Vaubaillon J.,IMCCE |
Maquet L.,Paris Observatory |
Soja R.,University of Stuttgart
Monthly Notices of the Royal Astronomical Society | Year: 2014
Comet C/2013 A1 will make a very close approach with the planet Mars on 2014 October 19. For this event, we compute the density of cometary dust particles around the Mars Express spacecraft, in order to assess the real risk for space probes. We also estimate the zenithal hourly rate (ZHR) and discuss observational opportunities for the resulting Martian meteor shower. We find, for a surface of 2.7 m2, that the Mars Express spacecraft will experience approximately 10 impacts from particles larger than 100 μm in size. The fluence per square metre is found to be 3.5 during the encounter. The equivalent ZHR is computed to be ZHR ≃ 4.75 × 109 h-1, making this event the strongest meteor storm ever predicted.We call this event a 'meteor hurricane', which we define to be a meteor shower with ZHR exceeding 106 h-1. The event will last approximately 5 h in total, and peak around 20:00 UT (Earth UT time). We call for observations of this unique event by all possible means, but also warn operators of Mars-orbiting spacecraft against the risks of impacts from comet particles larger than 100 μm, with impacts speeds of 57.42 km s-1. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
Flower D.R.,Durham University |
Pineau des Forets G.,University Paris - Sud |
Pineau des Forets G.,Paris Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2012
We have developed further the technique of time-dependent modelling of magnetohydrodynamic shock waves, with a view to interpreting the molecular line emission from outflow sources. The extensively observed source L1157 B1 was chosen as an exemplar of the application of this technique. The dynamical age of the shock wave model was varied in the range 500 ≤t≤ 5000yr, with the best fit to the observed line intensities being obtained for t= 1000yr; this is of the same order as the dynamical age derived by Gueth, Guilloteau & Bachiller from their observations of L1157 B1. The emission line spectra of H 2, CO, SiO, ortho- and para-H 2O, ortho- and para-NH 3, and A- and E-type CH 3OH were calculated in parallel with the dynamical and chemical parameters of the model, using the 'large velocity gradient' (LVG) approximation to the line transfer problem. We compared the predictions of the models with the observed intensities of emission lines of H 2, CO, SiO, ortho-H 2O, ortho-NH 3 and CH 3OH, which include recent Herschel satellite measurements. In the case of SiO, we show (in Appendix A) that extrapolations of the collisional rate coefficients beyond the range of kinetic temperature for which they were originally calculated lead to spurious rotational line intensities and profiles. The computed emission-line spectra of SiO, NH 3 and CH 3OH are shown to depend on the assumed initial composition of the grain mantles, from whence they are released, by sputtering in the shock wave, into the gas phase. The dependence of the model predictions on the adopted form of the grain-size distribution is investigated in Appendix B; the corresponding integral line intensities are given in tabular form, for a range of C-type shock speeds, in the online Supporting Information. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.
Saucedo M.,French Institute of Health and Medical Research |
Saucedo M.,Paris Observatory |
Deneux-Tharaux C.,French Institute of Health and Medical Research |
Bouvier-Colle M.-H.,French Institute of Health and Medical Research
Obstetrics and Gynecology | Year: 2013
OBJECTIVE: To assess trends in the maternal mortality ratio over a 10-year period in France and the causes, risk factors, quality of care, and avoidability ofmaternal deaths. METHODS: Maternal deaths up to 1 year after the end of the pregnancy from 1998 to 2007 were identified and studied through the French Confidential Enquiry Into Maternal Deaths system. Time trends were analyzed by comparing the two 5-year periods for maternal mortality ratios, both overall and by women's characteristics, causes of death, existence of suboptimal care, and avoidability. RESULTS: For the 10-year period, 660 maternal deaths were identified. The maternal mortality ratio was similar in the two 5-year periods, 8.8 per 100,000 live births (95% confidence interval [CI] 7.8-9.8) for 1998-2002 and 8.4 per 100,000 live births (95% CI 7.6-9.4) for 2003-2007. The distributions of maternal age, nationality, and of causes of death did not change. Overall, hemorrhage was the leading cause of death, responsible for 18% of maternal deaths, followed by amniotic fluid embolism, thromboembolism, hypertensive disorders, and cardiovascular conditions, each of which contributed to 10-12% of deaths. Suboptimal care decreased from 70% in 1998-2002 to 60% in 2003-2007 (P,.03). Half of all deaths were considered avoidable and this proportion did not change. The most frequent contributory factor was inadequate management. CONCLUSION: The ratio and profile of maternal mortality in France remained unchanged from 1998 to 2007. Half of all maternal deaths are still considered avoidable, which indicates that improvement remains possible. © 2013 by The American College of Obstetricians and Gynecologists.
Encrenaz T.,Paris Observatory
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2014
The exploration of transiting extrasolar planets is an exploding research area in astronomy. With more than 400 transiting exoplanets identified so far, these discoveries have made possible the development of a new research field, the spectroscopic characterization of exoplanets' atmospheres, using both primary and secondary transits. However, these observations have been so far limited to a small number of targets. In this paper, we first review the advantages and limitations of both primary and secondary transit methods. Then, we analyse what kind of infrared spectra can be expected for different types of planets and discuss how to optimize the spectral range and the resolving power of the observations. Finally, we propose a list of favourable targets for present and future ground-based observations. © 2014 The Author(s) Published by the Royal Society.
Storey P.J.,University College London |
Zeippen C.J.,Paris Observatory
Astronomy and Astrophysics | Year: 2010
A new R-matrix calculation of rate coefficients for electron collisional excitation of Fe XIII is presented and compared to recent calculations of comparable complexity. At temperatures at which Fe12+ is typically found in the solar corona, the present results, which use the intermediate coupling frame transformation method, show significant differences compared to some earlier work. We use a large configuration interaction calculation with extensive correlation to assess the accuracy of our and earlier workers' scattering targets. © ESO 2010.