Analyses of 13 FEROS spectra from the ESO archive and 617 V-band photometric observations from the ASAS3 database allowed us to demonstrate that HD 165246 is a double-lined spectroscopic binary. As an earlier finding revealed, HD 165246 is also an eclipsing system. We were able to derive consistent orbital and light-curve solutions and all basic physical properties of the system. The period of this O8 V + B7 V binary is 4.d 592706 and the semiamplitudes of the radial-velocity curves are K 1 = 55.5 km s −1 and K 2 = 321 km s −1 . As the mass ratio is small (0.173), the secondary lines cannot be seen directly in the spectra; however the application of spectral disentangling allowed us to detect weak Balmer and He i lines of the secondary component. The primary component rotates with a high projected velocity of v sin i = 243 km s −1 . A combined radial-velocity and light-curve solution led to the component masses and radii expected for the young stars of the given spectral types. Due to the high rotation velocity, the primary component might display changes in surface abundances of some elements. However, we did not find any significant differences with respect to the abundances of slowly rotating stars.

Context. In spite of the importance of massive O-type stars for astrophysics, their accurate masses and other fundamental properties are still a matter of debate. Determining them reliably is hampered by various factors (stellar winds and other forms of circumstellar matter), and the agreement of derived properties with the model predictions is far from satisfactory. Careful studies of O-type binaries, especially of those in stellar clusters, are therefore desirable. Aims. Having obtained new series of electronic spectra and UBV photometry of V1007 Sco, we analysed these data in an effort to check whether the observed properties of V1007 Sco indeed disagree with the prediction of stellar evolutionary models. We briefly analysed data for a few other binaries in NGC 6231, too. Methods. Spectral reductions were carried out with the MIDAS program, photometry reduced using the HEC22 program, the orbital elements were derived with the FOTEL program and the final solutions obtained with the program PHOEBE. Results. Our analysis led to an accurate determination of the apsidal advance,ω = (0.00884 ± 0.00012) deg d −1 , based on a simultaneous solution of all usable radial-velocity and photometric data. This implies an apsidal period of 111.5 years. It is also demonstrated that the orbital inclination must be close to 67• . We arrived at the following preliminary values for masses and radii: M 1 = (29.5 ± 0.4) M , M 2 = (30.1 ± 0.4) M , R 1 = (15.8 ± 0.7) R , and R 2 = (15.3 ± 0.5) R . These values clearly indicate a log g of about 3.5 [CGS], implying that the stars are giants and not supergiants, as the standard spectral classification criteria indicate.

For years, δ Orionis was considered a normal binary with an O9.5 II primary exhibiting apsidal-line advance. However, radial-velocity curves of both binary components have been derived from the IUE and optical spectra using the cross-correlation technique, and surprisingly low masses of 11.2 and 5.6 M were found. We obtained new spectra in the red spectral region and new UBV photometry. Using all published photometry and radial velocities, we deduced more accurate orbital and apsidal line periods. The main result of this paper is to show that the observed line spectra of δ Orionis are composed of the lines of the O9.5 II primary and a similarly hot tertiary, while the lines of a cooler B-type secondary are too faint to be detected in the available spectra. The character of the light curve (low-amplitude partial eclipses and a non-negligible scatter of the data) does not allow for a unique light-curve solution. Nevertheless, we show that the assumption of normal primary-component mass and radius corresponding to the O9.5 II classification (25 M , 16-17 R ) leads to consistent parameters for the system.

Context. Compact hierarchical systems are important because the effects caused by the dynamical interaction among its members occur on a human timescale. These interactions play a role in the formation of close binaries through Kozai cycles with tides. One such system is ξ Tauri: it has three hierarchical orbits: 7.14 d (eclipsing components Aa, Ab), 145 d (components Aa+Ab, B), and 51 yr (components Aa+Ab+B, C). Aims. We aim to obtain physical properties of the system and to study the dynamical interaction between its components. Methods. Our analysis is based on a large series of spectroscopic photometric (including space-borne) observations and long-baseline optical and infrared spectro-interferometric observations. We used two approaches to infer the system properties: a set of observation-specific models, where all components have elliptical trajectories, and an N-body model, which computes the trajectory of each component by integrating Newton's equations of motion. Results. The triple subsystem exhibits clear signs of dynamical interaction. The most pronounced are the advance of the apsidal line and eclipsetiming variations. We determined the geometry of all three orbits using both observation-specific and N-body models. The latter correctly accounted for observed effects of the dynamical interaction, predicted cyclic variations of orbital inclinations, and determined the sense of motion of all orbits. Using perturbation theory, we demonstrate that prominent secular and periodic dynamical effects are explainable with a quadrupole interaction. We constrained the basic properties of all components, especially of members of the inner triple subsystem and detected rapid low-amplitude light variations that we attribute to co-rotating surface structures of component B. We also estimated the radius of component B. Properties of component C remain uncertain because of its low relative luminosity. We provide an independent estimate of the distance to the system. Conclusions. The accuracy and consistency of our results make ξ Tau an excellent test bed for models of formation and evolution of hierarchical systems.

