References of "Astronomy and Astrophysics"
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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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See detailWR 134 line-profile variability revisited
Vreux, Jean-Marie ULg; Gosset, Eric ULg; Bohannan, B. et al

in Astronomy and Astrophysics (1992), 256

Line profile variations of WR 134 are analyzed on more than 200 spectra collected at Haute Provence Observatory and at Kitt Peak National Observatory. No conclusive evidence is found for a periodic ... [more ▼]

Line profile variations of WR 134 are analyzed on more than 200 spectra collected at Haute Provence Observatory and at Kitt Peak National Observatory. No conclusive evidence is found for a periodic behavior. However, for some frequencies, for example, the ones close to nu = (n x 0.5)/d, the data are ill-distributed, and the existence of a related periodic phenomenon cannot be completely ruled out. This does not mean that the variability presents a purely random behavior. Several new characteristics of the observed deformations are extracted from the analysis of the spectra and it is tentatively suggested that these could be the signature of a bipolar flow. [less ▲]

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See detailPhotometric variability of barium stars
Jorissen, A.; Manfroid, Jean ULg; Sterken, C.

in Astronomy and Astrophysics (1992), 253

Results are presented on uvby observations for up to 4 years of 19 southern barium stars. During the observation period, only two of the stars, HD 121447 and HD 46407, showed significant light variations ... [more ▼]

Results are presented on uvby observations for up to 4 years of 19 southern barium stars. During the observation period, only two of the stars, HD 121447 and HD 46407, showed significant light variations. These variables are the stars among the sample with the shortest orbital periods. In the case of HD 46407, evidence for eclipses was also found. It is noted that the evidence of varying phase shifts between the photometric eclipse and the spectroscopic ephemeris based on McClure and Woodsworth's (1990) orbital parameters makes it unlikely that the eclipsed light arises directly from the stellar companion of the barium star. It is also suggested that the flickering displayed by the reddest barium stars is a generic property of all red stars, because it was also observed for the comparison stars HD 204139 and HD 90677. [less ▲]

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See detailQ 1208 + 1011 - The most distant imaged quasar, or a binary?
Magain, Pierre ULg; Surdej, Jean ULg; Vanderriest, C. et al

in Astronomy and Astrophysics (1992), 253(Letters), 13-16

The paper reports the discovery of a new gravitational lens candidate: the high redshift (z = 3.803) and highly luminous (V = 17.5, M[SUB]V[/SUB] = -30.3) quasar Q 1208 + 1011. As derived from the ... [more ▼]

The paper reports the discovery of a new gravitational lens candidate: the high redshift (z = 3.803) and highly luminous (V = 17.5, M[SUB]V[/SUB] = -30.3) quasar Q 1208 + 1011. As derived from the analysis of direct CCD frames taken with the ESO/MPI 2.2 m telescope, this multiple quasar consists of two pointlike images, separated by 0.45 arcsec and characterized by a brightness ratio of 3.5, in red light. Existing spectroscopic data support the gravitational lens interpretation for this system but cannot exclude the hypothesis of a binary quasar. In the former case, the spectrum suggests that, if the metallic absorption line system reported by Steidel (1990) at a redshift z = 2.9157 is associated with the deflector, the mass of the lens should be of the order of M = 7.8 x 10 exp 11 solar masses. Evaluation of a recent HST PC frame obtained for Q 1208 + 1011 within the snapshot survey for gravitational lenses confirms the above results. [less ▲]

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See detailLifetimes in Fe II and the solar abundance of iron
Hannaford, P.; Lowe, R. M.; Grevesse, Nicolas ULg et al

in Astronomy and Astrophysics (1992), 259

New atomic lifetimes have been determined for eight quartet (z 4D, z 4F) levels and ten sextet (z 6D, z 6F, z 6P) levels in Fe II and the results for seven of these levels have been combined with existing ... [more ▼]

New atomic lifetimes have been determined for eight quartet (z 4D, z 4F) levels and ten sextet (z 6D, z 6F, z 6P) levels in Fe II and the results for seven of these levels have been combined with existing experimental branching fractions to obtain a revised set of log gf-values for 15 solar lines in Fe II. The new log gf data are used together with equivalent widths determined from the Liege solar atlas to derive a value for the iron photospheric abundance: 7.48 +/- 0.04, which is consistent with the currently accepted meteoritic result, 7.51 +/- 0.01. The results are compared with the atomic lifetime data, log gf data and solar analyses used in three other recent solar abundance determinations based on Fe II lines. [less ▲]

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See detailElectric Dipole Transitions in Atomic Oxygen and the lifetimes of the 2p3(4S°)3s5S° and 3S° States
Biémont, Emile ULg; Zeippen, C. J.

in Astronomy and Astrophysics (1992), 265

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