References of "Astronomy and Astrophysics"
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See detailThe enigmatic flarings of HR2517.
Sterken, C.; Manfroid, Jean ULg

in Astronomy and Astrophysics (1996), 305

We report the discovery of strong flaring of the B3 II-III star HR2517. The evidence is based on Stroemgren differential uvby photometry spanning more than a decade. We discuss the behaviour of HR2517 in ... [more ▼]

We report the discovery of strong flaring of the B3 II-III star HR2517. The evidence is based on Stroemgren differential uvby photometry spanning more than a decade. We discuss the behaviour of HR2517 in terms of two models, viz. a rooted bright spot suddenly appearing and developing with modulation in photospheric temperature producing periodic light and profile variations as the star rotates, or that HR2517 is a Be star in an eccentric (P~33-34d) high-mass X-ray binary (HMXB) with neutron star companion--one of the brightest such systems known. [less ▲]

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See detailJ03.13 A and B: a new multiply imaged QSO candidate.
Claeskens, Jean-François ULg; Surdej, Jean ULg; Remy, M.

in Astronomy and Astrophysics (1996), 305

Careful analysis of direct R CCD frames obtained for selected Highly Luminous Quasars in March 1993 with the MPI/ESO 2.2m telescope has revealed that the quasar J03.13 consists of at least two point-like ... [more ▼]

Careful analysis of direct R CCD frames obtained for selected Highly Luminous Quasars in March 1993 with the MPI/ESO 2.2m telescope has revealed that the quasar J03.13 consists of at least two point-like components, constituting therefore a new gravitational lens candidate. Follow-up direct imagery of this interesting object with the New Technology Telescope (NTT) + SUSI in February 1994, using the Bessel B, R and Gunn-i filters, tends to confirm the gravitational lens hypothesis. The mean angular separation and magnitude difference between the A & B images are found to be 0.84"+/-0.03" and 2.1+/-0.1mag, respectively. A spatially unresolved, medium resolution spectrum of J03.13, obtained with the NTT + EMMI in February 1994, shows that the QSO has a redshift z=2.55, with Lyalpha and CIV absorptions at z=2.34 and MgII, MgI and FeII absorptions at z=1.085. The latter absorptions might be associated with a sigma=206km/s lens galaxy. B, R and Gunn-i photometric observations of J03.13 during 1994 and 1995 do not show evidence for flux variations exceeding 0.03mag. HST direct imagery with WFPC2 and FOS spectroscopy of J03.13 A & B are planned during cycle 5. [less ▲]

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See detailTheoretical Radiative Lifetimes of 3p3(4S°)4s5S° and 3S° States in S I
Biémont, Emile ULg; Storey, P. J.; Zeippen, C. J.

in Astronomy and Astrophysics (1996), 309

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See detailPhotometric monitoring (1987 to 1994) of the gravitational lens candidate UM 425.
Courbin, F.; Magain, Pierre ULg; Remy, M. et al

in Astronomy and Astrophysics (1995), 303

We present the results of a 7 year long photometric monitoring of two components (A and B) of UM 425, thought to be images, separated by 6.5", of the same z=1.47 quasar. These components have been imaged ... [more ▼]

We present the results of a 7 year long photometric monitoring of two components (A and B) of UM 425, thought to be images, separated by 6.5", of the same z=1.47 quasar. These components have been imaged through an R filter in order to obtain their light curves. The photometry was obtained by simultaneously fitting a stellar two-dimensional profile on each component. The brightest image (component A, m_R_=15.7) shows a slow and smooth increase in brightness of 0.2 magnitude in seven years, while the faintest one (component B, m_R_=20.1) displays an outburst of 0.4 magnitude which lasts approximately two years. The variation of component B may be interpreted in two ways, assuming UM 425 is gravitationally lensed. If it is due to an intrinsic variation of the quasar, we derive a lower limit of 3 years on the time delay from the fact that it is not observed in component A. On the other hand, if it is a microlensing "High Amplification Event", we estimate the size of the source to be ~10^-3^pc, in agreement with standard models of AGNs. These observations are consistent with the gravitational lens interpretation of the object. Furthermore, all the CCD frames obtained under the best seeing conditions have been co-added, in an attempt to detect the deflector. The final R image reveals a rich field of faint galaxies in the magnitude range m_R_~22-24. No obvious deflector, nor any system of arcs or arclets is detected, down to a limiting magnitude of m_R_~24. [less ▲]

