Kavli Affiliate: Norbert S. Schulz
| First 5 Authors: Paul B. Hemphill, Norbert S. Schulz, Herman M. Marshall, Deepto Chakrabarty,
| Summary:
We present an analysis of chandra/LETGS observations of the ultracompact
X-ray binary (UCXB) 4U 1626$-$67, continuing our project to analyze the
existing
Chandra gratings data of this interesting source. The extremely low mass,
hydrogen-depleted donor star provides a unique opportunity to study the
properties and structure of the metal-rich accreted plasma. There are strong,
double-peaked emission features of OVII-VIII and Ne IX-X, but no other
identified emission lines are detected. Our spectral fit simultaneously
models the emission line profiles and the plasma parameters, using a
two-temperature collisionally-ionized plasma. Based on our line profile
fitting, we constrain the inclination of the system to 25–60$^{circ}$ and
the inner disk radius to $sim$1500 gravitational radii, in turn constraining
the donor mass to $lesssim$0.026 M_sun, while our plasma modeling confirms
previous reports of high neon abundance in the source, establishing a Ne/O
ratio in the system of $0.47 pm 0.04$, while simultaneously estimating a
very low Fe/O ratio of $0.0042 pm 0.0008$ and limiting the Mg/O ratio to
less than 1% by number. We discuss these results in light of previous work.
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