2. Observations and results
Using a CCD spectrograph attached to the Cassegrain focus of the 2.16 m telescope at Xinglong station of Beijing Astronomical Observatory, Academia Sinica, we have made spectroscopic observations of 1H2214+589/3G71 during our long-term monitoring programme for 12 Be/X-ray binaries and 34 classical Be stars since 1992. The spectra of 3G71 obtained on October 15, 1995 (JD 2450006) are shown in Figs. 1 and 2, with a reciprocal dispersion of 50mm-1 and spectral resolution of 1.22 pixel-1, covering the wavelength range 5500-6750 (Fig. 1) and 4300-5500 (Fig. 2), respectively. Data reductions were done with the IRAF package on Sun-4 Work Station. The influence of night sky light on the spectra has been eliminated. As one can see from the spectrum in Fig. 1, it is dominated by the extremely strong, single- peaked H emission line. In order to show some weak lines clearly, part of H emission line has to be truncated in Fig. 1 due to its too large intensity, while a reduced whole spectrum is appended to the upper left of the figure.
Our observations indicated that the Balmer emission of 3G71, though often highly variable, is still extremely strong. In fact, the peak intensity of H emission line relative to continuum changed between 15 and 20, and its equivalent width changed between 75 on October 15, 1995 and 103 on November 5, 1993 during our programme (Hang & Xia, 1997). The maximum equivalent width is larger than those of the 11 Be/X-ray binaries considered in the work by Reig, Fabregat, and Coe (1997) except He 3-640/A 1118-61 (Coe et al. 1994), which may be slightly larger. The H-Balmer lines exhibit obvious photospheric absorption with wide line wing except H line, which is completely filled in by its emission. Although H is also seen in strong emission, with its peak intensity relative to the continuum reaching 2.5 in 1995, it still shows obvious photospheric absorption. We find a strong asymmetry in the H absorption, that can be due either to an asymmetry in the velocity field or to the presence of weak emission features in its blue wing. The full width at zero intensity of H photospheric absorption profile amounts to 60 (see Fig. 2), corresponding to a velocity of about 3700 km s-1.
Some weaker lines of He I can be easily detected, such as He I 4471, 4713, 4921, 5876 and 6678. Among them He I 5876 is the most prominent line and possesses emissions in its absorption wings.
The following multiplets or strong multiplet components of Fe II emission are visible: (37)- 4629; (38)- 4583; (42)- 5169, 5018, 4923; (49)- 5316, 5275; (Z4D0-C4D)- 6318, 6384. Among them the multiplet (42) is the strongest.
Another distinct feature in the spectra is the appearance of a lot of forbidden lines. [O I] 6300 and [OI] 6364 are of considerable intensity, although [O I] 5577 is not present. In addition, [Fe II] 5527, 4889, 4814, 4415, 4359 and 4304 also appear clearly.
The intensity ratio of absorption lines Mg II 4481 and He I 4471 is about 0.7. This ratio is about 0.7 at B5 and about 1 at B8. The spectral type of 3G71 is approximately assigned as B5.
© European Southern Observatory (ESO) 1999
Online publication: March 18, 1999