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The short-period eclipsing X-ray binary in NGC 4214

Presentation #125.02 in the session Neutron Stars, Black Holes and Supernovae.

Published onJul 01, 2023
The short-period eclipsing X-ray binary in NGC 4214

We present analysis of recent Chandra X-ray and Hubble optical/NIR observations of the shortest known orbital period high-mass X-ray binary CXOU J1215 in NGC 4214 (X-1). A 3.6-hr eclipse period is measured with an eclipse egress much slower than the ingress suggesting it is due to either a bow shock formed in front of the compact object or a cometary tail ablated from the X-irradiated companion star. In either case, the material must form optically thick (partial covering) clumps as there is no large X-ray-obscuring column at any orbital phase merely a decrease in luminosity. We also constrain the mass and evolutionary phase of the donor star to be a stripped He star or WR star. While the Hubble photometry are consistent with this scenario, they also reveal a second strong red component consistent with a large, cool AGB star or possibly a RSG star or dust. This second component cannot be reconciled with the orbital constraints of the binary; perhaps it is an unrelated object coincident with the line of sight.

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