Philipp Podsiadlowski

Abstract:

The most complete atlas of modern spectrophotometric observations of symbiotic stars is presented. It contains observations of 137 objects on both hemispheres. All spectra are absolutely calibrated in flux, they have un-saturated emission lines and generally a high signal/noise in the continuum. Opportunities for statistically relevant investigations of emission line spectrum and cool giant classification are briefly discussed. Distribution policy is mentioned.

Abstract:

The radio millisecond pulsar PSR B1620-26 is part of an extraordinary triple star system in the globular cluster M4. The inner companion to the neutron star is thought to be a white dwarf of mass m(1) similar or equal to 0.3 M-circle dot in an orbit of period similar or equal to 0.5 yr. The nature and orbital characteristics of the second, more distant companion, have remained a mystery for many years. A theoretical analysis of the latest available radio pulsar timing data is presented here, allowing us to determine approximately the mass and orbital parameters of the second companion. Remarkably, the current best-fit parameters correspond to a second companion of planetary mass, with m(2)sin i(2) similar or equal to 7 x 10(-3) M-circle dot, in an orbit of eccentricity e(2) similar or equal to 0.45 and with a large semimajor axis a(2) similar or equal to 60 AU. The short dynamical lifetime of this very wide triple in M4 suggests that large numbers of such planets must be present in globular clusters. We also address the question of the anomalously high eccentricity of the inner binary pulsar. While this eccentricity could have been induced during the same dynamical interaction that created the triple, we find that it could also naturally arise from long-term secular perturbation effects in the triple, combining the general relativistic precession of the inner orbit with the Newtonian gravitational perturbation by the outer planet.

Abstract:

Binary population synthesis (BPS) is an algorithm to evolve millions of stars (including binaries) simultaneously. It plays an important role in the theory of stellar evolution and is potentially important in the study of galaxies. Previous studies of BPS employed different assumptions in the explanations of different objects, and sometimes adopted non-physical model parameters. We try to establish a self-consistent BPS model in order to explain many objects in a self-consistent way and to avoid unnatural model parameters. We present the model and some preliminary results in this paper.

Abstract:

The outbursts of black hole X-ray transients can be understood as caused by a limit cycle instability in the accretion disk, similar to dwarf nova outbursts. For adequately low mass overflow rates from the companion star long outburst recurrence times are expected. But the fact that we find predominantly long recurrence times or that only one X-ray nova outburst was detected at all poses a problem. The question arises whether any braking mechanism could act in a way that long recurrence times are favoured.We suggest that a circumbinary disk exists and brakes the orbital motion of the binary stars by tidal interaction. The irradiation during an outburst leads to mass loss by winds from the circumbinary disk, relieving the braking force until the removed matter is refilled by diffusion from outer parts. We show that this reduction of braking will self-adjust the mass transfer to the marginal rate that gives long recurrence times.

Abstract:

We have analyzed HST archival and IUE NEWSIPS archival SWP spectra of the dwarf novae CM Del and AH Her obtained when AAVSO light curve data indicated the occurrence of dwarf nova quiescence. HST archival outburst data for AH Her is examined as well. We have computed synthetic, high gravity spectra in LTE with solar composition using TLUSTY195 and SYNSPEC42 and carried out fits of these models to the far UV continuum and narrow absorption line spectra. For CM Del, we find that the far UV spectrum is dominated by a hot (T-eff = 22,000 K, log g = 8) white dwarf with subsolar Si abundance and all other observed metal transitions at essentially their solar values. For AH Her, we find evidence for a hot white dwarf with T-eff = 27,000 K, log g = 8 and subsolar Si abundances. An HST spectrum (GHRS G160M) of AH Her reveals blue-asymmetric SiIV profiles. If due to wind outflow, we derive a single-scattering upper limit mass loss rate of 10(-9) M./yr(-1). Synthetic profile fits to 12 coadded HST medium resolution G160M spectra of the Si IV (1393Angstrom, 1402Angstrom) resonance doublet of CM Del yield a white dwarf rotational velocity estimate of v sin i = 400 +70/-30 km/s(-1), T-wd = 27, 000K +/- 1000K and Si/H = 1 +0.5/-0.3 x solar. This value of v sin i is discussed in the context of angular momentum transfer and rotation rates for other CV primary degenerate stars.