2 Observations and reduction

The third historical outburst of V 592 Her was detected at visual magnitude 12.0 by the Finnish observer Timo Kinnunen on 1998 August 26.835 UT. The outburst was confirmed on August 27.181 UT by Lance Shaw in California (see also Waagen 1998). Observations reported to VSNET (http://www.kusastro.kyoto-u.ac.jp/vsnet/) indicate that the maximum occurred near the day of the detection. We observed V 592 Her both photometrically and spectroscopically. The photometry, obtained 10 days later than the spectroscopy, was already given in Duerbeck & Mennickent (1998), who confirmed the presence of superhumps, and thus the SU UMa star nature of V 592 Her, and constrained the superhump period to SHP $_{1} = 0.06391 \pm 0.00020$ days or SHP $_{2} = 0.06007\pm 0.00020$ days.

We obtained 40 optical spectra of V 592 Herculis with the EMMI spectrograph mounted at the ESO 3.5-m NTT at La Silla Observatory, during 1998 August 29 and 30. 3 spectra were obtained with grating #13, providing a wavelength range of 4010-9420 Å, and 37 spectra were obtained with grating #8, yielding a wavelength range of 4475-7040 Å. We used slit widths of 5 and 1 arcseconds, which yielded spectral resolutions of 5.5 and 2.5 Å, respectively. The standard star LTT 7379 was observed with a 5-arcsecond slit to flux-calibrate the spectra. He-Ar lamp exposures were taken after typically each hour of science exposures. We reduced the images using standard IRAF procedures, correcting for bias and flat field. In order to wavelength-calibrate the spectra, we used calibration functions obtained by fitting $\approx$30 He-Ar lines with a typical standard deviation of 0.4 Å  (18 km s^-1 at H$\alpha$). An observing log is given in Table 1. The superoutburst light curve, as constructed from the VSNET data archive, is shown in Fig. 1, indicating that our spectroscopic observations were obtained only a few days after the maximum.

Figure 1: The light curve of the 1998 superoutburst. Data are taken from the VSNET archive. The dates of our observations are indicated by vertical dashed lines.

 

Table 1: Journal of observations. Grating, resolution, exposure time and number of spectra are given. The zero point for Heliocentric Julian Day is HJD₀ = 2 451 000.

Grating	Res. (Å)	exptime (s)	HJD	N
Gr13	5.5	300	54.4826-4942	3
Gr8	2.5	300	54.4996-5888	18
Gr8	2.5	300	55.4884-5851	19