The diameters of $\alpha$ Centauri A and B - A comparison of the asteroseismic and VINCI/VLTI views
TL;DR: In this paper, the first direct angular diameter measurements were obtained on the closest stellar neighbor, Centauri, by using the VINCI instrument installed at ESO's VLT Interferometer (VLTI).
Abstract: We compare the first direct angular diameter measurements obtained on our closest stellar neighbour, Centauri, to recent model diameters constrained by asteroseismic observations. Using the VINCI instrument installed at ESO's VLT Interferometer (VLTI), the angular diameters of the two main components of the system, Cen A and B, were measured with a relative precision of 0.2% and 0.6% respectively. Particular care has been taken in the calibration of these measurements, considering that VINCI is estimating the fringe visibility using a broadband K filter. We obtain uniform disk angular diameters for Cen A and B ofUD(A) = 8:314 0:016 mas andUD(B) = 5:856 0:027 mas, and limb darkened angular diameters ofLD(A)= 8:511 0:020 mas andLD(B)= 6:001 0:034 mas. Combining these values with the parallax from Soderhjelm (1999), we derive linear diameters of D(A)= 1:224 0:003 D and D(B)= 0:863 0:005 D. These values are compatible with the masses published by Thevenin et al. (2002) for both stars.
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TL;DR: In this article, the authors presented a catalog of stellar properties for 1040 nearby F, G, and K stars that have been observed by the Keck, Lick, and AAT planet search programs.
Abstract: We present a uniform catalog of stellar properties for 1040 nearby F, G, and K stars that have been observed by the Keck, Lick, and AAT planet search programs. Fitting observed echelle spectra with synthetic spectra yielded effective temperature, surface gravity, metallicity, projected rotational velocity, and abundances of the elements Na, Si, Ti, Fe, and Ni, for every star in the catalog. Combining V-band photometry and Hipparcos parallaxes with a bolometric correction based on the spectroscopic results yielded stellar luminosity, radius, and mass. Interpolating Yonsei-Yale isochrones to the luminosity, effective temperature, metallicity, and α-element enhancement of each star yielded a theoretical mass, radius, gravity, and age range for most stars in the catalog. Automated tools provide uniform results and make analysis of such a large sample practical. Our analysis method differs from traditional abundance analyses in that we fit the observed spectrum directly, rather than trying to match equivalent widths, and we determine effective temperature and surface gravity from the spectrum itself, rather than adopting values based on measured photometry or parallax. As part of our analysis, we determined a new relationship between macroturbulence and effective temperature on the main sequence. Detailed error analysis revealed small systematic offsets with respect to the Sun and spurious abundance trends as a function of effective temperature that would be inobvious in smaller samples. We attempted to remove these errors by applying empirical corrections, achieving a precision per spectrum of 44 K in effective temperature, 0.03 dex in metallicity, 0.06 dex in the logarithm of gravity, and 0.5 km s-1 in projected rotational velocity. Comparisons with previous studies show only small discrepancies. Our spectroscopically determined masses have a median fractional precision of 15%, but they are systematically 10% higher than masses obtained by interpolating isochrones. Our spectroscopic radii have a median fractional precision of 3%. Our ages from isochrones have a precision that varies dramatically with location in the Hertzsprung-Russell diagram. We plan to extend the catalog by applying our automated analysis technique to other large stellar samples.
1,571 citations
TL;DR: In this paper, the authors present a critical compilation of accurate, fundamental determinations of stellar masses and radii, including stellar luminosity, effective temperature, metal abundance, and apsidal motion determinations.
