is decreasing with the disk evolution., 10 pages, 21 figures, A&A accepted

We present the results of the first long-term (2.2 years) spectroscopic monitoring of a gravitationally lensed quasar, namely the Einstein Cross Q2237+0305. The goal of this paper is to present the observational facts to be compared in follow-up papers with theoretical models to constrain the inner structure of the source quasar. We spatially deconvolve deep VLT/FORS1 spectra to accurately separate the spectrum of the lensing galaxy from the spectra of the quasar images. Accurate cross-calibration of the 58 observations at 31-epoch from October 2004 to December 2006 is carried out with non-variable foreground stars observed simultaneously with the quasar. The quasar spectra are further decomposed into a continuum component and several broad emission lines to infer the variations of these spectral components. We find prominent microlensing events in the quasar images A and B, while images C and D are almost quiescent on a timescale of a few months. The strongest variations are observed in the continuum of image A. Their amplitude is larger in the blue (0.7 mag) than in the red (0.5 mag), consistent with microlensing of an accretion disk. Variations in the intensity and profile of the broad emission lines are also reported, most prominently in the wings of the CIII] and center of the CIV emission lines. During a strong microlensing episode observed in June 2006 in quasar image A, the broad component of the CIII] is more highly magnified than the narrow component. In addition, the emission lines with higher ionization potentials are more magnified than the lines with lower ionization potentials, consistent with the results obtained with reverberation mapping. Finally, we find that the V-band differential extinction by the lens, between the quasar images, is in the range 0.1-0.3 mag., Comment: 16 pages, 16 figures, A&A accepted, corrected Fig. 16

We present a parameter study of self-consistent models of protoplanetary disks around Herbig AeBe stars. We use the code developed by Dullemond and Dominik, which solves the 2D radiative transfer problem including an iteration for the vertical hydrostatic structure of the disk. This grid of models will be used for several studies on disk emission and mineralogy in followup papers. In this paper we take a first look on the new models, compare them with previous modeling attempts and focus on the effects of various parameters on the overall structure of the SED that leads to the classification of Herbig AeBe stars into two groups, with a flaring (group I) or self-shadowed (group II) SED. We find that the parameter of overriding importance to the SED is the total mass in grains smaller than 25um, confirming the earlier results by Dullemond and Dominik. All other parameters studied have only minor influences, and will alter the SED type only in borderline cases. We find that there is no natural dichotomy between group I and II. From a modeling point of view, the transition is a continuous function of the small dust mass. We also show that moderate grain growth produces spectra with weak or no 1um feature, both for flaring (Group I) and non-flaring (Group II) sources. The fact that sources with weak features have been found mostly in Group I sources is therefore surprising and must be due to observational biases or evolutionary effects., Comment: 12 pages, 10 figures, Astronomy and Astrophysics, in press

We describe data reduction and analysis of fluctuations in the cosmic far-IR background (CFIB) in observations with the Multiband Imaging Photometer for Spitzer (MIPS) instrument 160 micron detectors. We analyzed observations of an 8.5 square degree region in the Lockman Hole, part of the largest low-cirrus mapping observation with this instrument. We measured the power spectrum of the CFIB in these observations by fitting a power law to the IR cirrus component, the dominant foreground contaminant, and subtracting this cirrus signal. The CFIB power spectrum in the range 0.2 arc min^{-1}, Comment: This is the version of the paper accepted by A&A, which includes various changes and new material. The superior-quality PDF with integrated figures may be downloaded at http://www-astro.lbl.gov/~bruce/spitzerpaper1/cfibaa_pub.pdf 15 pages, figures integrated with text. This paper supersedes astro-ph/0504167

This is the first paper presenting our long-term project aimed at studying the nature of bulges through the analysis of their stellar population gradients. We present deep spectroscopic observations along the minor axis and the data reduction for a sample of 32 bulges of edge-on spiral galaxies. We explain in detail our procedures to measure their dynamical parameters (rotation curves and velocity dispersion profiles) and line-strength indices, including the conversion to the Lick/IDS system. Tables giving the values of the dynamical parameters and line-strength indices at each galactocentric radius are presented (in electronic form) for each galaxy of the sample. The derived line-strength gradients from this dataset will be analyzed in a forthcoming paper to set constraints on the different scenarios for the formation of the bulges., Comment: Accepted for publication in A&A

