References of "Astronomy and Astrophysics"      in Complete repository Arts & humanities   Archaeology   Art & art history   Classical & oriental studies   History   Languages & linguistics   Literature   Performing arts   Philosophy & ethics   Religion & theology   Multidisciplinary, general & others Business & economic sciences   Accounting & auditing   Production, distribution & supply chain management   Finance   General management & organizational theory   Human resources management   Management information systems   Marketing   Strategy & innovation   Quantitative methods in economics & management   General economics & history of economic thought   International economics   Macroeconomics & monetary economics   Microeconomics   Economic systems & public economics   Social economics   Special economic topics (health, labor, transportation…)   Multidisciplinary, general & others Engineering, computing & technology   Aerospace & aeronautics engineering   Architecture   Chemical engineering   Civil engineering   Computer science   Electrical & electronics engineering   Energy   Geological, petroleum & mining engineering   Materials science & engineering   Mechanical engineering   Multidisciplinary, general & others Human health sciences   Alternative medicine   Anesthesia & intensive care   Cardiovascular & respiratory systems   Dentistry & oral medicine   Dermatology   Endocrinology, metabolism & nutrition   Forensic medicine   Gastroenterology & hepatology   General & internal medicine   Geriatrics   Hematology   Immunology & infectious disease   Laboratory medicine & medical technology   Neurology   Oncology   Ophthalmology   Orthopedics, rehabilitation & sports medicine   Otolaryngology   Pediatrics   Pharmacy, pharmacology & toxicology   Psychiatry   Public health, health care sciences & services   Radiology, nuclear medicine & imaging   Reproductive medicine (gynecology, andrology, obstetrics)   Rheumatology   Surgery   Urology & nephrology   Multidisciplinary, general & others Law, criminology & political science   Civil law   Criminal law & procedure   Criminology   Economic & commercial law   European & international law   Judicial law   Metalaw, Roman law, history of law & comparative law   Political science, public administration & international relations   Public law   Social law   Tax law   Multidisciplinary, general & others Life sciences   Agriculture & agronomy   Anatomy (cytology, histology, embryology...) & physiology   Animal production & animal husbandry   Aquatic sciences & oceanology   Biochemistry, biophysics & molecular biology   Biotechnology   Entomology & pest control   Environmental sciences & ecology   Food science   Genetics & genetic processes   Microbiology   Phytobiology (plant sciences, forestry, mycology...)   Veterinary medicine & animal health   Zoology   Multidisciplinary, general & others Physical, chemical, mathematical & earth Sciences   Chemistry   Earth sciences & physical geography   Mathematics   Physics   Space science, astronomy & astrophysics   Multidisciplinary, general & others Social & behavioral sciences, psychology   Animal psychology, ethology & psychobiology   Anthropology   Communication & mass media   Education & instruction   Human geography & demography   Library & information sciences   Neurosciences & behavior   Regional & inter-regional studies   Social work & social policy   Sociology & social sciences   Social, industrial & organizational psychology   Theoretical & cognitive psychology   Treatment & clinical psychology   Multidisciplinary, general & others     Showing results 541 to 560 of 812     23 24 25 26 27 28 29 30 31 32 33     Convection-pulsation coupling. I. A mixing-length perturbative theoryGrigahcène, A.; Dupret, Marc-Antoine ; Gabriel, Maurice et alin Astronomy and Astrophysics (2005), 434We present in details a time-dependent convection treatment in the frame of the Mixing-Length Theory (MLT). Following the original ideas by Unno (1967, PASJ, 19, 140), this theory has been developed by ... [more ▼]We present in details a time-dependent convection treatment in the frame of the Mixing-Length Theory (MLT). Following the original ideas by Unno (1967, PASJ, 19, 140), this theory has been developed by Gabriel et al. (1974, Bull. Ac. Roy. Belgique, Classe des Sciences, 60, 866) and Gabriel (1996, Bull. Astron. Soc. India, 24, 233). In this paper, we present it in a united form, we detail the basic derivations and approximations and give final improvements. A new perturbation of the energy closure equation is proposed for the first time, making it possible to avoid the occurrence of short wavelength spatial oscillations of the thermal eigenfunctions. This theory accounts for the perturbation of the convective flux, the turbulent Reynolds stress and the turbulent kinetic energy dissipation. It has been numerically implemented in a non-radial non-adiabatic pulsation code and the first results published in a Letter by Dupret et al. (2004a, A&A, 