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Danuta Sosnowska - One of the best experts on this subject based on the ideXlab platform.
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a multi site campaign to measure solar like oscillations in Procyon i observations data reduction and slow variations
arXiv: Astrophysics, 2008Co-Authors: T Arentoft, P. Eggenberger, T R Bedding, H Kjeldsen, Michaël Bazot, Thomas H. Dall, Christoffer Karoff, Fabien Carrier, Joergen Christensendalsgaard, Danuta SosnowskaAbstract:We have carried out a multi-site campaign to measure oscillations in the F5 star Procyon A. We obtained high-precision velocity observations over more than three weeks with eleven telescopes, with almost continuous coverage for the central ten days. This represents the most extensive campaign so far organized on any solar-type oscillator. We describe in detail the methods we used for processing and combining the data. These involved calculating weights for the velocity time series from the measurement uncertainties and adjusting them in order to minimize the noise level of the combined data. The time series of velocities for Procyon shows the clear signature of oscillations, with a plateau of excess power that is centred at 0.9 mHz and is broader than has been seen for other stars. The mean amplitude of the radial modes is 38.1 +/- 1.3 cm/s (2.0 times solar), which is consistent with previous detections from the ground and by the WIRE spacecraft, and also with the upper limit set by the MOST spacecraft. The variation of the amplitude during the observing campaign allows us to estimate the mode lifetime to be 1.5 d (+1.9/-0.8 d). We also find a slow variation in the radial velocity of Procyon, with good agreement between different telescopes. These variations are remarkably similar to those seen in the Sun, and we interpret them as being due to rotational modulation from active regions on the stellar surface. The variations appear to have a period of about 10 days, which presumably equals the stellar rotation period or, perhaps, half of it. The amount of power in these slow variations indicates that the fractional area of Procyon covered by active regions is slightly higher than for the Sun.
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A Multisite Campaign to Measure Solar-Like Oscillations in Procyon. I. Observations, Data Reduction and Slow Variations
The Astrophysical Journal, 2008Co-Authors: Torben Arentoft, Timothy R. Bedding, Jørgen Christensen-dalsgaard, Hans Kjeldsen, Michaël Bazot, Thomas H. Dall, Christoffer Karoff, Fabien Carrier, Patrick Eggenberger, Danuta SosnowskaAbstract:We have carried out a multisite campaign to measure oscillations in the F5 star Procyon A. We obtained high-precision velocity observations over more than three weeks with 11 telescopes, with almost continuous coverage for the central 10 days. This represents the most extensive campaign so far organized on any solar-type oscillator. We describe in detail the methods we used for processing and combining the data. These involved calculating weights for the velocity time series from the measurement uncertainties and adjusting them in order to minimize the noise level of the combined data. The time series of velocities for Procyon shows the clear signature of oscillations, with a plateau of excess power that is centered at 0.9 mHz and is broader than has been seen for other stars. The mean amplitude of the radial modes is 38:1 AE 1:3 cm s À1 (2.0 times solar), which is consistent with previous detections from the ground and by the WIRE spacecraft, and also with the upper limit set by the MOST spacecraft. The variation of the amplitude during the observing campaign allows us to estimate the mode lifetime to be 1:5 þ1:9 À0:8 days. We also find a slow variation in the radial velocity of Procyon, with good agreement between different telescopes. These variations are remarkably similar to those seen in the Sun, and we interpret them as being due to rotational modulation from active regions on the stellar surface. The variations appear to have a period of about 10 days, which presumably equals the stellar rotation period or, perhaps, half of it. The amount of power in these slow variations indicates that the fractional area of Procyon covered by active regions is slightly higher than for the Sun.
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Asteroseismology: oscillations on the star Procyon.