The purpose of the paper is to measure the degree of temperature anisotropy of the oxygen ions in the outer corona. The ratio of the Doppler dimmed OVI 1037-1032 line intensity as a function of the velocity of the fast solar wind, computed for typical values of coronal density, is consistent with the observed ratio, only when a significant temperature anisotropy is established in polar coronal holes. The oxygen ion velocity distribution is constrained to be bi-Maxwellian from 2Rto 3.7R� , where the lowest degree of anisotropy compatible with the observational data increases up to ∼ 7a t 2.9R� , proving that the oxygen ions are accelerated across the magnetic field, in accordance with a preferential energy deposition perpendicular to the field lines, consistent with the process of ion-cyclotron dissipation of Alfven waves. The most plausible evolution of the velocity distribution of the O +5 ions departs from the bi-Maxwellian configuration at 2R� , according to an anisotropy ratio that reaches its maximum value T⊥/T� ∼ 14 at 2.9R� ,a nd further out approaches isotropy, at 3.7R� . In response to the acceleration across the field, energy redistribution along the magnetic field lines accelerates the oxygen component of the solar wind to velocities of 760 km s −1 at 5R� . The variation of the anisotropy ratio with the heliocentric distance might be satisfactorily explained by theoretical models of the fast solar wind heating based on the oxygen cyclotron instability or the fast shock mechanism. The observations of the extended corona analyzed in this paper are performed with the Ultraviolet Coronagraph Spectrometer on board the Solar Heliospheric Observatory, during the solar minimum activity period 1996-1997.

In recent papers convincing evidence has been presented for chemical stratification in Ap star atmospheres, and surface abundance maps have been shown to correlate with the magnetic field direction. Radiatively driven diffusion in magnetic fields is among the processes responsible for these inhomogeneities. Here we explore the hypothesis that equilibrium stratifications can, in a number of cases, explain the observed abundance maps and vertical distributions of the various elements. The investigation of equilibrium stratifications in stellar atmospheres with temperatures from 8500K to 12000K and fields up to 10 kG reveals considerable variations in the vertical distribution of the 5 elements studied (Mg, Si, Ca, Ti, Fe), often with zones of large over- or under-abundances and with indications of other competing processes (such as mass loss). Horizontal magnetic fields can be very efficient in helping the accumulation of elements in higher layers. A comparison between our calculations and the vertical abundance profiles and surface maps derived by magnetic Doppler imaging reveals that equilibrium stratifications are in a number of cases consistent with the main trends inferred from observed spectra. However, it is not clear whether such equilibrium solutions will ever be reached during the evolution of an Ap star., 7 pages, 6 figures, the paper will be published in Astronomy & Astrophysics, on November 2007

Context. Planetary Nebulae (PNe) display complex radial surface brightness profiles whose understanding is crucial for a correct interpretation of their formation and evolution. In particular, the intermediate shells commonly observed around the bright rims of PNe contain important information for the discussion of the mass loss rate at the end of the AGB, for the determination of the post-AGB age of the central stars and the distance via the expansion parallax method, and for the analysis of line profiles for unresolved, faraway objects like extragalactic PNe. Aims. This paper describes the dynamical properties of PNe shells and presents a new practical method to properly determine their expansion velocity. Methods. The analysis is guided by realistic radiative-hydrodynamical simulations which allow to test and verify different methods for the kinematical study of PNe shells using high-resolution long-slit spectra. Results. We show that the use of the derivative of the line profile allows us to determine accurately the post-shock gas velocity in the shells. This method is generally superior to other techniques previously used. In addition, if applied to long-slit data, it allows to determine the velocities of the shells even when they are very close to those of the PNe rims. Its application to 10 real PNe confirms the model predictions and previous conclusions about the substantial mass loss increase during the latest AGB evolution. Conclusions. The method and discussion presented in this paper are meant to be used as a guide for a correct determination of some basic kinematic and evolutionary properties of Galactic and extragalactic PNe, including their expansion parallaxes.

The so-called Limber equation is widely used in the literature to relate the projected angular clustering of galaxies to the spatial clustering of galaxies in an approximate way. This paper gives estimates of where the regime of applicability of Limber's equation stops. Limber's equation is accurate for small galaxy separations but breaks down beyond a certain separation that depends mainly on the ratio sigma/R and to some degree on the power-law index, gamma, of spatial clustering xi; sigma is the one-sigma width of the galaxy distribution in comoving distance, and R the mean comoving distance. As rule-of-thumb, a 10% relative error is reached at 260 sigma/R arcmin for gamma~1.6, if the spatial clustering is a power-law. More realistic xi are discussed in the paper. Limber's equation becomes increasingly inaccurate for larger angular separations. Ignoring this effect and blindly applying Limber's equation can possibly bias results for the inferred spatial correlation. It is suggested to use in cases of doubt, or maybe even in general, the exact equation that can easily be integrated numerically in the form given in the paper., revised (extended) version, 8 pages, 4 figures, accepted by A&A as shortened version

This is the third in a series of papers that deal with angular momentum transport by internal gravity waves. We concentrate on the waves excited by core convection in a 3Msun, Pop I main sequence star. Here, we want to examine the role of the Coriolis acceleration in the equations of motion that describe the behavior of waves and to evaluate its impact on angular momentum transport. We use the so-called traditional approximation of geophysics, which allows variable separation in radial and horizontal components. In the presence of rotation, the horizontal structure is described by Hough functions instead of spherical harmonics. The Coriolis acceleration has two main effects on waves. It transforms pure gravity waves into gravito-inertial waves that have a larger amplitude closer to the equator, and it introduces new waves whose restoring force is mainly the conservation of vorticity. Taking the Coriolis acceleration into account changes the subtle balance between prograde and retrograde waves in non-rotating stars. It also introduces new types of waves that are either purely prograde or retrograde. We show in this paper where the local deposition of angular momentum by such waves is important., 9 pages, 10 figures, accepted for publication by A&A

