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See detailA photometric mode identification method, including an improved non-adiabatic treatment of the atmosphere
Dupret, Marc-Antoine ULg; De Ridder, J.; De Cat, P. et al

in Astronomy and Astrophysics (2003), 398

We present an improved version of the method of photometric mode identification of Heynderickx et al. (\cite{hey}). Our new version is based on the inclusion of precise non-adiabatic eigenfunctions ... [more ▼]

We present an improved version of the method of photometric mode identification of Heynderickx et al. (\cite{hey}). Our new version is based on the inclusion of precise non-adiabatic eigenfunctions determined in the outer stellar atmosphere according to the formalism recently proposed by Dupret et al. (\cite{dup}). Our improved photometric mode identification technique is therefore no longer dependent on ad hoc parameters for the non-adiabatic effects. It contains the complete physical conditions of the outer atmosphere of the star, provided that rotation does not play a key role. We apply our method to the two slowly pulsating B stars HD 74560 and HD 138764 and to the beta Cephei star EN (16) Lac. Besides identifying the degree l of the pulsating stars, our method is also a tool for improving the knowledge of stellar interiors and atmospheres, by imposing constraints on parameters such as the metallicity and the mixing-length parameter alpha (a procedure we label non-adiabatic asteroseismology). The non-adiabatic eigenfunctions needed for the mode identification are available upon request from the authors. [less ▲]

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See detailSpectroscopic mode identification for the beta Cephei star EN (16) Lacertae
Aerts, C.; Lehmann, H.; Briquet, Maryline ULg et al

in Astronomy and Astrophysics (2003), 399

We perform for the first time spectroscopic mode identification in the eclipsing binary beta Cephei star EN (16) Lac. This mode identification is based upon a time series of 942 line profiles of the He I ... [more ▼]

We perform for the first time spectroscopic mode identification in the eclipsing binary beta Cephei star EN (16) Lac. This mode identification is based upon a time series of 942 line profiles of the He I lambda lambda 6678 Åline in its spectrum. All three known frequencies f[SUB]1[/SUB], f,SUB>2,/SUB>, f[SUB]3[/SUB] of the star are present in the line-profile variations, but we failed to find additional modes. Using different identification methods we find conclusive evidence for the radial nature of the main mode and for the l=2, m=0 identification of the mode with frequency f[SUB]2[/SUB]. A unique identification of the third mode is not possible from the spectra, but we do derive that l[SUB]3[/SUB]<3. Fits to the amplitude and phase variability of the modes imply a rotation frequency between 0.1 and 0.4 c d[SUP]-1[/SUP]. The star's rotation axis is not aligned with the orbital axis. Based on observations gathered with the coudé spectrograph attached to the 2.0 m reflector telescope at Tautenburg Observatory. [less ▲]

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See detailA new version of the moment method, optimized for mode identification in multiperiodic stars
Briquet, Maryline ULg; Aerts, C.

in Astronomy and Astrophysics (2003), 398

We present a numerical version of the moment method for the identification of non-radial pulsation modes. The new version requires less computation time than the previous one, allowing users to consider ... [more ▼]

We present a numerical version of the moment method for the identification of non-radial pulsation modes. The new version requires less computation time than the previous one, allowing users to consider all the information contained in the first three moments of a multiperiodic star and to identify multiple modes simultaneously. This, together with the use of a new discriminant that considers the moments calculated at each time of observation, increases considerably the feasibility and the accuracy of the mode identification for multiperiodic stars. Moreover, the technique is extended to rotating pulsating stars. We apply the new version to three B stars showing multiperiodicity. Computer code for mode identification available upon request. Tables 1 to 8 are only available in electronic form at http://www.edpsciences.org [less ▲]

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See detailLine profile variability in the spectra of Oef stars. I. BD + 60deg 2522
Rauw, Grégor ULg; De Becker, Michaël ULg; Vreux, Jean-Marie ULg

in Astronomy and Astrophysics (2003), 399

We report the analysis of a long term observing campaign designed to monitor the spectroscopic variability of the Oef star BD +60deg 2522. We find that the double-peaked He {II} lambda 4686 emission line ... [more ▼]

