This paper first reviews specific classes of stars which are the outcome of binary evolution, put... more This paper first reviews specific classes of stars which are the outcome of binary evolution, putting emphasis on some recent results, not necessarily related to Gaia research: Algols, blue stragglers, barium stars and related families (barium dwarfs and giants, carbon dwarfs, subgiant CH and giant CH, CEMP-s, S stars without Tc), post-RGB stars, sdB stars, and (asymmetric) planetary nebulae. We then describe some of the assets that Gaia data offer to the binary-star researcher, stressing as well the pitfalls awaiting on the road, using as a specific example the placement of barium stars in the Hertzsprung-Russell diagram. In particular, we evaluate the usefulness of the Gaia DR2 RUWE (‘renormalised unit-weight error’) parameter in the context of identifying astrometric binaries.
The origin of the Li-rich K giants is still highly debated. Here, we investigate the incidence of... more The origin of the Li-rich K giants is still highly debated. Here, we investigate the incidence of binarity among this family from a nine-year radial-velocity monitoring of a sample of 11 Li-rich K giants using the HERMES spectrograph attached to the 1.2 m Mercator Telescope. A sample of 13 non-Li-rich giants (8 of them being surrounded by dust according to IRAS, WISE, and ISO data) was monitored alongside. When compared to the binary frequency in a reference sample of 190 K giants (containing 17.4% of definite spectroscopic binaries – SB – and 6.3% of possible spectroscopic binaries – SB?), the binary frequency appears normal among the Li-rich giants (2/11 definite binaries plus 2 possible binaries, or 18.2% SB + 18.2% SB?), after taking account of the small sample size through the hypergeometric probability distribution. Therefore, there appears to be no causal relationship between Li enrichment and binarity. Moreover, there is no correlation between Li enrichment and the presence ...
Many exciting developments have taken place in the last five years. In most cases, these developm... more Many exciting developments have taken place in the last five years. In most cases, these developments were driven by new instruments, in space or on the ground. Most remarkably, several among these were purely Belgian endeavours, which mark a new step in the history of astrophysics in our country. While there is a lot of activity on instrument design, implementation and exploitation, ultimately strong theoretical modelling forms a vital ingredient to interpret (and occasionally predict) observationally-acquired knowledge. And this modelling often requires extensive computing power. For French-speaking universities, the Consortium des Equipements de Calcul Intensif (CECI: http://hpc.montefiore.ulg.ac.be) offers a recent and powerful alternative to the set-up of many local computing clusters. In Flanders, the Vlaams Supercomputer Centrum (VSC: https://vscentrum.be/nl/en) plays a similar role. However, first and foremost, an efficient exploitation requires manpower and stable working e...
This work makes use of Hipparcos data to test the algorithms of (i) binary detection and (ii) orb... more This work makes use of Hipparcos data to test the algorithms of (i) binary detection and (ii) orbital-parameters determination, which could possibly be used in the GAIA pipeline. The first item is addressed in this paper, whereas the second one is addressed in a companion paper by Pourbaix, Jancart, & Jorissen (2004, this volume). Here we test the ability of the algorithm to detect binaries from scratch, i.e., from the astrometric data without any a priori knowledge of the orbital elements. The Hipparcos Intermediate Astrometric Data of a complete sample of 163 barium stars (supposed to be all members of binary systems from theoretical considerations) are used as a test bench. When \varpi > 5 mas and P < 4000 d, the binary detection rate is close to 100%, but it falls to 22% when considering the whole sample, because many barium stars have small parallaxes or very long periods.
Context. This paper is a follow-up on the vast effort to collect radial velocity data for stars b... more Context. This paper is a follow-up on the vast effort to collect radial velocity data for stars belonging to the Hipparcos survey. Aims. We aim at extending the orbital data available for binaries with M giant primaries. The data presented in this paper will be used in the companion papers of this series to (i) derive the binary frequency among M giants and compare it to that of K giants (Paper II); and (ii) analyse the eccentricity – period diagram and the mass-function distribution (Paper III). Methods. Keplerian solutions are fitted to radial-velocity data. However, for several stars, no satisfactory solution could be found, even though the radial-velocity standard deviation is greater than the instrumental error, because M giants suffer from intrinsic radialvelocity variations due to pulsations. We show that these intrinsic radial-velocity variations can be linked with both the average spectral-line width and the photometric variability. Results. We present an extensive collecti...