414, L17) indicate that the theory predicts the observed red border of the lower end of the instability strip and the driving mechanism of the recently discovered gamma Dor stars. [less ▲]Detailed reference viewed: 48 (2 ULg) Abundance correlations in mildly metal-poor stars. II. Light elements (C to Ca)Decauwer, Hélène; Jehin, Emmanuel ; Parmentier, Geneviève et alin Astronomy and Astrophysics (2005), 433Accurate relative abundances have been obtained for carbon, oxygen, sodium, aluminium, silicon, and calcium in a sample of mildly metal-poor stars. This analysis complements a previous study carried out ... [more ▼]Accurate relative abundances have been obtained for carbon, oxygen, sodium, aluminium, silicon, and calcium in a sample of mildly metal-poor stars. This analysis complements a previous study carried out by Jehin et al. ([CITE], A&A, 341, 241), which provided the basis for the EASE scenario. This scenario postulates that field metal-poor stars were born in self-enriched proto-globular cluster clouds. By further investigating the correlations between the different alpha-element abundances, we propose a modified scenario for the formation of intermediate metallicity stars, in which the stars exhibiting lower than average alpha/Fe abundance ratios would form in low mass clouds, unable to sustain the formation of very massive stars (M âª 30~M_o). Moreover, the carbon-to-iron ratio is found to decrease as one climbs the so-called Population IIb branch, i.e. when the s-element abundance increases. In the framework of the EASE scenario, we interpret this anticorrelation between the carbon and the s-element abundances as a signature of a hot bottom burning process in the metal-poor AGB stars which expelled the matter subsequently accreted by our Population IIb stars. Based on observations collected at the European Southern Observatory, La Silla, Chile (ESO Programmes 56.E-0384, 57.E-0400 and 59.E-0257). [less ▲]Detailed reference viewed: 21 (0 ULg) Spectroscopic determination of photospheric parameters and chemical abundances of 6 K-type starsAffer, L.; Micela, G.; Morel, Thierry et alin Astronomy and Astrophysics (2005), 433High resolution, high -S/N- ratio optical spectra have been obtained for a sample of 6 K-type dwarf and subgiant stars, and have been analysed with three different LTE methods in order to derive detailed ... [more ▼]High resolution, high -S/N- ratio optical spectra have been obtained for a sample of 6 K-type dwarf and subgiant stars, and have been analysed with three different LTE methods in order to derive detailed photospheric parameters and abundances and to compare the characteristics of analysis techniques. The results have been compared with the aim of determining the most robust method to perform complete spectroscopic analyses of K-type stars, and in this perspective the present work must be considered as a pilot study. In this context we have determined the abundance ratios with respect to iron of several elements. In the first method the photospheric parameters (T_eff, log g, and Î¾) and metal abundances are derived using measured equivalent widths and Kurucz LTE model atmospheres as input for the MOOG software code. The analysis proceeds in an iterative way, and relies on the excitation equilibrium of the ion{Fe}{i} lines for determining the effective temperature and microturbulence, and on the ionization equilibrium of the ion{Fe}{i} and ion{Fe}{ii} lines for determining the surface gravity and the metallicity. The second method follows a similar approach, but discards the ion{Fe}{i} low excitation potential transitions (which are potentially affected by non-LTE effects) from the initial line list, and relies on the B-V colour index to determine the temperature. The third method relies on the detailed fitting of the 6162 Ã ion{Ca}{i} line to derive the surface gravity, using the same restricted line list as the second method. Methods 1 and 3 give consistent results for the program stars; in particular the comparison between the results obtained shows that the ion{Fe}{i} low-excitation potential transitions do not appear significantly affected by non-LTE effects (at least for the subgiant stars), as suggested by the good agreement of the atmospheric parameters and chemical abundances derived. The second method leads to systematically lower T_eff and log g values with respect to the first one, and a similar trend is shown by the chemical abundances (with the exception of the oxygen abundance). These differences, apart from residual non-LTE effects, may be a consequence of the colour-T_eff scale used. The Î±-elements have abundance ratios consistent with the solar values for all the program stars, as expected for â normalâ disk stars. The first method appears to be the most reliable one, as it is self-consistent, it always leads to convergent solutions and the results obtained are in good agreement with previous determinations in the literature. