Constraining the dense matter equation-of-state with radio pulsars

Radio pulsars provide some of the most important constraints for our understanding of matter at supranuclear densities. So far, these constraints are mostly given by precision mass measurements of neutron stars (NS). By combining single measurements of the two most massive pulsars, J0348$+$0432 and J0740$+$6620, the resulting lower limit of 1.98 $M_\odot$ (99% confidence) of the maximum NS mass, excludes a large number of equations of state (EOSs). Further EOS constraints, complementary to other methods, are likely to come from the measurement of the moment of inertia (MOI) of binary pulsars in relativistic orbits. The Double Pulsar, PSR J0737$-$3039A/B, is the most promising system for the first measurement of the MOI via pulsar timing. Reviewing this method, based in particular on the first MeerKAT observations of the Double Pulsar, we provide well-founded projections into the future by simulating timing observations with MeerKAT and the SKA. For the first time, we account for the spin-down mass loss in the analysis. Our results suggest that an MOI measurement with 11% accuracy (68% confidence) is possible by 2030. If by 2030 the EOS is sufficiently well known, however, we find that the Double Pulsar will allow for a 7% test of Lense-Thirring precession, or alternatively provide a $\sim3\sigma$-measurement of the next-to-leading order gravitational wave damping in GR. Finally, we demonstrate that potential new discoveries of double NS systems with orbital periods shorter than that of the Double Pulsar promise significant improvements in these measurements and the constraints on NS matter.Comment: 13 pages, 8 figures. Accepted by MNRA

Experimental study of radiative shocks at PALS facility

We report on the investigation of strong radiative shocks generated with the high energy, sub-nanosecond iodine laser at PALS. These shock waves are characterized by a developed radiative precursor and their dynamics is analyzed over long time scales (~50 ns), approaching a quasi-stationary limit. We present the first preliminary results on the rear side XUV spectroscopy. These studies are relevant to the understanding of the spectroscopic signatures of accretion shocks in Classical T Tauri Stars.Comment: 21 pages, 1 table, 7 figure

New benzene absorption cross sections in the VUV, relevance for Titan’s upper atmosphere

This is a pre-print (pre-peer review) manuscript. It is moderately different from the accepted manuscript and from the published article. Citation of published article: Fernando J. Capalbo, Yves Bénilan, Nicolas Fray, Martin Schwell, Norbert Champion, Et-touhami Es-sebbar, Tommi T. Koskinen, Ivan Lehocki, Roger V. Yelle. Icarus, vol. 265, p. 95 - 109. February 2016. doi: 10.1016/j.icarus.2015.10.006.International audienceBenzene is an important molecule in Titan’s atmosphere because it is a potential link between the gas phase and the organic solid phase. We measured photoabsorption in the ultraviolet by benzene gas at temperatures covering the range from room temperature to 215 K. We derived benzene absorption cross sections and analyzed them in terms of the transitions observed. No significant variation with measurement temperature was observed. We discuss the implications of our measurements for the derivation of benzene abundance profiles in Titan’s thermosphere, by the Cassini/Ultraviolet Imaging Spectrograph (UVIS). The use of absorption cross sections at low temperature is recommended to avoid small systematic uncertainties in the profiles. We used our measurements, together with absorption cross sections from other molecules, to analyze four stellar occultations by Titan, measured by UVIS during flybys T21, T41, T41_II, and T53. We derived and compared benzene abundance profiles in Titan’s thermosphere between approximately 530 and 1000 km, for different dates and geographical locations. The comparisons of our benzene profiles with each other, and with profiles from models of the upper atmosphere, point to a complex behavior that is not explained by current photochemical models

Current results and future prospects from PSR J1757-1854, a highly-relativistic double neutron star binary

