Browsing by Author "Leahy, Denis Alan"
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- ItemOpen AccessA calculator for Roche lobe properties(SpringerOpen, 2015-05-06) Leahy, Denis Alan; Leahy, Janet CBackground The Roche lobe geometry is important to understand and study the properties of the mass-losing component in a semi-detached binary system. However it is not easy to calculate accurately, and existing tables usually do not include the parameters of the binary system under study, nor do they allow for non-synchronous rotation. Results A calculator for properties of the Roche lobe is presented in two formats. An easy-to-use Java version has a graphic interface, and a Fortran 90 version has a command line interface. The Fortran version allows for easy modifications by the user. Both versions have two basic output options: one provides values of a set of various quantities (such as the Lagrange points along the binary axis, and area and volume of the Roche lobe); the second provides , the distance from the stellar center to the stellar surface for any specified polar angle. A single set of input parameters can be entered directly or a large set of input parameters can be specified in a text file. The calculator includes the options to have non-synchronous rotation of the star, or to have the star underfill its Roche lobe. It can be used to calculate Roche lobe properties for the case of elliptical orbits, with some restrictions. Conclusions We present a convenient software tool for quickly and accurately calculating Roche lobe properties for mass ratio in the range 0.01 to 100, for Roche lobe fill-out factor in the range 0.1 to 1.0, and for dimensionless rotation rate of the star in the range 0.1 to 2.0. This will allow anyone working with a binary star system to obtain the Roche lobe or stellar surface geometry for their system.
- ItemOpen AccessSGRs and AXPs: Evidence for Delayed Amplification of Magnetic Field after Neutron Star Formation?(Hindawi Publishing Corporation, 2009) Leahy, Denis Alan; Ouyed, Rachid
- ItemOpen AccessTime Dependence of the RXTE X-ray Spectrum of Hercules X-1/HZ Hercules(2016) Abdallah, Mohammed Hassan; Leahy, Denis Alan; Jackel, Brian; Stil, Jeroen; Ouyed, RachidWe study the time dependence of the energy spectra (i.e. of the spectral model parameters, and the interpretation) of the X-ray binary system Hercules X-1/HZ Hercules (Her X-1/HZ Her) over the superorbital/35-day cycle. The results are discussed separately in two parts: one for the data during the main high state and one for the data obtained during low state and short high state. We made use of data collected by RXTE/PCA instrument in the standard-2 mode during the period from July,1996 to August of 2005 (MJD = 50290 - 53584) acquired as a result of 23 study proposals for observing the HZ Her/Her X-1 system. Observations made while the system was in anomalous low state (ALS) were removed, as the ALS are believed to be caused by a change in the status of the disc which results in disappearance of the 35-day superorbital cycle. In our data there are two anomalous low states (MJD = 51226.4 to 51756.9 & MJD = 52950.6 to 53159.4). Due to the rapid change of count rates and energy spectra during eclipse and dips periods, we remove these periods from our analysis. The main results during main high state are directly linked to the disc precession and its effect in occulting the central source and surrounding emission regions, while results obtained for the low state and short high state are related to the changing visibility of the irradiated face of HZ Her which contributes to the observed spectra by the reflected emission off of its heated face.