Observations and Data Reduction

Optical spectra of GRO J1655-40 were taken on the 3.9m AAT at Siding Springs using the RGO spectrograph with a 1200R grating, giving a resolution of 1.5ц…. Slit width was 1.5''. The exposure time was 900 sec for each spectrum and a total of seven spectra were obtained over two nights (13th and 14th April, 1999). Spectra of F-stars, ranging over F2-F8 III-V and having well-known rotational velocities (Hoffleit 1982) were also obtained.

The data was reduced using standard routines in IRAF. Each spectrum was telluric corrected, doppler corrected, de-reddened and normalised. All GRO J1655-40 spectra were then summed and the result is shown in Figure 1. The signal-to-noise ratio is 55. The two main lines are H and a blend of FeI, CaI and BaII (6495ц…). Other lines present are mainly FeI. If Li is present, we are unable to separate it from FeI in our spectrum.

Figure 1: Summed spectrum of GRO J1655-40 with lines identified.

б© Copyright Astronomical Society of Australia 1997