3 Discussion of spectral features

The interstellar, stellar and wind absorption lines are visible in several or different radial velocity components. We therefore list and describe all occuring radial velocity components in Table1.

We present tables of identified interstellar and stellar absorption lines. These tables show a running number for identification of the lines in the plots shown in the Appendix, the vacuum wavelength, the $\log(gf)$-value, the number of the radial velocity component (VC) applied as given in Table1, and some remarks or the transition for the H₂-lines. We will present and discuss the tables of molecular hydrogen lines, other interstellar lines, Lyman series lines and stellar absorption lines.

3.1 Radial velocity components

Table1 lists 7 components of radial velocities used to identify absorption lines and features in the spectrum. The first two components are the interstellar absorptions at -12 kms^-1 and -60 kms^-1, which are the two strongest of well known interstellar components (Grewing et al. [1978]; Keenan et al. [1995]; Spitzer & Fitzpatrick [1992], [1993]). No.3 gives the published value of the radial velocity of HD93521 of -16 kms^-1 (SIMBAD). No.4 is the velocity of the emission of the geocoronal Ly-$\alpha$ line. This emission line results from a completely illuminated entrance aperture of the Echelle spectrometer which had a projected diameter of 20 $^{\prime\prime}$. The velocity of 36.5 kms^-1 is the negative sum of two wavelength corrections applied to this spectrum: the heliocentric correction and the decentering correction (26.5 km s^-1 + 10 km s^-1).

Some stellar absorption lines show narrow absorption components resulting from winds, which have been observed previously (Bjorkman et al. [1994]), but which are varying in time. We have identified two such components in serveral lines and they are listed as numbers 5 and 6 in Table1. Component 7 represents the radial velocities of the strong SiIII $\lambda$$\lambda$1300 triplets, which are also due to stellar wind absorption (Massa [1995]).

 

Table 1: Table of radial velocity components (VC)

3.2 Interstellar molecular hydrogen

For most of the H₂-lines only the main velocity component No.1 was observed, but for some unblended lines the high velocity component could be seen also. A detailed discussion of column densities and curve of growths will be published in a separate paper (Gringel et al., in preparation).

Previous Copernicus measurements of selected $\rm H_{2}$-lines only led to an upper limit of $\log N({\rm H}_{2}) < 18.54$ (Savage et al. [1992]). The high velocity components were not detected by Copernicus.

3.3 Interstellar metal lines

Most of the metal lines can be observed in both interstellar components with the second component being only slightly weaker than the main component. High resolution spectra do show more components (Spitzer & Fitzpatrick [1993]), but in the ORFEUS echelle spectra only two well separated components are seen. The separation is best seen in the ArI lines $\lambda$1048 and $\lambda$1067 and the NI triplett $\lambda$1134. Interstellar OVI at $\lambda$1032 and $\lambda$1037 appears quite broad. Widmann estimated a $N({\rm O\,VI})\,=\,(0.99\pm0.15$)10¹⁴cm^-2 from these ORFEUS echelle spectra (Widmann et al. [1998]; Widmann [1999]).

 

Table 2: Table of identified or possible interstellar molecular hydrogen lines. VC is the velocity component as given in Table1

 

Table 2: continued

 

Table 2: continued

 

Table 2: continued

 

Table 3: Table of identified interstellar metal lines. For unresolved doublets and triplets an average wavelength and a calculated effective log(gf) are given. VC is the velocity component as given in Table 1

 

Table 3: continued

3.4 Lyman series lines

Of the Lyman series 14 lines are detectable, from which the lines below the $\lambda$915.824 line are not separated, so that this line marks the interstellar Lyman limit towards HD93521.

 

Table 4: Table of the identified interstellar Lyman-series (HI). All lines are doublets with a maximum separation of 5.4mÅ (at $\lambda$1216). The resulting wavelength and $\log(gf)$ is given. VC is the velocity component as given in Table1

3.5 Stellar lines

The two NV-lines at $\lambda$$\lambda$1239/1243 have a pronounced P-Cygni profile. Within the absorption part both lines show two significant narrow absorption components at -270 and -340 kms^-1. These narrow absorption components could be an indication for a disk in the wind of HD93521 (Bjorkman et al. [1994]). The same components are also visible in the SiIV doublet at $\lambda$$\lambda$1394/1403, in SiIV $\lambda$1073 and in SiIII $\lambda$1206.

The strong SiIII $\lambda$$\lambda$1300 triplets are seen as wind absorption lines (Massa [1995]). They appear at a range between -60 kms^-1 and -100 kms^-1, whereas Massa reports a value of -30 kms^-1. This difference could be due to some long term wind variability.

The comparatively strong stellar absorption at 1085Å could not be clearly identified, it is possibly a superposition of different lines. A candidate is the HeII $\lambda$1084.9 line, but as the next lower unblended HeII line at $\lambda$958.7 is rather weak, the identification is not sure. There is a FeII resonance line at $\lambda$1085.0 with a low $\log(gf)=-2.106$, but also non-resonance lines of FeII and FeIII are present in this region. So this line probably requires a more detailed analysis.

 

Table 5: Table of identified stellar (*) and stellar wind (w) lines. For the NIII doublets only the stronger of the two lines is listed. VC is the velocity component as given in Table1