Accurate stellar rotational velocities using the Fourier transform of the cross correlation maximum

Díaz, Cristóbal González; González, J. F.; Levato, H.; Grosso, M.

doi:10.1051/0004-6361/201016386

Cited by 63 publications

(40 citation statements)

References 35 publications

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“…The obtained secondary spectrum is consistent with a mid-A spectral type, which contributes only 7% to the total light of the system at λ5000. Since most lines in the spectrum of the secondary component are blended, the rotation velocity was determined using the technique developed by Díaz et al (2011). As a result, we obtain v sin i = 42.3 ± 1.5 km s With an orbital period of 6.39 d, the orbital phase difference between the two HARPS observations is 0.41.…”

Section: Results For Individual Targetsmentioning

confidence: 99%

Magnetic fields of HgMn stars

Hubrig

González

Ilyin

et al. 2012

A&A

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Context. The frequent presence of weak magnetic fields on the surface of spotted late-B stars with HgMn peculiarity in binary systems has been controversial during the two last decades. Recent studies of magnetic fields in these stars using the least-squares deconvolution (LSD) technique have failed to detect magnetic fields, indicating an upper limit on the longitudinal field between 8 and 15 G. In these LSD studies, assumptions were made that all spectral lines are identical in shape and can be described by a scaled mean profile. Aims. We re-analyse the available spectropolarimetric material by applying the moment technique on spectral lines of inhomogeneously distributed elements separately. Furthermore, we present new determinations of the mean longitudinal magnetic field for the HgMn star HD 65949 and the hotter analog of HgMn stars, the PGa star HD 19400, using FORS 2 installed at the VLT. We also give new measurements of the eclipsing system AR Aur with a primary star of HgMn peculiarity, which were obtained with the SOFIN spectropolarimeter installed at the Nordic Optical Telescope. Methods. We downloaded from the European Southern Observatory (ESO) archive the publically available HARPS spectra for eight HgMn stars and one normal and one superficially normal B-type star obtained in 2010. Out of this sample, three HgMn stars belong to spectroscopic double-lined systems. The application of the moment technique to the HARPS and SOFIN spectra allowed us to study the presence of the longitudinal magnetic field, the crossover effect, and quadratic magnetic fields. Results for the HgMn star HD 65949 and the PGa star HD 19400 are based on a linear regression analysis of low-resolution spectra obtained with FORS 2 in spectropolarimetric mode. Results. Our measurements of the magnetic field with the moment technique using spectral lines of several elements separately reveal the presence of a weak longitudinal magnetic field, a quadratic magnetic field, and the crossover effect on the surface of several HgMn stars as well as normal and superficially normal B-type stars. Furthermore, our analysis suggests the existence of intriguing correlations between the strength of the magnetic field, abundance anomalies, and binary properties. The results are discussed in the context of possible mechanisms responsible for the development of the element patches and complex magnetic fields on the surface of late B-type stars.

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Section: Results For Individual Targetsmentioning

confidence: 99%

Magnetic fields of HgMn stars

Hubrig

González

Ilyin

et al. 2012

A&A

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“…from Díaz et al (2011) provide accurate measurements of v sin i using FT of the cross-correlation function for 251 A-type stars in the southern hemisphere. Their method is much less sensitive to blends than the individual line measurements made in Paper I, and their v sin i values are 5% higher for v sin i > 150 km s −1 .…”