We report the analysis of a long term observing campaign designed to monitor the spectroscopic variability of the Oef star BD +60deg 2522. We find that the double-peaked He {II} lambda 4686 emission line undergoes strong profile variability on time scales of 2-3 day. However, the time scale as well as the pattern of these variations turn out to be epoch dependent and the phenomenon is thus most likely not ruled by a single stable clock. On the other hand, the absorption lines in the spectrum of BD +60deg 2522 display line profile variability on time scales of a few hours that might be related to non-radial pulsations. We tentatively propose that the beating of several non-radial pulsation modes triggers transient large-scale density perturbations in a confined stellar wind that produce the 2-3 day time scale variability. [less ▲]

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See detailRadiative lifetime and oscillator strength determinations in SmIII
Biémont, Emile ULg; Garnir, Henri-Pierre ULg; Litzen, U. et al

in Astronomy and Astrophysics (2003), 399(1), 343-349

Radiative lifetimes of 6 levels belonging to the 4f(5)((6)Hdegrees, (6)Fdegrees)5d configuration of Sm III have been measured for the first time using a time-resolved laser-induced fluorescence technique ... [more ▼]

Radiative lifetimes of 6 levels belonging to the 4f(5)((6)Hdegrees, (6)Fdegrees)5d configuration of Sm III have been measured for the first time using a time-resolved laser-induced fluorescence technique. Experimental data have been compared with semi-empirical calculations. The agreement is excellent for 4 levels with (6)Fdegrees as a parent term. Larger discrepancies (53 and 37%) are observed for 2 levels with (6)Hdegrees and (6)Fdegrees, respectively, as a parent term and are explainable by strong mixing and cancellation effects occurring in the line strength calculations which are responsible of "instabilities" occurring in the lifetimes considered as a function of J value within the term. Branching ratios for the lines depopulating the levels of interest have been measured by Fourier transform spectroscopy. A first set of oscillator strengths has been deduced for this ion. [less ▲]

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See detailLong-term optical spectrophotometric monitoring of comet C/1995 O1 (Hale-Bopp)
Rauer, H.; Helbert, J.; Arpigny, Claude ULg et al

in Astronomy and Astrophysics (2003), 397

We observed comet C/1995 O1 (Hale-Bopp) at 4.6-2.9 AU pre-perihelion and 2.8-12.8 AU post-perihelion with optical long-slit spectroscopy. Emission bands of CN, C[SUB]3[/SUB], C[SUB]2[/SUB] and NH[SUB]2 ... [more ▼]

We observed comet C/1995 O1 (Hale-Bopp) at 4.6-2.9 AU pre-perihelion and 2.8-12.8 AU post-perihelion with optical long-slit spectroscopy. Emission bands of CN, C[SUB]3[/SUB], C[SUB]2[/SUB] and NH[SUB]2[/SUB] have been covered. Emission of C[SUB]3[/SUB] was detected up to 7.0 AU, and CN could be followed up to 9.8 AU post-perihelion. Spatial column density profiles of the radicals have been used to derive effective parent Haser scale lengths for heliocentric distances beyond 3 AU. Production rates were derived based on these Haser scale lengths. The observations of CN are in agreement with HCN as the major parent molecule of this radical at large distances from the Sun (i.e. beyond ~ 3 AU). We compare the measured CN production rate to sublimation rates of HCN from a simple nucleus sublimation model. The variation of CN production rates with changing heliocentric distance gives no indication for sublimation from the interior and is consistent with very little thermal lag of the nucleus. Based on observations collected at the European Southern Observatory, Chile, and the Observatoire de Haute Provence, France. [less ▲]

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See detailClose pairs of quasars with different redshifts: New observations and results
Sluse, Dominique ULg; Surdej, Jean ULg; Claeskens, Jean-François ULg et al

in Astronomy and Astrophysics (2003), 397

Burbidge et al. (\cite {burbidge}) argue that the observed number of quasar pairs with small angular separations and different redshifts (typically Delta theta <= 5 arcsec and Delta z > 0.1 ) is not ... [more ▼]