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See detailHeavy elements in halo stars: the r/s-process controversy.
Magain, Pierre ULg

in Astronomy and Astrophysics (1995), 297

It has been suggested by Truran (1981) that rapid neutron captures (the r-process) dominate the production of heavy elements in very metal-poor stars. Several spectroscopic works analyzing that hypothesis ... [more ▼]

It has been suggested by Truran (1981) that rapid neutron captures (the r-process) dominate the production of heavy elements in very metal-poor stars. Several spectroscopic works analyzing that hypothesis are reviewed and rediscussed and it is shown that there is, in fact, no secure observational evidence in support of Truran's suggestion. A method to determine the odd-to-even isotopic ratio of barium, and thus to estimate the relative contributions of the r and s-processes, is presented. It takes advantage of the hyperfine structure affecting the spectral lines of the odd isotopes to distinguish them from the even isotopes. This method, applied to the classical metal-poor subgiant HD 140283, shows that the barium isotopic ratio in that star is in agreement with a pure s-process production, and excludes any significant enhancement of the r-process contribution, in disagreement with previous works based on elemental abundances. [less ▲]

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See detail(Erratum) Further observational evidence that MG J0414+0534 is a gravitational mirage.
Angonin-Willaime, M.-C.; Vanderriest, C.; Hammer, F. et al

in Astronomy and Astrophysics (1994), 292

In Sect. 3.3, the identifications of components A1 and A2 for the optical data were inadvertently inverted. This does not change substantially the discussion; just read A1 for A2 and vice versa. In ... [more ▼]

In Sect. 3.3, the identifications of components A1 and A2 for the optical data were inadvertently inverted. This does not change substantially the discussion; just read A1 for A2 and vice versa. In particular, the ratio A2/A1 = 0.3 cannot be made compatible with the radio value without one or several of the mechanisms we suggested. We apologize for the error and thank Dr S. Mao for bringing it to our attention. Erratum to Astron. Astrophys. 281, 388-394 (1994) [less ▲]

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See detailA dusty nebula around the luminous blue variable candidate HD 168625
Hutsemekers, Damien ULg; van Drom, E.; Gosset, Eric ULg et al

in Astronomy and Astrophysics (1994), 290

On the basis of narrow-band visible and near-infrared imagery as well as high-resolution spectroscopy, we report the discovery of a new LBV-type nebula around the B supergiant HD 168625. We find that it ... [more ▼]

On the basis of narrow-band visible and near-infrared imagery as well as high-resolution spectroscopy, we report the discovery of a new LBV-type nebula around the B supergiant HD 168625. We find that it essentially consists of a dusty expanding shell from which seems to emerge a bipolar emission nebula, the whole embedded in a reflection nebulosity. The inner shell is stratified: the continuum emission arises beyond the ionized gas, and is possibly due to scattering of stellar light by large dust grains or to non-equilibrium dust emission. The unexpected presence of unidentified infrared emission bands (UIRs) in the spectrum of this object is also discussed. We finally report the non-detection of a comparable nebula around the nearby LBV HD 168607. [less ▲]

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See detailPeriod of the Si-star in NGC 2169
Renson, Pierre ULg

in Astronomy and Astrophysics (1994), 285

For the Si Ap-star known in NGC 2169 (Gr.9 in the cluster), a period between 0.60 and 0.62 d, most likely about 0.606 d, agrees with all known observations, and is much more probable than the period 1.56 ... [more ▼]

For the Si Ap-star known in NGC 2169 (Gr.9 in the cluster), a period between 0.60 and 0.62 d, most likely about 0.606 d, agrees with all known observations, and is much more probable than the period 1.56 d proposed by Maitzen & Lebzelter (1993). The obtained period is among the shortest ones known for Ap stars. [less ▲]

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See detailFurther observational evidence that MG J0414+0534 is a gravitational mirage
Angonin-Willaime, M.-C.; Vanderriest, C.; Hammer, F. et al

in Astronomy and Astrophysics (1994), 281

Deep imaging of MG J0414+0534 with R and I filters reveals a faint, fuzzy and red object at the exact location expected for a lensing galaxy in the gravitational mirage hypothesis. Furthermore, the ... [more ▼]

