Constraining the difference in convective blueshift between the components of<i>α</i>Centauri with precise radial velocities

Pourbaix, Dimitri; Nidever, David L.; McCarthy, C.; Butler, R. Paul; Tinney, C. G.; Marcy, Geoffrey W.; Jones, H. R. A.; Penny, A. J.; Carter, B. D.; Bouchy, F.; Pepe, F.; Hearnshaw, John; Skuljan, J.; Ramm, D. J.; Kent, Dudley Charles

doi:10.1051/0004-6361:20020287

Cited by 131 publications

(184 citation statements)

References 14 publications

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“…The revised orbital parallax (743 ± 1.3 mas) is smaller than the value derived by Söderhjelm (1999) from the Hipparcos observations and adopted by Pourbaix et al (2002). It is somewhat closer to the original Hipparcos value, 742 ± 1.42 mas (ESA 1997) .…”

Section: Resultscontrasting

confidence: 40%

“…It is somewhat closer to the original Hipparcos value, 742 ± 1.42 mas (ESA 1997) . Diabolos denote the HARPS archived data and squares the older ESO data (Endl et al 2001) already used by Pourbaix et al (2002). On this portion of the orbit, fitting ΔV B or setting it to 0 is not visually distinguishable.…”

Section: Resultsmentioning

confidence: 99%

“…The outcome was a set precise radial velocities that were used to quantify the relative convective blue shift of both components, assuming the individual masses and the parallax of the system (Pourbaix et al 2002). Even if it turned out to be a false detection (Hatzes 2013;Rajpaul et al 2016), the announcement of a planetary companion around α Cen B (Dumusque et al 2012) suddenly resurrected the interest of the planet hunters for that stellar system (Kaltenegger & Haghighipour 2013).…”

Section: Introductionmentioning

confidence: 99%

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Parallax and masses ofαCentauri revisited

Pourbaix

Boffin

2016

A&A

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Context. Despite the thorough work of van Leeuwen, the parallax of α Centauri is still far from being carved in stone. Any derivation of the individual masses is therefore uncertain, if not questionable. And yet, that does not prevent this system from being used for calibration purpose in several studies. Aims. We aim for more accurate model-free parallax and individual masses of this system. Methods. With HARPS, the radial velocities are not only precise but also accurate. Ten years of HARPS data are enough to derive the complement of the visual orbit for a full 3D orbit of α Cen. Results. We locate α Cen (743 mas) right where Hipparcos had originally put it, i.e. slightly farther away than derived by Söderhjelm. The components are thus a bit more massive than previously thought (1.13 and 0.97 M for A and B, respectively). These values are now in excellent agreement with the latest asteroseismologic results.

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Section: Resultscontrasting

confidence: 40%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Parallax and masses ofαCentauri revisited

Pourbaix

Boffin

2016

A&A

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“…Consequently, the results from the five pre-main-sequence models, indicated by the circles, stand out as being the worst. In order to circumvent these difficulties, a Söderhjelm (1999), the interferometric observations from Kervella et al (2003) and the orbital parameters from Pourbaix et al (2002). (b) This study.…”

