Showing papers by "F. Thévenin published in 2004"
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
TL;DR: In this article, the smallest intrinsic dispersions of sigma < 1% on theta_LD are obtained for the relations based on the K and L magnitudes, for instance log theta-LD = 0.5170 - 0.2 L or log thea-LD= 0.0755 - 0.2 K. The results are valid between the spectral types A0 and M2 for dwarf stars (with a possible extension to later types when using the effective temperature).
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 allow to predict the limb darkened angular diameters theta_LD of dwarfs and subgiants using their dereddened Johnson magnitudes, or their effective temperature. The smallest intrinsic dispersions of sigma < 1% on theta_LD are obtained for the relations based on the K and L magnitudes, for instance log theta_LD = 0.0502 (B-L) + 0.5133 - 0.2 L or log theta_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 to estimate the angular size of calibrators for long baseline interferometry from readily available broadband photometry.
420 citations
TL;DR: In this article, the angular diameter of five nearby Vega-like stars, α PsA, β Leo, β Pic, � Eri and τ Cet, was estimated with a 1 to 2% accuracy.
Abstract: We report in this paper the direct interferometric measurement of the angular diameter of five nearby Vega-like stars: α PsA, β Leo, β Pic, � Eri and τ Cet. The near-infrared (K and H bands) observations were conducted at the VLTI during the commissioning period with the VINCI instrument and three different baselines ranging from 66 m to 140 m. The five stellar photospheres are resolved and we derive their angular diameters with a 1 to 2% accuracy, except for β Pic (14%). We discuss the detectability and the influence of a possible small amount of warm circumstellar dust on our measurements. In addition, we have used the stellar evolution code CESAM (Morel 1997) to compare the computed fundamental parameters to the observed values (linear diameter, luminosity, temperature and chemical abundance). As a result of the simulation, the age of the stars is inferred and found to be in good agreement with previous estimates from various other methods.
167 citations
TL;DR: The radial velocity spectrometer (RVS) as discussed by the authors is a 2.0 x 1.6 degree integral field spectrograph, dispersing the light of all sources entering its field of view with a resolving power R = lambda/Deltalambda = 11 500 over the wavelength range [848, 874] nm.
Abstract: The definition and optimization studies for the Gaia satellite spectrograph, the 'radial velocity spectrometer' (RVS), converged in late 2002 with the adoption of the instrument baseline. This paper reviews the characteristics of the selected configuration and presents its expected performance. The RVS is a 2.0 x 1.6 degree integral field spectrograph, dispersing the light of all sources entering its field of view with a resolving power R = lambda/Deltalambda = 11 500 over the wavelength range [848, 874] nm. The RVS will continuously and repeatedly scan the sky during the 5-yr Gaia mission. On average, each source will be observed 102 times over this period. The RVS will collect the spectra of about 100-150 million stars up to magnitude V similar or equal to 17-18. At the end of the mission, the RVS will provide radial velocities with precisions of similar to2 km s(-1) at V = 15 and similar to15-20 km s(-1) at V = 17, for a solar-metallicity G5 dwarf. The RVS will also provide rotational velocities, with precisions (at the end of the mission) for late-type stars of sigma(upsilonsin) similar or equal to (i) similar or equal to 5 km s(-1) at V similar or equal to 15 as well as atmospheric parameters up to V similar or equal to 14-15. The individual abundances of elements such as silicon and magnesium, vital for the understanding of Galactic evolution, will be obtained up to V similar or equal to 12-13. Finally, the presence of the 862.0-nm diffuse interstellar band (DIB) in the RVS wavelength range will make it possible to derive the three-dimensional structure of the interstellar reddening.
91 citations
TL;DR: The Radial Velocity Spectrometer (RVS) as discussed by the authors is a 2.0 by 1.6 degree integral field spectrograph, dispersing the light of all sources entering its field of view with a resolving power R=11 500 over the wavelength range [848, 874] nm.
