Mass transfer in asymptotic-giant-branch binary systems

TL;DR

This paper investigates mass transfer processes in binary systems with asymptotic-giant-branch stars, focusing on gas ejection, accretion, and nebula formation using advanced simulation techniques.

Contribution

It introduces radiative transfer into the AstroBEAR code to model mass transfer in AGB binary systems more accurately.

Findings

Gas ejection and accretion rates quantified.

Distribution of ejected gas linked to planetary nebula formation.

Enhanced simulation method for binary mass transfer processes.

Abstract

Binary stars can interact via mass transfer when one member (the primary) ascends onto a giant branch. The amount of gas ejected by the binary and the amount of gas accreted by the secondary over the lifetime of the primary influence the subsequent binary phenomenology. Some of the gas ejected by the binary will remain gravitationally bound and its distribution will be closely related to the formation of planetary nebulae. We investigate the nature of mass transfer in binary systems containing an AGB star by adding radiative transfer to the AstroBEAR AMR Hydro/MHD code.

Tables

Table 1. Table 1: The affected mass loss rate of the AGB star and the secondary.

model#	$m_{AGB}\left(M_{\odot }\right)$	$m_{sec}\left(M_{\odot }\right)$	$d\left(AU\right)$	${\dot{m}}_{AGB}\left(M_{\odot }/yr\right)$	${\dot{m}}_{sec}\left(M_{\odot }/yr\right)$
1	1.0	0.1	3	$3.4\times {10}^{-7}$	$-1.3\times {10}^{-7}$
2	1.0	0.5	4	$3.1\times {10}^{-7}$	$-1.0\times {10}^{-7}$
3	1.0	0.5	6	$2.8\times {10}^{-7}$	$-4.8\times {10}^{-8}$
4	1.0	0.5	10	$2.6\times {10}^{-7}$	$-5.8\times {10}^{-9}$

Full text

††volume: 323††journal: Planetary Nebulae††editors: X. Liu, L. Stanghellini, & A. Karakas. Editor, eds.

Introduction: Binaries are believed to be the progenitors of Type Ia supernovae, planetary nebulae and many other systems [Nordhaus & Blackman(2006), Ivanova et al. (2013), (Nordhaus & Blackman 2006; Ivanova 2013)]. In addition, many post-AGB stars show evidence for disks which must due to mass transfer with a companion. Our primary focus in this work is to study PNe projenitor binary systems with different orbital radii to explore changes in mass transfer.

**Model:**We first test our AGB-wind mass-loss model using an isolated AGB star. We model the AGB star with a pulsating ($P_{pulse}=365d$), luminous boundary and point gravity [Bowen (1988), (Bowen 1988)]. We assume dust forms when the equilibrium temperature is below the condensation temperature. The dust will change the opacity of the gas. We show in Fig. 1 that our AGB wind model produces a physically reasonable terminal velocity of $15\ km/s$ and average mass loss of $2.3\times 10^{-7}\ M_{\odot}/yr$.

We then place an accreting secondary [Krumholz et al. (2004), (Krumholz et al. 2004)] in circular orbit with the AGB star. The boundary condition of the AGB star is kept the same as in the isolated case discussed above. However, the mass of the secondary and the separation of the binary are allowed to vary. We calculate the affected mass-loss rate of the AGB star, the accretion rate of the secondary (Table 1), and examine the morphology of the outflows (Fig. 2).

Results:

1. The AGB mass-loss rate is changed by the presence of the accreting secondary.

2. The accretion rate onto the secondary can increase by up to $\sim$38% of the mass-loss rate. This exemplifies Wind-Roche-lobe-overflow [Podsiadlowski & Mohamed (2007), (Podsiadlowski & Mohamed 2007)].

3. Circumbinary disks and accretion disks (around the secondary) are conspicuously found in our calculations.

4. The resulting aspherical circumbinary density distribution provides insight for understanding aspects of aspherical planetary nebulae [Maercker et al. (2012), (Maercker et al. 2012)].