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Astron. Astrophys. 336, 960-965 (1998)

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2. Observations

2.1. Blue spectra

The spectra were obtained in service mode with the William Herschel Telescope, La Palma using ISIS with the TEK CCD camera and the R600B (0.79 Å pixel-1 dispersion, 1.6 Å pixel-1 resolution, range [FORMULA] 6350-6750 Å) and R1200R (0.41 Å pixel-1 dispersion, 0.8 Å pixel-1 resolution, range [FORMULA] 3900-4700 Å) gratings (Carter et al. 1993). The simultaneous observations of H[FORMULA] allowed us to assess any emission component that may be present in the bluer Balmer lines. H[FORMULA] was in emission at this time, see Paper I.

V635 Cas was observed over two nights (900 s and 2[FORMULA]1500 s on 1993 December 18 and 2[FORMULA]1000 s on 1993 December 19). The flux standard Hiltner 102 was also observed (300s on 1993 December 18). The seeing was poor on 1993 December 18. The data were reduced using the FIGARO and DIPSO packages (Shortridge & Meyerdicks 1996; Howarth 1996).

Fig. 1 is a plot of V635 Cas (upper) and Hiltner 102 (lower) obtained on 1993 December 19 and 18, respectively. The data have been smoothed with a Gaussian ([FORMULA] = 2, width = 5 pixels, 1 pixel = 0.8 Å). To normalise the spectra we fitted a third order polynomial to the continuum and then divided the spectra by this fit.

[FIGURE] Fig. 1. [FORMULA] 3900 Å-4700 Å Spectra: V635 Cas (upper) and Hiltner 102 (lower)

2.2. Red spectra

The far red spectra ([FORMULA] 6400-8900 Å, 5 Å pixel-1 dispersion, 11 Å resolution) were obtained using the all-transmission Mark IIIa spectrograph on the 1.3m McGraw-Hill telescope at Michigan-Dartmouth-MIT Observatory, Kitt Peak, Arizona. The detector was a TI-4849 CCD, inside the BRICC camera (Luppino 1989), except on 1991 October 27, when a Thomson chip was used. All spectra were taken through a [FORMULA] slit, with exposure times of 1800 s. There was cirrus on 1991 October 20.

Spectra of hot stars were taken to map the telluric atmospheric bands in this part of the spectrum, which were removed using the methods of Wade & Horne (1988). There is a wrinkle in the spectra at 7600 Å due to the removal of the A-band which is the strongest atmospheric feature. There is also an atmospheric absorption band in the region P11 to P7. Each time a spectrum of V635 Cas was taken, one spectrum each of two flux standards were also taken. These were G191B2B (Oke 1974) and HD 19445 (Oke & Gunn 1983). Comparing the individual spectra of these standards, taken at different epochs, we found the relative fluxes in the spectra to be consistent to within a few percent. Errors in relative fluxes due to losses from an unrotated slit were therefore not serious, unsurprising since these spectra are all so red (Filippenko 1982). Absolute fluxes were another matter: we estimate from the same spectra that the absolute flux levels should not be trusted to within 30%. Although this will effect flux measurements of the lines, it will not affect equivalent width or velocity measurements. The instrumental uncertainties do not account for the upturn in the spectrum on 1991 October 27 and we believe this to be real.

The [FORMULA] 6400 - 7500 Å and [FORMULA] 7600 - 8900 Å spectra are given in Fig. 2. The 1991 October 20 spectrum has been normalised to the continuum value at 7264 Å as the night was not photometric.

[FIGURE] Fig. 2. V635 Cas [FORMULA] 6400 Å-8900 Å Spectra

Tables 2 and 3 list the dereddened line fluxes. The spectra were dereddened assuming a standard Galactic extinction law (Rieke & Lebofsky 1985; Howarth 1983) and E(B-V) = 1.5 (Hutchings & Crampton 1981).


[TABLE]

Table 2. Line Parameters H[FORMULA] [FORMULA] 6563 Å- OI [FORMULA] 7772 Å.
Notes:
[FORMULA] TJD = JD - 2440000;
[FORMULA] Flux [FORMULA] erg s-1 cm-2 The line fluxes have been dereddened - see text.



[TABLE]

Table 3. Line Parameters P19 [FORMULA] 8413 Å-P11 [FORMULA] 8863 Å.
Notes:
[FORMULA] TJD = JD - 2440000;
[FORMULA] Flux [FORMULA] erg s-1 cm-2 The line fluxes have been dereddened - see text.
* blended, see Table 1.


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© European Southern Observatory (ESO) 1998

Online publication: July 27, 1998
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