Author name code: neven ADS astronomy entries on 2022-09-14 author:Neven, Luc ------------------------------------------------------------------------ Title: Atlas photometrique du spectre solaire de [lambda] 3000 a [lambda] 10000 Authors: Delbouille, L.; Roland, G.; Neven, L. Bibcode: 1990apds.book.....D Altcode: No abstract at ADS Title: Atlas photometrique du spectre solaire de [lambda] 3000 a [lambda] 10000. Vol.2 Authors: Delbouille, L.; Roland, G.; Neven, L. Bibcode: 1989apds.book.....D Altcode: No abstract at ADS Title: The Photospheric Velocity Field of Procyon Authors: de Jager, C.; Neven, L. Bibcode: 1982Ap&SS..84..297D Altcode: BUSS observations of the profiles of two well observed spectral lines in the ultraviolet spectrum of αCMi (Procyon; F5 IV V) are analysed with a Fourier transform method in order to determine values of various parameters of the velocity field of the upper photosphere. We find a microturbulent line-of-sight velocity componentL μ = 0.9 ± 0.4 km s-1, a macroturbulent velocity componentL M = 5.3 ± 0.2 km s-1, and a rotational velocity componentv R sini=10.0±1.2 km s-1. In these calculations a single-moded sinusoidal isotropic macroturbulent velocity function was assumed. The result appears to be sensitive to the assumed shape of the macroturbulence function: for an assumed Gaussian shape the observations can be described withv R sini=4 km s-1 andL M = 11.6 ± 2.7 km s-1. A comparison is made with other results and theoretical predictions. Title: Stellar Atmospheric Velocity Fields - the Beta-Cephei Variables Gamma-Pegasi and Beta-Cephei Authors: de Jager, C.; Sato, N.; Burger, M.; Neven, L. Bibcode: 1982Ap&SS..83..411D Altcode: The shape parameters of a number of selected ultraviolet lines in BUSS-spectra of the Beta Cephei stars γ Peg and β Cep have been analyzed to determine the principal parameters of the atmospheric velocity field. We find for both stars a fairly high value (∼5 km s-1) for the microturbulent line-of-sight velocity component, which confirms an earlier result based on lower resolution UV spectra. Macroturbulent and rotational velocities are virtually zero in the atmosphere of γ Peg; for β Cep we findv rotsini=40 km s-1. Title: The ultraviolet spectrum of BET CMa stars. Authors: Burger, M.; de Jager, C.; Kamperman, T. M.; Neven, L. Bibcode: 1980A&A....90..170B Altcode: Ultraviolet spectra of 15 beta Canis Majoris stars in wavelength bands of approximately 100 A around 2100, 2500, and 2800 A (resolution 1.8 A), obtained with the Ultraviolet Stellar Spectrophotometer S 59 on board the ESRO TD-1A satellite are discussed. In general the spectra are similar to those of 'normal' stars, only the star alpha Vir has He I, C II, and Mg II lines slightly weaker than normal. Comparison with theoretical computations shows that the Fe abundance in the beta CMa stars is solar and that the average microturbulent velocity is about 4 km/sec. The UV spectral lines of beta Cep do not show any significant variations in equivalent width with phase. Title: Analysis of spectra of α CMi and α Cen A observed with the orbiting stellar ultraviolet spectrophotometer S59 in ESRO's TD1A satellite Authors: de Jager, C.; Kamperman, T. M.; Neven, L. Bibcode: 1978Ap&SS..54..343D Altcode: Ultraviolet spectra of α CMi and α Cen A taken with moderate spectral resolution (approx. 1.8 Å) are used to analyse whether a determination of stellar chemical abundances of Fe and Cr and of the photospheric parameters is possible. For αCMi, for which good spectral data are available, we findT eff=7660±110 K; logg eff=3.05±0.1. Further, Δlogɛ(Fe)=-0.06±0.09; Δ log ɛ(Cr)=-0.01±0.09 with regard to ‘standard’ (solar) abundances. For α Cen A the resulting data — particularly the photospheric ones — are less certain, but it seems that the Fe abundance may be smaller than the ‘standard’ value. Title: The Radiation Field in Photospheric Models for Extreme Supergiants Authors: de Jager, C.; Neven, L. Bibcode: 1975Ap&SS..33..295D Altcode: On the basis of assumed photospheric temperature models for 36 extreme supergiants (logg e -values of 1, 0.5 and 0;T e ranging from approx. 