Hydrodynamic Simulations of Hα Emission in Algol‐Type Binaries

Abstract

Two-dimensional hydrodynamic simulations of mass transfer in short-period Algol-type binaries were performed using the numerical code Virginia Hydrodynamics 1. This code uses the piecewise parabolic method with a Lagrangian remap. Our version of the code also accounts for radiative cooling and collisional ionization and excitation processes. The purpose of performing the simulations was to study the Ha emission from circumstellar gas in the Algols. Using observational evidence from the literature to constrain the gas stream properties, hydrodynamic maps of the Ha emissivity in the two systems b Per (P \ 2.87 days) and TT Hya (P \ 6.95 days) were made in both Cartesian and velocity coordinates from the simulation data. The velocity maps were then compared to Doppler tomograms constructed from observed Ha line emission in these systems. Since the tomograms cannot be directly transformed to maps of emission in spatial coordinates, the simulated Cartesian maps enabled us to interpret the dynamical processes that produce the features observed in the Doppler tomograms. We Ðnd that the simulations produce asymmetric accretion structures with many features similar to those found in the Doppler tomograms of Algol systems.

Morphologies of Hα Accretion Regions in Algol Binaries

“…These studies show that CX Dra has strong, but complex, double-peaked Ha emission that can be seen in the observed proÐles. The source of the emission lines is a permanent accretion disk which is highly variable et al 1980 ;Peters & Polidan 1984 ;Horn (Koubsky et al 1992 ;Richards, & 1998 ; et Koubsky, S ‹ imon Koubsky al. 1998).…”

“…In this binary, the gas stream has just enough room to form a classical accretion disk. The formation of this disk has been examined with the aid of hydrodynamic simulations (Richards & Ratli † 1998). Algol binaries with periods longer than TT Hya almost always show double-peaked emission, indicating the presence of classical accretion disks in these systems.…”

Photometric Observations of Eccentric Accretion in Algol-type Binary Stars

“…As discussed by Richards & Ratliff (1998), short-period Algols tend to undergo direct mass transfer while longerperiod systems tend to build up stable accretion disks. The intermediate-period Algol systems will oscillate between states of direct impact and indirect accretion.…”

Tomography of Interacting Binary Systems: Algols to Gamma-Ray Binaries

“…Hydrodynamic simulations have been used to illustrate how the gas should be distributed between stars (e.g., in Algol binaries: Blondin, Richards & Malinkowski 1995;Richards & Ratliff 1998). However, direct images showing the flow of gas between stars in an interacting binary were first obtained by Karovska et al (2005) from soft X-ray Chandra and HST images of a system called Mira (o Ceti).…”