References of "Surdej, Jean"
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See detailDetermination of the pole orientation of an asteroid - The amplitude-aspect relation revisited
Pospieszalska-Surdej, Anna ULg; Surdej, Jean ULg

in Astronomy and Astrophysics (1985), 149

Near the opposition of a minor planet the geometrical approximation essentially constitutes a good representation of the Hapke-Irvine relation for describing the scattering properties of a surface layer ... [more ▼]

Near the opposition of a minor planet the geometrical approximation essentially constitutes a good representation of the Hapke-Irvine relation for describing the scattering properties of a surface layer, and the authors show that the normalized light curve of a three-axes ellipsoid model reduces to a straight line whose slope depends only on the aspect angle A and on the semi-axes ratios a/b, b/c of the ellipsoid. A set of non-linear equations is then solved by a least squares method in order to derive the four unknown parameters lambda[SUB]0[/SUB], beta[SUB]0[/SUB] (ecliptic coordinates of the pole) and a/b, b/c. The authors have applied this technique to published observations of two asteroids: For (624) Hektor two possible solutions are found; and for the case of (44) Nysa, they show that additional observations are needed in order to derive a self-consistent pole orientation. [less ▲]

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See detailTwo quasars seen near the spiral galaxy NGC 470
Arp, H.; Surdej, Jean ULg; Swings, Jean-Pierre ULg

in Astronomy and Astrophysics (1984), 138

The discovery of two quasars with 16arcsec separation from each other on the sky and within 95arcsec of the nucleus of the spiral galaxy NGC 470 is reported. The quasars were discovered in a search for ... [more ▼]

The discovery of two quasars with 16arcsec separation from each other on the sky and within 95arcsec of the nucleus of the spiral galaxy NGC 470 is reported. The quasars were discovered in a search for ultraviolet-excess objects in four overlapping fields of about 25 square degrees each. Preliminary spectroscopy of the quasars yields z = 1.875 (mv = 19.9 mag) and z = 1.533 (mv = 18.2 mag). [less ▲]

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See detailThe structure and physical conditions characterizing the emission-line galaxy He 2-10
Hutsemekers, Damien ULg; Surdej, Jean ULg

in Astronomy and Astrophysics (1984), 133

Direct plates taken through interference (Halpha+[N II] and [O III]) and broad band (B, R) filters at the prime focus of the ESO 3.6 m telescope reveal the structure of the emission-line galaxy He 2-10 ... [more ▼]

Direct plates taken through interference (Halpha+[N II] and [O III]) and broad band (B, R) filters at the prime focus of the ESO 3.6 m telescope reveal the structure of the emission-line galaxy He 2-10. The authors confirm that the broad emission band at lambda4660 Å first reported by Allen et al. (1976) essentially originates from the bright central nucleus. They estimate that the number of Wolf-Rayet (WC+WN) stars contributing to this feature is approximately 3.3×10[SUP]3[/SUP] and that the number of early-type stars (mainly O-type) necessary to account for the observed ionization of the emitting gas is of the same order. This result is compared to the stellar content derived for a few other galaxies and giant H II regions known to contain a large population of Wolf-Rayet stars. [less ▲]

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See detailPhotoelectric photometry of the peculiar emission-line star GG Carinae
Gosset, Eric ULg; Surdej, Jean ULg; Swings, J.-P.

in Astronomy and Astrophysics. Supplement Series (1984), 55

The first extensive sets of photoelectric observations of the peculiar emission-line star GG Carinae were obtained from 1977 to 1981, in both the standard UBV and Strömgren systems. A Fourier analysis of ... [more ▼]

The first extensive sets of photoelectric observations of the peculiar emission-line star GG Carinae were obtained from 1977 to 1981, in both the standard UBV and Strömgren systems. A Fourier analysis of 767 independent measurements leads to the determination of a period P = 31[SUP]d[/SUP].020 for the light variations. Different physical arguments based on the analysis of the present photoelectric - as well as previous photographic - data clearly indicate, however, that the true period is P = 62[SUP]d[/SUP].039. The resulting composite lightcurve displays two distinct maxima and minima with a total light amplitude Deltam â ¡ 0.5 mag. Additional interesting features are noticed in the mean lightcurve. Although it is not possible to classify GG Carinae among any known type of variable stars, the light variations of this object are similar to those observed for beta Lyrae-type systems. [less ▲]

