Philipp Podsiadlowski

Abstract:

I argue that magnetic torques inside stars are likely to maintain a state of approximately uniform rotation on the giant branch. The cores of giants are then very slowly rotating, and the rotation of white dwarfs and neutron stars is not a remnant of the rotation of their main sequence progenitors. The kicks associated with the observed proper motions of pulsars can explain the rotation rates of neutron stars, while slight non-axisymmetries in the mass loss during planetary nebula formation can explain the observed rotation of white dwarfs.

Abstract:

Recent X-ray timing and spectral observations of black hole binaries in outburst have redefined methods for investigating the properties of Galactic black holes and the physics of accretion flows. High-frequency X-ray QPOs in 5 systems (60-300 Hz) continue to be investigated as a possible means to constrain black hole mass and spin via interpretation as oscillations due to strong-field effects in General Relativity. In principle, black hole mass and spin may also be constrained via determination of the inner radius of the accretion disk, using spectro-scopic parallax of the X-ray thermal component. However, an accurate application of this technique is fraught with difficulties. Monitoring programs that track the evolution of the thermal and power-law components in the X-ray spectrum provide new insights into modes of energy flow and the formation of relativistic jets.

Abstract:

MACHO observations show that approximately 25% of semi-regular red variables in the LMC have a secondary period similar to10 times longer than the primary period of pulsation, which is usually the first overtone pulsation mode in these stars. Wood et al. (1999) have suggested that the long secondary periods (LSPs) may be due to the presence of a binary companion and associated dust cloud whose orbital period matches that of the LSP. In this poster, preliminary results of an investigation aimed at detecting the radial velocity variations associated with the proposed orbital motions are reported. There is tentative evidence that the red giants with LSPs do show velocity variations consistent with the presence of a companion and that a trailing, accreted dust cloud occupies approximately one quarter of the orbital plane.

Abstract:

A new idea for the mass transfer in detached binary systems including a mass losing red giant is proposed. When the red giants fill about a half of the Roche lobes, our formula gives mass transfer rates 3 similar to 9 times higher than those expected from the capture of the stellar wind. The new mass transfer rates of some symbiotic stars are sufficiently high to maintain nuclear burning on the hot components.

Abstract:

We have constructed theoretical light curves for recurrent nova outbursts based on a thermonuclear runaway model. Fitting theoretical light curves with the observations of the eight known recurrent novae provides us with important information about these systems including the mass of the white dwarf, envelope mass at optical maximum, hydrogen content of the white dwarf envelope, and so on. The mass of the white dwarf ranges from 1.35-1.37 M. for seven recurrent novae except for T Pyx which has a less massive white dwarf of 1.2 M.. Further, we have determined net rates of increase for the white dwarf mass as large as similar to(0.1-1.0) x 10(-7) M. yr(-1), and found that the eight known recurrent nova systems will certainly explode as a Type Ia supernova if the donor is massive enough.