The purpose of the paper is to extend the measurement of the kinetic temperature and outflow velocity of the oxygen ions in the outer corona above polar holes out to 5 $R_\odot$. An analytical model of the solar corona at the minimum of activity has been employed in order to synthesize the spectral line profiles to be fitted with the data: the kinetic temperature of the O +5 ions on the plane of the sky is derived from the width of the O VI 1031.9 A line by applying the $\chi^2$ minimization. The oxygen temperature peaks at about 2.9 $R_\odot$, reaching a value of 1.5 $\times$ 10 8 K, and further out it is somehow flattening. The outflow velocity of the oxygen component of the fast solar wind, derived from the intensity ratio of the Doppler dimmed O VI doublet, increases outward to reach $550{-}760$ km s -1 at 5 $R_\odot$. The upper and lower limits of the outflow speed are due to the fact that its measurement depends on the velocity distribution of the oxygen ions which cannot be directly measured along the radial direction, but only along the line of sight. Hence the uncertainty is related to the temperature anisotropy assumed in the analysis. For this reason in this paper the measurement of the temperature anisotropy, found beyond 2 $R_\odot$ according to the previous literature on UVCS results, has been as well extended at higher altitudes, and it is found that above 3.7 $R_\odot$ anisotropy can still exist but not necessarily. The observations of the extended corona analyzed in this paper are performed with the Ultraviolet Coronagraph Spectrometer on board the Solar Heliospheric Observatory, during the solar minimum activity period 1996-1997.

The HARPS high-resolution high-accuracy spectrograph is offered to the astronomical community since the second half of 2003. Since then, we have been using this instrument for monitoring radial velocities of a large sample of Solar-type stars (~1400 stars) in order to search for their possible low-mass companions. Amongst the goals of our survey, one is to significantly increase the number of detected extra-solar planets in a volume-limited sample to improve our knowledge of their orbital elements distributions and thus obtain better constraints for planet-formation models. In this paper, we present the HARPS radial-velocity data and orbital solutions for 3 Solar-type stars: HD 100777, HD 190647, and HD 221287. The radial-velocity data of HD 100777 is best explained by the presence of a 1.1 M_Jup planetary companion on a 384--day eccentric orbit (e=0.36). The orbital fit obtained for the slightly evolved star HD 190647 reveals the presence of a long-period (P=1038 d) 1.9 M_Jup planetary companion on a moderately eccentric orbit (e=0.18). HD 221287 is hosting a 3.1 M_Jup planet on a 456--day orbit. The shape of this orbit is not very well constrained because of our non-optimal temporal coverage and because of the presence of abnormally large residuals. We find clues for these large residuals to result from spectral line profile variations probably induced by stellar activity related processes., 7 pages, 4 figures, RV data added in paper. A&A in press

The largest uncertainty for cosmological studies using clusters of galaxies is introduced by our limited knowledge of the statistics of galaxy cluster structure, and of the scaling relations between observables and cluster mass. To improve on this situation we have started an XMM-Newton Large Programme for the in-depth study of a representative sample of 33 galaxy clusters, selected in the redshift range z=0.055 to 0.183 from the REFLEX Cluster Survey, having X-ray luminosities above 0.4 X 10^44 h_70^-2 erg s^-1 in the 0.1 - 2.4 keV band. This paper introduces the sample, compiles properties of the clusters, and provides detailed information on the sample selection function. We describe the selection of a nearby galaxy cluster sample that makes optimal use of the XMM-Newton field-of-view, and provides nearly homogeneous X-ray luminosity coverage for the full range from poor clusters to the most massive objects in the Universe. For the clusters in the sample, X-ray fluxes are derived and compared to the previously obtained fluxes from the ROSAT All-Sky Survey. We find that the fluxes and the flux errors have been reliably determined in the ROSAT All-Sky Survey analysis used for the REFLEX Survey. We use the sample selection function documented in detail in this paper to determine the X-ray luminosity function, and compare it with the luminosity function of the entire REFLEX sample. We also discuss morphological peculiarities of some of the sample members. The sample and some of the background data given in this introductory paper will be important for the application of these data in the detailed studies of cluster structure, to appear in forthcoming publications., 17 pages, 17 figures; to appear in A&A. A pdf version with full-quality figures can be found at ftp://ftp.xray.mpe.mpg.de/people/gwp/xmmlp/xmmlp.pdf