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See detailQuasars et lentilles gravitationnelles
Surdej, Jean ULg

Article for general public (1984)

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See detailPhotoelectric lightcurves and rotation period of the minor planet 201 Penelope
Surdej, Jean ULg; Louis, B.; Cramer, N. et al

in Astronomy and Astrophysics. Supplement Series (1983), 54

Results of photoelectric observations of the asteroid 201 Penelope carried out at the European Southern Observatory and Perth Observatory during the 1980 opposition of the asteroid between October 6 and ... [more ▼]

Results of photoelectric observations of the asteroid 201 Penelope carried out at the European Southern Observatory and Perth Observatory during the 1980 opposition of the asteroid between October 6 and November 7 are presented. Observations were made in the standard UBV and Geneva systems at ESO, and in V-prime at Perth. Examination of composite light curves shows the presence of two distinct maxima and two distinct minima, with a total amplitude of the V light curve of 0.52 magnitudes. A mean synodic rotation period of 3 h, 44 min, 51.6 + or - 7.4 sec is derived. Using a mean phase coefficient beta[SUB]V[/SUB] = 0.037 mag/deg, a primary V (1,0) maximum of 8.51 + or - 0.01 magnitudes is obtained. Color indices are measured as B-V = 0.70 + or - 0.01 and U-B = 0.23 + or - 0.02 magnitudes, and previously reported color variations (Surdej and Cramer, 1980) are attributed to a failure in the reduction procedure. [less ▲]

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See detailUBV photometry of the minor planets 86 Semele, 521 Brixia, 53 Kalypso and 113 Amalthea
Surdej, Jean ULg; Surdej, Anna ULg; Louis, B.

in Astronomy and Astrophysics. Supplement Series (1983), 52

The asteroids were observed photometrically during the 1980 and 1981 oppositions, respectively. The V lightcurve of 86 Semele displays two asymmetric maxima and minima with a total amplitude DeltaV = 0.18 ... [more ▼]

The asteroids were observed photometrically during the 1980 and 1981 oppositions, respectively. The V lightcurve of 86 Semele displays two asymmetric maxima and minima with a total amplitude DeltaV = 0.18 mag. Its synodic rotation period is P[SUB]s[/SUB] = 16h38m02" ± 16" and the color indices B-V = 0.690 ± 0.011 and U-B = 0.320 ± 0.015 mag. 521 Brixia is a slow rotator (P[SUB]s[/SUB] > 24h) showing light variations greater than DeltaV â 0.09 mag and with color indices B-V = 0.714 ± 0.008 and U-B = 0.337 ± 0.011 mag. 53 Kalypso rotates with a period P[SUB]s[/SUB] = 26h33m ± 4m with a total light amplitude DeltaV > 0.10 mag and color indices B-V = 0.692 ± 0.015 and U-B = 0.341 ± 0.022 mag. The lightcurve of 113 Amalthea shows large amplitude variations (DeltaV > 0.26 mag) with a broad minimum and the rotation period is greater than 12h with color indices B-V = 0.888 ± 0.012 and U-B = 0.487 ± 0.019 mag. [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 detailMore on the reflection nebula surrounding HD 87643 and the non-uniform atmosphere of the central star
Surdej, Jean ULg; Swings, Jean-Pierre ULg

in Astronomy and Astrophysics (1983), 117

Different equivalent widths and line displacements of Hbeta and Fe II are observed in spectra of two condensations located within the reflection nebula surrounding HD 87643: they indicate important ... [more ▼]

