The detailed analysis of high resolution, high signal-to-noise spectra of four G and K dwarfs lying within 10 pc of the Sun is presented. This analysis is part of a project aiming at building up a homogeneous set of reliable atmospheric parameters for all F, G and K stars nearer than 10 pc according to the Gliese catalogue.

The solar flux atlas is presented and some basic information on the observations is given.

A fine analysis of Alpha Cen A relative to the Sun has been carried out. Over 500 absorption lines have been used in deriving a consistent solution involving abundances, Teff, log, g, microturbulence and blanketing. Light elements, up to zinc, are overabundant by around 0.15 dex, while heavy elements have solar abundances.

In collaboration with D. Lambert and J. Tomkin high resolution, high S/N spectra have been obtained for about 250 disk population F0-G2 dwarfs. The aim of this large programme is to study various abundance ratios as a function of [Fe/H] and stellar age. A detailed description of the project and some preliminary results were given by Nissen et al. (1985).

We present a spectroscopic analysis for the gravity determination of τ Ceti on the basis of a new and high quality set of data. The iron lines are studied by using the Oxford oscillator strengths. The results are compared with those obtained with “solar” oscillator strengths. Non-LTE effects seem to be important in this star. The Fel at λ 526.955 nm line is used to apply the Blackwell and Willis (1977) method to determine the surface gravity. The derived log g is 4.70±0.1.

Iron abundances, [Fe/H] have been studied in G and K dwarfs of the four nearest clusters. With the exception of the Pleiades stars which are all fainter than the 10th magnitude, the observational material consists of high resolution, high S/N spectra taken at the coudé Reticon spectrograph of the Canada, France Hawaii Telescope. The Hyades is the only cluster with a significative overmetallicity with respect to the Sun.

Differential detailed analyses with respect to ε Vir of the four Hyades giants have been carried out on high resolution high S/N CFHT Reticon spectra. The preliminary results are given below.

Technetium abundances in the atmospheres of S- and C-stars are estimated by comparing the synthetic spectra and high dispersion observed spectra for the TcI λ 5924.47 region. It was found that reliable estimates are possible only for the pure S-stars and SC-stars. For the late carbon stars only the upper limit of the Tc abundance can be found. For TX Psc (C6.5) it was found to be lgεTc = 0.5.

The “lithium gap” observed in the Hyades and other galactic clusters by Ann Boesgaard and her collaborators (Boesgaard and Tripicco 1986, Boesgaard 1987, Boesgaard, Budge and Burck 1987) gives a challenge to theoreticians. Indeed a good fit between the theoretical results and the observations will give a clue for our understanding of the stellar internal structure and evolution.

Selecting stars with previously measured or estimated rotational periods we measured Li equivalent widths in 8 stars of the Hyades late main sequence. Combining our data with literature values, we derive a homogeneous set of Li abundances. Plotting log N(Li) against Rossby number we can separate the effects of temperature and rotation. We find for stars later than F8 increased depletion with longer period, at constant surface temperature. Discounting, as improbable, spurious abundances due to surface activity effects, we give a tentative view of the implications of these results for stellar modelling.

Spectra of resolution λ/Δλ∼2 ×104 and good S:N ratio are presented in the range containing the 7Li doublet at 6707 Å for 9 main sequence or slightly evolved stars in NGC 752 (age ∼2 ×109 years). We investigate the suggested main sequence bimodality using spectroscopic indications of binarity and high rotational velocity, as well as the Li abundance to supplement previous photometry.

The abundance patterns in Population II red giants provide information about galactic chemical evolution and nucleosynthesis sites for various chemical elements. These patterns were first revealed by moderate-S/N photographic spectra and are now being refined and extended to additional chemical elements and fainter stars with high-S/N data. The well-established features include overabundances of O and Ca, underabundances of s-process elements, and solar ratios of heavy r-process elements. An excess of nickel found by us on moderate-S/N spectra is less certain, and should be checked with high-S/N data. New information on oxygen abundances in Population II red giants is becoming available from high-S/N observations of weak [O I] lines, and consistently indicates an oxygen overabundance due to the preferential sampling in Population II stars of ejecta from massive stars of previous generations. Recent studies of highly evolved, post-AGB Population II stars are revealing remarkable overabundances of light elements (C, N, O, and S) and deficiencies of the heaviest elements; these are probably signatures of internal nucleosynthesis followed by mixing up to, or exposure by mass loss at, the stellar surface.

The possible existence of departures from LTE affecting the abundance analyses of halo dwarfs and subgiants is analysed from the observational point of view, and illustrated by the case of the intermediate halo subgiant HD 76932. High resolution and high S/N Reticon and CCD spectra have been obtained with the ESO Coude Echelle Spectrometer. A detailed model atmosphere analysis has been carried out, which reveals a number of inconsistencies. In particular, the iron abundance derived from the neutral lines shows a very clear excitation potential dependence. Similar effects appear for oxygen and calcium and, possibly, for magnesium, chromium and ionized iron. Some overionization also seems to be present in a number of elements. The impact of these effects on the derived abundances may be rather large (some 0.2 to 0.6 dex). In particular, doubts might be raised about the reality of the oxygen overabundance and the odd-even effect in Na, Mg and Al.

