The influence of metal abundance and gravity on the relation between spectral type and effective temperatures of late G and K type stars is investigated and calibrated using metal abundances from narrow-band photometry, near infrared photometry and independent luminosity estimates.

Colour variations for Mira stars of spectrum Me and Se are deduced from the two micron survey of Neugebauer and Leighton and concurrent visual observations of the same stars.

The colours change cyclically during the periodic change of brightness. Colour is a function of maximal spectrum and also of period. Mira stars of class Se are bluer than those of Me of similar period.

Following a discussion of two recent papers by Schmidt (1973, 1975), we conclude that for the large amplitude, longer period Cepheids (log P greater than about 1.1), the small colour excesses derived from the six-colour photometry (traditional method or Parsons method) are to be preferred to the large colour excesses derived from the γ-index photometry (Kraft's scale).

Stellar evolution near the main-sequence is still subject to many discussions. In addition to the case of the cluster M 67 (Racine, 1971), quite systematic differences have been encountered during the comparison of theoretical isochrones and observed sequences in the colour-magnitude diagram of the old open star clusters (Maeder, 1974). In the case of M 67 and NGC 188, many attempts to discuss the characteristics of their sequences (such as the gap corresponding to the hydrogen-exhaustion phase) in terms of chemical composition have been made (e.g. Aizenman et al., 1969; Demarque and Schlesinger, 1969; Demarque and Heasley, 1971; Torres-Peimbert, 1971; Hejlesen et al., 1972; Caloi et al., 1974); some of these works have suggested to explain the gap parameters by a high metal content. Attemps to explain the differences between models and observations by means of simplified models with overshooting from convective cores have also been made (Maeder, 1973; Prather and Demarque, 1974). Let us also note that it has been shown that it is unlikely that the anomalies found are due to systematic effects, like the interstellar reddening, binarity, rotation or effects in calibrations or composition of the initial homogeneous models.

A method is described by means of which the chemical composition parameters (X, Y, Z) may be derived for galactic clusters that contain evolved red giant members and for which the cluster reddening and distance moduli are known. The method is based on observations of the evolved stars utilizing the DDO intermediate-band system. First, the DDO photometry by itself allows one to separate with a high degree of certainty the physical members of the clusters from the field stars. In cases where membership in the cluster can be confirmed, the unreddened DDO colours can be used to obtain the effective temperatures, surface gravities and metal abundances (Z) of the stars. These data combined with the absolute magnitudes available from the distance modulus permit the masses to be calculated. Finally, if some of the observed red giants form part of a clump on the giant brach in the HR diagram, the helium abundance (Y) of the clusters can be estimated by comparing the derived physical parameters of these stars with theoretical models. An example of the application of the method to the galactic cluster NGC 2420 is given.

The paper attempts to put together the spectroscopic definitions used in the literature for different groups of peculiar objects linked with abundance anomalies.

The groups discussed are:

• O-type subdwarfs

• CNO stars

• He-strong stars

• He-weak stars

• B-type subdwarfs

• Ap stars

• Am stars

• λ Boo stars

• δ Del stars

• Fm stars

• A-F-G stars with weak metal lines

• Stars with CN anomalies

• Stars with CH anomalies

• Ba stars

In each case the useful range in dispersion is quoted and bibliographic references are provided.

The HD stars between δ = −90° and −53° have been classified on the MK system, using Michigan 4° +6° objective-prism Schmidt plates (108 Å mm−1) taken at Cerro Tololo, Chile, and the results are published in Vol. 1 of the University of Michigan Catalogue, Catalogue of Two-Dimensional Types for the HD Stars. First, various statistics on the 32 500 normal stars and 2500 peculiar stars found are presented. Peculiar/normal ratios for various types of stars are given, along with discussion of the assumptions made. About 40% of the peculiar stars are of the Am or Ap types, and these will be covered in detail. Secondly, what notation to use for spectral types of stars with peculiar abundances is discussed and an explanation given of the notation used in Vol. 1 of the Michigan Catalogue for Am, Ap, strong and weak CN, weak metal, and other categories of peculiar stars.

