Accurate mass ratio and heating effects in the dual - line millisecond binary pulsar in NGC 6397
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13 pages
Published in:
- Astrophys.J.Lett. 584 (2003) L13-L16
e-Print:
- astro-ph/0301244 [astro-ph]
DOI:
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Abstract: (arXiv)
By means of high-resolution spectra we have measured radial velocities of the companion (hereafter COM J1740-5340) to the eclipsing millisecond pulsar PSR J1740-5340 in the Galactic globular cluster NGC 6397. The radial-velocity curve fully confirms that COM J1740-5340 is orbiting the pulsar and enables us to derive the most accurate mass ratio (M_ PSR/M_COM=5.85+/-0.13) for any non-relativistic binary system containing a neutron star. Assuming a pulsar mass in the range 1.3-1.9 Msun, the mass of COM J1740-5340 spans the interval 0.22-0.32 Msun, the inclination of the system is constrained within 56 deg <= i <= 47 deg and the Roche lobe radius is r_RL ~ 1.5-1.7 Rsun. A preliminary chemical abundance analysis confirms that COM J1740-5340 has a metallicity compatible with that measured for other stars in this metal-poor globular, but the unexpected detection of strong He I absorption lines implies the existence of regions at T>10,000 K, significantly warmer than the rest of the star. The intensity of this line correlates with the orbital phase, suggesting the presence of a region on the companion surface, heated by the millisecond pulsar flux.References(17)
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