Relativistic ionized accretion disc models of MCG–6-30-15

We present BeppoSAX observations of Nova Velorum 1999 (V382 Vel), carried out in a broad X-ray band covering 0.1–300 keV only 15 d after the discovery and again after 6 months. The nova was detected at day 15 with the BeppoSAX instruments which measured a flux F _x≃1.8×10⁻¹¹ erg cm⁻² s⁻¹ in the 0.1–10 keV range and a 2 σ upper limit F _x<6.7×10⁻¹² erg cm⁻² s⁻¹ in the 15–60 keV range. We attribute the emission to shocked nebular ejecta at a plasma temperature kT ≃6 keV . At six months no bright component emerged in the 15–60 keV range, but a bright central supersoft X-ray source appeared. The hot nebular component previously detected had cooled to a plasma temperature kT <1 keV . There was strong intrinsic absorption of the ejecta in the first observation and not in the second, because the column density of neutral hydrogen decreased from N (H)≃1.7×10²³ to N (H)≃10²¹ cm⁻² (close to the interstellar value). The unabsorbed X-ray flux also decreased from F _x=4.3×10⁻¹¹ to F _x≃10⁻¹² erg cm⁻² s⁻¹ .     

Analysis of the Historical Light Curve of the UX Ori Star CQ Tau

An historical light curve for the UX Ori star CQ Tau is constructed for the period from 1939 through 2003. The star’s photometric behavior includes a cyclical component with a period of about 21 years. An analysis of the periodogram reveals a shorter cycle with a duration of about 1020 days after this cycle is subtracted. Since the photometric activity of UX Ori type stars is caused by variations in the circumstellar extinction, both of these cycles indicate the existence of large-scale deviations from axial symmetry in the distribution of matter in the circumstellar disk of CQ Tau. The orbiting of these inhomogeneities about the star also causes oscillatory variations in its brightness. An analysis of the color-magnitude diagrams reveals differences in the optical parameters of the circumstellar dust along the line of sight in various phases of the 21-year cycle: absorption by larger particles predominates near the brightness maximum of CQ Tau. This means that the reduced circumstellar extinction in this part of the circumstellar disk is the result of a smaller contribution from small particles; this may be evidence of the onset of a process of coagulation of the dust particles and their conversion into large-scale bodies and planetesimals.__________Translated from Astrofizika, Vol. 48, No. 2, pp. 165–174 (May 2005).     

Statistical probability distribution of snow depth at the model sub‐grid cell spatial scale

Comprehensive snow depth data, collected using georadar and hand probing, were used for statistical analyses of snow depths inside 1 km grid cells. The sub‐grid cell spatial scale was 100 m. Statistical distribution functions were found to have varying parameters, and an attempt was made to connect these statistical parameters to different terrain variables. The results showed that the two parameters mean and standard deviation of snow depth were significantly related to the sub‐grid terrain characteristics. Linear regression models could explain up to 50% of the variation for both of the snowcover parameters mentioned. Copyright © 2004 John Wiley & Sons, Ltd.     

Are superhumps good measures of the mass ratio for AM CVn systems?

We extend recent work that included the effect of pressure forces to derive the precession rate of eccentric accretion discs in cataclysmic variables to the case of double degenerate systems. We find that the logical scaling of the pressure force in such systems results in predictions of unrealistically high primary masses. Using the prototype AM CVn as a calibrator for the magnitude of the effect, we find that there is no scaling that applies consistently to all the systems in the class. We discuss the reasons for the lack of a superhump period to mass ratio relationship analogous to that known for SU UMa systems and suggest that this is because these secondaries do not have a single valued mass–radius relationship. We highlight the unreliability of mass ratios derived by applying the SU UMa expression to the AM CVn binaries.     

Multiple relativistic outbursts of GRS 1915+105: radio emission and internal shocks

We present 5-GHz Multi-Element Radio-Linked Interferometer Network (MERLIN) radio images of the microquasar GRS 1915+105 during two separate outbursts in 2001 March and July, following the evolution of the jet components as they move outwards from the core of the system. Proper motions constrain the intrinsic jet speed to be  >0.57 c   , but the uncertainty in the source distance prevents an accurate determination of the jet speed. No deceleration is observed in the jet components out to an angular separation of ∼300 mas. Linear polarization is observed in the approaching jet component, with a gradual rotation in position angle and a decreasing fractional polarization with time. Our data lend support to the internal shock model whereby the jet velocity increases leading to internal shocks in the pre-existing outflow before the jet switches off. The compact nuclear jet is seen to reestablish itself within 2 d, and is visible as core emission at all epochs. The energetics of the source are calculated for the possible range of distances; a minimum power of 1–10 per cent of the Eddington luminosity ( L _Edd) is required to launch the jet.     

Asteroseismology of δ Scuti and γ Doradus stars

We give an overview of past and present efforts to make seismology of δ Scuti and γ Doradus stars possible. Previous work has not led to the observational detection and identification of a sufficient number of pulsation modes for these pulsators for the construction of unique seismic models. However, recent efforts including large ground-based observational campaigns, work on pre-main sequence pulsators, asteroseismic satellite missions, theoretical advances on mode identification methods, and the discovery of a star showing simultaneous self-excited δ Scuti and γ Doradus oscillations suggest that we may be able to explore the interiors of these pulsators in the very near future.