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See detailThe XMM-LSS survey - First high redshift galaxy clusters: Relaxed and collapsing systems
Valtchanov, I.; Pierre, M.; Willis, J. et al

in Astronomy and Astrophysics (2004), 423(1), 75-85

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 ... [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 ▲]

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See detailEarly-type stars in the young open cluster IC 1805 - I. The SB2 system BD+60 degrees 497 and the probably single stars BD+60 degrees 501 and BD+60 degrees 513
Rauw, Grégor ULg; De Becker, Michaël ULg

in Astronomy and Astrophysics (2004), 421(2), 693-702

We investigate the multiplicity of three O-type stars in the very young open cluster IC 1805. All our targets were previously considered as spectroscopic binaries, but no orbital solution was available ... [more ▼]

We investigate the multiplicity of three O-type stars in the very young open cluster IC 1805. All our targets were previously considered as spectroscopic binaries, but no orbital solution was available for any of them. Our results confirm the binarity of BD+60degrees 497 and we provide the very first orbital solution for this double-lined spectroscopic binary. This is only the second O-star binary in IC 1805, and the first SB2 system, for which an orbital solution is now available. BD+60degrees 497 has an orbital period of 3.96 days and consists of an evolved 06.5 V((f)) primary and an 08.5-9.5 V((f)) secondary with minimum masses of m, sin(3) i = 13.9 M-circle dot and m(2) sin 3 i = 10.9 M-circle dot. The observed primary/secondary mass ratio (1.28) appears lower than expected from a comparison with single star evolutionary models (1.60-1.74). For the other two stars, BD+60degrees 501 and BD+60degrees 513, we find no significant radial velocity variations, suggesting that they are most probably single. Although a fraction of binaries among the early-type stars of IC 1805 as high as 80% has been advocated in the literature, our results suggest that this number might be overestimated. [less ▲]

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See detailErratum: VLT + UVES spectroscopy of the low-ionization intrinsic absorber in SDSS J001130.56+005550.7
Hutsemekers, Damien ULg; Hall, Patrick; Brinkmann, J.

in Astronomy and Astrophysics (2004), 422

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See detailProbable detection of radial magnetic field gradients in the atmospheres of Ap stars
Nesvacil, N.; Hubrig, S.; Jehin, Emmanuel ULg

in Astronomy and Astrophysics (2004), 422

For the first time the possible presence of radial gradients of magnetic fields in the atmospheres of three magnetic Ap stars has been critically examined by measurements of the mean magnetic field ... [more ▼]

For the first time the possible presence of radial gradients of magnetic fields in the atmospheres of three magnetic Ap stars has been critically examined by measurements of the mean magnetic field modulus from spectral lines resolved into magnetically split components lying on the different sides of the Balmer jump. A number of useful diagnostic lines below and above the Balmer discontinuity, only slightly affected by blends, with simple doublet and triplet Zeeman pattern have been identified from the comparison between synthetic spectra computed with the SYNTHMAG code and the high resolution and S/N spectra obtained in unpolarized light with the ESO VLT UVES spectrograph. For all three stars of our sample, HD 965, HD 116114 and 33 Lib, an increase of the magnetic field strength of the order of a few hundred Gauss has been detected bluewards of the Balmer discontinuity. These results should be taken into account in future modelling of the geometric structure of Ap star magnetic fields and the determination of the chemical abundances in Ap stars with strong magnetic fields. Based on observations obtained at the European Southern Observatory, Paranal, Chile (ESO program No. 70.D-0470). [less ▲]

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See detailWR 20a: A massive cornerstone binary system comprising two extreme early-type stars
Rauw, Grégor ULg; De Becker, Michaël ULg; Nazé, Yaël ULg et al

in Astronomy and Astrophysics (2004), 420(2), 9-13

We analyse spectroscopic observations of WR20a revealing that this star is a massive early-type binary system with a most probable orbital period of similar to3.675 days. Our spectra indicate that both ... [more ▼]

