I describe here a new technique for precision radial velocity measurements, using an iodine absorption cell in front of the slit of a high resolution spectrograph. A CCD in a continuous readout mode records a timeseries of stellar spectra with a duty cycle of unity. In January 1987, observations were obtained on two clear nights with bad seeing. No oscillations were detected in the data, but the technique shows promise for significantly better results under better conditions.

The spectra of PMS stars usually are superpositions of contributions from a relatively normal photosphere, an often strongly enhanced chromosphere, and of circumstellar matter related to stellar winds, accreation flows, jets, and cool circumstellar disks. Only high S/N data allows a reliable separation of these different contributions. Because of the high optical depths of PMS chromospheres, the PMS photospheres often can be observed in the very weak spectral lines only, which are undectable on low S/N spectrograms. Finally, magnetic fields are assumed to play a particularly important role for the appearance and evolution of PMS objects. Their spectroscopic measurement requires very high S/N data.

Until 1980, only a handful of low-mass, active pre-main sequence (pms) stars had known rotation velocities (vsini) /1/. Since then, increasingly sensitive detectors coupled to large telescopes led to high–resolution (a few 104) spectroscopic studies of these faint stars (mv = 10–13), with S/N ratio of the order of 100. The measurement of vsini for large samples of pms stars that resulted brought new insights on various pressing questions related to stellar formation and early stellar evolution : how do the rotation rates of pms stars compare with those expected from models of stellar formation ? how does the stellar angular momentum change during pms evolution ? is pms activity linked with rotation as would be expected if activity were triggered by magnetic processes ?

This is a very brief review of the high resolution line profile work that has been done on very young stars. The spectral anamolies peculiar to these stars are mentioned, with some discussion of what may give rise to them. The Hα line is discussed most extensively, as the most work has been done with it. While progress has been made in understanding the general nature of T Tauri spectra, there are very large gaps in our current understanding of the emission lines from these stars.

The Herbig Ae/Be stars (Herbig, 1960; Finkenzeller and Hundt, 1984) are widely believed to be intermediate mass (2-5 M⊙) pre-main sequence stars. In the past few years, a big effort has been made to model their outer layers, and it has been shown that they possess stellar winds and extended chromospheres (Catala et al., 1984; Catala et al., 1986a; Catala and Kunasz, 1987).

We present a preliminary report on simultaneous optical and infrared observations on a sample of Herbig Ae/Be stars carried out at the European Southern Observatory in La Silla-Chile in March 1984 and in March-April 1985. In this paper Z CMa, V380 Ori, R Mon and HD53367 are analyzed A strong variability in both energy distribution and Ha line profile is detected in Z CMa, while for HD53367 only He I and Ha profile's variations are revealed; V380 Ori and R Mon show non significant variability.

Improved non-LTE model atmospheres designed for the analysis of very hot subluminous O stars are presented. The calculations are based on the new method of the accelerated lambda iteration (ALI) which proves capable of treating up to 100 levels of various ions. Presented here are improved calculations for (i) pure hydrogen model atmospheres including Stark broadening, (ii) for hydrogen- and helium-composed model atmospheres and (iii) first preliminary models which include in addition a detailed carbon model atom. These models remove an apparent mismatch of Balmer line profiles noted previously and fit high S/N, high-resolution hydrogen and helium spectra obtained with the ESO-Cassegrain echelle spectrograph very well.

For more than ten years now, a controversial issue in studies of stellar winds has concerned the existence or not of a coronal zone (T ∼ 106 K) at the base of the cool winds (T ∼ Teff) of early-type stars. The latest revival of interest in this possibility is due to Wolfire et al. (1985) who showed that Waldron's (1984) recombination stellar wind (RSW) version of the hot corona – cool wind model (Hearn 1975; Cassinelli et al. 1978) yields models for ξ Puppis (O4 If) that are consistent with both IRAS and Einstein IPC data, thus refuting an earlier claim (Lamers et al. 1984) to have excluded the existence of a coronal zone.

Analysis of line profiles obtained with astronomical instrumentation capable of high signal-to-noise ratio spectroscopy have contributed significant new precision to the determination of the basic stellar parameters of hot, luminous, mass-loosing stars. Accurate measurement of such stellar properties as effective temperature and helium abundance for stars of spectral type O and early B is important not only to the physics of these stars but also to the environment in which they are located. The overall goals of the work we summarize here are to refine the spectral-type vs. temperature calibration for the most massive stars and to determine helium abundances for stars that are loosing mass at a rate sufficiently high to affect their evolution. Details of our procedures are described in the analysis of ξ Puppis by Bohannan et al. (1986).

Rapid variability in Be stars could be understood by non radial pulsations or by rotation of an inhomogeous surface brightness distribution…

The structure and the variability of the Hα and of the HeI λ6678 lines have been investigated with an optical fiber spectrograph and a CCD camera. The signal to noise ratio, measured in the continuum, is between 300 and 500.

Weak changes in the Hα emission line profile of γ Cas have been detected on time-scale of hours and days. This line has an asymmetric profile exhibiting only one blue-shifted maximum while the HeI λ6678 has a double-peak emission, superimposed to the photospheric contribution, with a violet to red peak ratio V/R >1.

The Hα emission line of φ Per exhibits a complex structure with significant changes in its core, from night to night and on a short time scale <lhr. The HeI λ6678 presents a blue-shifted asymmetric emission (red-winged) superimposed to the photospheric contribution.

Furthermore the Hel photospheric line λ6678 of the B6 star o And has presented notable variations in its profile during the 2 observational campaigns, which do not seem correlated to the photometric period of 1.57 day.

