Metal Abundances of Accretion Discs in AM CVn Binaries

Transcription

1 Metal Abundances of Accretion Discs in AM CVn Binaries Thorsten Nagel D.-J. Kusterer, T. Rauch, K. Werner Institut für Astronomie/Astrophysik Kepler Center for Astro and Particle Physics Universität Tübingen

2 Outline AM CVn Binaries Modelling of Accretion Discs Models vs. Observation Summary

3 AM CVn Binaries short orbital periods (< 65 minutes) accretor: white dwarf donor star still discussed (e.g. Nelemans et al. 2001): low mass white dwarf helium star He-rich core of evolved CV secondary

4 AM CVn Binaries spectra are helium dominated low state systems: low mass transfer rate, emission lines outburst systems: medium mass transfer rate, emission and absorption high state systems: high mass transfer rate, absorption lines

5 Modelling of Accretion Discs Assumptions: geometrically thin α-disc (Shakura & Sunyaev 1973) axial symmetry Divide disc into set of concentric rings Each ring: plane-parallel radiating slab Calculate detailed vertical structure and synthetic spectrum with AcDc (Accretion Disc code, Nagel et al. 2004)

6 Modelling of Accretion Discs hydrostatic equilibrium (gas and radiation pressure) radiative equilibrium (full line blanketing, no convection) NLTE rate equations radiation transfer eqs. (irradiation by primary can be considered)

7 Modelling of Accretion Discs Vertical structure and spectrum for each disc ring Integration of all disc ring intensities, rotational broadening NLTE accretion disc spectra for different inclinations disc spectrum can be used as input for our accretion disc wind models (see poster by D.-J. Kusterer)

8 Modelling of Accretion Discs Input data mass and radius of central object mass accretion rate extension of accretion disc Reynolds number chemical abundances ( donor star) irradiation: temperature/spectrum of central object irradiation angle

9 The Model Grid mass of primary: 0.6 and 1.0 M mass accretion rate: 10-8, and M /y radial extension: R * variation of C, N, O, Si abundances

10

11

12

13

14 C,O 0.1 x solar, N 10 x solar, Si solar abundance

15 C,O 0.1 x solar, N 10 x solar, Si x solar

16

17 C 0.1 x solar

18 C x solar

19

20 C,O 0.1 x solar, N 10 x solar, Si solar abundance

21 C,O 0.1 x solar, N 10 x solar, Si x solar

22 C O Si: x solar N: 10 x solar C O Si: 0.1 x solar N: 10 x solar

23 Summary learning about donor stars by analysing accretion discs reproduction of absorption and emission line spectra for high and low state indication of underabundance of Si and C model grid will be extended to 5 primary masses at 4 mass accretion rates