References of "Astrophysics & Space Science"
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See detailA new database of astrophysical interest
Biémont, Emile ULg; Palmeri, P.; Quinet, Pascal ULg

in Astrophysics & Space Science (1999), 269-270

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See detailCyclical Spectral and Photometric Variations of the Apparently Single Wolf-Rayet Star WR 134
Morel, Thierry ULg; Marchenko, S. V.; Eenens, P. R. J. et al

in Astrophysics & Space Science (1998), 260

Evidence is presented for the existence of a 2.3 day periodicity in the line-profile changes of the apparently singleWolf-Rayet star WR 134. This cyclical variability may be induced either by the presence ... [more ▼]

Evidence is presented for the existence of a 2.3 day periodicity in the line-profile changes of the apparently singleWolf-Rayet star WR 134. This cyclical variability may be induced either by the presence of an orbiting collapsed companion, or by the rotational modulation of a largely inhomogeneous outflow. [less ▲]

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See detailFurther results on the line-profile variability of WR 134
Gosset, Eric ULg; Vreux, Jean-Marie ULg; Andrillat, Y.

in Astrophysics & Space Science (1994, November 01), 221

We discuss a few conclusions previously derived from the analysis of the line-profile variability of the Wolf-Rayet star WR 134, some details are made more explicit. In addition, we present a new set of ... [more ▼]

We discuss a few conclusions previously derived from the analysis of the line-profile variability of the Wolf-Rayet star WR 134, some details are made more explicit. In addition, we present a new set of data and briefly comment on recent results deduced from its analysis. [less ▲]

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See detailThe use of gravitational microlensing to scan the structure of BAL QSOs
Hutsemekers, Damien ULg; Surdej, Jean ULg; van Drom, E.

in Astrophysics & Space Science (1994), 216

Approximately 10% of the quasi-stellar objects (QSOs) show broad absorption lines (BAL) in their spectra which, if interpreted in terms of Doppler velocities, reveal the presence of high velocity gas ... [more ▼]

Approximately 10% of the quasi-stellar objects (QSOs) show broad absorption lines (BAL) in their spectra which, if interpreted in terms of Doppler velocities, reveal the presence of high velocity gas outflows. One of these BAL QSOs is known to be gravitationally lensed. It therefore constitutes a good candidate to search for microlensing effects, i.e., the selective amplification of different line forming regions. Considering current models for the BAL region, we have investigated the effects of moving microlenses on the line profiles, and we conclude that these effects strongly depend on the adopted model. A regular spectroscopic monitoring of lensed BAL QSOs would therefore be highly valuable to distinguish between the various models proposed so far to interpret the origin of broad absorption lines. [less ▲]

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See detailThe binning analysis - Towards a better significance test
Gosset, Eric ULg; Louis, Benoit

in Astrophysics & Space Science (1986), 120

The authors demonstrate that the problems encountered with the binning analysis essentially lie in the significance test which is used. They review and analyse most of the existing significance tests and ... [more ▼]

The authors demonstrate that the problems encountered with the binning analysis essentially lie in the significance test which is used. They review and analyse most of the existing significance tests and show that the use of those based on randomization processes considerably improves the situation. For the one-dimensional binning analysis, they apply the '2 within 4' randomization test whereas for the two- and the three-dimensional binning analyses they introduce two innovations: the '4 within 16' randomization test and the '8 within 64' randomization test, respectively. [less ▲]

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See detailThe short time-scale light variability of HD 153919 revisited
Gosset, Eric ULg

in Astrophysics & Space Science (1985), 108

Using Fourier analysis techniques, the available sets of visual photometric data concerning the X-ray binary HD 153919 are analyzed in order to clear up the controversy on the possible existence or ... [more ▼]

Using Fourier analysis techniques, the available sets of visual photometric data concerning the X-ray binary HD 153919 are analyzed in order to clear up the controversy on the possible existence or absence of the small-amplitude light variability (T = about 90 min). In this work, great effort has been made to keep a good level of homogeneity and objectivity. The main conclusion is that at the 99.4-percent confidence level, a periodicty (v = 15.5/day) is detected in one data set. In this case, it is possible to conclude that the short time-scale variability does exist. No other self-conclusive detection can be definitely reported; nevertheless, at the 90-percent confidence level, the star has a tendency to vary with characteristic frequencies of about 15/day, 30/day, and possibly higher multiples. [less ▲]