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roche de los Muchachos of the Instituto de Astrofisica de Canarias. Table 6 is only available in electronic form at http://www.edpsciences.org [less ▲]Detailed reference viewed: 21 (2 ULg) New optical polarization measurements of quasi-stellar objects. The dataSluse, Dominique ; Hutsemekers, Damien ; Lamy, H. et alin Astronomy and Astrophysics (2005), 433New linear polarization measurements (mainly in the V band) are presented for 203 quasi-stellar objects (QSOs). The sample is made up of 94 QSOs located in the North Galactic Pole (NGP) region and of 109 ... [more ▼]New linear polarization measurements (mainly in the V band) are presented for 203 quasi-stellar objects (QSOs). The sample is made up of 94 QSOs located in the North Galactic Pole (NGP) region and of 109 QSOs in the South Galactic Pole (SGP) region. First time measurements have been obtained for 184 QSOs. Among them, 109 known radio-emitters, 42 known Broad Absorption Line (BAL) QSOs, and 1 gravitationally lensed quasi-stellar object. We found high polarization levels (p > 3%) for 12 QSOs, including the BAL QSO SDSS J1409+0048. For 10 objects, measurements obtained at different epochs do exist. Two of them show evidence for variability: the highly polarized BL Lac candidate PKS 1216-010 and the radio source PKS 1222+037. Based on observations collected at the European Southern Observatory (ESO, La Silla and Paranal). Table 4 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/433/757 [less ▲]Detailed reference viewed: 51 (3 ULg) A study of bright southern slowly pulsating B stars. III. Mode identification for singly-periodic targets in spectroscopyDe Cat, P.; Briquet, Maryline ; Daszynska-Daszkiewicz, J. et alin Astronomy and Astrophysics (2005), 432We present the results of the mode identification for a sample of 7 bright southern slowly pulsating B stars showing one pulsation frequency in the lambdalambda 413 nm Si II profiles. We combined the ... [more ▼]We present the results of the mode identification for a sample of 7 bright southern slowly pulsating B stars showing one pulsation frequency in the lambdalambda 413 nm Si II profiles. We combined the results from (1) the method of photometric amplitudes; (2) the moment method; and (3) the amplitude and phase variation across the profile to search for the l and m values of the modes best fitting the data. It is the first time that the applicability of these techniques is tested to a sample of main-sequence g-mode pulsators. Combining the moment method with the amplitude and phase variations across the observed line profile gives an improvement in spectroscopic identification of low degree l g-mode pulsations. Using the variations of the higher order even moments < v[SUP]4[/SUP]> and < v[SUP]6[/SUP]> of the moment method solutions can also help. For HD 181558, HD 24587, HD 140873 and HD 177863, the photometric and spectroscopic results are compatible and point towards (l,m) = (1, +1) sectoral modes. For HD 215573, HD 53921 and HD 92287, the results are inconclusive. Our proposed methodology for mode identification is also applicable to gamma Doradus stars. Based on observations collected with the CAT Telescope of the European Southern Observatory and with the Swiss Photometric Telescope of the Geneva Observatory, both situated at La Silla in Chile. [less ▲]Detailed reference viewed: 11 (1 ULg) Isotopic abundance of nitrogen and carbon in distant cometsManfroid, Jean ; Jehin, Emmanuel ; Hutsemekers, Damien et alin Astronomy and Astrophysics (2005), 432(Letters), 5-8The [SUP]12[/SUP]C[SUP]14[/SUP]N/[SUP]12[/SUP]C[SUP]15[/SUP]N and [SUP]12[/SUP]C[SUP]14[/SUP]N/[SUP]13[/SUP]C[SUP]14[/SUP]N isotopic ratios have been determined in comets C/1995 O1 (Hale-Bopp), C/2001 Q4 ... [more ▼]The [SUP]12[/SUP]C[SUP]14[/SUP]N/[SUP]12[/SUP]C[SUP]15[/SUP]N and [SUP]12[/SUP]C[SUP]14[/SUP]N/[SUP]13[/SUP]C[SUP]14[/SUP]N isotopic ratios have been determined in comets C/1995 O1 (Hale-Bopp), C/2001 Q4 (NEAT) and C/2003 K4 (LINEAR) at heliocentric distances of, respectively, 2.7, 3.7 and 2.6 AU. These ratios have also been measured at rË 1 AU. No significant differences were found between all determinations, nor with the value obtained for other comets. If confirmed, the discrepancy between the nitrogen isotopic ratios from optical and millimeter measurements on CN and HCN would rule out HCN as a major parent of the cometary CN radicals. Based on observations collected at the European Southern Observatory, Paranal, Chile (ESO Programmes 270.C-5043, 073.C-0525 and 274.C-5015). [less ▲]Detailed reference viewed: 21 (1 ULg) Disentangling component spectra of κ Scorpii, a spectroscopic binary with a pulsating primary. II. Interpretation of the line-profile variabilityUytterhoeven, K.; Briquet, Maryline ; Aerts, C. et alin Astronomy and Astrophysics (2005), 432We analyse the complex short-term SiIII line-profile variability of the spectroscopic binary β Cep star κ Scorpii after orbit subtraction, before and after spectral disentangling. We