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M2-9 is not a bona fide planetary, nor simply a star: it most probably is a planetary nebula in the formative stages. High densities, the presence of , Fell and [Fell] emission lines, and prominent infrared continua are characteristic of such objects. There is a striking progression of their spectra from B[e] stars such as HD45677 to M2-9 itself; Merrill's class of objects intermediate between Be stars and planetary nebulae is represented e.g. by MWC 645, HD 51585, V 1016 Cygni, HM Sagittae, and MIVC 349. Remarkable similarities exist between the spectra of the latter objects and that of M2-9, especially in the recently covered region between 8000 and 11000 Å which is rich in emission lines of the Paschen series, of Hel, 01, [SIII], Fell and [Fell] (Andrillat and Swings, 1977, in preparation).
New results are presented based on several statistical analyses of a 25 square degree field around NGC450. They include the detection of a clustering on a small scale (⋍ 10 arcminutes) and possible large scale inhomogeneities.
There has been a marked change in the past few years in the incidence of interest in stellar spectra. The great initial task of classification has attained its first objective—though the Henry Draper Extension, and other investigations are still progressing. Perhaps a million stars are still accessible to classification with existing instruments; but more and more time is being spent upon individual spectra, and upon theoretical investigations. In these fields progress has been very rapid, and only some of the more important results may be mentioned here.
This report deals mainly with the study of spectra secured with a 4° objective prism attached to the 24–36-inch Schmidt-type telescope of the Warner and Swasey Observatory of the Case Institute of Technology. The dispersion at Hγ is 283 A./mm. Spectra obtained with a 2° objective prism will be dealt with briefly. We will consider first spectra secured by means of long exposures intended to be used for statistical studies; second, spectra of relatively short exposures for detailed study of individual stars and, third, infra-red spectra for the classification of low-temperature stars.
1. Le rapport distribué aux personnes présentes commence par un court aperçu des principaux travaux faits dans le domaine des spectres stellaires depuis l’assemblée précédente. Le Président demande si l’une ou l’autre personne désire suggérer des modifications ou compléments à cet exposé. Aucune observation n’est présentée.
2. Le rapport du sous-comité chargé de l’examen des critères de classification des spectres stellaires est ensuite mis en discussion. Une lettre de Mme Payne-Gaposchkin a été reçue à ce sujet; Mme Payne-Gaposchkin signale que des détails manquent dans le rapport du sous-comité; elle demande aussi que soient définis clairement les types A7 et K7 actuellement utilisés fréquemment, ainsi que les symboles g et d distinguant les étoiles géantes et naines.
Two-thirds of the members of the Commission have replied to the request of the chairman for an expression of their opinion. Most of them are in general well satisfied with the existing system of classification and nomenclature. Lindblad reports on successful work upon the determination of absolute magnitudes of faint stars, in many ways. Adams writes: “I might suggest that attention be called in the report to the fact that the ultra-violet spectra, even of stars like β Orionis, show large numbers of lines. As you probably remember, the spectrum of Sirius resembles, at first sight, the solar spectrum. If all observatories had the facilities for getting spectra in the far ultra-violet, this region would probably furnish the best criteria for spectral type.” Merrill suggests: “The nomenclature which, upon the basis of atomic transition, assigns the adjective ‘nebular’ to lines which may not occur in nebulae, and ‘ auroral ‘ to lines which may not occur in the aurora, is surely not an ideal one.
U, B, V photometric observations performed in February 1977 at the European Southern Observatory (62 cm Bochum telescope) show that for the star B2IV[e] HD 45677 some of the magnitudes and related color indices may vary by as much as 0.03 mag. over one night, and about 0.1 mag. from night to night. The conclusion derived from our photometric run confirm those published by Feinstein et al (1976), namely that “A variation in V is almost systematically accompanied by a change in B-V but of opposite sign”. We further find that a variation in V is well correlated with a similar change of the U-B index: such a correlation existed in the data of Feinstein and coworkers, although it had not been reported.
Our spectroscopic material, that was obtained simultaneously with the photometry mentioned above, consists, of 38 spectra that cover the blue region at a dispersion of 20 A mm-1. Such an important sample of spectrograms has not yet been analysed in great detail for intensities, radial velocities, etc. . We will only report here on striking variations that were detected in the profiles of the following lines: Hγ, Hδ, Hε, Ca II(H) and Mg II λ 4481.
Ultraviolet low resolution spectra of most of the B stars observed with the S2/68 experiment onboard the TD1 satellite in the spectral range 1350 A - 2500 A are computer-investigated in order to define a grid of standard behaviors (J.M. Vreux and J.P. Swings, 1976 Astron. Astrophys., in press). The behavior of the relative intensities of the Balmer and Paschen continua is studied as a function of the spectral type and the visible photometric index Q: both relations are shown to be luminosity dependent. A comparison to theoretical predictions and to previous studies is also presented. A measure of the slope of the pseudo-continuum drawn between ~ λ 1660 A and ~ λ 2550 A is studied in the same way: the effect of luminosity is discussed in connection with recently proposed temperature scales for super-giants. The behavior of the depths of the absorption features at λλ 1550 A, 1940 A, 2000 A, 2055 A, 2105 A, 2340 A and 2395 A with respect to the spectral type, the Q index and the luminosity class is also briefly presented. Special emphasis is given to the absorption features at λ 1550 A in connection to the discussion of the Felll lines in the ultraviolet spectra of early B stars by J.P. Swings, M. Klutz, J.M. Vreux and E. Peytremann (1976, Astron. Astrophys. Suppl. 25, 193). Preliminary results of a study of high resolution Copernicus spectra in the A 1550 A region are also presented: it is shown that the role of Felll remains predominant for stars of spectral type as early as about BIII - BIIII (J.P. Swings and J.M. Vreux, to be published).