We analyse spectroscopic observations of WR20a revealing that this star is a massive early-type binary system with a most probable orbital period of similar to3.675 days. Our spectra indicate that both components are most likely of WN6ha or 031f*/WN6ha spectral type. The orbital solution for a period of 3.675 days yields extremely large minimum masses of 70.7 +/- 4.0 and 68.8 +/- 3.8 M. for the two stars. These properties make WR 20a a cornerstone system for the study of massive star evolution. [less ▲]

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See detailQuasi-simultaneous XMM-Newton and VLA observation of the non-thermal radio emitter HD 168112 (O5.5III(f+))
De Becker, Michaël ULg; Rauw, Grégor ULg; Blomme, Ronny et al

in Astronomy and Astrophysics (2004), 420

We report the results of a multiwavelength study of the non-thermal radio emitter HD 168112 (O5.5III(f+)). The detailed analysis of two quasi-simultaneous XMM-Newton and VLA observations reveals strong ... [more ▼]

We report the results of a multiwavelength study of the non-thermal radio emitter HD 168112 (O5.5III(f+)). The detailed analysis of two quasi-simultaneous XMM-Newton and VLA observations reveals strong variability of this star both in the X-ray and radio ranges. The X-ray observations separated by five months reveal a decrease of the X-ray flux of ˜30%. The radio emission on the other hand increases by a factor 5-7 between the two observations obtained roughly simultaneously with the XMM-Newton pointings. The X-ray data reveal a hard emission that is most likely produced by a thermal plasma at kT ˜ 2-3 keV while the VLA data confirm the non-thermal status of this star in the radio waveband. Comparison with archive X-ray and radio data confirms the variability of this source in both wavelength ranges over a yet ill defined time scale. The properties of HD 168112 in the X-ray and radio domain point towards a binary system with a significant eccentricity and an orbital period of a few years. However, our optical spectra reveal no significant changes of the star's radial velocity suggesting that if HD 168112 is indeed a binary, it must be seen under a fairly low inclination. [less ▲]

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See detailXMM-Newton observations of the giant H II region N 11 in the LMC
Nazé, Yaël ULg; Antokhin, I. I.; Rauw, Grégor ULg et al

in Astronomy and Astrophysics (2004), 418(3), 841-855

Using the sensitive XMM-Newton observatory, we have observed the giant H II region N11 in the LMC for similar to30 ks. We have detected several large areas of soft diffuse X-ray emission along with 37 ... [more ▼]

Using the sensitive XMM-Newton observatory, we have observed the giant H II region N11 in the LMC for similar to30 ks. We have detected several large areas of soft diffuse X-ray emission along with 37 point sources. One of the most interesting results is the possible association of a faint X-ray source with BSDL 188, a small extended object of uncertain nature, The OB associations in the field-of-view (LH9, LH10 and LH13) are all detected with XMM-Newton, but they appear very different from one another. The diffuse soft X-ray emission associated with LH9 peaks near HD 32228, a dense cluster of massive stars. The combined emission of all individual massive stars of LH9 and of the superbubble they have created is not sufficient to explain the high level of emission observed: hidden SNRs, colliding-wind binaries and the numerous pre-main sequence stars of the cluster are most likely the cause of this discrepancy. The superbubble may also be leaking some hot gas in the ISM since faint, soft emission can be observed to the south of the cluster. The X-ray emission from LH10 consists of three pointlike sources and a soft extended emission of low intensity. The two brightest point sources are clearly associated with the fastest expanding bubbles blown by hot stars in the SW part of the cluster. The total X-ray emission from LH10 is rather soft, although it presents a higher temperature than the other soft emissions of the field. The discrepancy between the combined emission of the stars and the observed luminosity is here less severe than for LH9 and could be explained in terms of hot gas filling the wind-blown bubbles. On the other hand, the case of LH13 is different: it does not harbour any extended emission and its X-ray emission could most probably be explained by the Sk -66degrees41 cluster alone. Finally, our XMM-Newton observation included simultaneous observations with the OM camera that provide us with unique UV photometry of more than 6000 sources and enable the discovery of the UV emission from the SNR N11L. [less ▲]

