3 Spectroscopy

We obtained high-resolution spectra with two telescopes and spectrographs at the ESO La Silla Observatory: in 1992 and 1993, the ESO 1.5 m telescope equipped with the ECHELEC spectrograph, in 1994 the 1.4 m CAT telescope with coudé echelle spectrograph (CES) were used. The spectra are listed in Table 1. They were reduced with the MIDAS package; details of the reduction procedure were described by Mayer et al. (1997). The S/N ratio of the ECHELEC spectra is about 150, in case of CAT/CES spectra about 250. The most pronounced lines are H$\beta$ and He I 4922. Unfortunately, a CCD defect between 4914 and 4917 Å was present close to the He I line in our 1992 spectra. The H$\beta$ line is rather wide, and the stellar components are more severely blended than in the case of the He I line, rendering H$\beta$ less suitable for radial velocity determinations. Examples for profiles of the He I 4922 line are presented in Fig. 3.

In one night, two spectra were obtained in the H$\alpha$ region (CAT 5.1 and 5.2 in Table 1; see Fig. 4 for CAT 5.2). These profiles confirm the presence of emission in the Balmer line, as already found by MC. The line is asymmetric - the red wing being less steep, with a peak emission of about 20% above continuum level at zero velocity. The spike at -10 kms^-1 is probably due to the $\eta$ Carinae nebulae (MC give a nebular velocity of -27 kms^-1). There is a P Cygni-type absorption component centered atabout -250 kms^-1, which could be attributed to the expansion velocity of an envelope. On the red side the emission reaches about +500 kms^-1. It is of course not possible to judge the nature and origin of the emission from only these two spectra.

Figure 3: Examples of profiles of the He I 4922 line. Labels near profiles give phases according to ephemeris (1); the step width between continuum levels is 10% of the normalized flux

Figure 4: Profile of H$\alpha$ line (spectrum CAT 5.2)

 

 

Table 1: Journal of QZ Car spectra and radial velocities of component A1

hel. JD	exposure	$\Phi_{\rm A}$	$V_{\rm A}$	equivalent	$\Phi_{\rm B}$	spectral range (Å)	instrument and
$-2\,400\,000$	(s)		(kms-1)	width (Å)		or observed line	identification
48759.5206	3000	0.3975	-5.6	0.45	0.0617	4628-4953	ECH 1
48760.5324	4500	0.4463	4.0	0.28	0.2304	4628-4953	ECH 2
48760.5914	4500	0.4491	4.0	0.40	0.2402	4628-4953	ECH 3
48760.6511	4500	0.4520	0.3	0.34	0.2502	4628-4953	ECH 4
48761.5434	4500	0.4950	10.5	0.22	0.3989	4628-4953	ECH 5
48761.6011	4500	0.4978	-1.7	0.22	0.4085	4628-4953	ECH 6
48761.6629	4188	0.5008	-2.3	0.29	0.4188	4628-4953	ECH 7
48762.6087	3600	0.5464	17.0	0.25	0.5765	4628-4953	ECH 8
48762.6636	3600	0.5491	25.5	0.28	0.5856	4628-4953	ECH 9
48763.5482	3600	0.5917	13.1	0.34	0.7331	4628-4953	ECH 10
49023.5824	3600	0.1320	-65.8	0.29	0.0779	4628-4953	ECH 11
49024.5867	4200	0.1804	-53.7	0.24	0.2453	4628-4953	ECH 12
49025.7387	3000	0.2360	-26.4	0.40	0.4373	4628-4953	ECH 13
49026.7533	3600	0.2849	-15.5	0.28	0.6064	4628-4953	ECH 14
49027.5791	4200	0.3247	-15.6	0.30	0.7441	4628-4953	ECH 15
49027.6242	3600	0.3269	-14.4	0.31	0.7516	4628-4953	ECH 16
49027.7721	3600	0.3340	-9.5	0.31	0.7763	4628-4953	ECH 17
49028.6659	4800	0.3771	-14.6	0.32	0.9252	4628-4953	ECH 18
49147.4747	3600	0.1068	-79.0	0.24	0.7293	4826-5143	ECH 19
49148.5718	5400	0.1597	-71.9	0.31	0.9122	4826-5143	ECH 20
49448.5536	1800	0.6264	17.5	0.20	0.9159	He 4922	CAT 1
49449.6870	1800	0.6811	14.8	0.28	0.1048	He 4922	CAT 2
49450.5099	2400	0.7207	4.9	0.27	0.2419	He 4922	CAT 3
49451.5703	1800	0.7718	22.8	0.30	0.4187	He 4922	CAT 4
49452.5932	2100	0.8211			0.5893	H$\alpha$	CAT 5.1
49452.6398	1200	0.8234			0.5970	H$\alpha$	CAT 5.2
49453.5870	1800	0.8691	-10.6	0.21	0.7549	He 4922	CAT 6