Different equivalent widths and line displacements of Hbeta and Fe II are observed in spectra of two condensations located within the reflection nebula surrounding HD 87643: they indicate important relative motions (Deltav â ¡ 150 km s[SUP]-1[/SUP]) between various parts of the nebulosity and demonstrate that the stellar atmosphere in which the lines are formed is not isotropic and/or not homogeneous. The spectrum of another reflection nebula situated in the vicinity of HD 87643 is also briefly described. [less ▲]

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See detailA new very interesting pair of quasars - Q0107 - 025 A and B
Surdej, Jean ULg; Swings, Jean-Pierre ULg; Henry, A. et al

in 24th Liege International Astrophysical Colloquium: "Quasars and gravitational lenses" (1983)

A search for ultraviolet-excess objects in a field centered around NGC 450 has revealed the presence of two quasar-candidates (18.2 and 17.4 mag) fairly near one another (separation of 77 arcsec ... [more ▼]

A search for ultraviolet-excess objects in a field centered around NGC 450 has revealed the presence of two quasar-candidates (18.2 and 17.4 mag) fairly near one another (separation of 77 arcsec). Preliminary spectroscopy with the Palomar 5 m telescope shows that these objects are indeed two quasars (Q0107 - 025 A and B) having very similar spectra and redshifts (of about 0.96), suggesting a new possible case of twin quasars or of a gravitational lens. Although the analysis (to be published elsewhere) of additional spectroscopic data collected with the ESO 3.6 m telescope rather favors the first interpretation, higher resolution data are still necessary before rejecting definitely the second possibility. Deep multi-color CCD frames obtained with the Danish 1.5 m telescope clearly show that a group (or cluster) of faint galaxies is detected in the vicinity of the two quasars. [less ▲]

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See detailA Survey of Ultraviolet Excess Quasar Candidates in a Large Field around NGC450
Swings, Jean-Pierre ULg; Arp, H.; Surdej, Jean ULg et al

in LIAC Colloq. 24: Quasars and Gravitational Lenses (1983)

Preliminary results of a search for QSO candidates in a 25 square degree field around NGC 450 are presented.

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See detailDetermination of mass-loss rates from early-type stars on the basis of 'log(W1)-log(W1 0)' diagrams
Surdej, Jean ULg

in Astronomy and Astrophysics (1983), 127

Using realistic expressions for the velocity and opacity distributions in rapidly expanding atmospheres, the author presents numerical results for the first order moment W[SUB]1[/SUB] of a P Cygni line ... [more ▼]

Using realistic expressions for the velocity and opacity distributions in rapidly expanding atmospheres, the author presents numerical results for the first order moment W[SUB]1[/SUB] of a P Cygni line profile calculated as a function of the parameter W[SUB]1[/SUB][SUP]0[/SUP] â Mn(level), where Mrepresents the mass-loss rate and n(level) the average fractional abundance of the relevant ion. The calculations clearly show that the resulting "log(W[SUB]1[/SUB]) - log(W[SUB]1[/SUB][SUP]0[/SUP])" curves depend almost essentially on the opacity distribution and that for unsaturated P Cygni line profiles the relation W[SUB]1[/SUB] â Mn(level) holds irrespective of the both distributions. For W[SUB]1[/SUB] ⪠0.24, the line profiles become saturated and the first order moment W[SUB]1[/SUB] does not provide anymore accurate information on the mass-loss rate. This technique of mass-loss determination and that which consists in fitting observed line profiles with theoretical ones are compared. [less ▲]

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See detailThe far-UV spectrum of the low-excitation planetary nebula HD 138403
Surdej, Jean ULg; Heck, A.

in Astronomy and Astrophysics (1982), 116

Two high-resolution far-UV spectra of the low-excitation planetary nebula HD 138403 are analyzed which were obtained with the IUE satellite over the wavelength range from 1170 to 2070 A. It is shown that ... [more ▼]