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See detailHD 108: The mystery deepens with XMM-Newton observations
Nazé, Yaël ULg; Rauw, Grégor ULg; Vreux, Jean-Marie ULg et al

in Astronomy and Astrophysics (2004), 417(2), 667-677

In 2001, using a large spectroscopic dataset from an extensive monitoring campaign, we discovered that the peculiar Of star HD 108 displayed extreme line variations. This strange behaviour could be ... [more ▼]

In 2001, using a large spectroscopic dataset from an extensive monitoring campaign, we discovered that the peculiar Of star HD 108 displayed extreme line variations. This strange behaviour could be attributed to a variety of models, and an investigation of the high energy properties of HD 108 was needed to test the predictions from these models. Our dedicated XMM-Newton observation of HD 108 shows that its spectrum is well represented by a two temperature thermal plasma model with kT(1) similar to 0.2 keV and kT(2) similar to 1.4 keV. In addition, we find that the star does not display any significant short-term changes during the XMM-Newton exposure. Compared to previous Einstein and ROSAT detections, it also appears that HD 108 does not present long-term flux variations either. While the line variations continue to modify HD 108's spectrum in the optical domain, the X-ray emission of the star appears thus surprisingly stable: no simple model is for the moment able to explain such an unexpected behaviour. Thanks to its high sensitivity, the XMM-Newton observatory has also enabled the serendipitous discovery of 57 new X-ray sources in the field of HD 108. Their properties are also discussed in this paper. [less ▲]

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See detailLong-term multicolour photometry and high-resolution spectroscopy of the two gamma Doradus stars HD 12901 and HD 48501
Aerts, C.; Cuypers, J.; De Cat, P. et al

in Astronomy and Astrophysics (2004), 415

We gathered long-term multicolour Geneva UB[SUB]1[/SUB]BB[SUB]2[/SUB]V[SUB]1[/SUB]VG photometric and high-resolution (R=40 000) spectroscopic data of the two gamma Doradus stars HD 12901 and HD 48501. The ... [more ▼]

We gathered long-term multicolour Geneva UB[SUB]1[/SUB]BB[SUB]2[/SUB]V[SUB]1[/SUB]VG photometric and high-resolution (R=40 000) spectroscopic data of the two gamma Doradus stars HD 12901 and HD 48501. The photometry reveals three frequencies for each of the two stars: f[SUB]1[/SUB]=1.21563 c d[SUP]-1[/SUP], f[SUB]2[/SUB]=1.39594 c d[SUP]-1[/SUP] and f[SUB]3[/SUB]=2.18636 c d[SUP]-1[/SUP] for HD 12901 and f[SUB]1[/SUB]=1.09408 c d[SUP]-1[/SUP], f[SUB]2[/SUB]=1.29054 c d[SUP]-1[/SUP] and f[SUB]3[/SUB]=1.19924 c d[SUP]-1[/SUP] for HD 48501. The photometric amplitude is each time largest in the Geneva B[SUB]1[/SUB] filter and the variations in all the different filters are perfectly in phase within the measurement errors. Mode identification points out that the six modes are all l=1 modes and that the non-adiabatic temperature variations are extremely small, in contradiction to current theoretical predictions. Our spectra show that all the observed frequencies are intrinsic to the stars and cannot be due to binarity. We detect clear line-profile variations at low amplitude (<1 km s[SUP]-1[/SUP]) due to the oscillations of both targets. The estimated v sin i from the spectra are Ë 53 km s[SUP]-1[/SUP] for HD 12901 and Ë 29 km s[SUP]-1[/SUP] for HD 48501. It is at present unclear if the triplet-like structure for HD 48501 is the consequence of rotational splitting or of the large separation expected for high-order gravity modes in the asymptotic regime. Based on observations gathered with the Swiss 0.7 m telescope equipped with the photometer P 7 and with the Swiss 1.2 m Euler telescope equipped with the spectrograph CORALIE, both situated at La Silla, Chile. Reduced data available upon request from the first author. [less ▲]

