Spectre continu dans le proche infrarouge de deux étoiles Be: HD 50138 et HD 51585

Continuous spectra of the Be objects HD 50138 and HD 51585 have been investigated between 1.6 and 1.2 ^-1. The infrared gradient _IR of HD 50138 (B5eV) is found to be 2.09±0.10, while the typical B5V star And indicates _IR=1.17. A B5V (HD 16219) star located at about the same distance as HD 50138 has _IR=1.29 and it is shown that interstellar reddening may account for _IR between HD 16219 and And. The difference in gradient between HD 50138 and HD 16219 ( _IR=0.8) may be explained by a continuous reemission in a lenticular envelope with a radius equal to 4R _*. The peculiar object HD 51585 exhibits a B0.5 continuous spectrum, for which the value d logI /d(1/) should be 1.13 according to model atmospheres computations. The distance as derived from color excess leads to disagreement between measured and computed (for a B0.5 star) values of d logI /d(1/). The reddening may be explained by reemission in an envelope the radius of which is smaller than 5R_*. In conclusion, the narrowness of the spectral range under consideration does not permit to decide whether the observed reddening is due to recombination to the third level of the hydrogen atom or whether it is part a thermal reemission in a circumstellar cloud at lower temperature, as it has been observed around 10 by various authors.

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Les spectres utilisés dans ce travail ont été obtenus à l'aide des téléscopes de 193 cm et 120 cm de l'Observatoire de Haute-Provence (CNRS).     

Atmospheric properties of ENSO: models versus observations

Two important atmospheric features affecting El Niño-Southern Oscillation (ENSO) are atmospheric noise and a nonlinear atmospheric response to SST. In this article, we investigate the roles of these atmospheric features in ENSO in observations and coupled Global Climate Models (GCMs). We first quantify the most important linear couplings between the ocean and atmosphere. We then characterize atmospheric noise by its patterns of standard deviation and skewness and by spatial and temporal correlations. GCMs tend to simulate lower noise amplitudes than observations. Additionally, we investigate the strength of a nonlinear response of wind stress to SST. Some GCMs are able to simulate a nonlinear response of wind stress to SST, although weaker than in observations. These models simulate the most realistic SST skewness. The influence of the couplings and noise terms on ENSO are studied with an Intermediate Climate Model (ICM). With couplings and noise terms fitted to either observations or GCM output, the simulated climates of the ICM versions show differences in ENSO characteristics similar to differences in ENSO characteristics in the original data. In these model versions the skewness of noise is of minor influence on ENSO than the standard deviation of noise. Both the nonlinear response of wind stress to SST anomalies and the relation of noise to the background SST contribute to SST skewness. The ICM is not yet fully evolved, the results rather show that this is a promising route. Overall, atmospheric noise with realistic standard deviation pattern and spatial correlations seems to be important for simulating an irregular ENSO. Both a nonlinear atmospheric response to SST and the dependence of noise on the background SST influence the El Niño/La Niña asymmetry.     

Nova Delphini 1967. Observations du spectre nebulaire entre 5600 et 8800 Å en 1970

Five 230 Å/mm infrared spectra of Nova Delphini 1967 have been obtained from May to September 1970 on Kodak hypersensitized IN plates. Visual brightness has dropped by one magnitude between fall 1969 and fall 1970. The continuous spectrum remains strong and a mean value of 2.35 is found for the gradient in the region 6000–8000 Å, indicating a slight increase in temperature since 1969. Permitted lines ofHi,Oi, Hei, Feii are weakening, while intensities of forbidden transitions due [Nii], [Fevii], [Oi], [Oii], [Aiii], [Av], [Fevii], [Fex], [Fexi], [Fexi], [Nixv] are much more stable At the dispersion of our spectra, there is little evidence of activity in the nova shell during 1970. Temperature seems to be slightly increasing in the lower layers as well as in the external, low density regions.

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Les observations ont été effectuées à l'Observatoire de Haute-Provence (C.N.R.S.)     