Burbidge et al. (\cite {burbidge}) argue that the observed number of quasar pairs with small angular separations and different redshifts (typically Delta theta <= 5 arcsec and Delta z > 0.1 ) is not compatible with a random distribution of quasars over the sky. After a brief review of all known quasar pairs with different redshifts, we show by means of very simple calculations that the probability of finding the three accepted pairs accidentally is of the order of 10%. We conclude that, under realistic hypotheses, the observed number of quasar pairs with different redshifts is not unlikely. We also present arguments showing that gravitational lensing biases are probably not strong enough to significantly increase the expected number of quasar pairs. The failure to detect with HST a secondary lensed image of the background quasar near the foreground one in these three pairs supports this view. [less ▲]

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See detailThe spectrum of the roAp star HD 101065 (Przybylski's star) in the Li I 6708 A spectral region
Shavrina, A V; Polosukhina, N S; Pavlenko, Ya V et al

in Astronomy and Astrophysics (2003), 409

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See detailOn-axis spatially resolved spectroscopy of low redshift quasar host galaxies: HE 1503+0228, at z=0.135
Courbin, F.; Letawe, Géraldine ULg; Magain, Pierre ULg et al

in Astronomy and Astrophysics (2002), 394

We present the first result of a comprehensive spectroscopic study of quasar host galaxies. On-axis, spatially resolved spectra of low redshift quasars have been obtained with FORS1, mounted on the 8.2 m ... [more ▼]

We present the first result of a comprehensive spectroscopic study of quasar host galaxies. On-axis, spatially resolved spectra of low redshift quasars have been obtained with FORS1, mounted on the 8.2 m ESO Very Large Telescope, Antu. The spectra are spatially deconvolved using a spectroscopic version of the ``MCS deconvolution algorithm''. The algorithm decomposes two dimensional spectra into the individual spectra of the central point-like nucleus and of its host galaxy. Applied to HE 1503+0228 at z=0.135 (M[SUB]B[/SUB]=-23.0), it provides us with the spectrum of the host galaxy between 3600 Å and 8500 Å (rest-frame), at a mean resolving power of 700. The data allow us to measure several of the important Lick indices. The stellar populations and gas ionization state of the host galaxy of HE 1503+0228 are very similar to the ones measured for normal non-AGN galaxies. Dynamical information is also available for the gas and stellar components of the galaxy. Using deconvolution and a deprojection algorithm, velocity curves are derived for emission lines, from the center up to 4\arcsec away from the nucleus of the galaxy. Fitting a simple three-components mass model (point mass, spherical halo of dark matter, disk) to the position-velocity diagram, we infer a mass of M(r<1 kpc) = (2.0 +/- 0.3)x 10[SUP]10[/SUP] M[SUB]sun[/SUB] within the central kiloparsec of the galaxy, and a mass integrated over 10 kpc of M(r<10 kpc) = (1.9 +/- 0.3) x 10[SUP]11[/SUP] M[SUB]sun[/SUB], with an additional 10% error due to the uncertainty on the inclination of the galaxy. This, in combination with the analysis of the stellar populations indicates that the host galaxy of HE 1503+0228, is a normal spiral galaxy. Based on observations made with ANTU/UT1 at ESO-Paranal observatory in Chile (program 65.P-0361(A)), and with the ESO 3.5 m NTT, at La Silla observatory (program 62.P-0643(B)). [less ▲]

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See detailAn XMM-Newton observation of the Lagoon Nebula and the very young open cluster NGC 6530
Rauw, Grégor ULg; Nazé, Yaël ULg; Gosset, Eric ULg et al

in Astronomy and Astrophysics (2002), 395(2), 499-513

We report the results of an XMM-Newton observation of the Lagoon Nebula (M8). Our EPIC images of this region reveal a cluster of point sources, most of which have optical counterparts inside the very ... [more ▼]

