A Michelson interferometer was put into operation during the year 1972 at the Coudé focus of the Haute-Provence Observatory’s 76-in. telescope. We built this instrument at Aimé Cotton Laboratory (Orsay-France) where the method of Fourier Transform Spectroscopy has been largely developed in the direction of very high resolution work. A complete description of this device has been given elsewhere (Guelachvili and Maillard, 1970) and further details on the present study are reported by Maillard (1973).

A summary is given of the molecular bands occurring in the near-infrared spectra of cool stars, especially those having sufficient strength and freedom from contamination to be measurable by narrow-band photometry. In some cases useful indices of both temperature and luminosity can be obtained from such measurements. Several bands remain unidentified, including the 9910 Å band in late M dwarfs and at least nine bands in cool S stars.

Three topics of a spectroscopic nature are discussed. (1) In Mira variables, grossly different spectral types are sometimes obtained from zero-volt and excited TiO bands of the same band system. (2) A few M stars have been found to show bands of’ both VO and CN at the same time. They may be the coolest known supergiants, although there remains some doubt as to their luminosities. (3) The first results are given from a program of measuring crude C12/C13 ratios from narrow-band photometry of sensitive points on the profile of the ∆υ = + 2 band sequence of CN. The observations require only a few minutes per star, and the method can be applied to G and K giants and supergiants as well as to carbon stars.

The role of medium resolution spectroscopy in the two micron region is discussed. Examples of the spectral features amenable to observation are shown. These include the vibration rotation bands of the important molecules 12C16O, 13C16O, H2O and CN, as well as the By line of hydrogen. Band strength-colour and -luminosity relations for the CO and H2O bands have been derived from observations of approximately 100 stars of spectral types later than G5. The interpretation of these and the outstanding problems (such as the colour dependence of the CO band strengths in carbon stars) are discussed.

Examples of the use of two-micron spectroscopy in the spectral classification of infrared sources, and the infrared components of symbiotic stars, etc., are shown. The extension of this kind of observation to the nuclei of galaxies is briefly discussed in relation to stellar population studies.

A Fourier Transform Spectrometer has been employed to obtain low and medium resolution spectrophotometry in the range 700 to 10000 cm-1. The method is described briefly and typical data are shown. The technique is applied to a study of 15 K giants, and spectra of 4 and 16 cm-1resolution in the range 4000 to 6500 cm-1 are discussed briefly. CN strong stars are found to be CO strong as well. Five K giants are found to have a relative 13C enhancement over probable primordial abundances.

The first part of this paper presents a grid of model atmospheres for carbon stars in which the most striking feature is the inclusion of the molecular line blanketing effect of CO, CN and C2 through opacity probability distribution functions. The techniques and the main results have been fully discussed in previous papers (Querci, 1972; Querci et al., 1972 and 1973), and consequently we will give just a rapid description asking the reader to refer to these papers for details. However, the grid has been extended here to lower temperatures.

The second part presents original results from the M. Querci’s ‘Thèse d’Etat’ (1974), and concerns the computation of synthetic spectra. A kind of grid of synthetic spectra has been computed from each model atmosphere, that is to say for each particular effective temperature and gravity, over a selected spectral range. The influence of the gravity and of the effective temperature on the computed spectra and the problem of the line cutting procedure are considered. Finally, comparisons with a high resolution infrared spectrum of a carbon star are made.

The conclusion summarizes the experimental progress that must be made in order to be able to make meaningful comparisons between predictions and observations.

This is a progress report on the program of stellar spectroscopy at 1.1 μ reported on by Vaughan and Zirin (1968) and by Zirin (1971). About 450 plates of about 200 stars have been obtained, using a magnetically focused RCA image converter with the 144” and 72” Palomar coudé cameras, giving dispersion of 8 and 17 Å mm-1 respectively. Most of the plates were taken at the latter dispersion and cover about 300 Å. In good seeing a star with J = 3 is obtained in about 90 min. A tube with a fibre optic backplate is now in use. Cooling such a tube is difficult because the cathode is held at high voltage. By completely insulating the cold box, we may use dry ice cooling, and 2 h exposures, reaching J = 5, may be made with this ITT tube.

