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Pierre F. L. Maxted - One of the best experts on this subject based on the ideXlab platform.
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the catalogue of radial Velocity Variable hot subluminous stars from the muchfuss project
Astronomy and Astrophysics, 2015Co-Authors: S. Geier, U. Heber, Thomas Kupfer, V. Schaffenroth, Brad N. Barlow, Roy Ostensen, E. Ziegerer, C. Heuser, S J Otoole, Pierre F. L. MaxtedAbstract:The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims to find sdBs with compact companions like massive white dwarfs, neutron stars or black holes. Here we provide classifications, atmospher ic parameters and a complete radial Velocity (RV) catalogue containing 1914 single measurements for an sample of 177 hot subluminous stars discovered based on SDSS DR7. 110 stars show significant RV va riability, while 67 qualify as candidates. We constrain the fraction of close massive compact companions of hydrogen-rich hot subdwarfs in our sample to be smaller than ∼ 1.3%, which is already close to the theoretical predictions. However, the sample might still contain such binaries with longer periods exceeding∼ 8 d. We detect a
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The catalogue of radial Velocity Variable hot subluminous stars from the MUCHFUSS project
Astronomy & Astrophysics, 2015Co-Authors: S. Geier, Thomas Kupfer, V. Schaffenroth, Ulrich Heber, Brad N. Barlow, R. H. O Stensen, Simon J. O'toole, E. Ziegerer, C. Heuser, Pierre F. L. MaxtedAbstract:The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims to find sdBs with compact companions like massive white dwarfs, neutron stars or black holes. Here we provide classifications, atmospheric parameters and a complete radial Velocity (RV) catalogue containing 1914 single measurements for an sample of 177 hot subluminous stars discovered based on SDSS DR7. 110 stars show significant RV variability, while 67 qualify as candidates. We constrain the fraction of close massive compact companions {of hydrogen-rich hot subdwarfs} in our sample to be smaller than $\sim1.3\%$, which is already close to the theoretical predictions. However, the sample might still contain such binaries with longer periods exceeding $\sim8\,{\rm d}$. We detect a mismatch between the $\Delta RV_{\rm max}$-distribution of the sdB and the more evolved sdOB and sdO stars, which challenges our understanding of their evolutionary connection. Furthermore, irregular RV variations of unknown origin with amplitudes of up to $\sim180\,{\rm km\,s^{-1}}$ on timescales of years, days and even hours have been detected in some He-sdO stars. They might be connected to irregular photometric variations in some cases.
S. Geier - One of the best experts on this subject based on the ideXlab platform.
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radial Velocity Variable hot post agb stars from the muchfuss project classification atmospheric parameters formation scenarios
Astronomy and Astrophysics, 2016Co-Authors: N. Reindl, S. Geier, U. Heber, Thomas Kupfer, V. Schaffenroth, Brad N. Barlow, S Bloemen, Roy OstensenAbstract:In the course of the MUCHFUSS project we recently discovered four radial Velocity (RV) Variable, hot (T_(eff)≈ 80 000−110 000 K) post-asymptotic giant branch (AGB) stars. Among them, we found the first known RV Variable O(He) star, the only second known RV Variable PG 1159 close binary candidate, as well as the first two naked (i.e., without planetary nebula (PN)) H-rich post-AGB stars of spectral type O(H) that show significant RV variations. We present a non-LTE spectral analysis of these stars along with one further O(H)-type star whose RV variations were found to be not significant. We also report the discovery of a far-infrared excess in the case of the PG 1159 star. None of the stars in our sample displays nebular emission lines, which can be explained well in terms of a very late thermal pulse evolution in the case of the PG 1159 star. The “missing” PNe around the O(H)-type stars seems strange, since we find that several central stars of PNe have much longer post-AGB times. Besides the non-ejection of a PN, the occurrence of a late thermal pulse, or the re-accretion of the PN in the previous post-AGB evolution offer possible explanations for those stars not harbouring a PN (anymore). In the case of the O(He) star J0757, we speculate that it might have been previously part of a compact He transferring binary system. In this scenario, the mass transfer must have stopped after a certain time, leaving behind a low-mass close companion that may be responsible for the extreme RV shift of 107.0 ± 22.0 km s^(-1) that was measured within only 31 min.