We report the results of an XMM-Newton observation of the Lagoon Nebula (M8). Our EPIC images of this region reveal a cluster of point sources, most of which have optical counterparts inside the very young open cluster NGC6530. The bulk of these X-ray sources are probably associated with low and intermediate mass pre-main sequence stars. One of the sources experienced a flare-like increase of its X-ray flux making it the second brightest source in M8 after the O4 star 9 Sgr. The X-ray spectra of most of the brightest sources can be fitted with thermal plasma models with temperatures of kT similar to a few keV. Only a few of the X-ray selected PMS candidates are known to display Halpha emission and were previously classified as classical T Tauri stars. This suggests that most of the X-ray emitting PMS stars in NGC6530 are weak-line T Tauri stars. In addition to 9 Sgr, our EPIC field of view contains also a few early-type stars. The X-ray emission from HD 164816 is found to be typical for an O9.5 III-IV star. At least one of the known Herbig Be stars in NGC6530 ( LkHalpha 115) exhibits a relatively strong X-ray emission, while most of the main sequence stars of spectral type B1 and later are not detected. We also detect ( probably) diffuse X-ray emission from the Hourglass Region that might reveal a hot bubble blown by the stellar wind of Herschel 36, the ionizing star of the Hourglass Region. [less ▲]

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See detailA multi-wavelength investigation of the non-thermal radio emitting O-star 9 Sgr
Rauw, Grégor ULg; Blomme, R.; Waldron, W. L. et al

in Astronomy and Astrophysics (2002), 394(3), 993-1008

We report the results of a multi-wavelength investigation of the O4 V star 9 Sgr (= HD164794). Our data include observations in the X-ray domain with XMM-Newton, in the radio domain with the VLA as well ... [more ▼]

We report the results of a multi-wavelength investigation of the O4 V star 9 Sgr (= HD164794). Our data include observations in the X-ray domain with XMM-Newton, in the radio domain with the VLA as well as optical spectroscopy. 9 Sgr is one of a few presumably single OB stars that display non-thermal radio emission. This phenomenon is attributed to synchrotron emission by relativistic electrons accelerated in strong hydrodynamic shocks in the stellar wind. Given the enormous supply of photospheric UV photons in the wind of 9 Sgr, inverse Compton scattering by these relativistic electrons is a priori expected to generate a non-thermal power law tail in the X-ray spectrum. Our EPIC and RGS spectra of 9 Sgr reveal a more complex situation than expected from this simple theoretical picture. While the bulk of the thermal X-ray emission from 9 Sgr arises most probably in a plasma at temperature similar to3 x 10(6) K distributed throughout the wind, the nature of the hard emission in the X-ray spectrum is less clear. Assuming a non-thermal origin, our best fitting model yields a photon index of greater than or equal to2.9 for the power law component which would imply a low compression ratio of less than or equal to1.79 for the shocks responsible for the electron acceleration. However, the hard emission can also be explained by a thermal plasma at a temperature greater than or equal to2 x 10(7) K. Our VLA data indicate that the radio emission of 9 Sgr was clearly non-thermal at the time of the XMM-Newton observation. Again, we derive a low compression ratio (1.7) for the shocks that accelerate the electrons responsible for the synchrotron radio emission. Finally, our optical spectra reveal long-term radial velocity variations suggesting that 9 Sgr could be a long-period spectroscopic binary. [less ▲]

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See detailCerium: The lithium substitute in post-AGB stars
Reyniers, M.; Winckel, H. V.; Biémont, Emile ULg et al

in Astronomy and Astrophysics (2002), 395(2), 35-38

In this letter we present an alternative identification for the line detected in the spectra of s-process enriched low-mass post-AGB stars around 6708 Angstrom and which was interpreted in the literature ... [more ▼]

