arXiv subjects

F. Carrier

Publications and source records attributed to F. Carrier.

49 records · Page 3Linked to original sources

arXiv2005

Solar-like oscillations in the F9 V beta Virginis

This paper presents the analysis of Doppler p-modes of the F9 V star beta Virginis obtained with the spectrograph CORALIE in March 2003. Eleven nights of observations have made it possible to collect 1293 radial velocity measurements with a standard deviation of about 2.2 m s^-1. The power spectrum of the high precision velocity time series clearly presents several identifiable peaks between 0.7 and 2.4 mHz showing regularity with a large and small spacings of Delta_nu = 72.1 uHz and delta_nu_02 = 6.3 uHz respectively. Thirty-one individual modes have been identified with amplitudes in the range 23 to 46 cm s^-1, i.e. with a signal to noise between 3 and 6.

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arXiv2005

Models of Procyon A including seismic constraints

Detailed models of Procyon A based on new asteroseismic measurements by Eggenberger et al (2004) have been computed using the Geneva evolution code including shellular rotation and atomic diffusion. By combining all non-asteroseismic observables now available for Procyon A with these seismological data, we find that the observed mean large spacing of 55.5 +- 0.5 uHz favours a mass of 1.497 M_sol for Procyon A. We also determine the following global parameters of Procyon A: an age of t=1.72 +- 0.30 Gyr, an initial helium mass fraction Y_i=0.290 +- 0.010, a nearly solar initial metallicity (Z/X)_i=0.0234 +- 0.0015 and a mixing-length parameter alpha=1.75 +- 0.40. Moreover, we show that the effects of rotation on the inner structure of the star may be revealed by asteroseismic observations if frequencies can be determined with a high precision. Existing seismological data of Procyon A are unfortunately not accurate enough to really test these differences in the input physics of our models.

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arXiv2005

Solar-like oscillations in Procyon A

The F5 subgiant Procyon A (alpha CMi, HR 2943) was observed with the Coralie fiber-fed echelle spectrograph on the 1.2-m Swiss telescope at La Silla in February 1999. The resulting 908 high-accuracy radial velocities exhibit a mean noise level in the amplitude spectrum of 0.11 m s^-1 at high frequency. These measurements show significant excess in the power spectrum between 0.6-1.6 mHz with 0.60 m s^-1 peak amplitude. An average large spacing of 55.5 uHz has been determined and twenty-three individual frequencies have been identified.

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arXiv2005

New seismological results on the G0 IV eta Bootis

Several attempts have been made to detect solar-like oscillations in the G0 IV star eta Boo. We present here new observations on this star simultaneously conducted with two spectrographs: Coralie mounted on the 1.2-m Swiss telescope at the ESO La Silla Observatory (Chile) and Elodie based on the 1.93-m telescope at the Observatoire de Haute Provence (France). In total, 1239 spectra were collected over 13 nights. The power spectrum of the high precision velocity time series clearly presents several identifiable peaks between 0.4 and 1.0 mHz showing regularity with a large and small separations of Delta_nu = 39.9 uHz and delta_nu02 = 3.95 uHz respectively. Twenty-two individual frequencies have been identified. Detailed models based on these measurements and non-asteroseismic observables were computed using the Geneva evolution code including shellular rotation and atomic diffusion. By combining these seismological data with non-asteroseismic observations, we determine the following global parameters for eta Boo: a mass of 1.57 +- 0.07 M_sol, an age t=2.67 +- 0.10 Gyr and an initial metallicity Z/X_i=0.0391 +- 0.0070. We also show that the mass of eta Boo is very sensitive to the choice of the observed metallicity, while the age of eta Boo depends on the input physics used. Indeed, a higher metallicity favours a higher mass, while non-rotating models without overshooting predict a smaller age.

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arXiv2004

Analysis of alpha Centauri AB including seismic constraints

Detailed models of alpha Cen A and B based on new seismological data for alpha Cen B by Carrier & Bourban (2003) have been computed using the Geneva evolution code including atomic diffusion. Taking into account the numerous observational constraints now available for the alpha Cen system, we find a stellar model which is in good agreement with the astrometric, photometric, spectroscopic and asteroseismic data. The global parameters of the alpha Cen system are now firmly constrained to an age of t=6.52+-0.30 Gyr, an initial helium mass fraction Y_i=0.275+-0.010 and an initial metallicity (Z/X)_i=0.0434+-0.0020. Thanks to these numerous observational constraints, we confirm that the mixing-length parameter alpha of the B component is larger than the one of the A component, as already suggested by many authors (Noels et al. 1991, Fernandes & Neuforge 1995 and Guenther & Demarque 2000): alpha_B is about 8% larger than alpha_A (alpha_A=1.83+-0.10 and alpha_B=1.97+-0.10). Moreover, we show that asteroseismic measurements enable to determine the radii of both stars with a very high precision (errors smaller than 0.3%). The radii deduced from seismological data are compatible with the new interferometric results of Kervella et al. (2003) even if they are slightly larger than the interferometric radii (differences smaller than 1%).

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arXiv2004

Simulating stochastically excited oscillations. The mode lifetime of xi Hya

The discovery of solar-like oscillations in the giant star xy Hya (G7III) was reported by Frandsen et al. (2002). Their frequency analysis was very limited due to alias problems in the data set (caused by single-site observations). The extent to which the aliasing affected their analysis was unclear due to the unknown damping time of the stellar oscillation modes. In this paper we describe a simulator created to generate time series of stochastically excited oscillations, which takes as input an arbitrary window function and includes both white and non-white noise. We also outline a new method to compare a large number of simulated time series with an observed time series to determine the damping time, amplitude, and limited information on the degree of the stochastically excited modes. For xi Hya we find the most likely amplitude to be ~ 2 m/s, in good agreement with theory (Houdek & Gough, 2002), and the most likely damping time to be ~ 2 days, which is much shorter than the theoretical value of 15-20 days calculated by Houdek & Gough (2002).

