The uniqueness problem in Doppler imaging is discussed. Most of the problem appears to be confusion between different meanings of the word “uniqueness”. According to specific definitions presented in this study, there should not be any uniqueness problem.

In this contribution the radial velocity (RV) variations expected for starspots on solar-type stars are examined. The spot-induced RV amplitude is found to vary linearly with spot filling factor and is less than 1 m−1 for spot sizes comparable to large sunspots and as high as 20 m s−1 for spot filling factors of 1%. Also, for a given spot size the RV amplitude increases linearly with υ sin i. All of these findings confirm the results of Saar & Donahue (1997). It is also shown that two spectral lines with different temperature sensitivity can have different RV amplitudes which may provide a diagnostic for confirming planet detections. The RV variations due to starspots correlate well with the displacement of the line core and centroid and this can be used to correct RV measurements for the effects of cool starspots.

We investigate the oscillation properties of є Cep using a series of specialized techniques designed to extract and analyze time variations in absorption line profiles. To obtain the necessary temporal coverage for this investigation, multi-site observations were collected at 3 sites (China, France, Arizona) all equipped with high-resolution échelle spectrographs. From these observations, we find evidence for a very rich spectrum of modes in є Cep.

Wavelength positions of photospheric absorption lines may be affected by surface convection (stellar granulation). Asymmetries and wavelength shifts originate from correlated velocity and brightness patterns: rising (blueshifted) elements are hot (bright), and convective blueshifts result from a larger contribution of such blueshifted photons than of redshifted ones from the sinking and cooler (darker) gas. For the Sun, the effect is around 300 m s−1, expected to increase in F-type stars, and in giants. Magnetic fields affect convection and induce lineshift variations over stellar activity cycles. A sufficient measuring precision reveals also the temporal variability of line wavelengths (due to the evolution of granules on the stellar surface). A major future development to come from adaptive optics and optical interferometry will be the study of wavelength variations across spatially resolved stars, together with their spatially resolved time variability. Thus, precise radial velocities should soon open up new vistas in stellar atmospheric physics.

Small < 10 m s−1 variations of radial velocity (RV) with multi-year periods in solar-type stars may be indistinguishable from the effects induced on lines by stellar activity cycles (Dravins 1985; Saar & Donahue 1997). Dravins (1992) recommended a resolving power R > 3 × 105 to measure accurately the subtle changes in the shapes of bisectors of photospheric absorption lines driven by changes of granular convection in slowly rotating dwarf stars. Butler et al. (1996) measure impressively small amplitudes of RVs by using echelle spectrographs that cover a broad spectrum. However, to cover a broad spectrum the resolving power is typically limited to < 7 × 104, and the necessary presence of the iodine absorption spectrum may make it difficult to measure convective line shifts contemporaneously with the RV time series. Furthermore, to reach an RV accuracy of ± 3 ms−1 the whole profile of each line is used, thus maximizing the possibility that changes in the shapes of the lines’ C-bisectors could induce an apparent variation of RV.

Dravins (1985) recommended the exclusive use of the steep flanks of photospheric absorption lines to minimize the effects of convection on apparent RV. McMillan et al. (1993, 1994) demonstrated that such RV measurements made with a Fabry-Perot etalon (FPE) interferometer in transmission can be stable in the presence of stellar line variations seen by other investigators whose measurements were not based exclusively on line flanks. Dravins also prescribed high resolving power, high signal-to-noise ratio, high instrumental contrast, and low instrumental wings to analyze the rest of the line profile for convectively-driven changes (Dravins 1978, 1987, 1992). A double- or multiple-pass FPE scanning whole line profiles can provide high R, high contrast, low wings, and a stable, symmetrical line spread function with small (portable) optics, although the low photon efficiency will restrict its use to a few carefully selected stars. The spectral classes of these stars should span the spectral classes of the stars being monitored by others for planets. We describe a possible implementation of this concept that has the potential for adequate photon flux: observing symbiotically through another instrument on a 6-m to 10-m class telescope.

The convection in stellar atmospheres causes spectral lines to be more or less blue-shifted. The differential wavelength shift between two groups of spectral lines could be used to characterize the convection. This paper describes such an effort using cross-correlations between R ≈ 40 000 échelle spectra and laboratory wavelength templates.