Pulsars, rapidly-rotating highly-magnetised neutron stars, can serve as useful laboratories for probing aspects of fundamental physics. Binary pulsars, especially those in tight binary systems with massive, compact companions, are useful in testing different theories of gravity, the current paradigm being General Relativity (GR). Additionally, binary pulsars can also be utilised to explore other areas of fundamental physics, such as the behaviour of matter at ultra-high densities and the neutron star moment of inertia. A standout example is PSR J1757-1854, a 21.5-ms pulsar in a highly-eccentric (e=0.61), 4.4-hr orbit around a neutron star companion. This pulsar exhibits some of the most extreme relativistic parameters ever observed in a binary pulsar, reaching a maximum line-of-sight acceleration of close to 700 m/s/s and displaying among the strongest relativistic effects due to gravitational wave damping. To date, five post-Keplerian parameters have been measured in PSR J1757-1854, allowing for three independent tests of gravity to be conducted (of which GR passes all three) and for the component neutron star masses to be separated. The extreme properties of this system (particularly its high eccentricity) are expected to allow for future measurements of Lense-Thirring precession effects (allow for a measurement of the neutron star moment of inertia) and the relativistic deformation of the orbit, both of which remain almost completely unexplored by other binary systems. Although first discovered by the Parkes Radio Telescope in 2016 as part of the High Time Resolution Universe Southern Galactic Plane survey, it is ongoing observations with the Green Bank Telescope (GBT) which have provided the backbone of PSR J1757-1854’s continuing study. The large-bandwidth, high-precision observations afforded by the GBT played a fundamental role in delivering the science derived from the pulsar so far, and will be critical in allowing it to reach its full scientific potential going forward. In this talk I will provide a progress report on the ongoing timing of the system, including a review of the latest mass measurements and gravity tests, with an emphasis towards the future science which this pulsar will make possible

Experimental study of strong shocks driven by compact pulsed power

International audienceposter P.We₇

Photoionization mass spectrometric studies of N-methyl formamide and N,N'-dimethyl formamide in the 7-18 eV photon energy range

International audienceA photoionization mass spectrometric study of N-methyl formamide and N,N'-dimethyl formamide has been made using synchrotron radiation over the photon energy range 8-20 eV. Photoion yield curves were measured for the parent ion in both species and for six fragment ions in N-methyl formamide. Assignments of the fragment ions and the pathways of their formation by dissociative photoionization were made on the basis of ion appearance energies in conjunction with thermochemical data and the results of electron impact mass spectral studies. Our results illuminate aspects of the effects of methylation of formamide on ionization energies and dissociative ionization channels, as well as on the relative order of analogous molecular orbitals. The principal dissociative ionization process in both compounds involves HCO-loss. This neutral product may be formed in an electronic excited state. A comparison between the ionization properties, in particular the heats of formation of the cations, of the methyl derivatives of formamide and acetamide, shows that the ionization energies of the latter require re-investigation

VUV Dissociative Photoionization of Quinoline in the 7–26 eV Photon Energy Range

International audienc

Lanceur électromagnétique de chocs forts pour l'astrophysique de laboratoire : principe et premiers résultats

International audienceParmi les chocs forts présents en astrophysique, comme les chocs daccrétion lors de la formation des étoiles jeunes, les chocs radiatifs sont caractérisés par un pic de température localisé et une forte émission de rayonnement capable de structurer le choc. Par exemple, lionisation par ce rayonnement chauffe la matière en amont et modifie la propagation du choc (phénomène précurseur). Lastrophysique de laboratoire étudie ces chocs depuis une décennie en générant des chocs quasi plans par impact laser à haut flux. Récemment les auteurs ont ainsi pu mesurer des vitesses de 50 km/s dans le xénon dense. Il est apparu utile de créer des chocs forts par un moyen plus commode à mettre en uvre au laboratoire, permettant détudier une large gamme de chocs, de multiplier les expériences et de développer des diagnostics avec des contraintes dencombrement réduites. Or, des chocs daccrétion en gaz peu denses ont été documentés dans les années 70 dans les canons à plasma coaxiaux. Dans ces dispositifs, la pression magnétique générée par un courant fort (100 kA et plus) accélère une lame de plasma, ce qui constitue le lanceur du dispositif dit plasma focus. La puissance instantanée dun tel générateur ultra compact dépasse alors couramment les 500MWe. Après avoir obtenu dempêcher létape de focalisation du plasma, il a été possible de montrer quun choc quasi plan est créé et se déplace à une vitesse élevée dans un tube dont les dimensions sont dun ordre de grandeur supérieures à celles dun tube pour choc induit par laser. On présentera le mécanisme de formation et daccélération du plasma puis un modèle paramétrique régissant la vitesse terminale. Des exemples de mesures de la vitesse (de 5 à 20 km/s) et du profil du choc seront également présentés. Ce travail est soutenu par le DIM ACAV 2012 et par lOBSPM