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Post Info TOPIC: AU Monocerotis
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RE: AU Monocerotis
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Title: Modelling the Accretion Structure of AU Mon
Authors: Corwin Atwood-Stone, Brendan P. Miller, Mercedes T. Richards, Jan Budaj, Geraldine J. Peters

AU Mon is a long-period (11.113 d) Algol-type binary system with a persistent accretion disk that is apparent as double-peaked H-alpha emission. We present previously unpublished optical spectra of AU Mon which were obtained over several years with dense orbital phase coverage. We utilise these data, along with archival UV spectra, to model the temperature and structure of the accretion disk and the gas stream. Synthetic spectral profiles for lines including H-alpha, H-beta, and the Al III and Si IV doublets were computed with the Shellspec program. The best match between the model spectra and the observations is obtained for an accretion disk of inner/outer radius 5.1/23 solar radii, thickness of 5.2 solar radii, density of 1.0e-13 g/cm³, and maximum temperature of 14000 K, along with a gas stream at a temperature of ~8000 K transferring ~2.4e-9 solar masses/yr. We show H-alpha Doppler tomograms of the velocity structure of the gas, constructed from difference profiles calculated through sequentially subtracting contributions from the stars and accretion structures. The tomograms provide independent support for the Shellspec modelling, while also illustrating that residual emission at sub-Keplerian velocities persists even after subtracting the disk and stream emission. Spectral variability in the H-alpha profile beyond that expected from either the orbital or the long-period cycle is present on both multi-week and multi-year timescales, and may reflect quasi-random changes in the mass transfer rate or the disk structure. Finally, a transient UV spectral absorption feature may be modelled as an occasional outflow launched from the vicinity of the disk-stream interaction region.

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Blobrana


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Posts: 131433
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Title: CoRoT photometry and high-resolution spectroscopy of the interacting eclipsing binary AU Mon
Authors: M. Desmet, Y. Fr'emat, F. Baudin, P. Harmanec, P. Lampens, E. Janot Pacheco, M. Briquet, P. Degroote, C. Neiner, P. Mathias, E. Poretti, M. Rainer, K. Uytterhoeven, P. J. Amado, J.-C. Valtier, A. Prsa, C. Maceroni, C. Aerts

Analyses of very accurate CoRoT space photometry, past Johnson V photoelectric photometry and high-resolution echelle spectra led to the determination of improved and consistent fundamental stellar properties of both components of AU Mon. We derived new, accurate ephemerides for both the orbital motion (with a period of 11.113d) and the long-term, overall brightness variation (with a period of 416.9d) of this strongly interacting Be + G semi-detached binary. It is shown that this long-term variation must be due to attenuation of the total light by some variable circumbinary material. We derived the binary mass ratio M_G /M_B = 0.17\p0.03 based on the assumption that the G-type secondary fills its Roche lobe and rotates synchronously. Using this value of the mass ratio as well as the radial velocities of the G-star, we obtained a consistent light curve model and improved estimates of the stellar masses, radii, luminosities and effective temperatures. We demonstrate that the observed lines of the B-type primary may not be of photospheric origin. We also discover rapid and periodic light changes visible in the high-quality residual CoRoT light curves. AU Mon is put into perspective by a comparison with known binaries exhibiting long-term cyclic light changes.

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