This is the second of a series of papers in which the kinematics of disk galaxies is studied by analysing spectroscopic data. Making use of the methods presented in Paper I, this work focuses on the large-scale distribution of disk and Dark Matter halo material by analysing the structure of warped galaxies. H I observations of three disk galaxies showing regular large-scale ("grand-design") warps are presented and their structure is analysed. The kinematics and geometry of the galaxies are modelled by fitting a tilted-ring model directly to the data cube, thereby avoiding problems due to orbit crowding or beam smearing. The galaxies follow the previously known "rules for the behaviour of warps". Furthermore, at large radii the Hi disk settles into a relatively coplanar disk that is inclined with respect to the inner one. With increasing radius, the measured rotation velocity shows a rise. In one of the cases, NGC 5204, the rotation curve shows a jump at the transition radius. While the best fits in the other two cases also suggest that such a jump is present, the change in rotation velocity is compatible with a gradual rise. In two cases, the surface density of the warped H I layer shows a clear drop at the transition radius and decreases only very slowly further out, while this feature is not as clear for UGC 3580. A literature search shows that these properties are shared by a number of other galaxies. In all cases, an additional, slowly rotating gas layer is found to be present. The change in the rotation velocity and the remarkable geometry of the disks together indicate that the radius at which the warp starts marks the transition between two dynamical regimes, an inner one governed by the stellar disk and an outer one determined by the Dark Matter halo.

Context. HH 30 is a Herbig-Haro (HH) jet showing a chain of aligned knots (with knots covering a range of sizes and knot separations), pointing towards what appears to be a highly fragmented “head”. The chain of knots is detected out to ∼140 �� , and the head is an elongated group of knots centred at a distance of ∼290 �� from the source. Aims. In the paper of Anglada et al. (2006, A&A, submitted), it is suggested that this jet is the result of a multi-period variable velocity ejection, and also having a precession of the outflow axis. The question that we address in our paper is whether or not this ejection variability results in a leading working surface with the high fragmentation of the “head” of the HH 30 jet. Methods. In order to do this, we take at face value the parameters calculated by Anglada et al. (2006) for the ejection variability and the precession and use them to compute a 3D, radiative jet simulation. Our simulation includes a treatment of the non-equilibrium ionization state of the gas, and allows us to compute synthetic emission line maps, which can be compared directly with previously published images of HH 30. Results. We find that our simulation does produce a leading working surface with a striking resemblance to the head of HH 30. We obtain a fragmented emission structure with an extent both along and across the outflow axis that agrees well with the observed jet head. Conclusions. It then appears to be clear that the variable ejection implied by the chain of knots close to the HH 30 source has a direct effect on the head of the jet, producing a highly fragmented structure that is comparable with observations. This is the first time that such a connection has been proven for an HH outflow.

Mass is clearly the most important parameter of a star as it determines the phases it will go through, its physical parameters, the elements produced and its life span. Two important processes that occur simultaneously in young stars are directly related to the final mass a star ends up with; the accretion of material onto the star from a circumstellar disk and the bipolar outflow of material from the star. These processes are related since the infalling material drives the outflow. The life span of circumstellar disks is also important for the possibility of life, as this limits the time available for planet formation. This may depend on the stellar mass and its environment.Three detailed observational case-studies are presented, a globule (B335) that is forming only one or two stars, a medium-sized star formation region (L1551) and a large cluster of young stars (YSOs) in a part of our nearest giant molecular cloud (L1641N).The first part of this thesis concerns finding YSOs by looking for mid-IR excess, indicative of circumstellar disks, using the ISO and Spitzer satellites in combination with ground-based observations. Other signs of youth are also used; H-alpha in emission (accretion), Li 6707 in absorption (Li is destroyed with age) and cloud membership based on extinction. The detection of 15 new YSO candidates in L1551 (Paper I) and 89 YSOs in L1641N (Paper II) is presented. In L1641N, distributions are presented of stellar age and mass. An empirical extinction law is found and the star formation history is presented. There seems to be an accelerated star formation with time. This can however also be explained, at least partly, by migration of older stars from the cluster - a migration that may very well be mass dependent.The second part concerns bipolar outflows. The discovery of six Herbig-Haro objects and at least 15 H2 objects in B335 is presented (Paper III) as well as proper motions for previously known objects. A planar shock model is used to calculate shock velocities. In L1641N (Paper IV) we discover a new outflow source and connect this to a number of H2 objects that are found to be part of this flow from proper motion measurements.

