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

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5. High dispersion spectra

Tracings of some selected regions of high dispersion spectra obtained on 1995 September 12, October 13 and December 4 are shown in Figs. 11-14. One more spectrum was taken on December 6, which is, however, not presented here, because it was effectively the same as that of December 4. Unit of ordinates is 10-12erg cm-2sec-1Å-1, but, because of the distortion of the spectra, there is large ambiguity in the absolute intensities of the high dispersion spectra.

[FIGURE] Fig. 11. Tracings of high dispersion spectra of V723 Cas in H[FORMULA] region

[FIGURE] Fig. 12. Tracings of high dispersion spectra of V723 Cas in H[FORMULA] region

[FIGURE] Fig. 13. Tracings of high dispersion spectra of V723 Cas in Na I D1 and D2 region

[FIGURE] Fig. 14. Tracings of high dispersion spectra of V723 Cas in Si II 6347 and 6371 region. The multiple absorption components of Fe II at 641.7 nm are indicated by lines

Heliocentric radial velocities of emission and absorption components of some selected lines are given in Table 3, and their equivalent widths are given in Table 4. The observational error in the radial velocities is about [FORMULA] km s-1 and that in the equivalent widths is about [FORMULA]. Wavelengths, equivalent widths, and identifications of all emission and absorption components in the spectra of September 12 and December 4 are presented in Table 5.


[TABLE]

Table 3. Radial velocities in km s-1 of emission (em.) and absorption (ab.) components of selected lines of V723 Cas



[TABLE]

Table 4. Equivalent widths in Å of emission (em.) and absorption (ab.) components of selected lines of V723 Cas


Hutchings (1971) observed multiple absorption components of H[FORMULA] in the early stage of evolution of HR Del. Such a feature was not detected on the H I lines (Figs. 11 and 12) in our high dispersion spectra. The absorption line in the blue-ward side of H[FORMULA] should be identified as Ti II at 433.79 nm. Some lines of Fe II seem to have had multiple absorption components. For example, Fe II at 641.7 nm may have had three absorption components on September 12 and December 4, which are indicated by lines in Fig. 14. The blue-shifts of these three absorption components with respect to the emission component were -179.0, -144.4, and -102.8 km s-1 on September 12 and -157.9, -111.2, and -75.7 km s-1 on December 4. The multiple absorption components, however, were not common among Fe II lines. As seen in Fig. 12, Fe II at 492.4 nm didn't show such a profile. Both Fe II lines at 641.7 and 645.6 nm depend on the same multiplet No. 74, but the line at 645.6 nm had only two absorption components whose blue-shifts were -169.1 and -119.4 km s-1 on September 12 and -148.2 and -103.6 km s-1 on December 4.

Large changes of profile were seen on the absorption components of Si II lines at 634.7 and 637.1 nm (Fig. 14). In contrast to the other lines, Si II had well separated two absorption components on September 12. The same lines had only one absorption component on October 13, then the double absorptions appeared again on December 4 (Fig. 14). Since the excitation potentials of these lines are higher than those of the other metallic lines, Si II lines may have been formed in a deeper region of the atmosphere. The large difference between the profiles of Si II lines and those of the other metallic lines suggests a complicated motion in the atmosphere of the nova. The real motion in the atmosphere seems to be different from a simple acceleration or deceleration.

Some new lines of low excitation potential appeared at later stages. For example, no trace of absorption nor emission of Ba II at 493.4 nm and Y II lines at 488.4 and 490.0 nm was seen on September 12 (upper panel of Fig. 12), whereas weak traces of these lines were seen in absorption on October 13 then they were prominent absorptions on December 4 (lower panel of Fig. 12). The new born lines were mainly due to Fe I, Fe II, Ba II, Sc II, Y II, etc. (Table 5), which suggests a decreasing of temperature of the photosphere.

The interstellar absorption components of Na I D1 and D2 lines were much deeper than the stellar ones in September (upper panel of Fig. 13), then the stellar absorption and emission components strengthened in October. Equivalent widths of the emission components were not measured, because they were blended with the interstellar components. The stellar absorption components became deeper and slightly wider in December (lower panel of Fig. 13). The asymmetry of the profile of the absorptions of Na I D1 and D2 on December 4 suggests an emergence of a new high velocity component. Radial velocities of the interstellar components of Na I D1 and D2 lines are [FORMULA] and [FORMULA] km s-1, respectively and their equivalent widths are [FORMULA] and [FORMULA] Å.

There is one unidentified absorption line at 449.5 nm, the equivalent width of which was 0.15 Å on September 12 and 0.06 Å on December 4 (Table 5). Its laboratory wavelength may be 449.71[FORMULA]0.02 nm.

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© European Southern Observatory (ESO) 1998

Online publication: September 17, 1998
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