3.1 The HeI 4922/OII 4925 line blend

As known from previous studies, the most prominent feature in the He I 4922 line profile corresponds to the primary component of the long-period binary (A1). In some spectra taken near quadratures of the short-period binary, it is apparent that lines of both stars are present. It is however also evident that all line components are changing their strengths with time or phase. The equivalent width of A1 lines is considerably larger than that of B1 and B2 lines, which makes the disentangling of spectral features a difficult task. We tried to use the KOREL code (Hadrava 1995) for this purpose. The line of star A1 was of course always dominant, and the orbit derived with the KOREL program had appropriate parameters. The short-period orbit is masked to such extent, that the automatic disentangling procedure was not able to extract its spectral features. Therefore, we tried to deconvolve the spectra by multiple Gaussian profile fitting (using MIDAS routines). The positions, depths and widths of the A1, B1 and B2 He I 4922 line components were iteratively optimized, while a fourth component in the blend was attributed to the O II 4925 line of star A1. In a paper on KX Vel (Mayer et al. 1997) we found that in this binary with a spectral type practically identical to A1 the equivalent width of the O II line equals approximately one sixth of the He I 4922 line. Therefore, we assumed the same relative strength for this line here too, and kept the ratio fixed at this value; for the two system B stars, we neglected any contribution of O II 4925 to the blend.

Being aware that automatic procedures can easily converge in local minima of the parameter space, we searched for a best fit solution following both the visual appearance of the computed profile blend and the value of sum of squared residuals O-C. We believe that the values given in Table 1 are the best obtainable. In some cases however it was not possible to fully reconstruct the profile using the four adapted line components. In cases close to conjunction of the short-period orbit, the Gaussian profile parameters have larger error margins than close to quadrature phases.

3.2 Other HeI and HeII lines

Among other lines, only He I 4713 and 5015 appear suitable for radial velocity determinations. Unfortunately, the B2 component cannot be identified reliably in any of them.

Conti et al. (1977) classified the integral spectrum as O9.5 Ib(f), i.e., they should have seen He II 4686 in emission. However, such emission is not mentioned in the MC paper, and also Walborn's classification does not refer to it. Our spectra can possibly explain this situation, because emission is also not always visible there. Several examples of the line profile are shown in Fig. 6. Due to the clear variability of the emission, the A1 contribution to the $\lambda$ 4686 line is unpredictably affected by the superimposed emission and hence not suitable for radial velocity measurements.

 

 

Table 2: Radial velocity curve solution - system A

Element	MC solution	MC &
	for He I	present data
period	20 $.\!\!^{\rm d}$73	20 $.\!\!^{\rm d}$73596
semi-amplitude K (kms-1)	49	49.6
MC systemic velocity (kms-1)	-7	-8.1
present data systemic velocity (kms-1)		-19.1
eccentricity	0.34	0.342
longitude of periastron $\omega$	131 $\hbox{$^\circ$ }$	143.6 $\hbox{$^\circ$ }$
time of periastron	2442530.0	2442530.49
rms of MC data (kms-1)		11.9
rms of present data (kms-1)		6.9
$a \sin i$ (km)	$1.31\, 10^7$	$1.33\, 10^7$
mass function ($M_{\odot}$)	0.21	0.218