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See detailA generalized method for deriving mass-loss rates - The first order moment of unsaturated P Cygni line profiles
Surdej, Jean ULg

in Astrophysics & Space Science (1983), 90

For the case of optically thin lines, we show that the relation existing between the first order moment W1 ~ j (E(2)/E~ - 1)(2 - 212) d2 of a P Cygni profile and the quantity ii~in(1eve1), where M is the ... [more ▼]

For the case of optically thin lines, we show that the relation existing between the first order moment W1 ~ j (E(2)/E~ - 1)(2 - 212) d2 of a P Cygni profile and the quantity ii~in(1eve1), where M is the mass-loss rate of the central star and n(level) the fractional abundance of the ion under study, is in fact independent of any Sobolev-type approximations used for the transfer of line radiation, contrary to what has been assumed in some previous works (Castor eta!., 1981; Surdej, 1982). Consequently, all results established in the context of'very rapidly' expanding atmospheres and mainly referring to the non-dependence of W1 vs various physical (underlying photospheric absorption line, limb darkening, etc.) and geometrical (velocity field v(r), etc.) effects remain unchanged for arbitrary (e.g. non-Sobolev type) outward-accelerating velocity laws. Whenever applied with caution, Equation (50) thus provides a very powerful means of deriving mass-loss rates - with a total uncertainty less than 60 percent - from the measurement W1 of unsaturated P Cygni profiles observed in the spectrum of early - as well as late - type stars, quasars, etc [less ▲]

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See detailDetermination of mass-loss rates from the first order moment W1 of unsaturated Cygni line profiles
Surdej, Jean ULg

in Astrophysics & Space Science (1982), 88

The relationship between the first order moment and the mass loss rate is investigated within the framework of the Sobolev approximation (1947, 1957, 1958) under various physical and geometrical ... [more ▼]

The relationship between the first order moment and the mass loss rate is investigated within the framework of the Sobolev approximation (1947, 1957, 1958) under various physical and geometrical conditions. By assuming that the size of the expanding envelope from which the observed P Cygni profiles arise is large with respect to the central stellar core, a general expression for the n-th order moment is obtained for the case of a point-like source in terms of the usual parameters inherent to Sobolev-type theories. It is then shown how the first result is altered when considering separately the effects due to collisions and rotation, the presence of the underlying photospheric absorption line, the finite size of the central core, and the limb-darkening of the stellar core. It is concluded that the total uncertainty of the mass loss rate determination made with the approach proposed here should be less than 60 percent. [less ▲]

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See detailFormation of P Cygni profiles with limb darkening of the stellar core
Surdej, Jean ULg

in Astrophysics & Space Science (1981), 79

In the framework of the Sobolev approximation, the effects of limb darkening of the stellar core on the formation of line profiles in rapidly expanding envelopes are investigated. For the case of outward ... [more ▼]

In the framework of the Sobolev approximation, the effects of limb darkening of the stellar core on the formation of line profiles in rapidly expanding envelopes are investigated. For the case of outward-accelerating envelopes, it is shown that the P Cygni profiles, calculated with and without limb darkening, do appear almost identical as long as the size of the envelope remains large with respect to the radius of the star. As the extent of the envelope decreases, the resulting profiles are found to differ appreciably close to the line center. When considering outward-decelerating (or equivalently inward-accelerating) envelopes, calculations with the limb darkening effects reveal that the P Cygni profiles are more strongly affected than in the previous case. These effects are specially important in the blue wing and near the center of the resulting line profiles, irrespective of the size of the envelope. [less ▲]

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See detailFormation of resonance doublet profiles in rapidly expanding envelopes
Surdej, Jean ULg

in Astrophysics & Space Science (1980), 73

Sobolev's escape probability method is used to investigate the transfer of spectral line radiation for a resonance doublet in a rapidly expanding envelope. A three-level atom model is used to derive ... [more ▼]

Sobolev's escape probability method is used to investigate the transfer of spectral line radiation for a resonance doublet in a rapidly expanding envelope. A three-level atom model is used to derive expressions for the spectral radiation fields J12 and J13, the resulting radiative force exerted per atom, and the resonance doublet profile for the cases of outward-accelerating (or equivalently inward-decelerating) and outward-decelerating (or equivalently inward-accelerating) envelopes. Criteria are deduced under which resonance doublet profiles formed in outward-accelerating and/or outward-decelerating envelopes would appear to be resolved into double P Cygni profiles. [less ▲]

