4U 1626-67: The Binary with the Smallest Known Mass Function
Abstract
The pulsating X-ray source 4U 1626-67 is an accreting neutron star in a binary system with a very low mass companion. The authors observed the source with EXOSAT continuously for 23 hr on 1986 March 30 - 31 UT. These observations allow them to set a stringent upper limit on the projected semimajor axis of the orbit of the neutron star. The corresponding upper limit on the mass function is 1.3×10-6M_sun;. The authors conclude that if the orbital inclination angle, i, equals 90°, then the optical companion star has a mass of ⪉0.02 M_sun;. However, they find that a companion star mass ≥0.06 M_sun; is required if gravitational radiation is responsible for driving the mass transfer in this system. Only for i ⪉ 16° can a companion star mass this large be accomodated by the limit on the orbital amplitude. The authors also present in this work their results on the flaring activity in 4U 1626-67 on time scales of ≡1000 s, the energy-dependent pulse profiles, and the pulse period history over the past decade.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 1988
- DOI:
- 10.1086/166230
- Bibcode:
- 1988ApJ...327..732L
- Keywords:
-
- Gravitational Fields;
- Mass Transfer;
- Neutron Stars;
- Stellar Mass;
- Stellar Rotation;
- X Ray Binaries;
- Blue Stars;
- Computational Astrophysics;
- Exosat Satellite;
- Pulsars;
- X Ray Sources;
- Astrophysics;
- STARS: BINARIES;
- STARS: INDIVIDUAL ALPHANUMERIC: 4U 1626-67;
- X-RAYS: BINARIES