An investigation of the close environment of<i>β</i>Cephei with the VEGA/CHARA interferometer

Nardetto, N.; Mourard, D.; Tallon–Bosc, I.; Tallon, Michel; Bério, Philippe; Chapellier, E.; Bonneau, D.; Chesneau, O.; Mathias, P.; Perraut, K.; Stee, Philippe; Blazit, A.; Clausse, J. M.; Delaa, O.; Marcotto, A.; Millour, F.; Roussel, André; Spang, A.; McAlister, Harold A.; Brummelaar, T. ten; Sturmann, J.; Sturmann, L.; Turner, N.; Farrington, C.; Goldfinger, P. J.

doi:10.1051/0004-6361/201015408

Cited by 8 publications

(4 citation statements)

References 27 publications

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“…The close environment of β Cep was recently investigated with interferometry by Nardetto et al (2011) with a spatial resolution of 1 mas. They concluded that a circular ring (instead of a uniform disk) gives the best fit with a geometry and orientation similar to the magnetic equator, as described above, which is a remarkable result.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

Discovery of the magnetic field in the pulsating B starβCephei

Henrichs

Jong

Verdugo

et al. 2013

A&A

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Context. Although the star itself is not helium enriched, the periodicity and the variability in the UV wind lines of the pulsating B1 IV star β Cephei are similar to what is observed in magnetic helium-peculiar B stars, suggesting that β Cep is magnetic. Aims. We searched for a magnetic field using high-resolution spectropolarimetry. From UV spectroscopy, we analysed the wind variability and investigated the correlation with the magnetic data. Methods. Using 130 time-resolved circular polarisation spectra that were obtained with the MuSiCoS échelle spectropolarimeter at the 2m Telescope Bernard Lyot from 1998, when β Cep was discovered to be magnetic, until 2005, we applied the least-squares deconvolution method on the Stokes V spectra and derived the longitudinal component of the integrated magnetic field over the visible hemisphere of the star. We performed a period analysis on the magnetic data and on equivalent-width measurements of UV wind lines obtained over 17 years. We also analysed the short-and long-term radial velocity variations, which are due to the pulsations and the 90-year binary motion, respectively. Results. β Cep hosts a sinusoidally varying magnetic field with an amplitude 97 ± 4 G and an average value −6 ± 3 G. From the UV wind line variability, we derive a period of 12.00075(11) days, which is the rotation period of the star, and is compatible with the observed magnetic modulation. Phases of maximum and minimum field match those of maximum emission in the UV wind lines, strongly supporting an oblique magnetic-rotator model. We discuss the magnetic behaviour as a function of pulsation behaviour and UV line variability. Conclusions. This paper presents the analysis of the first confirmed detection of a dipolar magnetic field in an upper main-sequence pulsating star. Maximum wind absorption originates in the magnetic equatorial plane. Maximum emission occurs when the magnetic north pole points to the Earth. Radial velocities agree with the ∼90-year orbit around its Be-star binary companion.

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Section: Conclusion and Discussionmentioning

confidence: 99%

Discovery of the magnetic field in the pulsating B starβCephei

Henrichs

Jong

Verdugo

et al. 2013

A&A

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“…Enfin, en étudiant l'environnement de l'étoile prototype des β Céphéides, nous avons découvert à l'aide de l'instrument visible VEGA/CHARA un environnement visible contribuant pour 23 ± 2% du flux. Mais la situation semble a priori différente de celle de δ Cep dans la mesure où un champ magnétique pourrait être responsable du confinement d'un disque en co-rotation autour de l'étoile (Nardetto et al 2011b) (voir l'annexe T).…”

Section: Une Piste De Recherche : La Comparaison Avec Les Autres Type...unclassified

Calibrating the Cepheid period-luminosity relation from the infrared surface brightness technique

