Random-error minimization during cross-correlation of early-type spectra

Verschueren, W.; David, M.

doi:10.1051/aas:1999236

Cited by 11 publications

(10 citation statements)

References 13 publications

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“…The principles for a single-star spectrum are elaborated in several papers, e.g. Verschueren & David (1999) and for a binary in Hensberge et al (2000). The latter uncertainties essentially contain a correction factor (relative to the single-star case) for the correlation at a given orbital phase between the spectral gradients in the Doppler-shifted component spectra, and a multiplicative factor inversely proportional to the contribution of the component to the total light (Vaz et al, in prep.).…”

Section: Input Radial Velocities and Their Uncertaintiesmentioning

confidence: 99%

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

Torres

Lampens

Frémat

et al. 2010

A&A

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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.

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Section: Input Radial Velocities and Their Uncertaintiesmentioning

confidence: 99%

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

Torres

Lampens

Frémat

et al. 2010

A&A

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“…A different error estimate would result if the template is also taken to be a noisy spectrum, as is sometimes assumed in the literature (e.g., Verschueren & David 1999) and thus the procedure would have to estimate the 'true' template using the spectrum and the template. The formal calculations are much more complicated in this case and the resulting error estimate is approximately √ 2 times larger than the one quoted above.…”

Section: Error Estimatementioning

confidence: 99%

Cross-correlation and maximum-likelihood analysis: a new approach to combining cross-correlation functions

Zucker

2003

Monthly Notices of the Royal Astronomical Society

149

165

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This paper presents a new approach to combining cross‐correlation functions. The combination is based on a maximum‐likelihood approach and uses a non‐linear combination scheme. It can be effective for radial velocity analysis of multi‐order spectra, or for analysis of multiple exposures of the same object. Simulations are presented to show the potential of the suggested combination scheme. The technique has already been used to detect a very faint companion of HD 41004.

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“…The effects caused by the mismatch between a spectrum template for a slow-rotation star and a rapidly rotating A-type star may exceed 1 km s −1 (Verschueren & David 1999). The origin of these effects is the rotational line-broadening and the ensuing blending of spectral lines, significant when a given star is observed equator-on, but disappearing when viewed pole-on.…”

Section: Effects Of Stellar Rotationmentioning

confidence: 99%

“…The influence of stellar rotation has been realised, especially for earlier-type stars with their often rapid rotation (Andersen & Nordström 1983;Verschueren & David 1999;Griffin et al 2000). The effects caused by the mismatch between a spectrum template for a slow-rotation star and a rapidly rotating A-type star may exceed 1 km s −1 (Verschueren & David 1999).…”

Section: Effects Of Stellar Rotationmentioning

confidence: 99%

The fundamental definition of “radial velocity”

Lindegren¹,

Dravins²

2003

A&A

181

163

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Abstract. Accuracy levels of metres per second require the fundamental concept of "radial velocity" for stars and other distant objects to be examined, both as a physical velocity, and as measured by spectroscopic and astrometric techniques. Already in a classical (non-relativistic) framework the line-of-sight velocity component is an ambiguous concept, depending on whether, e.g., the time of light emission (at the object) or that of light detection (by the observer) is used for recording the time coordinate. Relativistic velocity effects and spectroscopic measurements made inside gravitational fields add further complications, causing wavelength shifts to depend, e.g., on the transverse velocity of the object and the gravitational potential at the source. Aiming at definitions that are unambiguous at accuracy levels of 1 m s −1 , we analyse different concepts of radial velocity and their interrelations. At this accuracy level, a strict separation must be made between the purely geometric concepts on one hand, and the spectroscopic measurement on the other. Among the geometric concepts we define kinematic radial velocity, which corresponds most closely to the "textbook definition" of radial velocity as the line-of-sight component of space velocity; and astrometric radial velocity, which can be derived from astrometric observations. Consistent with these definitions, we propose strict definitions also of the complementary kinematic and astrometric quantities, namely transverse velocity and proper motion. The kinematic and astrometric radial velocities depend on the chosen spacetime metric, and are accurately related by simple coordinate transformations. On the other hand, the observational quantity that should result from accurate spectroscopic measurements is the barycentric radial-velocity measure. This is independent of the metric, and to first order equals the line-ofsight velocity. However, it is not a physical velocity, and cannot be accurately transformed to a kinematic or astrometric radial velocity without additional assumptions and data in modelling the process of light emission from the source, the transmission of the signal through space, and its recording by the observer. For historic and practical reasons, the spectroscopic radial-velocity measure is expressed in velocity units as cz B , where c is the speed of light and z B is the observed relative wavelength shift reduced to the solar-system barycentre, at an epoch equal to the barycentric time of light arrival. The barycentric radial-velocity measure and the astrometric radial velocity are defined by recent resolutions adopted by the International Astronomical Union (IAU), the motives and consequences of which are explained in this paper.Key words. techniques: radial velocities -techniques: spectroscopic -astrometry -reference systems -stars: kinematicsmethods: data analysis The need for stringent definitionsRadial velocity is an omnipresent concept in astronomy, and a quantity whose precision of determination has improved significantly in recent...

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Random-error minimization during cross-correlation of early-type spectra

Cited by 11 publications

References 13 publications

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

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

Cross-correlation and maximum-likelihood analysis: a new approach to combining cross-correlation functions

The fundamental definition of “radial velocity”

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Random-error minimization during cross-correlation of early-type spectra

Cited by 11 publications

References 13 publications

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

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

Cross-correlation and maximum-likelihood analysis: a new approach to combining cross-correlation functions

The fundamental definition of “radial velocity”

Contact Info

Product

Resources

About

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

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