Nature, 2004Co-Authors: Francois Bouchy, Andre Maeder, Michel Mayor, Denis Megevand, Francesco Pepe, Danuta SosnowskaAbstract:Arising from: J. M. Matthews et al. Nature 430, 51–53 (2004) Stars are spheres of hot gas whose interiors transmit acoustic waves very efficiently. Geologists learn about the interior structure of Earth by monitoring how seismic waves propagate through it and, in a similar way, the interior of a star can be probed using the periodic motions on the surface that arise from such waves. Matthews et al. claim that the star Procyon does not have acoustic surface oscillations of the strength predicted1. However, we show here, using ground-based spectroscopy, that Procyon is oscillating, albeit with an amplitude that is only slightly greater than the noise level observed by Matthews et al. using spaced-based photometry.
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Oscillations on the star Procyon
Nature, 2004Co-Authors: Francois Bouchy, Andre Maeder, Michel Mayor, Denis Megevand, Francesco Pepe, Danuta SosnowskaAbstract:Stars are sphere of hot gas whose interiors transmit acoustic waves very efficiently. Geologists learn about the interior structure of Earth by monitoring how seismic waves propagate through it and, in a similar way, the interior of a star can be probed using the periodic motions on the surface that arise from such waves. Matthews et al. claim that the star Procyon does not have acoustic surface oscillations of the strength predicted. However, we show here, using ground-based spectroscopy, that Procyon is oscillating, albeit with an amplitude that is only slightly greater than the noise level observed by Matthews et al. using spaced-based photometry.
Peter Predehl - One of the best experts on this subject based on the ideXlab platform.
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Helium-like triplet density diagnostics - Applications to CHANDRA-LETGS X-ray observations of Capella and Procyon
Astronomy & Astrophysics, 2001Co-Authors: Jan-uwe Ness, R. Mewe, J. H. M. M. Schmitt, A. J. J. Raassen, D. Porquet, Jelle Kaastra, R. L. J. Van Der Meer, Vadim Burwitz, Peter PredehlAbstract:Electron density diagnostics based on the triplets of helium-like C v ,N vi ,a nd Ovii are applied to the X-ray spectra of Capella and Procyon measured with the Low Energy Transmission Grating Spectrometer (LETGS) on board the Chandra X-ray Observatory. New theoretical models for the calculation of the line ratios between the forbidden (f), intercombination (i), and the resonance (r) lines of the helium-like triplets are used. The (logarithmic) electron densities (in cgs units) derived from the f=i ratios for Capella are < 9:38 cm 3 for O vii (2 upper limit) (f=i =4 :0 0:25), 9:86 0:12 cm 3 for N vi (f=i =1 :78 0:25), and 9:42 0:21 cm 3 for C v (f=i =1 :48 0:34), while for Procyon we obtain 9:28 +0:4 9:28 cm 3 for O vii (f=i =3 :28 0:3), 9:96 0:23 cm 3 for N vi (f=i =1 :33 0:28), and < 8:92 cm 3 for C v (f=i =0 :48 0:12). These densities are quite typical of densities found in the solar active regions, and also pressures and temperatures in Procyon's and Capella's corona at a level of T 10 6 K are quite similar. We nd no evidence for densities as high as measured in solar flares. Comparison of our Capella and Procyon measurements with the Sun shows little dierence in the physical properties of the layers producing the C v ,N vi ,a nd Ovii emission. Assuming the X-ray emitting plasma to be conned in magnetic loops, we obtain typical loop length scales of LCapella 8 LProcyon from the loop scaling laws, implying that the magnetic structures in Procyon and Capella are quite dierent. The total mean surface fluxes emitted in the helium- and hydrogen-like ions are quite similar for Capella and Procyon, but exceed typical solar values by one order of magnitude. We thus conclude that Procyon's and Capella's coronal lling factors are larger than corresponding solar values.