Convection plays a major part in many astrophysical processes, including energy transport, pulsat... more Convection plays a major part in many astrophysical processes, including energy transport, pulsation, dynamos and winds on evolved stars, in dust clouds and on brown dwarfs. Most of our knowledge about stellar convection has come from studying the Sun: about two million convective cells with typical sizes of around 2,000 kilometres across are present on the surface of the Sun-a phenomenon known as granulation. But on the surfaces of giant and supergiant stars there should be only a few large (several tens of thousands of times larger than those on the Sun) convective cells, owing to low surface gravity. Deriving the characteristic properties of convection (such as granule size and contrast) for the most evolved giant and supergiant stars is challenging because their photospheres are obscured by dust, which partially masks the convective patterns. These properties can be inferred from geometric model fitting, but this indirect method does not provide information about the physical or...
No analytic formulation is currently available to correctly treat the exchange of mass and angula... more No analytic formulation is currently available to correctly treat the exchange of mass and angular momentum between an AGB star and its low-mass mainsequence companion. The goal of our research is to derive prescriptions for the rates of mass and angular-momentum transfer by wind in long-period binary systems, based on 3D SPH simulations. In this poster, we present the first steps towards a consistent modeling of such mass transfer. A special attention is paid to the physics of mass loss by the giant star. One of the major achievements of our approach is the ability to fully reproduce for the first time in 3D the standard dust-driven wind model developed by Bowen. 1. 3D simulation of a dust-driven pulsating wind We use the N-body SPH code Phantom developed by Daniel Price (Price & Federrath 2010). The wind is modeled by ejecting smooth (geodesic) spheres of gas particles in the SPH simulation. Rotations between two consecutive spheres avoid geometric artifacts. The equations describing dust-driven winds derived by Bowen (1988) have been implemented in the Phantom code. These equations take into account the radiative acceleration and cooling due to the formation of dust, and the stellar pulsation is approximated by a piston. Figure 1 shows the comparison between the 1D simulation of Bowen and our 3D SPH simulation. We consider an AGB Mira-variable star with a pulsation period of 350 days (M∗ = 1.2 M , R∗ = 1.26 au). In this simulation, the wind is launched beyond the dust formation front at r = 4.8 au. The 3D SPH simulations can accurately reproduce the shock features, as well as the amplitudes and spatial variation of the wind velocity, pressure and temperature. 2. Binary system (Mira-like) We simulated the interaction of the dust-driven wind with a binary companion. The system consists of a 1.2+0.6 M binary with an orbital period of 67 years. As shown in Fig. 1, an accretion wake forms (Fig.1 right). A typical spiral structure develops as seen for example in R Sculptoris (Maercker et al. 2012) or AFGL 3068 (Mauron &
This paper first reviews specific classes of stars which are the outcome of binary evolution, put... more This paper first reviews specific classes of stars which are the outcome of binary evolution, putting emphasis on some recent results, not necessarily related to Gaia research: Algols, blue stragglers, barium stars and related families (barium dwarfs and giants, carbon dwarfs, subgiant CH and giant CH, CEMP-s, S stars without Tc), post-RGB stars, sdB stars, and (asymmetric) planetary nebulae. We then describe some of the assets that Gaia data offer to the binary-star researcher, stressing as well the pitfalls awaiting on the road, using as a specific example the placement of barium stars in the Hertzsprung-Russell diagram. In particular, we evaluate the usefulness of the Gaia DR2 RUWE (‘renormalised unit-weight error’) parameter in the context of identifying astrometric binaries.
The origin of the Li-rich K giants is still highly debated. Here, we investigate the incidence of... more The origin of the Li-rich K giants is still highly debated. Here, we investigate the incidence of binarity among this family from a nine-year radial-velocity monitoring of a sample of 11 Li-rich K giants using the HERMES spectrograph attached to the 1.2 m Mercator Telescope. A sample of 13 non-Li-rich giants (8 of them being surrounded by dust according to IRAS, WISE, and ISO data) was monitored alongside. When compared to the binary frequency in a reference sample of 190 K giants (containing 17.4% of definite spectroscopic binaries – SB – and 6.3% of possible spectroscopic binaries – SB?), the binary frequency appears normal among the Li-rich giants (2/11 definite binaries plus 2 possible binaries, or 18.2% SB + 18.2% SB?), after taking account of the small sample size through the hypergeometric probability distribution. Therefore, there appears to be no causal relationship between Li enrichment and binarity. Moreover, there is no correlation between Li enrichment and the presence ...
Many exciting developments have taken place in the last five years. In most cases, these developm... more Many exciting developments have taken place in the last five years. In most cases, these developments were driven by new instruments, in space or on the ground. Most remarkably, several among these were purely Belgian endeavours, which mark a new step in the history of astrophysics in our country. While there is a lot of activity on instrument design, implementation and exploitation, ultimately strong theoretical modelling forms a vital ingredient to interpret (and occasionally predict) observationally-acquired knowledge. And this modelling often requires extensive computing power. For French-speaking universities, the Consortium des Equipements de Calcul Intensif (CECI: http://hpc.montefiore.ulg.ac.be) offers a recent and powerful alternative to the set-up of many local computing clusters. In Flanders, the Vlaams Supercomputer Centrum (VSC: https://vscentrum.be/nl/en) plays a similar role. However, first and foremost, an efficient exploitation requires manpower and stable working e...
