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Jordan C.,University of Oxford | Ness J.-U.,Newton Science Operations Center
Monthly Notices of the Royal Astronomical Society | Year: 2012

Emission line fluxes from cool stars are widely used to establish an apparent emission measure distribution, Emd app(T e), between temperatures characteristic of the low transition region and the low corona. The true emission measure distribution, Emd t(T e), is determined by the energy balance and geometry adopted and, with a numerical model, can be used to predict Emd app(T e), to guide further modelling. The scaling laws that exist between coronal parameters arise from the dimensions of the terms in the energy balance equation. Here, analytical approximations to numerical solutions for Emd t(T e) are presented, which show how the constants in the coronal scaling laws are determined. The apparent emission measure distributions show a minimum value at some T o and a maximum at the mean coronal temperature T c (although in some stars, emission from active regions can contribute). It is shown that, for the energy balance and geometry adopted, the analytical values of the emission measure and electron pressure at T o and T c depend on only three parameters: the stellar surface gravity and the values of T o and T c. The results are tested against full numerical solutions for ε Eri (K2 V) and are applied to Procyon (α CMi, F5 IV/V). The analytical approximations can be used to restrict the required range of full numerical solutions, to check the assumed geometry and to show where the adopted energy balance may not be appropriate. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source

Schartel N.,Newton Science Operations Center
Astronomische Nachrichten | Year: 2012

The historical development of ground based astronomical telescopes leads us to expect that space-based astronomical telescopes will need tobe operational for many decades. The exchange of scientific instruments in space will be a prerequisite for the long lasting scientific success of such missions. Operationally, the possibility to repair or replace key spacecraft components in space will be mandatory. We argue that these requirements can be fulfilled with robotic missions and see the development of the required engineering as the main challenge. Ground based operations, scientifically and technically, will require a low operational budget of the running costs. These can be achieved through enhanced autonomy of the spacecraft and mission independent concepts for the support of the software. This concept can be applied to areas where the mirror capabilities do not constrain the lifetime of the mission. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Read A.M.,University of Leicester | Guainazzi M.,Newton Science Operations Center | Sembay S.,University of Leicester
Astronomy and Astrophysics | Year: 2014

Aims. We aim to examine the relative cross-calibration accuracy of the on-axis effective areas of the XMM-Newton EPIC pn and MOS instruments. Methods. Spectra from a sample of 46 bright, high-count, non-piled-up, isolated on-axis point sources are stacked together, and model residuals are examined to characterize the EPIC MOS-to-pn inter-calibration. Results. The MOS1-to-pn and MOS2-to-pn results are broadly very similar. The cameras show the closest agreement below 1 keV, with MOS excesses over pn of 0-2% (MOS1/pn) and 0-3% (MOS2/pn). Above 3 keV, the MOS/pn ratio is consistent with energy-independent (or only mildly increasing) excesses of 7-8% (MOS1/pn) and 5-8% (MOS2/pn). In addition, between 1-2 keV there is a "silicon bump"-an enhancement at a level of 2-4% (MOS1/pn) and 3-5% (MOS2/pn). Tests suggest that the methods employed here are stable and robust. Conclusions. The results presented here provide the most accurate cross-calibration of the effective areas of the XMM-Newton EPIC pn and MOS instruments to date. They suggest areas of further research where causes of the MOS-to-pn differences might be found, and allow the potential for corrections and possible rectification of the EPIC cameras to be made in the future. © 2014 ESO. Source

Done C.,Durham University | Trigo M.D.,Newton Science Operations Center
Monthly Notices of the Royal Astronomical Society | Year: 2010

The detection of an extremely broad iron line in XMM-Newton MOS data from the low/hard state of the black hole binary GX339-4 is the only piece of evidence which unambiguously conflicts with the otherwise extremely successful truncated disc interpretation of this state. However, it also conflicts with some aspect of observational data for all other alternative geometries of the low/hard state, including jet models, making it very difficult to understand. We re-analyse these data and showthat they are strongly affected by pile-up evenwith extensive centroid removal as the source is ~200 times brighter than the recommended maximum count rate. Instead, we extract the simultaneous PN timing-mode data which should not be affected by pile-up. These show a line which is significantly narrower than in the MOS data. Thus these data are easily consistent with a truncated disc, and indeed, strongly support such an interpretation. © 2010 The Authors. Journal compilation. © 2010 RAS. Source

Dobrotka A.,Slovak University of Technology in Bratislava | Ness J.-U.,Newton Science Operations Center
Monthly Notices of the Royal Astronomical Society | Year: 2015

An optical light curve of SU UMa type dwarf nova V1504 Cyg taken by Kepler was analysed in order to study fast optical variability (flickering). We calculated power density spectra and rms-flux relations for two different stages of activity, i.e. quiescence and regular outbursts. A multicomponent power density spectrum with two break frequencies was found during both activity stages. The rms-flux relation is obvious only in the quiescent data. However, while the collection of all outburst data do not show this variability, every individual outburst does show it in the majority of cases keeping the rms value approximately in the same interval. Furthermore, the same analysis was performed for light-curve subsamples taken from the beginning, middle and the end of the supercycle both for quiescence and regular outbursts. Every light-curve subsample shows the same multicomponent power density spectrum. The stability of the break frequencies over the supercycle can be confirmed for all frequencies except for the high break frequency during outburst, which shows variability, but with rather low confidence. Finally, the low break frequency can be associated with the geometrically thin disc or its inner edge, while the high break frequency can originate from the inner geometrically thick hot disc. Furthermore, with our statistical method to simulate flickering light curves, we show that the outburst flickering light curve of V1504 Cyg needs an additional constant flux level to explain the observed rms-flux behaviour. Therefore, during the outbursts another non-turbulent radiation source should be present. © 2015 The Authors. Source

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