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Astron. Astrophys. 359, 299-305 (2000)

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3. Results

During the period covered by our observations the hydrogen and helium lines underwent significant variations.

Fig. 1 illustrates the main types of H[FORMULA] and H[FORMULA] profiles observed in 1994-1999. Four consecutive stages of the profile evolution during this period can be distinguished: a) the low-state phase in 1994-1995; b) the high-activity phase in the middle of 1997; c) the short period of activity decrease between the end of 1997 and spring 1998; and d) the new low-state phase in 1998-1999.

[FIGURE] Fig. 1. Typical H[FORMULA] (left) and H[FORMULA] (right) profiles normalized to the continuum (Fc) illustrating the evolution of the HD 200775 spectrum in 1994-1999. The positions of the water vapor lines (short vertical lines) were derived for zero heliocentric velocity. The photospheric H[FORMULA] profile (dotted line) was calculated using the models by Kurucz (1979) for [FORMULA] =19000 K and log g = 4.0.

During the 1994/5 low-state phase the H[FORMULA] and H[FORMULA] lines had emission profiles with two peaks separated by a redshifted absorption at [FORMULA] 20 km s-1. At the same time, the He I line profile possessed a rather complex structure (Fig. 2), which included at least three components: a symmetric absorption core seemingly fitting the synthetic photospheric profile (taken from Böhm & Catala 1995), broad absorption wings, and a blue variable emission bump extending up to -500 km s-1. The latter may be attributed to the Fe II 5872 Å line, but other Fe II lines seen in the OHP spectra usually have double-peaked profiles and do not change so drastically over the period of observations.

[FIGURE] Fig. 2. Typical profiles of the He I line observed in the spectrum of HD 200775 (left panel) and their residuals with respect to the synthetic photospheric profile (right panel). The synthetic photospheric profile taken from Böhm & Catala (1995) is shown in the left panel by dotted lines. Dotted lines in the right panel represent the profile of 07.06.95 to show the variations.

Fig. 3 shows the spectral evolution of HD 200775 throughout the period of observations in 1994-1999. The onset of the high-activity phase was marked by: a) a significant rise of the equivalent width of H[FORMULA] (upper panel) and H[FORMULA]; b) the appearance of blueshifted absorption features in their profiles in addition to redshifted ones (middle panel); c) a monotonic increase in the velocity of the redshifted absorptions from [FORMULA] +20 to [FORMULA] +40 km s-1 (middle panel); and d) a notable red shift and asymmetry of the He I line absorption core (lower panel and also Fig. 2). The He I core velocity (up to +20 km s-1) was measured as the centroid of the part of the profile where the intensity was below 0.9 [FORMULA]. During this phase, the behaviour of the H[FORMULA] and H[FORMULA] profiles demonstrated not only similarities but some differences as well. For example, the blueshifted absorption in H[FORMULA] appeared much earlier than the corresponding feature in H[FORMULA]. However, unlike H[FORMULA], H[FORMULA] retained its redshifted absorption component throughout the high-activity phase and, moreover, the [FORMULA] ratio of the H[FORMULA] emission peaks was more than 1 all the time.

[FIGURE] Fig. 3. Temporal behaviour of the line variations in the spectrum of HD 200775 in 1994-1999. The H[FORMULA] line EWs are shown in the upper panel, the radial velocities of the absorption features in the H[FORMULA] and H[FORMULA] profiles in the middle panel, and the radial velocity of the He I absorption core in the lower panel. The circles, squares and triangles correspond to the data obtained at the OHP, CrAO and Ritter observatories, respectively. The filled and open symbols used in the middle panel concern H[FORMULA] and H[FORMULA], respectively. The dotted, dashed, and dash-dotted lines in the middle panel mark the positional trends of the blueshifted, undisplaced, and redshifted absorption features, respectively.

The high-activity phase occurred in three distinct stages:

  1. March, 1997: extrema in the velocities of the He I core and of the blueshifted absorption features of both H[FORMULA] and H[FORMULA] were observed simultaneously;

  2. September - October, 1997: a) the blueshifted H[FORMULA]/H[FORMULA] absorption features quickly moved to zero velocity and disappeared; b) the EW of H[FORMULA] achieved its maximum value and began to decrease; c) the redshifted H[FORMULA] absorption suddenly became much wider and deeper (see Fig. 1);

  3. February - March, 1998: a) a small new blueshifted absorption feature was observed in H[FORMULA] during 50 days; b) the redshifted H[FORMULA]/H[FORMULA] absorptions achieved their maximum velocity (+40 km s-1) and then abruptly vanished. A new absorption feature at nearly zero velocity appeared instead.

The active phase seems to have been over by October, 1998. H[FORMULA] and H[FORMULA] returned to a double-peaked morphology, but their central absorptions were weaker and more nearly unshifted than in 1994-1995. In this period the He I line profile was the same as it was before the activity event, but a new positive trend in the velocity of the central core was detected in 1999 (see Fig. 3).

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© European Southern Observatory (ESO) 2000

Online publication: June 30, 2000