Correlated Radial Velocity and X-Ray Variations in HD 154791/4U 1700+24
Abstract
We present evidence for approximately 400 day variations in the radial velocity of HD 154791 (V934 Her), the suggested optical counterpart of 4U 1700+24. The variations are correlated with the previously reported ~400 day variations in the X-ray flux of 4U 1700+24, which supports the association of these two objects, as well as the identification of this system as the second known X-ray binary in which a neutron star accretes from the wind of a red giant. The HD 154791 radial velocity variations can be fitted with an eccentric orbit with period 404+/-3 days, amplitude K=0.75+/-0.12kms-1, and eccentricity e=0.26+/-0.15. There are also indications of variations on longer timescales >~2000 days. We have reexamined all available All-Sky Monitor (ASM) data following an unusually large X-ray outburst in 1997-1998 and confirm that the 1 day averaged 2-10 keV X-ray flux from 4U 1700+24 is modulated with a period of 400+/-20 days. The mean profile of the persistent X-ray variations was approximately sinusoidal, with an amplitude of 0.108+/-0.012 ASM counts s-1 (corresponding to 31% rms). The epoch of X-ray maximum was approximately 40 days after the time of periastron, according to the eccentric orbital fit. If the 400 day oscillations from HD 154791/4U 1700+24 are due to orbital motion, then the system parameters are probably close to those of the only other neutron star symbiotic-like binary, GX 1+4. We discuss the similarities and differences between these two systems.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 2002
- DOI:
- 10.1086/343798
- arXiv:
- arXiv:astro-ph/0207594
- Bibcode:
- 2002ApJ...580.1065G
- Keywords:
-
- Stars: Binaries: Symbiotic;
- Stars: Individual: Henry Draper Number: HD 154791;
- Stars: Neutron;
- X-Rays: Binaries;
- Astrophysics
- E-Print:
- 6 pages, 2 figures