TY  - JOUR
A1  - Seiss, Martin
A1  - Spahn, Frank
T1  - Hydrodynamics of saturn's dense rings
JF  - Mathematical modelling of natural phenomena
N2  - The space missions Voyager and Cassini together with earthbound observations revealed a wealth of structures in Saturn's rings. There are, for example, waves being excited at ring positions which are in orbital resonance with Saturn's moons. Other structures can be assigned to embedded moons like empty gaps, moon induced wakes or S-shaped propeller features. Furthermore, irregular radial structures are observed in the range from 10 meters until kilometers. Here some of these structures will be discussed in the frame of hydrodynamical modeling of Saturn's dense rings. For this purpose we will characterize the physical properties of the ring particle ensemble by mean field quantities and point to the special behavior of the transport coefficients. We show that unperturbed rings can become unstable and how diffusion acts in the rings. Additionally, the alternative streamline formalism is introduced to describe perturbed regions of dense rings with applications to the wake damping and the dispersion relation of the density waves.
KW  - granular gas
KW  - instabilities
KW  - hydrodynamics
KW  - planetary rings
Y1  - 2011
U6  - https://doi.org/10.1051/mmnp/20116409
SN  - 0973-5348
SN  - 1760-6101
VL  - 6
IS  - 4
SP  - 191
EP  - 218
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Parkin, E. R.
A1  - Broos, Patrick  S.
A1  - Townsley, L. K.
A1  - Pittard, J. M.
A1  - Moffat, Anthony F. J.
A1  - Naze, Y.
A1  - Rauw, G.
A1  - Oskinova, Lida
A1  - Waldron, W. L.
T1  - X-RAY EMISSION FROM THE DOUBLE-BINARY OB-STAR SYSTEM QZ CAR (HD 93206)
JF  - ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES
N2  - X-ray observations of the double-binary OB-star system QZ Car (HD 93206) obtained with the Chandra X-ray Observatory over a period of roughly 2 years are presented. The respective orbits of systems A (O9.7 I+b2 v, P-A = 21 days) and B (O8 III+o9 v, P-B = 6 days) are reasonably well sampled by the observations, allowing the origin of the X-ray emission to be examined in detail. The X-ray spectra can be well fitted by an attenuated three-temperature thermal plasma model, characterized by cool, moderate, and hot plasma components at kT similar or equal to 0.2, 0.7, and 2 keV, respectively, and a circumstellar absorption of similar or equal to 0.2 x 10(22) cm(-2). Although the hot plasma component could be indicating the presence of wind-wind collision shocks in the system, the model fluxes calculated from spectral fits, with an average value of similar or equal to 7x10(-13) erg s(-1) cm(-2), do not show a clear correlation with the orbits of the two constituent binaries. A semi-analytical model of QZ Car reveals that a stable momentum balance may not be established in either system A or B. Yet, despite this, system B is expected to produce an observed X-ray flux well in excess of the observations. If one considers the wind of the O8 III star to be disrupted by mass transfer, the model and observations are in far better agreement, which lends support to the previous suggestion of mass transfer in the O8 III+o9 v binary. We conclude that the X-ray emission from QZ Car can be reasonably well accounted for by a combination of contributions mainly from the single stars and the mutual wind-wind collision between systems A and B.
KW  - hydrodynamics
KW  - stars: early-type
KW  - stars: individual (QZ Carinae)
KW  - stars: massive
KW  - stars: winds, outflows
KW  - X-rays: stars
Y1  - 2011
U6  - https://doi.org/10.1088/0067-0049/194/1/8
SN  - 0067-0049
VL  - 194
IS  - 1
PB  - IOP PUBLISHING LTD
CY  - BRISTOL
ER  -