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See detailAn XMM-Newton observation of the massive binary HD 159176
De Becker, Michaël ULg; Rauw, Grégor ULg; Pittard, J. M. et al

in Astronomy and Astrophysics (2004), 416(1), 221-233

We report the analysis of an XMM-Newton observation of the close binary HD 159176 (O7 V + O7 V). The observed L-x/L-bol ratio reveals an X-ray luminosity exceeding by a factor similar to7 the expected ... [more ▼]

We report the analysis of an XMM-Newton observation of the close binary HD 159176 (O7 V + O7 V). The observed L-x/L-bol ratio reveals an X-ray luminosity exceeding by a factor similar to7 the expected value for X-ray emission from single O-stars. therefore suggesting a wind-wind interaction scenario. EPIC and RGS spectra are fitted consistently with a two temperature mekal optically thin thermal plasma model, with temperatures ranging from similar to2 to 6 x 10(6) K. At first sight, these rather low temperatures are consistent with the expectations for a close binary system where the winds collide well before reaching their terminal velocities. We also investigate the variability of the X-ray light curve of HD,159176 on various short time scales. No significant variability is found and we-conclude that if hydrodynamical instabilities exist in the wind interaction region of HD 159176, they are not sufficient to produce an observable signature in the X-ray emission. Hydrodynamic simulations using wind parameters from the literature reveal some puzzling discrepancies. The most-striking one concerns the predicted X-ray luminosity which is one or more orders of magnitude larger than the observed one. A significant reduction of the mass loss rate of the components compared to the values quoted in the literature alleviates the discrepancy but is not sufficient to fully account for the observed luminosity. Because hydrodynamical models are best for the adiabatic case whereas the colliding winds in HD 159176 are most likely highly radiative, a totally new approach has been envisaged, using a geometrical steady-state colliding wind model suitable for the case of radiative winds. This model successfully reproduces the spectral shape of the EPIC spectrum, but further developments are still needed to alleviate the disagreement between theoretical and observed X-ray luminosities. [less ▲]

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See detailNon-adiabatic theoretical observables in delta Scuti stars
Moya, A.; Garrido, R.; Dupret, Marc-Antoine ULg

in Astronomy and Astrophysics (2004), 414

Phase differences and amplitude ratios at different colour photometric bands are currently being used to discriminate pulsation modes to facilitate mode identification of kappa-driven non-radial pulsating ... [more ▼]

Phase differences and amplitude ratios at different colour photometric bands are currently being used to discriminate pulsation modes to facilitate mode identification of kappa-driven non-radial pulsating stars. In addition to physical inputs (e.g., mass, T_eff, etc.), these quantities depend on the non-adiabatic treatment of the atmosphere. This paper presents theoretical results concerning delta Scuti pulsating stars. The envelope of each of these stellar structures possesses a convection zone whose development is determined by various factors. An interacting pulsation-atmosphere physical treatment is introduced which supplies two basic non-adiabatic physical quantities: the relative effective temperature variation and the phase lag phi[SUP]T[/SUP], defined as the angle between effective temperature variation and radial displacement. These quantities can be used to derive the phase differences and amplitude ratios. Numerivalues for these quantities depend critically on the alpha MLT parameter used to calculate the convection in the envelope. The dependence on alpha was analyzed and it was found that the use of colour observations may be of considerable importance in testing the MLT. Finally, examples are given of how alpha introduces uncertainties in the theoretical predictions regarding phases and amplitudes of photometric variations in delta Scuti pulsating stars. [less ▲]

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See detailVLT + UVES spectroscopy of the low-ionization intrinsic absorber in SDSS J001130.56+005550.7
Hutsemekers, Damien ULg; Hall, Patrick; Brinkmann, J.

in Astronomy and Astrophysics (2004), 415

We analyse high-resolution VLT+UVES spectra of the low-ionization intrinsic absorber observed in the BAL QSO SDSS J001130.56+005550.7. Two narrow absorption systems at velocities -600 km s[SUP]-1[/SUP ... [more ▼]