Context. In many papers, the flows in Herbig-Haro (HH) jets have been modeled as collimated outflows with a time-dependent ejection. In particular, a supersonic variability of the ejection velocity leads to the production of "internal working surfaces" which (for appropriate forms of the time-variability) can produce emitting knots that resemble the chains of knots observed along HH jets. Aims. In this paper, we present axisymmetric simulations of an "internal working surface" in a radiative jet (produced by an ejection velocity variability). We concentrate on a given parameter set (i.e., on a jet with a constante ejection density, and a sinusoidal velocity variability with a 20 yr period and a 40 km s -1 half-amplitude), and carry out a study of the behaviour of the solution for increasing numerical resolutions. Methods. In our simulations, we solve the gasdynamic equations together with a 17-species atomic/ionic network, and we are therefore able to compute emission coefficients for different emission lines. Results. We compute 3 adaptive grid simulations, with 20, 163 and 1310 grid points (at the highest grid resolution) across the initial jet radius. From these simulations we see that successively more complex structures are obtained for increasing numerical resolutions. Such an effect is seen in the stratifications of the flow variables as well as in the predicted emission line intensity maps. Conclusions. We find that while the detailed structure of an internal working surface depends on resolution, the predicted emission line luminosities (integrated over the volume of the working surface) are surprisingly stable. This is definitely good news for the future computation of predictions from radiative jet models for carrying out comparisons with observations of HH objects.

We describe in detail the nature of XMM-Newton EPIC background and its various complex components, summarising the new findings of the XMM-Newton EPIC background working group, and provide XMM-Newton background blank sky event files for use in the data analysis of diffuse and extended sources. Blank sky event file data sets are produced from the stacking of data, taken from 189 observations resulting from the Second XMM-Newton Serendipitous Source Catalogue (2XMMp) reprocessing. The data underwent several filtering steps, using a revised and improved method over previous work, which we describe in detail. We investigate several properties of the final blank sky data sets. The user is directed to the location of the final data sets. There is a final data set for each EPIC instrument-filter-mode combination., Comment: Paper accepted by A&A 22 December 2006. 14 pages, 8 figures. Paper can also be found at http://www.star.le.ac.uk/~jac48/publications/

The OSIRIS camera onboard the Rosetta spacecraft has been acquiring images of the comet 67P/Churyumov-Gerasimenko (67P)'s nucleus at spatial resolutions down to ~0.17 m/px ever since Aug. 2014. These images have yielded unprecedented insight into the morphological diversity of the comet's surface. This paper presents an overview of the regional morphology of comet 67P. Methods: We used the images that were acquired at orbits ~20-30 km from the center of the comet to distinguish different regions on the surface and introduce the basic regional nomenclature adopted by all papers in this Rosetta special feature that address the comet's morphology and surface processes. We used anaglyphs to detect subtle regional and topographical boundaries and images from close orbit (~10 km from the comet's center) to investigate the fine texture of the surface. Results: Nineteen regions have currently been defined on the nucleus based on morphological and/or structural boundaries, and they can be grouped into distinctive region types. Consolidated, fractured regions are the most common region type. Some of these regions enclose smooth units that appear to settle in gravitational sinks or topographically low areas. Both comet lobes have a significant portion of their surface covered by a dusty coating that appears to be recently placed and shows signs of mobilization by aeolian-like processes. The dusty coatings cover most of the regions on the surface but are notably absent from a couple of irregular large depressions that show sharp contacts with their surroundings and talus-like deposits in their interiors, which suggests that short-term explosive activity may play a significant role in shaping the comet's surface in addition to long-term sublimation loss. Finally, the presence of layered brittle units showing signs of mechanical failure predominantly in one of the comet's lobes can indicate a compositional heterogeneity between the two lobes.

In this paper we study the infall, by dynamical friction, of rigid "satellites" taken in a variety of initial configurations and models. We thus measure how dynamical friction depends on the density concentration and on the pressure anisotropy of the host galaxy and, separately, the response of the galaxy during the process. The investigation is carried out by using a numerical laboratory set up in previous papers of this series. We find that the pressure anisotropy present in the host galaxy has little effect on dynamical friction. Instead, the shape of the galaxy density profile is very important. The classical idealized description appears to be applicable to galaxy models characterized by a small density gradient but not to concentrated models. In contrast to the behavior found in small density gradient models, the orbits of satellites captured in concentrated models are not circularized by dynamical friction. The induced evolution in the host galaxy reflects the initial conditions adopted for the captured satellite. Satellites spiraling in on quasi-circular orbits tend to modify the pressure tensor of the host galaxy in the tangential direction and the galaxy shape from spherical to oblate, while satellites captured along quasi-radial orbits tend to induce pressure anisotropy in the radial direction and to generate a prolate shape. This result suggests that the shape of early-type galaxies may result from occasional mergers rather than being directly related to the effectiveness of the radial-orbit instability during the process of formation via collisionless collapse, as often argued in the past., Comment: 16 pages, 18 figures, accepted by Astronomy & Astrophysics

Context. The stability properties of filamentary magnetic structures are relevant for the storage and dynamics of magnetic fields in stellar convection zones and possibly also in other astrophysical contexts. Aims. In a series of papers we study the effect of external and internal flows on the stability of magnetic flux tubes. In this paper we consider the effect of a flow perpendicular to a straight, horizontal flux tube embedded in a gravitationally stratified fluid. The flow acts on the flux tube by exerting an aerodynamic drag force and by modifying the pressure stratification in the background medium. Methods. We carry out a Lagrangian linear stability analysis in the framework of the approximation of thin magnetic flux tubes. Results. The external flow can drive monotonic and oscillatory instability (overstability). The stability condition depends on direction and magnitude of the external velocity as well as on its first and second derivatives with respect to depth. The range of the flow-driven instabilities typically extends to modes with much shorter wavelengths than for the buoyancy-driven undulatory Parker instability. Conclusions. Perpendicular flows with Alfvenic Mach number of order unity can drive monotonic as well as oscillatory instability of thin magnetic flux tubes. Such instability can affect the storage of magnetic flux in stellar interiors.