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helium like triplet density diagnostics applications to chandra letgs x ray observations of capella and Procyon
arXiv: Astrophysics, 2000Co-Authors: Jan-uwe Ness, R. Mewe, J. H. M. M. Schmitt, A. J. J. Raassen, D. Porquet, Jelle Kaastra, R. L. J. Van Der Meer, Vadim Burwitz, Peter PredehlAbstract:Electron density diagnostics based on the triplets of Helium-like CV, NVI, and OVII are applied to the X-ray spectra of Capella and Procyon measured with the Low Energy Transmission Grating Spectrometer (LETGS) on board the Chandra X-ray Observatory. New theoretical models for the calculation of the line ratios between the forbidden (f), intercombination (i), and the resonance (r) lines of the helium-like triplets are used. The derived densities are quite typical of densities found in the solar active regions, and also pressures and temperatures in Procyon's and Capella's corona at a level of T=10^6K are quite similar. We find no evidence for densities as high as measured in solar flares. Comparison of our Capella and Procyon measurements with the Sun shows little difference in the physical properties of the layers producing the CV, NVI, and OVII emission. Assuming the X-ray emitting plasma to be confined in magnetic loops, we obtain typical loop length scales of L_Capella > 8 L_Procyon from the loop scaling laws, implying that the magnetic structures in Procyon and Capella are quite different. The total mean surface fluxes emitted in the helium- and hydrogen-like ions are quite similar for Capella and Procyon, but exceed typical solar values by one order of magnitude. We thus conclude that Procyon's and Capella's coronal filling factors are larger than corresponding solar values.
Janine Provost - One of the best experts on this subject based on the ideXlab platform.
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Asteroseismology and evolutionary status of Procyon A
Astronomy & Astrophysics, 2006Co-Authors: Janine Provost, Gabrielle Berthomieu, M. Martic, Pierre MorelAbstract:Models of Procyon A satisfying the actual observational constraints, particularly the asteroseismic ones, are discussed. The oscillations of these models were computed and analysed. We looked for seismic signatures of the evolutionary status of Procyon A. We show that the behavior of the small frequency spacings, particularly allows us to distinguish between main sequence and post-main sequence models, all satisfying the observational constraints on mass, effective temperature, radius, and surface metallicity of Procyon A. We also introduce a new seismic evolution criterion, , based on the comparison of the low and high frequency parts of the power spectrum. The comparison of the seismic properties of the models with the available asteroseismic observations does not allow us to definitely decide on the stage of evolution of Procyon A. Much more accurate frequencies must be obtained especially in the low-frequency domain to distinguish between the models.
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About Procyon modeling
2006Co-Authors: Janine Provost, Gabrielle Berthomieu, M. MartićAbstract:Models of Procyon satisfying the actual observational constraints, particularly the asteroseismic ones, are discussed. It is shown that much more accurate frequencies must be obtained by asteroseismic observations especially in the low frequency domain below 800 μHertz to determine the Procyon evolutionary stage.
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The diameter and evolutionary state of Procyon A
Astronomy & Astrophysics, 2003Co-Authors: Pierre Kervella, Gabrielle Berthomieu, Pierre Morel, Frédéric Thévenin, Pascal Bordé, Janine ProvostAbstract:We report the angular diameter measurement obtained with the VINCI/VLTI instrument on the nearby star Procyon A (alpha CMi A, F5IV-V), at a relative precision of +/- 0.9%. We obtain a uniform disk angular diameter in the K band of UD = 5.376 +/- 0.047 mas and a limb darkened value of LD = 5.448 +/- 0.053 mas. Together with the Hipparcos parallax, this gives a linear diameter of 2.048 +/- 0.025 D_sun. 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 Delta nu_0 = 54.7 microHz. 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_sun than to 1.5 M_sun. We conclude that Procyon is currently ending its life on the main sequence, as its luminosity class indicates.