In this letter we present an alternative identification for the line detected in the spectra of s-process enriched low-mass post-AGB stars around 6708 Angstrom and which was interpreted in the literature as due to Li. Newly released line lists of lanthanide species reveal, however, the likely identification of the line to be due to a Ce II transition. We argue that this identification is consistent with the Ce abundance of all the objects discussed in the literature and conclude that in none of the low-mass s-process enriched post-AGB stars there is indication for Li-production. [less ▲]

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See detailTransition probabilities in GdIII
Biémont, Emile ULg; Kohnen, G.; Quinet, Pascal ULg

in Astronomy and Astrophysics (2002), 393(2), 717-720

Theoretical lifetimes, calculated with inclusion of core-polarization effects, have been determined for five 4f(7) 6p levels of doubly ionized gadolinium. They agree quite well with recent experimental ... [more ▼]

Theoretical lifetimes, calculated with inclusion of core-polarization effects, have been determined for five 4f(7) 6p levels of doubly ionized gadolinium. They agree quite well with recent experimental values measured by time-resolved laser-induced fluorescence spectroscopy. From this agreement, the accuracy of a first set of Gd III transition probabilities, calculated for 4f(7) 5d- 4f(7) 6p and 4f(7) 6s- 4f(7) 6p transitions of astrophysical interest, has been assessed. [less ▲]

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See detailThe evolved early-type binary HDE 228766 revisited
Rauw, Grégor ULg; Crowther, P. A.; Eenens, P. R. J. et al

in Astronomy and Astrophysics (2002), 392(2), 563-574

We use an extensive set of spectroscopic observations to reinvestigate the properties of the massive binary HDE 228766. Conventional classification criteria suggest that HDE 228766 consists of an O7 ... [more ▼]

We use an extensive set of spectroscopic observations to reinvestigate the properties of the massive binary HDE 228766. Conventional classification criteria suggest that HDE 228766 consists of an O7 primary and an Of(+) secondary. However, several spectral features of the secondary, such as the simultaneous presence of N III, N IV and N V emissions, make it a rather unusual object. We find that the orbital motion of the secondary is probably best described by the radial velocities of the narrow N III emission lines. Our orbital solution yields m(1) sin(3) i = 31:7 and m(2) sin(3) i = 25:5 M. for the primary and secondary respectively. The He II lambda 4542 absorption in the secondary's spectrum appears considerably blue-shifted with respect to the narrow emission lines, indicating that the absorption is probably formed in the accelerating part of the secondary's wind. We use a tomographic technique to investigate the profile variability of the broader emission lines. In addition to a strong emission from the secondary, the Halpha line displays a weak emission feature that is probably associated with a wind interaction region located near the surface of the primary star. Finally, our analysis of the spectrum with a non-LTE code indicates that the secondary is an evolved object that exhibits some CNO processed material in its atmosphere and has a large mass loss rate. Assuming a distance of 3.5 kpc (which follows from adopting M-V,M-s = -6 for the secondary) we infer (M) over dot similar or equal to 10(5) M. yr(-1) for the secondary. Our results suggest that HDE 228766 could be in a post-Roche lobe overflow stage. The secondary may be classified as WN8ha and is currently in a transition stage between a "normal" Of staranda WNL-type Wolf-Rayet star. [less ▲]

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See detailTime delay and lens redshift for the doubly imaged BAL quasar SBS 1520+530
Burud, I.; Hjorth, J.; Courbin, F. et al

in Astronomy and Astrophysics (2002), 391

We present optical R-band light curves of the gravitationally lensed quasar <ASTROBJ>SBS 1520+530</ASTROBJ> derived from data obtained at the Nordic Optical Telescope. A time delay of 130+/-3 days (1sigma ... [more ▼]