The general context of this paper is the study of magnetic fields in the pre-main sequence intermediate mass Herbig Ae/Be stars. Magnetic fields are likely to play an important role in pre-main sequence evolution at these masses, in particular in controlling the gains and losses of stellar angular momentum. The particular aim of this paper is to announce the detection of a structured magnetic field in the Herbig Ae star HD 190073, and to discuss various scenarii for the geometry of the star, its environment and its magnetic field. We have used the ESPaDOnS spectropolarimeter at CFHT in 2005 and 2006 to obtain high-resolution and signal-to-noise circular polarization spectra which demonstrate unambiguously the presence of a magnetic field in the photosphere of this star. Nine circular polarization spectra were obtained, each one showing a clear Zeeman signature. This signature is suggestive of a magnetic field structured on large scales. The signature, which corresponds to a longitudinal magnetic field of 74+- 10 G, does not vary detectably on a one-year timeframe, indicating either an azimuthally symmetric field, a zero inclination angle between the rotation axis and the line of sight, or a very long rotation period. The optical spectrum of HD 190073 exhibits a large number of emission lines. We discuss the formation of these emission lines in the framework of a model involving a turbulent heated region at the base of the stellar wind, possibly powered by magnetic accretion. This magnetic detection brings an important element for our understanding of stellar magnetism at intermediate masses., Comment: 10 pages, 6 figures. accepted by Astronomy & Astrophysics

Stellar oscillations are excited in non-synchronously rotating stars in binary systems due to the tidal forces. Tangential components of the tides can drive a shear flow which behaves as a differentially forced rotating structure in a stratified outer medium. In this paper we show that our single-layer approximation for the calculation of the forced oscillations yields results that are consistent with the predictions for the synchronization timescales in circular orbits. In addition, calibrating our model results to fit Zahn's relationship between synchronization timescales and orbital separation, we are able to constrain the value of the kinematical viscosity parameter. For the 4Mo+5Mo binary modeled in this paper, the kinematical viscosity is in the range 0.0015 -- 0.0043 Ro^2/d for orbital periods in the range 2.5 -- 25 d. Furthermore, the energy dissipation rate due to the shear flow is found to decrease by ~2 orders of magnitude as synchronization is approached, implying that binary systems may approach synchronization relatively quickly but that it takes a much longer timescale to actually attain this condition. Our model can be used to calculate the energy dissipation rates throughout the orbital cycle for arbitrary values of eccentricity and stellar rotational velocity. We suggest that the asymmetric distribution of energy dissipation over the stellar surface may lead to the appearance of localized regions of enhanced surface activity., Comment: 9 pages, 5 figures

Aims: This is the first paper in a series dedicated to investigating the kinematic properties of nearby associations of young stellar objects. Here we study the Taurus-Auriga association, with the primary objective of deriving kinematic parallaxes for individual members of this low-mass star-forming region. Methods: We took advantage of a recently published catalog of proper motions for pre-main sequence stars, which we supplemented with radial velocities from various sources found in the CDS databases. We searched for stars of the Taurus-Auriga region that share the same space velocity, using a modified convergent point method that we tested with extensive Monte Carlo simulations. Results: Among the sample of 217 Taurus-Auriga stars with known proper motions, we identify 94 pre-main sequence stars that are probable members of the same moving group and several additional candidates whose pre-main sequence evolutionary status needs to be confirmed. We derive individual parallaxes for the 67 moving group members with known radial velocities and give tentative parallaxes for other members based on the average spatial velocity of the group. The Hertzsprung-Russell diagram for the moving group members and a discussion of their masses and ages are presented in a companion paper., Comment: accepted for publication by A&A

Aims. Hard X-ray (HXR) emission in the footpoints of flaring loops often indicates an asymmetry, where brighter X-ray flux usually appears in the footpoint with a weaker magnetic field. This is explained by the fact that more electrons can reach the chromosphere in the weaker magnetic field. However, there are numerous exceptions to above rule, where the stronger HXR source is located in the loop's foot that is rooted in the stronger magnetic field. In our paper we analyse three such exceptional events from the paper by Goff et al. (2004, A&A, 423, 363). For all three events, we found evidence of the magnetic loops interactions near a brighter footpoint. Such loop interactions suggest that for these flares the energy release is located closer to one end of the loop. Methods. We analysed the process of electron transport in detail in the dense flaring loop as a possible cause of the observed asymmetry. Using the flare parameters derived from observations, we calculated how the collisional energy losses in the loop reduce the number of electrons impacting the chromosphere at the other footpoint. Results. We show that these calculations reproduce the observed flux ratios within the error limits in both footpoints for each of the analysed events. Thus we conclude that the injection of electrons near one of the footpoints, together with enhanced density in the flaring loop, can explain observed HXR footpoints asymmetry.