Abstract. UBV photometry of the central star of the Trifid nebula -HD 164492, which has so far been suspected of photometric as well as of radial velocity variability -is presented. The results of our photometry do not confirm any variability. Moreover, based on new high resolution CCD spectra any radial velocity variability can be discarded. Photometry of several other members of the multiple stellar system is included; according to this photometry, the system is a physical one. Equivalent widths for the main component of HD 164492 are given. Positions measured on CCD exposures are presented too.

Abstract. New spectroscopic data were obtained for the early-type binaries V337 Aql, V649 Cas, V382 Cyg, and V431 Pup. Their radial velocity curves are presented. These are the first such data for V337 Aql and V431 Pup. In the case of V382 Cyg, our data confirm previously obtained results. Especially for V649 Cas our radial velocity curve yields important new implications for the component masses: the detection of third body lines, which are blended with the lines of the primary component, solves the problem of the unacceptably small masses formerly deduced for this binary; now we determine masses closer to the values expected for spectral type B 0. V431 Pup is an important object, because it is a new member of the small group of early-type eclipsing binaries with an evolved component. A published light curve of V337 Aql is solved by the MORO code, and system parameters are derived. The period of V649 Cas is found to be variable, and a more accurate period is calculated for V431 Pup.

We present the first orbital elements for the massive close binary HD 101131, one of the brightest objects in the young open cluster IC 2944. This system is a double-lined spectroscopic binary in an elliptical orbit with a period of 1 Guest Observer, Mount Stromlo and Siding Springs Observatories, Australia 2 Guest Observer, Complejo Astronomico El Leoncito (CASLEO), San Juan, Argentina -2 -9.64659 ± 0.00012 days. It is a young system of unevolved stars (approximately 2 million years old) that are well within their critical Roche surfaces. We use a Doppler tomography algorithm to reconstruct the individual component optical spectra, and we apply well known criteria to arrive at classifications of O6.5 V((f)) and O8.5 V for the primary and secondary, respectively. We compare the reconstructed spectra of the components to single-star spectrum standards to determine a flux ratio of f 2 /f 1 = 0.55 ± 0.08 in the V -band. Both components are rotating faster than synchronously. We estimate the temperatures and luminosities of the components from the observed spectral classifications, composite V magnitude, and cluster distance modulus. The lower limits on the masses derived from the orbital elements and the lack of eclipses are 25M ⊙ and 14M ⊙ for the primary and secondary, respectively. These limits are consistent with the larger masses estimated from the positions of the stars in the Hertzsprung-Russell diagram and evolutionary tracks for single stars.

Abstract.We present an analysis of the early-type quadruple system QZ Car, consisting of an eclipsing and a non-eclipsing binary. The spectroscopic investigation is based on new high dispersion echelle and CAT/CES spectra of H and He lines. The elements for the orbit of the non-eclipsing pair could be refined. Lines of the brighter component of the eclipsing binary were detected in near-quadrature spectra, while signatures of the fainter component could be identified in only few spectra. Lines of the primary component of the non-eclipsing pair and of both components of the eclipsing pair were found to be variable in position and strength; in particular, the He ii 4686 emission line of the brighter eclipsing component is strongly variable. An ephemeris for the eclipsing binary QZ Car valid at present was derived Prim. Min. = hel. JD 2448687.16 + 5.d 9991 · E. The relative orbit of the two binary constituents of the multiple system is discussed. In contrast to earlier investigations we found radial velocity changes of the systemic velocities of both binaries, which were used -together with an O-C analysis of the expected light-time effect -to derive approximate parameters of the mutual orbit of the two pairs. It is shown that this orbit and the distance to QZ Car can be further refined by minima timing and interferometry.