Chandra/LETGS Studies of the Collisional Plasma in 4U 1626-67
Abstract
We present an analysis of Chandra/LETGS observations of the ultracompact X-ray binary (UCXB)4U 1626-67, continuing our project to analyze the existing Chandra gratings data of this interesting source. The extremely-low-mass, hydrogen-depleted donor star provides a unique opportunity to study the properties and structure of the metal-rich accreted plasma. There are strong, double-peaked emission features of O VII-VIII and Ne IX-X, but no other identified emission lines are detected. Our spectral fit simultaneously models the emission-line profiles and the plasma parameters, using a two-temperature collisionally-ionized plasma. Based on our line-profile fitting, we constrain the inclination of the system to 25-60° and the inner disk radius to ~1500 gravitational radii, in turn constraining the donor mass to ≲0.026 M⊙, while our plasma modeling confirms previous reports of high neon abundance in the source, establishing a Ne/O ratio in the system of 0.47 ± 0.04, while simultaneously estimating a very low Fe/O ratio of 0.0042 ± 0.0008 and limiting the Mg/O ratio to less than 1% by number. We discuss these results in light of previous work.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 2021
- DOI:
- 10.3847/1538-4357/ac0ade
- arXiv:
- arXiv:2106.06558
- Bibcode:
- 2021ApJ...920..142H
- Keywords:
-
- Neutron stars;
- Stellar accretion disks;
- Low-mass x-ray binary stars;
- High resolution spectroscopy;
- Pulsars;
- Compact binary stars;
- Plasma astrophysics;
- White dwarf stars;
- 1108;
- 1579;
- 939;
- 2096;
- 1306;
- 283;
- 1261;
- 1799;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- accepted by the Astrophysical Main Journal, 16 pages, 13 figures