Our principal interest in this region of the spectrum is the He I 10830 line, but there are other features of interest such as Paschen y and a series of CN bands, λ 10830 is of particular interest because it is produced at relatively high temperatures and thus its presence in stars later than B5 can only be explained by the existence of a high temperature corona or chromosphere or of a strong ultraviolet source, which amounts to the same thing. Vaughan and Zirin found the presence of such chromospheres in a number of stars, and I have pursued the matter since then to determine the existence of chromospheric variability. The 10830 absorption in the Sun is very small from the normal chromosphere and is principally due to the presence of active regions. Emission is only found in large flares. Thus cyclic variations in Sun-like stars could be attributed to sunspot cycles. Unfortunately, main sequence stars are near the limit of our observations. Although definite 10830 absorption has been found in such main sequence stars as 61 Cyg A and B, 70 Oph br, K Cet and ε Eri, the absorption is just barely detectable and variation from plate to plate could be explained by variable quality.

This introductory paper is divided into two sections.

In the first section a short summary is given of the IAU Colloquium No. 17 on Stellar Ages held in Paris-Meudon Observatory in September 1972. The summary will concern particularly those subjects relevant to this Joint Discussion.

In the second part the ages of nearby stars located in the subgiant region of the (log Teff, Mbol) diagram are discussed.

The zone of bright stars inclined 20° to the galactic plane, pointed out by John Herschel (1847) and by Gould (1874,1879), is generally referred to as Gould’s Belt. This General Assembly is well timed. With the splendour of the centre of the Milky Way in the zenith in the early hours of the night anyone who comes out of the city-lights of Sydney can try to convince himself of the reality of this phenomenon.

Shapley and Cannon (1922, 1924) showed that the concentration towards Gould’s Belt is very pronounced for the brighter B. stars, while the fainter ones are highly concentrated towards the galactic plane. Their results indicated the radius of this local system to be of the order of 500 pc. The motions of the B. stars brighter than a magnitude of about 5m.5 are characterized by the K-effect, which thus seems to be a property of this local Gould Belt system.

This contribution gives some results on the kinematics and ages of stars near the Sun. These results are mainly based on the catalogue of nearby stars compiled by Gliese (1957, 1969 and minor recent modifications). Table I shows the number of objects under consideration. While the old catalogue (1957) contained only stars with distances r up to 20 pc, the new edition (1969) includes many stars with slightly larger distances. In Table I, a ‘system’ is either a single star or a binary or a multiple system. The number of systems with known space velocities nearer than 20 pc has increased by about 30% from 1957 to 1969. The first edition of Gliese’s catalogue (1957) has been analyzed in detail by Gliese (1956) and von Hoerner (1960).

The velocity moments through the fourth order were calculated for a subset of 870 astrophysically selected stars from Gliese’s catalog. An essential part of this program was the determination of the covariances of estimates of the moments; both sampling and observational error contributions were taken into account in evaluating the total covariance matrix. In applications to the study of galactic structure, the Gliese stars are regarded as tracers of the galactic potential. The moments found are consistent with conventional assumptions about symmetries of the galaxy. Certain galactic parameters, such as the curvature in the law of rotation and the asymmetric drift, were studied with the help of the values obtained for the moments.

Donna Weistrop, a student of Maarten Schmidt’s, has found evidence for an unexpectedly high space density of very faint M-dwarfs. This was confirmed by Murray and Sanduleak. The space density inferred from these investigations is comparable to, or possibly higher than, the local gas density. Because there is evidence that the stars concerned are young this appears to present a problem.