This paper reports an abundance analysis of spectra of 10 extremely metal-poor giants, including two in the globular cluster M92, in collaboration with Robert Kurucz and Eugene Avrett of the Center for Astrophysics and Bruce Carney of the University of North Carolina. An intercomparison of equivalent widths indicates that Luck and Bond have seriously overestimated the strengths of very weak lines and so deduced a spuriously high nickel abundance in the most metal-poor stars. A review of line-formation effects in the Sun strongly suggests that the rather high metallicities found for some extremely metal-poor stars by Pilachowski and coworkers is due to errors in their solar gf values, which unfortunately are unpublished. In our own analyses, stars with asymmetric H-alpha line profiles tend to have an excitation temperature at odds with the effective temperature found from infrared photometry. The discrepancy is removed by lowering the surface temperature by 100 K or by increasing the microturbulent velocity, either by a constant 0.5 km/s or by an amount which increases toward the surface. These changes have the most impact on those abundances deduced from strong lines or low-excitation lines of the neutral species; this includes sodium and barium as well as all the Fe I lines with very accurate gf values. Despite these difficulties, our findings reveal a low abundance for M92, and intrinsic scatter in the relationship between the relative abundances of sodium and oxygen and the overall iron abundance. In one field star, oxygen is apparently overabundant by an order of magnitude or more, while in the two M92 giants, the sodium abundance appears to differ by nearly this much.

High-resolution, high S/N spectra have been obtained for 22 giant stars in the globular cluster ω Cen. These stars span a wide range of temperature and position on the giant branch and include some of the S-type and Barium star members. Spectra were obtained on the CTIO 4m telescope with the echelle spectrograph and CCD detector. Initial abundance results for Iron, Calcium, and Oxygen are presented for three stars: one of the most luminous cluster red-giants, a giant on the blue edge of the ω Cen giant branch, and an extreme Barium star member.

This paper provides the first reliable determination of the iron abundance of the Magellanic Clouds. There is clear evidence for carbon and nitrogen depletion, with respect to iron, in the Clouds which can be explained by the relative youth of the Clouds compared to our own Galaxy. Oxygen depletion relative to iron is also in evidence and it is suggested here that this is due to preferential loss of ejecta from high mass stars. Finally, our discovery of an extremely low abundance star in the SMC, coupled with the identification of a similar star by Spite et al. (1987), calls in to question whether or not the SMC is indeed a well mixed system as previously assumed.

A few high S/N spectra of F-G supergiants in the field of the Magellanic Clouds, and a spectrum of a star in the in the young SMC cluster NGC330 have been obtained at the échelle spectrograph of the 3.6m telescope of ESO (CASPEC). Preliminary results of the analysis of these stars and their consequences in the evolution of the clouds are presented here.

The Ofpe/WN9 stars R84 and S61 of the LMC have been studied with high-dispersion spectroscopy in the optical and satellite-UV range. The high resolution and high S/N spectra in the optical range are particularly distinguished by strong emission lines of H, HeI and [NII]. The comparison of R84 with S61 shows that the peculiar emission line spectrum is not caused by the previously found late type companion of R84. We find that the UV spectra of both stars closely resemble those of late O-supergiants but all absorption lines are violet-shifted by about 250 km s−1 (R84) and about 200 km s−1 (S61). The absorption lines are stronger than in normal O-type stars. The UV-resonance lines indicate low terminal wind velocities of ≈ 900 km s−1 only. Unlike to normal O-type stars the AlIII-resonance lines also show pronounced P Cygni profiles with an even lower edge velocity (vedge ≈ 400 km s−1). Tne mass loss rates (>6.10−6 Mo yr−1) are comparable to rates found in normal luminous hot stars. However, the wind appears to be much more gradually accelerated similar to the wind of the galactic supergiant P Cygni. It is suggested that the Ofpe/WN9 transition type stars are the hotter counterparts of the early B-type P Cygni stars.

The LMC star R127 was classified as O Iafpe extr. by Walborn (1977). Later, Walborn (1982) noted the spectral similarity to late WN stars and classified R127 as Ofpe/WN9 star. Stahl et al. (1983) discovered an S Dor outburst of R127. It has now been monitored photometrically almost continuously for more than four years. In addition, several high-dispersion and high signal-to-noise spectra were taken with the ESO CASPEC and CES spectrographs. In 1986 R127 became the visually brightest star of the LMC until it was surpassed by SN1987A in Feb. 1987.

Digital spectra of 7 B-type supergiants in the Milky Way and 15 B-type supergiants in the Large Magellanic Cloud (LMC) were obtained in December 1986 using the “2-D Frutti” detector (2-DF) and the Carnegie Image Tube Spectrograph on the 1-m telescope at the Cerro Tololo Inter-American Observatory. The 2-DF is a photon counting, 2-dimensional Shechtman-type detector, now available on both the 1-m and 4-m telescopes at CTIO. The detector/spectrograph configuration used for the December observing run yielded spectra covering the classical blue region, 3800-5000 Å, with a resolution of approximately 3 Å. The typical observing procedure was to obtain spectra for each star at several locations along the slit. The individual spectra were then averaged (to reduce the detector fixed pattern noise) resulting in S/N ratios of 50-60 in the 4300 Å region.