We present optical R-band light curves of the gravitationally lensed quasar <ASTROBJ>SBS 1520+530</ASTROBJ> derived from data obtained at the Nordic Optical Telescope. A time delay of 130+/-3 days (1sigma ) is determined from the light curves. In addition, spectra of <ASTROBJ>SBS 1520+530</ASTROBJ> obtained at the Keck Observatory are spatially deconvolved in order to extract the spectrum of the faint lensing galaxy, free of any contamination by the light from the bright quasar images. This spectrum indicates a lens redshift z=0.717, in agreement with one of the absorption systems found in the quasar spectra. The best mass model of the system includes a second nearby galaxy and a cluster of galaxies in addition to the main lensing galaxy. Adopting this model and an Omega =0.3, Lambda =0.7 cosmology, our time-delay measurement yields a Hubble constant of H[SUB]0[/SUB]=51 +/- 9 km s[SUP]-1[/SUP] Mpc[SUP]-1[/SUP] (1sigma error). Based on observations made with the Nordic Optical, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias and the W. M. Keck Observatory which is operated jointly by the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. Table 2 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/391/481 [less ▲]

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See detailHST STIS observations of four QSO pairs
Aracil, B.; Petitjean, P.; Smette, A. et al

in Astronomy and Astrophysics (2002), 391(1), 1-12

We present HST STIS observations of four quasar pairs with redshifts 0.84<z(em)<1.56 and angular separation 2-3 arcmin corresponding to ∼1-1.5 h(50)(-1) Mpc transverse proper distance at zsimilar to0.9 ... [more ▼]

We present HST STIS observations of four quasar pairs with redshifts 0.84<z(em)<1.56 and angular separation 2-3 arcmin corresponding to ∼1-1.5 h(50)(-1) Mpc transverse proper distance at zsimilar to0.9. We study the distribution of velocity differences between nearest neighbor HI Lyman-alpha absorption lines detected in the spectra of adjacent QSOs in order to search for the possible correlation caused by the extent or the clustering properties of the structures traced by the absorption lines over such a scale. The significance of the correlation signal is determined by comparison with Monte-Carlo simulations of spectra with randomly distributed absorption lines. We find an excess of lines with a velocity separation smaller than DeltaV=500 km s(-1) significant at the 99.97% level. This clearly shows that the Lyman-alpha forest is correlated on scales larger than 1 h(50)(-1) Mpc at zsimilar to1. However, out of the 20 detected coincidences within this velocity bin, 12 have V>200 km s(-1). This probably reflects the fact that the scale probed by our observations is not related to the real size of individual absorbers but rather to large scale correlation. Statistics are too small to conclude about any difference between pairs separated by either 2 or 3 arcmin. A damped Lyman-alpha system is detected at z(abs)=1.2412 toward LBQS 0019-0145A with log N(HI)similar to20.5. From the absence of ZnII absorption, we derive a metallicity relative to solar [Zn/H]< -1.75. [less ▲]

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See detailStudy of CCD mosaic configurations for the ILMT: Astrometry and photometry of point sources in the absence of a TDI corrector
Vangeyte, B.; Manfroid, Jean ULg; Surdej, Jean ULg

in Astronomy and Astrophysics (2002), 388(2), 712-731

The image deformations induced by the time-delay integration (TDI) mode, used with a CCD camera at the prime focus of a Liquid Mirror Telescope (LMT), can be corrected for by a system of lenses ... [more ▼]

The image deformations induced by the time-delay integration (TDI) mode, used with a CCD camera at the prime focus of a Liquid Mirror Telescope (LMT), can be corrected for by a system of lenses, simultaneously with the optical aberrations. However, before adopting the design of a TDI corrector, we may wonder what is the importance of the TDI image deformations and how to possibly reduce these by choosing optimal mosaic configurations of CCDs, covering an equivalent field of view. In a first step, we have simulated the point spread function (PSF) deformation due to the TDI mode only, for different selected mosaic configurations. We have then estimated the importance of the astrometric and photometric errors induced by the TDI deformation. By simulating star fields with the same synthetic PSF and taking into account realistic sources of noise (cf. CCD readout noise, photon noise and sky background), we have derived the limiting magnitudes for photometry and astrometry for the case of a 4 m LMT. [less ▲]