A computer code that solves the transfer equation in moving atmosphere is prepared for analysis of variability in circumstellar spectral lines. This model gives a theoretical line shape, which consists of a symmetric photospheric line and superposed on it a P-Cyg type component originated in the envelope. Comparison between calculated and observed line profiles will be used to analyze 6 A/mm spectra of F-K supergiants.

Profiles of the hydrogen Paß, Paγ and Brγ lines of an A0IV star γ Gem were obtained at a high resolution to investigate at what degree the hydrogen IR lines can be useful for fine tests of the NLTE model atmospheres. All three lines show a deep and narrow absorption core in a good qualitative agreement with the predictions of the available NLTE models for B stars, thus proving that the NLTE effects are important for A stars as well. New NLTE models were computed to extend the grid down to 9500 °K and to include 8 discrete levels of H atom into the energy balance. However, further theoretical work is necessary to compare the observed profiles and the theory.

We present new high resolution profiles of Ha emissions in radially pulsating stars (RR Lyrae, W Virginis, RV Tauri, Mira stars and Classical Cepheids). Depending on phase, these profiles can show an apparent absorption within the emission close to the Hα laboratory wavelength. The origin of this feature is discussed in the framework : (a) of a composite of a single emission and a deep photospheric absorption (RR Lyrae, W Virginis and RV Tauri stars); (b) of a true absorption caused by cool hydrogen above the shock wave producing the emission; (c) of a geometric model in which the absorption is a lack of emission. Recent observations (Hα profiles of Mira stars S Car and T Cen), which show that the absorption dip is below the continuum level, are in favour of the true absorption model.

High signal to noise spectra are required in chromospheric modelling because chromospheric emission lines are formed in a boundary layer under conditions of NLTE and in non-hydrostatic equilibrium, as well as in multiple magnetically-controlled streams, with horizontal structure on several scales, and vertical velocity fields. To obtain useable estimates of energy dissipation with height we have obtained sequences of spectra from F8 to K5 and for stars of different activity levels. These comprise Call H and K, the IR triplet, and MgII h and k obtained with the ESO CAT+CES or IUE. We outline the constraints such observations place on models and indicate theoretical and observational difficulties.

In this paper we have applied to the Sun a method for calibrating, in absolute flux units, Ca II H profiles of late-type stars. After comparing, in the region 3948-3882 A, an LTE synthetic spectrum with the data of the solar flux Atlas by Kurucz et al. (1984), we have defined the wavelength ranges where observations agree with computations, based on specific radiative equilibrium models and collisional broadening parameters. By fitting in these regions the spectrum of the moon observed at ESO with the corresponding synthetic spectrum, we derived a calibration factor that enables us to calibrate, in absolute flux units, the whole observed range.

After nine years of operation the IUE satellite continues to provide valuable spectra of cool stars from 1200 to 3100 Å. The impact of these spectra has been greatest in studies of the outer regions of the atmospheres, above the photospheres, allowing the general properties of stellar chromospheres, transition regions and winds to be established. After outlining these properties, I focus on studies based on high signal–to–noise echelle spectra (λ/Δλ ∼1.2 ×104) of single stars, showing how high quality emission line profiles have been used to derive constraints on the outer atmospheric structure, which in turn have been used to examine models of heating and mass loss.

In this paper, we present new observations of β Cephei stars made with the CFHT coudé Reticon. Spectral sequences of the extreme star BW Vulpeculae show large velocity and line profile changes in Ha and in the C II doublet (λλ6578,6582) over 0.04 of a cycle, during three different cycles on three different nights. In fact, there are two such phases of line doubling where the velocities are nearly discontinuous before and after the so-called velocity “stillstand” (near maximum light). Also, the line doubling phases coincide with pronounced peaks in the Ha core residual intensity. The most straightforward interpretation of these observations is that there are two shock waves, separated by about 50 minutes, which generate double absorption components. For v Eridani and γ Pegasi, there are no discernible changes in the Ha profiles, despite rather regular velocity variations. This argues against the shock-wave interpretation for “classical” β Cephei stars.

The goal is largely historical, 30 years of instrumental progress in a difficult new field, faint white dwarfs, and some results. High signal-to-noise spectrophotometry at 40–160 Å resolution revealed the separation between hydrogen- and helium-rich atmospheres, and provided a temperature scale from models. The white-dwarf color-luminosity relation proved narrow. Their simple spectra made brute-force averaging possible to 14th magnitude at good photographic resolution. Features as shallow as 5% and 200 Å wide included C2, but in magnetic stars some strong absorptions remain unidentified. Metals are deficient, gravitational diffusion setting the surface composition. The Palomar double CCD spectrograph can now give S/N ≈ 100 to 17m. Some polarized white dwarfs have Zeeman triplets in magnetic fields near 20 megagauss. In one, Zeeman components are shifted up to 2000 Å at 300 megagauss. Rotation is small in all white dwarfs, angular momentum mostly lost. Non-LTE cores of Hα, Hβ exist and permit improved gravitational redshifts. An evolutionary phenomenon is progressive steepening of the Balmer decrement below 7000 K, cool atmospheres being helium-dominated.

High S/N is a good first step toward accurate profiles.

Line profile–variability (LPV) is very wide–spread among early–type stars. With the exception of inhomogeneous surface abundance distributions associated with magnetic fields, the LPV of bona fide non–magnetic stars is consistent with (often only with) nonradial pulsation (NRP). Peculiar surface chemistry and NRP may even be mutually exclusive, and there are other indications that in spite of the ubiquity of NRPs the distribution of their characterizing parameters in the HRD is far from being uniform. This may be important for uncovering the driving mechanism of NRPs in early–type stars.