This work makes use of Hipparcos data to test the algorithms of (i) binary detection and (ii) orb... more This work makes use of Hipparcos data to test the algorithms of (i) binary detection and (ii) orbital-parameters determination, which could possibly be used in the GAIA pipeline. The first item is addressed in this paper, whereas the second one is addressed in a companion paper by Pourbaix, Jancart, & Jorissen (2004, this volume). Here we test the ability of the algorithm to detect binaries from scratch, i.e., from the astrometric data without any a priori knowledge of the orbital elements. The Hipparcos Intermediate Astrometric Data of a complete sample of 163 barium stars (supposed to be all members of binary systems from theoretical considerations) are used as a test bench. When \varpi > 5 mas and P < 4000 d, the binary detection rate is close to 100%, but it falls to 22% when considering the whole sample, because many barium stars have small parallaxes or very long periods.
Context. This paper is a follow-up on the vast effort to collect radial velocity data for stars b... more Context. This paper is a follow-up on the vast effort to collect radial velocity data for stars belonging to the Hipparcos survey. Aims. We aim at extending the orbital data available for binaries with M giant primaries. The data presented in this paper will be used in the companion papers of this series to (i) derive the binary frequency among M giants and compare it to that of K giants (Paper II); and (ii) analyse the eccentricity – period diagram and the mass-function distribution (Paper III). Methods. Keplerian solutions are fitted to radial-velocity data. However, for several stars, no satisfactory solution could be found, even though the radial-velocity standard deviation is greater than the instrumental error, because M giants suffer from intrinsic radialvelocity variations due to pulsations. We show that these intrinsic radial-velocity variations can be linked with both the average spectral-line width and the photometric variability. Results. We present an extensive collecti...
Convection plays a major part in many astrophysical processes, including energy transport, pulsat... more Convection plays a major part in many astrophysical processes, including energy transport, pulsation, dynamos and winds on evolved stars, in dust clouds and on brown dwarfs. Most of our knowledge about stellar convection has come from studying the Sun: about two million convective cells with typical sizes of around 2,000 kilometres across are present on the surface of the Sun-a phenomenon known as granulation. But on the surfaces of giant and supergiant stars there should be only a few large (several tens of thousands of times larger than those on the Sun) convective cells, owing to low surface gravity. Deriving the characteristic properties of convection (such as granule size and contrast) for the most evolved giant and supergiant stars is challenging because their photospheres are obscured by dust, which partially masks the convective patterns. These properties can be inferred from geometric model fitting, but this indirect method does not provide information about the physical or...
No analytic formulation is currently available to correctly treat the exchange of mass and angula... more No analytic formulation is currently available to correctly treat the exchange of mass and angular momentum between an AGB star and its low-mass mainsequence companion. The goal of our research is to derive prescriptions for the rates of mass and angular-momentum transfer by wind in long-period binary systems, based on 3D SPH simulations. In this poster, we present the first steps towards a consistent modeling of such mass transfer. A special attention is paid to the physics of mass loss by the giant star. One of the major achievements of our approach is the ability to fully reproduce for the first time in 3D the standard dust-driven wind model developed by Bowen. 1. 3D simulation of a dust-driven pulsating wind We use the N-body SPH code Phantom developed by Daniel Price (Price & Federrath 2010). The wind is modeled by ejecting smooth (geodesic) spheres of gas particles in the SPH simulation. Rotations between two consecutive spheres avoid geometric artifacts. The equations describing dust-driven winds derived by Bowen (1988) have been implemented in the Phantom code. These equations take into account the radiative acceleration and cooling due to the formation of dust, and the stellar pulsation is approximated by a piston. Figure 1 shows the comparison between the 1D simulation of Bowen and our 3D SPH simulation. We consider an AGB Mira-variable star with a pulsation period of 350 days (M∗ = 1.2 M , R∗ = 1.26 au). In this simulation, the wind is launched beyond the dust formation front at r = 4.8 au. The 3D SPH simulations can accurately reproduce the shock features, as well as the amplitudes and spatial variation of the wind velocity, pressure and temperature. 2. Binary system (Mira-like) We simulated the interaction of the dust-driven wind with a binary companion. The system consists of a 1.2+0.6 M binary with an orbital period of 67 years. As shown in Fig. 1, an accretion wake forms (Fig.1 right). A typical spiral structure develops as seen for example in R Sculptoris (Maercker et al. 2012) or AFGL 3068 (Mauron &
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Papers by Alain Jorissen