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Discovery of radial Velocity Variable post-AGB stars from the MUCHFUSS project
EAS Publications Series, 2015Co-Authors: N. Reindl, S. Geier, Thomas Kupfer, V. Schaffenroth, Ulrich Heber, Brad N. Barlow, Roy OstensenAbstract:In the course of the MUCHFUSS project we have discovered five radial Velocity (RV) post-AGB stars. Among them, we found the first known RV Variable O(He) star, the only second known RV Variable PG 1159 close binary candidate and three RV Variable, H-rich post-AGB stars of O(H)-type.
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the catalogue of radial Velocity Variable hot subluminous stars from the muchfuss project
Astronomy and Astrophysics, 2015Co-Authors: S. Geier, U. Heber, Thomas Kupfer, V. Schaffenroth, Brad N. Barlow, Roy Ostensen, E. Ziegerer, C. Heuser, S J Otoole, Pierre F. L. MaxtedAbstract:The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims to find sdBs with compact companions like massive white dwarfs, neutron stars or black holes. Here we provide classifications, atmospher ic parameters and a complete radial Velocity (RV) catalogue containing 1914 single measurements for an sample of 177 hot subluminous stars discovered based on SDSS DR7. 110 stars show significant RV va riability, while 67 qualify as candidates. We constrain the fraction of close massive compact companions of hydrogen-rich hot subdwarfs in our sample to be smaller than ∼ 1.3%, which is already close to the theoretical predictions. However, the sample might still contain such binaries with longer periods exceeding∼ 8 d. We detect a
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The catalogue of radial Velocity Variable hot subluminous stars from the MUCHFUSS project
Astronomy & Astrophysics, 2015Co-Authors: S. Geier, Thomas Kupfer, V. Schaffenroth, Ulrich Heber, Brad N. Barlow, R. H. O Stensen, Simon J. O'toole, E. Ziegerer, C. Heuser, Pierre F. L. MaxtedAbstract:The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims to find sdBs with compact companions like massive white dwarfs, neutron stars or black holes. Here we provide classifications, atmospheric parameters and a complete radial Velocity (RV) catalogue containing 1914 single measurements for an sample of 177 hot subluminous stars discovered based on SDSS DR7. 110 stars show significant RV variability, while 67 qualify as candidates. We constrain the fraction of close massive compact companions {of hydrogen-rich hot subdwarfs} in our sample to be smaller than $\sim1.3\%$, which is already close to the theoretical predictions. However, the sample might still contain such binaries with longer periods exceeding $\sim8\,{\rm d}$. We detect a mismatch between the $\Delta RV_{\rm max}$-distribution of the sdB and the more evolved sdOB and sdO stars, which challenges our understanding of their evolutionary connection. Furthermore, irregular RV variations of unknown origin with amplitudes of up to $\sim180\,{\rm km\,s^{-1}}$ on timescales of years, days and even hours have been detected in some He-sdO stars. They might be connected to irregular photometric variations in some cases.
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Radial Velocity Variable sdO/Bs from SPY - Preliminary Orbits of Three New Short Period Binaries
arXiv: Astrophysics, 2008Co-Authors: S. Geier, U. Heber, Ralf NapiwotzkiAbstract:We present new results from follow-up time-resolved spectroscopy of radial Velocity Variable hot subdwarfs from the SPY project. Medium resolution spectra were taken at the ESO NTT. Preliminary orbital solutions are presented for three single-lined sdO/B binaries. The orbital periods of all binaries are short and the companions are most likely white dwarfs or late main-sequence stars. Follow-up time-resolved spectroscopy is necessary to measure the orbital parameters with higher accuracy. Light curves should be taken in order to search for reflection effects and or eclipses.
Laurent Desvillettes - One of the best experts on this subject based on the ideXlab platform.
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on the trend to global equilibrium in spatially inhomogeneous entropy dissipating systems the linear fokker planck equation
Communications on Pure and Applied Mathematics, 2001Co-Authors: Laurent Desvillettes, Cedric VillaniAbstract:We study the long-time behavior of kinetic equations in which transport and spatial confinement (in an exterior potential or in a box) are associated with a (degenerate) collision operator acting only in the Velocity Variable. We expose a general method, based on logarithmic Sobolev inequalities and the entropy, to overcome the well-known problem, due to the degeneracy in the position Variable, of the existence of infinitely many local equilibria. This method requires that the solution be somewhat smooth. In this paper, we apply it to the linear Fokker-Planck equation and prove decay to equilibrium faster than O(t−1/ϵ) for all ϵ > 0. © 2001 John Wiley & Sons, Inc.