Work on the third part of the Bonner Spectral Atlas: Peculiar Stars has well progressed during the past year. Observations of the more than 200 stars – photographed with a dispersion of 240 Å mm−1 at Hγ on I-N plates – is nearing completion.

The arrangement of the spectra will be as follows:

1. 1. WR-stars

2. 2. O-stars Of sequence

3. 3. Peculiar B-type stars emission-line objects

4. 4. Ap-stars with various sequences: Cr-Mn-Hg-rare earths

5. 5. Asi-stars

6. 6. Am-stars

7. 7. Late-type peculiar stars Ba II, CH

8. 8. C-stars

9. 9. Late M-type stars

10. 10. S-stars

11. 11. Composite spectra

12. 12. Spectra with large rotational broadening

The 12 groups are displayed on 40 plates, each with 6–8 objects. Stars of groups 8 to 10 will be presented with different exposures in order to facilitate the discovery of faint objects.

Sample plates will be shown and discussed.

The eighth magnitude star HD 101065 has an extremely peculiar spectrum dominated by numerous lines of the rare earths and lacking the lines of ‘normal’ elements, such as iron peak elements and lighter elements. For this reason it cannot be fitted into the adopted framework of spectral classification. The spectral type of this star can be defined only by fixing its effective temperature, which is 6040 ± 100 K. However, because of the extremely high blanketing the temperature of the continuum is about 450 K higher. This means that HD 101065 is a late F type star.

The possibility of obtaining a segregation between stars of different chemical constitution using the BCD classification is reviewed.

Five stars, including ζ Cyg, which had been classified as G6 II to G8 II bright giants, were found by O. C. Wilson to have K-line luminosities close to those of class III giants. These stars show enhancement of the lines of Ba II and other heavy-metal ions also. To eliminate the serious effect of this abundance anomaly on the spectroscopic luminosities new luminosity criteria involving only intercomparisons of lines of elements of the fourth period (Ti, Fe, etc.) were applied on 9 Å mm−1 Coudé spectrograms taken by O. C. Wilson. This Coudé classification gave luminosity classes near IIIa for these stars, implying absolute magnitudes considerably below those of bright giants but somewhat above Wilson's MK values.

Another advantage of Coudé classification is the possibility of estimating luminosities for individual barium stars. From Wilson's plate of HD 205011 a luminosity class of III-IIIa is derived. This is consistent with the mean value of Mv = −0.4 derived from statistical parallaxes by MacConnell, Frye and Upgren (Astron. J. 77, (1972), 384) for the barium stars.

The detailed account of this investigation will be published elsewhere.

This paper presents results obtained in classifying 26 supergiants of the Small Magellanic Cloud. The main results are:

1. – The hydrogen lines are not as sharp as expected for such luminous stars.

2. – Generally, for the A-type stars, the calcium K-line is too strong compared to the other metallic lines.

3. – There are differences in the behaviour of the different metals.

4. – Often, the stars present variations in their spectra.

5. – 50% of the stars brighter than mv = 11.3 have an enhancement of the H8 Balmer line, which is one of the characteristics of a shell star.

6. – The comparison with the Radcliffe classification and Dachs classification is, except in very few cases, in good agreement.

The following new OBN and OBC stars have been found: HD 75860, BC 2 Iab; HD 104565, OC 9.7 Ia; HD 123008, ON 9.7 Iab; and HD 150574, ON 9 III(n). Examples of morphologically more moderate CNO anomalies in OB spectra are also discussed; it is concluded that the O9-B0 7 supergiants of the Orion Belt and NGC 6231 (the nuclear cluster of Scorpius OB1) are systematically nitrogen-deficient. One possible explanation of these nitrogen-deficient supergiants in sub-associations is that they may have formed from nitrogen-deficient clouds; another could be that the more numerous morphologically normal supergiants show the effects of mixing in their spectra, while the nitrogen-deficient ones are relatively younger or have not yet been red supergiants. No red supergiants are found in Sco OB1, whereas NGC 3293 contains two B0 supergiants with normal CNO spectra together with a red supergiant. The paper will appear in the Astrophysical Journal, April 15, 1976.

