Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002aas...201.5420h&link_type=abstract
American Astronomical Society, 201st AAS Meeting, #54.20; Bulletin of the American Astronomical Society, Vol. 34, p.1201
Astronomy and Astrophysics
Astronomy
Scientific paper
We have obtained Hubble Space Telescope/STIS low-resolution ultraviolet spectra of the X-ray pulsar 4U 1626-67 (=KZ TrA). This system is unusual even among X-ray pulsars due to its ultra-short binary period (P=41.4 min) and remarkably low mass-function (<1.3*E-6Msun). The 32ks far-UV spectrum reveals numerous broad emission and prominent narrower absorption lines. Most of the absorption lines are consistent in strength with a purely interstellar origin, although CI and CIV appear to need additional absorbing gas local to the system. Unusual abundance ratios are also indicated by the emission lines; the usual prominent lines of NV and HeII are absent, whilst both OIV and OV are relatively strong and we see the unusual ~1660Å OIII] multiplet. Our ultraviolet spectra therefore provide independent support for the recent suggestion that the mass donor is the chemically fractionated core of either a C-O-Ne or O-Ne-Mg white dwarf; as proposed to explain the results of Chandra high-resolution X-ray spectroscopy. Furthermore, our ultraviolet line profiles are in overall agreement with the Doppler pairs found in the X-ray spectra, being in all cases broad and/or flat-topped, or even double-peaked. Both the X-ray and far-UV lines are plausibly formed in (or in an corona just above) a Keplerian accretion disc; hence the combination of ultraviolet and X-ray spectral data may provide a rich data set for follow-on detailed models of the disk dynamics and ionization structure in this highly unusual low-mass X-ray pulsar system. Support for this work was provided by NASA through STScI grant GO-06624.01 and LTSA grant NAG5-7932.
Anderson Scott F.
Homer Lee
Margon Bruce
Wachter Stefanie
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