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See detailThe pioneering investigations in the field of the interstellar molecules, 1935-1942.
Swings, Polydore ULg

in Astrophysics & Space Science (1978), 55(1), 263-265

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See detailOn the effects of inhomogeneities in high excitation H II regions
Manfroid, Jean ULg

in Astrophysics & Space Science (1978), 53

The hypothesis that observations of inhomogeneities in H II regions would be changed by adopting a filling factor other than one is investigated by comparing models of H II regions with filling factors of ... [more ▼]

The hypothesis that observations of inhomogeneities in H II regions would be changed by adopting a filling factor other than one is investigated by comparing models of H II regions with filling factors of one and one eighth. Attention is given to conditions when the hydrogen and helium fronts are close together, i.e. high excitation H II regions. Results obtained through use of an iterative scheme, whereby the nebula is divided into concentric shells with variable thickness, indicate that some emission lines, e.g., O II, S II, S III, N II, are substantially altered when the filling factor is smaller than one [less ▲]

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See detailThe forbidden line spectrum in the edges of H II regions
Manfroid, Jean ULg

in Astrophysics & Space Science (1977), 48

It is shown analytically that the motion of exciting stars can affect the forbidden emission-line spectra of H II regions in an observable manner. A model is used which comprises a small solid angle of a ... [more ▼]

It is shown analytically that the motion of exciting stars can affect the forbidden emission-line spectra of H II regions in an observable manner. A model is used which comprises a small solid angle of a spherical nebula that is symmetric with respect to the direction of stellar motion and consists of a mixture of H, He, C, N, O, and Ne with ionization states up to He II, C III, N III, O III, and Ne III. Consideration is given to the case of a 36-solar-mass O5 star with an effective temperature of 43,000 K moving at a velocity of 10 km/s in a nebula having a density of 10 times the proton mass per cu cm. The results obtained indicate that: (1) the region where forbidden lines characteristic of ionization fronts are produced is broadened considerably at the trailing edge of the nebula; (2) the spectrum in this region is comparable to that of fossil H II regions; and (3) the ionization front at the leading edge is sharper, the temperature there is higher, and the forbidden-line spectrum is similar to that of young ionization fronts. [less ▲]

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See detailOn the evolution of ionized gas around hot stars
Manfroid, Jean ULg

in Astrophysics & Space Science (1976), 41

The initial evolution of a uniform H II region around a star of 36 solar masses is described. The general equations of the problem are solved numerically by a finite-difference method. Forbidden-line ... [more ▼]

The initial evolution of a uniform H II region around a star of 36 solar masses is described. The general equations of the problem are solved numerically by a finite-difference method. Forbidden-line emission by ions of C, N, O, and Ne is taken into account. [less ▲]

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See detailObservations of southern nebulae
Danks, A. C.; Houziaux, Léo ULg; Manfroid, Jean ULg

in Astrophysics & Space Science (1976), 39

Spectroscopic observations of 10 H II regions in the southern hemisphere are presented. The observations cover the spectral region 3600-8000 A.

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See detailSur les déplacements radiaux de différents éléments dans alpha2 CVn
Renson, Pierre ULg

in Astrophysics & Space Science (1972), 17

Curves of radial displacements for alpha2 CVn are obtained by mechanical integration of radial velocity curves deduced from measures by Struve and Swings and by Babcock and Burd for EuII, CrII, FeI and II ... [more ▼]

Curves of radial displacements for alpha2 CVn are obtained by mechanical integration of radial velocity curves deduced from measures by Struve and Swings and by Babcock and Burd for EuII, CrII, FeI and II, and by Pyper for EuII.. In order to proceed to the comparison, a value as accurate as possible is sought for the period. If we take all the known photometric observations into account, we get 5.4693+-0.0001 d. Small differences between the curves for a given ion are noted, especially when using Pyper's measures. However these discrepancies do not necessarily prove the existence of secular variations; in the binary model, they can be interpreted mainly in terms of the Ovenden effect. Too large displacements, and other peculiarities in the variations, may also be attributed to that effect, and to circumstellar currents. The ranges of the velocity variations and of the radial displacements are also discussed for other Ap stars. [less ▲]

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