Super-Eddington Winds from Type I X-Ray Bursts
Name
Yu_2018_ApJ_863_53.pdf
Description
Published version
Size
1.18 MB
Format
Adobe PDF
Checksum (MD5)
3a0272678ab8a4d20292840b3ae44ea3
Author(s)
Yu, Hang
Weinberg, Nevin N.
Date Issued
August 2018
Journal
Astrophysical Journal
Publisher
American Astronomical Society
Citation
Yu, Hang and Nevin N. Weinberg. "Super-Eddington Winds from Type I X-Ray Bursts." Astrophysical Journal 863, 1 (August 2018): 53 © 2018 The American Astronomical Society
Version
Final published version
Abstract
We present hydrodynamic simulations of spherically symmetric super-Eddington winds from radius-expansion type I X-ray bursts. Previous studies assumed a steady-state wind and treated the mass-loss rate as a free parameter. Using MESA, we follow the multi-zone time-dependent burning, the convective and radiative heating of the atmosphere during the burst rise, and the launch and evolution of the optically thick radiation-driven wind as the photosphere expands outward to radii r ph ≳ 100 km. We focus on neutron stars (NSs) accreting pure helium and study bursts over a range of ignition depths. We find that the wind ejects ≈0.2% of the accreted layer, nearly independent of ignition depth. This implies that ≈30% of the nuclear energy release is used to unbind matter from the NS surface. We show that ashes of nuclear burning are ejected in the wind and dominate the wind composition for bursts that ignite at column depths ≳10 9 g cm -2 . The ejecta are composed primarily of elements with mass numbers A > 40, which we find should imprint photoionization edges on the burst spectra. Evidence of heavy-element edges has been reported in the spectra of strong radius-expansion bursts. We find that after ≈1 s, the wind composition transitions from mostly light elements ( 4 He and 12 C), which sit at the top of the atmosphere, to mostly heavy elements (A > 40), which sit deeper down. This may explain why the photospheric radii of all superexpansion bursts show a transition after ≈1 s from a superexpansion () to a moderate expansion ().
MIT Department
Massachusetts Institute of Technology. Department of Physics
MIT Kavli Institute for Astrophysics and Space Research
Terms of Use
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.3847/1538-4357/aad045