As the investigation by Murray and Sanduleak is the simpler and more direct of the two I confine my discussion to this. The authors determined proper motions for 21 M dwarfs down to 17m found in an objective-prism survey at the Warner and Swasey Observatory in regions close to the North Galactic Pole. The distance of the stars can be inferred from the reflection of the solar motion. Assuming the ‘basic’ solar motion they found and a space density of 0.23 pc-3 for these stars, corresponding with a mass density of about 0.04 M⊚ pc-3. This is exceedingly high, in view of the fact that the average gas density near z = 0 is only 0.03 M⊚ pc-3. The problem is aggravated by the fact that the stars have low velocities, the dispersion in velocity in one coordinate coming out ± 10kms-1. This is considerably lower than the velocity dispersion of A-type stars, and shows that the stars are young, perhaps about 108 yr. How is it then that the gas has not been completely used up long ago?

The spatial and kinematical properties of galactic populations are very conservative for time changes. Therefore the study of these properties gives us certain information on the past dynamical evolution of the Galaxy, in particular on the evolution of star generating medium (interstellar gas, as generally accepted). The detailed study of spatial structure of stellar populations in our Galaxy is possible in exceptional cases only. But the study of kinematical properties is possible practically for all populations, which makes these studies very useful for cosmogonic purpose.

In order to obtain adequate quantitative information for the study of dynamical history of the Galaxy the statistical data on stellar velocities are to satisfy the following requirements: populations under study must be physically homogeneous; statistical samples of stars must be free from selection effects, especially from velocity selection; information on r.m.s. errors of observed quantities must be known in order to correct the results for accidental observational errors; the data for the determination of the age of the sample must be available.

In a Joint Discussion devoted to the ages and kinematics of the local stars, inclusion of a paper on the local gas may seem anomalous. There is, however, strong justification for considering such a topic. Newly formed stars retain many properties of the gas from which they originated. To understand the spatial and kinematic properties of local young stars, we must understand the spatial distribution and the kinematics of the local gas from which they were formed.

A cloud within the interstellar gas can collapse gravitationally if its mass, density, and temperature satisfy the Jeans Criterion. Collapse is favored by low temperature and high density.

Various investigators have pointed out that in the Lin Spiral Density Wave Theory a shock must occur on the inner edge of a spiral arm. Such a shock compresses the gas and hence promotes cloud formation with subsequent gravitational collapse to form stars. Shu and several collaborators have shown that such a shock is very effective in triggering cloud formation in a two-phase interstellar medium of the type discussed by Field et al. (1969), and it is widely believed that this is the principal step in the process of forming stars.

To investigate the nature and the extent of the influence of a spiral gravitational field on the observational determination of galactic structure, we examine several models of the solar vicinity, including a spiral gravitational field and the accompanying shocks. (These models are described in the Appendix.) We calculate the radial motions and the proper motions that would be observed from the solar vicinity. We then treat these theoretically calculated data by the conventional methods used for analyzing observational data. In this way, we hope to recover the galactic parameters originally adopted in our models. The accuracy of this process is then a measure of the uncertainty in the existing determinations of galactic constants, because of the influence of the spiral gravitational field.

The notion of the local Macroscopic Volume Element (MVE) is introduced in order to facilitate the application of hydro-dynamical methods of treating internal motions in stellar systems and in particular in our Galaxy. The MVE must characterize the properties of the stellar system in a given point within the system. Hence the diameter of the MVE must be taken as small as possible; it must, however, contain a sufficiently large number of stars in order that the laws of statistics might be applied. The greater is the local star density the smaller can be made the size of the MVE.

Modern catalogues of nearby stars by Gliese (1969) and Woolley et al. (1970) afford a good collection of data for a determination of local characteristics of the Galaxy in the immediate neighbourhood of the Sun. In the first section we discuss such characteristics as the local stellar density, the local luminosity function and the influence of observational selection upon them. In the second section we consider the local solar motion and the effect of the asymmetry of stellar motions. The responsibility for the content of paragraph 1 lies primarily upon T. A. Agekjan while that for paragraph 2 upon K. F. Ogorodnikov. We both are indebted to G. V. Ishkhanov and to L. V. Chuvicova for substantial help in numerical computations.