Aims. We present the results of the numerical simulations of the interaction between a magnetized star and an imperfectly conducting accretion disk. The star is rotating with constant angular velocity. The differentially rotating Keplerian disk is treated as a boundary condition. We are interested in the magnetic field topology dependence on the electrical conductivity of the disk. Methods. To analyze the “star–disk” interaction we numerically investigate the MHD equations using Godunov-type high resolution numerical methods. Results. It was found that in our model the “star–disk” interaction occurs with a quasi-periodic reconnection of the magnetic field coronal loops and plasmoid ejections. In the case of the perfect disk conductivity, the evolution of the coronal magnetic field leads to the periodic outflow of angular momentum from the disk. In the case of an imperfectly conducting disk, the configuration of the magnetic field is formed such that the disk angular momentum carried by the magnetic field is balanced by angular momentum carried by matter. It should be noted that we used the ideal MHD equation to obtain the solutions. The reconnection process in the disk corona depends on the numerical diffusivity that exists in our numerical code. Our simulations treat reconnection as occurring in current sheets. The thickness of the current sheet is broadened by numerical resistivity. Nevertheless, we suppose that the reconnection and plasmoid ejection takes place as well for real magnetic diffusivity. To verify the method and results we also used several more detailed grids to estimate the numerical diffusivity of the scheme. It is turned out that the setup model presented in the paper quite reasonable satisfies the goal of this paper, i.e., to investigate the regime of interaction between the magnetized star and the disk.

We describe a wide and deep search for optical GRB afterglows on images taken with MegaCAM at the Canada France Hawaii Telescope, within the framework of the CFHT Legacy Survey. This search is performed in near real-time thanks to a Real Time Analysis System called "Optically Selected GRB Afterglows", which has been completely realized and installed on a dedicated computer in Hawaii. This pipeline automatically and quickly analyzes Megacam images and extracts from them a list of astrometrically and photometrically variable objects which are displayed on a web page for validation by a member of the collaboration. In this paper, we comprehensively describe the RTAS process. We also present statistical results based on nearly one full year of operation, showing the quality of the images and the performance of the RTAS. Finally, we compare the efficiency of this study with similar searches, propose an ideal observational strategy using simulations, and discuss general considerations on the searches for GRB afterglows independently of the prompt emission. This is the first of a series of two papers. A second paper will discuss the characterization of variable objects we have found, as well as the GRB afterglow candidates and their nature. We will also estimate or at least constrain the collimation factor of GRB using the totality of the Very Wide Survey observations.

Aims: This paper commences a series devoted to the study of the stellar content of early-type galaxies. The goal of the series is to set constraints on the evolutionary status of these objects. Methods: In this paper we describe the details of the galaxy sample, the observations, and the data reduction. Line-strength indices and velocity dispersions sigma are measured in 98 early-type galaxies drawn from different environments, and the relation of the indices with the velocity dispersion analysed in detail. Results: The present sample indicates that some of the index-sigma relations depend on galaxy environment. In particular, the slope of the relation between Balmer lines and sigma is steeper for galaxies in the Virgo cluster, small groups, and in the field than for galaxies in the Coma cluster. In several indices there is also a significant offset in the zero point between the relations defined by the different subsamples. The slopes of the index-sigma relation for the Virgo and low-density environment galaxies are explained by a variation of both age and metallicity with velocity dispersion, as previously noted in other studies. For the galaxies in the Coma cluster, however, the relation of the indices with sigma only requires a variation of the abundance along the sigma sequence. In agreement with other studies we find that the models that better reproduce the slopes are those in which the alpha elements vary more than the Fe-peak elements along the sigma sequence, while, at a given sigma, older galaxies show an higher alpha/Fe ratio. Conclusions: The results can be explained assuming that galaxies in the Coma cluster have experienced a truncated star formation and chemical enrichment history compared to a more continuous time-extended history for their counterparts in lower density environments.

