MODELING THE ACCRETION STRUCTURE OF AU Mon

Abstract

AU Mon is a long-period (11.113 d) Algol-type binary system with a persistent accretion disk that is apparent as double-peaked Hα emission. We present previously unpublished optical spectra of AU Mon which were obtained over several years with dense orbital phase coverage. We utilize 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 Hα, Hβ, 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 R ⊙ , thickness of 5.2R ⊙ , density of 1.0 × 10 −13 g cm −3 , and maximum temperature of 14000 K, along with a gas stream at a temperature of ∼8000 K transferring ∼2.4 × 10 −9 M ⊙ yr −1 . We show Hα 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 modeling, while also illustrating that residual emission at sub-Keplerian velocities persists even after subtracting the disk and stream emission. Spectral variability in the Hα 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 modeled as an occasional outflow launched from the vicinity of the disk-stream interaction region.

On the Evolutionary Stage of the Interacting Binary AU Mon

“…The disc found by these authors is about twice the size found by Djurašević et al (2010); they argue that this is not inconsistent, since one model fits the optically thick disc component whereas the other is sensible to the optically thin disc envelope. It seems well established that the system shows stronger absorption lines during the low state (Peters 1994, Atwood-Stone et al 2012, Barría & Mennickent 2011. The eclipse-mapping reconstruction of the accretion disc by Mimica & Pavloski (2012) indicates a clumpy disc structure.…”

“…For instance,Atwood-Stone et al (2012) givesṀ c = 2.4 × 10 −9 M yr −1 , obtained from the physical parameters of the gas stream incorporated into the line profile models, although they…”

Doppler tomography of the Double periodic variable HD 170582 at low and high stage

“…This result shows the importance of imaging the circumstellar material with the aid of tomographic reconstructions, which are still scarce for the class of DPVs (Atwood-Stone et al 2012, Richards et al 2014, Mennickent et al 2012b.…”

Accretion disks in Algols: Progenitors and evolution

“…Masses and radii of β Lyr are from Zhao et al (2008), the effective temperatures and mass transfer rates from Harmanec (2002). Masses, radii and effective temperatures for AU Mon are from Desmet et al (2010) and Atwood-Stone et al (2012). We determined a very uncertain mass transfer rate applying the (O−C) method on the data found in the catalog of Kreiner et al (2001).…”