Abstract: This article presents and discusses a critical compilation of accurate, fundamental determinations of stellar masses and radii. We have identified 95 detached binary systems containing 190 stars (94 eclipsing systems, and α Centauri) that satisfy our criterion that the mass and radius of both stars be known within errors of ±3% accuracy or better. All of them are non-interacting systems, and so the stars should have evolved as if they were single. This sample more than doubles that of the earlier similar review by Andersen (Astron Astrophys Rev 3:91–126, 1991), extends the mass range at both ends and, for the first time, includes an extragalactic binary. In every case, we have examined the original data and recomputed the stellar parameters with a consistent set of assumptions and physical constants. To these we add interstellar reddening, effective temperature, metal abundance, rotational velocity and apsidal motion determinations when available, and we compute a number of other physical parameters, notably luminosity and distance. These accurate physical parameters reveal the effects of stellar evolution with unprecedented clarity, and we discuss the use of the data in observational tests of stellar evolution models in some detail. Earlier findings of significant structural differences between moderately fast-rotating, mildly active stars and single stars, ascribed to the presence of strong magnetic and spot activity, are confirmed beyond doubt. We also show how the best data can be used to test prescriptions for the subtle interplay between convection, diffusion, and other non-classical effects in stellar models. The amount and quality of the data also allow us to analyse the tidal evolution of the systems in considerable depth, testing prescriptions of rotational synchronisation and orbital circularisation in greater detail than possible before. We show that the formulae for pseudo-synchronisation of stars in eccentric orbits predict the observed rotations quite well, except for very young and/or widely separated stars. Deviations do occur, however, especially for stars with convective envelopes. The superior data set finally demonstrates that apsidal motion rates as predicted from General Relativity plus tidal theory are in good agreement with the best observational data. No reliable binary data exist, which challenge General Relativity to any significant extent. The new data also enable us to derive empirical calibrations of M and R for single (post-) main-sequence stars above $${0.6\,M_{\odot}}$$
. Simple, polynomial functions of T
eff, log g and [Fe/H] yield M and R within errors of 6 and 3%, respectively. Excellent agreement is found with independent determinations for host stars of transiting extrasolar planets, and good agreement with determinations of M and R from stellar models as constrained by trigonometric parallaxes and spectroscopic values of T
eff and [Fe/H]. Finally, we list a set of 23 interferometric binaries with masses known to be better than 3%, but without fundamental radius determinations (except α Aur). We discuss the prospects for improving these and other stellar parameters in the near future.
1,350 citations
TL;DR: In this article, the smallest intrinsic dispersions of σ ≤ 1% in θ LD are obtained for the surface brightness relations of these stars using exclusively direct angular diameter measurements.
Abstract: The availability of a number of new interferometric measurements of Main Sequence and subgiant stars makes it possible to calibrate the surface brightness relations of these stars using exclusively direct angular diameter measurements. These empirical laws make it possible to predict the limb darkened angular diameters θ LD of dwarfs and subgiants using their dereddened Johnson magnitudes, or their effective temperature. The smallest intrinsic dispersions of σ ≤ 1% in θ LD are obtained for the relations based on the K and L magnitudes, for instance log θ LD = 0.0502 (B - L) + 0.5133 - 0.2 L or log θ LD = 0.0755 (V - K) + 0.5170 - 0.2 K. Our calibrations are valid between the spectral types A0 and M2 for dwarf stars (with a possible extension to later types when using the effective temperature), and between A0 and K0 for subgiants. Such relations are particularly useful for estimating the angular sizes of calibrators for long-baseline interferometry from readily available broadband photometry.
488 citations
Cites methods from "The diameters of $\alpha$ Centauri ..."
...In addition, it is foreseen that shorter wavelengths will be implemented on the VLTI than the K band currently accessible with VINCI....
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...Over the past two years, sixteen new angular diameter measurements of nearby Main Sequence and subgiant stars were obtained with the VLT Interferometer (Glindemann et al. 2000, 2003a,b) equipped with the fiber-based beam combiner VINCI (Kervella et al. 2000, 2003a)....
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...As a remark, the agreement between the VLTI/VINCI results and the Mk III is remarkable, with no systematic deviation detectable at a level of a few tenths of a percent....
