Altair's inclination from line profile analysis

Reiners, A.; Royer, F.

doi:10.1051/0004-6361:20041315

Cited by 21 publications

(25 citation statements)

References 14 publications

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“…Other slightly different mass estimates exist since determining the mass of a single star, particularly a rapid rotator, is not a simple task, but the main results of this work do not critically depend on this value. We adopted the projected equatorial velocity v eq sin i = 227 km s −1 determined by Reiners & Royer (2004) from high spectral resolution observations. Their value is compatible with other recent measurements of v eq sin i within their error bars (e.g.…”

Section: Results From the χ 2 Analysismentioning

confidence: 99%

“…One important characteristic of Altair is its fast rotation. Spectroscopic and interferometric observations indicate a v eq sin i value between 190 km s −1 and 250 km s −1 (Abt & Morrell 1995;van Belle et al 2001;Royer et al 2002; among others); most recently Reiners & Royer (2004) determined v eq sin i = 227 ± 11 km s −1 from spectroscopy.…”

Section: Introductionmentioning

confidence: 93%

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Gravitational-darkening of Altair from interferometry

Souza¹,

Kervella

Jankov

et al. 2005

A&A

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Interferometric observations have revealed that the rapid rotator Altair is a flattened star with a non-centrally symmetric intensity distribution. In this work we perform for the first time a physically consistent analysis of all interferometric data available so far, corresponding to three different interferometers operating in several spectral bands. These observations include new data (squared visibilities in the H and K bands from VLTI-VINCI) as well as previously published data (squared visibilities in the K band from PTI and squared visibilities, triple amplitudes, and closure phases in the visible between 520 nm and 850 nm from NPOI). To analyze these data we perform a χ 2 minimization using an interferometry-oriented model for fast rotators, which includes Roche approximation, limb-darkening, and von Zeipel-like gravity-darkening. Thanks to the rich interferometric data set available and to this physical model, the main uniqueness problems were avoided. As a result, we show that the observations can only be explained if Altair has a gravity-darkening compatible with the expected value for hot stars, i.e., the von Zeipel effect (T eff ∝ g 0.25 ).

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Section: Results From the χ 2 Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 93%

Gravitational-darkening of Altair from interferometry

Souza¹,

Kervella

Jankov

et al. 2005

A&A

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“…Several interferometric and spectroscopic observations indicate a V eq sin i value between 190 km s −1 and 250 km s −1 (Abt & Morrell 1995;van Belle et al 2001;Royer et al 2002;Reiners & Royer 2004b, among others). Domiciano de Souza et al (2005) used the interferometer VINCI/VLTI and a model for fast rotators, including Roche approximation, limb-darkening, and von Zeipel gravity-darkening, to find the same value of V eq sin i = 227 km s −1 as in Reiners & Royer (2004a), who used spectroscopy for determine the constraints on Altairs inclination angle and differential rotation from the global rotational broadening profile derived from about 650 spectral absorption lines. Most recently, Monnier et al (2007) have reconstructed an image of the surface of Altair from CHARA observations, inferring several fundamental parameters: inclination, position angle, effective temperature, and radii of the pole and of the equator.…”

Section: The Sample Starsmentioning

confidence: 99%

Beyond the diffraction limit of optical/IR interferometers

Hadjara

Souza

Vakili

et al. 2014

A&A

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Context. As previously demonstrated on Achernar, one can derive the angular radius, rotational velocity, axis tilt, and orientation of a fast-rotating star from the differential phases obtained by spectrally resolved long baseline interferometry using earth-rotation synthesis.Aims. We applied this method on a small sample of stars for different spectral types and classes, in order to generalize the technique to other rotating stars across the H-R diagram and determine their fundamental parameters. Methods. We used differential phase data from the AMBER/VLTI instrument obtained prior to refurbishing its spectrometer in 2010. With the exception of Fomalhaut, which has been observed in the medium-resolution mode of AMBER (λ/δλ ≈ 1500), our three other targets, Achernar, Altair, and δ Aquilae offered high-resolution (λ/δλ ≈ 12 000) spectro-interferometric data around the Brγ absorption line in K band. These data were used to constrain the input parameters of an analytical, still realistic model to interpret the observations with a systematic approach for the error budget analysis in order to robustly conclude on the physics of our 4 targets. We applied the super resolution provided by differential phases φ diff to measure the size (equatorial radius R eq and angular diameter / eq ), the equatorial rotation velocity (V eq ), the inclination angle (i), and the rotation axis position angle (PA rot ) of 4 fast-rotating stars: Achernar, Altair, δ Aquilae, and Fomalhaut. The stellar parameters of the targets were constrained using a semi-analytical algorithm dedicated to fast rotators SCIROCCO. Results. The derived parameters for each star were R eq = 11.2 ± 0.5 R , V eq sin i = 290 ± 17 km s −1 , PA rot = 35.4• ± 1.4• , for Achernar; R eq = 2.0 ± 0.2 R , V eq sin i = 226 ± 34 km s −1 , PA rot = −65.5 • ± 5.5• , for Altair; R eq = 2.2 ± 0.3 R , V eq sin i = 74 ± 35 km s −1 , PA rot = −101.2• ± 14 • , for δ Aquilae; and R eq = 1.8 ± 0.2 R , V eq sin i = 93 ± 16 km s −1 , PA rot = 65.6 • ± 5 • , for Fomalhaut. They were found to be compatible with previously published values from differential phase and visibility measurements, while we were able to determine, for the first time, the inclination angle i of Fomalhaut (i = 90• ± 9 • ) and δ Aquilae (i = 81 • ± 13 • ), and the rotation-axis position angle PA rot of δ Aquilae. Conclusions. Beyond the theoretical diffraction limit of an interferometer (ratio of the wavelength to the baseline), spatial super resolution is well suited to systematically estimating the angular diameters of rotating stars and their fundamental parameters with a few sets of baselines and the Earth-rotation synthesis provided a high enough spectral resolution.

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“…However, the Mg ii line is actually a narrow blend, typically resulting in an overestimation of the v eq sin i by 10 km s −1 at these rotation velocities, and raising the q 2 /q 1 value appreciably. We checked if we could improve the shape of the rotational kernel by taking more lines into account (e.g., as was done in Reiners & Royer 2004a), but this was not case: there are far too few lines, and the continuum estimation for these few lines is not reliable enough.…”

Section: Fundamental Parametersmentioning

confidence: 99%

CoRoT’s view on variable B8/9 stars: spots versus pulsations

Degroote

Acke

Samadi

et al. 2011

A&A

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Context. There exist few variability studies of stars in the region in the Hertzsprung-Russell diagram between the A and B-star pulsational instability strips. With the aid of the high precision continuous measurements of the CoRoT space satellite, low amplitudes are more easily detected, making a study of this neglected region worthwhile. Aims. We collected a small sample of B stars observed by CoRoT to determine the origin of the different types of variability observed. Methods. We combine literature photometry and spectroscopy to measure the fundamental parameters of the stars in the sample, and compare asteroseismic modelling of the light curves with (differentially rotating) spotted star models. Results. We found strong evidence for the existence of spots and differential rotation in HD 174648, and formulated hypotheses for their origin. We show that the distinction between pulsations and rotational modulation is difficult to make solely based on the light curve, especially in slowly rotating stars.

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Altair's inclination from line profile analysis

Cited by 21 publications

References 14 publications

Gravitational-darkening of Altair from interferometry

Gravitational-darkening of Altair from interferometry

Beyond the diffraction limit of optical/IR interferometers

CoRoT’s view on variable B8/9 stars: spots versus pulsations

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