Section: Hd 49385mentioning

confidence: 99%

Estimating stellar mean density through seismic inversions

Reese

Marques

Goupil

et al. 2012

A&A

112

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Context. Determining the mass of stars is crucial both for improving stellar evolution theory and for characterising exoplanetary systems. Asteroseismology offers a promising way for estimating the stellar mean density. When combined with accurate radii determinations, such as are expected from Gaia, this yields accurate stellar masses. The main difficulty is finding the best way to extract the mean density of a star from a set of observed frequencies. Aims. We seek to establish a new method for estimating the stellar mean density, which combines the simplicity of a scaling law while providing the accuracy of an inversion technique. Methods. We provide a framework in which to construct and evaluate kernel-based linear inversions that directly yield the mean density of a star. We then describe three different inversion techniques (SOLA and two scaling laws) and apply them to the Sun, several test cases and three stars, α Cen B, HD 49933 and HD 49385, two of which are observed by CoRoT. Results. The SOLA (subtractive optimally localised averages) approach and the scaling law based on the surface correcting technique described by Kjeldsen et al. (2008, ApJ, 683, L175) yield comparable results that can reach an accuracy of 0.5% and are better than scaling the large frequency separation. The reason for this is that the averaging kernels from the two first methods are comparable in quality and are better than what is obtained with the large frequency separation. It is also shown that scaling the large frequency separation is more sensitive to near-surface effects, but is much less affected by an incorrect mode identification. As a result, one can identify pulsation modes by looking for an and n assignment which provides the best agreement between the results from the large frequency separation and those from one of the two other methods. Non-linear effects are also discussed, as is the effects of mixed modes. In particular, we show that mixed modes bring little improvement to the mean density estimates because of their poorly adapted kernels.

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“…Thus, the difference between the shifts in dwarf and giant stars is expected to be some 0.5 km s −1 , orders of magnitude greater than current measurement precision. These values are significant, both to study the precise dynamics in binaryand multiple-star systems (Griffin 1982;Pourbaix et al 2002), and distinguish the wavelength shifts caused by the stellar atmospheric dynamics of convective motions (e.g., Dravins 1982;Asplund 2005;. Together with photospheric line asymmetries, these intrinsic wavelength shifts represent significant diagnostic tools for probing the three dimensional (3D) structure of stellar atmospheres (Dravins 2008;Nagendra et al 2009), a field where additional diagnostics are needed to reliablydifferentiate between the hydrodynamic models predicting significantly different chemical compositions, oscillation properties, and so on.…”

Section: Gravitational Redshiftmentioning

confidence: 99%

Gravitational redshifts in main-sequence and giant stars

Pasquini

Melo

Chavero

et al. 2011

A&A

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Context. Precise analyses of stellar radial velocities is able to reveal intrinsic causes of the wavelength shifts of spectral lines (other than Doppler shifts due to radial motion), such as gravitational redshifts and convective blueshifts. Aims. Gravitational redshifts in solar-type main-sequence stars are expected to be some 500 m s −1 greater than those in giants. We search for this difference in redshifts among groups of open-cluster stars that share the same average space motion and thus have the same average Doppler shift. Methods. We observed 144 main-sequence stars and cool giants in the M 67 open cluster using the ESO FEROS spectrograph and obtained radial velocities by means of cross-correlation with a spectral template. Binaries and doubtful members were not analyzed, and average spectra were created for different classes of stars. Results. The M 67 dwarf and giant radial-velocity distributions are each well represented by Gaussian functions, which share the same apparent average radial velocity to within 100 m s −1 . In addition, dwarfs in M 67 appear to be dynamically hotter (σ = 0.90 km s −1 ) than giants (σ = 0.68 km s −1 ). Conclusions. We fail to detect any difference in the gravitational redshifts of giants and MS stars. This is probably because of the differential wavelength shifts produced by the different hydrodynamics of dwarf and giant atmospheres. Radial-velocity differences measured between unblended lines in averaged spectra vary with line-strength: stronger lines are more blueshifted in dwarfs than in giants, apparently removing any effect of the gravitational redshift. Synthetic high-resolution spectra are computed from three dimensional (3D) hydrodynamic model atmospheres for both giants and dwarfs, and synthetic wavelength shifts obtained. In agreement with observations, 3D models predict substantially smaller wavelength-shift differences than expected from gravitational redshifts only. The procedures developed could be used to test 3D models for different classes of stars, but will ultimately require high-fidelity spectra for measurements of wavelength shifts in individual spectral lines.

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Constraining the difference in convective blueshift between the components ofαCentauri with precise radial velocities

Cited by 131 publications

References 14 publications

Parallax and masses ofαCentauri revisited

Parallax and masses ofαCentauri revisited

Estimating stellar mean density through seismic inversions

Gravitational redshifts in main-sequence and giant stars

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