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Modeling of Alpha Cen and Procyon using VLTI observations
arXiv: Astrophysics, 2003Co-Authors: Pierre Kervella, Janine Provost, Gabrielle Berthomieu, Pierre Morel, Frédéric Thévenin, Pascal Bordé, Damien SégransanAbstract:We present a novel approach to model the nearby stars Alpha Cen A & B and Procyon A using asteroseismic and interferometric constraints. Using the VINCI instrument installed at the VLT Interferometer (VLTI), the angular diameters of the Alpha Centauri system were measured with a relative precision of 0.2% and 0.6%, respectively. From these values, we derive linear radii of R[A] = 1.224 +/- 0.003 R_sun and R[B] = 0.863 +/- 0.005 R_sun. These radii are in excellent agreement with the models of Thevenin et al. (2002), that use asteroseismic frequencies as constraints (Bouchy & Carrier 2001; Bouchy & Carrier 2002). With the same instrument, we also measured the angular diameter of Procyon A. Using the Hipparcos parallax, we obtain a linear radius of 2.048 +/- 0.025 R_sun. We use this result together with spectroscopic and photometric constraints to model this star with the CESAM code. We also computed the adiabatic oscillation spectrum of our model of Procyon A, giving a mean large frequency separation of Delta nu_0 = 54.8 uHz, in agreement with the seismic observations by Martic et al. (2001). Our model favours a mass around 1.4 M_sun for Procyon A.
Pierre Kervella - One of the best experts on this subject based on the ideXlab platform.
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Three-dimensional interferometric, spectrometric, and planetary views of Procyon
Astronomy & Astrophysics, 2012Co-Authors: Andrea Chiavassa, Pierre Kervella, L. Bigot, Alexis Matter, Bruno Lopez, Remo Collet, Zazralt Magic, Martin AsplundAbstract:We used a new realistic 3D radiative-hydrodynamical model atmosphere of Procyon generated with the Stagger Code and synthetic spectra computed with the radiative transfer code Optim3D to re-analyze interferometric and spectroscopic data from the optical to the infrared of Procyon. We compute intensity maps in two optical filters centered at 500 and 800 nm (MARK III) and one infrared filter centered at 2200 nm (VINCI). We constructed stellar disk images accounting for the center-to-limb variations and used them to derive visibility amplitudes and closure phases. We provide 3D limb-darkening coefficients in the optical as well as in the infrared. We show that visibility curves and closure phases show clear deviations from circular symmetry from the 3rd lobe on. These deviations are detectable with current interferometers using closure phases. We derive new angular diameters at different wavelengths with two independent methods based on 3D simulations. We find a diameter_Vinci = 5.390 \pm 0.03 mas that this is confirmed by an independent asteroseismic estimation. The resulting Teff is 6591 K, which is consistent with the infrared flux method determinations. We find also a value of the surface gravity log g = 4.01 \pm 0.03 that is larger by 0.05 dex from literature values. Spectrophotometric comparisons with observations provide very good agreement with the spectral energy distribution and photometric colors, allowing us to conclude that the thermal gradient of the simulation matches fairly well Procyon. Finally, we show that the granulation pattern of a planet hosting Procyon-like star has a non-negligible impact on the detection of hot Jupiters in the infrared using interferometry closure phases. It is then crucial to have a comprehensive knowledge of the host star to directly detect and characterize hot Jupiters. In this respect, RHD simulations are very important to reach this aim.
