Notes on the disentangling of spectra I. Enhancement in precision

Context: The technique of disentangling has been applied to numerous high-precision studies of spectroscopic binaries and multiple stars. Although, its possibilities have not yet been fully understood and exploited. Aims: Theoretical background aspects of the method, its latest improvements and hints for its use in practice are explained in this series of papers. Methods: In this first paper of the series, we discuss spectral-resolution limitations due to a discrete representation of the observed spectra and introduce a new method how to achieve a precision higher than the step of input-data binning. Results: Based on this principle, the latest version of the KOREL code for Fourier disentangling achieves an increase in precision for an order of magnitude.Comment: 2 figure

The radial velocity curve of HD153919 (4U1700-37) revisited

We have re-analysed all available high-resolution ultraviolet IUE spectra of the high-mass X-ray binary HD153919/4U1700-37. The radial velocity semi-amplitude of 20.6 +/- 1.0 km/s and orbital eccentricity of 0.22 +/- 0.04 agree very well with the values obtained earlier from optical spectra. They disagree with earlier conclusions for the same data reduced by Heap & Corcoran (1992) and by Stickland & Lloyd (1993).Comment: 6 pages, latex, figure included, Astronomy & Astrophysics, in pres

New distance and depth estimates from observations of eclipsing binaries in the SMC

A sample of 33 eclipsing binaries observed in a field of the SMC with FLAMES@VLT is presented. The radial velocity curves obtained, together with existing OGLE light curves, allowed the determination of all stellar and orbital parameters of these binary systems. The mean distance modulus of the observed part of the SMC is 19.05, based on the 26 most reliable systems. Assuming an average error of 0.1 mag on the distance modulus to an individual system, and a gaussian distribution of the distance moduli, we obtain a 2-sigma depth of 0.36 mag or 10.6 kpc. Some results on the kinematics of the binary stars and of the H II gas are also given.Comment: 6 pages, 4 figures, Proc. IAU Symp. No 256, The Magellanic System: Stars, Gas and Galaxies, eds. Jacco Th. van Loon & Joana M. Oliveir

Quantitative spectroscopy of close binary stars

The method of spectral disentangling has now created the opportunity for studying the chemical composition in previously inaccessible components of binary and multiple stars. This in turn makes it possible to trace their chemical evolution, a vital aspect in understanding the evolution of stellar systems. We review different ways to reconstruct individual spectra from eclipsing and non-eclipsing systems, and then concentrate on some recent applications to detached binaries with high-mass and intermediate-mass stars, and Algol-type mass-transfer systems.Comment: To appear in the Proceedings of IAU Symposium 282 'From Interacting Binaries to Exoplanets: Essential Modeling Tools

Absolute Dimensions and Apsidal Motion of the Young Detached System LT Canis Majoris

New high resolution spectra of the short period (P~1.76 days) young detached binary LT CMa are reported for the first time. By combining the results from the analysis of new radial velocity curves and published light curves, we determine values for the masses, radii and temperatures as follows: M_1= 5.59 (0.20) M_o, R_1=3.56 (0.07) R_o and T_eff1= 17000 (500) K for the primary and M_2=3.36 (0.14) M_o, R_2= 2.04 (0.05) R_o and T_eff2= 13140 (800) K for the secondary. Static absorbtion features apart from those coming from the close binary components are detected in the several spectral regions. If these absorbtion features are from a third star, as the light curve solutions support, its radial velocity is measured to be RV_3=70(8) km s^-1. The orbit of the binary system is proved to be eccentric (e=0.059) and thus the apsidal motion exists. The estimated linear advance in longitude of periastron corresponds to an apsidal motion of U=694+/-5 yr for the system. The average internal structure constant log k_2,obs=-2.53 of LT CMa is found smaller than its theoretical value of log k_2,theo=-2.22 suggesting the stars would have more central concentration in mass. The photometric distance of LT CMa (d=535+/-45 pc) is found to be much smaller than the distance of CMa OB1 association (1150 pc) which rules out membership. A comparison with current stellar evolution models for solar metallicity indicates that LT CMa (35 Myr) is much older than the CMa OB1 association (3 Myr), confirming that LT CMa is not a member of CMa OB1. The kinematical and dynamical analysis indicate LT CMa is orbiting the Galaxy in a circular orbit and belongs to the young thin-disk population.Comment: 19 pages, 6 figures and 6 tables, accepted for publication in Publication of the Astronomical Society of Japa

