Bibcode
DOI
González Hernández, Jonay I.; Rebolo, Rafael; Israelian, Garik; Casares, Jorge; Maeda, Keiichi; Bonifacio, Piercarlo; Molaro, Paolo
Bibliographical reference
The Astrophysical Journal, Volume 630, Issue 1, pp. 495-505.
Advertised on:
9
2005
Journal
Citations
29
Refereed citations
23
Description
Using a high-resolution spectrum of the secondary star in the neutron
star binary Cen X-4, we have derived the stellar parameters and veiling
caused by the accretion disk in a consistent way. We have used a
χ2 minimization procedure to explore a grid of 1,500,000
LTE synthetic spectra computed for a plausible range of both stellar and
veiling parameters. Adopting the best model parameters found, we have
determined atmospheric abundances of Fe, Ca, Ti, Ni, and Al. These
element abundances are supersolar ([Fe/H]=0.23+/-0.10), but only the
abundances of Ti and Ni appear to be moderately enhanced (>=1
σ) as compared with the average values of stars of similar iron
content. These element abundances can be explained if the secondary star
captured a significant amount of matter ejected from a spherically
symmetric supernova (SN) explosion of a 4 Msolar He core
progenitor and if we assume solar abundances as primordial abundances in
the secondary star. The kinematic properties of the system indicate that
the neutron star received a natal kick velocity through an aspherical SN
and/or an asymmetric neutrino emission. The former scenario might be
ruled out, since our model computations cannot produce acceptable fits
to the observed abundances. We have also examined whether this system
could have formed in the Galactic halo, and our simulations show that
this possibility seems unlikely. We also report a new determination of
the Li abundance, consistent with previous studies, that is unusually
high and close to the cosmic Li abundance in the Galactic disk.
Based on observations obtained with the UVES at the VLT Kueyen 8.2 m
telescope in program 65.H-0447.