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Modeling ofCen and Procyon using VLTI observations
2008Co-Authors: Pierre Kervella, Gabrielle BerthomieuAbstract:We present a novel approach to model the nearby starsCen A & B and Procyon A using asteroseismic and interferometric constraints. Using the VINCI instrument installed at the VLT Interferometer (VLTI), the angular diameters of theCentauri system were measured with a relative precision of 0.2% and 0.6%, respectively. From these values, we derive linear radii of R(A) = 1.224±0.003R⊙ and R(B) = 0.863 ± 0.005R⊙. These radii are in excellent agreement with the models of Thevenin et al. (2002), that use asteroseismic frequencies as constraints (Bouchy & Carrier 2001; Bouchy & Carrier 2002). With the same instrument, we also measured the angular diameter of Procyon A. Using the Hipparcos parallax, we obtain a linear radius of 2.048 ± 0.025R⊙. We use this result together with spectroscopic and photometric constraints to model this star with the CESAM code. We also computed the adiabatic oscillation spectrum of our model of Procyon A, giving a mean large frequency separation of ��0 = 54.8µHz, in agreement with the seismic observations by Martic et al. (2001). Our model favours a mass around 1.4M⊙ for
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The diameter and evolutionary state of Procyon A
Astronomy & Astrophysics, 2003Co-Authors: Pierre Kervella, Gabrielle Berthomieu, Pierre Morel, Frédéric Thévenin, Pascal Bordé, Janine ProvostAbstract:We report the angular diameter measurement obtained with the VINCI/VLTI instrument on the nearby star Procyon A (alpha CMi A, F5IV-V), at a relative precision of +/- 0.9%. We obtain a uniform disk angular diameter in the K band of UD = 5.376 +/- 0.047 mas and a limb darkened value of LD = 5.448 +/- 0.053 mas. Together with the Hipparcos parallax, this gives a linear diameter of 2.048 +/- 0.025 D_sun. 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 Delta nu_0 = 54.7 microHz. 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_sun than to 1.5 M_sun. We conclude that Procyon is currently ending its life on the main sequence, as its luminosity class indicates.
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Modeling of Alpha Cen and Procyon using VLTI observations
arXiv: Astrophysics, 2003Co-Authors: Pierre Kervella, Janine Provost, Gabrielle Berthomieu, Pierre Morel, Frédéric Thévenin, Pascal Bordé, Damien SégransanAbstract:We present a novel approach to model the nearby stars Alpha Cen A & B and Procyon A using asteroseismic and interferometric constraints. Using the VINCI instrument installed at the VLT Interferometer (VLTI), the angular diameters of the Alpha Centauri system were measured with a relative precision of 0.2% and 0.6%, respectively. From these values, we derive linear radii of R[A] = 1.224 +/- 0.003 R_sun and R[B] = 0.863 +/- 0.005 R_sun. These radii are in excellent agreement with the models of Thevenin et al. (2002), that use asteroseismic frequencies as constraints (Bouchy & Carrier 2001; Bouchy & Carrier 2002). With the same instrument, we also measured the angular diameter of Procyon A. Using the Hipparcos parallax, we obtain a linear radius of 2.048 +/- 0.025 R_sun. We use this result together with spectroscopic and photometric constraints to model this star with the CESAM code. We also computed the adiabatic oscillation spectrum of our model of Procyon A, giving a mean large frequency separation of Delta nu_0 = 54.8 uHz, in agreement with the seismic observations by Martic et al. (2001). Our model favours a mass around 1.4 M_sun for Procyon A.
Pierre Demarque - One of the best experts on this subject based on the ideXlab platform.
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Hubble Space Telescope Astrometry of the Procyon System
The Astrophysical Journal, 2015Co-Authors: Howard E Bond, Pierre Demarque, Ronald L Gilliland, Gail H Schaefer, T M Girard, J B Holberg, D H Gudehus, Brian D Mason, Vera Kozhurina-platais, M R BurleighAbstract:Abstract : The nearby star Procyon is a visual binary containing the F5 IV-V subgiant Procyon A, orbited in a 40.84-year period by the faint DQZ white dwarf (WD) Procyon B. Using images obtained over two decades with the Hubble Space Telescope, and historical measurements back to the 19th century, we have determined precise orbital elements. Combined with measurements of the parallax and the motion of the A component, these elements yield dynamical masses of 1.478 plus or minus 0.012M and 0.592 plus or minus 0.006M for A and B, respectively. The mass of Procyon A agrees well with theoretical predictions based on asteroseismology and its temperature and luminosity. Use of a standard core-overshoot model agrees best for a surprisingly high amount of core overshoot. Under these modeling assumptions, Procyon A's age is approximately 2.7 Gyr. Procyon B's location in the H-R diagram is in excellent agreement with theoretical cooling tracks for WDs of its dynamical mass. Its position in the mass-radius plane is also consistent with theory, assuming a carbon-oxygen core and a helium-dominated atmosphere. Its progenitor's mass was 1.9-2.2M, depending on its amount of core overshoot. Several astrophysical puzzles remain. In the progenitor system, the stars at periastron were separated by only approximately AU, which might have led to tidal interactions and even mass transfer; yet there is no direct evidence that these have occurred. Moreover the orbital eccentricity has remained high (approximately 0.40). The mass of Procyon B is somewhat lower than anticipated from the initial-to-final-mass relation seen in open clusters. The presence of heavy elements in its atmosphere requires ongoing accretion, but the place of origin is uncertain.