3700 33 000 K) photospheric fluxesS(τλ) were computed for 36 wavelengths ranging from 100 Å to 60 000 Å. The hot models are in perfect radiative equilibrium; the cooler show deviations up to 10%, sometimes even larger. Only in the relatively deep parts of the photospheres (τ5≳1) the radiation field at each geometrical level can be characterized by one unique radiation temperature; for smaller τ5-values there are large deviations from local thermal equilibrium. The influence of deviations from local thermodynamical equilibrium on the fluxes is briefly examined, and appears small but for the shortest wavelengths. In tables and graphs we give for these models πF(γ)-values, integrated fluxes, effective temperatures, coloursU, B andV, and the Balmer discontinuityD. Title: Atlas photometrique du spectre solaire de [lambda] 3000 a [lambda] 10000 Authors: Delbouille, L.; Roland, G.; Neven, L. Bibcode: 1973apds.book.....D Altcode: 1973QB551.D423..... No abstract at ADS Title: The empirical determination of line source functions, β L -values, and the microturbulent and convective velocity components as functions of depth in the photosphere-chromosphere transition region Authors: De Jager, C.; Neven, L. Bibcode: 1972SoPh...25..277D Altcode: An empirical method for determining line source functions, previously applied by us to the cores of infrared lines has now been extended to the whole line profile and was applied to centre-limb observations of sixteen lines of five infrared multiplets, mainly of high excitation potential (Table I). The present investigation was performed in two steps. In the first part of the paper approximate values are derived for the depth dependence of the four functions named in the title of this paper, where βL is the ratio between the actual and the LTE population of the lower level of the transitions involved. In the second part of the paper we use these empirically derived functions to compute the line profiles. From the remaining differences between observed and computed profiles, corrections are derived to the four functions. The main results are: (a) Convective velocities: see Table IV.(b)(Micro-)turbulent velocities: see Figure 8. Between τ5 = 10-4 and 10-1: «υτ» ≈ 1.4 km s-1, which is an upper limit since an unknown contribution of macroscopic motions could not be separated, (c) Line source functions: see Figures 9, 15 and 16. The source functions are close to the black-body function for τ5≳ 10-3, slight deviations occur in higher levels. The interesting behaviour of the CaII source function near τ5 = 10-5 should be noted. (d) Non LTE-functions: first approximations for the functions log βL5) were derived empirically in the first part, and are shown in Figure 10; the second approximation shows them to be too large and the real values seem to be closer to one-half or one-third of these functions. Title: On the Applicability of Goldberg and Unno's Method to the Determination of Microturbulent Velocities in an Atmosphere with Convection Authors: De Jager, C.; Neven, L. Bibcode: 1972SoPh...22...49D Altcode: The method of Goldberg and Unno for the determination of microturbulent velocities in a stellar atmosphere is only applicable if there are no macroturbulent or convective motions. Title: Damping Constants for Infrared Fraunhofer Lines Authors: De Jager, C.; Neven, L. Bibcode: 1970SoPh...11....3D Altcode: Empirical values of solar damping constants and their variation with optical depth were derived according to a method developed earlier by the authors. The damping constants