Section: Merging and Scaling V Sin I Datamentioning

confidence: 99%

Rotational velocities of A-type stars

Zorec

Royer

2012

A&A

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Context. In previous works of this series, we have shown that late B-and early A-type stars have genuine bimodal distributions of rotational velocities and that late A-type stars lack slow rotators. The distributions of the surface angular velocity ratio Ω/Ω crit (Ω crit is the critical angular velocity) have peculiar shapes according to spectral type groups, which can be caused by evolutionary properties. Aims. We aim to review the properties of these rotational velocity distributions in some detail as a function of stellar mass and age. Methods. We have gathered v sin i for a sample of 2014 B6-to F2-type stars. We have determined the masses and ages for these objects with stellar evolution models. The (T eff , log L/L )-parameters were determined from the uvby-β photometry and the HIPPARCOS parallaxes.Results. The velocity distributions show two regimes that depend on the stellar mass. Stars less massive than 2.5 M have a unimodal equatorial velocity distribution and show a monotonical acceleration with age on the main sequence (MS). Stars more massive have a bimodal equatorial velocity distribution. Contrarily to theoretical predictions, the equatorial velocities of stars from about 1.7 M to 3.2 M undergo a strong acceleration in the first third of the MS evolutionary phase, while in the last third of the MS they evolve roughly as if there were no angular momentum redistribution in the external stellar layers. The studied stars might start in the ZAMS not necessarily as rigid rotators, but with a total angular momentum lower than the critical one of rigid rotators. The stars seem to evolve as differential rotators all the way of their MS life span and the variation of the observed rotational velocities proceeds with characteristic time scales δt ≈ 0.2 t MS , where t MS is the time spent by a star in the MS.

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“…We retrieved from the ESO Phase 3 Science Archive a UVES spectrum of Proxima obtained on 24 January 2005 UT08:21 4 (MJD = 53394.348). The mathematical expression of the rotation profile was defined following the formalism of Díaz et al (2011). For the limb darkening, we adopted the linear coefficient u R = 0.8557 derived by Claret et al (2012) for the R band (flux conservation, same model parameters as in Sect.…”

Section: Projected Rotational Velocities Heliocentric Radial Velocitmentioning

confidence: 99%

The red dwarf pair GJ65 AB: inflated, spinning twins of Proxima

Kervella

Mérand

Ledoux

et al. 2016

A&A

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The nearby red dwarf binary GJ65 AB (UV+BL Ceti, M5.5Ve+M6Ve) is a cornerstone system to probe the physics of very low-mass stars. The radii of the two stars are currently known only from indirect photometric estimates, however, and this prevents us from using GJ65 AB as calibrators for the mass-radius (M-R) relation. We present new interferometric measurements of the angular diameters of the two components of GJ65 with the VLTI/PIONIER instrument in the near-infrared H band: θ UD (A) = 0.558 ± 0.008 ± 0.020 mas and θ UD (B) = 0.539 ± 0.009 ± 0.020 mas. They translate into limb-darkened angular diameters of θ LD (A) = 0.573 ± 0.021 mas and θ LD (B) = 0.554 ± 0.022 mas. Based on the known parallax, the linear radii are R(A) = 0.165 ± 0.006 R and R(B) = 0.159 ± 0.006 R (σ(R)/R = 4%). We searched for the signature of flares and faint companions in the interferometric visibilities and closure phases, but we did not identify any significant signal. We also observed GJ65 with the VLT/NACO adaptive optics and refined the orbital parameters and infrared magnitudes of the system. We derived masses for the two components of m(A) = 0.1225 ± 0.0043 M and m(B) = 0.1195 ± 0.0043 M (σ(m)/m = 4%). To derive the radial and rotational velocities of the two stars as well as their relative metallicity with respect to Proxima, we also present new individual UVES high-resolution spectra of the two components. Placing GJ65 A and B in the mass-radius diagram shows that their radii exceed expectations from recent models by 14 ± 4% and 12 ± 4% , respectively. Following previous theories, we propose that this discrepancy is caused by the inhibition of convective energy transport by a strong internal magnetic field generated by dynamo effect in these two fast-rotating stars. A comparison with the almost identical twin Proxima, which is rotating slowly, strengthens this hypothesis because the radius of Proxima does not appear to be inflated compared to models.

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Accurate stellar rotational velocities using the Fourier transform of the cross correlation maximum

Cited by 63 publications

References 35 publications

Magnetic fields of HgMn stars

Magnetic fields of HgMn stars

Rotational velocities of A-type stars

The red dwarf pair GJ65 AB: inflated, spinning twins of Proxima

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