Chemical abundances of the secondary star in the Neutron star X-ray binary Cygnus X-2

Abstract

We present UES@WHT high-resolution spectra of the low-mass X-ray binary (LMXB) Cygnus X-2. We have derived the stellar parameters of the secondary star using ${\chi }^2$ minimisation procedure, and taking into account any possible veiling from the accretion disk. We determine a metallicity higher than solar ([Fe/H]$=0.27\pm 0.19$), as seen also in the neutron star X-ray binary Centaurus X-4. The high-quality of the secondary's spectrum allow us to determine the chemical abundances of O, Mg, Si, Ca, S, Ti, Fe and Ni. We found that some $\alpha$-elements (Mg, Si, S, Ti) are enhanced, consistent with a scenario of contamination of the secondary star during the supernova event. Surprisingly oxygen appears to be under-abundant, whereas enhanced abundances of Fe and Ni are measured. Assuming that these abundances come from matter that has been processed in the SN and then captured by the secondary star, we explore different SN explosion scenarios with diverse geometries. A non-spherically symmetric SN explosion, with a low mass cut, seems to reproduce better the observed abundance pattern of the secondary star compared to the spherical case.

arXiv comment14 pages, 12 figures. Accepted for publication in MNRAS

References in corpus (27)

• Chemical abundances of 1111 FGK stars from the HARPS GTO planet search program.Galactic stellar populations and planets
• Spin-orbit angle measurements for six southern transiting planets; New insights into the dynamical origins of hot Jupiters
• The photospheric solar oxygen project: I. Abundance analysis of atomic lines and influence of atmospheric models
• A Black Hole in the Superluminal source SAX J1819.3-2525 (V4641 Sgr)
• The mass of the neutron star in Cyg X-2 (V1341 Cyg)
• C, S, Zn and Cu abundances in planet-harbouring stars
• A Theory of Gamma-Ray Bursts
• Cygnus X-2, super-Eddington mass transfer, and pulsar binaries
• Formation of High Mass X-ray Black Hole Binaries
• Oxygen abundances in planet-harbouring stars. Comparison of different abundance indicators
• Oxygen Line Formation in Late-F through Early-K Disk/Halo Stars: Infrared O I Triplet and [O I] Lines
• Cygnus X-2: the Descendant of an Intermediate-Mass X-Ray Binary
• Optical Emission from Aspherical Supernovae and the Hypernova SN 1998bw
• The UV line spectrum of the soft X-ray transient XTE J1118+480: a CNO processed core exposed
• Formation of the Black Hole in Nova Scorpii
• On the mass of the neutron star in Cyg X-2
• Chemical Abundances of the Secondary Star in the Black Hole X-ray Binary XTE J1118+480
• Chemical Abundances in the Secondary Star in the Black Hole Binary A0620-00
• XTE J1118+480: A Metal-Rich Black Hole Binary in the Galactic Halo
• The Black Hole Binary Nova Scorpii 1994 (GRO J1655-40): An improved chemical analysis
• Chemical Abundances of the Secondary Star in the Black Hole X-Ray Binary V404 Cygni
• Chemical Abundances in the Secondary Star of the Neutron Star Binary Centaurus X-4
• The formation of black hole low-mass X-ray binaries: through case B or case C mass transfer?
• The isotopic 6Li/7Li ratio in Cen X-4 and the origin of Li in X-ray binaries
• On the kinematics of the neutron star low mass X-ray binary Cen X-4
• Simultaneous ASCA and HST/GHRS observations of Cygnus X-2/V1341 Cygni
• Chemical Abundances in the Secondary Star of the Black Hole Binary V4641 Sagittarii (SAX J1819.3-2525)

Cited by in corpus (4)

• A non-interacting Galactic black hole candidate in a binary system with a main-sequence star
• X-ray Binaries
• The Formation of Rapidly Rotating Black Holes in High Mass X-ray Binaries
• The peculiar chemical abundance of the transitional millisecond pulsar PSR J1023+0038 -- Li enhancement