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...Instrument N ∆ZMLDB(B − K) ∆ZMLDV (V − K) ∆ZMLDB(B − L) ∆ZMLDV (V − L) PTI 5 +0.48 ± 0.89% +0.82 ± 0.94% +0.63 ± 0.89% +0.89 ± 0.93% NII 5 +1.02 ± 1.42% +1.03 ± 1.46% +1.03 ± 1.58% +1.02 ± 1.63% Mk III 11 −0.11 ± 0.56% −0.12 ± 0.57% −0.06 ± 0.64% −0.11 ± 0.66% NPOI 5 −1.20 ± 1.20% −1.23 ± 1.24% −1.23 ± 1.24% −1.39 ± 1.53% VLTI/VINCI 16 −0.05 ± 0.49% −0.07 ± 0.51% −0.07 ± 0.51% −0.11 ± 0.68% the observed fringe contrast is used to estimate the instrumental transfer function (also called system visibility)....
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...As demonstrated by the VINCI observations of the nearby Be star αEri (Domiciano de Souza et al. 2003), the photosphere of these objects can be deformed by their fast rotation....
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TL;DR: The detection of an Earth-mass planet orbiting the authors' neighbour star α Centauri B, a member of the closest stellar system to the Sun, is reported.
Abstract: Exoplanets down to the size of Earth have been found, but not in the habitable zone—that is, at a distance from the parent star at which water, if present, would be liquid. There are planets in the habitable zone of stars cooler than our Sun, but for reasons such as tidal locking and strong stellar activity, they are unlikely to harbour water–carbon life as we know it. The detection of a habitable Earth-mass planet orbiting a star similar to our Sun is extremely difficult, because such a signal is overwhelmed by stellar perturbations. Here we report the detection of an Earth-mass planet orbiting our neighbour star α Centauri B, a member of the closest stellar system to the Sun. The planet has an orbital period of 3.236 days and is about 0.04 astronomical units from the star (one astronomical unit is the Earth–Sun distance). The detection of an Earth-mass planet orbiting our neighbour star α Centauri B is reported; the planet has an orbital period of 3.236 days and is about 0.04 astronomical units from the star. An exoplanet with an Earth-like mass has been discovered orbiting the nearby star α Centauri B. The planet is not in the habitable zone — it is much nearer to its star than we are to the Sun, orbiting at only about 0.04 astronomical units from its star (an astronomical unit is the mean distance between Earth and the Sun). Statistical studies suggest that low-mass planets form preferentially in multi-planet systems, so it is possible that other planets are orbiting α Centauri B, perhaps in its habitable zone.
466 citations
TL;DR: In this paper, the authors search the Hubble Space Telescope (HST) archive for previously unanalyzed observations of stellar H I Lyα emission lines, their primary purpose being to look for new detections of Lyα absorption from the outer heliosphere and to also search for analogous absorption of the astrospheres surrounding the observed stars.
Abstract: We search the Hubble Space Telescope (HST) archive for previously unanalyzed observations of stellar H I Lyα emission lines, our primary purpose being to look for new detections of Lyα absorption from the outer heliosphere and to also search for analogous absorption from the astrospheres surrounding the observed stars. The astrospheric absorption is of particular interest because it can be used to study solar-like stellar winds that are otherwise undetectable. We find and analyze 33 HST Lyα spectra in the archive. All the spectra were taken with the E140M grating of the Space Telescope Imaging Spectrograph (STIS) instrument on board HST. The HST STIS spectra yield four new detections of heliospheric absorption (70 Oph, ξ Boo, 61 Vir, and HD 165185) and seven new detections of astrospheric absorption (EV Lac, 70 Oph, ξ Boo, 61 Vir, δ Eri, HD 128987, and DK UMa), doubling the previous number of heliospheric and astrospheric detections. When combined with previous results, 10 of 17 lines of sight within 10 pc yield detections of astrospheric absorption. This high detection fraction implies that most of the ISM within 10 pc must be at least partially neutral, since the presence of H I within the ISM surrounding the observed star is necessary for an astrospheric detection. In contrast, the detection percentage is only 9.7% (3 out of 31) for stars beyond 10 pc. Our Lyα analyses provide measurements of ISM H I and D I column densities for all 33 lines of sight, and we discuss some implications of these results. Finally, we measure chromospheric Lyα fluxes from the observed stars. We use these fluxes to determine how Lyα flux correlates with coronal X-ray and chromospheric Mg II emission, and we also study how Lyα emission depends on stellar rotation.