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See detailPhase-resolved X-ray and optical spectroscopy of the massive binary HD 93403
Rauw, Grégor ULg; Vreux, Jean-Marie ULg; Stevens, I. R. et al

in Astronomy and Astrophysics (2002), 388(2), 552-562

We report the first results of a campaign aimed at the study of early-type binaries with the XMM-Newton observatory. Phase-resolved EPIC spectroscopy of the eccentric binary HD93403 reveals a clear ... [more ▼]

We report the first results of a campaign aimed at the study of early-type binaries with the XMM-Newton observatory. Phase-resolved EPIC spectroscopy of the eccentric binary HD93403 reveals a clear orbital modulation of the X-ray luminosity as a function of the orbital phase. Below 1.0 keV, the observed X-ray flux is modulated by the opacity of the primary wind. Above 1.0 keV, the observed variation of the X-ray flux is roughly consistent with a 1/r dependence expected for an adiabatic colliding wind interaction. HD93403 appears less overluminuous in X-rays than previously thought and a significant fraction of the total X-ray emission arises probably within the winds of the individual components of the binary. Optical monitoring of the system reveals strong variability of the He II lambda 4686 and Halpha line profiles. The He II lambda 4686 line displays a broad asymmetrical emission component which is found to be significantly stronger between phases 0.80 and 0.15 than around apastron. This suggests that part of the emission arises in the interaction region and most probably in the trailing arm of a shock cone wrapped around the secondary. Some absorption lines of the secondary's spectrum display equivalent width variations reminiscent of the so-called Struve-Sahade effect. The differences in behaviour between individual lines suggest that the temperature may not be the only relevant parameter that controls this effect. [less ▲]

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See detailOptimal extraction of multiple overlapping spectra using a maximum entropy algorithm
Khmil, S. V.; Surdej, Jean ULg

in Astronomy and Astrophysics (2002), 387(1), 347-355

A general algorithm of slit spectra extraction for a system of point-like sources (e.g. multiple lensed images of a quasar) has been developed, assuming that the point-spread function (PSF) induced by the ... [more ▼]

A general algorithm of slit spectra extraction for a system of point-like sources (e.g. multiple lensed images of a quasar) has been developed, assuming that the point-spread function (PSF) induced by the measuring instrument and/or atmosphere and the positions of the spectra relative to the CCD frame are unknown. The main idea of the algorithm is to successively apply the maximum entropy method to each set of parameters, such as the spectra, the PSF, and the spectra positions, in order to iteratively improve their values. The algorithm uses all the a priori knowledge about the spectra (e.g. flux positivity, flux ratios between the components, astrometry, etc.) to compute the initial parameter sets. The main features of the algorithm, its implementation, as well as some important aspects of its practical use, are discussed in detail. Two sets of simulated spectroscopic data have been built in order to show the most characteristic properties of the algorithm and to justify its aplication to the spectra extraction of the gravitational lens system Q1009-0252 A [less ▲]

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See detailInfluence of non-adiabatic temperature variations on line profile variations of slowly rotating beta Cephei stars and SPBs. II. Simulations of line profile time series
De Ridder, J.; Dupret, Marc-Antoine ULg; Neuforge, C. et al

in Astronomy and Astrophysics (2002), 385

We investigate to what extent non-adiabatic temperature variations at the surface of slowly rotating non-radially pulsating beta Cephei stars and slowly pulsating B stars affect silicon line profile ... [more ▼]

We investigate to what extent non-adiabatic temperature variations at the surface of slowly rotating non-radially pulsating beta Cephei stars and slowly pulsating B stars affect silicon line profile variations. We use the non-adiabatic amplitudes of the effective temperature and gravity variation presented in Dupret et al. (\cite{Dupret02}), together with a Kurucz intensity grid, to compute time series of line profile variations. Our simulations point out that the line shapes do not change significantly due to temperature variations. We find equivalent width variations of at most two percent of the mean equivalent width. We confront our results with observational equivalent width variations and with photometrically obtained effective temperature variations. Based on observations obtained with the Swiss photometric telescope and with the ESO/CAT telescope, at La Silla in Chile. [less ▲]

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