COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3340 Konkoly Observatory Budapest 19 June 1989 HU ISSN 0374 - 0676 SPECTROSCOPY OF VW Hyi Spectroscopic observations of VW Hyi during quiescence are presented in this study. The spectroscopic data were obtained between 1985 December 5, UT=06h45m - 08h18m (10 spectra) and December 6, UT=06h32m - 08h23m (13 spectra) with the Image Dissector Scanner (IDS) in the ESO 1.52 meter telescope equipped with the Boller-Chivens Cassegrain Spectrograph (Haefner and Schoembs 1987). Table I gives the journal of observations and radial velocity measurements. Table I HJD H_alpha H_beta H_gamma 2446400+ (km/s) (km/s) (km/s) 5.786 -81 76 -275 5.794 -74 2 42 5.801 -32 157 314 5.808 -72 -67 -68 5.816 -122 23 63 5.822 -128 50 -156 5.829 -101 140 77 5.836 -56 91 44 5.842 -72 167 195 5.849 -87 104 -36 6.775 -118 32 -18 6.782 -162 -45 -202 6.788 -120 -45 -307 6.795 -178 213 362 6.801 -12 179 343 6.807 -42 197 -224 6.814 11 213 85 6.820 -55 102 232 6.827 -60 22 -22 6.833 -69 157 256 6.840 -70 129 317 6.846 -74 37 -203 6.852 -115 -160 -129 The wavelength range lambda lambda 3760 - 7180 was covered, with a dispersion of 172 A/mm. The exposure time was about 10 minutes on the first night and 8 minutes on the second night for each spectrum. The reduction was carried out [FIGURE 1] with the standard IHAP software in the ESO Headquarters in Garching. The wavelength calibration of the spectra was obtained from the helium-argon lamp (HEAR) exposure before and after the observations every night. No drift in these HEAR spectra was found. The probable wavelength errors were tested by the radial velocity variations of OI lambda5017, OI lambda6100 A and beginning wavelength of the atmospheric oxigen band 6878 A. The probable pixel-defects of the IDS were tested especially around the H_alpha emission lines. The calibration of this part of the spectra was repeated using a large number of calibration lines. There was not found any pixel defect. Absolute flux calibration was deduced from observations of the white dwarf standard star Feige 15. The reduction procedure was repeated at least two times. The spectra were obtained at quiescence and, all spectra are dominated by H_alpha, HeI 5876, H_beta, H_gamma, H_delta emission lines. Since the sensibility of IDS is not enough for short wavelengths, the blue sides of the spectra are too noisy. The sum spectrum is given in Figure 1. The H_alpha, H_beta, and H_gamma Balmer emission lines were used for the determination of the radial velocity curves. The emission lines were fitted by a Gaussian profile (double Gaussian profile for H_alpha lines, single Gaussian profile for the relatively weak H_beta and H_gamma lines ). Figure 2 shows the radial velocity curves of VW Hyi. The symbols refer to different observing nights: open circles to JD 2446405, and the dots to JD 2446406. The solid line is the fitted sine curve. The phases refer to the elements: HJD(max)=2440128.0222+0.0742711d*E (Vogt, 1974). The radial velocity amplitudes of H_alpha, H_gamma and H_delta [FIGURE 2] are 39+-11 km/s, 85+-23 km/s, 113+-59 km/s. The systemic velocities are -78.9+-8 km/s, 83.3+-17 km/s, 62.6+-24 km/s for these lines respectively. The earth velocity factor, -5 km/s, is not included in the radial velocities. In the earlier study of Schoembs and Vogt (1981) the semi-amplitude of the H_alpha line was obtained as 78+-14 km/s, and the systemic velocity was zero. Their observations were obtained at quiescence and during the late decline from an outburst. These observations are insufficient to account for the differences in radial velocity curves, because such differences might occur from time to time. A search for similar cases was carried out in other cataclysmic variables. In the UX UMa star PHL 227 Haefner and Schoembs (1987) found the values of K_1 and gamma velocities from H_alpha and H_beta lines as follows: K_1alpha=124+-20 km/s, K_1beta=87+-15 km/s, gamma_alpha=43+-13 km/s, and gamma_beta=-58+-10 km/s, respectively. In V2051 Oph (Watts et al., 1986) the values of K_1 from the H_beta and H_gamma lines are consistent with each other yielding the mean result K_1=111+-12 km/s, (K_beta=108+-14 km/s, K_1gamma=116+- 23 km/s). The gamma systemic velocities are significantly different by 90 km/s (gamma_beta=-55+-9 km/s, gamma_gamma=35+-15 km/s). In RW Tri Kaitchuck et al. (1983) found a difference 115 km/s between the gamma for the redshifted component of the H_beta and H_gamma lines. More spectroscopic observations with high dispersion are needed in order to understand these differences in the radial velocity curves and semi-amplitudes of VW Hyi. A. TALAT SAYGAC Istanbul University Observatory 34452- Univ. Istanbul Turkey References: Haefner, R., and Schoembs, 1987, Mon. Nor. R. astr. Soc., 224, 231. [BIBCODE 1987MNRAS.224..231H ] Kaitchuck, R.H., et al. 1983, Astrophys. J., 267, 239. [BIBCODE 1983ApJ...267..239K ] Schoembs, R., and Vogt, N. 1981, Astron. Astrophys., 97, 185. [BIBCODE 1981A&A....97..185S ] Vogt, N. 1974, Astron. Astrophys., 36, 369. [BIBCODE 1974A&A....36..369V ] Watts, et al. 1986, Astron. Astrophys., 154, 197. [BIBCODE 1986A&A...154..197W ]