Deep imaging of MG J0414+0534 with R and I filters reveals a faint, fuzzy and red object at the exact location expected for a lensing galaxy in the gravitational mirage hypothesis. Furthermore, the (extremely red and almost featureless) spectra of the 2 brightest components are very similar. These are strong indications that the system results from multiple gravitational imaging of a single source, but the nature of this source is not yet clear. It could be the nucleus of a low metallicity galaxy at a high redshift or a new type of object. Significant differences are observed between the flux ratios of the images at radio and optical wavelenghts. The most likely explanation for this effect is a differential amplification of the image pair A[SUB]1[/SUB]-A[SUB]2[/SUB] because of the large magnification gradient near a caustic. [less ▲]

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See detailPhotometric variations of Ap stars
Manfroid, Jean ULg; Renson, Pierre ULg

in Astronomy and Astrophysics (1994), 281

The photometric variations of seven Ap stars have been analyzed from observations mainly obtained in the framework of the Long-Term Photometry of Variables project at European Southern Observatory (ESO ... [more ▼]

The photometric variations of seven Ap stars have been analyzed from observations mainly obtained in the framework of the Long-Term Photometry of Variables project at European Southern Observatory (ESO). New values for the periods and detailed light curves in the uvby system are provided. Alpha Scl is shown to display anomalous variations that set it apart from the other stars. [less ▲]

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See detailEvidence for violent ejection of nebulae from massive stars
Hutsemekers, Damien ULg

in Astronomy and Astrophysics (1994), 281(Letters), 81-84

We report the results of a systematic search for nebulae around Luminous Blue Variable LBVs) and the discovery of a strong correlation between the mass of the nebulae and the luminosity of the central ... [more ▼]

We report the results of a systematic search for nebulae around Luminous Blue Variable LBVs) and the discovery of a strong correlation between the mass of the nebulae and the luminosity of the central stars. This correlation holds for both the dust and ionized gas masses of the nebulae. The existence of a 'nebular mass-stellar luminosity' relation and the fact that not all LBVs are presently associated with a nebula give evidence against a continuous mass-loss mechanism for the formation of these nebulae. Further, the good agreement found between the observed relation and predictions by Maeder (1989), suggests that all these nebulae may be due to a violent ejection of matter caused by an instability of structural origin. [less ▲]

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See detailPole, albedo and shape of the minor planets 624 Hektor and 43 Ariadne: Two tests for comparing four different pole determination methods
Detal, Alain ULg; Hainaut, O.; Pospieszalska-Surdej, A. et al

in Astronomy and Astrophysics (1994), 281

Asteroids 624 Hektor and 43 Ariadne have been observed photometrically at the European Southern Observatory (La Silla, Chile) in order to determine their pole orientation. The lightcurves (1984 and 1991 ... [more ▼]

Asteroids 624 Hektor and 43 Ariadne have been observed photometrically at the European Southern Observatory (La Silla, Chile) in order to determine their pole orientation. The lightcurves (1984 and 1991 oppositions for Hektor, and 1985 for Ariadne) are presented. Some of the traditional pole determination methods have been improved, and completely original ones have been developed. They are described and applied to the newly recorded and previously published light curves. The results are commented and compared with previous ones. In addition to the pole orientation, we also derive some information on the shape or the albedo distribtuion of the objects. With the aim of optimizing future observations of these asteroids, we present some graphs showing the best longitudes where they should be measured. Finally, we suggest some improvements in the pole determination and modeling methods based upon photometric data. [less ▲]

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See detailThe 4s-4p Transitions in Neutral Phosphorus
Biémont, Emile ULg; Martin, F.; Quinet, Pascal ULg et al

in Astronomy and Astrophysics (1994), 283

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See detailSelective gravitational microlensing and line profile variations in the BAL quasar H 1413+117
Hutsemekers, Damien ULg

in Astronomy and Astrophysics (1993), 280

In order to interpret the spectral differences observed between the four images of the gravitationally lensed broad absorption line (BAL) quasar H 1413+117, we have investigated the effect on the line ... [more ▼]

