Des mesures spectrophotométriques effectuées aux Observatoires de Haute Provence et de Toulouse ont permis d'etablir une relation entre l'intensite des raies D du sodium et la température de vibration déduite des quatre séquences suivantes: séquences + 4 et + 5 pour CN (syst. rouge) et séquences — 1 et — 2 pour C2 (syst. de Swan). Ces deux quantites et la considération de l'intensité de la bande 6260 A. constituent trois critères de classification situés dans une zone spectrale relativement etroite (5400-6800 A.) et toujours observable, ces critères montrent que la classe des étoiles carbonnées se divise en trois sous-classes distinctes qui se raccordent aux environs de C 6.

The violet and ultra-violet regions of the spectra of the cool carbon stars are notoriously difficult to photograph. This is so particularly for the late N-type stars with which the present paper deals. The spectra of R-type and early N-type stars can be photographed down to ƛ3500 by exposures several times as long as for M-type stars of comparable class. However, the later N-type spectra fall so rapidly in intensity from ƛ4400 and so even more extremely from ƛ4100 to shorter wave-lengths that the spectra of the brightest stars have not been recorded below ƛ3900.

The spectrum of η Carinae as recorded by the two-prism Cassegrain spectrograph of the Radcliffe Observatory in the range 3677-8863 A. consists of over 300 rather sharp bright lines, of which the identified lines are distributed among the elements as follows:

Nos observations ont été faites à l'Observatoire de Haute-Provence, de 1946 à 1952.

Les spectres de Z Andromedae(1), AG Pegasi(z), T Coronae Borealis(3) montrent le même aspect général: la superposition d'un spectre de type M et. d'un spectre de raies brillantes de haute excitation, correspondant surtout à He II, N III et aux transitions interdites de N II, O III et Ne III. Les intensités de ces raies, et le maximum d'excitation qu'elles représentent, sont différents d'une étoile à l'autre.

1. This problem might be deprecated as requiring for its solution more evidence than now exists; but, even though it cannot yet be conclusively solved, it will introduce some consideration of possible interactions between binary components and between different atmospheric regions of a single star, which may help to explain other peculiar variable spectra.

WY Velorum(1) is a southern peculiar star discovered at Harvard(2) as being variable both in light and spectrum.

The available light observations start as far back as 1890. The first reference(2) to magnitude observations covers the years 1890-1922 and is based on 101 photographs which are distributed rather evenly throughout the interval, they show that from 1890 to 1901 there was a slow and apparently steady increase in light from magnitude 9·8 to 9·2; and since 1902 the light has slowly decreased.

T Coronae Borealis is a well-known recurrent nova which has undergone two outbursts: in 1886 and in 1946. In both cases the star declined very fast after maximum and reach in less than two months the premaximum magnitude, shortly afterwards, there a small increase to a secondary very flat maximum followed by a slower decrease.

The symbiotic spectrum observed at minimum is usually interpreted as due to a binary involved in a small nebula; the excitation of the nebular spectrum is provided by shot fainter star, which undergoes the nova outbursts, while the brighter star (a normal ant) is constant in brightness. Sanford(1) has found the radial velocity of the M star 2 variable with a period of 774 days and a semi-amplitude of 21 km./sec.

The abnormal weakness of the hydrogen lines in the spectra of the stars of the R CrB type has been long known. Berman's work on the spectrum of the prototype established the presence of strong high-level absorption lines of neutral carbon and of weak bands of C2, and his analysis of the spectrum, carried out by the method of curve of growth, led him to conclude that carbon is by far the most abundant element in the atmosphere of R CrB, and that hydrogen is greatly deficient. Recent work at the McDonald Observatory has shown that in addition to the high-level lines of neutral carbon, other lines arising from very high levels of neutral oxygen and neutral nitrogen are also present in unusual strength in the visual region of the spectrum of this star. The presence of these other high-excitation lines strongly suggests that reliable values of the relative abun¬dances of the elements C, N, and O in the R CrB stars must await detailed studies using the method of model stellar atmospheres.