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Astron. Astrophys. 327, 245-251 (1997)

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3. IUE observations

We obtained three IUE UV spectra of V2301 Oph using the short (SWP) and long wavelength (LWP) cameras with the large aperture and in low dispersion ([FORMULA]) mode (see Table 1). In order to save read-out time and to achieve reasonable S/N, we exposed the SWP camera displacing V2301 Oph at two positions in the large aperture at an offset of 8" from each other, accumulating two segments of 90 minutes each during the out-eclipse phases at one position and four segments of 8 minutes each during the eclipse phases at the other. We also acquired two LWP spectra. While the first exposure was very short (35 min.) and was used to check the centering procedure of the target for the multiple exposures, the second spectrum was a longer one and obtained accumulating two segments of 90 minutes and 13 minutes for a total of 103 minutes during out-of-eclipse phases.

The IUE spectra have been processed using the standard IUE software package (IUESIPS) at VILSPA. Since IUESIPS does not handle multiple exposures, we extracted the spectra from the the line-by-line IUESIPS processed images using standard MIDAS routines and applied IUESIPS camera sensitivity functions and time degradation corrections as it is currently done with the new software package (NEWSIPS). Before extraction, the images were inspected line-by-line for spurious features like cosmic rays.

The out-of-eclipse SWP spectrum shows a weak blue continuum and emission lines of NV [FORMULA] 1240, the SiIII/SiII/OI blend around 1300 Å, CII [FORMULA] 1335, SiIV [FORMULA] 1397, CIV [FORMULA] 1550, HeII [FORMULA] 1640, NIV [FORMULA] 1718, CIII [FORMULA] 1176, and Al III [FORMULA] 1855. In the longer exposure LWP spectrum a weak MgII [FORMULA] 2800 line is observed. During the eclipse phases no spectrum was detected. The average out-of-eclipse UV spectrum is shown in Fig. 4 with no evidence of any 2200 Å interstellar absorption feature.

[FIGURE] Fig. 4. IUE spectrum of V2301 Oph. The exes show the positions of cosmic ray events and reseaux marks.

While the strongest lines as NV, SiIV, CIV, HeII are typically observed in both non magnetic and magnetic CVs, the presence of a wide range of ionization states from CIV to CII, from NV to NIV and from SiIV to SiIII/SiII appears to be a characteristics of AM Her stars (de Martino 1995). Line flux ratios NV:SiIV:CIV:HeII (1.4:3.8:13.5:2.0 [FORMULA] erg cm-2 s-1) of V2301 Oph are typical for those observed in CVs (Mauche, Lee & Kallman 1997). The NV/SiIV ratio (0.36) fits into the range observed for AM Hers whereas all intermediate polars except EX Hya and FO Aqr have values greater than 1.0 (de Martino 1995; Szkody & Silber 1996).

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© European Southern Observatory (ESO) 1997

Online publication: April 8, 1998
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