refer to six infrared multiplets (24 lines). The average optical depths range from τ0 = 0.5 to 2.2. Corresponding theoretical damping constants were computed, mainly on the basis of Van der Waals damping, and with the help of detailed computations of the mean square radii of the atomic levels by Van Rensbergen. The empirical values are systematically larger than the theoretical ones, with factors ranging between 1.8 and 4.9. Some speculations about the source of this discrepancy are given. Title: On the Occurrence of Convective Motions in the Upper Photosphere Authors: De Jager, C.; Neven, L. Bibcode: 1968SoPh....4..379D Altcode: We have examined whether the motion field in the photosphere in the range of optical depths 0.25< τ0< 0.6 is dominated by thermal convection or by vibrations. The observed asymmetries of infrared Fraunhofer lines indicate the presence of motions, and the fact that the asymmetry is zero for lines of low excitation and increases with the excitation potential shows that these motions are chiefly convective in this part of the photosphere: upward moving elements appear to be hotter than downward moving ones. Title: Source Functions in the Cores of Infrared Fraunhofer Lines Authors: De Jager, C.; Neven, L. Bibcode: 1968SoPh....3..159D Altcode: No abstract at ADS Title: Errata Authors: de Jaher, C.; Neven, L. Bibcode: 1968BANS....2..291D Altcode: No abstract at ADS Title: A Systematic Method for the Analysis of High-Resolution Fraunhofer Line Profiles Authors: De Jager, C.; Neven, L. Bibcode: 1967SoPh....1...27D Altcode: A fraunhofer line profile depends on various parameters, partly related to the photospheric structure (T, Pg, Pe, vconv, vturb), partly to the atom or ion involved (such as oscillator strength, energy levels), partly also resulting from the interaction of the relevant kind of particles with the photosphere, and the photospheric radiation field. In this paper we shall mainly pay attention to the determination of: the macroturbulent (convective) velocities, vconv (τ); the damping constant γ (τ); the abundance, Ael; the distribution function ϕ(vconv, τ) of the convective velocities at each depth τ; the source function, S (τ); the microturbulent velocities, vturb (τ). Title: Observation of solar line profiles. I. The centre-to-limb variation of profiles of fifty lines in the near infrared solar spectrum Authors: de Jager, C.; Neven, L. Bibcode: 1967BANS....1..325D Altcode: 1966BANS....1..325N; 1966BANS....1..325D No abstract at ADS Title: Spectroscopic data for sixty new model photospheres Authors: de Jager, C.; Neven, L. Bibcode: 1967BANS....2..125D Altcode: No abstract at ADS Title: Observation of solar line profiles. I. The centre-to-limb variation of profiles of fifty lines in the near infrared solar spectrum (Abstract) Authors: de Jager, C.; Neven, L. Bibcode: 1967BAN....19..160D Altcode: No abstract at ADS Title: Spectroscopic data for sixty new model photospheres Authors: de Jager, Cornelis; Neven, L. Bibcode: 1967sdsn.book.....D Altcode: 1967QB1.B94v2n4.... No abstract at ADS Title: Note on the influence of the apparatus profile on spectral line profiles Authors: de Jager, C.; Neven, L. Bibcode: 1966BAN....18..306D Altcode: No abstract at ADS Title: Deviations from LTE in the Catom and the Abundance of C in the Solar Photosphere Authors: de Jager, C.; Neven, L. Bibcode: 1966IAUS...26..149D Altcode: No abstract at ADS Title: The profile of the infrared He I lines over the undisturbed solar disk Authors: de Jager, C.; Namba, O.; Neven, L. Bibcode: 1966BAN....18..128D Altcode: No abstract at ADS Title: The Computation of Spectroscopic Data for 60 New Model Photopheres Authors: de Jager, C.; Neven, L. Bibcode: 1964SAOSR.167..270D Altcode: No abstract at ADS Title: The abundance of lead in the Sun Authors: de Jager, C.; Neven, L. Bibcode: 