Spectra disentangling applied to the Hyades binaryθ²   Tauri AB: new orbit, orbital parallax and component properties

Abstract

Aims. θ 2 Tau 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. Its light curve furthermore shows a complex pattern of δ Scuti-type pulsations. The secondary has a similar temperature but is less evolved and fainter than the primary. In addition, it is 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. Our aim is to reveal the spectrum of the fainter component and its corresponding Doppler shifts in order to improve the accuracy of the physical properties of this important "calibrator" system. Methods. Using high-resolution spectroscopic data recently obtained with the Elodie (Observatoire de Haute-Provence, France) and Hermes (Roque de Los Muchachos, La Palma, Spain) spectrographs, and applying a spectra disentangling algorithm to three independent data sets including CfA spectra (Oak Ridge Observatory, USA), we derived an improved spectroscopic orbit. We next used a code based on simulated annealing and general least-squares minimization to refine the orbital solution by performing a combined astrometric-spectroscopic analysis based on the new spectroscopy and the long-baseline data from the Mark III optical interferometer. Results. As a result of the performed disentangling, and notwithstanding the high degree of blending, 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 (still consistent with previous values). Our mass ratio is in good agreement with the older estimates of Peterson et al. (1991Peterson et al. ( , 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). Conclusions. The evolutionary status of both components is re-evaluated in the light of the revisited properties of θ 2 Tau AB. Due to the strategic position of the components in the turnoff region of the cluster, the new determinations imply stricter constraints for the age and the metallicity of the Hyades cluster. We conclude that the location of component B can be explained by current evolutionary models, but the location (and the status) of the more evolved component A is not trivially explained and requires a detailed abundance analysis of its disentangled spectrum. The improved accuracy (at the 2% level) on the stellar masses provides a useful basis for the comparison of the observed pulsation frequencies with suitable theoretical models.

Binary star astrometry with milli and sub-milli arcsecond precision

“…9) considered by . Torres et al (2011) determined a new orbit for θ 2 Tau, an orbital parallax of 20.90 ± 0.14 mas and component masses M A = 2.86 ± 0.06M and M B = 2.16 ± 0.02M . Combined Mark III and NPOI analyses were completed for: ζ 1 UMa or Mizar (Fig.…”

“…Another example is the system η And (Fig. In order to refine the orbital solution for θ 2 Tau, by performing a combined astrometric and spectroscopic analysis based on the new spectroscopy and longbaseline data from the Mark III optical interferometer, Torres et al (2011) determined a new orbit for θ 2 Tau, an orbital parallax of 20.90 ± 0.14 mas and component masses M A = 2.86 ± 0.06M and M B = 2.16 ± 0.02M , the mass ratio being in good agreement with the older estimates of Peterson et al (1991), Peterson et al (1993), but the mass of the primary being 15-25% higher than the more recent estimates by Torres et al (1997) and Armstrong et al (2006). They found M A = 2.59 ± 0.30M and M B = 2.34±0.22M for the component masses and 76 ± 2 pc for the distance to η And.…”

V2368 Ophiuchi: an eclipsing and double-lined spectroscopic binary used as a photometric comparison star for U Ophiuchi

“…It is notable that in their detailed study of another evolved A-type binary with eccentric orbit, θ 2 Tau, Torres et al (2011) also found the projected rotational velocity for the secondary roughly twice as high as for the primary.…”

Aprendendo física com as estrelas binárias

“…Ainda nesta figura, os pontos indicam os valores medidos de velocidades radiais, enquanto que as curvas sólidas indicam os melhores ajustes para os pontos obtidos. Os astrônomos investigadores deste sistema binário estimaram o período orbital em aproximadamente 140 dias [17]. Podemos notar também que as curvas de velocidades radiais para este sistema não são simétricas ou não possuem os formatos simples de senos e cossenos, indicando que á orbitaé bem excêntrica, ou seja, está bem distante do formato circular.…”