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hubble space telescope astrometry of the Procyon system
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: Howard E Bond, Pierre Demarque, Ronald L Gilliland, Gail H Schaefer, T M Girard, J B Holberg, D H Gudehus, Brian D Mason, V Kozhurinaplatais, M R BurleighAbstract:The nearby star Procyon is a visual binary containing the F5 IV-V subgiant Procyon A, orbited in a 40.84 yr period by the faint DQZ white dwarf Procyon B. Using images obtained over two decades with the Hubble Space Telescope, and historical measurements back to the 19th century, we have determined precise orbital elements. Combined with measurements of the parallax and the motion of the A component, these elements yield dynamical masses of 1.478 +/- 0.012 Msun and 0.592 +/- 0.006 Msun for A and B, respectively. The mass of Procyon A agrees well with theoretical predictions based on asteroseismology and its temperature and luminosity. Use of a standard core-overshoot model agrees best for a surprisingly high amount of core overshoot. Under these modeling assumptions, Procyon A's age is ~2.7 Gyr. Procyon B's location in the H-R diagram is in excellent agreement with theoretical cooling tracks for white dwarfs of its dynamical mass. Its position in the mass-radius plane is also consistent with theory, assuming a carbon-oxygen core and a helium-dominated atmosphere. Its progenitor's mass was 1.9-2.2 Msun, depending on its amount of core overshoot. Several astrophysical puzzles remain. In the progenitor system, the stars at periastron were separated by only ~5 AU, which might have led to tidal interactions and even mass transfer; yet there is no direct evidence that these have occurred. Moreover the orbital eccentricity has remained high (~0.40). The mass of Procyon B is somewhat lower than anticipated from the initial-to-final-mass relation seen in open clusters. The presence of heavy elements in its atmosphere requires ongoing accretion, but the place of origin is uncertain.
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modeling convective core overshoot and diffusion in Procyon constrained by asteroseismic data
arXiv: Solar and Stellar Astrophysics, 2014Co-Authors: D. B. Guenther, Pierre Demarque, M GruberbauerAbstract:We compare evolved stellar models, which match Procyons mass and position in the HR diagram, to current ground-based asteroseismic observations. Diffusion of helium and metals along with two conventional core overshoot descriptions and the Kuhfuss nonlocal theory of convection are considered. We establish that one of the two published asteroseismic data reductions for Procyon, which mainly differ in their identification of even versus odd l-values, is a significantly more probable and self-consistent match to our models than the other. The most probable models according to our Bayesian analysis have evolved to just short of turnoff, still retaining a hydrogen convective core. Our most probable models include Y and Z diffusion and have conventional core overshoot between 0.9 and 1.5 pressure scale heights, which increases the outer radius of the convective core by between 22% to 28%, respectively. We discuss the significance of this comparatively higher than expected core overshoot amount in terms of internal mixing during evolution. The parameters of our most probable models are similar regardless of whether adiabatic or nonadiabatic model p-mode frequencies are compared to the observations, although, the Bayesian probabilities are greater when the nonadiabatic model frequencies are used. All the most probable models (with or without core overshoot, adiabatic or nonadiabatic model frequencies, diffusion or no diffusion, including priors for the observed HRD location and mass or not) have masses that are within one sigma of the observed mass 1.497+/-0.037 Msun.