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On the trend to global equilibrium in spatially inhomogeneous entropy‐dissipating systems: The linear Fokker‐Planck equation
Communications on Pure and Applied Mathematics, 2000Co-Authors: Laurent Desvillettes, Cedric VillaniAbstract:We study the long-time behavior of kinetic equations in which transport and spatial confinement (in an exterior potential or in a box) are associated with a (degenerate) collision operator acting only in the Velocity Variable. We expose a general method, based on logarithmic Sobolev inequalities and the entropy, to overcome the well-known problem, due to the degeneracy in the position Variable, of the existence of infinitely many local equilibria. This method requires that the solution be somewhat smooth. In this paper, we apply it to the linear Fokker-Planck equation and prove decay to equilibrium faster than O(t−1/ϵ) for all ϵ > 0. © 2001 John Wiley & Sons, Inc.
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Regularization properties of the 2-dimensional non radially symmetric non cutoff spatially homogeneous Boltzmann equation for Maxwellian molecules
Transport Theory and Statistical Physics, 1997Co-Authors: Laurent DesvillettesAbstract:Abstract We prove in this work that the solution of the two-dimensional spatially homogeneous Boltzmann equation with Maxwellian molecules lies “almost” in H 1 (in the Velocity Variable) as soon as the initial datum has finite mass, energy and entropy. No assumption of radial symmetry of the solution is made in this paper.
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About the regularizing properties of the non-cut-off Kac equation
Communications in Mathematical Physics, 1995Co-Authors: Laurent DesvillettesAbstract:We prove in this work that under suitable assumptions, the solution of the spatially homogeneous non-cut-off Kac equation (or of the spatially homogeneous non cut-off 2D Boltzmann equation with Maxwellian molecules in the radial case) becomes very regular with respect to the Velocity Variable as soon as the time is strictly positive.
Tong Yang - One of the best experts on this subject based on the ideXlab platform.
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Local existence of polynomial decay solutions to the Boltzmann equation for soft potentials
Analysis and Applications, 2015Co-Authors: Yoshinori Morimoto, Tong YangAbstract:The existence of classical solutions to the Cauchy problem for the Boltzmann equation without angular cutoff has been extensively studied in the framework when the solution has Maxwellian decay in the Velocity Variable, cf. [6, 8] and the references therein. In this paper, we prove local existence of solutions with polynomial decay in the Velocity Variable for the Boltzmann equation with soft potential. In the proof, the singular change of Variables between post- and pre-collision velocities plays an important role, as well as the regular one introduced in the celebrated cancelation lemma by Alexandre–Desvillettes–Villani–Wennberg [Entropy dissipation and long-range interactions, Arch. Ration. Mech. Anal. 152 (2000) 327–355].
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Smoothing effect of weak solutions for the spatially homogeneous Boltzmann Equation without angular cutoff
Kyoto Journal of Mathematics, 2012Co-Authors: Radjesvarane Alexandre, Yoshinori Morimoto, Seiji Ukai, Tong YangAbstract:In this paper, we consider the spatially homogeneous Boltzmann equation without angular cutoff. We prove that every $L^1$ weak solution to the Cauchy problem with finite moments of all order acquires the $C^\infty$ regularity in the Velocity Variable for the positive time.
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The Boltzmann equation without angular cutoff in the whole space: I, Global existence for soft potential
Journal of Functional Analysis, 2012Co-Authors: Radjesvarane Alexandre, Yoshinori Morimoto, Seiji Ukai, Tong YangAbstract:It is known that the singularity in the non-cutoff cross-section of the Boltzmann equation leads to the gain of regularity and a possible gain of weight in the Velocity Variable. By defining and analyzing a non-isotropic norm which precisely captures the dissipation in the linearized collision operator, we first give a new and precise coercivity estimate for the non-cutoff Boltzmann equation for general physical cross-sections. Then the Cauchy problem for the Boltzmann equation is considered in the framework of small perturbation of an equilibrium state. In this part, for the soft potential case in the sense that there is no positive power gain of weight in the coercivity estimate on the linearized operator, we derive some new functional estimates on the nonlinear collision operator. Together with the coercivity estimates, we prove the global existence of classical solutions for the Boltzmann equation in weighted Sobolev spaces.