Abstract: The definition and optimisation studies for the Gaia satellite spectrograph, the Radial Velocity Spectrometer (RVS), converged in late 2002 with the adoption of the instrument baseline. This paper reviews the characteristics of the selected configuration and presents its expected performance. The RVS is a 2.0 by 1.6 degree integral field spectrograph, dispersing the light of all sources entering its field of view with a resolving power R=11 500 over the wavelength range [848, 874] nm. The RVS will continuously and repeatedly scan the sky during the 5 years of the Gaia mission. On average, each source will be observed 102 times over this period. The RVS will collect the spectra of about 100-150 million stars up to magnitude V~17-18. At the end of the mission, the RVS will provide radial velocities with precisions of ~2 km/s at V=15 and \~15-20 km/s at V=17, for a solar metallicity G5 dwarf. The RVS will also provide rotational velocities, with precisions (at the end of the mission) for late type stars of sigma_vsini ~5 km/s at V~15 as well as atmospheric parameters up to V~14-15. The individual abundances of elements such as Silicon and Magnesium, vital for the understanding of Galactic evolution, will be obtained up to V~12-13. Finally, the presence of the 862.0 nm Diffuse Interstellar Band (DIB) in the RVS wavelength range will make it possible to derive the three dimensional structure of the interstellar reddening.
85 citations
TL;DR: In this paper, the angular diameter of Procyon A (aCMiA, F5IV-V) was measured with the VINCI/VLTI instrument with a relative precision of 0.9% using the CESAM code.
Abstract: We report the angular diameter measurement obtained with the VINCI/VLTI instrument on the nearby star Procyon A (aCMiA, F5IV-V), at a relative precision of ′0.9% We obtain a uniform disk angular diameter in the K band of θ U D = 5.376 ′ 0.047 mas and a limb darkened value of θ L D = 5.448 ′ 0.053 mas. Together with the HIPPARCOS parallax, this gives a linear diameter of 2.048 ′ 0.025 D O .. We use this result in combination with spectroscopic, photometric and asteroseismic constraints to model this star with the CESAM code. One set of modeling parameters that reproduces the observations within their error bars are an age of 2314 Myr, an initial helium mass fraction Y i = 0.301 and an initial mass ratio of heavy elements to hydrogen (Z/X) i = 0.0314. We also computed the adiabatic oscillation spectrum of our model of Procyon A, giving a mean large frequency separation of Δv 0 54.7 μHz. This value is in agreement with the seismic observations by Martic et al. (1999, 2001). The interferometric diameter and the asteroseismic large frequency spacing together suggest a mass closer to 1.4 M O . than to 1.5 M O .. We conclude that Procyon is currently ending its life on the main sequence, as its luminosity class indicates.
81 citations
TL;DR: In this paper, the chemical composition of nine UV-bright stars belonging to five Galactic globular clusters of various metallicities was derived based on high resolution spectra obtained with the UV-Visual Echelle Spectrograph (UVES) at VLT-UT2.
Abstract: We have derived the chemical composition of nine UV-bright stars belonging to five Galactic globular clusters of various metallicities ((Fe/H) from −1. 0t o−2.4 dex). The analyses are based on high resolution spectra obtained with the UV-Visual Echelle Spectrograph (UVES) at VLT-UT2. The evolutionary status of the stars is assessed from the chemical anal- ysis and location in the H-R diagram. The star ID7 in NGC 5986 is confirmed as a bona fide post-asymptotic giant branch star (post-AGB) whereas the high- luminosity star ID6 has probably left the AGB before the third dredge-up. ZNG 1 in NGC 6712 shows an overabundance of sodium, oxygen, and silicon similar to overabundances we find in the UV-bright star ID6 in NGC 5986; both stars could be in a post-early-AGB (PEAGB) phase of evolution. The UV-bright star ZNG 7 in NGC 6218 seems to be an AGB star. The stars V-4 and ZNG 5 in NGC 6656 are in a post-horizontal-branch phase of evolution, with V-4 being significantly overabun- dant in heavy elements. The origin of these overabundances is discussed in the context of the evolutionary versus primordial scenario. The three UV-bright stars K 260, K 996 and K 1082 observed in the very metal-deficient globular cluster NGC 7078 are post-horizontal-branch stars, one of them being slightly enriched in s-elements but with a luminosity too low for third dredge-up to have occured. The abundance patterns of K 1082 in NGC 7078 seem to indicate the presence of mild diffusion and a radiative levitation process, already reported in the blue HB stars of M 13 (Behr et al. 1999, ApJ, 517, L135) and NGC 6752 (Moehler et al. 1999, A&A, 339, 537).
25 citations