Two high-resolution far-UV spectra of the low-excitation planetary nebula HD 138403 are analyzed which were obtained with the IUE satellite over the wavelength range from 1170 to 2070 A. It is shown that the nebula's far-UV spectrum comprises a stellar continuum on which are superimposed a few emission lines, numerous interstellar absorption lines, and various types of P Cygni profiles. Evidence is examined for substantial mass loss from the central nucleus, with terminal velocities of the order of 800 km/s. The observed nebular emissions are used to derive the electron density in the main nebula. The results are taken as supporting the hypothesis that a bipolar structure is expanding around HD 138403 via a selective radiation process involving an edge- or line-locking mechanism or both. [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 detailAsteroid rotation - Hunting for a record: 1689 Floris-Jan
Schober, H. J.; Surdej, Jean ULg

in The Messenger (1982), 29

Last year, in June 1981 - ESO Messenger No. 24, p. 22-23 - H. J. Schober published areport on "Spinning Asteroids and Photometry". There he mainly gave a general introduction about what can be done using ... [more ▼]

Last year, in June 1981 - ESO Messenger No. 24, p. 22-23 - H. J. Schober published areport on "Spinning Asteroids and Photometry". There he mainly gave a general introduction about what can be done using UBV photometry in order to derive physical properties of asteroids such as geometrie forms, diameters, reflectance on the surface, bimodality of asteroids with respect to typology. A special effort was made to report about the activities to deal with asteroids as "variable objects" like variable stars - showing Iightcurves with defined rotation rates to be derived. Among asteroids it was stated that the longest rotation periods found before 1975 were not larger than 20 hours - followed by 654 Zelinda 31 ~9 (1975). 393 Lampetia 38h7, 128 Nemesis 39h0 (1979), 709 Fringilla 52h4 (1979) and 182 Eisa 80~00 (1980), the latter corresponding to 3d33. [less ▲]

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See detailQuasars in a control field far from bright galaxies
Arp, H.; Surdej, Jean ULg

in Astronomy and Astrophysics (1982), 109

The density of quasars in a control field of the sky selected to be free of bright galaxies is investigated in order to derive a value for the average background density of quasars and to analyze quasar ... [more ▼]

The density of quasars in a control field of the sky selected to be free of bright galaxies is investigated in order to derive a value for the average background density of quasars and to analyze quasar distribution within the field. Schmidt plates were obtained in the ultraviolet and blue for a control field surrounding SAO 45758 at R.A. 15 h 49 min, declination plus 48 deg 38 arcmin. Examination of the spectra of 25 of the 137 objects found to exhibit an ultraviolet excess reveals 12 of them to be quasars, indicating a quasar density of 6.7 plus or minus 0.9/sq deg down to a limiting magnitiude of 20 over the 19 sq deg area of the field. This value is noted to be in agreement with previous values of quasar background density deduced for other regions of the sky. Large fluctuations of quasar density are found, however, within the field which may be correlated with groups of intermediate brightness galaxies. [less ▲]

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See detailSpectroscopic observations of thirteen optically-selected QSOs in a large field centred around NGC 5334
Surdej, Jean ULg; Swings, Jean-Pierre ULg; Arp, H. C. et al

in Astronomy and Astrophysics (1982), 114

A large field (approximately 25 sq deg) around NGC 5334 was searched for QSO candidates with ultraviolet-excess, in order to investigate the space density, distribution, and luminosity of quasars near as ... [more ▼]

A large field (approximately 25 sq deg) around NGC 5334 was searched for QSO candidates with ultraviolet-excess, in order to investigate the space density, distribution, and luminosity of quasars near as well as far from bright galaxies. Spectroscopic data obtained with the European Southern Observatory 3.6 m telescope are presented for 13 quasars identified within a sample of 23 observed candidates. As expected, the redshift of these optically selected quasars was found to fall in the range 0.23-2.08, with only one exception. Two, and possibly three, of the quasars of the largest redshift show absorption lines, while the remaining 10 faint blue objects display zero-redshift stellar spectra. [less ▲]

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See detailThe six-day rotation period of 1689 Floris-Jan - A new record among slowly rotating asteroids
Schober, H. J.; Surdej, Jean ULg; Harris, A. W. et al

in Astronomy and Astrophysics (1982), 115

Abstract image available at: http://esoads.eso.org/abs/1982A&A...115..257S

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