An image-tube Cassegrain spectrograph, equipped with an S-1 photocathode enabled us to obtain infrared spectra of peculiar emission-line objects, as V 1016 Cyg, HBV 475, HD 51585, HD 45677, XX Oph and CI Cyg. Many of these objects display emission lines of H I, He I, He II, O I, N I, Ca II [S II] [S III], [Fe II]. The line intensities can be used together with data from other parts of the spectrum to determine relative abundances of these ions in the shells of these objects, which may be at a critical phase of their evolution.

Our programme involves the study of Am stars of differing temperatures and luminosities as well as of the Am stars deviating from the positions of the classical ones in the photometric diagrams. We have found for certain stars a significant disagreement between the so-called ‘abundance indices’ and the abundances determined at high dispersion. Often giants or spectroscopic binaries, or stars with a detectable rotation, are involved. However, there are no consistant relationships between these different peculiarities and the observed disagreements. We shall give some examples of stars studied by us. Are these ‘abundance indices’ really what they are supposed to be in all cases? In which cases are they not and why?

The ultraviolet spectra of B stars obtained with the sky scan telescope in the TD1 satellite have been used to obtain narrow-band magnitudes at several wavelengths. These photometric bands have an effective half-width of 100 Å. We have proposed a two-dimensional classification scheme based on ultraviolet colours, and some preliminary results are presented.

Detailed analyses giving the chemical composition have been carried out for twelve K dwarfs. Iron over hydrogen values have been found. Estimates of the masses of these stars are given.

We describe the results of analysis of the giant star HD 6497, which belongs to the Arcturus group.

The S2/S68 experiment on the satellite TD1A has supplied, in the wavelength region of 1350 Å to 2550 Å, a very large number of spectra of early stars.

A statistical study, as well as a general analysis of these spectra, has been carried out in order to establish criteria relative to the spectral region envisaged and independent of any previous study in the visible. On the basis of these criteria a system of classification has been outlined.

In a first stage, the spectra of stars visually classed from B0 to A5 have been considered. From four sets of spectrophotometric criteria a two-dimensional ultraviolet classification has been derived.

Stellar abundances are reviewed with emphasis on large-scale effects which may yield clues to galactic structure and evolution. Spectroscopic and indirect photoelectric abundance criteria are discussed, and utilized.

The abundance statistics of nearby galactic disk stars, dominated by M dwarfs, but observed at spectral types F and GV and K III, suggest a weak age-abundance relationship with a substantial dispersion at any time. Very metal-poor stars are extremely rare. Spatial abundance gradients, with higher metal abundances occurring nearer the galactic centre, are indicated. Disk abundance gradients are prevalent for light elements in other Sb and Sc galaxies.

The confusing status of supermetallicity is again reviewed. The super-metal-rich (SMR) giants (like μ Leo) are either over-abundant because of self-N-enrichment (from C–N–O processing?)and boundary-temperature cooling, or are really SMR. Each case may be reasonably argued. The old galactic clusters M67 and NGC 183 seem, by recent indirect acclaim, to be only slightly more metal-rich than the Sun. The Spinrad-Taylor data on the M67 giants would still seem to superficially suggest overabundances in Na and Mg, but other interpretations are possible.

SMR dwarfs, like HR 72, and subgiants, like 31 Aql are surely very old, and have metal abundances larger than the Hyades. However, they are, by number, only ≈ 5% of the local main sequence.

The galactic halo star tracers – red giants and RR Lyrae stars, have been observed extensively, lately. There is some indication of an abundance gradient from 5 or 10 kpc galactocentric radius out to r ~ 100 kpc. The most metal-poor stars observed in the Draco system are about 1000 times less abundant in heavy elements than is the Sun, and much of the galactic disk.

Abundances in other galaxies, as a function of their total mass, and stellar/gaseous composition are also reviewed. There is a clear dependence of abundance on galaxian total mass.