Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1988
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988mnras.233..285n&link_type=abstract
Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 233, July 15, 1988, p. 285-304.
Astronomy and Astrophysics
Astronomy
43
Radial Velocity, Stellar Motions, Stellar Spectra, X Ray Binaries, Astronomical Spectroscopy, Globular Clusters, Helium, Iue, Line Spectra
Scientific paper
The authors present the first phase-resolved optical spectroscopy of AC 211, the optical counterpart of the X-ray source in the core of M15. The spectrum is dominated by the variable and complex He II λ4686 emission, but the authors have also found He I in absorption. By following the motion of He I λ4471 they have discovered the binary period to be 9.1±0.5 hr, with a semi-amplitude of 40±15 km s-1. If this is interpreted as reflecting the orbital motion of the compact object, either the primary is 10 - 14 M_sun;, or the secondary is a very light (<0.4 M_sun;) giant. But, most remarkably, the authors find that the mean He I velocity is blueshifted by ≡150±10 km s-1 with respect to the rest of the cluster.
Charles Phil A.
Drew Janet E.
Hassall B. J. M.
Naylor Tim
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