1962BAN....16..307D Altcode: No abstract at ADS Title: Tables and graphs enabling the computation of the profiles of H [gamma] and H [delta] in stellar spectra Authors: de Jager, Cornelis; Neven, L. Bibcode: 1962AnOB....9.....D Altcode: 1962AnBel...9.....D No abstract at ADS Title: The Ultra-Violet and X-Ray Spectra of the Stars Authors: de Jager, C.; Neven, L. Bibcode: 1961LIACo..10..552D Altcode: 1961MSRSL...4..551D; 1961LIACo..10..551D No abstract at ADS Title: Observations of infrared solar line profiles Authors: Delbouille, L.; de Jager, C.; Neven, L. Bibcode: 1960AnAp...23..949D Altcode: No abstract at ADS Title: The computation of partition functions in a stellar atmosphere Authors: de Jager, C.; Neven, L. Bibcode: 1960BAN....15...55D Altcode: No abstract at ADS Title: A program for the computation of bn tables for H and He Authors: de Jager, C.; Kanno, M.; Neven, L. Bibcode: 1960AnAp...23..843D Altcode: No abstract at ADS Title: Saturation effects in very faint Fraunhofer lines Authors: de Jager, C.; Neven, L. Bibcode: 1959Obs....79..102D Altcode: No abstract at ADS Title: 36. The Influence of the Metal Abundance on the Continuous Stellar Spectra Authors: De Jager, C.; Neven, L. Bibcode: 1959LIACo...9..413D Altcode: 1959MSRSL...3..413D No abstract at ADS Title: Spectroscopic data for 50 model photospherese Authors: de Jager, Cornelis; Neven, L. Bibcode: 1957sdfm.book.....D Altcode: 1957QB4.U8l13p4.... No abstract at ADS Title: Spectroscopic data for 50 model photospheres Authors: de Jager, Cornelis; Neven, L. Bibcode: 1957AnOB....8.....D Altcode: 1957AnBel...8.....D No abstract at ADS Title: The Abundances of Diatomic Molecules of H, C, N, and O and of H2O in Stellar Atmospheres Authors: de Jager, C.; Neven, L. Bibcode: 1957LIACo...7..357D Altcode: No abstract at ADS Title: The profile of the Brackett α line in the solar spectrum Authors: de Jager, C.; Migeotte, M.; Neven, L. Bibcode: 1956AnAp...19....9D Altcode: No abstract at ADS Title: Observational models and helium abundances of the atmospheres of four B-type stars Authors: Neven, L.; de Jager, C. Bibcode: 1954BAN....12..103N Altcode: No abstract at ADS Title: La détermination de l'abondance relative de l'hélium dans les étoiles chaudes Authors: Neven, L. Bibcode: 1954LIACo...5..358N Altcode: 1954MSRSL...1..358N; 1954pna..conf..358N No abstract at ADS Title: High-Dispersion Solar Spectrograms Between 15μ and 24μ. Authors: Migeotte, M.; Neven, L. Bibcode: 1952ApJ...115..326M Altcode: No abstract at ADS Title: The interpretation of the observed hydrogen lines in the infrared solar spectrum II. Authors: de Jager, C.; Neven, L. Bibcode: 1952PRNAA..55..165D Altcode: 1952RNAAS..55..165D No abstract at ADS Title: Récents progrès dans l'observation du spectre infra-rouge du soleil a la station scientifique du Jungfraiijoch (Suisse) Authors: Migeotte, M.; Neven, L. Bibcode: 1952LIACo...3..165M Altcode: No abstract at ADS Title: The model of the solar atmosphere and the continuous absorption coefficient in the infrared Authors: Neven, L.; de Jager, C. Bibcode: 1951BAN....11..291N Altcode: No abstract at ADS Title: Nouvelles raies du méthane tellurique Authors: Migeotte, Marcel; Neven, L. Bibcode: 1951AnAp...14..315M Altcode: No abstract at ADS Title: The profiles of the lines of the Paschen and Brackett series of hydrogen in the solar spectrum. Authors: de Jager, C.; Neven, L. Bibcode: 1950PRNAA..53..157D Altcode: 1950RNAAS..53..157D No abstract at ADS Title: Mesures Micrometriques D'Etoiles Doubles Authors: Neven, L. Bibcode: 1949AnOB....4..201N Altcode: No abstract at ADS Title: Mesures micrometriques d'etoiles doubles Authors: Neven, L. Bibcode: 1948AnOB....4..201N Altcode: 1948AnBel...4..201N No abstract at ADS Title: Mesures micrometriques d'etoiles doubles Authors: Neven, L. Bibcode: 1948AnOB....4..277N Altcode: No abstract at ADS