Abundances from disentangled component spectra: the eclipsing binary V578 Mon

Chemical abundances of the early-B type components of the binary V578 Mon are derived from disentangled component spectra. This is a pilot study showing that, even with moderately high line-broadening, metal abundances can be derived from disentangled spectra with a precision 0.1 dex, relative to sharp-lined single stars of the same spectral type. This binary is well-suited for such an assessment because of its youth as a member of the Rosette Nebula cluster NGC 2244, strengthening the expectation of an unevolved ZAMS chemical composition. The method is of interest to study rotational driven mixing in main-sequence stars, with fundamental stellar parameters known with higher accuracy in (eclipsing) binaries. The paper also includes an evaluation of the bias that might be present in disentangled spectra.Comment: Accepted for publication in Astronomy & Astrophysics, 8 pages, 2 figure

Spectra disentangling applied to the Hyades binary Theta^2 Tau AB: new orbit, orbital parallax and component properties

Theta^2 Tauri is a detached and single-lined interferometric-spectroscopic binary as well as the most massive binary system of the Hyades cluster. The system revolves in an eccentric orbit with a periodicity of 140.7 days. The secondary has a similar temperature but is less evolved and fainter than the primary. It is also rotating more rapidly. Since the composite spectra are heavily blended, the direct extraction of radial velocities over the orbit of component B was hitherto unsuccessful. Using high-resolution spectroscopic data recently obtained with the Elodie (OHP, France) and Hermes (ORM, La Palma, Spain) spectrographs, and applying a spectra disentangling algorithm to three independent data sets including spectra from the Oak Ridge Observatory (USA), we derived an improved spectroscopic orbit and refined the solution by performing a combined astrometric-spectroscopic analysis based on the new spectroscopy and the long-baseline data from the Mark III optical interferometer. As a result, the velocity amplitude of the fainter component is obtained in a direct and objective way. Major progress based on this new determination includes an improved computation of the orbital parallax. Our mass ratio is in good agreement with the older estimates of Peterson et al. (1991, 1993), but the mass of the primary is 15-25% higher than the more recent estimates by Torres et al. (1997) and Armstrong et al. (2006). Due to the strategic position of the components in the turnoff region of the cluster, these new determinations imply stricter constraints for the age and the metallicity of the Hyades cluster. The location of component B can be explained by current evolutionary models, but the location of the more evolved component A is not trivially explained and requires a detailed abundance analysis of its disentangled spectrum.Comment: in press, 13 pages, 10 Postscript figures, 5 tables. Table~4 is available as online material. Keywords: astrometry - techniques: high angular resolution - stars: binaries: visual - stars: binaries: spectroscopic - stars: fundamental parameter

Tehnike razdvajanja za raspetljavanje složenih spektara

Disentangling of composite spectra is a promissing technique for the analysis of double-lined spectroscopic binary systems. The technique makes use of a separation routine to extract model-component spectra out of a time series of observed composite spectra. Focusing on the differences between two possible approaches in the implementation of the separation routine, we compare the resulting limitations. We perform test runs on artificial data and conclude that separation in the wavelength domain is more versatile in several aspects, while the computational efficiency of separation in the Fourier domain allows working with larger data sets which is beneficial in a fully-blown disentangling process.Raspetljavanje složenih spektara je obećavajuća metoda za proučavanje dvojnih zvjezdanih sustava. Ta metoda primjenjuje rutinu za razdvajanje kojom se izlučuje spektre zvijezda komponenata modela iz vremenskog niza opaženih složenih spektara. Usredotočujući se na razlike u pristupu pri izvedbi rutine za rastavljanje, uspoređujemo ograničenja koja iz njih proizlaze. Proveli smo ispitivanje s umjetnim podacima i zaključili da je rastavljanje u području valnih duljina svestranije u više pogleda, dok rastavljanje primjenom Fourierovog transformata dozvoljava rad s većim skupovima podataka, što je povoljno u potpunom procesu raspetljavanja složenih spektara