290 citations
References
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TL;DR: Wavelet transforms are recent mathematical techniques, based on group theory and square integrable representations, which allows one to unfold a signal, or a field, into both space and scale, and possibly directions.
Abstract: Wavelet transforms are recent mathematical techniques, based on group theory and square integrable representations, which allows one to unfold a signal, or a field, into both space and scale, and possibly directions. They use analyzing functions, called wavelets, which are localized in space. The scale decomposition is obtained by dilating or contracting the chosen analyzing wavelet before convolving it with the signal. The limited spatial support of wavelets is important because then the behavior of the signal at infinity does not play any role. Therefore the wavelet analysis or syn thesis can be performed locally on the signal, as opposed to the Fourier transform which is inherently nonlocal due to the space-filling nature of the trigonometric functions. Wavelet transforms have been applied mostly to signal processing, image coding, and numerical analysis, and they are still evolving. So far there are only two complete presentations of this topic, both written in French, one for engineers (Gasquet & Witomski 1 990) and the other for mathematicians (Meyer 1 990a), and two conference proceedings, the first in English (Combes et al 1 989), the second in French (Lemarie 1 990a). In preparation are a textbook (Holschneider 199 1 ), a course (Dau bee hies 1 99 1), three conference procecdings (Mcyer & Paul 199 1 , Beylkin et al 199 1b, Farge et al 1 99 1), and a special issue of IEEE Transactions
2,770 citations
"The diameters of $\alpha$ Centauri ..." refers methods in this paper
...We implemented in this code a time-frequency analysis (Ségransan et al. 1999) based on the continuous wavelet transform (Farge 1992)....
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TL;DR: In this article, the authors start from six absolutely calibrated continuous stellar spectra from 1.2 to 35?m for K0, K1.5, K3, K5, and M0 giants, and normalize each template by photometry for the individual stars using published and/or newly secured near and mid-infrared photometry obtained through fully characterized, absolutely calibrated, combinations of filter passband, detector radiance response, and mean terrestrial atmospheric transmission.
Abstract: We start from our six absolutely calibrated continuous stellar spectra from 1.2 to 35 ?m for K0, K1.5, K3, K5, and M0 giants. These were constructed as far as possible from actual observed spectral fragments taken from the ground, the Kuiper Airborne Observatory, and the IRAS Low Resolution Spectrometer, and all have a common calibration pedigree. From these we spawn 422 calibrated spectral templates for stars with spectral types in the ranges G9.5?K3.5 III and K4.5?M0.5 III. We normalize each template by photometry for the individual stars using published and/or newly secured near- and mid-infrared photometry obtained through fully characterized, absolutely calibrated, combinations of filter passband, detector radiance response, and mean terrestrial atmospheric transmission. These templates continue our ongoing effort to provide an all-sky network of absolutely calibrated, spectrally continuous, stellar standards for general infrared usage, all with a common, traceable calibration heritage. The wavelength coverage is ideal for calibration of many existing and proposed ground-based, airborne, and satellite sensors, particularly low- to moderate-resolution spectrometers. We analyze the statistics of probable uncertainties, in the normalization of these templates to actual photometry, that quantify the confidence with which we can assert that these templates truly represent the individual stars. Each calibrated template provides an angular diameter for that star. These radiometric angular diameters compare very favorably with those directly observed across the range from 1.6 to 21 mas.
585 citations
"The diameters of $\alpha$ Centauri ..." refers background or methods in this paper
...This calibrator was chosen for its stability and brightness in the list of standard stars compiled by Cohen et al. (1999) and verified by Fig....
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...Parameters of the primary (θ Cen) and secondary (58 Hya) calibrators. θCen 58 Hya HD 123139 HD 130694 mV 2.06 4.42 mK −0.10 1.13 Spectral type K0IIIb K4III Teff (K)a 4980 4040 Measurementλ (µm) 2.181 2.181 logg a 2.75 1.85 θLD (mas)b 5.46± 0.058 3.22± 0.035 θUD (mas)c 5.33± 0.057 3.12± 0.034 MeasuredθUD (mas) 5.305± 0.020 a Teff and logg from Cayrel de Strobel et al. (1997). b Catalogue value from Cohen et al. (1999). c Linear limb darkening from Claret (2000). of the interferometric efficiency....