Convective motions in the photospheres of the Sun and solar-type stars can be studied using spectral line asymmetries via line bisectors and line shifts. Over the past few years there has been an improvement in the precision of the line positions for Fe I, CO and OH. These improved positions can be combined with recent high resolution infrared spectra of the Sun to examine how their convective line asymmetries behave with respect to observable line parameters, such as wavenumber and depth. We have completed a survey of convective line shifts for over 650 Fe I lines, 1320 CO lines and 80 OH lines, between 0.9 and 11 μm. The behavior of the distributions of these features, with respect to observed characteristics, is examined. The use of different species allows for an exploration of convective motions at different levels in the solar atmosphere. The large size of the sample allows for a more complete statistical understanding of the distributions. This work complements surveys of line asymmetries in the visible region of the Solar spectrum, and provides a foundation for further studies of convective motions in the spectra of other stars.

Binary systems can be analyzed like clusters but with additional constraints from the orbit. The theories of stellar interiors and atmospheres are used to analyze the color-magnitude diagram and spectra to test the consistency of theory and observation and also to provide results on the distance, chemical composition, age, and individual masses, radii, and effective temperatures. Given the total mass resulting from the theoretical analysis, it is possible to determine the complete orbit of even long-period binaries if at least 6 components of the position, velocity and acceleration vectors have been observed.

For this paper we apply such a theoretical and orbital analysis to the ϒ Delphini binary consisting of a K1 IV primary (ϒ2 Del) and an F7 V secondary (ϒ1 Del). The primary has been observed with the preciseradial-velocity (PRV) technique and shows a radial acceleration of 2.2 ± 0.7 m s−1 yr−1 as well as a significant (false alarm probability < 0.01) periodic signature (P = 1.44 yr). At least three possible causes of this periodic signature are pulsation, rotation, or a planetary companion. The mass and radius results (M2 = 1.72M⊙, M1 = 1.57M⊙, R2 = 6.43R⊙, and R1 = 2.21R⊙) of our theoretical analysis help constrain the possibilities. The pulsational hypothesis requires more investigation of whether it is possible to excite a g-mode or an r-mode period that is much longer than the fundamental period of 0.5 dy derived from the mass-radius results. The rotational hypothesis leads to an inconsistency; the published value of υ sin i is a factor of 4.5 larger than the maximum value allowed by the radius and the PRV period of 1.44 yr. More investigation is required to determine whether increased macroturbulence and decreased υ sin i (by a factor of 4.5) is consistent with observed line profiles. From the PRV period and the primary mass a possible planetary companion would have υ sin i = 0.7 Jupiter masses with an orbital semimajor axis of 1.5 AU. The orbital results for the stellar binary (closest approach > 15 AU) shows there is room in the system for such a possible planetary companion of ϒ2 Del to survive the gravitational perturbations of ϒ1 Del.

We discuss the use of precise radial velocities for orbit studies of binary stars. Although they are desirable to achieve highly accurate masses for systems of large amplitude, their greatest value will be for systems of long period and low amplitude. These studies require high spectrograph stability, and in some cases resolution of the spectra may prove troublesome. Radial velocities must be combined with visual or interferometric observations for mass determination, since eclipsing binaries of long period are rare, but the number of resolved spectroscopic systems is increasing.

We review observational requirements, reduction techniques, and methods of solving for elements that satisfy simultaneously the observations in three dimensions, based on experience with radial velocities whose precision is near the lower limit for this Colloquium, obtained over the past 35 years with the Dominion Astrophysical Observatory (DAO) coudé spectrograph, and consider the gains that should be achievable over similar intervals in the future, by means of higher precision in all the relevant data. We discuss, from our own experience, the reasons why no masses have yet been determined by these methods, to an accuracy better than 2%.

Gamma-velocities of bright contact binary stars (VW Cep, SW Lac, AB And, OO Aql) have been computed using cross-correlation. The template spectra were synthesized with a newly developed computer code WGMODEL.

New radial velocity measurements of the Algol-type eclipsing binary BD +52 °2009, based on Reticon observations, are presented. The velocity measures are based on fitting theoretical profiles, generated by a physical model of the binary, to the observed cross-correlation function (ccf). Such profiles match this function very well, much better in fact than Gaussian profiles, which are generally used. Measuring the ccf’s with Gaussian profiles yields the following results: mp sin3i = 2.55 ± 0.05m⊙, ms sin3i = 1.14 ± 0.03m⊙, (ap + as) sin i = 7.34 ± 0.05R⊙, and mp/ms = 2.23 ± 0.05. However, measuring the ccf’s with theoretical profiles yields a mass ratio of 2.33 and following results: mp sin3i = 2.84 ± 0.05m⊙, ms sin3i = 1.22 ± 0.03m⊙, (ap + as) sin i = 7.56 ± 0.05R⊙. The system has a semi-detached configuration. By combining the solution of a previously published light curve with the spectroscopic orbit, one can obtain the following physical parameters: mp = 2.99m⊙, ms3 = 1.28m⊙, < Tp >= 9600K, < Ts >= 5400K, < Rp >= 2.35R⊙, < Rs >= 2.12R⊙. The system consists of an A0 primary and a G2 secondary.

