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Astron. Astrophys. 338, 1006-1014 (1998)

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4. Medium dispersion spectra

The first spectra were taken on 1995 August 26, when the nova reached the semi-steady level of V[FORMULA]9. Figs. 2 and 3 show the spectra in the blue and red regions. Unfortunately, because of cloudy sky, the spectrophotometric calibration was not applied. Prominent emission lines of H I and Fe II and some weak lines of Ti II, Mg II, and Cr II were seen on the blue spectrum (Fig. 2), while the red one showed a prominent emission of H[FORMULA], some emission lines of Fe II, and the absorptions of Si II at 634.7 and 637.1 nm (Fig. 3). As will be seen in the next section, the absorption of Na I D1+D2 in this stage was mainly interstellar origin. Numerous lines were accompanied by weakly blue-shifted absorption component. Nearly the same spectral feature was seen on 1995 September 6 (Fig. 4), where the unit of ordinate is [FORMULA] erg cm-2sec-1Å-1. The same unit is used also in the successive medium dispersion spectra.

[FIGURE] Fig. 2. Spectrum of V723 Cas on 1995 August 26. Flux calibration is not applied

[FIGURE] Fig. 3. Spectrum of V723 Cas on 1995 August 26. Flux calibration is not applied

[FIGURE] Fig. 4. Spectrum of V723 Cas on 1995 September 6. Unit of ordinate is 10-12erg cm-2sec-1Å-1

Significant variations were not seen on the V magnitude and colours until the end of October (Fig. 1). During the same time the emission lines gradually weakened and the absorption components developed. A spectrum in the blue region obtained on October 17 is shown in Fig. 5. In November, when the luminosity rose to V[FORMULA]8.6 (Fig. 1), the absorption components well developed. Only H[FORMULA] was in prominent emission in November 20[FORMULA]24. Spectra on November 20 are shown in Figs. 6 and 7, where H[FORMULA] and Fe II at 492.4, 501.8 and 516.9 nm were deep absorptions with weak traces of emission. Prior to the final rising to the principal light maximum, the emission lines of H[FORMULA] and Fe II appeared again at the beginning of December. A spectrum on December 10 is shown in Fig. 8. A pure absorption spectrum was found at the maximum luminosity on December 19 (Fig. 9). Unfortunately, the region of H[FORMULA] was not observed during the light maximum. A spectrum of an F type supergiant HR 382 (F0 Ia) obtained with the same instrument is shown in Fig. 10. It may be possible to see that the spectrum of the nova at the maximum luminosity was nearly identical with that of the F type supergiant.

[FIGURE] Fig. 5. Spectrum of V723 Cas on 1995 October 17

[FIGURE] Fig. 6. Spectrum of V723 Cas on 1995 November 23

[FIGURE] Fig. 7. Spectrum of V723 Cas on 1995 November 23

[FIGURE] Fig. 8. Spectrum of V723 Cas on 1995 December 10

[FIGURE] Fig. 9. Spectrum of V723 Cas on 1995 December 19 (at light maximum)

[FIGURE] Fig. 10. Spectrum of HR 382 (F0 Ia) obtained with the same instrument of V723 Cas

It is obvious from the high dispersion spectroscopy, which are presented in the next section, that most of the emission and absorption components in the medium dispersion spectra were blends of several lines. The equivalent widths of these components should have only restricted physical meanings. We have measured equivalent widths of a few selected lines which were relatively free from blending. The results are given in Table 2. These values may be used as a rough measure for strength of the emission and absorption components. Mean radial velocities of the absorption components of Fe II lines at 417.3, 417.9, 423.3, 431.4 and 454.9 nm are also given in Table 2. The observational error in the equivalent widths is about [FORMULA] and that in the mean radial velocities is about [FORMULA] km s-1.


[TABLE]

Table 2. Equivalent width in Å of three selected Fe II lines and mean radial velocity of absorption components of five Fe II lines (see text) measured on the medium dispersion spectra


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© European Southern Observatory (ESO) 1998

Online publication: September 17, 1998
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