The interpretation of inverse isochron diagrams in Ar/Ar geochronology

The concepts involved in the construction and interpretation of inverse isochron diagrams used in ⁴⁰Ar/³⁹Ar geochronology are reviewed. The diagrams can be useful as a means of recognising atmospheric argon and excess ⁴⁰Ar, incorporated in the mineral lattice, which cannot be recognised from ⁴⁰Ar/³⁹Ar spectra. The age established using an inverse isochron plot, unlike that yielded by a spectrum, is not affected by trapped argon ⁴⁰Ar/³⁶Ar ratios that are different from the atmospheric argon ratio (e.g. due to excess ⁴⁰Ar), and may contribute to a better age interpretation. However, a heterogeneous distribution of excess ⁴⁰Ar or heterogeneous argon loss can cause ‘false’ isochrons, with axial intercepts indicating an incorrect age and an incorrect trapped argon composition. Inconsistency between the ages from a spectrum and from the associated inverse isochron plot may indicate the degree of inaccuracy of isochrons. However, it is possible that both the spectrum and inverse isochron yield the same incorrect age. The importance of considering all possible interpretations before assigning an age to a specimen is stressed.     

Production of atmospheric condensation nuclei by solar radiation

Summary Air with a very low count of atmospheric condensation nuclei was irradiated by direct sunlight through an uviol glass window, or through ordinary glass or in a polyethylene balloon. The nucleus count rises immediately and reaches very high values.

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Zusammenfassung Luft mit sehr niedriger Zahl von atmosphärischen Kondensations-Kernen wurde mit direktem Sonnenlicht bestrahlt, entweder durch ein UV Glas oder durch gewöhnliches Glas oder durch einen Polyethylen-Ballon. Die Zahl der atmosphärischen Kondensations-Kerne steigt sogleich und erreicht sehr hohe Werte.

     

Spectres de quelques étoiles Be entre 7000 et 9600 Å

Kodak IM plates have been used in order to extend to 9600 Å the observed wavelength range for 23 O, B, Be Bp and A stars. The spectra are shown in the plate. Several atmospheric absorption bands perturb the continuum and line spectrum. Between 1.45 and 1.20 ^-1, we have measured the parameter d logI /d(1/). The results appear in the table and indicate that Be stars do not exhibit anomalous reddening in this spectral region. On the other hand the above parameter is much more sensitive to the reddening than to the star's effective temperature.

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Le matériel d'observation utilisé pour le présent travail a été obtenu à l'observatoire de Haute-Provence. (CNRS)     

Visible and/or near infrared spectral variations of v1016 Cygni,HM sagittae and MWC 349

The recent spectral evolution of the three peculiar emission-line objects with IR excess V1016 Cyg, HM Sge, and MWC 349 is described, on the basis of data obtained at the Asiago (blue and red spectral regions) and Haute Provence (near infrared) Observatories. In the near infrared spectral region, details are given concerning the data briefly described in IAU Circular No. 3498 (Andrillat and Swings, 1980).Based on observations performed at the Haute Provence (CNRS, France) and Asiago (Italy) Observatories.     

Raies nébulaires et coronales dans le spectre infrarouge de la Nova Delphini

Nova Delphini 1967 has been observed in the red and photographic infrared at the Haute-Provence Observatory from September 7 to November 12, 1968. Dispersions range from 230 Å/mm to 4 Å/mm. The slope of the continuous spectrum in the region 1.3–1.7 ^–1 leads to a gradient of 3.06, which did not appear to vary during the observing period. This gradient is, however, very different from the value 1.71 measured on plates secured in August 1968. Lines ofHi, Hei, Heii, Feii,Oi,Cii and forbidden transitions due toOi,Oii, Fevii, Fex, Fexi,Siii,Aiii,Av,Axi and Nixv have been identified. Their intensities at various dates are given in Table II. Line profiles could be measured for a few lines taken on a 39 Å/mm spectrogram on October 3. Hei 6678 and 7065 are displayed on Figures 2 and 3. Figure 4 gives the [Oii] doublet at 7319–7330, while the H profile, obtained on October 4 can be seen on Figure 5. The line extends over more than 45 Å and narrow absorptions are seen at 6551.05; 6555.75; 6563.15; 6571.49; 6574.45. Due to the absence of published data on radial velocities of absorption lines in the visible spectrum at that time, it is not possible to give a clear identification for these features. Some of them may belong to H, while others are probably due to metals.     

Structure of coronal holes from UV and radio observations

The coronal hole observed on May 31, 1973 is studied using extreme ultraviolet and radio observations. The EUV line is the Fe xv at = 284 Å and the radio frequencies are 169 and 408 MHz. An unsuccessful attempt to deduce an homogeneous model of the hole from these observations, shows that EUV and radio observations are inconsistent if interpreted in such a frame and if the EUV line intensity measurements in the hole are reliable.Inhomogeneities are therefore required to account for both observations. An inhomogeneous model consisting of hot (T2×10⁶K) elements covering 10% of the hole surface surrounded by regions of colder gas (T8×10⁵K) is able to explain both observations.