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...…logg a 2.75 1.85 θLD (mas)b 5.46± 0.058 3.22± 0.035 θUD (mas)c 5.33± 0.057 3.12± 0.034 MeasuredθUD (mas) 5.305± 0.020 a Teff and logg from Cayrel de Strobel et al. (1997). b Catalogue value from Cohen et al. (1999). c Linear limb darkening from Claret (2000). of the interferometric efficiency....
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...Unfortunately, the typical 1% precision of the Cohen et al. (1999) catalogue on the angular diameters, though very good in itself, is not sufficient due to the large size of this star and the correspondingly low visibility on the 66 meters baseline....
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...The VINCI/VLTI angular diameter found for this star agrees very well with the Cohen et al. (1999) value, while reducing significantly its uncertainty....
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Journal Article•
TL;DR: The Hipparcos Catalogue as mentioned in this paper is a materialisation of the ICRS reference system, coinciding with its principal axes at the level of ±0.6 mas, and with proper motions consistent with an inertial system at thelevel of ± 0.25 mas/yr.
Abstract: The principal observational characteristics of the Hipparcos Catalogue, and a summary of its main astrometric and photometric properties, are presented. Median astrometric standard errors (in position, parallax, and annual proper motion) are in the range 0.7-0.9 milliarcsec (mas) for stars brighter than 9 mag at the catalogue epoch (J1991.25). The catalogue is a materialisation of the ICRS reference system, coinciding with its principal axes at the level of ±0.6 mas, and with proper motions consistent with an inertial system at the level of ±0.25 mas/yr. The 118 218 constituent stars provide a mean sky density of ∼ 3 stars deg ―2 . The catalogue is available in printed and machine-readable forms.
450 citations
TL;DR: CESAM as mentioned in this paper is a consistent set of programs and routines which perform calculations of 1D quasi-static stellar evolution including diffusion and rotation, which allows stable and robust calculations and the exact restitution of the solution not only at grid points.
Abstract: The code CESAM is a consistent set of programs and routines which performs calculations of 1D quasi-static stellar evolution including diffusion and rotation. The principal new feature is the solution of the quasi-static equilibrium by collocation method based on piecewise polynomials approximations projected on their B-spline basis; that allows stable and robust calculations and the exact restitution of the solution not only at grid points. Another advantage is the monitoring by only one parameter of the accuracy and its improvement by superconvergence. An automatic mesh refinement has been designed for adjusting the localizations of grid points according to the changes of unknowns, each limit between a radiative and a convective zones being shifted to the closest grid point. For standard models, the evolution of the chemical composition is solved by stiffly stable schemes of orders up to four; for non-standard models the solution of the diffusion equation employs the Petrov-Galerkin scheme, with the mixing of chemicals in convective zones performed by strong turbulent diffusion. A precise restoration of the atmosphere is allowed for. CESAM computes evolution of stars from the pre-main sequence to the beginning of the 4 He burning cycle. In this paper a detailed description of the algorithms is presented.
398 citations
"The diameters of $\alpha$ Centauri ..." refers methods in this paper
...This calibration was based on stellar evolution models computed using the CESAM code (Morel 1997)....
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TL;DR: The Catalogue of [Fe/H] determinations as discussed by the authors contains 5946 determinations for 3247 stars, including 751 stars in 84 associations, clusters or galaxies, including field stars, stars in galactic associations and clusters, and stars in SMC, LMC, M33.
Abstract: A fifth Edition of the Catalogue of [Fe/H] determinations is presented herewith. It contains 5946 determinations for 3247 stars, including 751 stars in 84 associations, clusters or galaxies. The literature is complete up to December 1995. The 700 bibliographical references correspond to [Fe/H] determinations obtained from high resolution spectroscopic observations and detailed analyses, most of them carried out with the help of model-atmospheres. The Catalogue is made up of three formatted files: File 1: field stars, File 2: stars in galactic associations and clusters, and stars in SMC, LMC, M33, File 3: numbered list of bibliographical references.
222 citations