International audience; Context: .The 2006 IAU General Assembly has adopted the P03 model of Capitaine et al. (2003a) recommended by the WG on precession and the ecliptic (Hilton et al. 2006) to replace the IAU 2000 model, which comprised the Lieske et al. (1977) model with adjusted rates. Practical implementations of this new "IAU 2006" model are therefore required, involving choices of procedures and algorithms. Aims: .The purpose of this paper is to recommend IAU 2006 based precession-nutation computing procedures, suitable for different classes of application and achieving high standards of consistency. Methods: .We discuss IAU 2006 based procedures and algorithms for generating the rotation matrices that transform celestial to terrestrial coordinates, taking into account frame bias (B), P03 precession (P), P03-adjusted IAU 2000A nutation (N) and Earth rotation. The NPB portion can refer either to the equinox or to the celestial intermediate origin (CIO), requiring either the Greenwich sidereal time (GST) or the Earth rotation angle (ERA) as the measure of Earth rotation. Where GST is used, it is derived from ERA and the equation of the origins (EO) rather than through an explicit formula as in the past, and the EO itself is derived from the CIO locator. Results: .We provide precession-nutation procedures for two different classes of full-accuracy application, namely (i) the construction of algorithm collections such as the Standards Of Fundamental Astronomy (SOFA) library and (ii) IERS Conventions, and in addition some concise procedures for applications where the highest accuracy is not a requirement. The appendix contains a fully worked numerical example, to aid implementors and to illustrate the consistency of the two full-accuracy procedures which, for the test date, agree to better than 1 muas. Conclusions: .The paper recommends, for case (i), procedures based on angles to represent the PB and N components and, for case (ii), procedures based on series for the CIP X,Y. The two methods are of similar efficiency, and both support equinox based as well as CIO based applications.

Context. This is Paper V in a series on polarimetric aperture synthesis based on the algebra of 2 × 2 matrices. Aims. It validates the matrix self-calibration theory of the preceding Paper IV and outlines the algorithmic methods that had to be developed for its application. Methods. New avenues of polarimetric self-calibration opened up in Paper IV are explored by processing a simulated observation. To focus on the polarimetric issues, it is set up so as to sidestep some of the common complications of aperture synthesis, yet properly represent physical conditions. In addition to a representative collection of observing errors, the simulated instrument includes strongly varying Faraday rotation and antennas with unequal feeds. The selfcal procedure is described in detail, including aspects in which it differs from the scalar case, and its effects are demonstrated with a number of intermediate image results. Results. The simulation’s outcome is in full agreement with the theory. The nonlinear matrix equations for instrumental parameters are readily solved by iteration; a convergence problem is easily remedied with a new ancillary algorithm. Instrumental effects are cleanly separated from source properties without reference to changes in parallactic rotation during the observation. Polarimetric images of high purity and dynamic range result. As theory predicts, polarimetric errors that are common to all sources inevitably remain; prior knowledge of the statistics of linear and circular polarization in a typical observed field can be applied to eliminate most of them. Conclusions. The paper conclusively demonstrates that matrix selfcal per se is a viable method that may foster substantial advancement in the art of radio polarimetry. For its application in real observations, a number of issues must be resolved that matrix selfcal has in common with its scalar sibling, such as the treatment of extended sources and the familiar sampling and aliasing problems. The close analogy between scalar interferometry and its matrix-based generalisation suggests that one may apply well-developed methods of scalar interferometry. Marrying these methods to those of this paper will require a significant investment in new software. Two such developments are known to be foreseen or underway.

This paper is the first of a series of papers in which we will apply the methods we have developed for high-precision astrometry (and photometry) with the Hubble Space Telescope to the case of wide-field ground-based images. In particular, we adapt the software originally developed for WFPC2 to ground-based, wide field images from the WFI at the ESO 2.2m telescope. In this paper, we describe in details the new software, we characterize the WFI geometric distortion, discuss the adopted local transformation approach for proper-motion measurements, and apply the new technique to two-epoch archive data of the two closest Galactic globular clusters: NGC 6121 (M4) and NGC 6397. The results of this exercise are more than encouraging. We find that we can achieve a precision of ~7 mas (in each coordinate) in a single exposure for a well-exposed star, which allows a very good cluster-field separation in both M4, and NGC 6397, with a temporal baseline of only 2.8, and 3.1 years, respectively., Comment: 1 pages, 17 figures, 1 table. Accepted for publication in A&A, on April 15 2006. For high resolution version: http://www.eso.org/~lbedin/WFI_method/ms.ps.gz

I study the joint effect of dynamical friction, tidal torques and cosmological constant on clusters of galaxies formation I show that within high-density environments, such as rich clusters of galaxies, both dynamical friction and tidal torques slows down the collapse of low-? peaks producing an observable variation in the time of collapse of the perturbation and, as a consequence, a reduction in the mass bound to the collapsed perturbation Moreover, the delay of the collapse produces a tendency for less dense regions to accrete less mass, with respect to a classical spherical model, inducing a biasing of over-dense regions toward higher mass I show how the threshold of collapse is modified if dynamical friction, tidal torques and a non-zero cosmological constant are taken into account and I use the Extended Press Schecter (EPS) approach to calculate the effects on the mass function Then, I compare the numerical mass function given in Reed et al (2003) with the theoretical mass function obtained in the present paper I show that the barrier obtained in the present paper gives rise to a better description of the mass function evolution with respect to other previous models (Sheth & Tormen 1999, MNRAS, 308, 119 (hereafter ST); Sheth & Tormen 2002, MNRAS, 329, 61 (hereafter ST1))