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3. Results of the spectroscopy in Brazil and the polarimetry in South Africa

Profile variations of the Htex2html_wrap_inline1200, He I 5876 and DNaI lines for different observing runs are presented in Figs. 1 (click here)-5 (click here). To illustrate a character of the rapid variability on time scales from hours to days, the spectra obtained in neighbouring nights are gathered in separate groups. For comparison the profiles corresponding to the initial dates of each group are given as dotted lines.

3.1. Htex2html_wrap_inline1200

  figure258
Figure 1: Line profiles of Htex2html_wrap_inline1200 observed in the spectrum of HD163296\ in 1992 at the LNA. For the sake of comparison, the profiles obtained on 20.03 and 17.04 are also superimposed as dotted lines on the profiles of the respective next observing nights

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Figure 2: The same as Fig. 1 (click here) but for 1993. The dotted line shows the profile obtained on 01.05

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Figure 3: The same as Fig. 1 (click here) but for 1995. The dotted line shows the profile obtained on 13.04. The nightly mean profile for 20.06 is presented at the bottom

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Figure 4: Residuals with respect to the nightly mean Htex2html_wrap_inline1200 profile observed on 20.06.95

On the whole, the profile type of the Htex2html_wrap_inline1200 emission line was the same as in the ESO spectra of 1991-1992 (Paper I). However, as is clearly seen in Figs. 1 (click here)-3 (click here), the system of blueshifted absorption components turns out to be more complicated. In different observing nights it contains one component (20-21.03.92 and 02.03.93), two components (all the remaining dates except for 31.08.93) or three components (31.08.93). On the latter date a redshifted absorption feature was observed at about tex2html_wrap_inline1304.

The width of Htex2html_wrap_inline1200 profile remains practically constant with positional shift of the profile as a whole from tex2html_wrap_inline1308 (17.04.92) to tex2html_wrap_inline1310 (15.04.95). Residuals from the nightly mean spectrum observed on 20.06.95 (the only date when several spectra were obtained during a night) are presented in Fig. 4 (click here). They demonstrate the same character of rapid variability as in 1991-1992 (Paper I). It looks like monotonous changes of intensity within the narrow intervals of radial velocities without positional shifts (so called "standing waves'' in the residuals).

3.2. He I 5876

The He I 5876 line profile exhibits a somewhat smaller width in comparison with Htex2html_wrap_inline1200 (Fig. 5 (click here)) and a positional shift from tex2html_wrap_inline1322 (April, 1995) to tex2html_wrap_inline1324 (20.03.92). The majority of line profiles are blueshifted and double-peaked, with the blue emission peak being stronger and the central absorption being slightly redshifted. Occasionally, it acquires a reverse PCyg-type (16.04.95 and 20.06.95, (b)-profile), while the (a)-profile of 20.06.95 exhibits an intense additional emission peak near zero velocity.

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Figure 5: The same as Fig. 1 (click here) but for the He I 5876 and DNaI\ lines. The profiles obtained on 13.04.95 and 20.06.95 a) are also superimposed as dotted lines on the respective subsequent observations. The radial velocity scales for He I 5876 , and the D2 and D1 lines are given in tex2html_wrap_inline1330 at the bottom. Spectrum a) was taken at UTtex2html_wrap_inline1332, b) at tex2html_wrap_inline1334

3.3. DNaI lines

The DNaI lines are anomalously wide compared to classical Herbig Ae/Be stars (Fig. 5 (click here)): from tex2html_wrap_inline1338 (20.06.95) to tex2html_wrap_inline1340 (March, 1992). As a rule, the DNaI line profiles are of the same type as Htex2html_wrap_inline1200, but the set of absorption components is more diverse. Sometimes narrow redshifted features can be met in the DNaI profile, such as that seen at tex2html_wrap_inline1344 in the profile of 16.04.95.

3.4. Polarization parameters

tex2html_wrap_inline1204 polarimetric observations of HD163296 in July 17-31, 1995 give evidence of the presence of at least two variable linear polarization components. A detailed periodogram analysis of the Stokes parameters Q and U has been carried out by means of the Laefler-Kinman (1965) method implemented in a computer code by Pelt (1980). We have found the nightly mean values of the U-parameter to be satisfactorily approximated by a sinusoidal curve with a period tex2html_wrap_inline1356 days, superimposed on a linear trend with the same slope in all three bands and the mean value increasing towards longer wavelengths (Fig. 6 (click here)). Variations of the Q-parameter are of essentially lower amplitude. The noticeable difference of the trend component for the Q-parameter in the R passband can be caused by the distorting influence of the variable lowly-polarized emission in the Htex2html_wrap_inline1200 line. After subtraction of the trend, the variations of the Q parameter in the tex2html_wrap_inline1368-bands can be fitted by a sinusoidal curve with the same period (7.5 days) and tex2html_wrap_inline1372 phase shift relative to the corresponding U-curves, while in the I-band the sinusoidal variations disappear.

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Figure 6: Illustration of the cyclic variability of the nightly mean Q, U polarization parameters of HD163296\ in July, 1995
Measurements of circular polarization performed within the same observing set allowed to derive weighted mean values in excess of the tex2html_wrap_inline1378 noise level in all passbands, displaying an increase towards longer wavelengths (tex2html_wrap_inline1380 in the V band, tex2html_wrap_inline1384 in the R band, and tex2html_wrap_inline1388 in the I band). Variations of the nightly mean values are weekly correlated with those of the linear polarization degree. These results imply the presence of aligned particles in the dusty envelope of this object.


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