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arXiv2002

Detection of Solar-like Oscillations in the G7 Giant Star xi Hya

We report the firm discovery of solar-like oscillations in a giant star. We monitored the star xi Hya (G7III) continuously during one month with the CORALIE spectrograph attached to the 1.2m Swiss Euler telescope. The 433 high-precision radial-velocity measurements clearly reveal multiple oscillation frequencies in the range 50 - 130 uHz, corresponding to periods between 2.0 and 5.5 hours. The amplitudes of the strongest modes are slightly smaller than 2 m/s. Current model calculations are compatible with the detected modes.

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arXiv2002

Multiplicity among chemically peculiar stars II. Cool magnetic Ap stars

We present new orbits for sixteen Ap spectroscopic binaries, four of which might in fact be Am stars, and give their orbital elements. Four of them are SB2 systems: HD 5550, HD 22128, HD 56495 and HD 98088. The twelve other stars are : HD 9996, HD 12288, HD 40711, HD 54908, HD 65339, HD 73709, HD 105680, HD 138426, HD 184471, HD 188854, HD 200405 and HD 216533. Rough estimates of the individual masses of the components of HD 65339 (53 Cam) are given, combining our radial velocities with the results of speckle interferometry and with Hipparcos parallaxes. Considering the mass functions of 74 spectroscopic binaries from this work and from the literature, we conclude that the distribution of the mass ratio is the same for cool Ap stars as for normal G dwarfs. Therefore, the only differences between binaries with normal stars and those hosting an Ap star lie in the period distribution: except for the case of HD 200405, all orbital periods are longer than (or equal to) 3 days. A consequence of this peculiar distribution is a deficit of null eccentricities. There is no indication that the secondary has a special nature, like e.g. a white dwarf.

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arXiv2002

Asteroseismology and calibration of alpha Cen binary system

Using the oscillation frequencies of alpha Cen A recently discovered by Bouchy & Carrier, the available astrometric, photometric and spectroscopic data, we tried to improve the calibration of the visual binary system alpha Cen. With the revisited masses of Pourbaix et al. (2002) we do not succeed to obtain a solution satisfying all the seismic observational constraints. Relaxing the constraints on the masses, we have found an age t_alpha Cen=4850+-500 Myr, an initial helium mass fraction Y_i = 0.300+-0.008, and an initial metallicity (Z/X)_i=0.0459+-0.0019, with M_A=1.100+-0.006M_o and M_B=0.907+-0.006M_o for alpha Cen A&B.

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arXiv2002

The acoustic spectrum of alpha Cen A

This paper presents the analysis of Doppler p-mode observations of the G2V star $α$ Cen A obtained with the spectrograph CORALIE in May 2001. Thirteen nights of observations have made it possible to collect 1850 radial velocity measurements with a standard deviation of about 1.5 m s$^{-1}$. Twenty-eight oscillation modes have been identified in the power spectrum between 1.8 and 2.9 mHz with amplitudes in the range 12 to 44 cm s$^{-1}$. The average large and small spacing are respectively equal to 105.5 and 5.6 $μ$Hz. A comparison with stellar models of $α$ Cen A is presented.

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arXiv2002

Solar-Like Oscillations in beta Hydri: Evidence for Short-Lived High-Amplitude Oscillations

Velocity measurements of the G2 subgiant beta Hyi with both UCLES and CORALIE show a clear excess of power centred at 1.0 mHz. In the UCLES data we find evidence for a short-lived, high-amplitude oscillation event. If confirmed as a feature of subgiants, such `starquakes' would make it harder to measure accurate mode frequencies and perform asteroseismology.

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arXiv1998

Binaries among Ap and Am stars

The results of long-term surveys of radial velocities of cool Ap and Am stars are presented. There are two samples, one of about 100 Ap stars and the other of 86 Am stars. Both have been observed with the CORAVEL scanner from Observatoire de Haute-Provence (CNRS), France. The conspicuous lack of short-period binaries among cool Ap stars seems confirmed, although this may be the result of an observational bias; one system has a period as short as 1.6 days. A dozen new orbits could be determined, including that of one SB2 system. Considering the mass functions of 68 binaries from the literature and from our work, we conclude that the distribution of the mass ratios is the same for the Bp-Ap stars than for normal G dwarfs. Among the Am stars, we found 52 binaries, i.e. 60%; an orbit could be computed for 29 of them. Among these 29, there are 7 SB2 systems, one triple and one quadruple system. The 21 stars with an apparently constant radial velocity may show up later as long-period binaries with a high eccentricity. The mass functions of the SB1 systems are compatible with cool main-sequence companions, also suggested by ongoing spectral observations.

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arXiv1997

Multiplicity among peculiar A stars I. The Ap stars HD 8441 and HD 137909, and the Am stars HD 43478 and HD 96391

We present the first results of a radial-velocity survey of cool Ap and Am stars. HD 8441 is not only a double system with P = 106.357 days, but is a triple one, the third companion having an orbital period larger than 5000 days. Improved orbital elements are given for the classical Ap star HD 137909 = beta CrB by combining our radial velocities with published ones. We yield new orbital elements of the two Am, SB2 binaries HD 43478 and HD 96391. Good estimates of the individual masses of the components of HD 43478 can be given thanks to the eclipses of this system, for which an approximate photometric solution is also proposed.

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