The mass of the neutron star in Cyg X-2 (V1341 Cyg)
| dc.creator | Casares, Jorge | |
| dc.creator | Charles, Phil | |
| dc.creator | Kuulkers, Erik | |
| dc.date | 1997-11-20 | |
| dc.date.accessioned | 2026-07-07T12:01:05Z | |
| dc.date.available | 2026-07-07T12:01:05Z | |
| dc.description | Cygnus X-2 is one of the brightest and longest known X-ray sources. We present high resolution optical spectroscopy of Cyg X-2 obtained over 4 years which gives an improved mass function of 0.69 +/- 0.03 Msun (1 sigma error). In addition, we resolve the rotationally broadened absorption features of the secondary star for the first time, deriving a rotation speed of vsin(i) = 34.2 +/- 2.5 km per s (1 sigma error) which leads to a mass ratio of q = M_c/M_x = 0.34 +/- 0.04 (1 sigma error), assuming a tidally-locked and Roche lobe-filling secondary). Hence with the lack of X-ray eclipses (i.e. i <~ 73 degrees) we can set firm 95% confidence lower limits to the neutron star mass of M_x > 1.27 Msun and to the companion star mass of M_c > 0.39 Msun. However, by additionally requiring that the companion must exceed 0.75 Msun (as required theoretically to produce a steady low-mass X-ray binary), then M_x > 1.88 Msun and i < 61 degrees (95% confidence lower and upper limit, respectively), thereby making Cyg X-2 the highest mass neutron star measured to date. If confirmed this would set significant constraints on the equation of state of nuclear matter. | |
| dc.description | 16 pages, 4 figures, ApJ Letters, accepted, LaTeX, aasms4.sty | |
| dc.identifier | https://arxiv.org/abs/astro-ph/9711236 | |
| dc.identifier | http://arxiv.org/abs/astro-ph/9711236 | |
| dc.identifier | Astrophys.J.439:L39-L42,1995 | |
| dc.identifier | doi:10.1086/311124 | |
| dc.identifier.uri | http://salesiana.dossiersoluciones.com/handle/123456789/206990 | |
| dc.subject | Astrophysics | |
| dc.title | The mass of the neutron star in Cyg X-2 (V1341 Cyg) | |
| dc.type | text |