References of "Astronomy and Astrophysics"
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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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See detailThe evolution of atmospheric extinction at La Silla derived from measurements in the Stromgren photometric system
Sterken, C.; Manfroid, Jean ULg

in Astronomy and Astrophysics (1992), 266

We describe atmospheric extinction data obtained at the La Silla Observatory in the Stromgren photometric system. Our measurements, covering a time interval of almost fifteen years, show three episodes of ... [more ▼]

We describe atmospheric extinction data obtained at the La Silla Observatory in the Stromgren photometric system. Our measurements, covering a time interval of almost fifteen years, show three episodes of increased extinction due to airborne aerosols of volcanic origin. A small-amplitude seasonal variation and a short-timescale pseudo-periodic oscillation are also revealed. Implications on the observing procedures and photometric reduction schemes are discussed. [less ▲]

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See detailPhotometric accuracy - The impact of extrapolation in differing color-transformation schemes
Manfroid, Jean ULg; Sterken, C.; Gosset, Eric ULg

in Astronomy and Astrophysics (1992), 264

We discuss photometric errors that arise from the use of differing color-transformation schemes when extrapolating outside the range of the standard values that define the system. An example based on data ... [more ▼]

We discuss photometric errors that arise from the use of differing color-transformation schemes when extrapolating outside the range of the standard values that define the system. An example based on data from the Long-Term Photometry of Variables project (LTPV) at ESO is analyzed. Practically, the extrapolation errors are most evident as systematic brightness jumps of some program stars, seen when monitored over several observing runs. Conclusions are drawn about the choice of standard stars in the Stromgren system. [less ▲]

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See detailThe Beta Pictoris circumstellar disk. XIII - Survey of the variable CA II lines
Lagrange-Henri, A. M.; Gosset, Eric ULg; Beust, H. et al

in Astronomy and Astrophysics (1992), 264

Over 200 Ca II K and H spectra of Beta Pictoris taken between September 19, 1989 and December 19, 1990 are presented. Many new variable features are observed, at low and high redshifts, together with a ... [more ▼]

Over 200 Ca II K and H spectra of Beta Pictoris taken between September 19, 1989 and December 19, 1990 are presented. Many new variable features are observed, at low and high redshifts, together with a few blueshifted ones. The time scales for the variations are shown to be strongly dependent on the redshift of the variable lines. A rate of events of about 200/yr is derived; it is also shown that in some cases the absorbing cloud covers less than 40 percent of the stellar surface. The observed variations are analyzed and compared to those observed in the UV. These observations make it possible to test the present scenario of evaporating infalling bodies, in terms of velocity of variable lines, occurrence of variable events, small time-scale variations, and size of the absorbing cloud. It is shown that the observed velocity range for the variable components may be explained by the present scenario, as well as the size of the absorbing clouds. [less ▲]

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See detailThe outstanding photometric variations of the Ap star HD 7676 = VV Scl
Renson, Pierre ULg; Manfroid, Jean ULg

in Astronomy and Astrophysics (1992), 263

Contrary to what was formerly believed, VV Scl is not an eclipsing star but an Alpha CVn type variable with period P = 5.0976 +/- 0.0001 d. The range of the luminosity variation is remarkably large for an ... [more ▼]

Contrary to what was formerly believed, VV Scl is not an eclipsing star but an Alpha CVn type variable with period P = 5.0976 +/- 0.0001 d. The range of the luminosity variation is remarkably large for an Ap star, especially in B of Johnson's system, and in b and mostly in v of Stromgren's one. A secondary minimum appears near the maximum in B, b, an v. The main minima are in phase in all colors. [less ▲]

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See detailPhysical constraints on color transformations
Manfroid, Jean ULg

in Astronomy and Astrophysics (1992), 260

Color-transformation procedures in photometry should ideally obey physical principles. A few of these rules, of particular interest in the study of reddened stars, of multiple stars, stellar clusters and ... [more ▼]

Color-transformation procedures in photometry should ideally obey physical principles. A few of these rules, of particular interest in the study of reddened stars, of multiple stars, stellar clusters and galaxies are discussed. Directions to minimize the transformation errors for these objects are given. [less ▲]

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See detailSystematic color transformation effects in Stromgren photometry
Manfroid, Jean ULg; Sterken, C.

in Astronomy and Astrophysics (1992), 258

A major cause of errors in photometry is to be attributed to the color transformation. A thorough analysis of numerous observing runs carried out in the Stromgren system shows how reliable are the ... [more ▼]

A major cause of errors in photometry is to be attributed to the color transformation. A thorough analysis of numerous observing runs carried out in the Stromgren system shows how reliable are the transformations in the different indices. Conclusions are drawn about the reduction methods, the validity of homogenization procedures, and the choice of the standard stars which define the system. [less ▲]

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See detailLight curve of the Ap star TW Columbae
Renson, Pierre ULg; Manfroid, Jean ULg

in Astronomy and Astrophysics (1992), 256

The uvby light curves of the Ap star TW Col are analyzed. The presence of a small-scale dip in the curves appears to be in conflict with a simple spotted-rotator model. TW Col is the second star, after 46 ... [more ▼]

The uvby light curves of the Ap star TW Col are analyzed. The presence of a small-scale dip in the curves appears to be in conflict with a simple spotted-rotator model. TW Col is the second star, after 46 Eri, for which such a phenomenon seems to be confirmed. [less ▲]

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