refine the known ... [more ▼]We analyse the complex short-term SiIII line-profile variability of the spectroscopic binary β Cep star κ Scorpii after orbit subtraction, before and after spectral disentangling. We refine the known oscillation frequency of the star: f[SUB]1[/SUB]=4.99922 c d[SUP]-1[/SUP] and detect 2f[SUB]1[/SUB]. Variability is also found at frequencies near f[SUB]2[/SUB]≃ 4.85 c d[SUP]-1[/SUP] and f[SUB]3[/SUB]≃ 5.69 c d[SUP]-1[/SUP] or their aliases. These frequencies are not significant if we consider the spectra alone, but they survive our selection after the consideration that they were derived previously from independent ground-based and space photometry by different teams. Moreover, we find dominant variability in the equivalent width with a frequency in the interval [0.22,0.30] c d[SUP]-1[/SUP] which we interpret as the rotational frequency f[SUB]rot[/SUB] of the star. The complex window function does not allow us to determine definite values for f[SUB]2[/SUB], f[SUB]3[/SUB], f[SUB]rot[/SUB]. The variability with f[SUB]1[/SUB] is interpreted as a prograde non-radial oscillation mode with spherical wavenumbers (ℓ,m)=(2,-1) or (1,-1). The additional frequencies are explained in terms of rotational modulation superposed to the main oscillation. We also point out that we cannot disprove the variability in κ Scorpii to originate from co-rotating structures. KOREL disentangling preserves the large-amplitude line-profile variability but its performance for complex low-amplitude variability remains to be studied in detail. Based on observations obtained with the Coudé Échelle Spectrograph on the ESO CAT telescope and with the CORALIE échelle spectrograph on the 1.2-m Euler Swiss telescope, both situated at La Silla, Chile. [less ▲]Detailed reference viewed: 3 (0 ULg) The spectrum of the very massive binary system WR20a (WN6ha+WN6ha): Fundamental parameters and wind interactionsRauw, Grégor ; Crowther, P. A.; De Becker, Michaël et alin Astronomy and Astrophysics (2005), 432(3), 985-998We analyse the optical spectrum of the very massive binary system WR20a (WN6ha + WN6ha). The most prominent emission lines, Halpha and He II lambda4686, display strong phase-locked profile variability ... [more ▼]We analyse the optical spectrum of the very massive binary system WR20a (WN6ha + WN6ha). The most prominent emission lines, Halpha and He II lambda4686, display strong phase-locked profile variability. From the variations of their equivalent widths and from a tomographic analysis, we find that part of the line emission probably arises in a wind interaction region between the stars. Our analysis of the optical spectrum of WR20a indicates a reddening of A(nu) similar or equal to 6.0 mag and a distance of similar to 7.9 kpc, suggesting that the star actually belongs to the open cluster Westerlund 2. The location of the system at similar to 1.1 pc from the cluster core could indicate that WR20a was gently ejected from the core via dynamical interactions. Using a non-LTE model atmosphere code, we derive the fundamental parameters of each component: T-eff = 43 000 +/- 2000 K, log L-bol/ L-. similar or equal to 6.0, (M) over dot = 8.5 x 10(-6) M-. yr(-1) (assuming a clumped wind with a volume filling factor f = 0.1). Nitrogen is enhanced in the atmospheres of the components of WR20a, while carbon is definitely depleted. Finally, the position of the binary components in the Hertzsprung-Russell diagram suggests that they are core hydrogen burning stars in a pre-LBV stage and their current atmospheric chemical composition probably results from rotational mixing that might be enhanced in a close binary compared to a single star of same age. [less ▲]Detailed reference viewed: 32 (2 ULg) An optical time delay for the double gravitational lens system FBQ 0951+2635Jakobsson, P.; Hjorth, J.; Burud, I. et alin Astronomy and Astrophysics (2005), 431(1), 103-109We present optical R-band light curves of the double gravitationally lensed quasar FBQ 0951+2635 from observations obtained at the Nordic Optical Telescope between March 1999 and June 2001. A time delay ... [more ▼]We present optical R-band light curves of the double gravitationally lensed quasar FBQ 0951+2635 from observations obtained at the Nordic Optical Telescope between March 1999 and June 2001. A time delay of Deltatau = 16 +/- 2 days (1sigma) is determined from the light curves. New constraints on the lensing geometry are provided by the position and ellipticity of the lensing galaxy. For a (Omega(m), Omega(Lambda)) = (0.3, 0.7) cosmology, the time delay yields a Hubble parameter of H-0 = 60(-7)(+9) (random, 1sigma) +/-2 (systematic) km s(-1) Mpc(-1) for a singular isothermal ellipsoid model and H-0 = 63(-7)(+9) (random, 1sigma) +/-1 (systematic) km s(-1) Mpc(-1) for a constant mass-to-light ratio model. In both models, the errors are mainly due to the time-delay uncertainties. Non-parametric models yield H-0 = 64(-7)(+9) (random, 1sigma) +/- 14 (systematic) km