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Uniqueness of solutions for the non-cutoff Boltzmann equation with soft potential
Kinetic & Related Models, 2011Co-Authors: Radjesvarane Alexandre, Yoshinori Morimoto, Seiji Ukai, Tong YangAbstract:In this paper, we consider the Cauchy problem for the non-cutoff Boltzmann equation in the soft potential case. By using a singular change of Velocity Variables before and after collision, we prove the uniqueness of weak solutions to the Cauchy problem in the space of functions with polynomial decay in the Velocity Variable.
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BOUNDED SOLUTIONS OF THE BOLTZMANN EQUATION IN THE WHOLE SPACE
Kinetic and Related Models, 2011Co-Authors: Radjesvarane Alexandre, Yoshinori Morimoto, Seiji Ukai, Tong YangAbstract:We construct bounded classical solutions of the Boltzmann equation in the whole space without specifying any limit behaviors at the spatial infonity and without assuming the smallness condition on initial data. More precisely, we show that if the initial data is non-negative and belongs to a uniformly local Sobolev space in the space Variable and a standard Sobolev space with Maxwellian type decay property in the Velocity Variable, then the Cauchy problem of the Boltzmann equation possesses a unique non-negative local solution in the same function space, both for the cuto and non-cuto collision cross section with mild singularity. The known solutions such as solutions on the torus (space periodic solutions) and in the vacuum (solutions vanishing at the spatial innity), and solutions in the whole space having a limit equilibrium state at the spatial innity are included in our category.
Cedric Villani - One of the best experts on this subject based on the ideXlab platform.
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on the trend to global equilibrium in spatially inhomogeneous entropy dissipating systems the linear fokker planck equation
Communications on Pure and Applied Mathematics, 2001Co-Authors: Laurent Desvillettes, Cedric VillaniAbstract:We study the long-time behavior of kinetic equations in which transport and spatial confinement (in an exterior potential or in a box) are associated with a (degenerate) collision operator acting only in the Velocity Variable. We expose a general method, based on logarithmic Sobolev inequalities and the entropy, to overcome the well-known problem, due to the degeneracy in the position Variable, of the existence of infinitely many local equilibria. This method requires that the solution be somewhat smooth. In this paper, we apply it to the linear Fokker-Planck equation and prove decay to equilibrium faster than O(t−1/ϵ) for all ϵ > 0. © 2001 John Wiley & Sons, Inc.
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On the Boltzmann equation for long-range interactions
Communications on Pure and Applied Mathematics, 2001Co-Authors: Radjesvarane Alexandre, Cedric VillaniAbstract:We study the Boltzmann equation without Grad's angular cutoff assumption. We introduce a suitable renormalized formulation that allows the cross section to be singular in both the angular and the relative Velocity Variables. Angular singularities occur as soon as one is interested in long-range interactions, while singularities in the relative Velocity Variable occur in the study of soft potentials, in particular, Coulomb interaction. Together with several new estimates, this new formulation enables us to prove existence of weak solutions and to give a proof of a conjecture by Lions (appearance of strong compactness) under general, fully realistic assumptions. © 2001 John Wiley & Sons, Inc.
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On the trend to global equilibrium in spatially inhomogeneous entropy‐dissipating systems: The linear Fokker‐Planck equation
Communications on Pure and Applied Mathematics, 2000Co-Authors: Laurent Desvillettes, Cedric VillaniAbstract:We study the long-time behavior of kinetic equations in which transport and spatial confinement (in an exterior potential or in a box) are associated with a (degenerate) collision operator acting only in the Velocity Variable. We expose a general method, based on logarithmic Sobolev inequalities and the entropy, to overcome the well-known problem, due to the degeneracy in the position Variable, of the existence of infinitely many local equilibria. This method requires that the solution be somewhat smooth. In this paper, we apply it to the linear Fokker-Planck equation and prove decay to equilibrium faster than O(t−1/ϵ) for all ϵ > 0. © 2001 John Wiley & Sons, Inc.