We analyse high-resolution VLT+UVES spectra of the low-ionization intrinsic absorber observed in the BAL QSO SDSS J001130.56+005550.7. Two narrow absorption systems at velocities -600 km s[SUP]-1[/SUP] and -22 000 km s[SUP]-1[/SUP] are detected. The low-velocity system is part of the broad absorption line (BAL), while the high-velocity one is well detached. While most narrow absorption components are only detected in the high-ionization species, the lowest velocity component is detected in both high- and low-ionization species, including in the excited Si II[SUP]*[/SUP] and C II[SUP]*[/SUP] lines. From the analysis of doublet lines, we find that the narrow absorption lines at the low-velocity end of the BAL trough are completely saturated but do not reach zero flux, their profiles being dominated by a velocity-dependent covering factor. The covering factor is significantly smaller for Mg II than for Si IV and N V , which demonstrates the intrinsic nature of absorber. From the analysis of the excited Si II[SUP]*[/SUP] and C II[SUP]*[/SUP] lines in the lowest velocity component, we find an electron density ~=10[SUP]3[/SUP] cm[SUP]-3[/SUP]. Assuming photoionization equilibrium, we derive a distance ~=20 kpc between the low-ionization region and the quasar core. The correspondence in velocity of the high- and low-ionization features suggests that all these species must be closely associated, hence formed at the same distance of Ë 20 kpc, much higher than the distance usually assumed for BAL absorbers. Based on observations collected at the European Southern Observatory, Cerro Paranal, Chile (ESO 267.A-5698). [less ▲]

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See detailAsteroseismology of the beta Cep star HD 129929. I. Observations, oscillation frequencies and stellar parameters
Aerts, C.; Waelkens, C.; Daszynska-Daszkiewicz, J. et al

in Astronomy and Astrophysics (2004), 415

We have gathered and analysed a timeseries of 1493 high-quality multicolour Geneva photometric data of the B3V beta Cep star HD 129929. The dataset has a time base of 21.2 years. The occurrence of a ... [more ▼]

We have gathered and analysed a timeseries of 1493 high-quality multicolour Geneva photometric data of the B3V beta Cep star HD 129929. The dataset has a time base of 21.2 years. The occurrence of a beating phenomenon is evident from the data. We find evidence for the presence of at least six frequencies, among which we see components of two frequency multiplets with an average spacing of Ë 0.0121 c d[SUP]-1[/SUP] which points towards very slow rotation. This result is in agreement with new spectroscopic data of the star and also with previously taken UV spectra. We provide the amplitudes of the six frequencies in all seven photometric filters. The metal content of the star is Z=0.018± 0.004. All these observational results will be used to perform detailed seismic modelling of this massive star in a subsequent paper. Based on data gathered with the Swiss 0.7m telescope equipped with the photometer P7 of the Geneva Observatory and with the FEROS spectrograph attached to the ESO 2.2 m telescope, both situated at La Silla in Chile; the reduced photometric multicolour data are provided in Table 1, which 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/415/241 [less ▲]

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See detailAsteroseismology of the beta Cep star HD 129929. II. Seismic constraints on core overshooting, internal rotation and stellar parameters
Dupret, Marc-Antoine ULg; Thoul, Anne ULg; Scuflaire, Richard ULg et al

in Astronomy and Astrophysics (2004), 415

We perform a detailed seismic study of the beta Cep star HD 129929. Our analysis is based on the recent derivation of six pulsation frequencies. These frequencies are unambiguously identified from the ... [more ▼]

We perform a detailed seismic study of the beta Cep star HD 129929. Our analysis is based on the recent derivation of six pulsation frequencies. These frequencies are unambiguously identified from the seismic modelling and the photometric amplitudes to be the radial fundamental, the l=1, p[SUB]1[/SUB] triplet, two consecutive components of the l=2, g[SUB]1[/SUB] quintuplet. A non-adiabatic analysis allows us to constrain the metallicity of the star to Z \in [0.016, 0.022]. In addition, the fitting of three independent frequencies, two of which correspond to axisymmetric (m=0) modes, allows us to constrain the core overshooting parameter to alpha[SUB]ov[/SUB]=0.10 ± 0.05, as well as the other global parameters of the star. Finally, from the observation of the l=1 triplet and part of the l=2 quintuplet, we derive constraints on the internal rotation of this star. [less ▲]