s(-1) Mpc(-1). [less ▲]Detailed reference viewed: 10 (0 ULg) An XMM-Newton look at the Wolf-Rayet star WR 40 - The star itself, its nebula and its neighboursGosset, Eric ; Nazé, Yaël ; Claeskens, Jean-François et alin Astronomy and Astrophysics (2005), 429(2), 685-704We present the results of an XMM-Newton observation of the field of the Wolf-Rayet star WR 40. Despite a nominal exposure of 20 ks and the high sensitivity of the satellite, the star itself is not ... [more ▼]We present the results of an XMM-Newton observation of the field of the Wolf-Rayet star WR 40. Despite a nominal exposure of 20 ks and the high sensitivity of the satellite, the star itself is not detected: we thus derive an upper limit on its X-ray flux and luminosity. Joining this result to recent reports of a non-detection of some WC stars, we suggest that the X-ray emission from single normal Wolf-Rayet stars could often be insignificant despite remarkable instabilities in the wind. On the basis of a simple modelling of the opacity of the Wolf-Rayet wind of WR 40, we show that any X-ray emission generated in the particular zone where the shocks are supposed to be numerous will indeed have little chance to emerge from the dense wind of the Wolf-Rayet star. We also report the non-detection of the ejecta nebula RCW 58 surrounding WR 40. Concerning the field around these objects, we detected 33 X-ray sources, most of them previously unknown: we establish a catalog of these sources and cross-correlate it with catalogs of optical/infrared sources. [less ▲]Detailed reference viewed: 31 (8 ULg) Solitary waves in self-gravitating molecular cloudsCattaert, Tom ; Verheest, F.in Astronomy and Astrophysics (2005), 438(1), 23-29Molecular clouds are self-gravitating fluids that support different waves and contain highly nonlinear clumps and filaments, for which explanations have been sought in terms of solitons. The present paper ... [more ▼]Molecular clouds are self-gravitating fluids that support different waves and contain highly nonlinear clumps and filaments, for which explanations have been sought in terms of solitons. The present paper explores the possibility that several ( neutral) species with different thermal speeds coexist, as in a molecular cloud consisting of gas and dust, or of a mixture of normal matter and dark matter. It is shown that this model can support soliton formation, both with humps or dips in the self-gravitational potential. The existence domain has been given in terms of the hot species Mach number and fractional mass density, in a gas-dynamic description which emphasizes the constraints coming from the sonic and neutral points, and from the limits due to infinite compression or total rarefaction. One species is compressed while the other is rarefied, allowing the system to reach a mass neutral point outside equilibrium. In this way, solitons are possible without invoking interaction with a weakly ionized cloud component or involving envelope solitons that are not really stationary structures. [less ▲]Detailed reference viewed: 19 (4 ULg) Hard X-ray emission clumps in the gamma-Cygni supernova remnant: An INTEGRAL-ISGRI viewBykov, A. M.; Krassilchtchikov, A. M.; Uvarov, Y. A. et alin Astronomy and Astrophysics (2004), 427(3), 21-24Spatially resolved images of the galactic supernova remnant G78.2+2.1 (gamma-Cygni) in hard X-ray energy bands from 25 keV to 120 keV are obtained with the IBIS-ISGRI imager aboard the International Gamma ... [more ▼]Spatially resolved images of the galactic supernova remnant G78.2+2.1 (gamma-Cygni) in hard X-ray energy bands from 25 keV to 120 keV are obtained with the IBIS-ISGRI imager aboard the International Gamma-Ray Astrophysics Laboratory INTEGRAL. The images are dominated by localized clumps of about ten arcmin in size. The flux of the most prominent North-Western (NW) clump is (1.7+/-0.4)x10(-11) erg cm(-2) s(-1) in the 25-40 keV band. The observed X-ray fluxes are in agreement with extrapolations of soft X-ray imaging observations of gamma-Cyg by ASCA GIS and spatially unresolved RXTE PCA data. The positions of the hard X-ray clumps correlate with bright patches of optical line emission, possibly indicating the presence of radiative shock waves in a shocked cloud. The observed spatial structure and spectra are consistent with model predictions of hard X-ray emission from nonthermal electrons accelerated by a radiative shock in a supernova interacting with an interstellar cloud, but the powerful stellar wind of the O9V star HD 193322 is a plausible candidate for the NW source as well. [less ▲]Detailed reference viewed: 57 (0 ULg) Line profile variability in the spectra of Oef stars - II. HD192281, HD14442 and HD14434De Becker, Michaël ; Rauw, Grégor in Astronomy and Astrophysics (2004), 427(3), 995-1008We present the very first analysis of the spectroscopic variability of the three rapidly rotating Oef stars HD 192281 (O5(ef)), HD14442 (O5.5ef) and HD 14434 (O6.5( ef)). Radial velocities of the He II ... [more ▼]We present the very first analysis of the spectroscopic variability of the three rapidly rotating Oef stars HD 192281 (O5(ef)), HD14442 (O5.5ef) and HD 14434 (O6.5( ef)). Radial velocities of the He II lambda 4541 line reveal no evidence of binarity on time scales of a few days, or from one year to the next, for any of the targets. The He II lambda 4686 double-peaked emission and, to some extent, the H absorption line display significant profile variability in the spectra of all three stars. Data gathered during different observing runs spread over six years reveal a rather stable time scale for HD 192281 and HD14442, whereas the variability pattern changes significantly from one year to the other. The case of HD 14434 is less clear as no obvious time scale emerges from our analysis. In a tentative way to interpret this variability, stellar rotation remains a possible clock for HD 192281 and HD14442. However, currently available models addressing stellar rotation fail to explain some crucial aspects of the observed variability behaviour, which appear to be even more complex in the case of HD 14434. [less ▲]Detailed reference viewed: 21 (3 ULg) The photospheric abundances of active binaries. III. Abundance peculiarities at high activity levelsMorel, Thierry ; Micela, G.; Favata, F. et alin Astronomy and Astrophysics (2004), 426We report the determination from high-resolution spectra of the atmospheric parameters and abundances of 13 chemical species (among which lithium) in 8 single-lined active binaries. These data are ... [more ▼]We report the determination from high-resolution spectra of the atmospheric parameters and abundances of 13 chemical species (among which lithium) in 8 single-lined active binaries. These data are combined with our previous results for 6 other RS CVn systems to examine a possible relationship between the photospheric abundance patterns and the stellar activity level. The stars analyzed are generally found to exhibit peculiar abundance ratios compared to inactive, Galactic disk stars of similar metallicities. We argue that this behaviour is unlikely to be an artefact of errors in the determination of the atmospheric parameters or non-standard mixing processes along the red giant branch, but diagnoses instead the combined action of various physical processes related to activity. The most promising candidates are cool spot groups covering a very substantial fraction of the stellar photosphere or NLTE effects arising from nonthermal excitation. However, we cannot exclude the possibility that more general shortcomings in our understanding of K-type stars (e.g. inadequacies in the atmospheric models) also play a significant role. Lastly, we call attention to the unreliability of the (V-R) and (V-I) colour indices as temperature indicators in chromospherically active stars. Based on observations collected at the European Southern Observatory, Chile (Proposals 64.L-0249 and 071.D-0260). Table A.1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/426/1007 [less ▲]Detailed reference viewed: 31 (2 ULg) Polarization properties of broad absorption line QSOs: New statistical cluesLamy, H.; Hutsemekers, Damien in Astronomy and Astrophysics (2004), 427We report the results of several statistical tests performed on a large sample of 139 broad absorption line (BAL) QSOs with good quality optical spectra and/or optical polarization data. Correlations ... [more ▼]We report the results of several statistical tests performed on a large sample of 139 broad absorption line (BAL) QSOs with good quality optical spectra and/or optical polarization data. Correlations between ten optical indices and the polarization degree p[SUB]0[/SUB] are systematically searched for. We find six significant non-trivial correlations. In order to identify the most important correlations, we perform a principal component analysis with a sample of 30 BAL QSOs and eight quantities (including p[SUB]0[/SUB]). Most of the variance (Ë 57%) in the data is contained in two principal components called PC1 and PC2. PC1 is mainly dominated by the correlation between the balnicity index BI and the strength of the Fe II emission; it may be driven by the accretion rate of matter onto the central compact object. The variance in PC2 is essentially due to the anti-correlation between p[SUB]0[/SUB] and the detachment index DI, indicating that BAL QSOs with P Cygni profiles (DIâ ª) are usually more polarized than those objects with C IV absorption troughs well detached from the corresponding emission lines (DIâ «). We show that PC2 may be related to the orientation of the BAL QSOs with respect to the line of sight. We also present new spectropolarimetric observations of six BAL QSOs. By adding spectropolarimetric data from the literature, we build a sample of 21 BAL QSOs for which we define four spectropolarimetric indices describing the polarization properties of the absorption and emission lines. We find that the polarization of the C III]] emission