In order to interpret the spectral differences observed between the four images of the gravitationally lensed broad absorption line (BAL) quasar H 1413+117, we have investigated the effect on the line profiles of the selective magnification of individual BAL clouds by gravitational microlenses. Since microlenses magnify both the selected cloud and the whole BAL region, this effect is only differential, and general constraints on its capability to produce spectral variations have been derived. Considering simple but realistic models for the microlenses, we find that the selective magnification of a relatively large optically thick BAL cloud can be at the origin of the spectral differences reported between the components of H 1413+117. However, a very precise configuration is needed: the magnified cloud must be at the border of the BAL region which must itself partially lie in a region of strong de-magnification. The fine tuning of the parameters mecessary to reproduce the observations either seriously questions this kind of interpretation or puts strong constraints on the lensing models. Another interpretation of the observed line profile differences in terms of effects due to microlensing is also briefly discussed. [less ▲]

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See detailErratum - Q:1208+1011 - the Most Distant Multiply Imaged Quasar or a Binary
Magain, Pierre ULg; Surdej, Jean ULg; Vanderriest, C. et al

in Astronomy and Astrophysics (1993), 272

In the title of this Letter, the word "multiply" was accidentally omitted. The correct title is shown above.

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See detailOn the reduction of narrow-band photometry
Manfroid, Jean ULg

in Astronomy and Astrophysics (1993), 271

A method for the reduction of narrow-band photometry is presented based on a multi-night, multi-star, multi-telescope model, and incorporating the spectral properties of the atmosphere.

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See detailBarium isotopes in the very metal-poor star HD 140283
Magain, Pierre ULg; Zhao, G.

in Astronomy and Astrophysics (1993), 268

The fractions of odd and even isotopes of barium in the metal-poor star HD140283 are determined from an analysis of the profile of the Ba II resonance line, taking advantage of the differences in ... [more ▼]

The fractions of odd and even isotopes of barium in the metal-poor star HD140283 are determined from an analysis of the profile of the Ba II resonance line, taking advantage of the differences in hyperfine structure splitting between the different isotopes. Although one would expect an increased contribution of the r-process in very metal-poor stars, it is found that the isotopic ratio is very close to solar. [less ▲]

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See detailOptical imaging of the gravitational lens system B 1422+231
Remy; Surdej, Jean ULg; Smette, A. et al

in Astronomy and Astrophysics (1993), 278

Direct optical images (Bessel V, R and Gunn i; average seeing of 0.88 seconds) of B1422+231, obtained in March 1993 at European Southern Observatory (ESO) (La Silla), have been decomposed by fitting ... [more ▼]

Direct optical images (Bessel V, R and Gunn i; average seeing of 0.88 seconds) of B1422+231, obtained in March 1993 at European Southern Observatory (ESO) (La Silla), have been decomposed by fitting multiple Point Spread Functions (PSFs). We detect the optical counterparts of the four known radio point-like components. No additional optical image is found, but due to the compactness of the configuration, our detection limit for additional point sources is rather low (19.3 in R). The deduced positions and photometry of the four optical components agree pretty well with the radio and IR observations and this study provides further evidence supporting the gravitational lens origin of B1422+231. [less ▲]

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See detailTi-ii transition probabilities and radiative lifetimes in TI and the solar titanium abundance
Bizzarri, A.; Huber, M. C. E.; Noels-Grötsch, Arlette ULg et al

in Astronomy and Astrophysics (1993), 273

Transition probabilities of 100 Ti-II emission lines, originating from 7 different atomic levels, have been determined by combining branching fractions with radiative lifetimes. The branching fractions ... [more ▼]

Transition probabilities of 100 Ti-II emission lines, originating from 7 different atomic levels, have been determined by combining branching fractions with radiative lifetimes. The branching fractions were measured using Fourier transform spectroscopy on a hollow cathode. The radiative lifetimes of these 7 - and 35 additional - levels were measured using time resolved laser-induced fluorescence on a slow Ti ion beam. The transition probabilities of 21 very weak lines have been used to derive a solar titanium abundance of α[SUB]Ti[/SUB] = log(N[SUB]Ti[/SUB]/N[SUB]H[/SUB]) + 12=5.04±0.04 dex, which is insensitive to the solar model. This value is in disagreement with the meteoritic titanium abundance (4.93±0.02). [less ▲]

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See detailRadiative Lifetime Measurements in Dy II and the Solar Abundance of Dysprosium
Biémont, Emile ULg; Löwe, R. M.

in Astronomy and Astrophysics (1993), 273

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