Other
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aas...19111013d&link_type=abstract
American Astronomical Society, 191st AAS Meeting, #110.13; Bulletin of the American Astronomical Society, Vol. 29, p.1389
Other
Scientific paper
The spectrum of V2116 Oph, the counterpart of GX1+4 (=X1728--247), is exotic, even among the unusual spectra of other optical counterparts of compact Galactic X-ray sources. The optical spectrum of the object has shown higher excitation emission lines than any other known X-ray star, extremely strong Hα emission, and marked time variability on scales from minutes to years. The second strongest emission line is a rare and remarkable one, namely extremely prominent OI lambda 8446, which is likely to result from pumping by an intense Lybeta radiation field. As the X-radiation from GX1+4 is steadily pulsed, with typical pulsed fractions of 0.4, it is possible that the OI lambda 8446 emission in V2116 Oph may also be strongly modulated with the current 120 s period of the X-ray source. If so, this may well allow us to obtain high signal-to-noise radial velocity measurements, and thus to determine the system parameters. In order to study the pulsations of OI lambda 8446 emission from V2116 Oph, we have used innovative features of the Taurus Tunable Filter (TTF) instrument on the AAT. After the TTF was tuned to a bandpass of 7 Angstroms at the center of the line, we repeatedly imaged V2116 Oph and a reference star through a 6'' by 3' slit, shuffling the charge down 10 pixels after each 12 s exposure. After this is done 102 times, the chip is full and is read out completely. Differential photometry with nearby reference stars reveals that despite the constantly variable clouds and poor seeing conditions, we may set an upper limit of ~ 3% (full-amplitude) on periodic lambda 8446 oscillations at the X-ray frequency. This value is comparable to the amplitude of continuum oscillations observed on some nights by other workers. Therefore we are able to rule out an enhancement of the pulsation amplitude in OI emission, at least at the time of our observations.
Bland-Hawthorn Jonathan
Deutsch Eric W.
Margon Bruce
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