line is systematically higher than the polarization of the C IV emission line, and that the highest polarization in the troughs is correlated to the balnicity index. Another important result emerging from the statistical tests performed on this spectropolarimetric sample is a possible anti-correlation between the detachment index and a quantity SI which measures the ratio of the depths of the C IV absorption in the polarized flux and in the total flux. This correlation indicates that in BAL QSOs with P cygni profiles, the BAL troughs in the polarized flux are nearly as deep as in the total flux while, in BAL QSOs with detached absorptions, the BAL troughs in the polarized flux are much weaker than in the total flux. We show that our main results may be explained in the framework of a two-component'' wind model which is a natural extension of the classical wind-from-disk models. In this model, the broad absorption occurs in a dense equatorial wind emerging from the accretion disk, while scattering and polarization mainly take place in a polar region. The orientation relative to the observer drives the correlations p[SUB]0[/SUB] - DI and DI - SI. While most of our observations can be explained within this framework, there are also several indications that other polarization mechanisms, and more particularly resonance scattering, may also be at work. Based on observations collected at the European Southern Observatory (ESO, La Silla). Table 1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http: / / cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/427/107 [less ▲]Detailed reference viewed: 51 (0 ULg) Abundance analysis of targets for the COROT/MONS asteroseismology missions. II. Abundance analysis of the COROT main targetsBruntt, H.; Bikmaev, I. F.; Catala, C. et alin Astronomy and Astrophysics (2004), 425One of the goals of the ground-based support program for the COROT and MONS/RÖMER satellite missions is to characterize suitable target stars for the part of the missions dedicated to asteroseismology. We ... [more ▼]One of the goals of the ground-based support program for the COROT and MONS/RÖMER satellite missions is to characterize suitable target stars for the part of the missions dedicated to asteroseismology. We present the detailed abundance analysis of nine of the potential COROT main targets using the semi-automatic software VWA. For two additional COROT targets we could not perform the analysis due to the high rotational velocity of these stars. For five stars with low rotational velocity we have also performed abundance analysis by a classical equivalent width method in order to test the reliability of the VWA software. The agreement between the different methods is good. We find that it is necessary to measure abundances extracted from each line relative to the abundances found from a spectrum of the Sun in order to remove systematic errors. We have constrained the global atmospheric parameters T[SUB]eff[/SUB], log g, and [Fe/H] to within 70-100 K, 0.1-0.2 dex, and 0.1 dex for five stars which are slow rotators (v sin i < 15 km s[SUP]-1[/SUP]). For most of the stars we find good agreement with the parameters found from line depth ratios, H alpha lines, Strömgren indices, previous spectroscopic studies, and also log g determined from the HIPPARCOS parallaxes. For the fast rotators (v sin i > 60 km s[SUP]-1[/SUP]) it is not possible to constrain the atmospheric parameters. Based on observations obtained with the 193 cm telescope at Observatoire de Haute Provence, France. [less ▲]Detailed reference viewed: 28 (3 ULg) On-axis spectroscopy of the z =0.144 radio-loud quasar HE 1434-1600: an elliptical host with a highly ionized ISMLetawe, Géraldine ; Courbin, F.; Magain, Pierre et alin Astronomy and Astrophysics (2004), 424VLT on-axis optical spectroscopy of the z=0.144 radio-loud quasar HE 1434-1600 is presented. The spatially resolved spectra of the host galaxy are deconvolved and separated from those of the central ... [more ▼]VLT on-axis optical spectroscopy of the z=0.144 radio-loud quasar HE 1434-1600 is presented. The spatially resolved spectra of the host galaxy are deconvolved and separated from those of the central quasar in order to study the dynamics of the stars and gas as well as the physical conditions of the ISM. We find that the host of HE 1434-1600 is an elliptical galaxy that resides in a group of at least 5 member galaxies, and that most likely experienced a recent collision with its nearest companion. Compared with other quasar host galaxies, HE 1434-1600 has a highly ionized ISM. The ionization state corresponds to that of typical Seyferts, but the ionized regions are not distributed in a homogeneous way around the QSO, and are located preferentially several kiloparsecs away from it. While the stellar absorption lines do not show any significant velocity field, the gas emission lines do. The observed gas velocity field is hard to reconcile with dynamical models involving rotating