Storm

Gieren

Fouqué

et al. 2011

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Aims. We determine period-luminosity relations for Milky Way Cepheids in the optical and near-IR bands. These relations can be used directly as reference for extra-galactic distance determination to Cepheid populations with solar metallicity, and they form the basis for a direct comparison with relations obtained in exactly the same manner for stars in the Magellanic Clouds, presented in an accompanying paper. In that paper we show that the metallicity effect is very small and consistent with a null effect, particularly in the near-IR bands, and we combine here all 111 Cepheids from the Milky Way, the LMC and SMC to form a best relation. Methods. We employ the near-IR surface brightness (IRSB) method to determine direct distances to the individual Cepheids after we have recalibrated the projection factor using the recent parallax measurements to ten Galactic Cepheids and the constraint that Cepheid distances to the LMC should be independent of pulsation period. Results. We confirm our earlier finding that the projection factor for converting radial velocity to pulsational velocity depends quite steeply on pulsation period, p = 1.550− 0.186 log(P) in disagrement with recent theoretical predictions. We find PL relations based on 70 Milky Way fundamental mode Cepheids of M K = −3.33(±0.09)(log(P) − 1.0) − 5.66(±0.03), W VI = −3.26(±0.11)(log(P) − 1.0) − 5.96(±0.04). Combining the 70 Cepheids presented here with the results for 41 Magellanic Cloud Cepheids which are presented in an accompanying paper, we find M K = −3.30(±0.06)(log(P) − 1.0) − 5.65(±0.02), W VI = −3.32(±0.08)(log(P) − 1.0) − 5.92(±0.03). Conclusions. We delineate the Cepheid PL relation using 111 Cepheids with direct distances from the IRSB analysis. The relations are by construction in agreement with the recent HST parallax distances to Cepheids and slopes are in excellent agreement with the slopes of apparent magnitudes versus period observed in the LMC.

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“…It stands at 7σ from the relation. It is a β Cepheid and the photometric contamination by a surrounding environment and/or a close companion is not excluded (Sadsaoud et al 1994;Nardetto et al 2011).…”

Section: A Revised Sbc Relation For Late-and Early-type Starsmentioning

confidence: 99%

Improving the surface brightness-color relation for early-type stars using optical interferometry

Challouf

Nardetto

Mourard

et al. 2014

A&A

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Context. The method of distance determination of eclipsing binaries consists in combining the radii of both components determined from spectro-photometric observations with their respective angular diameters derived from the surface brightness-color relation (SBC). However, the largest limitation of the method comes from the uncertainty on the SBC relation: about 2% for late-type stars (or 0.04 magnitude) and more than 10% for early-type stars (or 0.2 mag). Aims. The aim of this work is to improve the SBC relation for early-type stars in the −1 ≤ V − K ≤ 0 color domain, using optical interferometry. Methods. Observations of eight B-and A-type stars were secured with the VEGA/CHARA instrument in the visible. The derived uniform disk angular diameters were converted into limb darkened angular diameters and included in a larger sample of 24 stars, already observed by interferometry, in order to derive a revised empirical relation for O, B, A spectral type stars with a V − K color index ranging from −1 to 0. We also took the opportunity to check the consistency of the SBC relation up to V − K 4 using 100 additional measurements. Results. We determined the uniform disk angular diameter for the eight following stars: γ Ori, ζ Per, 8 Cyg, ι Her, λ Aql, ζ Peg, γ Lyr, and δ Cyg with V − K color ranging from −0.70 to 0.02 and typical precision of about 1.5%. Using our total sample of 132 stars with V − K colors index ranging from about −1 to 4, we provide a revised SBC relation. For late-type stars (0 ≤ V − K ≤ 4), the results are consistent with previous studies. For early-type stars (−1 ≤ V − K ≤ 0), our new VEGA/CHARA measurements combined with a careful selection of the stars (rejecting stars with environment or stars with a strong variability), allows us to reach an unprecedented precision of about 0.16 magnitude or 7% in terms of angular diameter. Conclusions. We derive for the first time a SBC relation for stars between O9 and A3, which provides a new and reliable tool for the distance scale calibration.

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An investigation of the close environment ofβCephei with the VEGA/CHARA interferometer

Cited by 8 publications

References 27 publications

Discovery of the magnetic field in the pulsating B starβCephei

Discovery of the magnetic field in the pulsating B starβCephei

Calibrating the Cepheid period-luminosity relation from the infrared surface brightness technique

Improving the surface brightness-color relation for early-type stars using optical interferometry

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