5 V382 Cyg

Figure 10: Spectrum of V382 Cyg; at approximate phase 0.75 for $\lambda$ 4523 to 4887 Å, at phase 0.29 for $\lambda$ 4828 to 5038 Å (shifted in flux by +0.10).

 

 

Table 5: Comparison of V382 Cyg parameters.

Author	K1	K2	$V\gamma$
	(km s-1)	(km s-1)	(km s-1)
Popper (1978)	255	360
Popper & Hill (1971)	$276 \pm 4$	$400 \pm 6$
Harries et al. (1997)	$260.2 \pm 2.8$	$350.8 \pm 3.8$	$8 \pm 3.6$
Harries et al. (corr.)	271.1	352.0	8

Orbital elements of V382 Cyg (HD 228854) were published by Pearce (1952), but without the measured radial velocities. Popper (1978) obtained spectra of various dispersions and measured velocity amplitudes for several lines. Later Popper's spectra with a reciprocal dispersion of 45 Å mm^-1 were analyzed by Popper & Hill (1991) using a cross-correlation method. In a recent paper by Harries et al. (1997) the radial velocity curve was obtained using 17 CCD spectra in the wavelength region 4700-5950 Å, with a mean reciprocal dispersion of 0.3 Å pixel^-1. Results of these studies are listed in Table 5.

Light curves for this binary were measured several times, always using standard UBV filters (Landolt 1964, 1975; Bloomer et al. 1979; Degirmenci et al. 1999). The light curve analysis shows that the binary is in a contact configuration, with an orbital inclination of about 85$\degr$. The period is variable (e.g., Mayer et al. 1998; Degirmenci et al. 1999), probably due to strong mass loss via stellar wind (Koch et al. 1979). Note that the variability of the period was not taken into account by Harries et al. (1997). The correct ephemeris for the epoch of their spectra was

$${\rm Prim.~~min.} = {\rm HJD}~~2436814.680 + 1\fd8855328 \cdot E$$

(this ephemeris is valid for our spectra, too). The phases of the Harries et al. velocities should then be smaller by 0$\fp$025, and recalculated K₁ and K₂ are larger by several kilometers, see Table 5.

Examples of our spectra are displayed in Fig. 10, and for H$\alpha$ in Fig. 7. To find the radial velocity curve, we gave highest weight to the He  II 4686 line, since both its components are narrower than in other lines, and hence can be better resolved. Our results are listed in Table 1, and the radial velocity curve is presented in Fig. 11.

Figure 11: Radial velocity curve of V382 Cyg; open circles - He  II 4542, filled circles - He  II 4686, crosses - H$\beta$.

As judged by the weakness of the He  I lines 4713 and 4922, the star is considerably earlier than O 8, i.e. the classification by Pearce (1952) as O 6.5 for the primary and O 7.5 for the secondary appears more correct than that by Hiltner (1956) (O 8). It should be remarked that the equivalent widths, as well as FWHMs, are larger for He  II 4541 than for He  II 4686 line. According to atmospheric models (Napiwotzki 2001) the equivalent widths of He  II 4686 should be larger than that of He  II 4541; but the models do explain the larger FWHM of He  II 4541. One may compare the V382 Cyg spectra with those of other O-type stars published by Walborn & Fitzpatrick (1990); among supergiants, He  II 4686 appears as an emission line. In our spectra of V382 Cyg, He  II 4686 is a net absorption line, though an emission contribution probably reduces the absorption strength. One effect will be that in near quadrature spectra the emission will be most evident at wavelengths between the two binary components, i.e. around  $V_{\gamma}$, the result would be as observed, and amplitudes of both components should be smaller than derived from the 4686 line. Velocities obtained from He  II 4541 would then be more realistic, i.e., both K_1,2 would be smaller by several percent, and masses would be smaller by about 10%.

Another effect of an emission contribution would be that the weakness of the 4686 line relative to He  II 4541 as observed in our spectra would be in better agreement with the theoretical line ratio deduced from the models of Napiwotzki (2001).