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See detailTheoretical instability strips for delta Scuti and gamma Doradus stars
Dupret, Marc-Antoine ULg; Grigahcène, A.; Garrido, R. et al

in Astronomy and Astrophysics (2004), 414

New theoretical instability strips for delta Sct and gamma Dor stars are presented. These results have been obtained taking into account the perturbation of the convective flux following the treatment of ... [more ▼]

New theoretical instability strips for delta Sct and gamma Dor stars are presented. These results have been obtained taking into account the perturbation of the convective flux following the treatment of Gabriel (\cite{Gabriel1996}). For the first time, the red edge of the delta Sct instability strip for non-radial modes is obtained. The influence of this time-dependent convection (TDC) on the driving of the gamma Dor gravity modes is investigated. The results obtained for different values of the mixing-length parameter alpha are compared for the gamma Dor models. A good agreement with observations is found for models with alpha between 1.8 and 2.0. [less ▲]

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See detailHe and Si surface inhomogeneities of four Bp variable stars
Briquet, Maryline ULg; Aerts, C.; Lüftinger, T. et al

in Astronomy and Astrophysics (2004), 413

We present ground-based multi-colour Geneva photometry and high-resolution spectra of four variable B-type stars: HD 105382, HD 131120, HD 138769 and HD 55522. All sets of data reveal monoperiodic stars ... [more ▼]

We present ground-based multi-colour Geneva photometry and high-resolution spectra of four variable B-type stars: HD 105382, HD 131120, HD 138769 and HD 55522. All sets of data reveal monoperiodic stars. A comparison of moment variations of two spectral lines, one silicon line and one helium line, allows us to exclude the pulsation model as being the cause of the observed variability of the four stars. We therefore delete the four stars from the list of candidate slowly pulsating B stars. We attribute the line-profile variations to non-homogeneous distributions of elements on the stellar surface and we derive abundance maps for both elements on the stellar surface by means of the Doppler Imaging technique. We confirm HD 131120 to be a He-weak star and we classify HD 105382, HD 138769 as new He-weak stars. HD 55522 has the solar helium abundance but the mean abundance value of He varies by 0.8 dex during the stellar rotation. For HD 131120 and HD 105382, helium is enhanced in regions of the stellar surface where silicon is depleted and depleted in regions where silicon is enhanced. Based on observations obtained with the Swiss photometric telescope and ESO's CAT/CES telescope, both situated at La Silla, Chile. Appendix A, Tables 1 and 2 and Figs. 9, 11, 13 are only available in electronic form at http://www.edpsciences.org [less ▲]

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See detailNonlinear electromagnetic modes in astrophysical plasmas with dust distributions
Verheest, F.; Cattaert, Tom ULg

in Astronomy and Astrophysics (2004), 421(1), 17-21

A derivative nonlinear Schrodinger equation is obtained for parallel electromagnetic modes in plasmas containing polydisperse charged dust. The coefficient of the dispersive term in that equation is ... [more ▼]

A derivative nonlinear Schrodinger equation is obtained for parallel electromagnetic modes in plasmas containing polydisperse charged dust. The coefficient of the dispersive term in that equation is dominated by the dust rather than the (plasma) ions, and polydisperse dust yields a larger coefficient in absolute value than an equivalent monodisperse description. This leads to a significant broadening of the nonlinear structure due to the presence of polydisperse rather than monodisperse dust, the latter contributing in itself already to a substantial increase in the width of envelope solitons compared to dust-free plasmas. When modelling the charged dust by a power-law distribution occurring in planetary ring and other astrophysical systems, it depends very much on the power-law index whether the smaller or the larger grains are more important. For certain indices the more numerous smaller grains determine the charge and mass densities, but the larger dust dominates the linear and nonlinear dispersive effects. [less ▲]