The magnetic field investigations of the rapidly-oscillating (ro)Ap star ϒ Equ show a very long magnetic (rotational) period of about 74 years (Leroy et al. 1994; Bychkov & Shtol 1997). No significant changes of radial velocities were detected during the history of investigations of this star. Recently, Scholz et al. (1997) (hereafter S97) reported a rapid increase of radial velocity (RV) of ϒ Equ from the mean value of -16.81 km s−1 up to a maximum at -4.28 km s−1 within the interval JD 2449608 – JD 2450356, and suggested that ϒ Equ is a long-period binary star with high eccentricity. Such a probable discovery of binary motion of ϒ Equ is very interesting, since it opens the possibility to compare asteroseismic parameters of the star with those obtained from the binary orbit.

A new calibration of the α Cen system is presented. It shows that a theoretical model consistent with the observations and with the higher masses determined by Pourbaix (1999) can be obtained. Our model of α Cen A has a convective core. This could serve as a discriminant in a future asteroseismological calibration of the system.

Precise radial velocities lately published (Murdoch, Hearnshaw & Clark 1993) allow a simultaneous least-squares adjustment of all visual and spectroscopic observations. Starting with the same data as Murdoch & Hearnshaw (1993), we obtain a mass ratio that agrees better with Kamper & Wesselink’s (1978) astrometric estimate. Our results suggest upward revisions of the distance to the system as well as of the individual masses of the components.

A radial velocity survey of the components of visual multiple stars has been done since 1994 with the correlation radial velocity spectrometer. About 50 spectroscopic sub-systems have been discovered, and a summary of the 30 published orbits is given. Difficulties of measuring the radial velocities of multiple stars are discussed and illustrated by 2 examples. New discoveries will lead to a better understanding of the formation of multiple stellar systems. Close and wide sub-systems can not be considered as a result of independent random combination, but are related by common origin. Almost all close binaries with periods less than 6 days possibly have more distant components which assisted in the formation of close pairs by taking away their angular momentum. On the other hand, among the distant visual tertiary companions the frequency of sub-systems with periods under 100 days is about 3 times higher than for field G dwarfs.

We review the history of the IAU Radial Velocity Standard Stars and give a status report on recent efforts at the Harvard-Smithsonian Center for Astrophysics to establish an absolute velocity zero point for these stars and to improve their usefulness for intercomparing the results from different instruments and observatories.

20 years of CORAVEL photoelectric radial-velocity measurements associated with the high precision achieved by the ELODIE spectrograph on a fair time span allow us to propose a new list of high-precision radial-velocity standards with velocity variations lower than a few times 10 m s−1.

A search for constant velocity B and A stars for use as early-type radial-velocity standards has continued for 15 years. For the past decade observations of over two dozen stars have been obtained with the KPNO coudé feed telescope, spectrograph, and a CCD detector. Mean velocities are given for 26 B and A stars plus HR 5447, an F2 V star. Unfortunately, most of the early and mid B-type stars have variable velocities. However, a number of slowly rotating, late B and A-type stars that have constant velocities are identified. From 53 velocities covering nearly 20 years, a preliminary orbit for the early-A star HR 8641 = o Peg has been determined. It has a period of 10.8 years and a total velocity amplitude of 2.4 km s−1.

A preliminary analysis of a sample of more than hundred stars, used as radial-velocity standards and followed with the CORAVEL spectrographs over 1 to 2 decades, is presented. Stars with intrinsic variability or orbital motions are pointed out.

A number of long baseline optical/infrared interferometers have commenced their scientific programs or are under development. These instruments will provide accurate measurements of the angular sizes of single stars and the angular separations of binary systems at resolutions impossible with conventional telescopes. The combination of interferometric data with the results of high-resolution spectroscopy will, for many classes of objects, provide a powerful method for studying them that neither technique can do alone. Examples include the combination of interferometric and spectroscopic data for spectroscopic binaries and, in particular, for double-lined binaries, and single-lined binaries of known parallax, to determine fundamental stellar quantities. Another example concerns the study of Cepheid variables, where the combination of the data can provide an independent calibration of the zero point of the luminosity scale. The requirements and potential of these combined interferometric-spectroscopic studies are discussed.