disk, modified Hubble laws or power laws, that all require extreme central masses (M>10[SUP]9[/SUP] M[SUB]o[/SUB]) to provide only poor fit to the data. Power law models, which best fit the data, provide a total mass of M(<10 kpc) = 9.2 × 10[SUP]10[/SUP] M[SUB]o[/SUB]. We conclude that the recent interaction between HE 1434-1600 and its closest companion has strongly affected the gas velocity and ionization state, from the center of the galaxy to its most external parts. Based on observations made with the ESO Very Large Telescope ANTU/UT1 at ESO-Paranal observatory, Chile (program 65.P-0361(A)). [less ▲]Detailed reference viewed: 27 (1 ULg) A spectroscopic study of the non-thermal radio emitter Cyg OB2#8A: Discovery of a new binary systemDe Becker, Michaël ; Rauw, Grégor ; Manfroid, Jean in Astronomy and Astrophysics (2004), 424(3), 39-42We present the results of a spectroscopic campaign revealing that the non-thermal radio emitter Cyg OB2 #8A is an O6+O5.5 binary system. We propose the very first orbital solution indicating a period of ... [more ▼]We present the results of a spectroscopic campaign revealing that the non-thermal radio emitter Cyg OB2 #8A is an O6+O5.5 binary system. We propose the very first orbital solution indicating a period of about 21.9 days. The system appears to be eccentric (0.24+/-0.04) and is likely seen under a rather low inclination angle. The mass ratio of the components is close to unity. The impact of the binarity of this star in the framework of our understanding of non-thermal radio emission from early-type stars is briefly discussed. [less ▲]Detailed reference viewed: 11 (3 ULg) On the determination of oxygen abundances in chromospherically active starsMorel, Thierry ; Micela, G.in Astronomy and Astrophysics (2004), 423We discuss oxygen abundances derived from [O I] Î»6300s and the O I triplet in stars spanning a wide range in chromospheric activity level, and show that these two indicators yield increasingly discrepant ... [more ▼]We discuss oxygen abundances derived from [O I] Î»6300s and the O I triplet in stars spanning a wide range in chromospheric activity level, and show that these two indicators yield increasingly discrepant results with higher chromospheric/coronal activity measures. While the forbidden and permitted lines give fairly consistent results for solar-type disk dwarfs, spuriously high O I triplet abundances are observed in young Hyades and Pleiades stars, as well as in individual components of RS CVn binaries (up to 1.8 dex). The distinct behaviour of the [O I]-based abundances which consistently remain near-solar suggests that this phenomenon mostly results from large departures from LTE affecting the O I triplet at high activity level that are currently unaccounted for, but also possibly from a failure to adequately model the atmospheres of K-type stars. These results suggest that some caution should be exercised when interpreting oxygen abundances in active binaries or young open cluster stars. Based on observations collected at the European Southern Observatory, Chile (Proposals 64.L-0249 and 071.D-0260). Table \ref{tab_data} is only available in electronic form at http://www.edpsciences.org [less ▲]Detailed reference viewed: 23 (3 ULg) The XMM-LSS survey - First high redshift galaxy clusters: Relaxed and collapsing systemsValtchanov, I.; Pierre, M.; Willis, J. et alin Astronomy and Astrophysics (2004), 423(1), 75-85We present five newly found galaxy clusters at z > 0.6 from the XMM Large-Scale Structure Survey (XMM-LSS). All five objects are extended X-ray sources in the XMM images. For three of them we have ... [more ▼]We present five newly found galaxy clusters at z > 0.6 from the XMM Large-Scale Structure Survey (XMM-LSS). All five objects are extended X-ray sources in the XMM images. For three of them we have sufficient spectroscopically confirmed member galaxies that an estimate of the velocity dispersion is possible: XLSSC 001 at z = 0.613 and sigma(nu) = 867(-60)(+80) km s(-1), XLSSC 002 at z = 0.772 and sigma(nu) = 524(-116)(+267) km s(-1) and XLSSC 003 at z = 0.839 and sigma(V) = 780(-75)(+137) km s(-1). These three clusters have X-ray bolometric luminosities L-X similar to 1-3 x 10(44) erg s(-1) and temperatures 2-4 keV, and consequently are less massive than previously known clusters at similar redshifts, but nevertheless they follow the low redshift scaling relations between L-X, T and sigma(upsilon), within the limits of the measurement errors. One of the clusters, XLSSC 004, is detected independently as an over-density of galaxies of a colour R - z' = 1.4 that matches the redshift of the central galaxy z = 0.87, although it cannot unambiguously be confirmed by the spectroscopic observations alone. The highest redshift candidate cluster pertaining to this paper, XLSSC 005, is most likely a double cluster complex at a redshift around unity, associated with an extended X-ray source with probable substructure. [less ▲]Detailed reference viewed: 42 (1 ULg)