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See detailThe photospheric abundances of active binaries. II. Atmospheric parameters and abundance patterns for 6 single-lined RS CVn systems
Morel, Thierry ULg; Micela, G.; Favata, F. et al

in Astronomy and Astrophysics (2003), 412

Photospheric parameters and abundances are presented for a sample of single-lined chromospherically active binaries from a differential LTE analysis of high-resolution spectra. Abundances have been ... [more ▼]

Photospheric parameters and abundances are presented for a sample of single-lined chromospherically active binaries from a differential LTE analysis of high-resolution spectra. Abundances have been derived for 13 chemical species, including several key elements such as Li, Mg, and Ca. Two methods have been used. The effective temperatures, surface gravities and microturbulent velocities were first derived from a fully self-consistent analysis of the spectra, whereby the temperature is determined from the excitation equilibrium of the Fe I lines. The second approach relies on temperatures derived from the (B-V) colour index. These two methods give broadly consistent results for the stars in our sample, suggesting that the neutral iron lines are formed under conditions close to LTE. We discuss the reliability in the context of chromospherically active stars of various colour indices used as temperature indicators, and conclude that the (V-R) and (V-I) colours are likely to be significantly affected by activity processes. Irrespective of the method used, our results indicate that the X-ray active binaries studied are not as metal poor as previously claimed, but are at most mildly iron-depleted relative to the Sun (-0.41protect <~ [Fe/H]protect la +0.11). A significant overabundance of several chemical species is observed (e.g., the alpha -synthezised elements). These abundance patterns are discussed in relation to stellar activity. Based on observations collected at ESO (La Silla, Chile). 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/412/495 [less ▲]

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See detailOMC: An Optical Monitoring Camera for INTEGRAL - Instrument description and performance
Mas-Hesse, J. M.; Gimenez, A.; Culhane, J. L. et al

in Astronomy and Astrophysics (2003), 411(1), 261-268

The Optical Monitoring Camera (OMC) will observe the optical emission from the prime targets of the gammaray instruments onboard the ESA mission INTEGRAL, with the support of the JEM-X monitor in the X ... [more ▼]

The Optical Monitoring Camera (OMC) will observe the optical emission from the prime targets of the gammaray instruments onboard the ESA mission INTEGRAL, with the support of the JEM-X monitor in the X-ray domain. This capability will provide invaluable diagnostic information on the nature and the physics of the sources over a broad wavelength range. Its main scientific objectives are: ( 1) to monitor the optical emission from the sources observed by the gamma- and X-ray instruments, measuring the time and intensity structure of the optical emission for comparison with variability at high energies, and ( 2) to provide the brightness and position of the optical counterpart of any gamma- or X-ray transient taking place within its field of view. The OMC is based on a refractive optics with an aperture of 50 mm focused onto a large format CCD (1024 x 2048 pixels) working in frame transfer mode (1024 x 1024 pixels imaging area). With a field of view of 5degrees x 5degrees it will be able to monitor sources down to magnitude V = 18. Typical observations will perform a sequence of different integration times, allowing for photometric uncertainties below 0.1 mag for objects with V less than or equal to 16. [less ▲]

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See detailAn XMM-Newton observation of the very young open cluster NGC 6383
Rauw, Grégor ULg; De Becker, Michaël ULg; Gosset, Eric ULg et al

in Astronomy and Astrophysics (2003), 407(3), 925-15

We report the detection of a number of X-ray sources associated with the very young open cluster NGC6383. About two thirds of these objects are correlated with a rather faint optical source and all but ... [more ▼]

We report the detection of a number of X-ray sources associated with the very young open cluster NGC6383. About two thirds of these objects are correlated with a rather faint optical source and all but one have at least one infrared counterpart within a correlation radius of 8 arcsec. Although NGC6383 is not associated with a prominent star forming region, the overall properties of many of the X-ray sources suggest that they may be candidates for low-mass pre-main sequence stars. The number of X-ray sources increases towards the cluster center suggesting that there exists a close relation between the massive O-star binary system HD159176 in the cluster core and the population of X-ray bright low-mass objects in NGC 6383. [less ▲]

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