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Comparing convection in the Sun with Procyon A
Proceedings of the International Astronomical Union, 2006Co-Authors: Frank Robinson, Pierre DemarqueAbstract:AbstractAs well as reproducing observable features like solar granulation, 3D simulations can provide useful information for local or non-local stellar modeling. Examples include testing out the mixing length theory in the surface layers, providing the turbulent correction for stellar models ofp-mode frequencies, testing eddy viscocity prescriptions used in tidal dissipation models and comparing different closures of higher order moments. Having validated the 3D code with the sun we applied it to other stars. For Procyon A the turbulence is about twice as strong as it is in the Sun (estimated by the peak root mean square vertical velocity which is about 6.5 km/s) and the granules are nearly an order of magnitude larger, with plumes regularly extending down 2-3 pressure scale heights below the surface of Procyon A. An interesting feature of the Procyon simulation is that the horizontal layers in the vicinity of the granules appear to radially pulsate in a quasi-periodic manner. This makes the superadiabatic layer move in and out over a distance of about half a pressure scale height in a time of about 20-30 minutes. This motion appears to be tied to the granulation but there may be other phenomena involved such as some kind of local kappa-mechanism confined to the granulation surface layers. We find similar behaviour in a simulation of an 11 Gyr subgiant sun. As the velocities are more like the sun (about 3km/s), the time period of the pulsation in the subgiant is 2-3 times longer than in Procyon A.
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Simulating the outer layers of Procyon A: a comparison with the Sun
Monthly Notices of the Royal Astronomical Society, 2005Co-Authors: Frank Robinson, Pierre Demarque, David B. Guenther, Yong Cheol Kim, Kwing L. ChanAbstract:We compare a new 3D radiative hydrodynamical simulation of the surface layers of Procyon A to a similar 3D simulation of the surface layers of the Sun. Both simulations include realistic input physics and are performed using the same numerical techniques and computer codes. Convection in the surface layers of Procyon A is very different from the Sun. Compared with the Sun, the atmospheric structure and convective flow in Procyon A exhibit the following characteristics. (i)The highly superadiabatic transition layer (SAL) is located at a much shallower optical depth; it is in a dynamically active region and its outer region is sometimes located in the optically thin atmosphere. (ii)The outer region of the SAL moves from an optically thin region to a thick region and back again over a time of 20‐30 min. This motion, which is driven by the granulation, takes place in a time approximately half the turnover time of the largest granules. (iii)The peak rms velocity in the vertical direction is much larger in Procyon A. The main reason for the radically different radiative‐convective behaviour in Procyon A compared with the Sun is the role played by turbulent eddies in determining the overall flow/thermal structure. The turbulent pressure and turbulent kinetic energy can exceed 50 per cent of the local gas pressure (compared with about 10‐20 per cent in the Sun). In such regions, the mixing lengthy theory is a poor approximation. The Procyon A simulation thus reveals two distinct time-scales: the autocorrelation time of the vertical velocity and the characteristic time-scale of the SAL, which is tied to granulation. Just below the surface, the autocorrelation decay time is about 5 min in Procyon A and the SAL motion time-scale is 20‐30 min. In the simulations, the peak value of the superadiabaticity varies between 0.5 and 3. When the SAL penetrates the optically thin region, there are efficient radiative losses and the peak of the SAL is low. We speculate that these losses damp out the relative amplitudes in luminosity (temperature fluctuations) compared with velocity (Doppler). Although this will not affect the frequencies of the peaks in the power spectrum, it will probably lower the average amplitude of the peaks relative to the noise background.
